[NETFILTER]: remove unneeded rcu_dereference() calls
[linux-2.6.git] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the presence of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks.
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/mm.h>
67 #include <linux/module.h>
68 #include <linux/sysctl.h>
69 #include <net/tcp.h>
70 #include <net/inet_common.h>
71 #include <linux/ipsec.h>
72 #include <asm/unaligned.h>
73 #include <net/netdma.h>
74
75 int sysctl_tcp_timestamps __read_mostly = 1;
76 int sysctl_tcp_window_scaling __read_mostly = 1;
77 int sysctl_tcp_sack __read_mostly = 1;
78 int sysctl_tcp_fack __read_mostly = 1;
79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn __read_mostly;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
84
85 int sysctl_tcp_stdurg __read_mostly;
86 int sysctl_tcp_rfc1337 __read_mostly;
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 int sysctl_tcp_frto __read_mostly = 2;
89 int sysctl_tcp_frto_response __read_mostly;
90 int sysctl_tcp_nometrics_save __read_mostly;
91
92 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
93 int sysctl_tcp_abc __read_mostly;
94
95 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
96 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
97 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
98 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
99 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
100 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
101 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
102 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
103 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
104 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
105 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
106 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
107 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
108
109 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
110 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
111 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
112 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
113 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
114
115 #define IsSackFrto() (sysctl_tcp_frto == 0x2)
116
117 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
118 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
119
120 /* Adapt the MSS value used to make delayed ack decision to the
121  * real world.
122  */
123 static void tcp_measure_rcv_mss(struct sock *sk,
124                                 const struct sk_buff *skb)
125 {
126         struct inet_connection_sock *icsk = inet_csk(sk);
127         const unsigned int lss = icsk->icsk_ack.last_seg_size;
128         unsigned int len;
129
130         icsk->icsk_ack.last_seg_size = 0;
131
132         /* skb->len may jitter because of SACKs, even if peer
133          * sends good full-sized frames.
134          */
135         len = skb_shinfo(skb)->gso_size ?: skb->len;
136         if (len >= icsk->icsk_ack.rcv_mss) {
137                 icsk->icsk_ack.rcv_mss = len;
138         } else {
139                 /* Otherwise, we make more careful check taking into account,
140                  * that SACKs block is variable.
141                  *
142                  * "len" is invariant segment length, including TCP header.
143                  */
144                 len += skb->data - skb_transport_header(skb);
145                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
146                     /* If PSH is not set, packet should be
147                      * full sized, provided peer TCP is not badly broken.
148                      * This observation (if it is correct 8)) allows
149                      * to handle super-low mtu links fairly.
150                      */
151                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
152                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
153                         /* Subtract also invariant (if peer is RFC compliant),
154                          * tcp header plus fixed timestamp option length.
155                          * Resulting "len" is MSS free of SACK jitter.
156                          */
157                         len -= tcp_sk(sk)->tcp_header_len;
158                         icsk->icsk_ack.last_seg_size = len;
159                         if (len == lss) {
160                                 icsk->icsk_ack.rcv_mss = len;
161                                 return;
162                         }
163                 }
164                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
165                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
166                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
167         }
168 }
169
170 static void tcp_incr_quickack(struct sock *sk)
171 {
172         struct inet_connection_sock *icsk = inet_csk(sk);
173         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
174
175         if (quickacks==0)
176                 quickacks=2;
177         if (quickacks > icsk->icsk_ack.quick)
178                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
179 }
180
181 void tcp_enter_quickack_mode(struct sock *sk)
182 {
183         struct inet_connection_sock *icsk = inet_csk(sk);
184         tcp_incr_quickack(sk);
185         icsk->icsk_ack.pingpong = 0;
186         icsk->icsk_ack.ato = TCP_ATO_MIN;
187 }
188
189 /* Send ACKs quickly, if "quick" count is not exhausted
190  * and the session is not interactive.
191  */
192
193 static inline int tcp_in_quickack_mode(const struct sock *sk)
194 {
195         const struct inet_connection_sock *icsk = inet_csk(sk);
196         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
197 }
198
199 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
200 {
201         if (tp->ecn_flags&TCP_ECN_OK)
202                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
203 }
204
205 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
206 {
207         if (tcp_hdr(skb)->cwr)
208                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
209 }
210
211 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
212 {
213         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
214 }
215
216 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
217 {
218         if (tp->ecn_flags&TCP_ECN_OK) {
219                 if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
220                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
221                 /* Funny extension: if ECT is not set on a segment,
222                  * it is surely retransmit. It is not in ECN RFC,
223                  * but Linux follows this rule. */
224                 else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
225                         tcp_enter_quickack_mode((struct sock *)tp);
226         }
227 }
228
229 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
230 {
231         if ((tp->ecn_flags&TCP_ECN_OK) && (!th->ece || th->cwr))
232                 tp->ecn_flags &= ~TCP_ECN_OK;
233 }
234
235 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
236 {
237         if ((tp->ecn_flags&TCP_ECN_OK) && (!th->ece || !th->cwr))
238                 tp->ecn_flags &= ~TCP_ECN_OK;
239 }
240
241 static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
242 {
243         if (th->ece && !th->syn && (tp->ecn_flags&TCP_ECN_OK))
244                 return 1;
245         return 0;
246 }
247
248 /* Buffer size and advertised window tuning.
249  *
250  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
251  */
252
253 static void tcp_fixup_sndbuf(struct sock *sk)
254 {
255         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
256                      sizeof(struct sk_buff);
257
258         if (sk->sk_sndbuf < 3 * sndmem)
259                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
260 }
261
262 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
263  *
264  * All tcp_full_space() is split to two parts: "network" buffer, allocated
265  * forward and advertised in receiver window (tp->rcv_wnd) and
266  * "application buffer", required to isolate scheduling/application
267  * latencies from network.
268  * window_clamp is maximal advertised window. It can be less than
269  * tcp_full_space(), in this case tcp_full_space() - window_clamp
270  * is reserved for "application" buffer. The less window_clamp is
271  * the smoother our behaviour from viewpoint of network, but the lower
272  * throughput and the higher sensitivity of the connection to losses. 8)
273  *
274  * rcv_ssthresh is more strict window_clamp used at "slow start"
275  * phase to predict further behaviour of this connection.
276  * It is used for two goals:
277  * - to enforce header prediction at sender, even when application
278  *   requires some significant "application buffer". It is check #1.
279  * - to prevent pruning of receive queue because of misprediction
280  *   of receiver window. Check #2.
281  *
282  * The scheme does not work when sender sends good segments opening
283  * window and then starts to feed us spaghetti. But it should work
284  * in common situations. Otherwise, we have to rely on queue collapsing.
285  */
286
287 /* Slow part of check#2. */
288 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
289 {
290         struct tcp_sock *tp = tcp_sk(sk);
291         /* Optimize this! */
292         int truesize = tcp_win_from_space(skb->truesize)/2;
293         int window = tcp_win_from_space(sysctl_tcp_rmem[2])/2;
294
295         while (tp->rcv_ssthresh <= window) {
296                 if (truesize <= skb->len)
297                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
298
299                 truesize >>= 1;
300                 window >>= 1;
301         }
302         return 0;
303 }
304
305 static void tcp_grow_window(struct sock *sk,
306                             struct sk_buff *skb)
307 {
308         struct tcp_sock *tp = tcp_sk(sk);
309
310         /* Check #1 */
311         if (tp->rcv_ssthresh < tp->window_clamp &&
312             (int)tp->rcv_ssthresh < tcp_space(sk) &&
313             !tcp_memory_pressure) {
314                 int incr;
315
316                 /* Check #2. Increase window, if skb with such overhead
317                  * will fit to rcvbuf in future.
318                  */
319                 if (tcp_win_from_space(skb->truesize) <= skb->len)
320                         incr = 2*tp->advmss;
321                 else
322                         incr = __tcp_grow_window(sk, skb);
323
324                 if (incr) {
325                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
326                         inet_csk(sk)->icsk_ack.quick |= 1;
327                 }
328         }
329 }
330
331 /* 3. Tuning rcvbuf, when connection enters established state. */
332
333 static void tcp_fixup_rcvbuf(struct sock *sk)
334 {
335         struct tcp_sock *tp = tcp_sk(sk);
336         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
337
338         /* Try to select rcvbuf so that 4 mss-sized segments
339          * will fit to window and corresponding skbs will fit to our rcvbuf.
340          * (was 3; 4 is minimum to allow fast retransmit to work.)
341          */
342         while (tcp_win_from_space(rcvmem) < tp->advmss)
343                 rcvmem += 128;
344         if (sk->sk_rcvbuf < 4 * rcvmem)
345                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
346 }
347
348 /* 4. Try to fixup all. It is made immediately after connection enters
349  *    established state.
350  */
351 static void tcp_init_buffer_space(struct sock *sk)
352 {
353         struct tcp_sock *tp = tcp_sk(sk);
354         int maxwin;
355
356         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
357                 tcp_fixup_rcvbuf(sk);
358         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
359                 tcp_fixup_sndbuf(sk);
360
361         tp->rcvq_space.space = tp->rcv_wnd;
362
363         maxwin = tcp_full_space(sk);
364
365         if (tp->window_clamp >= maxwin) {
366                 tp->window_clamp = maxwin;
367
368                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
369                         tp->window_clamp = max(maxwin -
370                                                (maxwin >> sysctl_tcp_app_win),
371                                                4 * tp->advmss);
372         }
373
374         /* Force reservation of one segment. */
375         if (sysctl_tcp_app_win &&
376             tp->window_clamp > 2 * tp->advmss &&
377             tp->window_clamp + tp->advmss > maxwin)
378                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
379
380         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
381         tp->snd_cwnd_stamp = tcp_time_stamp;
382 }
383
384 /* 5. Recalculate window clamp after socket hit its memory bounds. */
385 static void tcp_clamp_window(struct sock *sk)
386 {
387         struct tcp_sock *tp = tcp_sk(sk);
388         struct inet_connection_sock *icsk = inet_csk(sk);
389
390         icsk->icsk_ack.quick = 0;
391
392         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
393             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
394             !tcp_memory_pressure &&
395             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
396                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
397                                     sysctl_tcp_rmem[2]);
398         }
399         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
400                 tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
401 }
402
403
404 /* Initialize RCV_MSS value.
405  * RCV_MSS is an our guess about MSS used by the peer.
406  * We haven't any direct information about the MSS.
407  * It's better to underestimate the RCV_MSS rather than overestimate.
408  * Overestimations make us ACKing less frequently than needed.
409  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
410  */
411 void tcp_initialize_rcv_mss(struct sock *sk)
412 {
413         struct tcp_sock *tp = tcp_sk(sk);
414         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
415
416         hint = min(hint, tp->rcv_wnd/2);
417         hint = min(hint, TCP_MIN_RCVMSS);
418         hint = max(hint, TCP_MIN_MSS);
419
420         inet_csk(sk)->icsk_ack.rcv_mss = hint;
421 }
422
423 /* Receiver "autotuning" code.
424  *
425  * The algorithm for RTT estimation w/o timestamps is based on
426  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
427  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
428  *
429  * More detail on this code can be found at
430  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
431  * though this reference is out of date.  A new paper
432  * is pending.
433  */
434 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
435 {
436         u32 new_sample = tp->rcv_rtt_est.rtt;
437         long m = sample;
438
439         if (m == 0)
440                 m = 1;
441
442         if (new_sample != 0) {
443                 /* If we sample in larger samples in the non-timestamp
444                  * case, we could grossly overestimate the RTT especially
445                  * with chatty applications or bulk transfer apps which
446                  * are stalled on filesystem I/O.
447                  *
448                  * Also, since we are only going for a minimum in the
449                  * non-timestamp case, we do not smooth things out
450                  * else with timestamps disabled convergence takes too
451                  * long.
452                  */
453                 if (!win_dep) {
454                         m -= (new_sample >> 3);
455                         new_sample += m;
456                 } else if (m < new_sample)
457                         new_sample = m << 3;
458         } else {
459                 /* No previous measure. */
460                 new_sample = m << 3;
461         }
462
463         if (tp->rcv_rtt_est.rtt != new_sample)
464                 tp->rcv_rtt_est.rtt = new_sample;
465 }
466
467 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
468 {
469         if (tp->rcv_rtt_est.time == 0)
470                 goto new_measure;
471         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
472                 return;
473         tcp_rcv_rtt_update(tp,
474                            jiffies - tp->rcv_rtt_est.time,
475                            1);
476
477 new_measure:
478         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
479         tp->rcv_rtt_est.time = tcp_time_stamp;
480 }
481
482 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
483 {
484         struct tcp_sock *tp = tcp_sk(sk);
485         if (tp->rx_opt.rcv_tsecr &&
486             (TCP_SKB_CB(skb)->end_seq -
487              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
488                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
489 }
490
491 /*
492  * This function should be called every time data is copied to user space.
493  * It calculates the appropriate TCP receive buffer space.
494  */
495 void tcp_rcv_space_adjust(struct sock *sk)
496 {
497         struct tcp_sock *tp = tcp_sk(sk);
498         int time;
499         int space;
500
501         if (tp->rcvq_space.time == 0)
502                 goto new_measure;
503
504         time = tcp_time_stamp - tp->rcvq_space.time;
505         if (time < (tp->rcv_rtt_est.rtt >> 3) ||
506             tp->rcv_rtt_est.rtt == 0)
507                 return;
508
509         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
510
511         space = max(tp->rcvq_space.space, space);
512
513         if (tp->rcvq_space.space != space) {
514                 int rcvmem;
515
516                 tp->rcvq_space.space = space;
517
518                 if (sysctl_tcp_moderate_rcvbuf &&
519                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
520                         int new_clamp = space;
521
522                         /* Receive space grows, normalize in order to
523                          * take into account packet headers and sk_buff
524                          * structure overhead.
525                          */
526                         space /= tp->advmss;
527                         if (!space)
528                                 space = 1;
529                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
530                                   16 + sizeof(struct sk_buff));
531                         while (tcp_win_from_space(rcvmem) < tp->advmss)
532                                 rcvmem += 128;
533                         space *= rcvmem;
534                         space = min(space, sysctl_tcp_rmem[2]);
535                         if (space > sk->sk_rcvbuf) {
536                                 sk->sk_rcvbuf = space;
537
538                                 /* Make the window clamp follow along.  */
539                                 tp->window_clamp = new_clamp;
540                         }
541                 }
542         }
543
544 new_measure:
545         tp->rcvq_space.seq = tp->copied_seq;
546         tp->rcvq_space.time = tcp_time_stamp;
547 }
548
549 /* There is something which you must keep in mind when you analyze the
550  * behavior of the tp->ato delayed ack timeout interval.  When a
551  * connection starts up, we want to ack as quickly as possible.  The
552  * problem is that "good" TCP's do slow start at the beginning of data
553  * transmission.  The means that until we send the first few ACK's the
554  * sender will sit on his end and only queue most of his data, because
555  * he can only send snd_cwnd unacked packets at any given time.  For
556  * each ACK we send, he increments snd_cwnd and transmits more of his
557  * queue.  -DaveM
558  */
559 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
560 {
561         struct tcp_sock *tp = tcp_sk(sk);
562         struct inet_connection_sock *icsk = inet_csk(sk);
563         u32 now;
564
565         inet_csk_schedule_ack(sk);
566
567         tcp_measure_rcv_mss(sk, skb);
568
569         tcp_rcv_rtt_measure(tp);
570
571         now = tcp_time_stamp;
572
573         if (!icsk->icsk_ack.ato) {
574                 /* The _first_ data packet received, initialize
575                  * delayed ACK engine.
576                  */
577                 tcp_incr_quickack(sk);
578                 icsk->icsk_ack.ato = TCP_ATO_MIN;
579         } else {
580                 int m = now - icsk->icsk_ack.lrcvtime;
581
582                 if (m <= TCP_ATO_MIN/2) {
583                         /* The fastest case is the first. */
584                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
585                 } else if (m < icsk->icsk_ack.ato) {
586                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
587                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
588                                 icsk->icsk_ack.ato = icsk->icsk_rto;
589                 } else if (m > icsk->icsk_rto) {
590                         /* Too long gap. Apparently sender failed to
591                          * restart window, so that we send ACKs quickly.
592                          */
593                         tcp_incr_quickack(sk);
594                         sk_stream_mem_reclaim(sk);
595                 }
596         }
597         icsk->icsk_ack.lrcvtime = now;
598
599         TCP_ECN_check_ce(tp, skb);
600
601         if (skb->len >= 128)
602                 tcp_grow_window(sk, skb);
603 }
604
605 static u32 tcp_rto_min(struct sock *sk)
606 {
607         struct dst_entry *dst = __sk_dst_get(sk);
608         u32 rto_min = TCP_RTO_MIN;
609
610         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
611                 rto_min = dst->metrics[RTAX_RTO_MIN-1];
612         return rto_min;
613 }
614
615 /* Called to compute a smoothed rtt estimate. The data fed to this
616  * routine either comes from timestamps, or from segments that were
617  * known _not_ to have been retransmitted [see Karn/Partridge
618  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
619  * piece by Van Jacobson.
620  * NOTE: the next three routines used to be one big routine.
621  * To save cycles in the RFC 1323 implementation it was better to break
622  * it up into three procedures. -- erics
623  */
624 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
625 {
626         struct tcp_sock *tp = tcp_sk(sk);
627         long m = mrtt; /* RTT */
628
629         /*      The following amusing code comes from Jacobson's
630          *      article in SIGCOMM '88.  Note that rtt and mdev
631          *      are scaled versions of rtt and mean deviation.
632          *      This is designed to be as fast as possible
633          *      m stands for "measurement".
634          *
635          *      On a 1990 paper the rto value is changed to:
636          *      RTO = rtt + 4 * mdev
637          *
638          * Funny. This algorithm seems to be very broken.
639          * These formulae increase RTO, when it should be decreased, increase
640          * too slowly, when it should be increased quickly, decrease too quickly
641          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
642          * does not matter how to _calculate_ it. Seems, it was trap
643          * that VJ failed to avoid. 8)
644          */
645         if (m == 0)
646                 m = 1;
647         if (tp->srtt != 0) {
648                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
649                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
650                 if (m < 0) {
651                         m = -m;         /* m is now abs(error) */
652                         m -= (tp->mdev >> 2);   /* similar update on mdev */
653                         /* This is similar to one of Eifel findings.
654                          * Eifel blocks mdev updates when rtt decreases.
655                          * This solution is a bit different: we use finer gain
656                          * for mdev in this case (alpha*beta).
657                          * Like Eifel it also prevents growth of rto,
658                          * but also it limits too fast rto decreases,
659                          * happening in pure Eifel.
660                          */
661                         if (m > 0)
662                                 m >>= 3;
663                 } else {
664                         m -= (tp->mdev >> 2);   /* similar update on mdev */
665                 }
666                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
667                 if (tp->mdev > tp->mdev_max) {
668                         tp->mdev_max = tp->mdev;
669                         if (tp->mdev_max > tp->rttvar)
670                                 tp->rttvar = tp->mdev_max;
671                 }
672                 if (after(tp->snd_una, tp->rtt_seq)) {
673                         if (tp->mdev_max < tp->rttvar)
674                                 tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
675                         tp->rtt_seq = tp->snd_nxt;
676                         tp->mdev_max = tcp_rto_min(sk);
677                 }
678         } else {
679                 /* no previous measure. */
680                 tp->srtt = m<<3;        /* take the measured time to be rtt */
681                 tp->mdev = m<<1;        /* make sure rto = 3*rtt */
682                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
683                 tp->rtt_seq = tp->snd_nxt;
684         }
685 }
686
687 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
688  * routine referred to above.
689  */
690 static inline void tcp_set_rto(struct sock *sk)
691 {
692         const struct tcp_sock *tp = tcp_sk(sk);
693         /* Old crap is replaced with new one. 8)
694          *
695          * More seriously:
696          * 1. If rtt variance happened to be less 50msec, it is hallucination.
697          *    It cannot be less due to utterly erratic ACK generation made
698          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
699          *    to do with delayed acks, because at cwnd>2 true delack timeout
700          *    is invisible. Actually, Linux-2.4 also generates erratic
701          *    ACKs in some circumstances.
702          */
703         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
704
705         /* 2. Fixups made earlier cannot be right.
706          *    If we do not estimate RTO correctly without them,
707          *    all the algo is pure shit and should be replaced
708          *    with correct one. It is exactly, which we pretend to do.
709          */
710 }
711
712 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
713  * guarantees that rto is higher.
714  */
715 static inline void tcp_bound_rto(struct sock *sk)
716 {
717         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
718                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
719 }
720
721 /* Save metrics learned by this TCP session.
722    This function is called only, when TCP finishes successfully
723    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
724  */
725 void tcp_update_metrics(struct sock *sk)
726 {
727         struct tcp_sock *tp = tcp_sk(sk);
728         struct dst_entry *dst = __sk_dst_get(sk);
729
730         if (sysctl_tcp_nometrics_save)
731                 return;
732
733         dst_confirm(dst);
734
735         if (dst && (dst->flags&DST_HOST)) {
736                 const struct inet_connection_sock *icsk = inet_csk(sk);
737                 int m;
738
739                 if (icsk->icsk_backoff || !tp->srtt) {
740                         /* This session failed to estimate rtt. Why?
