net/netfilter/nf_conntrack_pptp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Connection tracking support for PPTP (Point to Point Tunneling Protocol).
   4  * PPTP is a protocol for creating virtual private networks.
   5  * It is a specification defined by Microsoft and some vendors
   6  * working with Microsoft.  PPTP is built on top of a modified
   7  * version of the Internet Generic Routing Encapsulation Protocol.
   8  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
   9  * PPTP can be found in RFC 2637
  10  *
  11  * (C) 2000-2005 by Harald Welte <[email protected]>
  12  *
  13  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  14  *
  15  * (C) 2006-2012 Patrick McHardy <[email protected]>
  16  *
  17  * Limitations:
  18  *       - We blindly assume that control connections are always
  19  *         established in PNS->PAC direction.  This is a violation
  20  *         of RFC 2637
  21  *       - We can only support one single call within each session
  22  * TODO:
  23  *       - testing of incoming PPTP calls
  24  */
  25
  26 #include <linux/module.h>
  27 #include <linux/skbuff.h>
  28 #include <linux/in.h>
  29 #include <linux/tcp.h>
  30
  31 #include <net/netfilter/nf_conntrack.h>
  32 #include <net/netfilter/nf_conntrack_core.h>
  33 #include <net/netfilter/nf_conntrack_helper.h>
  34 #include <net/netfilter/nf_conntrack_zones.h>
  35 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  36 #include <linux/netfilter/nf_conntrack_pptp.h>
  37
  38 #define NF_CT_PPTP_VERSION "3.1"
  39
  40 MODULE_LICENSE("GPL");
  41 MODULE_AUTHOR("Harald Welte <[email protected]>");
  42 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
  43 MODULE_ALIAS("ip_conntrack_pptp");
  44 MODULE_ALIAS_NFCT_HELPER("pptp");
  45
  46 static DEFINE_SPINLOCK(nf_pptp_lock);
  47
  48 const struct nf_nat_pptp_hook __rcu *nf_nat_pptp_hook;
  49 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook);
  50
  51 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
  52 /* PptpControlMessageType names */
  53 static const char *const pptp_msg_name_array[PPTP_MSG_MAX + 1] = {
  54         [0]                             = "UNKNOWN_MESSAGE",
  55         [PPTP_START_SESSION_REQUEST]    = "START_SESSION_REQUEST",
  56         [PPTP_START_SESSION_REPLY]      = "START_SESSION_REPLY",
  57         [PPTP_STOP_SESSION_REQUEST]     = "STOP_SESSION_REQUEST",
  58         [PPTP_STOP_SESSION_REPLY]       = "STOP_SESSION_REPLY",
  59         [PPTP_ECHO_REQUEST]             = "ECHO_REQUEST",
  60         [PPTP_ECHO_REPLY]               = "ECHO_REPLY",
  61         [PPTP_OUT_CALL_REQUEST]         = "OUT_CALL_REQUEST",
  62         [PPTP_OUT_CALL_REPLY]           = "OUT_CALL_REPLY",
  63         [PPTP_IN_CALL_REQUEST]          = "IN_CALL_REQUEST",
  64         [PPTP_IN_CALL_REPLY]            = "IN_CALL_REPLY",
  65         [PPTP_IN_CALL_CONNECT]          = "IN_CALL_CONNECT",
  66         [PPTP_CALL_CLEAR_REQUEST]       = "CALL_CLEAR_REQUEST",
  67         [PPTP_CALL_DISCONNECT_NOTIFY]   = "CALL_DISCONNECT_NOTIFY",
  68         [PPTP_WAN_ERROR_NOTIFY]         = "WAN_ERROR_NOTIFY",
  69         [PPTP_SET_LINK_INFO]            = "SET_LINK_INFO"
  70 };
  71
  72 const char *pptp_msg_name(u_int16_t msg)
  73 {
  74         if (msg > PPTP_MSG_MAX)
  75                 return pptp_msg_name_array[0];
  76
  77         return pptp_msg_name_array[msg];
  78 }
  79 EXPORT_SYMBOL(pptp_msg_name);
  80 #endif
  81
  82 #define SECS *HZ
  83 #define MINS * 60 SECS
  84 #define HOURS * 60 MINS
  85
  86 #define PPTP_GRE_TIMEOUT                (10 MINS)
  87 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
  88
  89 static void pptp_expectfn(struct nf_conn *ct,
  90                          struct nf_conntrack_expect *exp)
  91 {
  92         const struct nf_nat_pptp_hook *hook;
  93         struct net *net = nf_ct_net(ct);
  94         pr_debug("increasing timeouts\n");
  95
  96         /* increase timeout of GRE data channel conntrack entry */
  97         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
  98         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
  99
 100         /* Can you see how rusty this code is, compared with the pre-2.6.11
 101          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
 102
 103         hook = rcu_dereference(nf_nat_pptp_hook);
 104         if (hook && ct->master->status & IPS_NAT_MASK)
 105                 hook->expectfn(ct, exp);
 106         else {
 107                 struct nf_conntrack_tuple inv_t;
 108                 struct nf_conntrack_expect *exp_other;
 109
 110                 /* obviously this tuple inversion only works until you do NAT */
 111                 nf_ct_invert_tuple(&inv_t, &exp->tuple);
 112                 pr_debug("trying to unexpect other dir: ");
