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 <net/netfilter/nf_conntrack_zones.h>
  32 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  33 #include <linux/netfilter/nf_conntrack_pptp.h>
  34
  35 #define NF_CT_PPTP_VERSION "3.1"
  36
  37 MODULE_LICENSE("GPL");
  38 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  39 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
  40 MODULE_ALIAS("ip_conntrack_pptp");
  41 MODULE_ALIAS_NFCT_HELPER("pptp");
  42
  43 static DEFINE_SPINLOCK(nf_pptp_lock);
  44
  45 int
  46 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
  47                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  48                              struct PptpControlHeader *ctlh,
  49                              union pptp_ctrl_union *pptpReq) __read_mostly;
  50 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
  51
  52 int
  53 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
  54                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  55                             struct PptpControlHeader *ctlh,
  56                             union pptp_ctrl_union *pptpReq) __read_mostly;
  57 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
  58
  59 void
  60 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
  61                             struct nf_conntrack_expect *expect_reply)
  62                             __read_mostly;
  63 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
  64
  65 void
  66 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
  67                              struct nf_conntrack_expect *exp) __read_mostly;
  68 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
  69
  70 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
  71 /* PptpControlMessageType names */
  72 const char *const pptp_msg_name[] = {
  73         "UNKNOWN_MESSAGE",
  74         "START_SESSION_REQUEST",
  75         "START_SESSION_REPLY",
  76         "STOP_SESSION_REQUEST",
  77         "STOP_SESSION_REPLY",
  78         "ECHO_REQUEST",
  79         "ECHO_REPLY",
  80         "OUT_CALL_REQUEST",
  81         "OUT_CALL_REPLY",
  82         "IN_CALL_REQUEST",
  83         "IN_CALL_REPLY",
  84         "IN_CALL_CONNECT",
  85         "CALL_CLEAR_REQUEST",
  86         "CALL_DISCONNECT_NOTIFY",
  87         "WAN_ERROR_NOTIFY",
  88         "SET_LINK_INFO"
  89 };
  90 EXPORT_SYMBOL(pptp_msg_name);
  91 #endif
  92
  93 #define SECS *HZ
  94 #define MINS * 60 SECS
  95 #define HOURS * 60 MINS
  96
  97 #define PPTP_GRE_TIMEOUT                (10 MINS)
  98 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
  99
 100 static void pptp_expectfn(struct nf_conn *ct,
 101                          struct nf_conntrack_expect *exp)
 102 {
 103         struct net *net = nf_ct_net(ct);
 104         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
 105         pr_debug("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                 pr_debug("trying to unexpect other dir: ");
 125                 nf_ct_dump_tuple(&inv_t);
 126
 127                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
 128                 if (exp_other) {
 129                         /* delete other expectation.  */
 130                         pr_debug("found\n");
 131                         nf_ct_unexpect_related(exp_other);
 132                         nf_ct_expect_put(exp_other);
 133                 } else {
 134                         pr_debug("not found\n");
 135                 }
 136         }
 137         rcu_read_unlock();
 138 }
 139
 140 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
 141                                   const struct nf_conntrack_tuple *t)
 142 {
 143         const struct nf_conntrack_tuple_hash *h;
 144         struct nf_conntrack_expect *exp;
 145         struct nf_conn *sibling;
 146         u16 zone = nf_ct_zone(ct);
 147
 148         pr_debug("trying to timeout ct or exp for tuple ");
 149         nf_ct_dump_tuple(t);
 150
 151         h = nf_conntrack_find_get(net, zone, t);
 152         if (h)  {
 153                 sibling = nf_ct_tuplehash_to_ctrack(h);
 154                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
 155                 sibling->proto.gre.timeout        = 0;
 156                 sibling->proto.gre.stream_timeout = 0;
 157                 if (del_timer(&sibling->timeout))
 158                         sibling->timeout.function((unsigned long)sibling);
 159                 nf_ct_put(sibling);
 160                 return 1;
 161         } else {
 162                 exp = nf_ct_expect_find_get(net, zone, t);
 163                 if (exp) {
 164                         pr_debug("unexpect_related of expect %p\n", exp);
 165                         nf_ct_unexpect_related(exp);
 166                         nf_ct_expect_put(exp);
