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Linux/net/netfilter/nf_conntrack_pptp.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  * Connection tracking support for PPTP (Point to Point Tunneling Protocol).
  4  * PPTP is a protocol for creating virtual private networks.
  5  * It is a specification defined by Microsoft and some vendors
  6  * working with Microsoft.  PPTP is built on top of a modified
  7  * version of the Internet Generic Routing Encapsulation Protocol.
  8  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
  9  * PPTP can be found in RFC 2637
 10  *
 11  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
 12  *
 13  * Development of this code funded by Astaro AG (http://www.astaro.com/)
 14  *
 15  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
 16  *
 17  * Limitations:
 18  *       - We blindly assume that control connections are always
 19  *         established in PNS->PAC direction.  This is a violation
 20  *         of RFC 2637
 21  *       - We can only support one single call within each session
 22  * TODO:
 23  *       - testing of incoming PPTP calls
 24  */
 25 
 26 #include <linux/module.h>
 27 #include <linux/skbuff.h>
 28 #include <linux/in.h>
 29 #include <linux/tcp.h>
 30 
 31 #include <net/netfilter/nf_conntrack.h>
 32 #include <net/netfilter/nf_conntrack_core.h>
 33 #include <net/netfilter/nf_conntrack_helper.h>
 34 #include <net/netfilter/nf_conntrack_zones.h>
 35 #include <linux/netfilter/nf_conntrack_proto_gre.h>
 36 #include <linux/netfilter/nf_conntrack_pptp.h>
 37 
 38 #define NF_CT_PPTP_VERSION "3.1"
 39 
 40 MODULE_LICENSE("GPL");
 41 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
 42 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
 43 MODULE_ALIAS("ip_conntrack_pptp");
 44 MODULE_ALIAS_NFCT_HELPER("pptp");
 45 
 46 static DEFINE_SPINLOCK(nf_pptp_lock);
 47 
 48 int
 49 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
 50                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 51                              unsigned int protoff, struct PptpControlHeader *ctlh,
 52                              union pptp_ctrl_union *pptpReq) __read_mostly;
 53 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
 54 
 55 int
 56 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
 57                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
 58                             unsigned int protoff, struct PptpControlHeader *ctlh,
 59                             union pptp_ctrl_union *pptpReq) __read_mostly;
 60 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
 61 
 62 void
 63 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
 64                             struct nf_conntrack_expect *expect_reply)
 65                             __read_mostly;
 66 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
 67 
 68 void
 69 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
 70                              struct nf_conntrack_expect *exp) __read_mostly;
 71 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
 72 
 73 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
 74 /* PptpControlMessageType names */
 75 static const char *const pptp_msg_name_array[PPTP_MSG_MAX + 1] = {
 76         [0]                             = "UNKNOWN_MESSAGE",
 77         [PPTP_START_SESSION_REQUEST]    = "START_SESSION_REQUEST",
 78         [PPTP_START_SESSION_REPLY]      = "START_SESSION_REPLY",
 79         [PPTP_STOP_SESSION_REQUEST]     = "STOP_SESSION_REQUEST",
 80         [PPTP_STOP_SESSION_REPLY]       = "STOP_SESSION_REPLY",
 81         [PPTP_ECHO_REQUEST]             = "ECHO_REQUEST",
 82         [PPTP_ECHO_REPLY]               = "ECHO_REPLY",
 83         [PPTP_OUT_CALL_REQUEST]         = "OUT_CALL_REQUEST",
 84         [PPTP_OUT_CALL_REPLY]           = "OUT_CALL_REPLY",
 85         [PPTP_IN_CALL_REQUEST]          = "IN_CALL_REQUEST",
 86         [PPTP_IN_CALL_REPLY]            = "IN_CALL_REPLY",
 87         [PPTP_IN_CALL_CONNECT]          = "IN_CALL_CONNECT",
 88         [PPTP_CALL_CLEAR_REQUEST]       = "CALL_CLEAR_REQUEST",
 89         [PPTP_CALL_DISCONNECT_NOTIFY]   = "CALL_DISCONNECT_NOTIFY",
 90         [PPTP_WAN_ERROR_NOTIFY]         = "WAN_ERROR_NOTIFY",
 91         [PPTP_SET_LINK_INFO]            = "SET_LINK_INFO"
 92 };
 93 
 94 const char *pptp_msg_name(u_int16_t msg)
 95 {
 96         if (msg > PPTP_MSG_MAX)
 97                 return pptp_msg_name_array[0];
 98 
 99         return pptp_msg_name_array[msg];
100 }
101 EXPORT_SYMBOL(pptp_msg_name);
102 #endif
103 
104 #define SECS *HZ
105 #define MINS * 60 SECS
106 #define HOURS * 60 MINS
107 
108 #define PPTP_GRE_TIMEOUT                (10 MINS)
109 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
110 
111 static void pptp_expectfn(struct nf_conn *ct,
112                          struct nf_conntrack_expect *exp)
113 {
114         struct net *net = nf_ct_net(ct);
115         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
116         pr_debug("increasing timeouts\n");
117 
118         /* increase timeout of GRE data channel conntrack entry */
119         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
120         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
121 
122         /* Can you see how rusty this code is, compared with the pre-2.6.11
