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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                 nf_ct_kill(sibling);
161                 nf_ct_put(sibling);
162                 return 1;
163         } else {
164                 exp = nf_ct_expect_find_get(net, zone, t);
165                 if (exp) {
166                         pr_debug("unexpect_related of expect %p\n", exp);
167                         nf_ct_unexpect_related(exp);
168                         nf_ct_expect_put(exp);
169                         return 1;
170                 }
171         }
172         return 0;
173 }
174 
175 /* timeout GRE data connections */
176 static void pptp_destroy_siblings(struct nf_conn *ct)
177 {
178         struct net *net = nf_ct_net(ct);
179         const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
180         struct nf_conntrack_tuple t;
181 
182         nf_ct_gre_keymap_destroy(ct);
183 
184         /* try original (pns->pac) tuple */
185         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
186         t.dst.protonum = IPPROTO_GRE;
187         t.src.u.gre.key = ct_pptp_info->pns_call_id;
188         t.dst.u.gre.key = ct_pptp_info->pac_call_id;
189         if (!destroy_sibling_or_exp(net, ct, &t))
190                 pr_debug("failed to timeout original pns->pac ct/exp\n");
191 
192         /* try reply (pac->pns) tuple */
193         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
194         t.dst.protonum = IPPROTO_GRE;
195         t.src.u.gre.key = ct_pptp_info->pac_call_id;
196         t.dst.u.gre.key = ct_pptp_info->pns_call_id;
197         if (!destroy_sibling_or_exp(net, ct, &t))
198                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
199 }
200 
201 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
202 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
203 {
204         struct nf_conntrack_expect *exp_orig, *exp_reply;
205         enum ip_conntrack_dir dir;
206         int ret = 1;
207         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
208 
209         exp_orig = nf_ct_expect_alloc(ct);
210         if (exp_orig == NULL)
211                 goto out;
212 
213         exp_reply = nf_ct_expect_alloc(ct);
214         if (exp_reply == NULL)
215                 goto out_put_orig;
216 
217         /* original direction, PNS->PAC */
218         dir = IP_CT_DIR_ORIGINAL;
219         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
220                           nf_ct_l3num(ct),
221                           &ct->tuplehash[dir].tuple.src.u3,
222                           &ct->tuplehash[dir].tuple.dst.u3,
223                           IPPROTO_GRE, &peer_callid, &callid);
224         exp_orig->expectfn = pptp_expectfn;
225 
226         /* reply direction, PAC->PNS */
227         dir = IP_CT_DIR_REPLY;
228         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
229                           nf_ct_l3num(ct),
230                           &ct->tuplehash[dir].tuple.src.u3,
231                           &ct->tuplehash[dir].tuple.dst.u3,
232                           IPPROTO_GRE, &callid, &peer_callid);
233         exp_reply->expectfn = pptp_expectfn;
234 
235         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
236         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
237                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
238         if (nf_ct_expect_related(exp_orig) != 0)
239                 goto out_put_both;
240         if (nf_ct_expect_related(exp_reply) != 0)
241                 goto out_unexpect_orig;
242 
243         /* Add GRE keymap entries */
244         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
245                 goto out_unexpect_both;
246         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
247                 nf_ct_gre_keymap_destroy(ct);
248                 goto out_unexpect_both;
249         }
250         ret = 0;
251 
252 out_put_both:
253         nf_ct_expect_put(exp_reply);
254 out_put_orig:
255         nf_ct_expect_put(exp_orig);
256 out:
257         return ret;
258 
259 out_unexpect_both:
260         nf_ct_unexpect_related(exp_reply);
261 out_unexpect_orig:
262         nf_ct_unexpect_related(exp_orig);
263         goto out_put_both;
264 }
265 
266 static inline int
267 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
268                  struct PptpControlHeader *ctlh,
269                  union pptp_ctrl_union *pptpReq,
270                  unsigned int reqlen,
271                  struct nf_conn *ct,
272                  enum ip_conntrack_info ctinfo)
273 {
274         struct nf_ct_pptp_master *info = nfct_help_data(ct);
275         u_int16_t msg;
276         __be16 cid = 0, pcid = 0;
277         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
278 
279         msg = ntohs(ctlh->messageType);
280         pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
281 
282         switch (msg) {
283         case PPTP_START_SESSION_REPLY:
284                 /* server confirms new control session */
285                 if (info->sstate < PPTP_SESSION_REQUESTED)
286                         goto invalid;
287                 if (pptpReq->srep.resultCode == PPTP_START_OK)
288                         info->sstate = PPTP_SESSION_CONFIRMED;
289                 else
290                         info->sstate = PPTP_SESSION_ERROR;
291                 break;
292 
293         case PPTP_STOP_SESSION_REPLY:
294                 /* server confirms end of control session */
295                 if (info->sstate > PPTP_SESSION_STOPREQ)
296                         goto invalid;
297                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
298                         info->sstate = PPTP_SESSION_NONE;
299                 else
300                         info->sstate = PPTP_SESSION_ERROR;
301                 break;
302 
303         case PPTP_OUT_CALL_REPLY:
304                 /* server accepted call, we now expect GRE frames */
305                 if (info->sstate != PPTP_SESSION_CONFIRMED)
306                         goto invalid;
307                 if (info->cstate != PPTP_CALL_OUT_REQ &&
308                     info->cstate != PPTP_CALL_OUT_CONF)
309                         goto invalid;
310 
311                 cid = pptpReq->ocack.callID;
312                 pcid = pptpReq->ocack.peersCallID;
313                 if (info->pns_call_id != pcid)