741                          * Probably, no packets returned in time.
742                          * Reset our results.
743                          */
744                         if (!(dst_metric_locked(dst, RTAX_RTT)))
745                                 dst->metrics[RTAX_RTT-1] = 0;
746                         return;
747                 }
748
749                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
750
751                 /* If newly calculated rtt larger than stored one,
752                  * store new one. Otherwise, use EWMA. Remember,
753                  * rtt overestimation is always better than underestimation.
754                  */
755                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
756                         if (m <= 0)
757                                 dst->metrics[RTAX_RTT-1] = tp->srtt;
758                         else
759                                 dst->metrics[RTAX_RTT-1] -= (m>>3);
760                 }
761
762                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
763                         if (m < 0)
764                                 m = -m;
765
766                         /* Scale deviation to rttvar fixed point */
767                         m >>= 1;
768                         if (m < tp->mdev)
769                                 m = tp->mdev;
770
771                         if (m >= dst_metric(dst, RTAX_RTTVAR))
772                                 dst->metrics[RTAX_RTTVAR-1] = m;
773                         else
774                                 dst->metrics[RTAX_RTTVAR-1] -=
775                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
776                 }
777
778                 if (tp->snd_ssthresh >= 0xFFFF) {
779                         /* Slow start still did not finish. */
780                         if (dst_metric(dst, RTAX_SSTHRESH) &&
781                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
782                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
783                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
784                         if (!dst_metric_locked(dst, RTAX_CWND) &&
785                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
786                                 dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
787                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
788                            icsk->icsk_ca_state == TCP_CA_Open) {
789                         /* Cong. avoidance phase, cwnd is reliable. */
790                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
791                                 dst->metrics[RTAX_SSTHRESH-1] =
792                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
793                         if (!dst_metric_locked(dst, RTAX_CWND))
794                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
795                 } else {
796                         /* Else slow start did not finish, cwnd is non-sense,
797                            ssthresh may be also invalid.
798                          */
799                         if (!dst_metric_locked(dst, RTAX_CWND))
800                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
801                         if (dst->metrics[RTAX_SSTHRESH-1] &&
802                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
803                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
804                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
805                 }
806
807                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
808                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
809                             tp->reordering != sysctl_tcp_reordering)
810                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
811                 }
812         }
813 }
814
815 /* Numbers are taken from RFC3390.
816  *
817  * John Heffner states:
818  *
819  *      The RFC specifies a window of no more than 4380 bytes
820  *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
821  *      is a bit misleading because they use a clamp at 4380 bytes
822  *      rather than use a multiplier in the relevant range.
823  */
824 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
825 {
826         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
827
828         if (!cwnd) {
829                 if (tp->mss_cache > 1460)
830                         cwnd = 2;
831                 else
832                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
833         }
834         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
835 }
836
837 /* Set slow start threshold and cwnd not falling to slow start */
838 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
839 {
840         struct tcp_sock *tp = tcp_sk(sk);
841         const struct inet_connection_sock *icsk = inet_csk(sk);
842
843         tp->prior_ssthresh = 0;
844         tp->bytes_acked = 0;
845         if (icsk->icsk_ca_state < TCP_CA_CWR) {
846                 tp->undo_marker = 0;
847                 if (set_ssthresh)
848                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
849                 tp->snd_cwnd = min(tp->snd_cwnd,
850                                    tcp_packets_in_flight(tp) + 1U);
851                 tp->snd_cwnd_cnt = 0;
852                 tp->high_seq = tp->snd_nxt;
853                 tp->snd_cwnd_stamp = tcp_time_stamp;
854                 TCP_ECN_queue_cwr(tp);
855
856                 tcp_set_ca_state(sk, TCP_CA_CWR);
857         }
858 }
859
860 /*
861  * Packet counting of FACK is based on in-order assumptions, therefore TCP
862  * disables it when reordering is detected
863  */
864 static void tcp_disable_fack(struct tcp_sock *tp)
865 {
866         tp->rx_opt.sack_ok &= ~2;
867 }
868
869 /* Take a notice that peer is sending D-SACKs */
870 static void tcp_dsack_seen(struct tcp_sock *tp)
871 {
872         tp->rx_opt.sack_ok |= 4;
873 }
874
875 /* Initialize metrics on socket. */
876
877 static void tcp_init_metrics(struct sock *sk)
878 {
879         struct tcp_sock *tp = tcp_sk(sk);
880         struct dst_entry *dst = __sk_dst_get(sk);
881
882         if (dst == NULL)
883                 goto reset;
884
885         dst_confirm(dst);
886
887         if (dst_metric_locked(dst, RTAX_CWND))
888                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
889         if (dst_metric(dst, RTAX_SSTHRESH)) {
890                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
891                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
892                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
893         }
894         if (dst_metric(dst, RTAX_REORDERING) &&
895             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
896                 tcp_disable_fack(tp);
897                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
898         }
899
900         if (dst_metric(dst, RTAX_RTT) == 0)
901                 goto reset;
902
903         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
904                 goto reset;
905
906         /* Initial rtt is determined from SYN,SYN-ACK.
907          * The segment is small and rtt may appear much
908          * less than real one. Use per-dst memory
909          * to make it more realistic.
910          *
911          * A bit of theory. RTT is time passed after "normal" sized packet
912          * is sent until it is ACKed. In normal circumstances sending small
913          * packets force peer to delay ACKs and calculation is correct too.
914          * The algorithm is adaptive and, provided we follow specs, it
915          * NEVER underestimate RTT. BUT! If peer tries to make some clever
916          * tricks sort of "quick acks" for time long enough to decrease RTT
917          * to low value, and then abruptly stops to do it and starts to delay
918          * ACKs, wait for troubles.
919          */
920         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
921                 tp->srtt = dst_metric(dst, RTAX_RTT);
922                 tp->rtt_seq = tp->snd_nxt;
923         }
924         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
925                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
926                 tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
927         }
928         tcp_set_rto(sk);
929         tcp_bound_rto(sk);
930         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
931                 goto reset;
932         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
933         tp->snd_cwnd_stamp = tcp_time_stamp;
934         return;
935
936 reset:
937         /* Play conservative. If timestamps are not
938          * supported, TCP will fail to recalculate correct
939          * rtt, if initial rto is too small. FORGET ALL AND RESET!
940          */
941         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
942                 tp->srtt = 0;
943                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
944                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
945         }
946 }
947
948 static void tcp_update_reordering(struct sock *sk, const int metric,
949                                   const int ts)
950 {
951         struct tcp_sock *tp = tcp_sk(sk);
952         if (metric > tp->reordering) {
953                 tp->reordering = min(TCP_MAX_REORDERING, metric);
954
955                 /* This exciting event is worth to be remembered. 8) */
956                 if (ts)
957                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
958                 else if (tcp_is_reno(tp))
959                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
960                 else if (tcp_is_fack(tp))
961                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
962                 else
963                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
964 #if FASTRETRANS_DEBUG > 1
965                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
966                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
967                        tp->reordering,
968                        tp->fackets_out,
969                        tp->sacked_out,
970                        tp->undo_marker ? tp->undo_retrans : 0);
971 #endif
972                 tcp_disable_fack(tp);
973         }
974 }
975
976 /* This procedure tags the retransmission queue when SACKs arrive.
977  *
978  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
979  * Packets in queue with these bits set are counted in variables
980  * sacked_out, retrans_out and lost_out, correspondingly.
981  *
982  * Valid combinations are:
983  * Tag  InFlight        Description
984  * 0    1               - orig segment is in flight.
985  * S    0               - nothing flies, orig reached receiver.
986  * L    0               - nothing flies, orig lost by net.
987  * R    2               - both orig and retransmit are in flight.
988  * L|R  1               - orig is lost, retransmit is in flight.
989  * S|R  1               - orig reached receiver, retrans is still in flight.
990  * (L|S|R is logically valid, it could occur when L|R is sacked,
991  *  but it is equivalent to plain S and code short-curcuits it to S.
992  *  L|S is logically invalid, it would mean -1 packet in flight 8))
993  *
994  * These 6 states form finite state machine, controlled by the following events:
995  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
996  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
997  * 3. Loss detection event of one of three flavors:
998  *      A. Scoreboard estimator decided the packet is lost.
999  *         A'. Reno "three dupacks" marks head of queue lost.
1000  *         A''. Its FACK modfication, head until snd.fack is lost.
1001  *      B. SACK arrives sacking data transmitted after never retransmitted
1002  *         hole was sent out.
1003  *      C. SACK arrives sacking SND.NXT at the moment, when the
1004  *         segment was retransmitted.
1005  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1006  *
1007  * It is pleasant to note, that state diagram turns out to be commutative,
1008  * so that we are allowed not to be bothered by order of our actions,
1009  * when multiple events arrive simultaneously. (see the function below).
1010  *
1011  * Reordering detection.
1012  * --------------------
1013  * Reordering metric is maximal distance, which a packet can be displaced
1014  * in packet stream. With SACKs we can estimate it:
1015  *
1016  * 1. SACK fills old hole and the corresponding segment was not
1017  *    ever retransmitted -> reordering. Alas, we cannot use it
1018  *    when segment was retransmitted.
1019  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1020  *    for retransmitted and already SACKed segment -> reordering..
1021  * Both of these heuristics are not used in Loss state, when we cannot
1022  * account for retransmits accurately.
1023  *
1024  * SACK block validation.
1025  * ----------------------
1026  *
1027  * SACK block range validation checks that the received SACK block fits to
1028  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1029  * Note that SND.UNA is not included to the range though being valid because
1030  * it means that the receiver is rather inconsistent with itself reporting
1031  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1032  * perfectly valid, however, in light of RFC2018 which explicitly states
1033  * that "SACK block MUST reflect the newest segment.  Even if the newest
1034  * segment is going to be discarded ...", not that it looks very clever
1035  * in case of head skb. Due to potentional receiver driven attacks, we
1036  * choose to avoid immediate execution of a walk in write queue due to
1037  * reneging and defer head skb's loss recovery to standard loss recovery
1038  * procedure that will eventually trigger (nothing forbids us doing this).
1039  *
1040  * Implements also blockage to start_seq wrap-around. Problem lies in the
1041  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1042  * there's no guarantee that it will be before snd_nxt (n). The problem
1043  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1044  * wrap (s_w):
1045  *
1046  *         <- outs wnd ->                          <- wrapzone ->
1047  *         u     e      n                         u_w   e_w  s n_w
1048  *         |     |      |                          |     |   |  |
1049  * |<------------+------+----- TCP seqno space --------------+---------->|
1050  * ...-- <2^31 ->|                                           |<--------...
1051  * ...---- >2^31 ------>|                                    |<--------...
1052  *
1053  * Current code wouldn't be vulnerable but it's better still to discard such
1054  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1055  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1056  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1057  * equal to the ideal case (infinite seqno space without wrap caused issues).
1058  *
1059  * With D-SACK the lower bound is extended to cover sequence space below
1060  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1061  * again, D-SACK block must not to go across snd_una (for the same reason as
1062  * for the normal SACK blocks, explained above). But there all simplicity
1063  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1064  * fully below undo_marker they do not affect behavior in anyway and can
1065  * therefore be safely ignored. In rare cases (which are more or less
1066  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1067  * fragmentation and packet reordering past skb's retransmission. To consider
1068  * them correctly, the acceptable range must be extended even more though
1069  * the exact amount is rather hard to quantify. However, tp->max_window can
1070  * be used as an exaggerated estimate.
1071  */
1072 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1073                                   u32 start_seq, u32 end_seq)
1074 {
1075         /* Too far in future, or reversed (interpretation is ambiguous) */
1076         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1077                 return 0;
1078
1079         /* Nasty start_seq wrap-around check (see comments above) */
1080         if (!before(start_seq, tp->snd_nxt))
1081                 return 0;
1082
1083         /* In outstanding window? ...This is valid exit for D-SACKs too.
1084          * start_seq == snd_una is non-sensical (see comments above)
1085          */
1086         if (after(start_seq, tp->snd_una))
1087                 return 1;
1088
1089         if (!is_dsack || !tp->undo_marker)
1090                 return 0;
1091
1092         /* ...Then it's D-SACK, and must reside below snd_una completely */
1093         if (!after(end_seq, tp->snd_una))
1094                 return 0;
1095
1096         if (!before(start_seq, tp->undo_marker))
1097                 return 1;
1098
1099         /* Too old */
1100         if (!after(end_seq, tp->undo_marker))
1101                 return 0;
1102
1103         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1104          *   start_seq < undo_marker and end_seq >= undo_marker.
1105          */
1106         return !before(start_seq, end_seq - tp->max_window);
1107 }
1108
1109 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1110  * Event "C". Later note: FACK people cheated me again 8), we have to account
1111  * for reordering! Ugly, but should help.
1112  *
1113  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1114  * less than what is now known to be received by the other end (derived from
1115  * SACK blocks by the caller). Also calculate the lowest snd_nxt among the
1116  * remaining retransmitted skbs to avoid some costly processing per ACKs.
1117  */
1118 static int tcp_mark_lost_retrans(struct sock *sk, u32 received_upto)
1119 {
1120         struct tcp_sock *tp = tcp_sk(sk);
1121         struct sk_buff *skb;
1122         int flag = 0;
1123         int cnt = 0;
1124         u32 new_low_seq = tp->snd_nxt;
1125
1126         tcp_for_write_queue(skb, sk) {
1127                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1128
1129                 if (skb == tcp_send_head(sk))
1130                         break;
1131                 if (cnt == tp->retrans_out)
1132                         break;
1133                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1134                         continue;
1135
1136                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1137                         continue;
1138
1139                 if (after(received_upto, ack_seq) &&
1140                     (tcp_is_fack(tp) ||
1141                      !before(received_upto,
1142                              ack_seq + tp->reordering * tp->mss_cache))) {
1143                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1144                         tp->retrans_out -= tcp_skb_pcount(skb);
1145
1146                         /* clear lost hint */
1147                         tp->retransmit_skb_hint = NULL;
1148
1149                         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1150                                 tp->lost_out += tcp_skb_pcount(skb);
1151                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1152                                 flag |= FLAG_DATA_SACKED;
1153                                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1154                         }
1155                 } else {
1156                         if (before(ack_seq, new_low_seq))
1157                                 new_low_seq = ack_seq;
1158                         cnt += tcp_skb_pcount(skb);
1159                 }
1160         }
1161
1162         if (tp->retrans_out)
1163                 tp->lost_retrans_low = new_low_seq;
1164
1165         return flag;
1166 }
1167
1168 static int tcp_check_dsack(struct tcp_sock *tp, struct sk_buff *ack_skb,
1169                            struct tcp_sack_block_wire *sp, int num_sacks,
1170                            u32 prior_snd_una)
1171 {
1172         u32 start_seq_0 = ntohl(get_unaligned(&sp[0].start_seq));
1173         u32 end_seq_0 = ntohl(get_unaligned(&sp[0].end_seq));
1174         int dup_sack = 0;
1175
1176         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1177                 dup_sack = 1;
1178                 tcp_dsack_seen(tp);
1179                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
1180         } else if (num_sacks > 1) {
1181                 u32 end_seq_1 = ntohl(get_unaligned(&sp[1].end_seq));
1182                 u32 start_seq_1 = ntohl(get_unaligned(&sp[1].start_seq));
1183
1184                 if (!after(end_seq_0, end_seq_1) &&
1185                     !before(start_seq_0, start_seq_1)) {
1186                         dup_sack = 1;
1187                         tcp_dsack_seen(tp);
1188                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
1189                 }
1190         }
1191
1192         /* D-SACK for already forgotten data... Do dumb counting. */
1193         if (dup_sack &&
1194             !after(end_seq_0, prior_snd_una) &&
1195             after(end_seq_0, tp->undo_marker))
1196                 tp->undo_retrans--;
1197
1198         return dup_sack;
1199 }
1200
1201 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1202  * the incoming SACK may not exactly match but we can find smaller MSS
1203  * aligned portion of it that matches. Therefore we might need to fragment
1204  * which may fail and creates some hassle (caller must handle error case
1205  * returns).
1206  */
1207 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1208                                  u32 start_seq, u32 end_seq)
1209 {
1210         int in_sack, err;
1211         unsigned int pkt_len;
1212
1213         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1214                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1215
1216         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1217             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1218
1219                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1220
1221                 if (!in_sack)
1222                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1223                 else
1224                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1225                 err = tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size);
1226                 if (err < 0)
1227                         return err;
1228         }
1229
1230         return in_sack;
1231 }
1232
1233 static int
1234 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
1235 {
1236         const struct inet_connection_sock *icsk = inet_csk(sk);
1237         struct tcp_sock *tp = tcp_sk(sk);
1238         unsigned char *ptr = (skb_transport_header(ack_skb) +
1239                               TCP_SKB_CB(ack_skb)->sacked);
1240         struct tcp_sack_block_wire *sp = (struct tcp_sack_block_wire *)(ptr+2);
1241         struct sk_buff *cached_skb;
1242         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
1243         int reord = tp->packets_out;
1244         int prior_fackets;
1245         u32 highest_sack_end_seq = tp->lost_retrans_low;
1246         int flag = 0;
1247         int found_dup_sack = 0;
1248         int cached_fack_count;
1249         int i;
1250         int first_sack_index;
1251         int force_one_sack;
1252
1253         if (!tp->sacked_out) {
1254                 if (WARN_ON(tp->fackets_out))
1255                         tp->fackets_out = 0;
1256                 tp->highest_sack = tp->snd_una;
1257         }
1258         prior_fackets = tp->fackets_out;
1259
1260         found_dup_sack = tcp_check_dsack(tp, ack_skb, sp,
1261                                          num_sacks, prior_snd_una);
1262         if (found_dup_sack)
1263                 flag |= FLAG_DSACKING_ACK;
1264
1265         /* Eliminate too old ACKs, but take into
1266          * account more or less fresh ones, they can
1267          * contain valid SACK info.
1268          */
1269         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1270                 return 0;
1271
1272         /* SACK fastpath:
1273          * if the only SACK change is the increase of the end_seq of
1274          * the first block then only apply that SACK block
1275          * and use retrans queue hinting otherwise slowpath */
1276         force_one_sack = 1;
1277         for (i = 0; i < num_sacks; i++) {
1278                 __be32 start_seq = sp[i].start_seq;
1279                 __be32 end_seq = sp[i].end_seq;
1280
1281                 if (i == 0) {
1282                         if (tp->recv_sack_cache[i].start_seq != start_seq)
1283                                 force_one_sack = 0;
1284                 } else {
1285                         if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
1286                             (tp->recv_sack_cache[i].end_seq != end_seq))
1287                                 force_one_sack = 0;
1288                 }
1289                 tp->recv_sack_cache[i].start_seq = start_seq;
1290                 tp->recv_sack_cache[i].end_seq = end_seq;
1291         }
1292         /* Clear the rest of the cache sack blocks so they won't match mistakenly. */
1293         for (; i < ARRAY_SIZE(tp->recv_sack_cache); i++) {
1294                 tp->recv_sack_cache[i].start_seq = 0;
1295                 tp->recv_sack_cache[i].end_seq = 0;
1296         }
1297
1298         first_sack_index = 0;
1299         if (force_one_sack)
1300                 num_sacks = 1;
1301         else {
1302                 int j;
1303                 tp->fastpath_skb_hint = NULL;
1304
1305                 /* order SACK blocks to allow in order walk of the retrans queue */
1306                 for (i = num_sacks-1; i > 0; i--) {
1307                         for (j = 0; j < i; j++){
1308                                 if (after(ntohl(sp[j].start_seq),
1309                                           ntohl(sp[j+1].start_seq))){
1310                                         struct tcp_sack_block_wire tmp;
1311
1312                                         tmp = sp[j];
1313                                         sp[j] = sp[j+1];
1314                                         sp[j+1] = tmp;
1315
1316                                         /* Track where the first SACK block goes to */
1317                                         if (j == first_sack_index)
1318                                                 first_sack_index = j+1;
1319                                 }
1320
1321                         }
1322                 }
1323         }
1324
1325         /* Use SACK fastpath hint if valid */
1326         cached_skb = tp->fastpath_skb_hint;
1327         cached_fack_count = tp->fastpath_cnt_hint;
1328         if (!cached_skb) {
1329                 cached_skb = tcp_write_queue_head(sk);
1330                 cached_fack_count = 0;
1331         }
1332
1333         for (i = 0; i < num_sacks; i++) {
1334                 struct sk_buff *skb;
1335                 __u32 start_seq = ntohl(sp->start_seq);
1336                 __u32 end_seq = ntohl(sp->end_seq);
1337                 int fack_count;
1338                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1339                 int next_dup = (found_dup_sack && (i+1 == first_sack_index));
1340
1341                 sp++;
1342
1343                 if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq)) {
1344                         if (dup_sack) {
1345                                 if (!tp->undo_marker)
1346                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDNOUNDO);
1347                                 else
1348                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDOLD);
1349                         } else {
1350                                 /* Don't count olds caused by ACK reordering */
1351                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1352                                     !after(end_seq, tp->snd_una))
1353                                         continue;
1354                                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKDISCARD);
1355                         }
1356                         continue;
1357                 }
1358
1359                 skb = cached_skb;
1360                 fack_count = cached_fack_count;
1361
1362                 /* Event "B" in the comment above. */
1363                 if (after(end_seq, tp->high_seq))
1364                         flag |= FLAG_DATA_LOST;
1365
1366                 tcp_for_write_queue_from(skb, sk) {
1367                         int in_sack = 0;
1368                         u8 sacked;
1369
1370                         if (skb == tcp_send_head(sk))
1371                                 break;
1372
1373                         cached_skb = skb;
1374                         cached_fack_count = fack_count;
1375                         if (i == first_sack_index) {
1376                                 tp->fastpath_skb_hint = skb;
1377                                 tp->fastpath_cnt_hint = fack_count;
1378                         }
1379
1380                         /* The retransmission queue is always in order, so
1381                          * we can short-circuit the walk early.
