git.oblomov.eu Git - linux-2.6/blob - 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 **pskb,
  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 **pskb,
  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 #if 0
  69 /* PptpControlMessageType names */
  70 const char *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 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, __FUNCTION__, ## args)
  90 #else
  91 #define DEBUGP(format, args...)
  92 #endif
  93
  94 #define SECS *HZ
  95 #define MINS * 60 SECS
  96 #define HOURS * 60 MINS
  97
  98 #define PPTP_GRE_TIMEOUT                (10 MINS)
  99 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
 100
 101 static void pptp_expectfn(struct nf_conn *ct,
 102                          struct nf_conntrack_expect *exp)
 103 {
 104         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
 105         DEBUGP("increasing timeouts\n");
 106
 107         /* increase timeout of GRE data channel conntrack entry */
 108         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
 109         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
 110
 111         /* Can you see how rusty this code is, compared with the pre-2.6.11
 112          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
 113
 114         rcu_read_lock();
 115         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
 116         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
 117                 nf_nat_pptp_expectfn(ct, exp);
 118         else {
 119                 struct nf_conntrack_tuple inv_t;
 120                 struct nf_conntrack_expect *exp_other;
 121
 122                 /* obviously this tuple inversion only works until you do NAT */
 123                 nf_ct_invert_tuplepr(&inv_t, &exp->tuple);
 124                 DEBUGP("trying to unexpect other dir: ");
 125                 NF_CT_DUMP_TUPLE(&inv_t);
 126
 127                 exp_other = nf_conntrack_expect_find_get(&inv_t);
 128                 if (exp_other) {
 129                         /* delete other expectation.  */
 130                         DEBUGP("found\n");
 131                         nf_conntrack_unexpect_related(exp_other);
 132                         nf_conntrack_expect_put(exp_other);
 133                 } else {
 134                         DEBUGP("not found\n");
 135                 }
 136         }
 137         rcu_read_unlock();
 138 }
 139
 140 static int destroy_sibling_or_exp(const struct nf_conntrack_tuple *t)
 141 {
 142         struct nf_conntrack_tuple_hash *h;
 143         struct nf_conntrack_expect *exp;
 144         struct nf_conn *sibling;
 145
 146         DEBUGP("trying to timeout ct or exp for tuple ");
 147         NF_CT_DUMP_TUPLE(t);
 148
 149         h = nf_conntrack_find_get(t, NULL);
 150         if (h)  {
 151                 sibling = nf_ct_tuplehash_to_ctrack(h);
 152                 DEBUGP("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_conntrack_expect_find_get(t);
 161                 if (exp) {
 162                         DEBUGP("unexpect_related of expect %p\n", exp);
 163                         nf_conntrack_unexpect_related(exp);
 164                         nf_conntrack_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 nf_conn_help *help = nfct_help(ct);
 175         struct nf_conntrack_tuple t;
 176
 177         nf_ct_gre_keymap_destroy(ct);
 178
 179         /* try original (pns->pac) tuple */
 180         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
 181         t.dst.protonum = IPPROTO_GRE;
 182         t.src.u.gre.key = help->help.ct_pptp_info.pns_call_id;
 183         t.dst.u.gre.key = help->help.ct_pptp_info.pac_call_id;
 184         if (!destroy_sibling_or_exp(&t))
 185                 DEBUGP("failed to timeout original pns->pac ct/exp\n");
 186
 187         /* try reply (pac->pns) tuple */
 188         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
 189         t.dst.protonum = IPPROTO_GRE;
 190         t.src.u.gre.key = help->help.ct_pptp_info.pac_call_id;
 191         t.dst.u.gre.key = help->help.ct_pptp_info.pns_call_id;
 192         if (!destroy_sibling_or_exp(&t))
 193                 DEBUGP("failed to timeout reply pac->pns ct/exp\n");
 194 }
 195
 196 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
 197 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
 198 {
 199         struct nf_conntrack_expect *exp_orig, *exp_reply;
