x25: use limited socket backlog
[linux-2.6.git] / net / netfilter / nf_conntrack_pptp.c
1 /*
2  * Connection tracking support for PPTP (Point to Point Tunneling Protocol).
3  * PPTP is a a protocol for creating virtual private networks.
4  * It is a specification defined by Microsoft and some vendors
5  * working with Microsoft.  PPTP is built on top of a modified
6  * version of the Internet Generic Routing Encapsulation Protocol.
7  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
8  * PPTP can be found in RFC 2637
9  *
10  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
11  *
12  * Development of this code funded by Astaro AG (http://www.astaro.com/)
13  *
14  * Limitations:
15  *       - We blindly assume that control connections are always
16  *         established in PNS->PAC direction.  This is a violation
17  *         of RFFC2673
18  *       - We can only support one single call within each session
19  * TODO:
20  *       - testing of incoming PPTP calls
21  */
22
23 #include <linux/module.h>
24 #include <linux/skbuff.h>
25 #include <linux/in.h>
26 #include <linux/tcp.h>
27
28 #include <net/netfilter/nf_conntrack.h>
29 #include <net/netfilter/nf_conntrack_core.h>
30 #include <net/netfilter/nf_conntrack_helper.h>
31 #include <net/netfilter/nf_conntrack_zones.h>
32 #include <linux/netfilter/nf_conntrack_proto_gre.h>
33 #include <linux/netfilter/nf_conntrack_pptp.h>
34
35 #define NF_CT_PPTP_VERSION "3.1"
36
37 MODULE_LICENSE("GPL");
38 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
39 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
40 MODULE_ALIAS("ip_conntrack_pptp");
41 MODULE_ALIAS_NFCT_HELPER("pptp");
42
43 static DEFINE_SPINLOCK(nf_pptp_lock);
44
45 int
46 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
47                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
48                              struct PptpControlHeader *ctlh,
49                              union pptp_ctrl_union *pptpReq) __read_mostly;
50 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
51
52 int
53 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
54                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
55                             struct PptpControlHeader *ctlh,
56                             union pptp_ctrl_union *pptpReq) __read_mostly;
57 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
58
59 void
60 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
61                             struct nf_conntrack_expect *expect_reply)
62                             __read_mostly;
63 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
64
65 void
66 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
67                              struct nf_conntrack_expect *exp) __read_mostly;
68 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
69
70 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
71 /* PptpControlMessageType names */
72 const char *const pptp_msg_name[] = {
73         "UNKNOWN_MESSAGE",
74         "START_SESSION_REQUEST",
75         "START_SESSION_REPLY",
76         "STOP_SESSION_REQUEST",
77         "STOP_SESSION_REPLY",
78         "ECHO_REQUEST",
79         "ECHO_REPLY",
80         "OUT_CALL_REQUEST",
81         "OUT_CALL_REPLY",
82         "IN_CALL_REQUEST",
83         "IN_CALL_REPLY",
84         "IN_CALL_CONNECT",
85         "CALL_CLEAR_REQUEST",
86         "CALL_DISCONNECT_NOTIFY",
87         "WAN_ERROR_NOTIFY",
88         "SET_LINK_INFO"
89 };
90 EXPORT_SYMBOL(pptp_msg_name);
91 #endif
92
93 #define SECS *HZ
94 #define MINS * 60 SECS
95 #define HOURS * 60 MINS
96
97 #define PPTP_GRE_TIMEOUT                (10 MINS)
98 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
99
100 static void pptp_expectfn(struct nf_conn *ct,
101                          struct nf_conntrack_expect *exp)
102 {
103         struct net *net = nf_ct_net(ct);
104         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
105         pr_debug("increasing timeouts\n");
106
107         /* increase timeout of GRE data channel conntrack entry */
108         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
109         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
110
111         /* Can you see how rusty this code is, compared with the pre-2.6.11
112          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
113
114         rcu_read_lock();
115         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
116         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
117                 nf_nat_pptp_expectfn(ct, exp);
118         else {
119                 struct nf_conntrack_tuple inv_t;
120                 struct nf_conntrack_expect *exp_other;
121
122                 /* obviously this tuple inversion only works until you do NAT */
123                 nf_ct_invert_tuplepr(&inv_t, &exp->tuple);
124                 pr_debug("trying to unexpect other dir: ");
125                 nf_ct_dump_tuple(&inv_t);
126
127                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
128                 if (exp_other) {
129                         /* delete other expectation.  */
130                         pr_debug("found\n");