 113                 nf_ct_dump_tuple(&inv_t);
 114
 115                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
 116                 if (exp_other) {
 117                         /* delete other expectation.  */
 118                         pr_debug("found\n");
 119                         nf_ct_unexpect_related(exp_other);
 120                         nf_ct_expect_put(exp_other);
 121                 } else {
 122                         pr_debug("not found\n");
 123                 }
 124         }
 125 }
 126
 127 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
 128                                   const struct nf_conntrack_tuple *t)
 129 {
 130         const struct nf_conntrack_tuple_hash *h;
 131         const struct nf_conntrack_zone *zone;
 132         struct nf_conntrack_expect *exp;
 133         struct nf_conn *sibling;
 134
 135         pr_debug("trying to timeout ct or exp for tuple ");
 136         nf_ct_dump_tuple(t);
 137
 138         zone = nf_ct_zone(ct);
 139         h = nf_conntrack_find_get(net, zone, t);
 140         if (h)  {
 141                 sibling = nf_ct_tuplehash_to_ctrack(h);
 142                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
 143                 sibling->proto.gre.timeout        = 0;
 144                 sibling->proto.gre.stream_timeout = 0;
 145                 nf_ct_kill(sibling);
 146                 nf_ct_put(sibling);
 147                 return 1;
 148         } else {
 149                 exp = nf_ct_expect_find_get(net, zone, t);
 150                 if (exp) {
 151                         pr_debug("unexpect_related of expect %p\n", exp);
 152                         nf_ct_unexpect_related(exp);
 153                         nf_ct_expect_put(exp);
 154                         return 1;
 155                 }
 156         }
 157         return 0;
 158 }
 159
 160 /* timeout GRE data connections */
 161 static void pptp_destroy_siblings(struct nf_conn *ct)
 162 {
 163         struct net *net = nf_ct_net(ct);
 164         const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
 165         struct nf_conntrack_tuple t;
 166
 167         nf_ct_gre_keymap_destroy(ct);
 168
 169         /* try original (pns->pac) tuple */
 170         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
 171         t.dst.protonum = IPPROTO_GRE;
 172         t.src.u.gre.key = ct_pptp_info->pns_call_id;
 173         t.dst.u.gre.key = ct_pptp_info->pac_call_id;
 174         if (!destroy_sibling_or_exp(net, ct, &t))
 175                 pr_debug("failed to timeout original pns->pac ct/exp\n");
 176
 177         /* try reply (pac->pns) tuple */
 178         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
 179         t.dst.protonum = IPPROTO_GRE;
 180         t.src.u.gre.key = ct_pptp_info->pac_call_id;
 181         t.dst.u.gre.key = ct_pptp_info->pns_call_id;
 182         if (!destroy_sibling_or_exp(net, ct, &t))
 183                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
 184 }
 185
 186 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
 187 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
 188 {
 189         struct nf_conntrack_expect *exp_orig, *exp_reply;
 190         const struct nf_nat_pptp_hook *hook;
 191         enum ip_conntrack_dir dir;
 192         int ret = 1;
 193
 194         exp_orig = nf_ct_expect_alloc(ct);
 195         if (exp_orig == NULL)
 196                 goto out;
 197
 198         exp_reply = nf_ct_expect_alloc(ct);
 199         if (exp_reply == NULL)
 200                 goto out_put_orig;
 201
 202         /* original direction, PNS->PAC */
 203         dir = IP_CT_DIR_ORIGINAL;
 204         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
 205                           nf_ct_l3num(ct),
 206                           &ct->tuplehash[dir].tuple.src.u3,
 207                           &ct->tuplehash[dir].tuple.dst.u3,
 208                           IPPROTO_GRE, &peer_callid, &callid);
 209         exp_orig->expectfn = pptp_expectfn;
 210
 211         /* reply direction, PAC->PNS */
 212         dir = IP_CT_DIR_REPLY;
 213         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
 214                           nf_ct_l3num(ct),
 215                           &ct->tuplehash[dir].tuple.src.u3,
 216                           &ct->tuplehash[dir].tuple.dst.u3,
 217                           IPPROTO_GRE, &callid, &peer_callid);
 218         exp_reply->expectfn = pptp_expectfn;
 219
 220         hook = rcu_dereference(nf_nat_pptp_hook);
 221         if (hook && ct->status & IPS_NAT_MASK)
 222                 hook->exp_gre(exp_orig, exp_reply);
 223         if (nf_ct_expect_related(exp_orig, 0) != 0)
 224                 goto out_put_both;
 225         if (nf_ct_expect_related(exp_reply, 0) != 0)