 200         enum ip_conntrack_dir dir;
 201         int ret = 1;
 202         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
 203
 204         exp_orig = nf_conntrack_expect_alloc(ct);
 205         if (exp_orig == NULL)
 206                 goto out;
 207
 208         exp_reply = nf_conntrack_expect_alloc(ct);
 209         if (exp_reply == NULL)
 210                 goto out_put_orig;
 211
 212         /* original direction, PNS->PAC */
 213         dir = IP_CT_DIR_ORIGINAL;
 214         nf_conntrack_expect_init(exp_orig, ct->tuplehash[dir].tuple.src.l3num,
 215                                  &ct->tuplehash[dir].tuple.src.u3,
 216                                  &ct->tuplehash[dir].tuple.dst.u3,
 217                                  IPPROTO_GRE, &peer_callid, &callid);
 218         exp_orig->expectfn = pptp_expectfn;
 219
 220         /* reply direction, PAC->PNS */
 221         dir = IP_CT_DIR_REPLY;
 222         nf_conntrack_expect_init(exp_reply, ct->tuplehash[dir].tuple.src.l3num,
 223                                  &ct->tuplehash[dir].tuple.src.u3,
 224                                  &ct->tuplehash[dir].tuple.dst.u3,
 225                                  IPPROTO_GRE, &callid, &peer_callid);
 226         exp_reply->expectfn = pptp_expectfn;
 227
 228         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
 229         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
 230                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
 231         if (nf_conntrack_expect_related(exp_orig) != 0)
 232                 goto out_put_both;
 233         if (nf_conntrack_expect_related(exp_reply) != 0)
 234                 goto out_unexpect_orig;
 235
 236         /* Add GRE keymap entries */
 237         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
 238                 goto out_unexpect_both;
 239         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
 240                 nf_ct_gre_keymap_destroy(ct);
 241                 goto out_unexpect_both;
 242         }
 243         ret = 0;
 244
 245 out_put_both:
 246         nf_conntrack_expect_put(exp_reply);
 247 out_put_orig:
 248         nf_conntrack_expect_put(exp_orig);
 249 out:
 250         return ret;
 251
 252 out_unexpect_both:
 253         nf_conntrack_unexpect_related(exp_reply);
 254 out_unexpect_orig:
 255         nf_conntrack_unexpect_related(exp_orig);
 256         goto out_put_both;
 257 }
 258
 259 static inline int
 260 pptp_inbound_pkt(struct sk_buff **pskb,
 261                  struct PptpControlHeader *ctlh,
 262                  union pptp_ctrl_union *pptpReq,
 263                  unsigned int reqlen,
 264                  struct nf_conn *ct,
 265                  enum ip_conntrack_info ctinfo)
 266 {
 267         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 268         u_int16_t msg;
 269         __be16 cid = 0, pcid = 0;
 270         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
 271
 272         msg = ntohs(ctlh->messageType);
 273         DEBUGP("inbound control message %s\n", pptp_msg_name[msg]);
 274
 275         switch (msg) {
 276         case PPTP_START_SESSION_REPLY:
 277                 /* server confirms new control session */
 278                 if (info->sstate < PPTP_SESSION_REQUESTED)
 279                         goto invalid;
 280                 if (pptpReq->srep.resultCode == PPTP_START_OK)
 281                         info->sstate = PPTP_SESSION_CONFIRMED;
 282                 else
 283                         info->sstate = PPTP_SESSION_ERROR;
 284                 break;
 285
 286         case PPTP_STOP_SESSION_REPLY:
 287                 /* server confirms end of control session */
 288                 if (info->sstate > PPTP_SESSION_STOPREQ)
 289                         goto invalid;
 290                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
 291                         info->sstate = PPTP_SESSION_NONE;
 292                 else
 293                         info->sstate = PPTP_SESSION_ERROR;
 294                 break;
 295
 296         case PPTP_OUT_CALL_REPLY:
 297                 /* server accepted call, we now expect GRE frames */
 298                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 299                         goto invalid;
 300                 if (info->cstate != PPTP_CALL_OUT_REQ &&
 301                     info->cstate != PPTP_CALL_OUT_CONF)