131                         nf_ct_unexpect_related(exp_other);
132                         nf_ct_expect_put(exp_other);
133                 } else {
134                         pr_debug("not found\n");
135                 }
136         }
137         rcu_read_unlock();
138 }
139
140 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
141                                   const struct nf_conntrack_tuple *t)
142 {
143         const struct nf_conntrack_tuple_hash *h;
144         struct nf_conntrack_expect *exp;
145         struct nf_conn *sibling;
146         u16 zone = nf_ct_zone(ct);
147
148         pr_debug("trying to timeout ct or exp for tuple ");
149         nf_ct_dump_tuple(t);
150
151         h = nf_conntrack_find_get(net, zone, t);
152         if (h)  {
153                 sibling = nf_ct_tuplehash_to_ctrack(h);
154                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
155                 sibling->proto.gre.timeout        = 0;
156                 sibling->proto.gre.stream_timeout = 0;
157                 if (del_timer(&sibling->timeout))
158                         sibling->timeout.function((unsigned long)sibling);
159                 nf_ct_put(sibling);
160                 return 1;
161         } else {
162                 exp = nf_ct_expect_find_get(net, zone, t);
163                 if (exp) {
164                         pr_debug("unexpect_related of expect %p\n", exp);
165                         nf_ct_unexpect_related(exp);
166                         nf_ct_expect_put(exp);
167                         return 1;
168                 }
169         }
170         return 0;
171 }
172
173 /* timeout GRE data connections */
174 static void pptp_destroy_siblings(struct nf_conn *ct)
175 {
176         struct net *net = nf_ct_net(ct);
177         const struct nf_conn_help *help = nfct_help(ct);
178         struct nf_conntrack_tuple t;
179
180         nf_ct_gre_keymap_destroy(ct);
181
182         /* try original (pns->pac) tuple */
183         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
184         t.dst.protonum = IPPROTO_GRE;
185         t.src.u.gre.key = help->help.ct_pptp_info.pns_call_id;
186         t.dst.u.gre.key = help->help.ct_pptp_info.pac_call_id;
187         if (!destroy_sibling_or_exp(net, ct, &t))
188                 pr_debug("failed to timeout original pns->pac ct/exp\n");
189
190         /* try reply (pac->pns) tuple */
191         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
192         t.dst.protonum = IPPROTO_GRE;
193         t.src.u.gre.key = help->help.ct_pptp_info.pac_call_id;
194         t.dst.u.gre.key = help->help.ct_pptp_info.pns_call_id;
195         if (!destroy_sibling_or_exp(net, ct, &t))
196                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
197 }
198
199 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
200 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
201 {
202         struct nf_conntrack_expect *exp_orig, *exp_reply;
203         enum ip_conntrack_dir dir;
204         int ret = 1;
205         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
206
207         exp_orig = nf_ct_expect_alloc(ct);
208         if (exp_orig == NULL)
209                 goto out;
210
211         exp_reply = nf_ct_expect_alloc(ct);
212         if (exp_reply == NULL)
213                 goto out_put_orig;
214
215         /* original direction, PNS->PAC */
216         dir = IP_CT_DIR_ORIGINAL;
217         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
218                           nf_ct_l3num(ct),
219                           &ct->tuplehash[dir].tuple.src.u3,
220                           &ct->tuplehash[dir].tuple.dst.u3,
221                           IPPROTO_GRE, &peer_callid, &callid);
222         exp_orig->expectfn = pptp_expectfn;
223
224         /* reply direction, PAC->PNS */
225         dir = IP_CT_DIR_REPLY;
226         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
227                           nf_ct_l3num(ct),
228                           &ct->tuplehash[dir].tuple.src.u3,
229                           &ct->tuplehash[dir].tuple.dst.u3,
230                           IPPROTO_GRE, &callid, &peer_callid);
231         exp_reply->expectfn = pptp_expectfn;
232
233         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
234         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
235                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
236         if (nf_ct_expect_related(exp_orig) != 0)
237                 goto out_put_both;
238         if (nf_ct_expect_related(exp_reply) != 0)
239                 goto out_unexpect_orig;
240
241         /* Add GRE keymap entries */
242         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
243                 goto out_unexpect_both;
244         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
245                 nf_ct_gre_keymap_destroy(ct);
246                 goto out_unexpect_both;
247         }
248         ret = 0;
249
250 out_put_both:
251         nf_ct_expect_put(exp_reply);
252 out_put_orig:
253         nf_ct_expect_put(exp_orig);
254 out:
255         return ret;
256