1382                          */
1383                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1384                                 break;
1385
1386                         dup_sack = (found_dup_sack && (i == first_sack_index));
1387
1388                         /* Due to sorting DSACK may reside within this SACK block! */
1389                         if (next_dup) {
1390                                 u32 dup_start = ntohl(sp->start_seq);
1391                                 u32 dup_end = ntohl(sp->end_seq);
1392
1393                                 if (before(TCP_SKB_CB(skb)->seq, dup_end)) {
1394                                         in_sack = tcp_match_skb_to_sack(sk, skb, dup_start, dup_end);
1395                                         if (in_sack > 0)
1396                                                 dup_sack = 1;
1397                                 }
1398                         }
1399
1400                         /* DSACK info lost if out-of-mem, try SACK still */
1401                         if (in_sack <= 0)
1402                                 in_sack = tcp_match_skb_to_sack(sk, skb, start_seq, end_seq);
1403                         if (in_sack < 0)
1404                                 break;
1405
1406                         fack_count += tcp_skb_pcount(skb);
1407
1408                         sacked = TCP_SKB_CB(skb)->sacked;
1409
1410                         /* Account D-SACK for retransmitted packet. */
1411                         if ((dup_sack && in_sack) &&
1412                             (sacked & TCPCB_RETRANS) &&
1413                             after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1414                                 tp->undo_retrans--;
1415
1416                         /* The frame is ACKed. */
1417                         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
1418                                 if (sacked&TCPCB_RETRANS) {
1419                                         if ((dup_sack && in_sack) &&
1420                                             (sacked&TCPCB_SACKED_ACKED))
1421                                                 reord = min(fack_count, reord);
1422                                 } else {
1423                                         /* If it was in a hole, we detected reordering. */
1424                                         if (fack_count < prior_fackets &&
1425                                             !(sacked&TCPCB_SACKED_ACKED))
1426                                                 reord = min(fack_count, reord);
1427                                 }
1428
1429                                 /* Nothing to do; acked frame is about to be dropped. */
1430                                 continue;
1431                         }
1432
1433                         if (!in_sack)
1434                                 continue;
1435
1436                         if (!(sacked&TCPCB_SACKED_ACKED)) {
1437                                 if (sacked & TCPCB_SACKED_RETRANS) {
1438                                         /* If the segment is not tagged as lost,
1439                                          * we do not clear RETRANS, believing
1440                                          * that retransmission is still in flight.
1441                                          */
1442                                         if (sacked & TCPCB_LOST) {
1443                                                 TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1444                                                 tp->lost_out -= tcp_skb_pcount(skb);
1445                                                 tp->retrans_out -= tcp_skb_pcount(skb);
1446
1447                                                 /* clear lost hint */
1448                                                 tp->retransmit_skb_hint = NULL;
1449                                         }
1450                                 } else {
1451                                         /* New sack for not retransmitted frame,
1452                                          * which was in hole. It is reordering.
1453                                          */
1454                                         if (!(sacked & TCPCB_RETRANS) &&
1455                                             fack_count < prior_fackets)
1456                                                 reord = min(fack_count, reord);
1457
1458                                         if (sacked & TCPCB_LOST) {
1459                                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1460                                                 tp->lost_out -= tcp_skb_pcount(skb);
1461
1462                                                 /* clear lost hint */
1463                                                 tp->retransmit_skb_hint = NULL;
1464                                         }
1465                                         /* SACK enhanced F-RTO detection.
1466                                          * Set flag if and only if non-rexmitted
1467                                          * segments below frto_highmark are
1468                                          * SACKed (RFC4138; Appendix B).
1469                                          * Clearing correct due to in-order walk
1470                                          */
1471                                         if (after(end_seq, tp->frto_highmark)) {
1472                                                 flag &= ~FLAG_ONLY_ORIG_SACKED;
1473                                         } else {
1474                                                 if (!(sacked & TCPCB_RETRANS))
1475                                                         flag |= FLAG_ONLY_ORIG_SACKED;
1476                                         }
1477                                 }
1478
1479                                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1480                                 flag |= FLAG_DATA_SACKED;
1481                                 tp->sacked_out += tcp_skb_pcount(skb);
1482
1483                                 if (fack_count > tp->fackets_out)
1484                                         tp->fackets_out = fack_count;
1485
1486                                 if (after(TCP_SKB_CB(skb)->seq, tp->highest_sack)) {
1487                                         tp->highest_sack = TCP_SKB_CB(skb)->seq;
1488                                         highest_sack_end_seq = TCP_SKB_CB(skb)->end_seq;
1489                                 }
1490                         } else {
1491                                 if (dup_sack && (sacked&TCPCB_RETRANS))
1492                                         reord = min(fack_count, reord);
1493                         }
1494
1495                         /* D-SACK. We can detect redundant retransmission
1496                          * in S|R and plain R frames and clear it.
1497                          * undo_retrans is decreased above, L|R frames
1498                          * are accounted above as well.
1499                          */
1500                         if (dup_sack &&
1501                             (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
1502                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1503                                 tp->retrans_out -= tcp_skb_pcount(skb);
1504                                 tp->retransmit_skb_hint = NULL;
1505                         }
1506                 }
1507         }
1508
1509         if (tp->retrans_out &&
1510             after(highest_sack_end_seq, tp->lost_retrans_low) &&
1511             icsk->icsk_ca_state == TCP_CA_Recovery)
1512                 flag |= tcp_mark_lost_retrans(sk, highest_sack_end_seq);
1513
1514         tcp_verify_left_out(tp);
1515
1516         if ((reord < tp->fackets_out) && icsk->icsk_ca_state != TCP_CA_Loss &&
1517             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1518                 tcp_update_reordering(sk, ((tp->fackets_out + 1) - reord), 0);
1519
1520 #if FASTRETRANS_DEBUG > 0
1521         BUG_TRAP((int)tp->sacked_out >= 0);
1522         BUG_TRAP((int)tp->lost_out >= 0);
1523         BUG_TRAP((int)tp->retrans_out >= 0);
1524         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1525 #endif
1526         return flag;
1527 }
1528
1529 /* If we receive more dupacks than we expected counting segments
1530  * in assumption of absent reordering, interpret this as reordering.
1531  * The only another reason could be bug in receiver TCP.
1532  */
1533 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1534 {
1535         struct tcp_sock *tp = tcp_sk(sk);
1536         u32 holes;
1537
1538         holes = max(tp->lost_out, 1U);
1539         holes = min(holes, tp->packets_out);
1540
1541         if ((tp->sacked_out + holes) > tp->packets_out) {
1542                 tp->sacked_out = tp->packets_out - holes;
1543                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1544         }
1545 }
1546
1547 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1548
1549 static void tcp_add_reno_sack(struct sock *sk)
1550 {
1551         struct tcp_sock *tp = tcp_sk(sk);
1552         tp->sacked_out++;
1553         tcp_check_reno_reordering(sk, 0);
1554         tcp_verify_left_out(tp);
1555 }
1556
1557 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1558
1559 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1560 {
1561         struct tcp_sock *tp = tcp_sk(sk);
1562
1563         if (acked > 0) {
1564                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1565                 if (acked-1 >= tp->sacked_out)
1566                         tp->sacked_out = 0;
1567                 else
1568                         tp->sacked_out -= acked-1;
1569         }
1570         tcp_check_reno_reordering(sk, acked);
1571         tcp_verify_left_out(tp);
1572 }
1573
1574 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1575 {
1576         tp->sacked_out = 0;
1577 }
1578
1579 /* F-RTO can only be used if TCP has never retransmitted anything other than
1580  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1581  */
1582 int tcp_use_frto(struct sock *sk)
1583 {
1584         const struct tcp_sock *tp = tcp_sk(sk);
1585         struct sk_buff *skb;
1586
1587         if (!sysctl_tcp_frto)
1588                 return 0;
1589
1590         if (IsSackFrto())
1591                 return 1;
1592
1593         /* Avoid expensive walking of rexmit queue if possible */
1594         if (tp->retrans_out > 1)
1595                 return 0;
1596
1597         skb = tcp_write_queue_head(sk);
1598         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
1599         tcp_for_write_queue_from(skb, sk) {
1600                 if (skb == tcp_send_head(sk))
1601                         break;
1602                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1603                         return 0;
1604                 /* Short-circuit when first non-SACKed skb has been checked */
1605                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED))
1606                         break;
1607         }
1608         return 1;
1609 }
1610
1611 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
1612  * recovery a bit and use heuristics in tcp_process_frto() to detect if
1613  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
1614  * keep retrans_out counting accurate (with SACK F-RTO, other than head
1615  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
1616  * bits are handled if the Loss state is really to be entered (in
1617  * tcp_enter_frto_loss).
1618  *
1619  * Do like tcp_enter_loss() would; when RTO expires the second time it
1620  * does:
1621  *  "Reduce ssthresh if it has not yet been made inside this window."
1622  */
1623 void tcp_enter_frto(struct sock *sk)
1624 {
1625         const struct inet_connection_sock *icsk = inet_csk(sk);
1626         struct tcp_sock *tp = tcp_sk(sk);
1627         struct sk_buff *skb;
1628
1629         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
1630             tp->snd_una == tp->high_seq ||
1631             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
1632              !icsk->icsk_retransmits)) {
1633                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1634                 /* Our state is too optimistic in ssthresh() call because cwnd
1635                  * is not reduced until tcp_enter_frto_loss() when previous F-RTO
1636                  * recovery has not yet completed. Pattern would be this: RTO,
1637                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
1638                  * up here twice).
1639                  * RFC4138 should be more specific on what to do, even though
1640                  * RTO is quite unlikely to occur after the first Cumulative ACK
1641                  * due to back-off and complexity of triggering events ...
1642                  */
1643                 if (tp->frto_counter) {
1644                         u32 stored_cwnd;
1645                         stored_cwnd = tp->snd_cwnd;
1646                         tp->snd_cwnd = 2;
1647                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1648                         tp->snd_cwnd = stored_cwnd;
1649                 } else {
1650                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1651                 }
1652                 /* ... in theory, cong.control module could do "any tricks" in
1653                  * ssthresh(), which means that ca_state, lost bits and lost_out
1654                  * counter would have to be faked before the call occurs. We
1655                  * consider that too expensive, unlikely and hacky, so modules
1656                  * using these in ssthresh() must deal these incompatibility
1657                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
1658                  */
1659                 tcp_ca_event(sk, CA_EVENT_FRTO);
1660         }
1661
1662         tp->undo_marker = tp->snd_una;
1663         tp->undo_retrans = 0;
1664
1665         skb = tcp_write_queue_head(sk);
1666         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1667                 tp->undo_marker = 0;
1668         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
1669                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1670                 tp->retrans_out -= tcp_skb_pcount(skb);
1671         }
1672         tcp_verify_left_out(tp);
1673
1674         /* Earlier loss recovery underway (see RFC4138; Appendix B).
1675          * The last condition is necessary at least in tp->frto_counter case.
1676          */
1677         if (IsSackFrto() && (tp->frto_counter ||
1678             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
1679             after(tp->high_seq, tp->snd_una)) {
1680                 tp->frto_highmark = tp->high_seq;
1681         } else {
1682                 tp->frto_highmark = tp->snd_nxt;
1683         }
1684         tcp_set_ca_state(sk, TCP_CA_Disorder);
1685         tp->high_seq = tp->snd_nxt;
1686         tp->frto_counter = 1;
1687 }
1688
1689 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1690  * which indicates that we should follow the traditional RTO recovery,
1691  * i.e. mark everything lost and do go-back-N retransmission.
1692  */
1693 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
1694 {
1695         struct tcp_sock *tp = tcp_sk(sk);
1696         struct sk_buff *skb;
1697
1698         tp->lost_out = 0;
1699         tp->retrans_out = 0;
1700         if (tcp_is_reno(tp))
1701                 tcp_reset_reno_sack(tp);
1702
1703         tcp_for_write_queue(skb, sk) {
1704                 if (skb == tcp_send_head(sk))
1705                         break;
1706                 /*
1707                  * Count the retransmission made on RTO correctly (only when
1708                  * waiting for the first ACK and did not get it)...
1709                  */
1710                 if ((tp->frto_counter == 1) && !(flag&FLAG_DATA_ACKED)) {
1711                         /* For some reason this R-bit might get cleared? */
1712                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1713                                 tp->retrans_out += tcp_skb_pcount(skb);
1714                         /* ...enter this if branch just for the first segment */
1715                         flag |= FLAG_DATA_ACKED;
1716                 } else {
1717                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1718                                 tp->undo_marker = 0;
1719                         TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1720                 }
1721
1722                 /* Don't lost mark skbs that were fwd transmitted after RTO */
1723                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) &&
1724                     !after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) {
1725                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1726                         tp->lost_out += tcp_skb_pcount(skb);
1727                 }
1728         }
1729         tcp_verify_left_out(tp);
1730
1731         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
1732         tp->snd_cwnd_cnt = 0;
1733         tp->snd_cwnd_stamp = tcp_time_stamp;
1734         tp->frto_counter = 0;
1735         tp->bytes_acked = 0;
1736
1737         tp->reordering = min_t(unsigned int, tp->reordering,
1738                                              sysctl_tcp_reordering);
1739         tcp_set_ca_state(sk, TCP_CA_Loss);
1740         tp->high_seq = tp->frto_highmark;
1741         TCP_ECN_queue_cwr(tp);
1742
1743         tcp_clear_retrans_hints_partial(tp);
1744 }
1745
1746 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
1747 {
1748         tp->retrans_out = 0;
1749         tp->lost_out = 0;
1750
1751         tp->undo_marker = 0;
1752         tp->undo_retrans = 0;
1753 }
1754
1755 void tcp_clear_retrans(struct tcp_sock *tp)
1756 {
1757         tcp_clear_retrans_partial(tp);
1758
1759         tp->fackets_out = 0;
1760         tp->sacked_out = 0;
1761 }
1762
1763 /* Enter Loss state. If "how" is not zero, forget all SACK information
1764  * and reset tags completely, otherwise preserve SACKs. If receiver
1765  * dropped its ofo queue, we will know this due to reneging detection.
1766  */
1767 void tcp_enter_loss(struct sock *sk, int how)
1768 {
1769         const struct inet_connection_sock *icsk = inet_csk(sk);
1770         struct tcp_sock *tp = tcp_sk(sk);
1771         struct sk_buff *skb;
1772
1773         /* Reduce ssthresh if it has not yet been made inside this window. */
1774         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1775             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1776                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1777                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1778                 tcp_ca_event(sk, CA_EVENT_LOSS);
1779         }
1780         tp->snd_cwnd       = 1;
1781         tp->snd_cwnd_cnt   = 0;
1782         tp->snd_cwnd_stamp = tcp_time_stamp;
1783
1784         tp->bytes_acked = 0;
1785         tcp_clear_retrans_partial(tp);
1786
1787         if (tcp_is_reno(tp))
1788                 tcp_reset_reno_sack(tp);
1789
1790         if (!how) {
1791                 /* Push undo marker, if it was plain RTO and nothing
1792                  * was retransmitted. */
1793                 tp->undo_marker = tp->snd_una;
1794                 tcp_clear_retrans_hints_partial(tp);
1795         } else {
1796                 tp->sacked_out = 0;
1797                 tp->fackets_out = 0;
1798                 tcp_clear_all_retrans_hints(tp);
1799         }
1800
1801         tcp_for_write_queue(skb, sk) {
1802                 if (skb == tcp_send_head(sk))
1803                         break;
1804
1805                 if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
1806                         tp->undo_marker = 0;
1807                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1808                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1809                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1810                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1811                         tp->lost_out += tcp_skb_pcount(skb);
1812                 }
1813         }
1814         tcp_verify_left_out(tp);
1815
1816         tp->reordering = min_t(unsigned int, tp->reordering,
1817                                              sysctl_tcp_reordering);
1818         tcp_set_ca_state(sk, TCP_CA_Loss);
1819         tp->high_seq = tp->snd_nxt;
1820         TCP_ECN_queue_cwr(tp);
1821         /* Abort F-RTO algorithm if one is in progress */
1822         tp->frto_counter = 0;
1823 }
1824
1825 static int tcp_check_sack_reneging(struct sock *sk)
1826 {
1827         struct sk_buff *skb;
1828
1829         /* If ACK arrived pointing to a remembered SACK,
1830          * it means that our remembered SACKs do not reflect
1831          * real state of receiver i.e.
1832          * receiver _host_ is heavily congested (or buggy).
1833          * Do processing similar to RTO timeout.
1834          */
1835         if ((skb = tcp_write_queue_head(sk)) != NULL &&
1836             (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
1837                 struct inet_connection_sock *icsk = inet_csk(sk);
1838                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1839
1840                 tcp_enter_loss(sk, 1);
1841                 icsk->icsk_retransmits++;
1842                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1843                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1844                                           icsk->icsk_rto, TCP_RTO_MAX);
1845                 return 1;
1846         }
1847         return 0;
1848 }
1849
1850 static inline int tcp_fackets_out(struct tcp_sock *tp)
1851 {
1852         return tcp_is_reno(tp) ? tp->sacked_out+1 : tp->fackets_out;
1853 }
1854
1855 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1856 {
1857         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1858 }
1859
1860 static inline int tcp_head_timedout(struct sock *sk)
1861 {
1862         struct tcp_sock *tp = tcp_sk(sk);
1863
1864         return tp->packets_out &&
1865                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
1866 }
1867
1868 /* Linux NewReno/SACK/FACK/ECN state machine.
1869  * --------------------------------------
1870  *
1871  * "Open"       Normal state, no dubious events, fast path.
1872  * "Disorder"   In all the respects it is "Open",
1873  *              but requires a bit more attention. It is entered when
1874  *              we see some SACKs or dupacks. It is split of "Open"
1875  *              mainly to move some processing from fast path to slow one.
1876  * "CWR"        CWND was reduced due to some Congestion Notification event.
1877  *              It can be ECN, ICMP source quench, local device congestion.
1878  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1879  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1880  *
1881  * tcp_fastretrans_alert() is entered:
1882  * - each incoming ACK, if state is not "Open"
1883  * - when arrived ACK is unusual, namely:
1884  *      * SACK
1885  *      * Duplicate ACK.
1886  *      * ECN ECE.
1887  *
1888  * Counting packets in flight is pretty simple.
1889  *
1890  *      in_flight = packets_out - left_out + retrans_out
1891  *
1892  *      packets_out is SND.NXT-SND.UNA counted in packets.
1893  *
1894  *      retrans_out is number of retransmitted segments.
1895  *
1896  *      left_out is number of segments left network, but not ACKed yet.
1897  *
1898  *              left_out = sacked_out + lost_out
1899  *
1900  *     sacked_out: Packets, which arrived to receiver out of order
1901  *                 and hence not ACKed. With SACKs this number is simply
1902  *                 amount of SACKed data. Even without SACKs
1903  *                 it is easy to give pretty reliable estimate of this number,
1904  *                 counting duplicate ACKs.
1905  *
1906  *       lost_out: Packets lost by network. TCP has no explicit
1907  *                 "loss notification" feedback from network (for now).
1908  *                 It means that this number can be only _guessed_.
1909  *                 Actually, it is the heuristics to predict lossage that
1910  *                 distinguishes different algorithms.
1911  *
1912  *      F.e. after RTO, when all the queue is considered as lost,
1913  *      lost_out = packets_out and in_flight = retrans_out.
1914  *
1915  *              Essentially, we have now two algorithms counting
1916  *              lost packets.
1917  *
1918  *              FACK: It is the simplest heuristics. As soon as we decided
1919  *              that something is lost, we decide that _all_ not SACKed
1920  *              packets until the most forward SACK are lost. I.e.
1921  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
1922  *              It is absolutely correct estimate, if network does not reorder
1923  *              packets. And it loses any connection to reality when reordering
1924  *              takes place. We use FACK by default until reordering
1925  *              is suspected on the path to this destination.
1926  *
1927  *              NewReno: when Recovery is entered, we assume that one segment
1928  *              is lost (classic Reno). While we are in Recovery and
1929  *              a partial ACK arrives, we assume that one more packet
1930  *              is lost (NewReno). This heuristics are the same in NewReno
1931  *              and SACK.
1932  *
1933  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
1934  *  deflation etc. CWND is real congestion window, never inflated, changes
1935  *  only according to classic VJ rules.