 302                         goto invalid;
 303
 304                 cid = pptpReq->ocack.callID;
 305                 pcid = pptpReq->ocack.peersCallID;
 306                 if (info->pns_call_id != pcid)
 307                         goto invalid;
 308                 DEBUGP("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
 309                         ntohs(cid), ntohs(pcid));
 310
 311                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
 312                         info->cstate = PPTP_CALL_OUT_CONF;
 313                         info->pac_call_id = cid;
 314                         exp_gre(ct, cid, pcid);
 315                 } else
 316                         info->cstate = PPTP_CALL_NONE;
 317                 break;
 318
 319         case PPTP_IN_CALL_REQUEST:
 320                 /* server tells us about incoming call request */
 321                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 322                         goto invalid;
 323
 324                 cid = pptpReq->icreq.callID;
 325                 DEBUGP("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 326                 info->cstate = PPTP_CALL_IN_REQ;
 327                 info->pac_call_id = cid;
 328                 break;
 329
 330         case PPTP_IN_CALL_CONNECT:
 331                 /* server tells us about incoming call established */
 332                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 333                         goto invalid;
 334                 if (info->cstate != PPTP_CALL_IN_REP &&
 335                     info->cstate != PPTP_CALL_IN_CONF)
 336                         goto invalid;
 337
 338                 pcid = pptpReq->iccon.peersCallID;
 339                 cid = info->pac_call_id;
 340
 341                 if (info->pns_call_id != pcid)
 342                         goto invalid;
 343
 344                 DEBUGP("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
 345                 info->cstate = PPTP_CALL_IN_CONF;
 346
 347                 /* we expect a GRE connection from PAC to PNS */
 348                 exp_gre(ct, cid, pcid);
 349                 break;
 350
 351         case PPTP_CALL_DISCONNECT_NOTIFY:
 352                 /* server confirms disconnect */
 353                 cid = pptpReq->disc.callID;
 354                 DEBUGP("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 355                 info->cstate = PPTP_CALL_NONE;
 356
 357                 /* untrack this call id, unexpect GRE packets */
 358                 pptp_destroy_siblings(ct);
 359                 break;
 360
 361         case PPTP_WAN_ERROR_NOTIFY:
 362         case PPTP_ECHO_REQUEST:
 363         case PPTP_ECHO_REPLY:
 364                 /* I don't have to explain these ;) */
 365                 break;
 366
 367         default:
 368                 goto invalid;
 369         }
 370
 371         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
 372         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
 373                 return nf_nat_pptp_inbound(pskb, ct, ctinfo, ctlh, pptpReq);
 374         return NF_ACCEPT;
 375
 376 invalid:
 377         DEBUGP("invalid %s: type=%d cid=%u pcid=%u "
 378                "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 379                msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 380                msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 381                ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 382         return NF_ACCEPT;
 383 }
 384
 385 static inline int
 386 pptp_outbound_pkt(struct sk_buff **pskb,
 387                   struct PptpControlHeader *ctlh,
 388                   union pptp_ctrl_union *pptpReq,
 389                   unsigned int reqlen,
 390                   struct nf_conn *ct,
 391                   enum ip_conntrack_info ctinfo)
 392 {
 393         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 394         u_int16_t msg;
 395         __be16 cid = 0, pcid = 0;
 396         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
 397
 398         msg = ntohs(ctlh->messageType);
 399         DEBUGP("outbound control message %s\n", pptp_msg_name[msg]);
 400
 401         switch (msg) {
 402         case PPTP_START_SESSION_REQUEST:
 403                 /* client requests for new control session */
 404                 if (info->sstate != PPTP_SESSION_NONE)
 405                         goto invalid;