123          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
124 
125         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
126         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
127                 nf_nat_pptp_expectfn(ct, exp);
128         else {
129                 struct nf_conntrack_tuple inv_t;
130                 struct nf_conntrack_expect *exp_other;
131 
132                 /* obviously this tuple inversion only works until you do NAT */
133                 nf_ct_invert_tuple(&inv_t, &exp->tuple);
134                 pr_debug("trying to unexpect other dir: ");
135                 nf_ct_dump_tuple(&inv_t);
136 
137                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
138                 if (exp_other) {
139                         /* delete other expectation.  */
140                         pr_debug("found\n");
141                         nf_ct_unexpect_related(exp_other);
142                         nf_ct_expect_put(exp_other);
143                 } else {
144                         pr_debug("not found\n");
145                 }
146         }
147 }
148 
149 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
150                                   const struct nf_conntrack_tuple *t)
151 {
152         const struct nf_conntrack_tuple_hash *h;
153         const struct nf_conntrack_zone *zone;
154         struct nf_conntrack_expect *exp;
155         struct nf_conn *sibling;
156 
157         pr_debug("trying to timeout ct or exp for tuple ");
158         nf_ct_dump_tuple(t);
159 
160         zone = nf_ct_zone(ct);
161         h = nf_conntrack_find_get(net, zone, t);
162         if (h)  {
163                 sibling = nf_ct_tuplehash_to_ctrack(h);
164                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
165                 sibling->proto.gre.timeout        = 0;
166                 sibling->proto.gre.stream_timeout = 0;
167                 nf_ct_kill(sibling);
168                 nf_ct_put(sibling);
169                 return 1;
170         } else {
171                 exp = nf_ct_expect_find_get(net, zone, t);
172                 if (exp) {
173                         pr_debug("unexpect_related of expect %p\n", exp);
174                         nf_ct_unexpect_related(exp);
175                         nf_ct_expect_put(exp);
176                         return 1;
177                 }
178         }
179         return 0;
180 }
181 
182 /* timeout GRE data connections */
183 static void pptp_destroy_siblings(struct nf_conn *ct)
184 {
185         struct net *net = nf_ct_net(ct);
186         const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
187         struct nf_conntrack_tuple t;
188 
189         nf_ct_gre_keymap_destroy(ct);
190 
191         /* try original (pns->pac) tuple */
192         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
193         t.dst.protonum = IPPROTO_GRE;
194         t.src.u.gre.key = ct_pptp_info->pns_call_id;
195         t.dst.u.gre.key = ct_pptp_info->pac_call_id;
196         if (!destroy_sibling_or_exp(net, ct, &t))
197                 pr_debug("failed to timeout original pns->pac ct/exp\n");
198 
199         /* try reply (pac->pns) tuple */
200         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
201         t.dst.protonum = IPPROTO_GRE;
202         t.src.u.gre.key = ct_pptp_info->pac_call_id;
203         t.dst.u.gre.key = ct_pptp_info->pns_call_id;
204         if (!destroy_sibling_or_exp(net, ct, &t))
205                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
206 }
207 
208 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
209 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
210 {
211         struct nf_conntrack_expect *exp_orig, *exp_reply;
212         enum ip_conntrack_dir dir;
213         int ret = 1;
214         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
215 
216         exp_orig = nf_ct_expect_alloc(ct);
217         if (exp_orig == NULL)
218                 goto out;
219 
220         exp_reply = nf_ct_expect_alloc(ct);
221         if (exp_reply == NULL)
222                 goto out_put_orig;
223 
224         /* original direction, PNS->PAC */
225         dir = IP_CT_DIR_ORIGINAL;
226         nf_ct_expect_init(exp_orig, 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, &peer_callid, &callid);
231         exp_orig->expectfn = pptp_expectfn;
232 
233         /* reply direction, PAC->PNS */
234         dir = IP_CT_DIR_REPLY;
235         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
236                           nf_ct_l3num(ct),
237                           &ct->tuplehash[dir].tuple.src.u3,
238                           &ct->tuplehash[dir].tuple.dst.u3,
239                           IPPROTO_GRE, &callid, &peer_callid);
240         exp_reply->expectfn = pptp_expectfn;
241 
242         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
243         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
244                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
245         if (nf_ct_expect_related(exp_orig, 0) != 0)
246                 goto out_put_both;
247         if (nf_ct_expect_related(exp_reply, 0) != 0)
248                 goto out_unexpect_orig;
249 
250         /* Add GRE keymap entries */
251         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