1936  *
1937  * Really tricky (and requiring careful tuning) part of algorithm
1938  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
1939  * The first determines the moment _when_ we should reduce CWND and,
1940  * hence, slow down forward transmission. In fact, it determines the moment
1941  * when we decide that hole is caused by loss, rather than by a reorder.
1942  *
1943  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
1944  * holes, caused by lost packets.
1945  *
1946  * And the most logically complicated part of algorithm is undo
1947  * heuristics. We detect false retransmits due to both too early
1948  * fast retransmit (reordering) and underestimated RTO, analyzing
1949  * timestamps and D-SACKs. When we detect that some segments were
1950  * retransmitted by mistake and CWND reduction was wrong, we undo
1951  * window reduction and abort recovery phase. This logic is hidden
1952  * inside several functions named tcp_try_undo_<something>.
1953  */
1954
1955 /* This function decides, when we should leave Disordered state
1956  * and enter Recovery phase, reducing congestion window.
1957  *
1958  * Main question: may we further continue forward transmission
1959  * with the same cwnd?
1960  */
1961 static int tcp_time_to_recover(struct sock *sk)
1962 {
1963         struct tcp_sock *tp = tcp_sk(sk);
1964         __u32 packets_out;
1965
1966         /* Do not perform any recovery during F-RTO algorithm */
1967         if (tp->frto_counter)
1968                 return 0;
1969
1970         /* Trick#1: The loss is proven. */
1971         if (tp->lost_out)
1972                 return 1;
1973
1974         /* Not-A-Trick#2 : Classic rule... */
1975         if (tcp_fackets_out(tp) > tp->reordering)
1976                 return 1;
1977
1978         /* Trick#3 : when we use RFC2988 timer restart, fast
1979          * retransmit can be triggered by timeout of queue head.
1980          */
1981         if (tcp_head_timedout(sk))
1982                 return 1;
1983
1984         /* Trick#4: It is still not OK... But will it be useful to delay
1985          * recovery more?
1986          */
1987         packets_out = tp->packets_out;
1988         if (packets_out <= tp->reordering &&
1989             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
1990             !tcp_may_send_now(sk)) {
1991                 /* We have nothing to send. This connection is limited
1992                  * either by receiver window or by application.
1993                  */
1994                 return 1;
1995         }
1996
1997         return 0;
1998 }
1999
2000 /* RFC: This is from the original, I doubt that this is necessary at all:
2001  * clear xmit_retrans hint if seq of this skb is beyond hint. How could we
2002  * retransmitted past LOST markings in the first place? I'm not fully sure
2003  * about undo and end of connection cases, which can cause R without L?
2004  */
2005 static void tcp_verify_retransmit_hint(struct tcp_sock *tp,
2006                                        struct sk_buff *skb)
2007 {
2008         if ((tp->retransmit_skb_hint != NULL) &&
2009             before(TCP_SKB_CB(skb)->seq,
2010             TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
2011                 tp->retransmit_skb_hint = NULL;
2012 }
2013
2014 /* Mark head of queue up as lost. */
2015 static void tcp_mark_head_lost(struct sock *sk, int packets)
2016 {
2017         struct tcp_sock *tp = tcp_sk(sk);
2018         struct sk_buff *skb;
2019         int cnt;
2020
2021         BUG_TRAP(packets <= tp->packets_out);
2022         if (tp->lost_skb_hint) {
2023                 skb = tp->lost_skb_hint;
2024                 cnt = tp->lost_cnt_hint;
2025         } else {
2026                 skb = tcp_write_queue_head(sk);
2027                 cnt = 0;
2028         }
2029
2030         tcp_for_write_queue_from(skb, sk) {
2031                 if (skb == tcp_send_head(sk))
2032                         break;
2033                 /* TODO: do this better */
2034                 /* this is not the most efficient way to do this... */
2035                 tp->lost_skb_hint = skb;
2036                 tp->lost_cnt_hint = cnt;
2037                 cnt += tcp_skb_pcount(skb);
2038                 if (cnt > packets || after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2039                         break;
2040                 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
2041                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2042                         tp->lost_out += tcp_skb_pcount(skb);
2043                         tcp_verify_retransmit_hint(tp, skb);
2044                 }
2045         }
2046         tcp_verify_left_out(tp);
2047 }
2048
2049 /* Account newly detected lost packet(s) */
2050
2051 static void tcp_update_scoreboard(struct sock *sk)
2052 {
2053         struct tcp_sock *tp = tcp_sk(sk);
2054
2055         if (tcp_is_fack(tp)) {
2056                 int lost = tp->fackets_out - tp->reordering;
2057                 if (lost <= 0)
2058                         lost = 1;
2059                 tcp_mark_head_lost(sk, lost);
2060         } else {
2061                 tcp_mark_head_lost(sk, 1);
2062         }
2063
2064         /* New heuristics: it is possible only after we switched
2065          * to restart timer each time when something is ACKed.
2066          * Hence, we can detect timed out packets during fast
2067          * retransmit without falling to slow start.
2068          */
2069         if (!tcp_is_reno(tp) && tcp_head_timedout(sk)) {
2070                 struct sk_buff *skb;
2071
2072                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
2073                         : tcp_write_queue_head(sk);
2074
2075                 tcp_for_write_queue_from(skb, sk) {
2076                         if (skb == tcp_send_head(sk))
2077                                 break;
2078                         if (!tcp_skb_timedout(sk, skb))
2079                                 break;
2080
2081                         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
2082                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2083                                 tp->lost_out += tcp_skb_pcount(skb);
2084                                 tcp_verify_retransmit_hint(tp, skb);
2085                         }
2086                 }
2087
2088                 tp->scoreboard_skb_hint = skb;
2089
2090                 tcp_verify_left_out(tp);
2091         }
2092 }
2093
2094 /* CWND moderation, preventing bursts due to too big ACKs
2095  * in dubious situations.
2096  */
2097 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2098 {
2099         tp->snd_cwnd = min(tp->snd_cwnd,
2100                            tcp_packets_in_flight(tp)+tcp_max_burst(tp));
2101         tp->snd_cwnd_stamp = tcp_time_stamp;
2102 }
2103
2104 /* Lower bound on congestion window is slow start threshold
2105  * unless congestion avoidance choice decides to overide it.
2106  */
2107 static inline u32 tcp_cwnd_min(const struct sock *sk)
2108 {
2109         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2110
2111         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2112 }
2113
2114 /* Decrease cwnd each second ack. */
2115 static void tcp_cwnd_down(struct sock *sk, int flag)
2116 {
2117         struct tcp_sock *tp = tcp_sk(sk);
2118         int decr = tp->snd_cwnd_cnt + 1;
2119
2120         if ((flag&(FLAG_ANY_PROGRESS|FLAG_DSACKING_ACK)) ||
2121             (tcp_is_reno(tp) && !(flag&FLAG_NOT_DUP))) {
2122                 tp->snd_cwnd_cnt = decr&1;
2123                 decr >>= 1;
2124
2125                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2126                         tp->snd_cwnd -= decr;
2127
2128                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
2129                 tp->snd_cwnd_stamp = tcp_time_stamp;
2130         }
2131 }
2132
2133 /* Nothing was retransmitted or returned timestamp is less
2134  * than timestamp of the first retransmission.
2135  */
2136 static inline int tcp_packet_delayed(struct tcp_sock *tp)
2137 {
2138         return !tp->retrans_stamp ||
2139                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2140                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
2141 }
2142
2143 /* Undo procedures. */
2144
2145 #if FASTRETRANS_DEBUG > 1
2146 static void DBGUNDO(struct sock *sk, const char *msg)
2147 {
2148         struct tcp_sock *tp = tcp_sk(sk);
2149         struct inet_sock *inet = inet_sk(sk);
2150
2151         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
2152                msg,
2153                NIPQUAD(inet->daddr), ntohs(inet->dport),
2154                tp->snd_cwnd, tcp_left_out(tp),
2155                tp->snd_ssthresh, tp->prior_ssthresh,
2156                tp->packets_out);
2157 }
2158 #else
2159 #define DBGUNDO(x...) do { } while (0)
2160 #endif
2161
2162 static void tcp_undo_cwr(struct sock *sk, const int undo)
2163 {
2164         struct tcp_sock *tp = tcp_sk(sk);
2165
2166         if (tp->prior_ssthresh) {
2167                 const struct inet_connection_sock *icsk = inet_csk(sk);
2168
2169                 if (icsk->icsk_ca_ops->undo_cwnd)
2170                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2171                 else
2172                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);
2173
2174                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2175                         tp->snd_ssthresh = tp->prior_ssthresh;
2176                         TCP_ECN_withdraw_cwr(tp);
2177                 }
2178         } else {
2179                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2180         }
2181         tcp_moderate_cwnd(tp);
2182         tp->snd_cwnd_stamp = tcp_time_stamp;
2183
2184         /* There is something screwy going on with the retrans hints after
2185            an undo */
2186         tcp_clear_all_retrans_hints(tp);
2187 }
2188
2189 static inline int tcp_may_undo(struct tcp_sock *tp)
2190 {
2191         return tp->undo_marker &&
2192                 (!tp->undo_retrans || tcp_packet_delayed(tp));
2193 }
2194
2195 /* People celebrate: "We love our President!" */
2196 static int tcp_try_undo_recovery(struct sock *sk)
2197 {
2198         struct tcp_sock *tp = tcp_sk(sk);
2199
2200         if (tcp_may_undo(tp)) {
2201                 /* Happy end! We did not retransmit anything
2202                  * or our original transmission succeeded.
2203                  */
2204                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2205                 tcp_undo_cwr(sk, 1);
2206                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2207                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2208                 else
2209                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
2210                 tp->undo_marker = 0;
2211         }
2212         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2213                 /* Hold old state until something *above* high_seq
2214                  * is ACKed. For Reno it is MUST to prevent false
2215                  * fast retransmits (RFC2582). SACK TCP is safe. */
2216                 tcp_moderate_cwnd(tp);
2217                 return 1;
2218         }
2219         tcp_set_ca_state(sk, TCP_CA_Open);
2220         return 0;
2221 }
2222
2223 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2224 static void tcp_try_undo_dsack(struct sock *sk)
2225 {
2226         struct tcp_sock *tp = tcp_sk(sk);
2227
2228         if (tp->undo_marker && !tp->undo_retrans) {
2229                 DBGUNDO(sk, "D-SACK");
2230                 tcp_undo_cwr(sk, 1);
2231                 tp->undo_marker = 0;
2232                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
2233         }
2234 }
2235
2236 /* Undo during fast recovery after partial ACK. */
2237
2238 static int tcp_try_undo_partial(struct sock *sk, int acked)
2239 {
2240         struct tcp_sock *tp = tcp_sk(sk);
2241         /* Partial ACK arrived. Force Hoe's retransmit. */
2242         int failed = tcp_is_reno(tp) || tp->fackets_out>tp->reordering;
2243
2244         if (tcp_may_undo(tp)) {
2245                 /* Plain luck! Hole if filled with delayed
2246                  * packet, rather than with a retransmit.
2247                  */
2248                 if (tp->retrans_out == 0)
2249                         tp->retrans_stamp = 0;
2250
2251                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2252
2253                 DBGUNDO(sk, "Hoe");
2254                 tcp_undo_cwr(sk, 0);
2255                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
2256
2257                 /* So... Do not make Hoe's retransmit yet.
2258                  * If the first packet was delayed, the rest
2259                  * ones are most probably delayed as well.
2260                  */
2261                 failed = 0;
2262         }
2263         return failed;
2264 }
2265
2266 /* Undo during loss recovery after partial ACK. */
2267 static int tcp_try_undo_loss(struct sock *sk)
2268 {
2269         struct tcp_sock *tp = tcp_sk(sk);
2270
2271         if (tcp_may_undo(tp)) {
2272                 struct sk_buff *skb;
2273                 tcp_for_write_queue(skb, sk) {
2274                         if (skb == tcp_send_head(sk))
2275                                 break;
2276                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2277                 }
2278
2279                 tcp_clear_all_retrans_hints(tp);
2280
2281                 DBGUNDO(sk, "partial loss");
2282                 tp->lost_out = 0;
2283                 tcp_undo_cwr(sk, 1);
2284                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2285                 inet_csk(sk)->icsk_retransmits = 0;
2286                 tp->undo_marker = 0;
2287                 if (tcp_is_sack(tp))
2288                         tcp_set_ca_state(sk, TCP_CA_Open);
2289                 return 1;
2290         }
2291         return 0;
2292 }
2293
2294 static inline void tcp_complete_cwr(struct sock *sk)
2295 {
2296         struct tcp_sock *tp = tcp_sk(sk);
2297         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2298         tp->snd_cwnd_stamp = tcp_time_stamp;
2299         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2300 }
2301
2302 static void tcp_try_to_open(struct sock *sk, int flag)
2303 {
2304         struct tcp_sock *tp = tcp_sk(sk);
2305
2306         tcp_verify_left_out(tp);
2307
2308         if (tp->retrans_out == 0)
2309                 tp->retrans_stamp = 0;
2310
2311         if (flag&FLAG_ECE)
2312                 tcp_enter_cwr(sk, 1);
2313
2314         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2315                 int state = TCP_CA_Open;
2316
2317                 if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2318                         state = TCP_CA_Disorder;
2319
2320                 if (inet_csk(sk)->icsk_ca_state != state) {
2321                         tcp_set_ca_state(sk, state);
2322                         tp->high_seq = tp->snd_nxt;
2323                 }
2324                 tcp_moderate_cwnd(tp);
2325         } else {
2326                 tcp_cwnd_down(sk, flag);
2327         }
2328 }
2329
2330 static void tcp_mtup_probe_failed(struct sock *sk)
2331 {
2332         struct inet_connection_sock *icsk = inet_csk(sk);
2333
2334         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2335         icsk->icsk_mtup.probe_size = 0;
2336 }
2337
2338 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
2339 {
2340         struct tcp_sock *tp = tcp_sk(sk);
2341         struct inet_connection_sock *icsk = inet_csk(sk);
2342
2343         /* FIXME: breaks with very large cwnd */
2344         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2345         tp->snd_cwnd = tp->snd_cwnd *
2346                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2347                        icsk->icsk_mtup.probe_size;
2348         tp->snd_cwnd_cnt = 0;
2349         tp->snd_cwnd_stamp = tcp_time_stamp;
2350         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2351
2352         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2353         icsk->icsk_mtup.probe_size = 0;
2354         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2355 }
2356
2357
2358 /* Process an event, which can update packets-in-flight not trivially.
2359  * Main goal of this function is to calculate new estimate for left_out,
2360  * taking into account both packets sitting in receiver's buffer and
2361  * packets lost by network.
2362  *
2363  * Besides that it does CWND reduction, when packet loss is detected
2364  * and changes state of machine.
2365  *
2366  * It does _not_ decide what to send, it is made in function
2367  * tcp_xmit_retransmit_queue().
2368  */
2369 static void
2370 tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2371 {
2372         struct inet_connection_sock *icsk = inet_csk(sk);
2373         struct tcp_sock *tp = tcp_sk(sk);
2374         int is_dupack = !(flag&(FLAG_SND_UNA_ADVANCED|FLAG_NOT_DUP));
2375         int do_lost = is_dupack || ((flag&FLAG_DATA_SACKED) &&
2376                                     (tp->fackets_out > tp->reordering));
2377
2378         /* Some technical things:
2379          * 1. Reno does not count dupacks (sacked_out) automatically. */
2380         if (!tp->packets_out)
2381                 tp->sacked_out = 0;
2382
2383         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2384                 tp->fackets_out = 0;
2385
2386         /* Now state machine starts.
2387          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2388         if (flag&FLAG_ECE)
2389                 tp->prior_ssthresh = 0;
2390
2391         /* B. In all the states check for reneging SACKs. */
2392         if (tp->sacked_out && tcp_check_sack_reneging(sk))
2393                 return;
2394
2395         /* C. Process data loss notification, provided it is valid. */
2396         if ((flag&FLAG_DATA_LOST) &&
2397             before(tp->snd_una, tp->high_seq) &&
2398             icsk->icsk_ca_state != TCP_CA_Open &&
2399             tp->fackets_out > tp->reordering) {
2400                 tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering);
2401                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
2402         }
2403
2404         /* D. Check consistency of the current state. */
2405         tcp_verify_left_out(tp);
2406
2407         /* E. Check state exit conditions. State can be terminated
2408          *    when high_seq is ACKed. */
2409         if (icsk->icsk_ca_state == TCP_CA_Open) {
2410                 BUG_TRAP(tp->retrans_out == 0);
2411                 tp->retrans_stamp = 0;
2412         } else if (!before(tp->snd_una, tp->high_seq)) {
2413                 switch (icsk->icsk_ca_state) {
2414                 case TCP_CA_Loss:
2415                         icsk->icsk_retransmits = 0;
2416                         if (tcp_try_undo_recovery(sk))
2417                                 return;
2418                         break;
2419
2420                 case TCP_CA_CWR:
2421                         /* CWR is to be held something *above* high_seq
2422                          * is ACKed for CWR bit to reach receiver. */
2423                         if (tp->snd_una != tp->high_seq) {
2424                                 tcp_complete_cwr(sk);
2425                                 tcp_set_ca_state(sk, TCP_CA_Open);
2426                         }
2427                         break;
2428
2429                 case TCP_CA_Disorder:
2430                         tcp_try_undo_dsack(sk);
2431                         if (!tp->undo_marker ||
2432                             /* For SACK case do not Open to allow to undo
2433                              * catching for all duplicate ACKs. */
2434                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2435                                 tp->undo_marker = 0;
2436                                 tcp_set_ca_state(sk, TCP_CA_Open);
2437                         }
2438                         break;
2439
2440                 case TCP_CA_Recovery:
2441                         if (tcp_is_reno(tp))
2442                                 tcp_reset_reno_sack(tp);
2443                         if (tcp_try_undo_recovery(sk))
2444                                 return;
2445                         tcp_complete_cwr(sk);
2446                         break;
2447                 }
2448         }
2449
2450         /* F. Process state. */
2451         switch (icsk->icsk_ca_state) {
2452         case TCP_CA_Recovery:
2453                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2454                         if (tcp_is_reno(tp) && is_dupack)
2455                                 tcp_add_reno_sack(sk);
2456                 } else
2457                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
2458                 break;
2459         case TCP_CA_Loss:
2460                 if (flag&FLAG_DATA_ACKED)
2461                         icsk->icsk_retransmits = 0;
2462                 if (!tcp_try_undo_loss(sk)) {
2463                         tcp_moderate_cwnd(tp);
2464                         tcp_xmit_retransmit_queue(sk);
2465                         return;
2466                 }
2467                 if (icsk->icsk_ca_state != TCP_CA_Open)
2468                         return;
2469                 /* Loss is undone; fall through to processing in Open state. */
2470         default:
2471                 if (tcp_is_reno(tp)) {
2472                         if (flag & FLAG_SND_UNA_ADVANCED)
2473                                 tcp_reset_reno_sack(tp);
2474                         if (is_dupack)
2475                                 tcp_add_reno_sack(sk);
2476                 }
2477
2478                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2479                         tcp_try_undo_dsack(sk);
2480
2481                 if (!tcp_time_to_recover(sk)) {
2482                         tcp_try_to_open(sk, flag);
2483                         return;
2484                 }
2485
2486                 /* MTU probe failure: don't reduce cwnd */
2487                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2488                     icsk->icsk_mtup.probe_size &&
2489                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2490                         tcp_mtup_probe_failed(sk);
2491                         /* Restores the reduction we did in tcp_mtup_probe() */
2492                         tp->snd_cwnd++;
2493                         tcp_simple_retransmit(sk);
2494                         return;
2495                 }
2496
2497                 /* Otherwise enter Recovery state */
2498
2499                 if (tcp_is_reno(tp))
2500                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2501                 else
2502                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2503
2504                 tp->high_seq = tp->snd_nxt;
2505                 tp->prior_ssthresh = 0;
2506                 tp->undo_marker = tp->snd_una;
2507                 tp->undo_retrans = tp->retrans_out;
2508
2509                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2510                         if (!(flag&FLAG_ECE))
2511                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2512                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2513                         TCP_ECN_queue_cwr(tp);
2514                 }
2515
2516                 tp->bytes_acked = 0;
2517                 tp->snd_cwnd_cnt = 0;
2518                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2519         }
2520
2521         if (do_lost || tcp_head_timedout(sk))
2522                 tcp_update_scoreboard(sk);
2523         tcp_cwnd_down(sk, flag);
2524         tcp_xmit_retransmit_queue(sk);
2525 }
2526
2527 /* Read draft-ietf-tcplw-high-performance before mucking
2528  * with this code. (Supersedes RFC1323)
2529  */
2530 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2531 {
2532         /* RTTM Rule: A TSecr value received in a segment is used to
2533          * update the averaged RTT measurement only if the segment
2534          * acknowledges some new data, i.e., only if it advances the
2535          * left edge of the send window.
2536          *
2537          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2538          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2539          *
2540          * Changed: reset backoff as soon as we see the first valid sample.