 406                 info->sstate = PPTP_SESSION_REQUESTED;
 407                 break;
 408
 409         case PPTP_STOP_SESSION_REQUEST:
 410                 /* client requests end of control session */
 411                 info->sstate = PPTP_SESSION_STOPREQ;
 412                 break;
 413
 414         case PPTP_OUT_CALL_REQUEST:
 415                 /* client initiating connection to server */
 416                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 417                         goto invalid;
 418                 info->cstate = PPTP_CALL_OUT_REQ;
 419                 /* track PNS call id */
 420                 cid = pptpReq->ocreq.callID;
 421                 DEBUGP("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 422                 info->pns_call_id = cid;
 423                 break;
 424
 425         case PPTP_IN_CALL_REPLY:
 426                 /* client answers incoming call */
 427                 if (info->cstate != PPTP_CALL_IN_REQ &&
 428                     info->cstate != PPTP_CALL_IN_REP)
 429                         goto invalid;
 430
 431                 cid = pptpReq->icack.callID;
 432                 pcid = pptpReq->icack.peersCallID;
 433                 if (info->pac_call_id != pcid)
 434                         goto invalid;
 435                 DEBUGP("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
 436                        ntohs(cid), ntohs(pcid));
 437
 438                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
 439                         /* part two of the three-way handshake */
 440                         info->cstate = PPTP_CALL_IN_REP;
 441                         info->pns_call_id = cid;
 442                 } else
 443                         info->cstate = PPTP_CALL_NONE;
 444                 break;
 445
 446         case PPTP_CALL_CLEAR_REQUEST:
 447                 /* client requests hangup of call */
 448                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 449                         goto invalid;
 450                 /* FUTURE: iterate over all calls and check if
 451                  * call ID is valid.  We don't do this without newnat,
 452                  * because we only know about last call */
 453                 info->cstate = PPTP_CALL_CLEAR_REQ;
 454                 break;
 455
 456         case PPTP_SET_LINK_INFO:
 457         case PPTP_ECHO_REQUEST:
 458         case PPTP_ECHO_REPLY:
 459                 /* I don't have to explain these ;) */
 460                 break;
 461
 462         default:
 463                 goto invalid;
 464         }
 465
 466         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
 467         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
 468                 return nf_nat_pptp_outbound(pskb, ct, ctinfo, ctlh, pptpReq);
 469         return NF_ACCEPT;
 470
 471 invalid:
 472         DEBUGP("invalid %s: type=%d cid=%u pcid=%u "
 473                "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 474                msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 475                msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 476                ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 477         return NF_ACCEPT;
 478 }
 479
 480 static const unsigned int pptp_msg_size[] = {
 481         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
 482         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
 483         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
 484         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
 485         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
 486         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
 487         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
 488         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
 489         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
 490         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
 491         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
 492         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
 493         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
 494 };
 495
 496 /* track caller id inside control connection, call expect_related */
 497 static int
 498 conntrack_pptp_help(struct sk_buff **pskb, unsigned int protoff,
