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Linux/net/netfilter/nf_conntrack_pptp.c

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  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  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 15  *
 16  * Limitations:
 17  *       - We blindly assume that control connections are always
 18  *         established in PNS->PAC direction.  This is a violation
 19  *         of RFC 2637
 20  *       - We can only support one single call within each session
 21  * TODO:
 22  *       - testing of incoming PPTP calls
 23  */
 24 
 25 #include <linux/module.h>
 26 #include <linux/skbuff.h>
 27 #include <linux/in.h>
 28 #include <linux/tcp.h>
 29 
 30 #include <net/netfilter/nf_conntrack.h>
 31 #include <net/netfilter/nf_conntrack_core.h>
 32 #include <net/netfilter/nf_conntrack_helper.h>
 33 #include <net/netfilter/nf_conntrack_zones.h>
 34 #include <linux/netfilter/nf_conntrack_proto_gre.h>
 35 #include <linux/netfilter/nf_conntrack_pptp.h>
 36 
 37 #define NF_CT_PPTP_VERSION "3.1"
 38 
 39 MODULE_LICENSE("GPL");
 40 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
 41 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
 42 MODULE_ALIAS("ip_conntrack_pptp");
 43 MODULE_ALIAS_NFCT_HELPER("pptp");
 44 
 45 static DEFINE_SPINLOCK(nf_pptp_lock);
 46 
 47 int
 48 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
 49                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 50                              unsigned int protoff, struct PptpControlHeader *ctlh,
 51                              union pptp_ctrl_union *pptpReq) __read_mostly;
 52 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
 53 
 54 int
 55 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
 56                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 57                             unsigned int protoff, struct PptpControlHeader *ctlh,
 58                             union pptp_ctrl_union *pptpReq) __read_mostly;
 59 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
 60 
 61 void
 62 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
 63                             struct nf_conntrack_expect *expect_reply)
 64                             __read_mostly;
 65 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
 66 
 67 void
 68 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
 69                              struct nf_conntrack_expect *exp) __read_mostly;
 70 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
 71 
 72 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
 73 /* PptpControlMessageType names */
 74 const char *const pptp_msg_name[] = {
 75         "UNKNOWN_MESSAGE",
 76         "START_SESSION_REQUEST",
 77         "START_SESSION_REPLY",
 78         "STOP_SESSION_REQUEST",
 79         "STOP_SESSION_REPLY",
 80         "ECHO_REQUEST",
 81         "ECHO_REPLY",
 82         "OUT_CALL_REQUEST",
 83         "OUT_CALL_REPLY",
 84         "IN_CALL_REQUEST",
 85         "IN_CALL_REPLY",
 86         "IN_CALL_CONNECT",
 87         "CALL_CLEAR_REQUEST",
 88         "CALL_DISCONNECT_NOTIFY",
 89         "WAN_ERROR_NOTIFY",
 90         "SET_LINK_INFO"
 91 };
 92 EXPORT_SYMBOL(pptp_msg_name);
 93 #endif
 94 
 95 #define SECS *HZ
 96 #define MINS * 60 SECS
 97 #define HOURS * 60 MINS
 98 
 99 #define PPTP_GRE_TIMEOUT                (10 MINS)
100 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
101 
102 static void pptp_expectfn(struct nf_conn *ct,
103                          struct nf_conntrack_expect *exp)
104 {
105         struct net *net = nf_ct_net(ct);
106         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
107         pr_debug("increasing timeouts\n");
108 
109         /* increase timeout of GRE data channel conntrack entry */
110         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
111         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
112 
113         /* Can you see how rusty this code is, compared with the pre-2.6.11
114          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
115 
116         rcu_read_lock();
117         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
118         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
119                 nf_nat_pptp_expectfn(ct, exp);
120         else {
121                 struct nf_conntrack_tuple inv_t;
122                 struct nf_conntrack_expect *exp_other;
123 
124                 /* obviously this tuple inversion only works until you do NAT */
125                 nf_ct_invert_tuplepr(&inv_t, &exp->tuple);
126                 pr_debug("trying to unexpect other dir: ");
127                 nf_ct_dump_tuple(&inv_t);
128 
129                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
130                 if (exp_other) {
131                         /* delete other expectation.  */
132                         pr_debug("found\n");
133                         nf_ct_unexpect_related(exp_other);
134                         nf_ct_expect_put(exp_other);
135                 } else {