2541          * If we do not, we get strongly overestimated rto. With timestamps
2542          * samples are accepted even from very old segments: f.e., when rtt=1
2543          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2544          * answer arrives rto becomes 120 seconds! If at least one of segments
2545          * in window is lost... Voila.                          --ANK (010210)
2546          */
2547         struct tcp_sock *tp = tcp_sk(sk);
2548         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2549         tcp_rtt_estimator(sk, seq_rtt);
2550         tcp_set_rto(sk);
2551         inet_csk(sk)->icsk_backoff = 0;
2552         tcp_bound_rto(sk);
2553 }
2554
2555 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2556 {
2557         /* We don't have a timestamp. Can only use
2558          * packets that are not retransmitted to determine
2559          * rtt estimates. Also, we must not reset the
2560          * backoff for rto until we get a non-retransmitted
2561          * packet. This allows us to deal with a situation
2562          * where the network delay has increased suddenly.
2563          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2564          */
2565
2566         if (flag & FLAG_RETRANS_DATA_ACKED)
2567                 return;
2568
2569         tcp_rtt_estimator(sk, seq_rtt);
2570         tcp_set_rto(sk);
2571         inet_csk(sk)->icsk_backoff = 0;
2572         tcp_bound_rto(sk);
2573 }
2574
2575 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2576                                       const s32 seq_rtt)
2577 {
2578         const struct tcp_sock *tp = tcp_sk(sk);
2579         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2580         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2581                 tcp_ack_saw_tstamp(sk, flag);
2582         else if (seq_rtt >= 0)
2583                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2584 }
2585
2586 static void tcp_cong_avoid(struct sock *sk, u32 ack,
2587                            u32 in_flight, int good)
2588 {
2589         const struct inet_connection_sock *icsk = inet_csk(sk);
2590         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight, good);
2591         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2592 }
2593
2594 /* Restart timer after forward progress on connection.
2595  * RFC2988 recommends to restart timer to now+rto.
2596  */
2597 static void tcp_rearm_rto(struct sock *sk)
2598 {
2599         struct tcp_sock *tp = tcp_sk(sk);
2600
2601         if (!tp->packets_out) {
2602                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2603         } else {
2604                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2605         }
2606 }
2607
2608 /* If we get here, the whole TSO packet has not been acked. */
2609 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
2610 {
2611         struct tcp_sock *tp = tcp_sk(sk);
2612         u32 packets_acked;
2613
2614         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
2615
2616         packets_acked = tcp_skb_pcount(skb);
2617         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2618                 return 0;
2619         packets_acked -= tcp_skb_pcount(skb);
2620
2621         if (packets_acked) {
2622                 BUG_ON(tcp_skb_pcount(skb) == 0);
2623                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
2624         }
2625
2626         return packets_acked;
2627 }
2628
2629 /* Remove acknowledged frames from the retransmission queue. If our packet
2630  * is before the ack sequence we can discard it as it's confirmed to have
2631  * arrived at the other end.
2632  */
2633 static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p)
2634 {
2635         struct tcp_sock *tp = tcp_sk(sk);
2636         const struct inet_connection_sock *icsk = inet_csk(sk);
2637         struct sk_buff *skb;
2638         u32 now = tcp_time_stamp;
2639         int fully_acked = 1;
2640         int flag = 0;
2641         int prior_packets = tp->packets_out;
2642         s32 seq_rtt = -1;
2643         ktime_t last_ackt = net_invalid_timestamp();
2644
2645         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
2646                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2647                 u32 end_seq;
2648                 u32 packets_acked;
2649                 u8 sacked = scb->sacked;
2650
2651                 if (after(scb->end_seq, tp->snd_una)) {
2652                         if (tcp_skb_pcount(skb) == 1 ||
2653                             !after(tp->snd_una, scb->seq))
2654                                 break;
2655
2656                         packets_acked = tcp_tso_acked(sk, skb);
2657                         if (!packets_acked)
2658                                 break;
2659
2660                         fully_acked = 0;
2661                         end_seq = tp->snd_una;
2662                 } else {
2663                         packets_acked = tcp_skb_pcount(skb);
2664                         end_seq = scb->end_seq;
2665                 }
2666
2667                 /* MTU probing checks */
2668                 if (fully_acked && icsk->icsk_mtup.probe_size &&
2669                     !after(tp->mtu_probe.probe_seq_end, scb->end_seq)) {
2670                         tcp_mtup_probe_success(sk, skb);
2671                 }
2672
2673                 if (sacked) {
2674                         if (sacked & TCPCB_RETRANS) {
2675                                 if (sacked & TCPCB_SACKED_RETRANS)
2676                                         tp->retrans_out -= packets_acked;
2677                                 flag |= FLAG_RETRANS_DATA_ACKED;
2678                                 seq_rtt = -1;
2679                                 if ((flag & FLAG_DATA_ACKED) ||
2680                                     (packets_acked > 1))
2681                                         flag |= FLAG_NONHEAD_RETRANS_ACKED;
2682                         } else if (seq_rtt < 0) {
2683                                 seq_rtt = now - scb->when;
2684                                 if (fully_acked)
2685                                         last_ackt = skb->tstamp;
2686                         }
2687
2688                         if (sacked & TCPCB_SACKED_ACKED)
2689                                 tp->sacked_out -= packets_acked;
2690                         if (sacked & TCPCB_LOST)
2691                                 tp->lost_out -= packets_acked;
2692
2693                         if ((sacked & TCPCB_URG) && tp->urg_mode &&
2694                             !before(end_seq, tp->snd_up))
2695                                 tp->urg_mode = 0;
2696                 } else if (seq_rtt < 0) {
2697                         seq_rtt = now - scb->when;
2698                         if (fully_acked)
2699                                 last_ackt = skb->tstamp;
2700                 }
2701                 tp->packets_out -= packets_acked;
2702
2703                 /* Initial outgoing SYN's get put onto the write_queue
2704                  * just like anything else we transmit.  It is not
2705                  * true data, and if we misinform our callers that
2706                  * this ACK acks real data, we will erroneously exit
2707                  * connection startup slow start one packet too
2708                  * quickly.  This is severely frowned upon behavior.
2709                  */
2710                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2711                         flag |= FLAG_DATA_ACKED;
2712                 } else {
2713                         flag |= FLAG_SYN_ACKED;
2714                         tp->retrans_stamp = 0;
2715                 }
2716
2717                 if (!fully_acked)
2718                         break;
2719
2720                 tcp_unlink_write_queue(skb, sk);
2721                 sk_stream_free_skb(sk, skb);
2722                 tcp_clear_all_retrans_hints(tp);
2723         }
2724
2725         if (flag & FLAG_ACKED) {
2726                 u32 pkts_acked = prior_packets - tp->packets_out;
2727                 const struct tcp_congestion_ops *ca_ops
2728                         = inet_csk(sk)->icsk_ca_ops;
2729
2730                 tcp_ack_update_rtt(sk, flag, seq_rtt);
2731                 tcp_rearm_rto(sk);
2732
2733                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
2734                 /* hint's skb might be NULL but we don't need to care */
2735                 tp->fastpath_cnt_hint -= min_t(u32, pkts_acked,
2736                                                tp->fastpath_cnt_hint);
2737                 if (tcp_is_reno(tp))
2738                         tcp_remove_reno_sacks(sk, pkts_acked);
2739
2740                 if (ca_ops->pkts_acked) {
2741                         s32 rtt_us = -1;
2742
2743                         /* Is the ACK triggering packet unambiguous? */
2744                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
2745                                 /* High resolution needed and available? */
2746                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
2747                                     !ktime_equal(last_ackt,
2748                                                  net_invalid_timestamp()))
2749                                         rtt_us = ktime_us_delta(ktime_get_real(),
2750                                                                 last_ackt);
2751                                 else if (seq_rtt > 0)
2752                                         rtt_us = jiffies_to_usecs(seq_rtt);
2753                         }
2754
2755                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
2756                 }
2757         }
2758
2759 #if FASTRETRANS_DEBUG > 0
2760         BUG_TRAP((int)tp->sacked_out >= 0);
2761         BUG_TRAP((int)tp->lost_out >= 0);
2762         BUG_TRAP((int)tp->retrans_out >= 0);
2763         if (!tp->packets_out && tcp_is_sack(tp)) {
2764                 icsk = inet_csk(sk);
2765                 if (tp->lost_out) {
2766                         printk(KERN_DEBUG "Leak l=%u %d\n",
2767                                tp->lost_out, icsk->icsk_ca_state);
2768                         tp->lost_out = 0;
2769                 }
2770                 if (tp->sacked_out) {
2771                         printk(KERN_DEBUG "Leak s=%u %d\n",
2772                                tp->sacked_out, icsk->icsk_ca_state);
2773                         tp->sacked_out = 0;
2774                 }
2775                 if (tp->retrans_out) {
2776                         printk(KERN_DEBUG "Leak r=%u %d\n",
2777                                tp->retrans_out, icsk->icsk_ca_state);
2778                         tp->retrans_out = 0;
2779                 }
2780         }
2781 #endif
2782         *seq_rtt_p = seq_rtt;
2783         return flag;
2784 }
2785
2786 static void tcp_ack_probe(struct sock *sk)
2787 {
2788         const struct tcp_sock *tp = tcp_sk(sk);
2789         struct inet_connection_sock *icsk = inet_csk(sk);
2790
2791         /* Was it a usable window open? */
2792
2793         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2794                    tp->snd_una + tp->snd_wnd)) {
2795                 icsk->icsk_backoff = 0;
2796                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2797                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2798                  * This function is not for random using!
2799                  */
2800         } else {
2801                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2802                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2803                                           TCP_RTO_MAX);
2804         }
2805 }
2806
2807 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2808 {
2809         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2810                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2811 }
2812
2813 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2814 {
2815         const struct tcp_sock *tp = tcp_sk(sk);
2816         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2817                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2818 }
2819
2820 /* Check that window update is acceptable.
2821  * The function assumes that snd_una<=ack<=snd_next.
2822  */
2823 static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
2824                                         const u32 ack_seq, const u32 nwin)
2825 {
2826         return (after(ack, tp->snd_una) ||
2827                 after(ack_seq, tp->snd_wl1) ||
2828                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2829 }
2830
2831 /* Update our send window.
2832  *
2833  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2834  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2835  */
2836 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
2837                                  u32 ack_seq)
2838 {
2839         struct tcp_sock *tp = tcp_sk(sk);
2840         int flag = 0;
2841         u32 nwin = ntohs(tcp_hdr(skb)->window);
2842
2843         if (likely(!tcp_hdr(skb)->syn))
2844                 nwin <<= tp->rx_opt.snd_wscale;
2845
2846         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2847                 flag |= FLAG_WIN_UPDATE;
2848                 tcp_update_wl(tp, ack, ack_seq);
2849
2850                 if (tp->snd_wnd != nwin) {
2851                         tp->snd_wnd = nwin;
2852
2853                         /* Note, it is the only place, where
2854                          * fast path is recovered for sending TCP.
2855                          */
2856                         tp->pred_flags = 0;
2857                         tcp_fast_path_check(sk);
2858
2859                         if (nwin > tp->max_window) {
2860                                 tp->max_window = nwin;
2861                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2862                         }
2863                 }
2864         }
2865
2866         tp->snd_una = ack;
2867
2868         return flag;
2869 }
2870
2871 /* A very conservative spurious RTO response algorithm: reduce cwnd and
2872  * continue in congestion avoidance.
2873  */
2874 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
2875 {
2876         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2877         tp->snd_cwnd_cnt = 0;
2878         tp->bytes_acked = 0;
2879         TCP_ECN_queue_cwr(tp);
2880         tcp_moderate_cwnd(tp);
2881 }
2882
2883 /* A conservative spurious RTO response algorithm: reduce cwnd using
2884  * rate halving and continue in congestion avoidance.
2885  */
2886 static void tcp_ratehalving_spur_to_response(struct sock *sk)
2887 {
2888         tcp_enter_cwr(sk, 0);
2889 }
2890
2891 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
2892 {
2893         if (flag&FLAG_ECE)
2894                 tcp_ratehalving_spur_to_response(sk);
2895         else
2896                 tcp_undo_cwr(sk, 1);
2897 }
2898
2899 /* F-RTO spurious RTO detection algorithm (RFC4138)
2900  *
2901  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
2902  * comments). State (ACK number) is kept in frto_counter. When ACK advances
2903  * window (but not to or beyond highest sequence sent before RTO):
2904  *   On First ACK,  send two new segments out.
2905  *   On Second ACK, RTO was likely spurious. Do spurious response (response
2906  *                  algorithm is not part of the F-RTO detection algorithm
2907  *                  given in RFC4138 but can be selected separately).
2908  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
2909  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
2910  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
2911  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
2912  *
2913  * Rationale: if the RTO was spurious, new ACKs should arrive from the
2914  * original window even after we transmit two new data segments.
2915  *
2916  * SACK version:
2917  *   on first step, wait until first cumulative ACK arrives, then move to
2918  *   the second step. In second step, the next ACK decides.
2919  *
2920  * F-RTO is implemented (mainly) in four functions:
2921  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
2922  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
2923  *     called when tcp_use_frto() showed green light
2924  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
2925  *   - tcp_enter_frto_loss() is called if there is not enough evidence
2926  *     to prove that the RTO is indeed spurious. It transfers the control
2927  *     from F-RTO to the conventional RTO recovery
2928  */
2929 static int tcp_process_frto(struct sock *sk, int flag)
2930 {
2931         struct tcp_sock *tp = tcp_sk(sk);
2932
2933         tcp_verify_left_out(tp);
2934
2935         /* Duplicate the behavior from Loss state (fastretrans_alert) */
2936         if (flag&FLAG_DATA_ACKED)
2937                 inet_csk(sk)->icsk_retransmits = 0;
2938
2939         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
2940             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
2941                 tp->undo_marker = 0;
2942
2943         if (!before(tp->snd_una, tp->frto_highmark)) {
2944                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
2945                 return 1;
2946         }
2947
2948         if (!IsSackFrto() || tcp_is_reno(tp)) {
2949                 /* RFC4138 shortcoming in step 2; should also have case c):
2950                  * ACK isn't duplicate nor advances window, e.g., opposite dir
2951                  * data, winupdate
2952                  */
2953                 if (!(flag&FLAG_ANY_PROGRESS) && (flag&FLAG_NOT_DUP))
2954                         return 1;
2955
2956                 if (!(flag&FLAG_DATA_ACKED)) {
2957                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
2958                                             flag);
2959                         return 1;
2960                 }
2961         } else {
2962                 if (!(flag&FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
2963                         /* Prevent sending of new data. */
2964                         tp->snd_cwnd = min(tp->snd_cwnd,
2965                                            tcp_packets_in_flight(tp));
2966                         return 1;
2967                 }
2968
2969                 if ((tp->frto_counter >= 2) &&
2970                     (!(flag&FLAG_FORWARD_PROGRESS) ||
2971                      ((flag&FLAG_DATA_SACKED) && !(flag&FLAG_ONLY_ORIG_SACKED)))) {
2972                         /* RFC4138 shortcoming (see comment above) */
2973                         if (!(flag&FLAG_FORWARD_PROGRESS) && (flag&FLAG_NOT_DUP))
2974                                 return 1;
2975
2976                         tcp_enter_frto_loss(sk, 3, flag);
2977                         return 1;
2978                 }
2979         }
2980
2981         if (tp->frto_counter == 1) {
2982                 /* Sending of the next skb must be allowed or no F-RTO */
2983                 if (!tcp_send_head(sk) ||
2984                     after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
2985                                      tp->snd_una + tp->snd_wnd)) {
2986                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3),
2987                                             flag);
2988                         return 1;
2989                 }
2990
2991                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
2992                 tp->frto_counter = 2;
2993                 return 1;
2994         } else {
2995                 switch (sysctl_tcp_frto_response) {
2996                 case 2:
2997                         tcp_undo_spur_to_response(sk, flag);
2998                         break;
2999                 case 1:
3000                         tcp_conservative_spur_to_response(tp);
3001                         break;
3002                 default:
3003                         tcp_ratehalving_spur_to_response(sk);
3004                         break;
3005                 }
3006                 tp->frto_counter = 0;
3007                 tp->undo_marker = 0;
3008                 NET_INC_STATS_BH(LINUX_MIB_TCPSPURIOUSRTOS);
3009         }
3010         return 0;
3011 }
3012
3013 /* This routine deals with incoming acks, but not outgoing ones. */
3014 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3015 {
3016         struct inet_connection_sock *icsk = inet_csk(sk);
3017         struct tcp_sock *tp = tcp_sk(sk);
3018         u32 prior_snd_una = tp->snd_una;
3019         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3020         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3021         u32 prior_in_flight;
3022         s32 seq_rtt;
3023         int prior_packets;
3024         int frto_cwnd = 0;
3025
3026         /* If the ack is newer than sent or older than previous acks
3027          * then we can probably ignore it.
3028          */
3029         if (after(ack, tp->snd_nxt))
3030                 goto uninteresting_ack;
3031
3032         if (before(ack, prior_snd_una))
3033                 goto old_ack;
3034
3035         if (after(ack, prior_snd_una))
3036                 flag |= FLAG_SND_UNA_ADVANCED;
3037
3038         if (sysctl_tcp_abc) {
3039                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3040                         tp->bytes_acked += ack - prior_snd_una;
3041                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3042                         /* we assume just one segment left network */
3043                         tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
3044         }
3045
3046         if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3047                 /* Window is constant, pure forward advance.
3048                  * No more checks are required.
3049                  * Note, we use the fact that SND.UNA>=SND.WL2.
3050                  */
3051                 tcp_update_wl(tp, ack, ack_seq);
3052                 tp->snd_una = ack;
3053                 flag |= FLAG_WIN_UPDATE;
3054
3055                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3056
3057                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
3058         } else {
3059                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3060                         flag |= FLAG_DATA;
3061                 else
3062                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
3063
3064                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3065
3066                 if (TCP_SKB_CB(skb)->sacked)
3067                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3068
3069                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3070                         flag |= FLAG_ECE;
3071
3072                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3073         }
3074
3075         /* We passed data and got it acked, remove any soft error
3076          * log. Something worked...
3077          */
3078         sk->sk_err_soft = 0;
3079         tp->rcv_tstamp = tcp_time_stamp;
3080         prior_packets = tp->packets_out;
3081         if (!prior_packets)
3082                 goto no_queue;
3083
3084         prior_in_flight = tcp_packets_in_flight(tp);
3085
3086         /* See if we can take anything off of the retransmit queue. */
3087         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
3088
3089         /* Guarantee sacktag reordering detection against wrap-arounds */
3090         if (before(tp->frto_highmark, tp->snd_una))
3091                 tp->frto_highmark = 0;
3092         if (tp->frto_counter)
3093                 frto_cwnd = tcp_process_frto(sk, flag);
3094
3095         if (tcp_ack_is_dubious(sk, flag)) {
3096                 /* Advance CWND, if state allows this. */
3097                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3098                     tcp_may_raise_cwnd(sk, flag))
3099                         tcp_cong_avoid(sk, ack, prior_in_flight, 0);
3100                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out, flag);
3101         } else {
3102                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3103                         tcp_cong_avoid(sk, ack, prior_in_flight, 1);
3104         }
3105
3106         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
3107                 dst_confirm(sk->sk_dst_cache);
3108
3109         return 1;
3110
3111 no_queue:
3112         icsk->icsk_probes_out = 0;
3113
3114         /* If this ack opens up a zero window, clear backoff.  It was
3115          * being used to time the probes, and is probably far higher than
3116          * it needs to be for normal retransmission.
3117          */
3118         if (tcp_send_head(sk))
3119                 tcp_ack_probe(sk);
3120         return 1;
3121
3122 old_ack:
3123         if (TCP_SKB_CB(skb)->sacked)
3124                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3125
3126 uninteresting_ack:
3127         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3128         return 0;
3129 }
3130
3131
3132 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3133  * But, this can also be called on packets in the established flow when
3134  * the fast version below fails.