257 out_unexpect_both:
258         nf_ct_unexpect_related(exp_reply);
259 out_unexpect_orig:
260         nf_ct_unexpect_related(exp_orig);
261         goto out_put_both;
262 }
263
264 static inline int
265 pptp_inbound_pkt(struct sk_buff *skb,
266                  struct PptpControlHeader *ctlh,
267                  union pptp_ctrl_union *pptpReq,
268                  unsigned int reqlen,
269                  struct nf_conn *ct,
270                  enum ip_conntrack_info ctinfo)
271 {
272         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
273         u_int16_t msg;
274         __be16 cid = 0, pcid = 0;
275         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
276
277         msg = ntohs(ctlh->messageType);
278         pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
279
280         switch (msg) {
281         case PPTP_START_SESSION_REPLY:
282                 /* server confirms new control session */
283                 if (info->sstate < PPTP_SESSION_REQUESTED)
284                         goto invalid;
285                 if (pptpReq->srep.resultCode == PPTP_START_OK)
286                         info->sstate = PPTP_SESSION_CONFIRMED;
287                 else
288                         info->sstate = PPTP_SESSION_ERROR;
289                 break;
290
291         case PPTP_STOP_SESSION_REPLY:
292                 /* server confirms end of control session */
293                 if (info->sstate > PPTP_SESSION_STOPREQ)
294                         goto invalid;
295                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
296                         info->sstate = PPTP_SESSION_NONE;
297                 else
298                         info->sstate = PPTP_SESSION_ERROR;
299                 break;
300
301         case PPTP_OUT_CALL_REPLY:
302                 /* server accepted call, we now expect GRE frames */
303                 if (info->sstate != PPTP_SESSION_CONFIRMED)
304                         goto invalid;
305                 if (info->cstate != PPTP_CALL_OUT_REQ &&
306                     info->cstate != PPTP_CALL_OUT_CONF)
307                         goto invalid;
308
309                 cid = pptpReq->ocack.callID;
310                 pcid = pptpReq->ocack.peersCallID;
311                 if (info->pns_call_id != pcid)
312                         goto invalid;
313                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
314                          ntohs(cid), ntohs(pcid));
315
316                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
317                         info->cstate = PPTP_CALL_OUT_CONF;
318                         info->pac_call_id = cid;
319                         exp_gre(ct, cid, pcid);
320                 } else
321                         info->cstate = PPTP_CALL_NONE;
322                 break;
323
324         case PPTP_IN_CALL_REQUEST:
325                 /* server tells us about incoming call request */
326                 if (info->sstate != PPTP_SESSION_CONFIRMED)
327                         goto invalid;
328
329                 cid = pptpReq->icreq.callID;
330                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
331                 info->cstate = PPTP_CALL_IN_REQ;
332                 info->pac_call_id = cid;
333                 break;
334
335         case PPTP_IN_CALL_CONNECT:
336                 /* server tells us about incoming call established */
337                 if (info->sstate != PPTP_SESSION_CONFIRMED)
338                         goto invalid;
339                 if (info->cstate != PPTP_CALL_IN_REP &&
340                     info->cstate != PPTP_CALL_IN_CONF)
341                         goto invalid;
342
343                 pcid = pptpReq->iccon.peersCallID;
344                 cid = info->pac_call_id;
345
346                 if (info->pns_call_id != pcid)
347                         goto invalid;
348
349                 pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
350                 info->cstate = PPTP_CALL_IN_CONF;
351
352                 /* we expect a GRE connection from PAC to PNS */
353                 exp_gre(ct, cid, pcid);
354                 break;
355
356         case PPTP_CALL_DISCONNECT_NOTIFY:
357                 /* server confirms disconnect */
358                 cid = pptpReq->disc.callID;
359                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
360                 info->cstate = PPTP_CALL_NONE;
361
362                 /* untrack this call id, unexpect GRE packets */
363                 pptp_destroy_siblings(ct);
364                 break;
365
366         case PPTP_WAN_ERROR_NOTIFY:
367         case PPTP_ECHO_REQUEST:
368         case PPTP_ECHO_REPLY:
369                 /* I don't have to explain these ;) */
370                 break;
371
372         default:
373                 goto invalid;
374         }
375
376         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
377         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
378                 return nf_nat_pptp_inbound(skb, ct, ctinfo, ctlh, pptpReq);
379         return NF_ACCEPT;
380
381 invalid:
382         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