136                         pr_debug("not found\n");
137                 }
138         }
139         rcu_read_unlock();
140 }
141 
142 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
143                                   const struct nf_conntrack_tuple *t)
144 {
145         const struct nf_conntrack_tuple_hash *h;
146         const struct nf_conntrack_zone *zone;
147         struct nf_conntrack_expect *exp;
148         struct nf_conn *sibling;
149 
150         pr_debug("trying to timeout ct or exp for tuple ");
151         nf_ct_dump_tuple(t);
152 
153         zone = nf_ct_zone(ct);
154         h = nf_conntrack_find_get(net, zone, t);
155         if (h)  {
156                 sibling = nf_ct_tuplehash_to_ctrack(h);
157                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
158                 sibling->proto.gre.timeout        = 0;
159                 sibling->proto.gre.stream_timeout = 0;
160                 if (del_timer(&sibling->timeout))
161                         sibling->timeout.function((unsigned long)sibling);
162                 nf_ct_put(sibling);
163                 return 1;
164         } else {
165                 exp = nf_ct_expect_find_get(net, zone, t);
166                 if (exp) {
167                         pr_debug("unexpect_related of expect %p\n", exp);
168                         nf_ct_unexpect_related(exp);
169                         nf_ct_expect_put(exp);
170                         return 1;
171                 }
172         }
173         return 0;
174 }
175 
176 /* timeout GRE data connections */
177 static void pptp_destroy_siblings(struct nf_conn *ct)
178 {
179         struct net *net = nf_ct_net(ct);
180         const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
181         struct nf_conntrack_tuple t;
182 
183         nf_ct_gre_keymap_destroy(ct);
184 
185         /* try original (pns->pac) tuple */
186         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
187         t.dst.protonum = IPPROTO_GRE;
188         t.src.u.gre.key = ct_pptp_info->pns_call_id;
189         t.dst.u.gre.key = ct_pptp_info->pac_call_id;
190         if (!destroy_sibling_or_exp(net, ct, &t))
191                 pr_debug("failed to timeout original pns->pac ct/exp\n");
192 
193         /* try reply (pac->pns) tuple */
194         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
195         t.dst.protonum = IPPROTO_GRE;
196         t.src.u.gre.key = ct_pptp_info->pac_call_id;
197         t.dst.u.gre.key = ct_pptp_info->pns_call_id;
198         if (!destroy_sibling_or_exp(net, ct, &t))
199                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
200 }
201 
202 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
203 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
204 {
205         struct nf_conntrack_expect *exp_orig, *exp_reply;
206         enum ip_conntrack_dir dir;
207         int ret = 1;
208         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
209 
210         exp_orig = nf_ct_expect_alloc(ct);
211         if (exp_orig == NULL)
212                 goto out;
213 
214         exp_reply = nf_ct_expect_alloc(ct);
215         if (exp_reply == NULL)
216                 goto out_put_orig;
217 
218         /* original direction, PNS->PAC */
219         dir = IP_CT_DIR_ORIGINAL;
220         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
221                           nf_ct_l3num(ct),
222                           &ct->tuplehash[dir].tuple.src.u3,
223                           &ct->tuplehash[dir].tuple.dst.u3,
224                           IPPROTO_GRE, &peer_callid, &callid);
225         exp_orig->expectfn = pptp_expectfn;
226 
227         /* reply direction, PAC->PNS */
228         dir = IP_CT_DIR_REPLY;
229         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
230                           nf_ct_l3num(ct),
231                           &ct->tuplehash[dir].tuple.src.u3,
232                           &ct->tuplehash[dir].tuple.dst.u3,
233                           IPPROTO_GRE, &callid, &peer_callid);
234         exp_reply->expectfn = pptp_expectfn;
235 
236         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
237         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
238                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
239         if (nf_ct_expect_related(exp_orig) != 0)
240                 goto out_put_both;
241         if (nf_ct_expect_related(exp_reply) != 0)
242                 goto out_unexpect_orig;
243 
244         /* Add GRE keymap entries */
245         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
246                 goto out_unexpect_both;
247         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
248                 nf_ct_gre_keymap_destroy(ct);
249                 goto out_unexpect_both;
250         }
251         ret = 0;
252 
253 out_put_both:
254         nf_ct_expect_put(exp_reply);
255 out_put_orig:
256         nf_ct_expect_put(exp_orig);
257 out:
258         return ret;
259 
260 out_unexpect_both:
261         nf_ct_unexpect_related(exp_reply);