 226                 goto out_unexpect_orig;
 227
 228         /* Add GRE keymap entries */
 229         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
 230                 goto out_unexpect_both;
 231         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
 232                 nf_ct_gre_keymap_destroy(ct);
 233                 goto out_unexpect_both;
 234         }
 235         ret = 0;
 236
 237 out_put_both:
 238         nf_ct_expect_put(exp_reply);
 239 out_put_orig:
 240         nf_ct_expect_put(exp_orig);
 241 out:
 242         return ret;
 243
 244 out_unexpect_both:
 245         nf_ct_unexpect_related(exp_reply);
 246 out_unexpect_orig:
 247         nf_ct_unexpect_related(exp_orig);
 248         goto out_put_both;
 249 }
 250
 251 static int
 252 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
 253                  struct PptpControlHeader *ctlh,
 254                  union pptp_ctrl_union *pptpReq,
 255                  unsigned int reqlen,
 256                  struct nf_conn *ct,
 257                  enum ip_conntrack_info ctinfo)
 258 {
 259         struct nf_ct_pptp_master *info = nfct_help_data(ct);
 260         const struct nf_nat_pptp_hook *hook;
 261         u_int16_t msg;
 262         __be16 cid = 0, pcid = 0;
 263
 264         msg = ntohs(ctlh->messageType);
 265         pr_debug("inbound control message %s\n", pptp_msg_name(msg));
 266
 267         switch (msg) {
 268         case PPTP_START_SESSION_REPLY:
 269                 /* server confirms new control session */
 270                 if (info->sstate < PPTP_SESSION_REQUESTED)
 271                         goto invalid;
 272                 if (pptpReq->srep.resultCode == PPTP_START_OK)
 273                         info->sstate = PPTP_SESSION_CONFIRMED;
 274                 else
 275                         info->sstate = PPTP_SESSION_ERROR;
 276                 break;
 277
 278         case PPTP_STOP_SESSION_REPLY:
 279                 /* server confirms end of control session */
 280                 if (info->sstate > PPTP_SESSION_STOPREQ)
 281                         goto invalid;
 282                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
 283                         info->sstate = PPTP_SESSION_NONE;
 284                 else
 285                         info->sstate = PPTP_SESSION_ERROR;
 286                 break;
 287
 288         case PPTP_OUT_CALL_REPLY:
 289                 /* server accepted call, we now expect GRE frames */
 290                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 291                         goto invalid;
 292                 if (info->cstate != PPTP_CALL_OUT_REQ &&
 293                     info->cstate != PPTP_CALL_OUT_CONF)
 294                         goto invalid;
 295
 296                 cid = pptpReq->ocack.callID;
 297                 pcid = pptpReq->ocack.peersCallID;
 298                 if (info->pns_call_id != pcid)
 299                         goto invalid;
 300                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name(msg),
 301                          ntohs(cid), ntohs(pcid));
 302
 303                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
 304                         info->cstate = PPTP_CALL_OUT_CONF;
 305                         info->pac_call_id = cid;
 306                         exp_gre(ct, cid, pcid);
 307                 } else
 308                         info->cstate = PPTP_CALL_NONE;
 309                 break;
 310
 311         case PPTP_IN_CALL_REQUEST:
 312                 /* server tells us about incoming call request */
 313                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 314                         goto invalid;
 315
 316                 cid = pptpReq->icreq.callID;
 317                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
 318                 info->cstate = PPTP_CALL_IN_REQ;
 319                 info->pac_call_id = cid;
 320                 break;
 321
 322         case PPTP_IN_CALL_CONNECT:
 323                 /* server tells us about incoming call established */
 324                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 325                         goto invalid;
 326                 if (info->cstate != PPTP_CALL_IN_REP &&
 327                     info->cstate != PPTP_CALL_IN_CONF)
 328                         goto invalid;
 329
 330                 pcid = pptpReq->iccon.peersCallID;
 331                 cid = info->pac_call_id;
 332
 333                 if (info->pns_call_id != pcid)
 334                         goto invalid;
 335
 336                 pr_debug("%s, PCID=%X\n", pptp_msg_name(msg), ntohs(pcid));
 337                 info->cstate = PPTP_CALL_IN_CONF;
 338
 339                 /* we expect a GRE connection from PAC to PNS */
 340                 exp_gre(ct, cid, pcid);
