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