262 out_unexpect_orig:
263         nf_ct_unexpect_related(exp_orig);
264         goto out_put_both;
265 }
266 
267 static inline int
268 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
269                  struct PptpControlHeader *ctlh,
270                  union pptp_ctrl_union *pptpReq,
271                  unsigned int reqlen,
272                  struct nf_conn *ct,
273                  enum ip_conntrack_info ctinfo)
274 {
275         struct nf_ct_pptp_master *info = nfct_help_data(ct);
276         u_int16_t msg;
277         __be16 cid = 0, pcid = 0;
278         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
279 
280         msg = ntohs(ctlh->messageType);
281         pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
282 
283         switch (msg) {
284         case PPTP_START_SESSION_REPLY:
285                 /* server confirms new control session */
286                 if (info->sstate < PPTP_SESSION_REQUESTED)
287                         goto invalid;
288                 if (pptpReq->srep.resultCode == PPTP_START_OK)
289                         info->sstate = PPTP_SESSION_CONFIRMED;
290                 else
291                         info->sstate = PPTP_SESSION_ERROR;
292                 break;
293 
294         case PPTP_STOP_SESSION_REPLY:
295                 /* server confirms end of control session */
296                 if (info->sstate > PPTP_SESSION_STOPREQ)
297                         goto invalid;
298                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
299                         info->sstate = PPTP_SESSION_NONE;
300                 else
301                         info->sstate = PPTP_SESSION_ERROR;
302                 break;
303 
304         case PPTP_OUT_CALL_REPLY:
305                 /* server accepted call, we now expect GRE frames */
306                 if (info->sstate != PPTP_SESSION_CONFIRMED)
307                         goto invalid;
308                 if (info->cstate != PPTP_CALL_OUT_REQ &&
309                     info->cstate != PPTP_CALL_OUT_CONF)
310                         goto invalid;
311 
312                 cid = pptpReq->ocack.callID;
313                 pcid = pptpReq->ocack.peersCallID;
314                 if (info->pns_call_id != pcid)
315                         goto invalid;
316                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
317                          ntohs(cid), ntohs(pcid));
318 
319                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
320                         info->cstate = PPTP_CALL_OUT_CONF;
321                         info->pac_call_id = cid;
322                         exp_gre(ct, cid, pcid);
323                 } else
324                         info->cstate = PPTP_CALL_NONE;
325                 break;
326 
327         case PPTP_IN_CALL_REQUEST:
328                 /* server tells us about incoming call request */
329                 if (info->sstate != PPTP_SESSION_CONFIRMED)
330                         goto invalid;
331 
332                 cid = pptpReq->icreq.callID;
333                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
334                 info->cstate = PPTP_CALL_IN_REQ;
335                 info->pac_call_id = cid;
336                 break;
337 
338         case PPTP_IN_CALL_CONNECT:
339                 /* server tells us about incoming call established */
340                 if (info->sstate != PPTP_SESSION_CONFIRMED)
341                         goto invalid;
342                 if (info->cstate != PPTP_CALL_IN_REP &&
343                     info->cstate != PPTP_CALL_IN_CONF)
344                         goto invalid;
345 
346                 pcid = pptpReq->iccon.peersCallID;
347                 cid = info->pac_call_id;
348 
349                 if (info->pns_call_id != pcid)
350                         goto invalid;
351 
352                 pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
353                 info->cstate = PPTP_CALL_IN_CONF;
354 
355                 /* we expect a GRE connection from PAC to PNS */
356                 exp_gre(ct, cid, pcid);
357                 break;
358 
359         case PPTP_CALL_DISCONNECT_NOTIFY:
360                 /* server confirms disconnect */
361                 cid = pptpReq->disc.callID;
362                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
363                 info->cstate = PPTP_CALL_NONE;
364 
365                 /* untrack this call id, unexpect GRE packets */
366                 pptp_destroy_siblings(ct);
367                 break;
368 
369         case PPTP_WAN_ERROR_NOTIFY:
370         case PPTP_SET_LINK_INFO:
371         case PPTP_ECHO_REQUEST:
372         case PPTP_ECHO_REPLY:
373                 /* I don't have to explain these ;) */
374                 break;
375 
376         default:
377                 goto invalid;
378         }
379 
380         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
381         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
382                 return nf_nat_pptp_inbound(skb, ct, ctinfo,