314                         goto invalid;
315                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
316                          ntohs(cid), ntohs(pcid));
317 
318                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
319                         info->cstate = PPTP_CALL_OUT_CONF;
320                         info->pac_call_id = cid;
321                         exp_gre(ct, cid, pcid);
322                 } else
323                         info->cstate = PPTP_CALL_NONE;
324                 break;
325 
326         case PPTP_IN_CALL_REQUEST:
327                 /* server tells us about incoming call request */
328                 if (info->sstate != PPTP_SESSION_CONFIRMED)
329                         goto invalid;
330 
331                 cid = pptpReq->icreq.callID;
332                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
333                 info->cstate = PPTP_CALL_IN_REQ;
334                 info->pac_call_id = cid;
335                 break;
336 
337         case PPTP_IN_CALL_CONNECT:
338                 /* server tells us about incoming call established */
339                 if (info->sstate != PPTP_SESSION_CONFIRMED)
340                         goto invalid;
341                 if (info->cstate != PPTP_CALL_IN_REP &&
342                     info->cstate != PPTP_CALL_IN_CONF)
343                         goto invalid;
344 
345                 pcid = pptpReq->iccon.peersCallID;
346                 cid = info->pac_call_id;
347 
348                 if (info->pns_call_id != pcid)
349                         goto invalid;
350 
351                 pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
352                 info->cstate = PPTP_CALL_IN_CONF;
353 
354                 /* we expect a GRE connection from PAC to PNS */
355                 exp_gre(ct, cid, pcid);
356                 break;
357 
358         case PPTP_CALL_DISCONNECT_NOTIFY:
359                 /* server confirms disconnect */
360                 cid = pptpReq->disc.callID;
361                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
362                 info->cstate = PPTP_CALL_NONE;
363 
364                 /* untrack this call id, unexpect GRE packets */
365                 pptp_destroy_siblings(ct);
366                 break;
367 
368         case PPTP_WAN_ERROR_NOTIFY:
369         case PPTP_SET_LINK_INFO:
370         case PPTP_ECHO_REQUEST:
371         case PPTP_ECHO_REPLY:
372                 /* I don't have to explain these ;) */
373                 break;
374 
375         default:
376                 goto invalid;
377         }
378 
379         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
380         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
381                 return nf_nat_pptp_inbound(skb, ct, ctinfo,
382                                            protoff, ctlh, pptpReq);
383         return NF_ACCEPT;
384 
385 invalid:
386         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
387                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
388                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
389                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
390                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
391         return NF_ACCEPT;
392 }
393 
394 static inline int
395 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
396                   struct PptpControlHeader *ctlh,
397                   union pptp_ctrl_union *pptpReq,
398                   unsigned int reqlen,
399                   struct nf_conn *ct,
400                   enum ip_conntrack_info ctinfo)
401 {
402         struct nf_ct_pptp_master *info = nfct_help_data(ct);
403         u_int16_t msg;
404         __be16 cid = 0, pcid = 0;
405         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
406 
407         msg = ntohs(ctlh->messageType);
408         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
409 
410         switch (msg) {
411         case PPTP_START_SESSION_REQUEST:
412                 /* client requests for new control session */
413                 if (info->sstate != PPTP_SESSION_NONE)
414                         goto invalid;
415                 info->sstate = PPTP_SESSION_REQUESTED;
416                 break;
417 
418         case PPTP_STOP_SESSION_REQUEST:
419                 /* client requests end of control session */
420                 info->sstate = PPTP_SESSION_STOPREQ;
421                 break;
422 
423         case PPTP_OUT_CALL_REQUEST:
424                 /* client initiating connection to server */
425                 if (info->sstate != PPTP_SESSION_CONFIRMED)
426                         goto invalid;
427                 info->cstate = PPTP_CALL_OUT_REQ;
428                 /* track PNS call id */
429                 cid = pptpReq->ocreq.callID;
430                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
431                 info->pns_call_id = cid;
432                 break;
433 
434         case PPTP_IN_CALL_REPLY:
435                 /* client answers incoming call */
436                 if (info->cstate != PPTP_CALL_IN_REQ &&
437                     info->cstate != PPTP_CALL_IN_REP)
438                         goto invalid;
439 
440                 cid = pptpReq->icack.callID;
441                 pcid = pptpReq->icack.peersCallID;
442                 if (info->pac_call_id != pcid)
443                         goto invalid;
444                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
445                          ntohs(cid), ntohs(pcid));
446 
447                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
448                         /* part two of the three-way handshake */
449                         info->cstate = PPTP_CALL_IN_REP;
450                         info->pns_call_id = cid;
451                 } else
452                         info->cstate = PPTP_CALL_NONE;
453                 break;
454 
455         case PPTP_CALL_CLEAR_REQUEST:
456                 /* client requests hangup of call */
457                 if (info->sstate != PPTP_SESSION_CONFIRMED)
458                         goto invalid;
459                 /* FUTURE: iterate over all calls and check if
460                  * call ID is valid.  We don't do this without newnat,
461                  * because we only know about last call */
462                 info->cstate = PPTP_CALL_CLEAR_REQ;
463                 break;
