d2dd5d3135563f9e17631f6ab72e8bd42bcad387
[linux-3.10.git] / net / ipv4 / netfilter / ip_nat_helper.c
1 /* ip_nat_helper.c - generic support functions for NAT helpers 
2  *
3  * (C) 2000-2002 Harald Welte <laforge@netfilter.org>
4  * (C) 2003-2004 Netfilter Core Team <coreteam@netfilter.org>
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  *
10  *      14 Jan 2002 Harald Welte <laforge@gnumonks.org>:
11  *              - add support for SACK adjustment 
12  *      14 Mar 2002 Harald Welte <laforge@gnumonks.org>:
13  *              - merge SACK support into newnat API
14  *      16 Aug 2002 Brian J. Murrell <netfilter@interlinx.bc.ca>:
15  *              - make ip_nat_resize_packet more generic (TCP and UDP)
16  *              - add ip_nat_mangle_udp_packet
17  */
18 #include <linux/config.h>
19 #include <linux/module.h>
20 #include <linux/kmod.h>
21 #include <linux/types.h>
22 #include <linux/timer.h>
23 #include <linux/skbuff.h>
24 #include <linux/netfilter_ipv4.h>
25 #include <net/checksum.h>
26 #include <net/icmp.h>
27 #include <net/ip.h>
28 #include <net/tcp.h>
29 #include <net/udp.h>
30
31 #define ASSERT_READ_LOCK(x)
32 #define ASSERT_WRITE_LOCK(x)
33
34 #include <linux/netfilter_ipv4/ip_conntrack.h>
35 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
36 #include <linux/netfilter_ipv4/ip_nat.h>
37 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
38 #include <linux/netfilter_ipv4/ip_nat_core.h>
39 #include <linux/netfilter_ipv4/ip_nat_helper.h>
40 #include <linux/netfilter_ipv4/listhelp.h>
41
42 #if 0
43 #define DEBUGP printk
44 #define DUMP_OFFSET(x)  printk("offset_before=%d, offset_after=%d, correction_pos=%u\n", x->offset_before, x->offset_after, x->correction_pos);
45 #else
46 #define DEBUGP(format, args...)
47 #define DUMP_OFFSET(x)
48 #endif
49
50 static DEFINE_SPINLOCK(ip_nat_seqofs_lock);
51
52 /* Setup TCP sequence correction given this change at this sequence */
53 static inline void 
54 adjust_tcp_sequence(u32 seq,
55                     int sizediff,
56                     struct ip_conntrack *ct, 
57                     enum ip_conntrack_info ctinfo)
58 {
59         int dir;
60         struct ip_nat_seq *this_way, *other_way;
61
62         DEBUGP("ip_nat_resize_packet: old_size = %u, new_size = %u\n",
63                 (*skb)->len, new_size);
64
65         dir = CTINFO2DIR(ctinfo);
66
67         this_way = &ct->nat.info.seq[dir];
68         other_way = &ct->nat.info.seq[!dir];
69
70         DEBUGP("ip_nat_resize_packet: Seq_offset before: ");
71         DUMP_OFFSET(this_way);
72
73         spin_lock_bh(&ip_nat_seqofs_lock);
74
75         /* SYN adjust. If it's uninitialized, or this is after last
76          * correction, record it: we don't handle more than one
77          * adjustment in the window, but do deal with common case of a
78          * retransmit */
79         if (this_way->offset_before == this_way->offset_after
80             || before(this_way->correction_pos, seq)) {
81                     this_way->correction_pos = seq;
82                     this_way->offset_before = this_way->offset_after;
83                     this_way->offset_after += sizediff;
84         }
85         spin_unlock_bh(&ip_nat_seqofs_lock);
86
87         DEBUGP("ip_nat_resize_packet: Seq_offset after: ");
88         DUMP_OFFSET(this_way);
89 }
90
91 /* Frobs data inside this packet, which is linear. */
92 static void mangle_contents(struct sk_buff *skb,
93                             unsigned int dataoff,
94                             unsigned int match_offset,
95                             unsigned int match_len,
96                             const char *rep_buffer,
97                             unsigned int rep_len)
98 {
99         unsigned char *data;
100
101         BUG_ON(skb_is_nonlinear(skb));
102         data = (unsigned char *)skb->nh.iph + dataoff;
103
104         /* move post-replacement */
105         memmove(data + match_offset + rep_len,