 167                         return 1;
 168                 }
 169         }
 170         return 0;
 171 }
 172
 173 /* timeout GRE data connections */
 174 static void pptp_destroy_siblings(struct nf_conn *ct)
 175 {
 176         struct net *net = nf_ct_net(ct);
 177         const struct nf_conn_help *help = nfct_help(ct);
 178         struct nf_conntrack_tuple t;
 179
 180         nf_ct_gre_keymap_destroy(ct);
 181
 182         /* try original (pns->pac) tuple */
 183         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
 184         t.dst.protonum = IPPROTO_GRE;
 185         t.src.u.gre.key = help->help.ct_pptp_info.pns_call_id;
 186         t.dst.u.gre.key = help->help.ct_pptp_info.pac_call_id;
 187         if (!destroy_sibling_or_exp(net, ct, &t))
 188                 pr_debug("failed to timeout original pns->pac ct/exp\n");
 189
 190         /* try reply (pac->pns) tuple */
 191         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
 192         t.dst.protonum = IPPROTO_GRE;
 193         t.src.u.gre.key = help->help.ct_pptp_info.pac_call_id;
 194         t.dst.u.gre.key = help->help.ct_pptp_info.pns_call_id;
 195         if (!destroy_sibling_or_exp(net, ct, &t))
 196                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
 197 }
 198
 199 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
 200 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
 201 {
 202         struct nf_conntrack_expect *exp_orig, *exp_reply;
 203         enum ip_conntrack_dir dir;
 204         int ret = 1;
 205         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
 206
 207         exp_orig = nf_ct_expect_alloc(ct);
 208         if (exp_orig == NULL)
 209                 goto out;
 210
 211         exp_reply = nf_ct_expect_alloc(ct);
 212         if (exp_reply == NULL)
 213                 goto out_put_orig;
 214
 215         /* original direction, PNS->PAC */
 216         dir = IP_CT_DIR_ORIGINAL;
 217         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
 218                           nf_ct_l3num(ct),
 219                           &ct->tuplehash[dir].tuple.src.u3,
 220                           &ct->tuplehash[dir].tuple.dst.u3,
 221                           IPPROTO_GRE, &peer_callid, &callid);
 222         exp_orig->expectfn = pptp_expectfn;
 223
 224         /* reply direction, PAC->PNS */
 225         dir = IP_CT_DIR_REPLY;
 226         nf_ct_expect_init(exp_reply, 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, &callid, &peer_callid);
 231         exp_reply->expectfn = pptp_expectfn;
 232
 233         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
 234         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
 235                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
 236         if (nf_ct_expect_related(exp_orig) != 0)
 237                 goto out_put_both;
 238         if (nf_ct_expect_related(exp_reply) != 0)
 239                 goto out_unexpect_orig;
 240
 241         /* Add GRE keymap entries */
 242         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
 243                 goto out_unexpect_both;
 244         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
 245                 nf_ct_gre_keymap_destroy(ct);
 246                 goto out_unexpect_both;
 247         }
 248         ret = 0;
 249
 250 out_put_both:
 251         nf_ct_expect_put(exp_reply);
 252 out_put_orig:
 253         nf_ct_expect_put(exp_orig);
 254 out:
 255         return ret;
 256
 257 out_unexpect_both:
 258         nf_ct_unexpect_related(exp_reply);
 259 out_unexpect_orig:
 260         nf_ct_unexpect_related(exp_orig);
 261         goto out_put_both;
 262 }
 263
 264 static inline int
 265 pptp_inbound_pkt(struct sk_buff *skb,
 266                  struct PptpControlHeader *ctlh,
 267                  union pptp_ctrl_union *pptpReq,
 268                  unsigned int reqlen,
 269                  struct nf_conn *ct,
 270                  enum ip_conntrack_info ctinfo)
 271 {
 272         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 273         u_int16_t msg;
 274         __be16 cid = 0, pcid = 0;
 275         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
 276
 277         msg = ntohs(ctlh->messageType);
 278         pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
 279
 280         switch (msg) {
 281         case PPTP_START_SESSION_REPLY:
 282                 /* server confirms new control session */
 283                 if (info->sstate < PPTP_SESSION_REQUESTED)
 284                         goto invalid;
 285                 if (pptpReq->srep.resultCode == PPTP_START_OK)
 286                         info->sstate = PPTP_SESSION_CONFIRMED;
 287                 else
 288                         info->sstate = PPTP_SESSION_ERROR;
 289                 break;
 290