252                 goto out_unexpect_both;
253         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
254                 nf_ct_gre_keymap_destroy(ct);
255                 goto out_unexpect_both;
256         }
257         ret = 0;
258 
259 out_put_both:
260         nf_ct_expect_put(exp_reply);
261 out_put_orig:
262         nf_ct_expect_put(exp_orig);
263 out:
264         return ret;
265 
266 out_unexpect_both:
267         nf_ct_unexpect_related(exp_reply);
268 out_unexpect_orig:
269         nf_ct_unexpect_related(exp_orig);
270         goto out_put_both;
271 }
272 
273 static int
274 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
275                  struct PptpControlHeader *ctlh,
276                  union pptp_ctrl_union *pptpReq,
277                  unsigned int reqlen,
278                  struct nf_conn *ct,
279                  enum ip_conntrack_info ctinfo)
280 {
281         struct nf_ct_pptp_master *info = nfct_help_data(ct);
282         u_int16_t msg;
283         __be16 cid = 0, pcid = 0;
284         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
285 
286         msg = ntohs(ctlh->messageType);
287         pr_debug("inbound control message %s\n", pptp_msg_name(msg));
288 
289         switch (msg) {
290         case PPTP_START_SESSION_REPLY:
291                 /* server confirms new control session */
292                 if (info->sstate < PPTP_SESSION_REQUESTED)
293                         goto invalid;
294                 if (pptpReq->srep.resultCode == PPTP_START_OK)
295                         info->sstate = PPTP_SESSION_CONFIRMED;
296                 else
297                         info->sstate = PPTP_SESSION_ERROR;
298                 break;
299 
300         case PPTP_STOP_SESSION_REPLY:
301                 /* server confirms end of control session */
302                 if (info->sstate > PPTP_SESSION_STOPREQ)
303                         goto invalid;
304                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
305                         info->sstate = PPTP_SESSION_NONE;
306                 else
307                         info->sstate = PPTP_SESSION_ERROR;
308                 break;
309 
310         case PPTP_OUT_CALL_REPLY:
311                 /* server accepted call, we now expect GRE frames */
312                 if (info->sstate != PPTP_SESSION_CONFIRMED)
313                         goto invalid;
314                 if (info->cstate != PPTP_CALL_OUT_REQ &&
315                     info->cstate != PPTP_CALL_OUT_CONF)
316                         goto invalid;
317 
318                 cid = pptpReq->ocack.callID;
319                 pcid = pptpReq->ocack.peersCallID;
320                 if (info->pns_call_id != pcid)
321                         goto invalid;
322                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name(msg),
323                          ntohs(cid), ntohs(pcid));
324 
325                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
326                         info->cstate = PPTP_CALL_OUT_CONF;
327                         info->pac_call_id = cid;
328                         exp_gre(ct, cid, pcid);
329                 } else
330                         info->cstate = PPTP_CALL_NONE;
331                 break;
332 
333         case PPTP_IN_CALL_REQUEST:
334                 /* server tells us about incoming call request */
335                 if (info->sstate != PPTP_SESSION_CONFIRMED)
336                         goto invalid;
337 
338                 cid = pptpReq->icreq.callID;
339                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
340                 info->cstate = PPTP_CALL_IN_REQ;
341                 info->pac_call_id = cid;
342                 break;
343 
344         case PPTP_IN_CALL_CONNECT:
345                 /* server tells us about incoming call established */
346                 if (info->sstate != PPTP_SESSION_CONFIRMED)
347                         goto invalid;
348                 if (info->cstate != PPTP_CALL_IN_REP &&
349                     info->cstate != PPTP_CALL_IN_CONF)
350                         goto invalid;
351 
352                 pcid = pptpReq->iccon.peersCallID;
353                 cid = info->pac_call_id;
354 
355                 if (info->pns_call_id != pcid)
356                         goto invalid;
357 
358                 pr_debug("%s, PCID=%X\n", pptp_msg_name(msg), ntohs(pcid));
359                 info->cstate = PPTP_CALL_IN_CONF;
360 
361                 /* we expect a GRE connection from PAC to PNS */
362                 exp_gre(ct, cid, pcid);
363                 break;
364 
365         case PPTP_CALL_DISCONNECT_NOTIFY:
366                 /* server confirms disconnect */
367                 cid = pptpReq->disc.callID;
368                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
369                 info->cstate = PPTP_CALL_NONE;
370 
371                 /* untrack this call id, unexpect GRE packets */
372                 pptp_destroy_siblings(ct);
373                 break;
374 
375         case PPTP_WAN_ERROR_NOTIFY:
376         case PPTP_SET_LINK_INFO:
377         case PPTP_ECHO_REQUEST:
378         case PPTP_ECHO_REPLY:
379                 /* I don't have to explain these ;) */
380                 break;
381 
382         default:
383                 goto invalid;
384         }
385 
386         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
387         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
388                 return nf_nat_pptp_inbound(skb, ct, ctinfo,
389                                            protoff, ctlh, pptpReq);
390         return NF_ACCEPT;
391 
392 invalid:
393         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
394                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
395                  pptp_msg_name(msg),
396                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
397                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
398         return NF_ACCEPT;
399 }
400 
401 static int
402 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
403                   struct PptpControlHeader *ctlh,
404                   union pptp_ctrl_union *pptpReq,
405                   unsigned int reqlen,
406                   struct nf_conn *ct,
407                   enum ip_conntrack_info ctinfo)
408 {
409         struct nf_ct_pptp_master *info = nfct_help_data(ct);
410         u_int16_t msg;
411         __be16 cid = 0, pcid = 0;
412         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
413 
414         msg = ntohs(ctlh->messageType);
415         pr_debug("outbound control message %s\n", pptp_msg_name(msg));
416 
417         switch (msg) {
418         case PPTP_START_SESSION_REQUEST:
419                 /* client requests for new control session */
420                 if (info->sstate != PPTP_SESSION_NONE)
421                         goto invalid;
422                 info->sstate = PPTP_SESSION_REQUESTED;
423                 break;
424 
425         case PPTP_STOP_SESSION_REQUEST:
426                 /* client requests end of control session */
427                 info->sstate = PPTP_SESSION_STOPREQ;
428                 break;
429 
430         case PPTP_OUT_CALL_REQUEST:
431                 /* client initiating connection to server */
432                 if (info->sstate != PPTP_SESSION_CONFIRMED)
433                         goto invalid;
434                 info->cstate = PPTP_CALL_OUT_REQ;
435                 /* track PNS call id */
436                 cid = pptpReq->ocreq.callID;
437                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
438                 info->pns_call_id = cid;
439                 break;
440 
441         case PPTP_IN_CALL_REPLY:
442                 /* client answers incoming call */
443                 if (info->cstate != PPTP_CALL_IN_REQ &&
444                     info->cstate != PPTP_CALL_IN_REP)
445                         goto invalid;
446 
447                 cid = pptpReq->icack.callID;
448                 pcid = pptpReq->icack.peersCallID;
449                 if (info->pac_call_id != pcid)
450                         goto invalid;
451                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name(msg),
452                          ntohs(cid), ntohs(pcid));
453 
454                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
455                         /* part two of the three-way handshake */
456                         info->cstate = PPTP_CALL_IN_REP;
457                         info->pns_call_id = cid;
458                 } else
459                         info->cstate = PPTP_CALL_NONE;
460                 break;
461 
462         case PPTP_CALL_CLEAR_REQUEST:
463                 /* client requests hangup of call */
464                 if (info->sstate != PPTP_SESSION_CONFIRMED)
465                         goto invalid;
466                 /* FUTURE: iterate over all calls and check if
467                  * call ID is valid.  We don't do this without newnat,
468                  * because we only know about last call */
469                 info->cstate = PPTP_CALL_CLEAR_REQ;
470                 break;
471 
472         case PPTP_SET_LINK_INFO:
473         case PPTP_ECHO_REQUEST:
474         case PPTP_ECHO_REPLY:
475                 /* I don't have to explain these ;) */
476                 break;
477 
478         default:
479                 goto invalid;
480         }
481 
482         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
483         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
484                 return nf_nat_pptp_outbound(skb, ct, ctinfo,
485                                             protoff, ctlh, pptpReq);
486         return NF_ACCEPT;
487 
488 invalid:
489         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
490                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
491                  pptp_msg_name(msg),
492                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
493                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
494         return NF_ACCEPT;
495 }
496 
497 static const unsigned int pptp_msg_size[] = {
498         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
499         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
500         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
501         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
502         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
503         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