106                 data + match_offset + match_len,
107                 skb->tail - (data + match_offset + match_len));
108
109         /* insert data from buffer */
110         memcpy(data + match_offset, rep_buffer, rep_len);
111
112         /* update skb info */
113         if (rep_len > match_len) {
114                 DEBUGP("ip_nat_mangle_packet: Extending packet by "
115                         "%u from %u bytes\n", rep_len - match_len,
116                        skb->len);
117                 skb_put(skb, rep_len - match_len);
118         } else {
119                 DEBUGP("ip_nat_mangle_packet: Shrinking packet from "
120                         "%u from %u bytes\n", match_len - rep_len,
121                        skb->len);
122                 __skb_trim(skb, skb->len + rep_len - match_len);
123         }
124
125         /* fix IP hdr checksum information */
126         skb->nh.iph->tot_len = htons(skb->len);
127         ip_send_check(skb->nh.iph);
128 }
129
130 /* Unusual, but possible case. */
131 static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
132 {
133         struct sk_buff *nskb;
134
135         if ((*pskb)->len + extra > 65535)
136                 return 0;
137
138         nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
139         if (!nskb)
140                 return 0;
141
142         /* Transfer socket to new skb. */
143         if ((*pskb)->sk)
144                 skb_set_owner_w(nskb, (*pskb)->sk);
145         kfree_skb(*pskb);
146         *pskb = nskb;
147         return 1;
148 }
149
150 /* Generic function for mangling variable-length address changes inside
151  * NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
152  * command in FTP).
153  *
154  * Takes care about all the nasty sequence number changes, checksumming,
155  * skb enlargement, ...
156  *
157  * */
158 int 
159 ip_nat_mangle_tcp_packet(struct sk_buff **pskb,
160                          struct ip_conntrack *ct,
161                          enum ip_conntrack_info ctinfo,
162                          unsigned int match_offset,
163                          unsigned int match_len,
164                          const char *rep_buffer,
165                          unsigned int rep_len)
166 {
167         struct iphdr *iph;
168         struct tcphdr *tcph;
169         int datalen;
170
171         if (!skb_make_writable(pskb, (*pskb)->len))
172                 return 0;
173
174         if (rep_len > match_len
175             && rep_len - match_len > skb_tailroom(*pskb)
176             && !enlarge_skb(pskb, rep_len - match_len))
177                 return 0;
178
179         SKB_LINEAR_ASSERT(*pskb);
180
181         iph = (*pskb)->nh.iph;
182         tcph = (void *)iph + iph->ihl*4;
183
184         mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4,
185                         match_offset, match_len, rep_buffer, rep_len);
186
187         datalen = (*pskb)->len - iph->ihl*4;
188         tcph->check = 0;
189         tcph->check = tcp_v4_check(tcph, datalen, iph->saddr, iph->daddr,
190                                    csum_partial((char *)tcph, datalen, 0));
191
192         if (rep_len != match_len) {
193                 set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
194                 adjust_tcp_sequence(ntohl(tcph->seq),
195                                     (int)rep_len - (int)match_len,
196                                     ct, ctinfo);
197                 /* Tell TCP window tracking about seq change */
198                 ip_conntrack_tcp_update(*pskb, ct, CTINFO2DIR(ctinfo));
199         }
200         return 1;
201 }
202                         
203 /* Generic function for mangling variable-length address changes inside
204  * NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
205  * command in the Amanda protocol)
206  *
207  * Takes care about all the nasty sequence number changes, checksumming,
208  * skb enlargement, ...