464 
465         case PPTP_SET_LINK_INFO:
466         case PPTP_ECHO_REQUEST:
467         case PPTP_ECHO_REPLY:
468                 /* I don't have to explain these ;) */
469                 break;
470 
471         default:
472                 goto invalid;
473         }
474 
475         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
476         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
477                 return nf_nat_pptp_outbound(skb, ct, ctinfo,
478                                             protoff, ctlh, pptpReq);
479         return NF_ACCEPT;
480 
481 invalid:
482         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
483                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
484                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
485                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
486                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
487         return NF_ACCEPT;
488 }
489 
490 static const unsigned int pptp_msg_size[] = {
491         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
492         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
493         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
494         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
495         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
496         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
497         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
498         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
499         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
500         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
501         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
502         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
503         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
504 };
505 
506 /* track caller id inside control connection, call expect_related */
507 static int
508 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
509                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
510 
511 {
512         int dir = CTINFO2DIR(ctinfo);
513         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
514         const struct tcphdr *tcph;
515         struct tcphdr _tcph;
516         const struct pptp_pkt_hdr *pptph;
517         struct pptp_pkt_hdr _pptph;
518         struct PptpControlHeader _ctlh, *ctlh;
519         union pptp_ctrl_union _pptpReq, *pptpReq;
520         unsigned int tcplen = skb->len - protoff;
521         unsigned int datalen, reqlen, nexthdr_off;
522         int oldsstate, oldcstate;
523         int ret;
524         u_int16_t msg;
525 
526         /* don't do any tracking before tcp handshake complete */
527         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
528                 return NF_ACCEPT;
529 
530         nexthdr_off = protoff;
531         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
532         BUG_ON(!tcph);
533         nexthdr_off += tcph->doff * 4;
534         datalen = tcplen - tcph->doff * 4;
535 
536         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
537         if (!pptph) {
538                 pr_debug("no full PPTP header, can't track\n");
539                 return NF_ACCEPT;
540         }
541         nexthdr_off += sizeof(_pptph);
542         datalen -= sizeof(_pptph);
543 
544         /* if it's not a control message we can't do anything with it */
545         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
546             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
547                 pr_debug("not a control packet\n");
548                 return NF_ACCEPT;
549         }
550 
551         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
552         if (!ctlh)
553                 return NF_ACCEPT;
554         nexthdr_off += sizeof(_ctlh);
555         datalen -= sizeof(_ctlh);
556 
557         reqlen = datalen;
558         msg = ntohs(ctlh->messageType);
559         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
560                 return NF_ACCEPT;
561         if (reqlen > sizeof(*pptpReq))
562                 reqlen = sizeof(*pptpReq);
563 
564         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
565         if (!pptpReq)
566                 return NF_ACCEPT;
567 
568         oldsstate = info->sstate;
569         oldcstate = info->cstate;
570 
571         spin_lock_bh(&nf_pptp_lock);
572 
573         /* FIXME: We just blindly assume that the control connection is always
574          * established from PNS->PAC.  However, RFC makes no guarantee */
575         if (dir == IP_CT_DIR_ORIGINAL)
576                 /* client -> server (PNS -> PAC) */
577                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
578                                         ctinfo);
579         else
580                 /* server -> client (PAC -> PNS) */
581                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
582                                        ctinfo);
583         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
584                  oldsstate, info->sstate, oldcstate, info->cstate);
585         spin_unlock_bh(&nf_pptp_lock);
586 
587         return ret;
588 }
589 
590 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
591         .max_expected   = 2,
592         .timeout        = 5 * 60,
593 };
594 
595 /* control protocol helper */
596 static struct nf_conntrack_helper pptp __read_mostly = {
597         .name                   = "pptp",
598         .me                     = THIS_MODULE,
599         .data_len               = sizeof(struct nf_ct_pptp_master),
600         .tuple.src.l3num        = AF_INET,
601         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
602         .tuple.dst.protonum     = IPPROTO_TCP,
603         .help                   = conntrack_pptp_help,
604         .destroy                = pptp_destroy_siblings,
605         .expect_policy          = &pptp_exp_policy,
606 };
607 
608 static int __init nf_conntrack_pptp_init(void)
609 {
610         return nf_conntrack_helper_register(&pptp);
611 }
612 
613 static void __exit nf_conntrack_pptp_fini(void)
614 {
615         nf_conntrack_helper_unregister(&pptp);
616 }
617 
618 module_init(nf_conntrack_pptp_init);
619 module_exit(nf_conntrack_pptp_fini);
620 

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