383                                            protoff, ctlh, pptpReq);
384         return NF_ACCEPT;
385 
386 invalid:
387         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
388                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
389                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
390                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
391                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
392         return NF_ACCEPT;
393 }
394 
395 static inline int
396 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
397                   struct PptpControlHeader *ctlh,
398                   union pptp_ctrl_union *pptpReq,
399                   unsigned int reqlen,
400                   struct nf_conn *ct,
401                   enum ip_conntrack_info ctinfo)
402 {
403         struct nf_ct_pptp_master *info = nfct_help_data(ct);
404         u_int16_t msg;
405         __be16 cid = 0, pcid = 0;
406         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
407 
408         msg = ntohs(ctlh->messageType);
409         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
410 
411         switch (msg) {
412         case PPTP_START_SESSION_REQUEST:
413                 /* client requests for new control session */
414                 if (info->sstate != PPTP_SESSION_NONE)
415                         goto invalid;
416                 info->sstate = PPTP_SESSION_REQUESTED;
417                 break;
418 
419         case PPTP_STOP_SESSION_REQUEST:
420                 /* client requests end of control session */
421                 info->sstate = PPTP_SESSION_STOPREQ;
422                 break;
423 
424         case PPTP_OUT_CALL_REQUEST:
425                 /* client initiating connection to server */
426                 if (info->sstate != PPTP_SESSION_CONFIRMED)
427                         goto invalid;
428                 info->cstate = PPTP_CALL_OUT_REQ;
429                 /* track PNS call id */
430                 cid = pptpReq->ocreq.callID;
431                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
432                 info->pns_call_id = cid;
433                 break;
434 
435         case PPTP_IN_CALL_REPLY:
436                 /* client answers incoming call */
437                 if (info->cstate != PPTP_CALL_IN_REQ &&
438                     info->cstate != PPTP_CALL_IN_REP)
439                         goto invalid;
440 
441                 cid = pptpReq->icack.callID;
442                 pcid = pptpReq->icack.peersCallID;
443                 if (info->pac_call_id != pcid)
444                         goto invalid;
445                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
446                          ntohs(cid), ntohs(pcid));
447 
448                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
449                         /* part two of the three-way handshake */
450                         info->cstate = PPTP_CALL_IN_REP;
451                         info->pns_call_id = cid;
452                 } else
453                         info->cstate = PPTP_CALL_NONE;
454                 break;
455 
456         case PPTP_CALL_CLEAR_REQUEST:
457                 /* client requests hangup of call */
458                 if (info->sstate != PPTP_SESSION_CONFIRMED)
459                         goto invalid;
460                 /* FUTURE: iterate over all calls and check if
461                  * call ID is valid.  We don't do this without newnat,
462                  * because we only know about last call */
463                 info->cstate = PPTP_CALL_CLEAR_REQ;
464                 break;
465 
466         case PPTP_SET_LINK_INFO:
467         case PPTP_ECHO_REQUEST:
468         case PPTP_ECHO_REPLY:
469                 /* I don't have to explain these ;) */
470                 break;
471 
472         default:
473                 goto invalid;
474         }
475 
476         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
477         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
478                 return nf_nat_pptp_outbound(skb, ct, ctinfo,
479                                             protoff, ctlh, pptpReq);
480         return NF_ACCEPT;
481 
482 invalid:
483         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
484                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
485                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
486                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
487                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
488         return NF_ACCEPT;
489 }
490 
491 static const unsigned int pptp_msg_size[] = {
492         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
493         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
494         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
495         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
496         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