209  *
210  * XXX - This function could be merged with ip_nat_mangle_tcp_packet which
211  *       should be fairly easy to do.
212  */
213 int 
214 ip_nat_mangle_udp_packet(struct sk_buff **pskb,
215                          struct ip_conntrack *ct,
216                          enum ip_conntrack_info ctinfo,
217                          unsigned int match_offset,
218                          unsigned int match_len,
219                          const char *rep_buffer,
220                          unsigned int rep_len)
221 {
222         struct iphdr *iph;
223         struct udphdr *udph;
224
225         /* UDP helpers might accidentally mangle the wrong packet */
226         iph = (*pskb)->nh.iph;
227         if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) + 
228                                match_offset + match_len)
229                 return 0;
230
231         if (!skb_make_writable(pskb, (*pskb)->len))
232                 return 0;
233
234         if (rep_len > match_len
235             && rep_len - match_len > skb_tailroom(*pskb)
236             && !enlarge_skb(pskb, rep_len - match_len))
237                 return 0;
238
239         iph = (*pskb)->nh.iph;
240         udph = (void *)iph + iph->ihl*4;
241         mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph),
242                         match_offset, match_len, rep_buffer, rep_len);
243
244         /* update the length of the UDP packet */
245         udph->len = htons((*pskb)->len - iph->ihl*4);
246
247         /* fix udp checksum if udp checksum was previously calculated */
248         if (udph->check) {
249                 int datalen = (*pskb)->len - iph->ihl * 4;
250                 udph->check = 0;
251                 udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
252                                                 datalen, IPPROTO_UDP,
253                                                 csum_partial((char *)udph,
254                                                              datalen, 0));
255         }
256
257         return 1;
258 }
259
260 /* Adjust one found SACK option including checksum correction */
261 static void
262 sack_adjust(struct sk_buff *skb,
263             struct tcphdr *tcph, 
264             unsigned int sackoff,
265             unsigned int sackend,
266             struct ip_nat_seq *natseq)
267 {
268         while (sackoff < sackend) {
269                 struct tcp_sack_block *sack;
270                 u_int32_t new_start_seq, new_end_seq;
271
272                 sack = (void *)skb->data + sackoff;
273                 if (after(ntohl(sack->start_seq) - natseq->offset_before,
274                           natseq->correction_pos))
275                         new_start_seq = ntohl(sack->start_seq) 
276                                         - natseq->offset_after;
277                 else
278                         new_start_seq = ntohl(sack->start_seq) 
279                                         - natseq->offset_before;
280                 new_start_seq = htonl(new_start_seq);
281
282                 if (after(ntohl(sack->end_seq) - natseq->offset_before,
283                           natseq->correction_pos))
284                         new_end_seq = ntohl(sack->end_seq)
285                                       - natseq->offset_after;
286                 else
287                         new_end_seq = ntohl(sack->end_seq)
288                                       - natseq->offset_before;
289                 new_end_seq = htonl(new_end_seq);
290
291                 DEBUGP("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
292                         ntohl(sack->start_seq), new_start_seq,
293                         ntohl(sack->end_seq), new_end_seq);
294
295                 tcph->check = 
296                         ip_nat_cheat_check(~sack->start_seq, new_start_seq,
297                                            ip_nat_cheat_check(~sack->end_seq, 
298                                                               new_end_seq,
299                                                               tcph->check));
300                 sack->start_seq = new_start_seq;
301                 sack->end_seq = new_end_seq;
302                 sackoff += sizeof(*sack);
303         }
304 }
305
306 /* TCP SACK sequence number adjustment */
307 static inline unsigned int
308 ip_nat_sack_adjust(struct sk_buff **pskb,
309                    struct tcphdr *tcph,
310                    struct ip_conntrack *ct,
311                    enum ip_conntrack_info ctinfo)
312 {
313         unsigned int dir, optoff, optend;
314
315         optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr);