3135  */
3136 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
3137 {
3138         unsigned char *ptr;
3139         struct tcphdr *th = tcp_hdr(skb);
3140         int length=(th->doff*4)-sizeof(struct tcphdr);
3141
3142         ptr = (unsigned char *)(th + 1);
3143         opt_rx->saw_tstamp = 0;
3144
3145         while (length > 0) {
3146                 int opcode=*ptr++;
3147                 int opsize;
3148
3149                 switch (opcode) {
3150                         case TCPOPT_EOL:
3151                                 return;
3152                         case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3153                                 length--;
3154                                 continue;
3155                         default:
3156                                 opsize=*ptr++;
3157                                 if (opsize < 2) /* "silly options" */
3158                                         return;
3159                                 if (opsize > length)
3160                                         return; /* don't parse partial options */
3161                                 switch (opcode) {
3162                                 case TCPOPT_MSS:
3163                                         if (opsize==TCPOLEN_MSS && th->syn && !estab) {
3164                                                 u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
3165                                                 if (in_mss) {
3166                                                         if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
3167                                                                 in_mss = opt_rx->user_mss;
3168                                                         opt_rx->mss_clamp = in_mss;
3169                                                 }
3170                                         }
3171                                         break;
3172                                 case TCPOPT_WINDOW:
3173                                         if (opsize==TCPOLEN_WINDOW && th->syn && !estab)
3174                                                 if (sysctl_tcp_window_scaling) {
3175                                                         __u8 snd_wscale = *(__u8 *) ptr;
3176                                                         opt_rx->wscale_ok = 1;
3177                                                         if (snd_wscale > 14) {
3178                                                                 if (net_ratelimit())
3179                                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3180                                                                                "scaling value %d >14 received.\n",
3181                                                                                snd_wscale);
3182                                                                 snd_wscale = 14;
3183                                                         }
3184                                                         opt_rx->snd_wscale = snd_wscale;
3185                                                 }
3186                                         break;
3187                                 case TCPOPT_TIMESTAMP:
3188                                         if (opsize==TCPOLEN_TIMESTAMP) {
3189                                                 if ((estab && opt_rx->tstamp_ok) ||
3190                                                     (!estab && sysctl_tcp_timestamps)) {
3191                                                         opt_rx->saw_tstamp = 1;
3192                                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
3193                                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
3194                                                 }
3195                                         }
3196                                         break;
3197                                 case TCPOPT_SACK_PERM:
3198                                         if (opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
3199                                                 if (sysctl_tcp_sack) {
3200                                                         opt_rx->sack_ok = 1;
3201                                                         tcp_sack_reset(opt_rx);
3202                                                 }
3203                                         }
3204                                         break;
3205
3206                                 case TCPOPT_SACK:
3207                                         if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3208                                            !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3209                                            opt_rx->sack_ok) {
3210                                                 TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3211                                         }
3212                                         break;
3213 #ifdef CONFIG_TCP_MD5SIG
3214                                 case TCPOPT_MD5SIG:
3215                                         /*
3216                                          * The MD5 Hash has already been
3217                                          * checked (see tcp_v{4,6}_do_rcv()).
3218                                          */
3219                                         break;
3220 #endif
3221                                 }
3222
3223                                 ptr+=opsize-2;
3224                                 length-=opsize;
3225                 }
3226         }
3227 }
3228
3229 /* Fast parse options. This hopes to only see timestamps.
3230  * If it is wrong it falls back on tcp_parse_options().
3231  */
3232 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3233                                   struct tcp_sock *tp)
3234 {
3235         if (th->doff == sizeof(struct tcphdr)>>2) {
3236                 tp->rx_opt.saw_tstamp = 0;
3237                 return 0;
3238         } else if (tp->rx_opt.tstamp_ok &&
3239                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3240                 __be32 *ptr = (__be32 *)(th + 1);
3241                 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3242                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3243                         tp->rx_opt.saw_tstamp = 1;
3244                         ++ptr;
3245                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3246                         ++ptr;
3247                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3248                         return 1;
3249                 }
3250         }
3251         tcp_parse_options(skb, &tp->rx_opt, 1);
3252         return 1;
3253 }
3254
3255 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3256 {
3257         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3258         tp->rx_opt.ts_recent_stamp = get_seconds();
3259 }
3260
3261 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3262 {
3263         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3264                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3265                  * extra check below makes sure this can only happen
3266                  * for pure ACK frames.  -DaveM
3267                  *
3268                  * Not only, also it occurs for expired timestamps.
3269                  */
3270
3271                 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
3272                    get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
3273                         tcp_store_ts_recent(tp);
3274         }
3275 }
3276
3277 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3278  *
3279  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3280  * it can pass through stack. So, the following predicate verifies that
3281  * this segment is not used for anything but congestion avoidance or
3282  * fast retransmit. Moreover, we even are able to eliminate most of such
3283  * second order effects, if we apply some small "replay" window (~RTO)
3284  * to timestamp space.
3285  *
3286  * All these measures still do not guarantee that we reject wrapped ACKs
3287  * on networks with high bandwidth, when sequence space is recycled fastly,
3288  * but it guarantees that such events will be very rare and do not affect
3289  * connection seriously. This doesn't look nice, but alas, PAWS is really
3290  * buggy extension.
3291  *
3292  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3293  * states that events when retransmit arrives after original data are rare.
3294  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3295  * the biggest problem on large power networks even with minor reordering.
3296  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3297  * up to bandwidth of 18Gigabit/sec. 8) ]
3298  */
3299
3300 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3301 {
3302         struct tcp_sock *tp = tcp_sk(sk);
3303         struct tcphdr *th = tcp_hdr(skb);
3304         u32 seq = TCP_SKB_CB(skb)->seq;
3305         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3306
3307         return (/* 1. Pure ACK with correct sequence number. */
3308                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3309
3310                 /* 2. ... and duplicate ACK. */
3311                 ack == tp->snd_una &&
3312
3313                 /* 3. ... and does not update window. */
3314                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3315
3316                 /* 4. ... and sits in replay window. */
3317                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3318 }
3319
3320 static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
3321 {
3322         const struct tcp_sock *tp = tcp_sk(sk);
3323         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
3324                 get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
3325                 !tcp_disordered_ack(sk, skb));
3326 }
3327
3328 /* Check segment sequence number for validity.
3329  *
3330  * Segment controls are considered valid, if the segment
3331  * fits to the window after truncation to the window. Acceptability
3332  * of data (and SYN, FIN, of course) is checked separately.
3333  * See tcp_data_queue(), for example.
3334  *
3335  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3336  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3337  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3338  * (borrowed from freebsd)
3339  */
3340
3341 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3342 {
3343         return  !before(end_seq, tp->rcv_wup) &&
3344                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3345 }
3346
3347 /* When we get a reset we do this. */
3348 static void tcp_reset(struct sock *sk)
3349 {
3350         /* We want the right error as BSD sees it (and indeed as we do). */
3351         switch (sk->sk_state) {
3352                 case TCP_SYN_SENT:
3353                         sk->sk_err = ECONNREFUSED;
3354                         break;
3355                 case TCP_CLOSE_WAIT:
3356                         sk->sk_err = EPIPE;
3357                         break;
3358                 case TCP_CLOSE:
3359                         return;
3360                 default:
3361                         sk->sk_err = ECONNRESET;
3362         }
3363
3364         if (!sock_flag(sk, SOCK_DEAD))
3365                 sk->sk_error_report(sk);
3366
3367         tcp_done(sk);
3368 }
3369
3370 /*
3371  *      Process the FIN bit. This now behaves as it is supposed to work
3372  *      and the FIN takes effect when it is validly part of sequence
3373  *      space. Not before when we get holes.
3374  *
3375  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3376  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3377  *      TIME-WAIT)
3378  *
3379  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3380  *      close and we go into CLOSING (and later onto TIME-WAIT)
3381  *
3382  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3383  */
3384 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3385 {
3386         struct tcp_sock *tp = tcp_sk(sk);
3387
3388         inet_csk_schedule_ack(sk);
3389
3390         sk->sk_shutdown |= RCV_SHUTDOWN;
3391         sock_set_flag(sk, SOCK_DONE);
3392
3393         switch (sk->sk_state) {
3394                 case TCP_SYN_RECV:
3395                 case TCP_ESTABLISHED:
3396                         /* Move to CLOSE_WAIT */
3397                         tcp_set_state(sk, TCP_CLOSE_WAIT);
3398                         inet_csk(sk)->icsk_ack.pingpong = 1;
3399                         break;
3400
3401                 case TCP_CLOSE_WAIT:
3402                 case TCP_CLOSING:
3403                         /* Received a retransmission of the FIN, do
3404                          * nothing.
3405                          */
3406                         break;
3407                 case TCP_LAST_ACK:
3408                         /* RFC793: Remain in the LAST-ACK state. */
3409                         break;
3410
3411                 case TCP_FIN_WAIT1:
3412                         /* This case occurs when a simultaneous close
3413                          * happens, we must ack the received FIN and
3414                          * enter the CLOSING state.
3415                          */
3416                         tcp_send_ack(sk);
3417                         tcp_set_state(sk, TCP_CLOSING);
3418                         break;
3419                 case TCP_FIN_WAIT2:
3420                         /* Received a FIN -- send ACK and enter TIME_WAIT. */
3421                         tcp_send_ack(sk);
3422                         tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3423                         break;
3424                 default:
3425                         /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3426                          * cases we should never reach this piece of code.
3427                          */
3428                         printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
3429                                __FUNCTION__, sk->sk_state);
3430                         break;
3431         }
3432
3433         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3434          * Probably, we should reset in this case. For now drop them.
3435          */
3436         __skb_queue_purge(&tp->out_of_order_queue);
3437         if (tcp_is_sack(tp))
3438                 tcp_sack_reset(&tp->rx_opt);
3439         sk_stream_mem_reclaim(sk);
3440
3441         if (!sock_flag(sk, SOCK_DEAD)) {
3442                 sk->sk_state_change(sk);
3443
3444                 /* Do not send POLL_HUP for half duplex close. */
3445                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3446                     sk->sk_state == TCP_CLOSE)
3447                         sk_wake_async(sk, 1, POLL_HUP);
3448                 else
3449                         sk_wake_async(sk, 1, POLL_IN);
3450         }
3451 }
3452
3453 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
3454 {
3455         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3456                 if (before(seq, sp->start_seq))
3457                         sp->start_seq = seq;
3458                 if (after(end_seq, sp->end_seq))
3459                         sp->end_seq = end_seq;
3460                 return 1;
3461         }
3462         return 0;
3463 }
3464
3465 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
3466 {
3467         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3468                 if (before(seq, tp->rcv_nxt))
3469                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
3470                 else
3471                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
3472
3473                 tp->rx_opt.dsack = 1;
3474                 tp->duplicate_sack[0].start_seq = seq;
3475                 tp->duplicate_sack[0].end_seq = end_seq;
3476                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
3477         }
3478 }
3479
3480 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
3481 {
3482         if (!tp->rx_opt.dsack)
3483                 tcp_dsack_set(tp, seq, end_seq);
3484         else
3485                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3486 }
3487
3488 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
3489 {
3490         struct tcp_sock *tp = tcp_sk(sk);
3491
3492         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3493             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3494                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3495                 tcp_enter_quickack_mode(sk);
3496
3497                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3498                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3499
3500                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3501                                 end_seq = tp->rcv_nxt;
3502                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
3503                 }
3504         }
3505
3506         tcp_send_ack(sk);
3507 }
3508
3509 /* These routines update the SACK block as out-of-order packets arrive or
3510  * in-order packets close up the sequence space.
3511  */
3512 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3513 {
3514         int this_sack;
3515         struct tcp_sack_block *sp = &tp->selective_acks[0];
3516         struct tcp_sack_block *swalk = sp+1;
3517
3518         /* See if the recent change to the first SACK eats into
3519          * or hits the sequence space of other SACK blocks, if so coalesce.
3520          */
3521         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
3522                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3523                         int i;
3524
3525                         /* Zap SWALK, by moving every further SACK up by one slot.
3526                          * Decrease num_sacks.
3527                          */
3528                         tp->rx_opt.num_sacks--;
3529                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3530                         for (i=this_sack; i < tp->rx_opt.num_sacks; i++)
3531                                 sp[i] = sp[i+1];
3532                         continue;
3533                 }
3534                 this_sack++, swalk++;
3535         }
3536 }
3537
3538 static inline void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
3539 {
3540         __u32 tmp;
3541
3542         tmp = sack1->start_seq;
3543         sack1->start_seq = sack2->start_seq;
3544         sack2->start_seq = tmp;
3545
3546         tmp = sack1->end_seq;
3547         sack1->end_seq = sack2->end_seq;
3548         sack2->end_seq = tmp;
3549 }
3550
3551 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3552 {
3553         struct tcp_sock *tp = tcp_sk(sk);
3554         struct tcp_sack_block *sp = &tp->selective_acks[0];
3555         int cur_sacks = tp->rx_opt.num_sacks;
3556         int this_sack;
3557
3558         if (!cur_sacks)
3559                 goto new_sack;
3560
3561         for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
3562                 if (tcp_sack_extend(sp, seq, end_seq)) {
3563                         /* Rotate this_sack to the first one. */
3564                         for (; this_sack>0; this_sack--, sp--)
3565                                 tcp_sack_swap(sp, sp-1);
3566                         if (cur_sacks > 1)
3567                                 tcp_sack_maybe_coalesce(tp);
3568                         return;
3569                 }
3570         }
3571
3572         /* Could not find an adjacent existing SACK, build a new one,
3573          * put it at the front, and shift everyone else down.  We
3574          * always know there is at least one SACK present already here.
3575          *
3576          * If the sack array is full, forget about the last one.
3577          */
3578         if (this_sack >= 4) {
3579                 this_sack--;
3580                 tp->rx_opt.num_sacks--;
3581                 sp--;
3582         }
3583         for (; this_sack > 0; this_sack--, sp--)
3584                 *sp = *(sp-1);
3585
3586 new_sack:
3587         /* Build the new head SACK, and we're done. */
3588         sp->start_seq = seq;
3589         sp->end_seq = end_seq;
3590         tp->rx_opt.num_sacks++;
3591         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3592 }
3593
3594 /* RCV.NXT advances, some SACKs should be eaten. */
3595
3596 static void tcp_sack_remove(struct tcp_sock *tp)
3597 {
3598         struct tcp_sack_block *sp = &tp->selective_acks[0];
3599         int num_sacks = tp->rx_opt.num_sacks;
3600         int this_sack;
3601
3602         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
3603         if (skb_queue_empty(&tp->out_of_order_queue)) {
3604                 tp->rx_opt.num_sacks = 0;
3605                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
3606                 return;
3607         }
3608
3609         for (this_sack = 0; this_sack < num_sacks; ) {
3610                 /* Check if the start of the sack is covered by RCV.NXT. */
3611                 if (!before(tp->rcv_nxt, sp->start_seq)) {
3612                         int i;
3613
3614                         /* RCV.NXT must cover all the block! */
3615                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
3616
3617                         /* Zap this SACK, by moving forward any other SACKS. */
3618                         for (i=this_sack+1; i < num_sacks; i++)
3619                                 tp->selective_acks[i-1] = tp->selective_acks[i];
3620                         num_sacks--;
3621                         continue;
3622                 }
3623                 this_sack++;
3624                 sp++;
3625         }
3626         if (num_sacks != tp->rx_opt.num_sacks) {
3627                 tp->rx_opt.num_sacks = num_sacks;
3628                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
3629         }
3630 }
3631
3632 /* This one checks to see if we can put data from the
3633  * out_of_order queue into the receive_queue.
3634  */
3635 static void tcp_ofo_queue(struct sock *sk)
3636 {
3637         struct tcp_sock *tp = tcp_sk(sk);
3638         __u32 dsack_high = tp->rcv_nxt;
3639         struct sk_buff *skb;
3640
3641         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
3642                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
3643                         break;
3644
3645                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
3646                         __u32 dsack = dsack_high;
3647                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
3648                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
3649                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
3650                 }
3651
3652                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3653                         SOCK_DEBUG(sk, "ofo packet was already received \n");
3654                         __skb_unlink(skb, &tp->out_of_order_queue);
3655                         __kfree_skb(skb);
3656                         continue;
3657                 }
3658                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
3659                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3660                            TCP_SKB_CB(skb)->end_seq);
3661
3662                 __skb_unlink(skb, &tp->out_of_order_queue);
3663                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3664                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3665                 if (tcp_hdr(skb)->fin)
3666                         tcp_fin(skb, sk, tcp_hdr(skb));
3667         }
3668 }
3669
3670 static int tcp_prune_queue(struct sock *sk);
3671
3672 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
3673 {
3674         struct tcphdr *th = tcp_hdr(skb);
3675         struct tcp_sock *tp = tcp_sk(sk);
3676         int eaten = -1;
3677
3678         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
3679                 goto drop;
3680
3681         __skb_pull(skb, th->doff*4);
3682
3683         TCP_ECN_accept_cwr(tp, skb);
3684
3685         if (tp->rx_opt.dsack) {
3686                 tp->rx_opt.dsack = 0;
3687                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
3688                                                     4 - tp->rx_opt.tstamp_ok);
3689         }
3690
3691         /*  Queue data for delivery to the user.
3692          *  Packets in sequence go to the receive queue.
3693          *  Out of sequence packets to the out_of_order_queue.
3694          */
3695         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3696                 if (tcp_receive_window(tp) == 0)
3697                         goto out_of_window;
3698
3699                 /* Ok. In sequence. In window. */
3700                 if (tp->ucopy.task == current &&
3701                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
3702                     sock_owned_by_user(sk) && !tp->urg_data) {
3703                         int chunk = min_t(unsigned int, skb->len,
3704                                                         tp->ucopy.len);
3705
3706                         __set_current_state(TASK_RUNNING);
3707
3708                         local_bh_enable();
3709                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
3710                                 tp->ucopy.len -= chunk;
3711                                 tp->copied_seq += chunk;
3712                                 eaten = (chunk == skb->len && !th->fin);
3713                                 tcp_rcv_space_adjust(sk);
3714                         }
3715                         local_bh_disable();
3716                 }
3717
3718                 if (eaten <= 0) {
3719 queue_and_out:
3720                         if (eaten < 0 &&
3721                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3722                              !sk_stream_rmem_schedule(sk, skb))) {
3723                                 if (tcp_prune_queue(sk) < 0 ||
3724                                     !sk_stream_rmem_schedule(sk, skb))
3725                                         goto drop;
3726                         }
3727                         sk_stream_set_owner_r(skb, sk);
3728                         __skb_queue_tail(&sk->sk_receive_queue, skb);
3729                 }
3730                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3731                 if (skb->len)
3732                         tcp_event_data_recv(sk, skb);
3733                 if (th->fin)
3734                         tcp_fin(skb, sk, th);
3735
3736                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
3737                         tcp_ofo_queue(sk);
3738
3739                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
3740                          * gap in queue is filled.
3741                          */
3742                         if (skb_queue_empty(&tp->out_of_order_queue))
3743                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3744                 }
3745
3746                 if (tp->rx_opt.num_sacks)
3747                         tcp_sack_remove(tp);
3748
3749                 tcp_fast_path_check(sk);
3750
3751                 if (eaten > 0)
3752                         __kfree_skb(skb);
3753                 else if (!sock_flag(sk, SOCK_DEAD))
3754                         sk->sk_data_ready(sk, 0);
3755                 return;
3756         }
3757
3758         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3759                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3760                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3761                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3762
3763 out_of_window:
3764                 tcp_enter_quickack_mode(sk);
3765                 inet_csk_schedule_ack(sk);
3766 drop:
3767                 __kfree_skb(skb);
3768                 return;
3769         }
3770
3771         /* Out of window. F.e. zero window probe. */
3772         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3773                 goto out_of_window;
3774
3775         tcp_enter_quickack_mode(sk);
3776
3777         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3778                 /* Partial packet, seq < rcv_next < end_seq */
3779                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3780                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3781                            TCP_SKB_CB(skb)->end_seq);
3782
3783                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3784
3785                 /* If window is closed, drop tail of packet. But after
3786                  * remembering D-SACK for its head made in previous line.
3787                  */
3788                 if (!tcp_receive_window(tp))
3789                         goto out_of_window;
3790                 goto queue_and_out;
3791         }
3792
3793         TCP_ECN_check_ce(tp, skb);
3794
3795         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3796             !sk_stream_rmem_schedule(sk, skb)) {
3797                 if (tcp_prune_queue(sk) < 0 ||
3798                     !sk_stream_rmem_schedule(sk, skb))
3799                         goto drop;
3800         }
3801
3802         /* Disable header prediction. */
3803         tp->pred_flags = 0;
3804         inet_csk_schedule_ack(sk);
3805
3806         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3807                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3808
3809         sk_stream_set_owner_r(skb, sk);
3810
3811         if (!skb_peek(&tp->out_of_order_queue)) {
3812                 /* Initial out of order segment, build 1 SACK. */
3813                 if (tcp_is_sack(tp)) {
3814                         tp->rx_opt.num_sacks = 1;
3815                         tp->rx_opt.dsack     = 0;
3816                         tp->rx_opt.eff_sacks = 1;
3817                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3818                         tp->selective_acks[0].end_seq =
3819                                                 TCP_SKB_CB(skb)->end_seq;
3820                 }
3821                 __skb_queue_head(&tp->out_of_order_queue,skb);
3822         } else {
3823                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3824                 u32 seq = TCP_SKB_CB(skb)->seq;
3825                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3826
3827                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3828                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3829
3830                         if (!tp->rx_opt.num_sacks ||
3831                             tp->selective_acks[0].end_seq != seq)
3832                                 goto add_sack;
3833
3834                         /* Common case: data arrive in order after hole. */
3835                         tp->selective_acks[0].end_seq = end_seq;
3836                         return;
3837                 }
3838
3839                 /* Find place to insert this segment. */
3840                 do {
3841                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3842                                 break;
3843                 } while ((skb1 = skb1->prev) !=
3844                          (struct sk_buff*)&tp->out_of_order_queue);
3845
3846                 /* Do skb overlap to previous one? */
3847                 if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
3848                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3849                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3850                                 /* All the bits are present. Drop. */
3851                                 __kfree_skb(skb);
3852                                 tcp_dsack_set(tp, seq, end_seq);
3853                                 goto add_sack;
3854                         }
3855                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3856                                 /* Partial overlap. */
3857                                 tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
3858                         } else {
3859                                 skb1 = skb1->prev;
3860                         }
3861                 }
3862                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
3863
3864                 /* And clean segments covered by new one as whole. */
3865                 while ((skb1 = skb->next) !=
3866                        (struct sk_buff*)&tp->out_of_order_queue &&
3867                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
3868                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3869                                tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
3870                                break;
3871                        }
3872                        __skb_unlink(skb1, &tp->out_of_order_queue);
3873                        tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
3874                        __kfree_skb(skb1);
3875                 }
3876
3877 add_sack:
3878                 if (tcp_is_sack(tp))
3879                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
3880         }
3881 }
3882
3883 /* Collapse contiguous sequence of skbs head..tail with
3884  * sequence numbers start..end.
