net/netfilter/nf_conntrack_pptp.c

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