383                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
384                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
385                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
386                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
387         return NF_ACCEPT;
388 }
389
390 static inline int
391 pptp_outbound_pkt(struct sk_buff *skb,
392                   struct PptpControlHeader *ctlh,
393                   union pptp_ctrl_union *pptpReq,
394                   unsigned int reqlen,
395                   struct nf_conn *ct,
396                   enum ip_conntrack_info ctinfo)
397 {
398         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
399         u_int16_t msg;
400         __be16 cid = 0, pcid = 0;
401         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
402
403         msg = ntohs(ctlh->messageType);
404         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
405
406         switch (msg) {
407         case PPTP_START_SESSION_REQUEST:
408                 /* client requests for new control session */
409                 if (info->sstate != PPTP_SESSION_NONE)
410                         goto invalid;
411                 info->sstate = PPTP_SESSION_REQUESTED;
412                 break;
413
414         case PPTP_STOP_SESSION_REQUEST:
415                 /* client requests end of control session */
416                 info->sstate = PPTP_SESSION_STOPREQ;
417                 break;
418
419         case PPTP_OUT_CALL_REQUEST:
420                 /* client initiating connection to server */
421                 if (info->sstate != PPTP_SESSION_CONFIRMED)
422                         goto invalid;
423                 info->cstate = PPTP_CALL_OUT_REQ;
424                 /* track PNS call id */
425                 cid = pptpReq->ocreq.callID;
426                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
427                 info->pns_call_id = cid;
428                 break;
429
430         case PPTP_IN_CALL_REPLY:
431                 /* client answers incoming call */
432                 if (info->cstate != PPTP_CALL_IN_REQ &&
433                     info->cstate != PPTP_CALL_IN_REP)
434                         goto invalid;
435
436                 cid = pptpReq->icack.callID;
437                 pcid = pptpReq->icack.peersCallID;
438                 if (info->pac_call_id != pcid)
439                         goto invalid;
440                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
441                          ntohs(cid), ntohs(pcid));
442
443                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
444                         /* part two of the three-way handshake */
445                         info->cstate = PPTP_CALL_IN_REP;
446                         info->pns_call_id = cid;
447                 } else
448                         info->cstate = PPTP_CALL_NONE;
449                 break;
450
451         case PPTP_CALL_CLEAR_REQUEST:
452                 /* client requests hangup of call */
453                 if (info->sstate != PPTP_SESSION_CONFIRMED)
454                         goto invalid;
455                 /* FUTURE: iterate over all calls and check if
456                  * call ID is valid.  We don't do this without newnat,
457                  * because we only know about last call */
458                 info->cstate = PPTP_CALL_CLEAR_REQ;
459                 break;
460
461         case PPTP_SET_LINK_INFO:
462         case PPTP_ECHO_REQUEST:
463         case PPTP_ECHO_REPLY:
464                 /* I don't have to explain these ;) */
465                 break;
466
467         default:
468                 goto invalid;
469         }
470
471         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
472         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
473                 return nf_nat_pptp_outbound(skb, ct, ctinfo, ctlh, pptpReq);
474         return NF_ACCEPT;
475
476 invalid:
477         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
478                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
479                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
480                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
481                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
482         return NF_ACCEPT;
483 }
484
485 static const unsigned int pptp_msg_size[] = {
486         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
487         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
488         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
489         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
490         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
491         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
492         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
493         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
494         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
495         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
496         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