497         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
498         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
499         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
500         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
501         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
502         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
503         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
504         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
505 };
506 
507 /* track caller id inside control connection, call expect_related */
508 static int
509 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
510                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
511 
512 {
513         int dir = CTINFO2DIR(ctinfo);
514         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
515         const struct tcphdr *tcph;
516         struct tcphdr _tcph;
517         const struct pptp_pkt_hdr *pptph;
518         struct pptp_pkt_hdr _pptph;
519         struct PptpControlHeader _ctlh, *ctlh;
520         union pptp_ctrl_union _pptpReq, *pptpReq;
521         unsigned int tcplen = skb->len - protoff;
522         unsigned int datalen, reqlen, nexthdr_off;
523         int oldsstate, oldcstate;
524         int ret;
525         u_int16_t msg;
526 
527         /* don't do any tracking before tcp handshake complete */
528         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
529                 return NF_ACCEPT;
530 
531         nexthdr_off = protoff;
532         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
533         BUG_ON(!tcph);
534         nexthdr_off += tcph->doff * 4;
535         datalen = tcplen - tcph->doff * 4;
536 
537         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
538         if (!pptph) {
539                 pr_debug("no full PPTP header, can't track\n");
540                 return NF_ACCEPT;
541         }
542         nexthdr_off += sizeof(_pptph);
543         datalen -= sizeof(_pptph);
544 
545         /* if it's not a control message we can't do anything with it */
546         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
547             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
548                 pr_debug("not a control packet\n");
549                 return NF_ACCEPT;
550         }
551 
552         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
553         if (!ctlh)
554                 return NF_ACCEPT;
555         nexthdr_off += sizeof(_ctlh);
556         datalen -= sizeof(_ctlh);
557 
558         reqlen = datalen;
559         msg = ntohs(ctlh->messageType);
560         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
561                 return NF_ACCEPT;
562         if (reqlen > sizeof(*pptpReq))
563                 reqlen = sizeof(*pptpReq);
564 
565         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
566         if (!pptpReq)
567                 return NF_ACCEPT;
568 
569         oldsstate = info->sstate;
570         oldcstate = info->cstate;
571 
572         spin_lock_bh(&nf_pptp_lock);
573 
574         /* FIXME: We just blindly assume that the control connection is always
575          * established from PNS->PAC.  However, RFC makes no guarantee */
576         if (dir == IP_CT_DIR_ORIGINAL)
577                 /* client -> server (PNS -> PAC) */
578                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
579                                         ctinfo);
580         else
581                 /* server -> client (PAC -> PNS) */
582                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
583                                        ctinfo);
584         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
585                  oldsstate, info->sstate, oldcstate, info->cstate);
586         spin_unlock_bh(&nf_pptp_lock);
587 
588         return ret;
589 }
590 
591 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
592         .max_expected   = 2,
593         .timeout        = 5 * 60,
594 };
595 
596 /* control protocol helper */
597 static struct nf_conntrack_helper pptp __read_mostly = {
598         .name                   = "pptp",
599         .me                     = THIS_MODULE,
600         .data_len               = sizeof(struct nf_ct_pptp_master),
601         .tuple.src.l3num        = AF_INET,
602         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
603         .tuple.dst.protonum     = IPPROTO_TCP,
604         .help                   = conntrack_pptp_help,
605         .destroy                = pptp_destroy_siblings,
606         .expect_policy          = &pptp_exp_policy,
607 };
608 
609 static int __init nf_conntrack_pptp_init(void)
610 {
611         return nf_conntrack_helper_register(&pptp);
612 }
613 
614 static void __exit nf_conntrack_pptp_fini(void)
615 {
616         nf_conntrack_helper_unregister(&pptp);
617 }
618 
619 module_init(nf_conntrack_pptp_init);
620 module_exit(nf_conntrack_pptp_fini);
621 

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