3885  * Segments with FIN/SYN are not collapsed (only because this
3886  * simplifies code)
3887  */
3888 static void
3889 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
3890              struct sk_buff *head, struct sk_buff *tail,
3891              u32 start, u32 end)
3892 {
3893         struct sk_buff *skb;
3894
3895         /* First, check that queue is collapsible and find
3896          * the point where collapsing can be useful. */
3897         for (skb = head; skb != tail; ) {
3898                 /* No new bits? It is possible on ofo queue. */
3899                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3900                         struct sk_buff *next = skb->next;
3901                         __skb_unlink(skb, list);
3902                         __kfree_skb(skb);
3903                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3904                         skb = next;
3905                         continue;
3906                 }
3907
3908                 /* The first skb to collapse is:
3909                  * - not SYN/FIN and
3910                  * - bloated or contains data before "start" or
3911                  *   overlaps to the next one.
3912                  */
3913                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
3914                     (tcp_win_from_space(skb->truesize) > skb->len ||
3915                      before(TCP_SKB_CB(skb)->seq, start) ||
3916                      (skb->next != tail &&
3917                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
3918                         break;
3919
3920                 /* Decided to skip this, advance start seq. */
3921                 start = TCP_SKB_CB(skb)->end_seq;
3922                 skb = skb->next;
3923         }
3924         if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
3925                 return;
3926
3927         while (before(start, end)) {
3928                 struct sk_buff *nskb;
3929                 unsigned int header = skb_headroom(skb);
3930                 int copy = SKB_MAX_ORDER(header, 0);
3931
3932                 /* Too big header? This can happen with IPv6. */
3933                 if (copy < 0)
3934                         return;
3935                 if (end-start < copy)
3936                         copy = end-start;
3937                 nskb = alloc_skb(copy+header, GFP_ATOMIC);
3938                 if (!nskb)
3939                         return;
3940
3941                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
3942                 skb_set_network_header(nskb, (skb_network_header(skb) -
3943                                               skb->head));
3944                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
3945                                                 skb->head));
3946                 skb_reserve(nskb, header);
3947                 memcpy(nskb->head, skb->head, header);
3948                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
3949                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
3950                 __skb_insert(nskb, skb->prev, skb, list);
3951                 sk_stream_set_owner_r(nskb, sk);
3952
3953                 /* Copy data, releasing collapsed skbs. */
3954                 while (copy > 0) {
3955                         int offset = start - TCP_SKB_CB(skb)->seq;
3956                         int size = TCP_SKB_CB(skb)->end_seq - start;
3957
3958                         BUG_ON(offset < 0);
3959                         if (size > 0) {
3960                                 size = min(copy, size);
3961                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
3962                                         BUG();
3963                                 TCP_SKB_CB(nskb)->end_seq += size;
3964                                 copy -= size;
3965                                 start += size;
3966                         }
3967                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
3968                                 struct sk_buff *next = skb->next;
3969                                 __skb_unlink(skb, list);
3970                                 __kfree_skb(skb);
3971                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
3972                                 skb = next;
3973                                 if (skb == tail ||
3974                                     tcp_hdr(skb)->syn ||
3975                                     tcp_hdr(skb)->fin)
3976                                         return;
3977                         }
3978                 }
3979         }
3980 }
3981
3982 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
3983  * and tcp_collapse() them until all the queue is collapsed.
3984  */
3985 static void tcp_collapse_ofo_queue(struct sock *sk)
3986 {
3987         struct tcp_sock *tp = tcp_sk(sk);
3988         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
3989         struct sk_buff *head;
3990         u32 start, end;
3991
3992         if (skb == NULL)
3993                 return;
3994
3995         start = TCP_SKB_CB(skb)->seq;
3996         end = TCP_SKB_CB(skb)->end_seq;
3997         head = skb;
3998
3999         for (;;) {
4000                 skb = skb->next;
4001
4002                 /* Segment is terminated when we see gap or when
4003                  * we are at the end of all the queue. */
4004                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
4005                     after(TCP_SKB_CB(skb)->seq, end) ||
4006                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4007                         tcp_collapse(sk, &tp->out_of_order_queue,
4008                                      head, skb, start, end);
4009                         head = skb;
4010                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
4011                                 break;
4012                         /* Start new segment */
4013                         start = TCP_SKB_CB(skb)->seq;
4014                         end = TCP_SKB_CB(skb)->end_seq;
4015                 } else {
4016                         if (before(TCP_SKB_CB(skb)->seq, start))
4017                                 start = TCP_SKB_CB(skb)->seq;
4018                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4019                                 end = TCP_SKB_CB(skb)->end_seq;
4020                 }
4021         }
4022 }
4023
4024 /* Reduce allocated memory if we can, trying to get
4025  * the socket within its memory limits again.
4026  *
4027  * Return less than zero if we should start dropping frames
4028  * until the socket owning process reads some of the data
4029  * to stabilize the situation.
4030  */
4031 static int tcp_prune_queue(struct sock *sk)
4032 {
4033         struct tcp_sock *tp = tcp_sk(sk);
4034
4035         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4036
4037         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
4038
4039         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4040                 tcp_clamp_window(sk);
4041         else if (tcp_memory_pressure)
4042                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4043
4044         tcp_collapse_ofo_queue(sk);
4045         tcp_collapse(sk, &sk->sk_receive_queue,
4046                      sk->sk_receive_queue.next,
4047                      (struct sk_buff*)&sk->sk_receive_queue,
4048                      tp->copied_seq, tp->rcv_nxt);
4049         sk_stream_mem_reclaim(sk);
4050
4051         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4052                 return 0;
4053
4054         /* Collapsing did not help, destructive actions follow.
4055          * This must not ever occur. */
4056
4057         /* First, purge the out_of_order queue. */
4058         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4059                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
4060                 __skb_queue_purge(&tp->out_of_order_queue);
4061
4062                 /* Reset SACK state.  A conforming SACK implementation will
4063                  * do the same at a timeout based retransmit.  When a connection
4064                  * is in a sad state like this, we care only about integrity
4065                  * of the connection not performance.
4066                  */
4067                 if (tcp_is_sack(tp))
4068                         tcp_sack_reset(&tp->rx_opt);
4069                 sk_stream_mem_reclaim(sk);
4070         }
4071
4072         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4073                 return 0;
4074
4075         /* If we are really being abused, tell the caller to silently
4076          * drop receive data on the floor.  It will get retransmitted
4077          * and hopefully then we'll have sufficient space.
4078          */
4079         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
4080
4081         /* Massive buffer overcommit. */
4082         tp->pred_flags = 0;
4083         return -1;
4084 }
4085
4086
4087 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4088  * As additional protections, we do not touch cwnd in retransmission phases,
4089  * and if application hit its sndbuf limit recently.
4090  */
4091 void tcp_cwnd_application_limited(struct sock *sk)
4092 {
4093         struct tcp_sock *tp = tcp_sk(sk);
4094
4095         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4096             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4097                 /* Limited by application or receiver window. */
4098                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4099                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4100                 if (win_used < tp->snd_cwnd) {
4101                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4102                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4103                 }
4104                 tp->snd_cwnd_used = 0;
4105         }
4106         tp->snd_cwnd_stamp = tcp_time_stamp;
4107 }
4108
4109 static int tcp_should_expand_sndbuf(struct sock *sk)
4110 {
4111         struct tcp_sock *tp = tcp_sk(sk);
4112
4113         /* If the user specified a specific send buffer setting, do
4114          * not modify it.
4115          */
4116         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4117                 return 0;
4118
4119         /* If we are under global TCP memory pressure, do not expand.  */
4120         if (tcp_memory_pressure)
4121                 return 0;
4122
4123         /* If we are under soft global TCP memory pressure, do not expand.  */
4124         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4125                 return 0;
4126
4127         /* If we filled the congestion window, do not expand.  */
4128         if (tp->packets_out >= tp->snd_cwnd)
4129                 return 0;
4130
4131         return 1;
4132 }
4133
4134 /* When incoming ACK allowed to free some skb from write_queue,
4135  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4136  * on the exit from tcp input handler.
4137  *
4138  * PROBLEM: sndbuf expansion does not work well with largesend.
4139  */
4140 static void tcp_new_space(struct sock *sk)
4141 {
4142         struct tcp_sock *tp = tcp_sk(sk);
4143
4144         if (tcp_should_expand_sndbuf(sk)) {
4145                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4146                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
4147                     demanded = max_t(unsigned int, tp->snd_cwnd,
4148                                                    tp->reordering + 1);
4149                 sndmem *= 2*demanded;
4150                 if (sndmem > sk->sk_sndbuf)
4151                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4152                 tp->snd_cwnd_stamp = tcp_time_stamp;
4153         }
4154
4155         sk->sk_write_space(sk);
4156 }
4157
4158 static void tcp_check_space(struct sock *sk)
4159 {
4160         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4161                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4162                 if (sk->sk_socket &&
4163                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4164                         tcp_new_space(sk);
4165         }
4166 }
4167
4168 static inline void tcp_data_snd_check(struct sock *sk)
4169 {
4170         tcp_push_pending_frames(sk);
4171         tcp_check_space(sk);
4172 }
4173
4174 /*
4175  * Check if sending an ack is needed.
4176  */
4177 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4178 {
4179         struct tcp_sock *tp = tcp_sk(sk);
4180
4181             /* More than one full frame received... */
4182         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
4183              /* ... and right edge of window advances far enough.
4184               * (tcp_recvmsg() will send ACK otherwise). Or...
4185               */
4186              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
4187             /* We ACK each frame or... */
4188             tcp_in_quickack_mode(sk) ||
4189             /* We have out of order data. */
4190             (ofo_possible &&
4191              skb_peek(&tp->out_of_order_queue))) {
4192                 /* Then ack it now */
4193                 tcp_send_ack(sk);
4194         } else {
4195                 /* Else, send delayed ack. */
4196                 tcp_send_delayed_ack(sk);
4197         }
4198 }
4199
4200 static inline void tcp_ack_snd_check(struct sock *sk)
4201 {
4202         if (!inet_csk_ack_scheduled(sk)) {
4203                 /* We sent a data segment already. */
4204                 return;
4205         }
4206         __tcp_ack_snd_check(sk, 1);
4207 }
4208
4209 /*
4210  *      This routine is only called when we have urgent data
4211  *      signaled. Its the 'slow' part of tcp_urg. It could be
4212  *      moved inline now as tcp_urg is only called from one
4213  *      place. We handle URGent data wrong. We have to - as
4214  *      BSD still doesn't use the correction from RFC961.
4215  *      For 1003.1g we should support a new option TCP_STDURG to permit
4216  *      either form (or just set the sysctl tcp_stdurg).
4217  */
4218
4219 static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
4220 {
4221         struct tcp_sock *tp = tcp_sk(sk);
4222         u32 ptr = ntohs(th->urg_ptr);
4223
4224         if (ptr && !sysctl_tcp_stdurg)
4225                 ptr--;
4226         ptr += ntohl(th->seq);
4227
4228         /* Ignore urgent data that we've already seen and read. */
4229         if (after(tp->copied_seq, ptr))
4230                 return;
4231
4232         /* Do not replay urg ptr.
4233          *
4234          * NOTE: interesting situation not covered by specs.
4235          * Misbehaving sender may send urg ptr, pointing to segment,
4236          * which we already have in ofo queue. We are not able to fetch
4237          * such data and will stay in TCP_URG_NOTYET until will be eaten
4238          * by recvmsg(). Seems, we are not obliged to handle such wicked
4239          * situations. But it is worth to think about possibility of some
4240          * DoSes using some hypothetical application level deadlock.
4241          */
4242         if (before(ptr, tp->rcv_nxt))
4243                 return;
4244
4245         /* Do we already have a newer (or duplicate) urgent pointer? */
4246         if (tp->urg_data && !after(ptr, tp->urg_seq))
4247                 return;
4248
4249         /* Tell the world about our new urgent pointer. */
4250         sk_send_sigurg(sk);
4251
4252         /* We may be adding urgent data when the last byte read was
4253          * urgent. To do this requires some care. We cannot just ignore
4254          * tp->copied_seq since we would read the last urgent byte again
4255          * as data, nor can we alter copied_seq until this data arrives
4256          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4257          *
4258          * NOTE. Double Dutch. Rendering to plain English: author of comment
4259          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4260          * and expect that both A and B disappear from stream. This is _wrong_.
4261          * Though this happens in BSD with high probability, this is occasional.
4262          * Any application relying on this is buggy. Note also, that fix "works"
4263          * only in this artificial test. Insert some normal data between A and B and we will
4264          * decline of BSD again. Verdict: it is better to remove to trap
4265          * buggy users.
4266          */
4267         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4268             !sock_flag(sk, SOCK_URGINLINE) &&
4269             tp->copied_seq != tp->rcv_nxt) {
4270                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4271                 tp->copied_seq++;
4272                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4273                         __skb_unlink(skb, &sk->sk_receive_queue);
4274                         __kfree_skb(skb);
4275                 }
4276         }
4277
4278         tp->urg_data   = TCP_URG_NOTYET;
4279         tp->urg_seq    = ptr;
4280
4281         /* Disable header prediction. */
4282         tp->pred_flags = 0;
4283 }
4284
4285 /* This is the 'fast' part of urgent handling. */
4286 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4287 {
4288         struct tcp_sock *tp = tcp_sk(sk);
4289
4290         /* Check if we get a new urgent pointer - normally not. */
4291         if (th->urg)
4292                 tcp_check_urg(sk,th);
4293
4294         /* Do we wait for any urgent data? - normally not... */
4295         if (tp->urg_data == TCP_URG_NOTYET) {
4296                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4297                           th->syn;
4298
4299                 /* Is the urgent pointer pointing into this packet? */
4300                 if (ptr < skb->len) {
4301                         u8 tmp;
4302                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4303                                 BUG();
4304                         tp->urg_data = TCP_URG_VALID | tmp;
4305                         if (!sock_flag(sk, SOCK_DEAD))
4306                                 sk->sk_data_ready(sk, 0);
4307                 }
4308         }
4309 }
4310
4311 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4312 {
4313         struct tcp_sock *tp = tcp_sk(sk);
4314         int chunk = skb->len - hlen;
4315         int err;
4316
4317         local_bh_enable();
4318         if (skb_csum_unnecessary(skb))
4319                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4320         else
4321                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4322                                                        tp->ucopy.iov);
4323
4324         if (!err) {
4325                 tp->ucopy.len -= chunk;
4326                 tp->copied_seq += chunk;
4327                 tcp_rcv_space_adjust(sk);
4328         }
4329
4330         local_bh_disable();
4331         return err;
4332 }
4333
4334 static __sum16 __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4335 {
4336         __sum16 result;
4337
4338         if (sock_owned_by_user(sk)) {
4339                 local_bh_enable();
4340                 result = __tcp_checksum_complete(skb);
4341                 local_bh_disable();
4342         } else {
4343                 result = __tcp_checksum_complete(skb);
4344         }
4345         return result;
4346 }
4347
4348 static inline int tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
4349 {
4350         return !skb_csum_unnecessary(skb) &&
4351                 __tcp_checksum_complete_user(sk, skb);
4352 }
4353
4354 #ifdef CONFIG_NET_DMA
4355 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, int hlen)
4356 {
4357         struct tcp_sock *tp = tcp_sk(sk);
4358         int chunk = skb->len - hlen;
4359         int dma_cookie;
4360         int copied_early = 0;
4361
4362         if (tp->ucopy.wakeup)
4363                 return 0;
4364
4365         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4366                 tp->ucopy.dma_chan = get_softnet_dma();
4367
4368         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4369
4370                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4371                         skb, hlen, tp->ucopy.iov, chunk, tp->ucopy.pinned_list);
4372
4373                 if (dma_cookie < 0)
4374                         goto out;
4375
4376                 tp->ucopy.dma_cookie = dma_cookie;
4377                 copied_early = 1;
4378
4379                 tp->ucopy.len -= chunk;
4380                 tp->copied_seq += chunk;
4381                 tcp_rcv_space_adjust(sk);
4382
4383                 if ((tp->ucopy.len == 0) ||
4384                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
4385                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
4386                         tp->ucopy.wakeup = 1;
4387                         sk->sk_data_ready(sk, 0);
4388                 }
4389         } else if (chunk > 0) {
4390                 tp->ucopy.wakeup = 1;
4391                 sk->sk_data_ready(sk, 0);
4392         }
4393 out:
4394         return copied_early;
4395 }
4396 #endif /* CONFIG_NET_DMA */
4397
4398 /*
4399  *      TCP receive function for the ESTABLISHED state.
4400  *
4401  *      It is split into a fast path and a slow path. The fast path is
4402  *      disabled when:
4403  *      - A zero window was announced from us - zero window probing
4404  *        is only handled properly in the slow path.
4405  *      - Out of order segments arrived.
4406  *      - Urgent data is expected.
4407  *      - There is no buffer space left
4408  *      - Unexpected TCP flags/window values/header lengths are received
4409  *        (detected by checking the TCP header against pred_flags)
4410  *      - Data is sent in both directions. Fast path only supports pure senders
4411  *        or pure receivers (this means either the sequence number or the ack
4412  *        value must stay constant)
4413  *      - Unexpected TCP option.
4414  *
4415  *      When these conditions are not satisfied it drops into a standard
4416  *      receive procedure patterned after RFC793 to handle all cases.
4417  *      The first three cases are guaranteed by proper pred_flags setting,
4418  *      the rest is checked inline. Fast processing is turned on in
4419  *      tcp_data_queue when everything is OK.
4420  */
4421 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
4422                         struct tcphdr *th, unsigned len)
4423 {
4424         struct tcp_sock *tp = tcp_sk(sk);
4425
4426         /*
4427          *      Header prediction.
4428          *      The code loosely follows the one in the famous
4429          *      "30 instruction TCP receive" Van Jacobson mail.
4430          *
4431          *      Van's trick is to deposit buffers into socket queue
4432          *      on a device interrupt, to call tcp_recv function
4433          *      on the receive process context and checksum and copy
4434          *      the buffer to user space. smart...
4435          *
4436          *      Our current scheme is not silly either but we take the
4437          *      extra cost of the net_bh soft interrupt processing...
4438          *      We do checksum and copy also but from device to kernel.
4439          */
4440
4441         tp->rx_opt.saw_tstamp = 0;
4442
4443         /*      pred_flags is 0xS?10 << 16 + snd_wnd
4444          *      if header_prediction is to be made
4445          *      'S' will always be tp->tcp_header_len >> 2
4446          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
4447          *  turn it off (when there are holes in the receive
4448          *       space for instance)
4449          *      PSH flag is ignored.
4450          */
4451
4452         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
4453                 TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4454                 int tcp_header_len = tp->tcp_header_len;
4455
4456                 /* Timestamp header prediction: tcp_header_len
4457                  * is automatically equal to th->doff*4 due to pred_flags
4458                  * match.
4459                  */
4460
4461                 /* Check timestamp */
4462                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
4463                         __be32 *ptr = (__be32 *)(th + 1);
4464
4465                         /* No? Slow path! */
4466                         if (*ptr != htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4467                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
4468                                 goto slow_path;
4469
4470                         tp->rx_opt.saw_tstamp = 1;
4471                         ++ptr;
4472                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
4473                         ++ptr;
4474                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
4475
4476                         /* If PAWS failed, check it more carefully in slow path */
4477                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
4478                                 goto slow_path;
4479
4480                         /* DO NOT update ts_recent here, if checksum fails
4481                          * and timestamp was corrupted part, it will result
4482                          * in a hung connection since we will drop all
4483                          * future packets due to the PAWS test.
4484                          */
4485                 }
4486
4487                 if (len <= tcp_header_len) {
4488                         /* Bulk data transfer: sender */
4489                         if (len == tcp_header_len) {
4490                                 /* Predicted packet is in window by definition.
4491                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4492                                  * Hence, check seq<=rcv_wup reduces to:
4493                                  */
4494                                 if (tcp_header_len ==
4495                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4496                                     tp->rcv_nxt == tp->rcv_wup)
4497                                         tcp_store_ts_recent(tp);
4498
4499                                 /* We know that such packets are checksummed
4500                                  * on entry.