 291         case PPTP_STOP_SESSION_REPLY:
 292                 /* server confirms end of control session */
 293                 if (info->sstate > PPTP_SESSION_STOPREQ)
 294                         goto invalid;
 295                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
 296                         info->sstate = PPTP_SESSION_NONE;
 297                 else
 298                         info->sstate = PPTP_SESSION_ERROR;
 299                 break;
 300
 301         case PPTP_OUT_CALL_REPLY:
 302                 /* server accepted call, we now expect GRE frames */
 303                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 304                         goto invalid;
 305                 if (info->cstate != PPTP_CALL_OUT_REQ &&
 306                     info->cstate != PPTP_CALL_OUT_CONF)
 307                         goto invalid;
 308
 309                 cid = pptpReq->ocack.callID;
 310                 pcid = pptpReq->ocack.peersCallID;
 311                 if (info->pns_call_id != pcid)
 312                         goto invalid;
 313                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
 314                          ntohs(cid), ntohs(pcid));
 315
 316                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
 317                         info->cstate = PPTP_CALL_OUT_CONF;
 318                         info->pac_call_id = cid;
 319                         exp_gre(ct, cid, pcid);
 320                 } else
 321                         info->cstate = PPTP_CALL_NONE;
 322                 break;
 323
 324         case PPTP_IN_CALL_REQUEST:
 325                 /* server tells us about incoming call request */
 326                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 327                         goto invalid;
 328
 329                 cid = pptpReq->icreq.callID;
 330                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 331                 info->cstate = PPTP_CALL_IN_REQ;
 332                 info->pac_call_id = cid;
 333                 break;
 334
 335         case PPTP_IN_CALL_CONNECT:
 336                 /* server tells us about incoming call established */
 337                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 338                         goto invalid;
 339                 if (info->cstate != PPTP_CALL_IN_REP &&
 340                     info->cstate != PPTP_CALL_IN_CONF)
 341                         goto invalid;
 342
 343                 pcid = pptpReq->iccon.peersCallID;
 344                 cid = info->pac_call_id;
 345
 346                 if (info->pns_call_id != pcid)
 347                         goto invalid;
 348
 349                 pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
 350                 info->cstate = PPTP_CALL_IN_CONF;
 351
 352                 /* we expect a GRE connection from PAC to PNS */
 353                 exp_gre(ct, cid, pcid);
 354                 break;
 355
 356         case PPTP_CALL_DISCONNECT_NOTIFY:
 357                 /* server confirms disconnect */
 358                 cid = pptpReq->disc.callID;
 359                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 360                 info->cstate = PPTP_CALL_NONE;
 361
 362                 /* untrack this call id, unexpect GRE packets */
 363                 pptp_destroy_siblings(ct);
 364                 break;
 365
 366         case PPTP_WAN_ERROR_NOTIFY:
 367         case PPTP_ECHO_REQUEST:
 368         case PPTP_ECHO_REPLY:
 369                 /* I don't have to explain these ;) */
 370                 break;
 371
 372         default:
 373                 goto invalid;
 374         }
 375
 376         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
 377         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
 378                 return nf_nat_pptp_inbound(skb, ct, ctinfo, ctlh, pptpReq);
 379         return NF_ACCEPT;
 380
 381 invalid:
 382         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 383                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 384                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 385                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 386                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 387         return NF_ACCEPT;
 388 }
 389
 390 static inline int
 391 pptp_outbound_pkt(struct sk_buff *skb,
 392                   struct PptpControlHeader *ctlh,
 393                   union pptp_ctrl_union *pptpReq,
 394                   unsigned int reqlen,
 395                   struct nf_conn *ct,
 396                   enum ip_conntrack_info ctinfo)
 397 {
 398         struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 399         u_int16_t msg;
 400         __be16 cid = 0, pcid = 0;
 401         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