504         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
505         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
506         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
507         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
508         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
509         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
510         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
511 };
512 
513 /* track caller id inside control connection, call expect_related */
514 static int
515 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
516                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
517 
518 {
519         int dir = CTINFO2DIR(ctinfo);
520         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
521         const struct tcphdr *tcph;
522         struct tcphdr _tcph;
523         const struct pptp_pkt_hdr *pptph;
524         struct pptp_pkt_hdr _pptph;
525         struct PptpControlHeader _ctlh, *ctlh;
526         union pptp_ctrl_union _pptpReq, *pptpReq;
527         unsigned int tcplen = skb->len - protoff;
528         unsigned int datalen, reqlen, nexthdr_off;
529         int oldsstate, oldcstate;
530         int ret;
531         u_int16_t msg;
532 
533 #if IS_ENABLED(CONFIG_NF_NAT)
534         if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
535                 struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
536 
537                 if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
538                         return NF_DROP;
539         }
540 #endif
541         /* don't do any tracking before tcp handshake complete */
542         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
543                 return NF_ACCEPT;
544 
545         nexthdr_off = protoff;
546         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
547         BUG_ON(!tcph);
548         nexthdr_off += tcph->doff * 4;
549         datalen = tcplen - tcph->doff * 4;
550 
551         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
552         if (!pptph) {
553                 pr_debug("no full PPTP header, can't track\n");
554                 return NF_ACCEPT;
555         }
556         nexthdr_off += sizeof(_pptph);
557         datalen -= sizeof(_pptph);
558 
559         /* if it's not a control message we can't do anything with it */
560         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
561             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
562                 pr_debug("not a control packet\n");
563                 return NF_ACCEPT;
564         }
565 
566         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
567         if (!ctlh)
568                 return NF_ACCEPT;
569         nexthdr_off += sizeof(_ctlh);
570         datalen -= sizeof(_ctlh);
571 
572         reqlen = datalen;
573         msg = ntohs(ctlh->messageType);
574         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
575                 return NF_ACCEPT;
576         if (reqlen > sizeof(*pptpReq))
577                 reqlen = sizeof(*pptpReq);
578 
579         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
580         if (!pptpReq)
581                 return NF_ACCEPT;
582 
583         oldsstate = info->sstate;
584         oldcstate = info->cstate;
585 
586         spin_lock_bh(&nf_pptp_lock);
587 
588         /* FIXME: We just blindly assume that the control connection is always
589          * established from PNS->PAC.  However, RFC makes no guarantee */
590         if (dir == IP_CT_DIR_ORIGINAL)
591                 /* client -> server (PNS -> PAC) */
592                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
593                                         ctinfo);
594         else
595                 /* server -> client (PAC -> PNS) */
596                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
597                                        ctinfo);
598         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
599                  oldsstate, info->sstate, oldcstate, info->cstate);
600         spin_unlock_bh(&nf_pptp_lock);
601 
602         return ret;
603 }
604 
605 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
606         .max_expected   = 2,
607         .timeout        = 5 * 60,
608 };
609 
610 /* control protocol helper */
611 static struct nf_conntrack_helper pptp __read_mostly = {
612         .name                   = "pptp",
613         .me                     = THIS_MODULE,
614         .tuple.src.l3num        = AF_INET,
615         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
616         .tuple.dst.protonum     = IPPROTO_TCP,
617         .help                   = conntrack_pptp_help,
618         .destroy                = pptp_destroy_siblings,
619         .expect_policy          = &pptp_exp_policy,
620 };
621 
622 static int __init nf_conntrack_pptp_init(void)
623 {
624         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
625 
626         return nf_conntrack_helper_register(&pptp);
627 }
628 
629 static void __exit nf_conntrack_pptp_fini(void)
630 {
631         nf_conntrack_helper_unregister(&pptp);
632 }
633 
634 module_init(nf_conntrack_pptp_init);
635 module_exit(nf_conntrack_pptp_fini);
636 

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