4501                                  */
4502                                 tcp_ack(sk, skb, 0);
4503                                 __kfree_skb(skb);
4504                                 tcp_data_snd_check(sk);
4505                                 return 0;
4506                         } else { /* Header too small */
4507                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4508                                 goto discard;
4509                         }
4510                 } else {
4511                         int eaten = 0;
4512                         int copied_early = 0;
4513
4514                         if (tp->copied_seq == tp->rcv_nxt &&
4515                             len - tcp_header_len <= tp->ucopy.len) {
4516 #ifdef CONFIG_NET_DMA
4517                                 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
4518                                         copied_early = 1;
4519                                         eaten = 1;
4520                                 }
4521 #endif
4522                                 if (tp->ucopy.task == current && sock_owned_by_user(sk) && !copied_early) {
4523                                         __set_current_state(TASK_RUNNING);
4524
4525                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
4526                                                 eaten = 1;
4527                                 }
4528                                 if (eaten) {
4529                                         /* Predicted packet is in window by definition.
4530                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4531                                          * Hence, check seq<=rcv_wup reduces to:
4532                                          */
4533                                         if (tcp_header_len ==
4534                                             (sizeof(struct tcphdr) +
4535                                              TCPOLEN_TSTAMP_ALIGNED) &&
4536                                             tp->rcv_nxt == tp->rcv_wup)
4537                                                 tcp_store_ts_recent(tp);
4538
4539                                         tcp_rcv_rtt_measure_ts(sk, skb);
4540
4541                                         __skb_pull(skb, tcp_header_len);
4542                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4543                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
4544                                 }
4545                                 if (copied_early)
4546                                         tcp_cleanup_rbuf(sk, skb->len);
4547                         }
4548                         if (!eaten) {
4549                                 if (tcp_checksum_complete_user(sk, skb))
4550                                         goto csum_error;
4551
4552                                 /* Predicted packet is in window by definition.
4553                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4554                                  * Hence, check seq<=rcv_wup reduces to:
4555                                  */
4556                                 if (tcp_header_len ==
4557                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4558                                     tp->rcv_nxt == tp->rcv_wup)
4559                                         tcp_store_ts_recent(tp);
4560
4561                                 tcp_rcv_rtt_measure_ts(sk, skb);
4562
4563                                 if ((int)skb->truesize > sk->sk_forward_alloc)
4564                                         goto step5;
4565
4566                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
4567
4568                                 /* Bulk data transfer: receiver */
4569                                 __skb_pull(skb,tcp_header_len);
4570                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4571                                 sk_stream_set_owner_r(skb, sk);
4572                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4573                         }
4574
4575                         tcp_event_data_recv(sk, skb);
4576
4577                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
4578                                 /* Well, only one small jumplet in fast path... */
4579                                 tcp_ack(sk, skb, FLAG_DATA);
4580                                 tcp_data_snd_check(sk);
4581                                 if (!inet_csk_ack_scheduled(sk))
4582                                         goto no_ack;
4583                         }
4584
4585                         __tcp_ack_snd_check(sk, 0);
4586 no_ack:
4587 #ifdef CONFIG_NET_DMA
4588                         if (copied_early)
4589                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
4590                         else
4591 #endif
4592                         if (eaten)
4593                                 __kfree_skb(skb);
4594                         else
4595                                 sk->sk_data_ready(sk, 0);
4596                         return 0;
4597                 }
4598         }
4599
4600 slow_path:
4601         if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
4602                 goto csum_error;
4603
4604         /*
4605          * RFC1323: H1. Apply PAWS check first.
4606          */
4607         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4608             tcp_paws_discard(sk, skb)) {
4609                 if (!th->rst) {
4610                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4611                         tcp_send_dupack(sk, skb);
4612                         goto discard;
4613                 }
4614                 /* Resets are accepted even if PAWS failed.
4615
4616                    ts_recent update must be made after we are sure
4617                    that the packet is in window.
4618                  */
4619         }
4620
4621         /*
4622          *      Standard slow path.
4623          */
4624
4625         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4626                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
4627                  * (RST) segments are validated by checking their SEQ-fields."
4628                  * And page 69: "If an incoming segment is not acceptable,
4629                  * an acknowledgment should be sent in reply (unless the RST bit
4630                  * is set, if so drop the segment and return)".
4631                  */
4632                 if (!th->rst)
4633                         tcp_send_dupack(sk, skb);
4634                 goto discard;
4635         }
4636
4637         if (th->rst) {
4638                 tcp_reset(sk);
4639                 goto discard;
4640         }
4641
4642         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4643
4644         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4645                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4646                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4647                 tcp_reset(sk);
4648                 return 1;
4649         }
4650
4651 step5:
4652         if (th->ack)
4653                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4654
4655         tcp_rcv_rtt_measure_ts(sk, skb);
4656
4657         /* Process urgent data. */
4658         tcp_urg(sk, skb, th);
4659
4660         /* step 7: process the segment text */
4661         tcp_data_queue(sk, skb);
4662
4663         tcp_data_snd_check(sk);
4664         tcp_ack_snd_check(sk);
4665         return 0;
4666
4667 csum_error:
4668         TCP_INC_STATS_BH(TCP_MIB_INERRS);
4669
4670 discard:
4671         __kfree_skb(skb);
4672         return 0;
4673 }
4674
4675 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
4676                                          struct tcphdr *th, unsigned len)
4677 {
4678         struct tcp_sock *tp = tcp_sk(sk);
4679         struct inet_connection_sock *icsk = inet_csk(sk);
4680         int saved_clamp = tp->rx_opt.mss_clamp;
4681
4682         tcp_parse_options(skb, &tp->rx_opt, 0);
4683
4684         if (th->ack) {
4685                 /* rfc793:
4686                  * "If the state is SYN-SENT then
4687                  *    first check the ACK bit
4688                  *      If the ACK bit is set
4689                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
4690                  *        a reset (unless the RST bit is set, if so drop
4691                  *        the segment and return)"
4692                  *
4693                  *  We do not send data with SYN, so that RFC-correct
4694                  *  test reduces to:
4695                  */
4696                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
4697                         goto reset_and_undo;
4698
4699                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4700                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
4701                              tcp_time_stamp)) {
4702                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
4703                         goto reset_and_undo;
4704                 }
4705
4706                 /* Now ACK is acceptable.
4707                  *
4708                  * "If the RST bit is set
4709                  *    If the ACK was acceptable then signal the user "error:
4710                  *    connection reset", drop the segment, enter CLOSED state,
4711                  *    delete TCB, and return."
4712                  */
4713
4714                 if (th->rst) {
4715                         tcp_reset(sk);
4716                         goto discard;
4717                 }
4718
4719                 /* rfc793:
4720                  *   "fifth, if neither of the SYN or RST bits is set then
4721                  *    drop the segment and return."
4722                  *
4723                  *    See note below!
4724                  *                                        --ANK(990513)
4725                  */
4726                 if (!th->syn)
4727                         goto discard_and_undo;
4728
4729                 /* rfc793:
4730                  *   "If the SYN bit is on ...
4731                  *    are acceptable then ...
4732                  *    (our SYN has been ACKed), change the connection
4733                  *    state to ESTABLISHED..."
4734                  */
4735
4736                 TCP_ECN_rcv_synack(tp, th);
4737
4738                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
4739                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4740
4741                 /* Ok.. it's good. Set up sequence numbers and
4742                  * move to established.
4743                  */
4744                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4745                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4746
4747                 /* RFC1323: The window in SYN & SYN/ACK segments is
4748                  * never scaled.
4749                  */
4750                 tp->snd_wnd = ntohs(th->window);
4751                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
4752
4753                 if (!tp->rx_opt.wscale_ok) {
4754                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
4755                         tp->window_clamp = min(tp->window_clamp, 65535U);
4756                 }
4757
4758                 if (tp->rx_opt.saw_tstamp) {
4759                         tp->rx_opt.tstamp_ok       = 1;
4760                         tp->tcp_header_len =
4761                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4762                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
4763                         tcp_store_ts_recent(tp);
4764                 } else {
4765                         tp->tcp_header_len = sizeof(struct tcphdr);
4766                 }
4767
4768                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
4769                         tcp_enable_fack(tp);
4770
4771                 tcp_mtup_init(sk);
4772                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4773                 tcp_initialize_rcv_mss(sk);
4774
4775                 /* Remember, tcp_poll() does not lock socket!
4776                  * Change state from SYN-SENT only after copied_seq
4777                  * is initialized. */
4778                 tp->copied_seq = tp->rcv_nxt;
4779                 smp_mb();
4780                 tcp_set_state(sk, TCP_ESTABLISHED);
4781
4782                 security_inet_conn_established(sk, skb);
4783
4784                 /* Make sure socket is routed, for correct metrics.  */
4785                 icsk->icsk_af_ops->rebuild_header(sk);
4786
4787                 tcp_init_metrics(sk);
4788
4789                 tcp_init_congestion_control(sk);
4790
4791                 /* Prevent spurious tcp_cwnd_restart() on first data
4792                  * packet.
4793                  */
4794                 tp->lsndtime = tcp_time_stamp;
4795
4796                 tcp_init_buffer_space(sk);
4797
4798                 if (sock_flag(sk, SOCK_KEEPOPEN))
4799                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
4800
4801                 if (!tp->rx_opt.snd_wscale)
4802                         __tcp_fast_path_on(tp, tp->snd_wnd);
4803                 else
4804                         tp->pred_flags = 0;
4805
4806                 if (!sock_flag(sk, SOCK_DEAD)) {
4807                         sk->sk_state_change(sk);
4808                         sk_wake_async(sk, 0, POLL_OUT);
4809                 }
4810
4811                 if (sk->sk_write_pending ||
4812                     icsk->icsk_accept_queue.rskq_defer_accept ||
4813                     icsk->icsk_ack.pingpong) {
4814                         /* Save one ACK. Data will be ready after
4815                          * several ticks, if write_pending is set.
4816                          *
4817                          * It may be deleted, but with this feature tcpdumps
4818                          * look so _wonderfully_ clever, that I was not able
4819                          * to stand against the temptation 8)     --ANK
4820                          */
4821                         inet_csk_schedule_ack(sk);
4822                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4823                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4824                         tcp_incr_quickack(sk);
4825                         tcp_enter_quickack_mode(sk);
4826                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4827                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4828
4829 discard:
4830                         __kfree_skb(skb);
4831                         return 0;
4832                 } else {
4833                         tcp_send_ack(sk);
4834                 }
4835                 return -1;
4836         }
4837
4838         /* No ACK in the segment */
4839
4840         if (th->rst) {
4841                 /* rfc793:
4842                  * "If the RST bit is set
4843                  *
4844                  *      Otherwise (no ACK) drop the segment and return."
4845                  */
4846
4847                 goto discard_and_undo;
4848         }
4849
4850         /* PAWS check. */
4851         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
4852                 goto discard_and_undo;
4853
4854         if (th->syn) {
4855                 /* We see SYN without ACK. It is attempt of
4856                  * simultaneous connect with crossed SYNs.
4857                  * Particularly, it can be connect to self.
4858                  */
4859                 tcp_set_state(sk, TCP_SYN_RECV);
4860
4861                 if (tp->rx_opt.saw_tstamp) {
4862                         tp->rx_opt.tstamp_ok = 1;
4863                         tcp_store_ts_recent(tp);
4864                         tp->tcp_header_len =
4865                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4866                 } else {
4867                         tp->tcp_header_len = sizeof(struct tcphdr);
4868                 }
4869
4870                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4871                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4872
4873                 /* RFC1323: The window in SYN & SYN/ACK segments is
4874                  * never scaled.
4875                  */
4876                 tp->snd_wnd    = ntohs(th->window);
4877                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
4878                 tp->max_window = tp->snd_wnd;
4879
4880                 TCP_ECN_rcv_syn(tp, th);
4881
4882                 tcp_mtup_init(sk);
4883                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4884                 tcp_initialize_rcv_mss(sk);
4885
4886
4887                 tcp_send_synack(sk);
4888 #if 0
4889                 /* Note, we could accept data and URG from this segment.
4890                  * There are no obstacles to make this.
4891                  *
4892                  * However, if we ignore data in ACKless segments sometimes,
4893                  * we have no reasons to accept it sometimes.
4894                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
4895                  * is not flawless. So, discard packet for sanity.
4896                  * Uncomment this return to process the data.
4897                  */
4898                 return -1;
4899 #else
4900                 goto discard;
4901 #endif
4902         }
4903         /* "fifth, if neither of the SYN or RST bits is set then
4904          * drop the segment and return."
4905          */
4906
4907 discard_and_undo:
4908         tcp_clear_options(&tp->rx_opt);
4909         tp->rx_opt.mss_clamp = saved_clamp;
4910         goto discard;
4911
4912 reset_and_undo:
4913         tcp_clear_options(&tp->rx_opt);
4914         tp->rx_opt.mss_clamp = saved_clamp;
4915         return 1;
4916 }
4917
4918
4919 /*
4920  *      This function implements the receiving procedure of RFC 793 for
4921  *      all states except ESTABLISHED and TIME_WAIT.
4922  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
4923  *      address independent.
4924  */
4925
4926 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
4927                           struct tcphdr *th, unsigned len)
4928 {
4929         struct tcp_sock *tp = tcp_sk(sk);
4930         struct inet_connection_sock *icsk = inet_csk(sk);
4931         int queued = 0;
4932
4933         tp->rx_opt.saw_tstamp = 0;
4934
4935         switch (sk->sk_state) {
4936         case TCP_CLOSE:
4937                 goto discard;
4938
4939         case TCP_LISTEN:
4940                 if (th->ack)
4941                         return 1;
4942
4943                 if (th->rst)
4944                         goto discard;
4945
4946                 if (th->syn) {
4947                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
4948                                 return 1;
4949
4950                         /* Now we have several options: In theory there is
4951                          * nothing else in the frame. KA9Q has an option to
4952                          * send data with the syn, BSD accepts data with the
4953                          * syn up to the [to be] advertised window and
4954                          * Solaris 2.1 gives you a protocol error. For now
4955                          * we just ignore it, that fits the spec precisely
4956                          * and avoids incompatibilities. It would be nice in
4957                          * future to drop through and process the data.
4958                          *
4959                          * Now that TTCP is starting to be used we ought to
4960                          * queue this data.
4961                          * But, this leaves one open to an easy denial of
4962                          * service attack, and SYN cookies can't defend
4963                          * against this problem. So, we drop the data
4964                          * in the interest of security over speed unless
4965                          * it's still in use.
4966                          */
4967                         kfree_skb(skb);
4968                         return 0;
4969                 }
4970                 goto discard;
4971
4972         case TCP_SYN_SENT:
4973                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
4974                 if (queued >= 0)
4975                         return queued;
4976
4977                 /* Do step6 onward by hand. */
4978                 tcp_urg(sk, skb, th);
4979                 __kfree_skb(skb);
4980                 tcp_data_snd_check(sk);
4981                 return 0;
4982         }
4983
4984         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4985             tcp_paws_discard(sk, skb)) {
4986                 if (!th->rst) {
4987                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4988                         tcp_send_dupack(sk, skb);
4989                         goto discard;
4990                 }
4991                 /* Reset is accepted even if it did not pass PAWS. */
4992         }
4993
4994         /* step 1: check sequence number */
4995         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4996                 if (!th->rst)
4997                         tcp_send_dupack(sk, skb);
4998                 goto discard;
4999         }
5000
5001         /* step 2: check RST bit */
5002         if (th->rst) {
5003                 tcp_reset(sk);
5004                 goto discard;
5005         }
5006
5007         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5008
5009         /* step 3: check security and precedence [ignored] */
5010
5011         /*      step 4:
5012          *
5013          *      Check for a SYN in window.
5014          */
5015         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5016                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
5017                 tcp_reset(sk);
5018                 return 1;
5019         }
5020
5021         /* step 5: check the ACK field */
5022         if (th->ack) {
5023                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
5024
5025                 switch (sk->sk_state) {
5026                 case TCP_SYN_RECV:
5027                         if (acceptable) {
5028                                 tp->copied_seq = tp->rcv_nxt;
5029                                 smp_mb();
5030                                 tcp_set_state(sk, TCP_ESTABLISHED);
5031                                 sk->sk_state_change(sk);
5032
5033                                 /* Note, that this wakeup is only for marginal
5034                                  * crossed SYN case. Passively open sockets
5035                                  * are not waked up, because sk->sk_sleep ==
5036                                  * NULL and sk->sk_socket == NULL.
5037                                  */
5038                                 if (sk->sk_socket) {
5039                                         sk_wake_async(sk,0,POLL_OUT);
5040                                 }
5041
5042                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5043                                 tp->snd_wnd = ntohs(th->window) <<
5044                                               tp->rx_opt.snd_wscale;
5045                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
5046                                             TCP_SKB_CB(skb)->seq);
5047
5048                                 /* tcp_ack considers this ACK as duplicate
5049                                  * and does not calculate rtt.
5050                                  * Fix it at least with timestamps.
5051                                  */
5052                                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
5053                                     !tp->srtt)
5054                                         tcp_ack_saw_tstamp(sk, 0);
5055
5056                                 if (tp->rx_opt.tstamp_ok)
5057                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5058
5059                                 /* Make sure socket is routed, for
5060                                  * correct metrics.
5061                                  */
5062                                 icsk->icsk_af_ops->rebuild_header(sk);
5063
5064                                 tcp_init_metrics(sk);
5065
5066                                 tcp_init_congestion_control(sk);
5067
5068                                 /* Prevent spurious tcp_cwnd_restart() on
5069                                  * first data packet.
5070                                  */
5071                                 tp->lsndtime = tcp_time_stamp;
5072
5073                                 tcp_mtup_init(sk);
5074                                 tcp_initialize_rcv_mss(sk);
5075                                 tcp_init_buffer_space(sk);
5076                                 tcp_fast_path_on(tp);
5077                         } else {
5078                                 return 1;
5079                         }
5080                         break;
5081
5082                 case TCP_FIN_WAIT1:
5083                         if (tp->snd_una == tp->write_seq) {
5084                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5085                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5086                                 dst_confirm(sk->sk_dst_cache);
5087
5088                                 if (!sock_flag(sk, SOCK_DEAD))
5089                                         /* Wake up lingering close() */
5090                                         sk->sk_state_change(sk);
5091                                 else {
5092                                         int tmo;
5093
5094                                         if (tp->linger2 < 0 ||
5095                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5096                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5097                                                 tcp_done(sk);
5098                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5099                                                 return 1;
5100                                         }
5101
5102                                         tmo = tcp_fin_time(sk);
5103                                         if (tmo > TCP_TIMEWAIT_LEN) {
5104                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5105                                         } else if (th->fin || sock_owned_by_user(sk)) {
5106                                                 /* Bad case. We could lose such FIN otherwise.
5107                                                  * It is not a big problem, but it looks confusing
5108                                                  * and not so rare event. We still can lose it now,
5109                                                  * if it spins in bh_lock_sock(), but it is really
5110                                                  * marginal case.
5111                                                  */
5112                                                 inet_csk_reset_keepalive_timer(sk, tmo);
5113                                         } else {
5114                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5115                                                 goto discard;
5116                                         }
5117                                 }
5118                         }
5119                         break;
5120
5121                 case TCP_CLOSING:
5122                         if (tp->snd_una == tp->write_seq) {
5123                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5124                                 goto discard;
5125                         }
5126                         break;
5127
5128                 case TCP_LAST_ACK:
5129                         if (tp->snd_una == tp->write_seq) {
5130                                 tcp_update_metrics(sk);
5131                                 tcp_done(sk);
5132                                 goto discard;
5133                         }
5134                         break;
5135                 }
5136         } else
5137                 goto discard;
5138
5139         /* step 6: check the URG bit */
5140         tcp_urg(sk, skb, th);
5141
5142         /* step 7: process the segment text */
5143         switch (sk->sk_state) {
5144         case TCP_CLOSE_WAIT:
5145         case TCP_CLOSING:
5146         case TCP_LAST_ACK:
5147                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5148                         break;
5149         case TCP_FIN_WAIT1:
5150         case TCP_FIN_WAIT2:
5151                 /* RFC 793 says to queue data in these states,
5152                  * RFC 1122 says we MUST send a reset.
5153                  * BSD 4.4 also does reset.
5154                  */
5155                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5156                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5157                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5158                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5159                                 tcp_reset(sk);
5160                                 return 1;
5161                         }
5162                 }
5163                 /* Fall through */
5164         case TCP_ESTABLISHED:
5165                 tcp_data_queue(sk, skb);
5166                 queued = 1;
5167                 break;
5168         }
5169
5170         /* tcp_data could move socket to TIME-WAIT */
5171         if (sk->sk_state != TCP_CLOSE) {
5172                 tcp_data_snd_check(sk);
5173                 tcp_ack_snd_check(sk);
5174         }
5175
5176         if (!queued) {
5177 discard:
5178                 __kfree_skb(skb);
5179         }
5180         return 0;
5181 }
5182
5183 EXPORT_SYMBOL(sysctl_tcp_ecn);
5184 EXPORT_SYMBOL(sysctl_tcp_reordering);
5185 EXPORT_SYMBOL(tcp_parse_options);
5186 EXPORT_SYMBOL(tcp_rcv_established);
5187 EXPORT_SYMBOL(tcp_rcv_state_process);
5188 EXPORT_SYMBOL(tcp_initialize_rcv_mss);