 402
 403         msg = ntohs(ctlh->messageType);
 404         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
 405
 406         switch (msg) {
 407         case PPTP_START_SESSION_REQUEST:
 408                 /* client requests for new control session */
 409                 if (info->sstate != PPTP_SESSION_NONE)
 410                         goto invalid;
 411                 info->sstate = PPTP_SESSION_REQUESTED;
 412                 break;
 413
 414         case PPTP_STOP_SESSION_REQUEST:
 415                 /* client requests end of control session */
 416                 info->sstate = PPTP_SESSION_STOPREQ;
 417                 break;
 418
 419         case PPTP_OUT_CALL_REQUEST:
 420                 /* client initiating connection to server */
 421                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 422                         goto invalid;
 423                 info->cstate = PPTP_CALL_OUT_REQ;
 424                 /* track PNS call id */
 425                 cid = pptpReq->ocreq.callID;
 426                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 427                 info->pns_call_id = cid;
 428                 break;
 429
 430         case PPTP_IN_CALL_REPLY:
 431                 /* client answers incoming call */
 432                 if (info->cstate != PPTP_CALL_IN_REQ &&
 433                     info->cstate != PPTP_CALL_IN_REP)
 434                         goto invalid;
 435
 436                 cid = pptpReq->icack.callID;
 437                 pcid = pptpReq->icack.peersCallID;
 438                 if (info->pac_call_id != pcid)
 439                         goto invalid;
 440                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
 441                          ntohs(cid), ntohs(pcid));
 442
 443                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
 444                         /* part two of the three-way handshake */
 445                         info->cstate = PPTP_CALL_IN_REP;
 446                         info->pns_call_id = cid;
 447                 } else
 448                         info->cstate = PPTP_CALL_NONE;
 449                 break;
 450
 451         case PPTP_CALL_CLEAR_REQUEST:
 452                 /* client requests hangup of call */
 453                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 454                         goto invalid;
 455                 /* FUTURE: iterate over all calls and check if
 456                  * call ID is valid.  We don't do this without newnat,
 457                  * because we only know about last call */
 458                 info->cstate = PPTP_CALL_CLEAR_REQ;
 459                 break;
 460
 461         case PPTP_SET_LINK_INFO:
 462         case PPTP_ECHO_REQUEST:
 463         case PPTP_ECHO_REPLY:
 464                 /* I don't have to explain these ;) */
 465                 break;
 466
 467         default:
 468                 goto invalid;
 469         }
 470
 471         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
 472         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
 473                 return nf_nat_pptp_outbound(skb, ct, ctinfo, ctlh, pptpReq);
 474         return NF_ACCEPT;
 475
 476 invalid:
 477         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 478                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 479                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 480                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 481                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 482         return NF_ACCEPT;
 483 }
 484
 485 static const unsigned int pptp_msg_size[] = {
 486         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
 487         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
 488         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
 489         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
 490         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
 491         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
 492         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
 493         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
 494         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
 495         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
 496         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
 497         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
 498         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
 499 };
 500
 501 /* track caller id inside control connection, call expect_related */
 502 static int
 503 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
 504                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 505
 506 {