 499                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 500
 501 {
 502         int dir = CTINFO2DIR(ctinfo);
 503         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 504         struct tcphdr _tcph, *tcph;
 505         struct pptp_pkt_hdr _pptph, *pptph;
 506         struct PptpControlHeader _ctlh, *ctlh;
 507         union pptp_ctrl_union _pptpReq, *pptpReq;
 508         unsigned int tcplen = (*pskb)->len - protoff;
 509         unsigned int datalen, reqlen, nexthdr_off;
 510         int oldsstate, oldcstate;
 511         int ret;
 512         u_int16_t msg;
 513
 514         /* don't do any tracking before tcp handshake complete */
 515         if (ctinfo != IP_CT_ESTABLISHED &&
 516             ctinfo != IP_CT_ESTABLISHED + IP_CT_IS_REPLY)
 517                 return NF_ACCEPT;
 518
 519         nexthdr_off = protoff;
 520         tcph = skb_header_pointer(*pskb, nexthdr_off, sizeof(_tcph), &_tcph);
 521         BUG_ON(!tcph);
 522         nexthdr_off += tcph->doff * 4;
 523         datalen = tcplen - tcph->doff * 4;
 524
 525         pptph = skb_header_pointer(*pskb, nexthdr_off, sizeof(_pptph), &_pptph);
 526         if (!pptph) {
 527                 DEBUGP("no full PPTP header, can't track\n");
 528                 return NF_ACCEPT;
 529         }
 530         nexthdr_off += sizeof(_pptph);
 531         datalen -= sizeof(_pptph);
 532
 533         /* if it's not a control message we can't do anything with it */
 534         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
 535             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
 536                 DEBUGP("not a control packet\n");
 537                 return NF_ACCEPT;
 538         }
 539
 540         ctlh = skb_header_pointer(*pskb, nexthdr_off, sizeof(_ctlh), &_ctlh);
 541         if (!ctlh)
 542                 return NF_ACCEPT;
 543         nexthdr_off += sizeof(_ctlh);
 544         datalen -= sizeof(_ctlh);
 545
 546         reqlen = datalen;
 547         msg = ntohs(ctlh->messageType);
 548         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
 549                 return NF_ACCEPT;
 550         if (reqlen > sizeof(*pptpReq))
 551                 reqlen = sizeof(*pptpReq);
 552
 553         pptpReq = skb_header_pointer(*pskb, nexthdr_off, reqlen, &_pptpReq);
 554         if (!pptpReq)
 555                 return NF_ACCEPT;
 556
 557         oldsstate = info->sstate;
 558         oldcstate = info->cstate;
 559
 560         spin_lock_bh(&nf_pptp_lock);
 561
 562         /* FIXME: We just blindly assume that the control connection is always
 563          * established from PNS->PAC.  However, RFC makes no guarantee */
 564         if (dir == IP_CT_DIR_ORIGINAL)
 565                 /* client -> server (PNS -> PAC) */
 566                 ret = pptp_outbound_pkt(pskb, ctlh, pptpReq, reqlen, ct,
 567                                         ctinfo);
 568         else
 569                 /* server -> client (PAC -> PNS) */
 570                 ret = pptp_inbound_pkt(pskb, ctlh, pptpReq, reqlen, ct,
 571                                        ctinfo);
 572         DEBUGP("sstate: %d->%d, cstate: %d->%d\n",
 573                 oldsstate, info->sstate, oldcstate, info->cstate);
 574         spin_unlock_bh(&nf_pptp_lock);
 575
 576         return ret;
 577 }
 578
 579 /* control protocol helper */
 580 static struct nf_conntrack_helper pptp __read_mostly = {
 581         .name                   = "pptp",
 582         .me                     = THIS_MODULE,
 583         .max_expected           = 2,
 584         .timeout                = 5 * 60,
 585         .tuple.src.l3num        = AF_INET,
 586         .tuple.src.u.tcp.port   = __constant_htons(PPTP_CONTROL_PORT),
 587         .tuple.dst.protonum     = IPPROTO_TCP,
 588         .mask.src.l3num         = 0xffff,
 589         .mask.src.u.tcp.port    = __constant_htons(0xffff),
 590         .mask.dst.protonum      = 0xff,
 591         .help                   = conntrack_pptp_help,
 592         .destroy                = pptp_destroy_siblings,
 593 };
 594
 595 static int __init nf_conntrack_pptp_init(void)
 596 {
 597         return nf_conntrack_helper_register(&pptp);
 598 }
 599
 600 static void __exit nf_conntrack_pptp_fini(void)
 601 {
 602         nf_conntrack_helper_unregister(&pptp);
 603         nf_ct_gre_keymap_flush();
 604 }
 605
 606 module_init(nf_conntrack_pptp_init);
 607 module_exit(nf_conntrack_pptp_fini);