316         optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4;
317
318         if (!skb_make_writable(pskb, optend))
319                 return 0;
320
321         dir = CTINFO2DIR(ctinfo);
322
323         while (optoff < optend) {
324                 /* Usually: option, length. */
325                 unsigned char *op = (*pskb)->data + optoff;
326
327                 switch (op[0]) {
328                 case TCPOPT_EOL:
329                         return 1;
330                 case TCPOPT_NOP:
331                         optoff++;
332                         continue;
333                 default:
334                         /* no partial options */
335                         if (optoff + 1 == optend
336                             || optoff + op[1] > optend
337                             || op[1] < 2)
338                                 return 0;
339                         if (op[0] == TCPOPT_SACK
340                             && op[1] >= 2+TCPOLEN_SACK_PERBLOCK
341                             && ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
342                                 sack_adjust(*pskb, tcph, optoff+2,
343                                             optoff+op[1],
344                                             &ct->nat.info.seq[!dir]);
345                         optoff += op[1];
346                 }
347         }
348         return 1;
349 }
350
351 /* TCP sequence number adjustment.  Returns 1 on success, 0 on failure */
352 int
353 ip_nat_seq_adjust(struct sk_buff **pskb, 
354                   struct ip_conntrack *ct, 
355                   enum ip_conntrack_info ctinfo)
356 {
357         struct tcphdr *tcph;
358         int dir, newseq, newack;
359         struct ip_nat_seq *this_way, *other_way;        
360
361         dir = CTINFO2DIR(ctinfo);
362
363         this_way = &ct->nat.info.seq[dir];
364         other_way = &ct->nat.info.seq[!dir];
365
366         if (!skb_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
367                 return 0;
368
369         tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
370         if (after(ntohl(tcph->seq), this_way->correction_pos))
371                 newseq = ntohl(tcph->seq) + this_way->offset_after;
372         else
373                 newseq = ntohl(tcph->seq) + this_way->offset_before;
374         newseq = htonl(newseq);
375
376         if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
377                   other_way->correction_pos))
378                 newack = ntohl(tcph->ack_seq) - other_way->offset_after;
379         else
380                 newack = ntohl(tcph->ack_seq) - other_way->offset_before;
381         newack = htonl(newack);
382
383         tcph->check = ip_nat_cheat_check(~tcph->seq, newseq,
384                                          ip_nat_cheat_check(~tcph->ack_seq, 
385                                                             newack, 
386                                                             tcph->check));
387
388         DEBUGP("Adjusting sequence number from %u->%u, ack from %u->%u\n",
389                 ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
390                 ntohl(newack));
391
392         tcph->seq = newseq;
393         tcph->ack_seq = newack;
394
395         if (!ip_nat_sack_adjust(pskb, tcph, ct, ctinfo))
396                 return 0;
397
398         ip_conntrack_tcp_update(*pskb, ct, dir);
399
400         return 1;
401 }
402
403 /* Setup NAT on this expected conntrack so it follows master. */
404 /* If we fail to get a free NAT slot, we'll get dropped on confirm */
405 void ip_nat_follow_master(struct ip_conntrack *ct,
406                           struct ip_conntrack_expect *exp)
407 {
408         struct ip_nat_range range;
409
410         /* This must be a fresh one. */
411         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
412
413         /* Change src to where master sends to */
414         range.flags = IP_NAT_RANGE_MAP_IPS;
415         range.min_ip = range.max_ip
416                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
417         /* hook doesn't matter, but it has to do source manip */
418         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
419
420         /* For DST manip, map port here to where it's expected. */
421         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
422         range.min = range.max = exp->saved_proto;
423         range.min_ip = range.max_ip
424                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
425         /* hook doesn't matter, but it has to do destination manip */
426         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
427 }