 507         int dir = CTINFO2DIR(ctinfo);
 508         const struct nf_ct_pptp_master *info = &nfct_help(ct)->help.ct_pptp_info;
 509         const struct tcphdr *tcph;
 510         struct tcphdr _tcph;
 511         const struct pptp_pkt_hdr *pptph;
 512         struct pptp_pkt_hdr _pptph;
 513         struct PptpControlHeader _ctlh, *ctlh;
 514         union pptp_ctrl_union _pptpReq, *pptpReq;
 515         unsigned int tcplen = skb->len - protoff;
 516         unsigned int datalen, reqlen, nexthdr_off;
 517         int oldsstate, oldcstate;
 518         int ret;
 519         u_int16_t msg;
 520
 521         /* don't do any tracking before tcp handshake complete */
 522         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 523                 return NF_ACCEPT;
 524
 525         nexthdr_off = protoff;
 526         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
 527         BUG_ON(!tcph);
 528         nexthdr_off += tcph->doff * 4;
 529         datalen = tcplen - tcph->doff * 4;
 530
 531         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
 532         if (!pptph) {
 533                 pr_debug("no full PPTP header, can't track\n");
 534                 return NF_ACCEPT;
 535         }
 536         nexthdr_off += sizeof(_pptph);
 537         datalen -= sizeof(_pptph);
 538
 539         /* if it's not a control message we can't do anything with it */
 540         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
 541             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
 542                 pr_debug("not a control packet\n");
 543                 return NF_ACCEPT;
 544         }
 545
 546         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
 547         if (!ctlh)
 548                 return NF_ACCEPT;
 549         nexthdr_off += sizeof(_ctlh);
 550         datalen -= sizeof(_ctlh);
 551
 552         reqlen = datalen;
 553         msg = ntohs(ctlh->messageType);
 554         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
 555                 return NF_ACCEPT;
 556         if (reqlen > sizeof(*pptpReq))
 557                 reqlen = sizeof(*pptpReq);
 558
 559         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
 560         if (!pptpReq)
 561                 return NF_ACCEPT;
 562
 563         oldsstate = info->sstate;
 564         oldcstate = info->cstate;
 565
 566         spin_lock_bh(&nf_pptp_lock);
 567
 568         /* FIXME: We just blindly assume that the control connection is always
 569          * established from PNS->PAC.  However, RFC makes no guarantee */
 570         if (dir == IP_CT_DIR_ORIGINAL)
 571                 /* client -> server (PNS -> PAC) */
 572                 ret = pptp_outbound_pkt(skb, ctlh, pptpReq, reqlen, ct,
 573                                         ctinfo);
 574         else
 575                 /* server -> client (PAC -> PNS) */
 576                 ret = pptp_inbound_pkt(skb, ctlh, pptpReq, reqlen, ct,
 577                                        ctinfo);
 578         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
 579                  oldsstate, info->sstate, oldcstate, info->cstate);
 580         spin_unlock_bh(&nf_pptp_lock);
 581
 582         return ret;
 583 }
 584
 585 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
 586         .max_expected   = 2,
 587         .timeout        = 5 * 60,
 588 };
 589
 590 /* control protocol helper */
 591 static struct nf_conntrack_helper pptp __read_mostly = {
 592         .name                   = "pptp",
 593         .me                     = THIS_MODULE,
 594         .tuple.src.l3num        = AF_INET,
 595         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
 596         .tuple.dst.protonum     = IPPROTO_TCP,
 597         .help                   = conntrack_pptp_help,
 598         .destroy                = pptp_destroy_siblings,
 599         .expect_policy          = &pptp_exp_policy,
 600 };
 601
 602 static void nf_conntrack_pptp_net_exit(struct net *net)
 603 {
 604         nf_ct_gre_keymap_flush(net);
 605 }
 606
 607 static struct pernet_operations nf_conntrack_pptp_net_ops = {
 608         .exit = nf_conntrack_pptp_net_exit,
 609 };
 610
 611 static int __init nf_conntrack_pptp_init(void)
 612 {
 613         int rv;
 614
 615         rv = nf_conntrack_helper_register(&pptp);
 616         if (rv < 0)
 617                 return rv;
 618         rv = register_pernet_subsys(&nf_conntrack_pptp_net_ops);
 619         if (rv < 0)
 620                 nf_conntrack_helper_unregister(&pptp);
 621         return rv;
 622 }
 623
 624 static void __exit nf_conntrack_pptp_fini(void)
 625 {
 626         nf_conntrack_helper_unregister(&pptp);
 627         unregister_pernet_subsys(&nf_conntrack_pptp_net_ops);
 628 }
 629
 630 module_init(nf_conntrack_pptp_init);
 631 module_exit(nf_conntrack_pptp_fini);