497         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
498         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
499 };
500
501 /* track caller id inside control connection, call expect_related */
502 static int
503 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
504                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
505
506 {
507         int dir = CTINFO2DIR(ctinfo);
508         const struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
509         const struct tcphdr *tcph;
510         struct tcphdr _tcph;
511         const struct pptp_pkt_hdr *pptph;
512         struct pptp_pkt_hdr _pptph;
513         struct PptpControlHeader _ctlh, *ctlh;
514         union pptp_ctrl_union _pptpReq, *pptpReq;
515         unsigned int tcplen = skb->len - protoff;
516         unsigned int datalen, reqlen, nexthdr_off;
517         int oldsstate, oldcstate;
518         int ret;
519         u_int16_t msg;
520
521         /* don't do any tracking before tcp handshake complete */
522         if (ctinfo != IP_CT_ESTABLISHED &&
523             ctinfo != IP_CT_ESTABLISHED + IP_CT_IS_REPLY)
524                 return NF_ACCEPT;
525
526         nexthdr_off = protoff;
527         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
528         BUG_ON(!tcph);
529         nexthdr_off += tcph->doff * 4;
530         datalen = tcplen - tcph->doff * 4;
531
532         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
533         if (!pptph) {
534                 pr_debug("no full PPTP header, can't track\n");
535                 return NF_ACCEPT;
536         }
537         nexthdr_off += sizeof(_pptph);
538         datalen -= sizeof(_pptph);
539
540         /* if it's not a control message we can't do anything with it */
541         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
542             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
543                 pr_debug("not a control packet\n");
544                 return NF_ACCEPT;
545         }
546
547         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
548         if (!ctlh)
549                 return NF_ACCEPT;
550         nexthdr_off += sizeof(_ctlh);
551         datalen -= sizeof(_ctlh);
552
553         reqlen = datalen;
554         msg = ntohs(ctlh->messageType);
555         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
556                 return NF_ACCEPT;
557         if (reqlen > sizeof(*pptpReq))
558                 reqlen = sizeof(*pptpReq);
559
560         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
561         if (!pptpReq)
562                 return NF_ACCEPT;
563
564         oldsstate = info->sstate;
565         oldcstate = info->cstate;
566
567         spin_lock_bh(&nf_pptp_lock);
568
569         /* FIXME: We just blindly assume that the control connection is always
570          * established from PNS->PAC.  However, RFC makes no guarantee */
571         if (dir == IP_CT_DIR_ORIGINAL)
572                 /* client -> server (PNS -> PAC) */
573                 ret = pptp_outbound_pkt(skb, ctlh, pptpReq, reqlen, ct,
574                                         ctinfo);
575         else
576                 /* server -> client (PAC -> PNS) */
577                 ret = pptp_inbound_pkt(skb, ctlh, pptpReq, reqlen, ct,
578                                        ctinfo);
579         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
580                  oldsstate, info->sstate, oldcstate, info->cstate);
581         spin_unlock_bh(&nf_pptp_lock);
582
583         return ret;
584 }
585
586 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
587         .max_expected   = 2,
588         .timeout        = 5 * 60,
589 };
590
591 /* control protocol helper */
592 static struct nf_conntrack_helper pptp __read_mostly = {
593         .name                   = "pptp",
594         .me                     = THIS_MODULE,
595         .tuple.src.l3num        = AF_INET,
596         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
597         .tuple.dst.protonum     = IPPROTO_TCP,
598         .help                   = conntrack_pptp_help,
599         .destroy                = pptp_destroy_siblings,
600         .expect_policy          = &pptp_exp_policy,
601 };
602
603 static void nf_conntrack_pptp_net_exit(struct net *net)
604 {
605         nf_ct_gre_keymap_flush(net);
606 }
607
608 static struct pernet_operations nf_conntrack_pptp_net_ops = {
609         .exit = nf_conntrack_pptp_net_exit,
610 };
611
612 static int __init nf_conntrack_pptp_init(void)
613 {
614         int rv;
615
616         rv = nf_conntrack_helper_register(&pptp);
617         if (rv < 0)
618                 return rv;
619         rv = register_pernet_subsys(&nf_conntrack_pptp_net_ops);
620         if (rv < 0)
621                 nf_conntrack_helper_unregister(&pptp);
622         return rv;
623 }
624
625 static void __exit nf_conntrack_pptp_fini(void)
626 {
627         nf_conntrack_helper_unregister(&pptp);
628         unregister_pernet_subsys(&nf_conntrack_pptp_net_ops);
629 }
630
631 module_init(nf_conntrack_pptp_init);
632 module_exit(nf_conntrack_pptp_fini);