 341                 break;
 342
 343         case PPTP_CALL_DISCONNECT_NOTIFY:
 344                 /* server confirms disconnect */
 345                 cid = pptpReq->disc.callID;
 346                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
 347                 info->cstate = PPTP_CALL_NONE;
 348
 349                 /* untrack this call id, unexpect GRE packets */
 350                 pptp_destroy_siblings(ct);
 351                 break;
 352
 353         case PPTP_WAN_ERROR_NOTIFY:
 354         case PPTP_SET_LINK_INFO:
 355         case PPTP_ECHO_REQUEST:
 356         case PPTP_ECHO_REPLY:
 357                 /* I don't have to explain these ;) */
 358                 break;
 359
 360         default:
 361                 goto invalid;
 362         }
 363
 364         hook = rcu_dereference(nf_nat_pptp_hook);
 365         if (hook && ct->status & IPS_NAT_MASK)
 366                 return hook->inbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
 367         return NF_ACCEPT;
 368
 369 invalid:
 370         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 371                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 372                  pptp_msg_name(msg),
 373                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 374                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 375         return NF_ACCEPT;
 376 }
 377
 378 static int
 379 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
 380                   struct PptpControlHeader *ctlh,
 381                   union pptp_ctrl_union *pptpReq,
 382                   unsigned int reqlen,
 383                   struct nf_conn *ct,
 384                   enum ip_conntrack_info ctinfo)
 385 {
 386         struct nf_ct_pptp_master *info = nfct_help_data(ct);
 387         const struct nf_nat_pptp_hook *hook;
 388         u_int16_t msg;
 389         __be16 cid = 0, pcid = 0;
 390
 391         msg = ntohs(ctlh->messageType);
 392         pr_debug("outbound control message %s\n", pptp_msg_name(msg));
 393
 394         switch (msg) {
 395         case PPTP_START_SESSION_REQUEST:
 396                 /* client requests for new control session */
 397                 if (info->sstate != PPTP_SESSION_NONE)
 398                         goto invalid;
 399                 info->sstate = PPTP_SESSION_REQUESTED;
 400                 break;
 401
 402         case PPTP_STOP_SESSION_REQUEST:
 403                 /* client requests end of control session */
 404                 info->sstate = PPTP_SESSION_STOPREQ;
 405                 break;
 406
 407         case PPTP_OUT_CALL_REQUEST:
 408                 /* client initiating connection to server */
 409                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 410                         goto invalid;
 411                 info->cstate = PPTP_CALL_OUT_REQ;
 412                 /* track PNS call id */
 413                 cid = pptpReq->ocreq.callID;
 414                 pr_debug("%s, CID=%X\n", pptp_msg_name(msg), ntohs(cid));
 415                 info->pns_call_id = cid;
 416                 break;
 417
 418         case PPTP_IN_CALL_REPLY:
 419                 /* client answers incoming call */
 420                 if (info->cstate != PPTP_CALL_IN_REQ &&
 421                     info->cstate != PPTP_CALL_IN_REP)
 422                         goto invalid;
 423
 424                 cid = pptpReq->icack.callID;
 425                 pcid = pptpReq->icack.peersCallID;
 426                 if (info->pac_call_id != pcid)
 427                         goto invalid;
 428                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name(msg),
 429                          ntohs(cid), ntohs(pcid));
 430
 431                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
 432                         /* part two of the three-way handshake */
 433                         info->cstate = PPTP_CALL_IN_REP;
 434                         info->pns_call_id = cid;
 435                 } else
 436                         info->cstate = PPTP_CALL_NONE;
 437                 break;
 438
 439         case PPTP_CALL_CLEAR_REQUEST:
 440                 /* client requests hangup of call */
 441                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 442                         goto invalid;
 443                 /* FUTURE: iterate over all calls and check if
 444                  * call ID is valid.  We don't do this without newnat,
 445                  * because we only know about last call */
 446                 info->cstate = PPTP_CALL_CLEAR_REQ;
 447                 break;
 448
 449         case PPTP_SET_LINK_INFO:
 450         case PPTP_ECHO_REQUEST:
 451         case PPTP_ECHO_REPLY:
 452                 /* I don't have to explain these ;) */
 453                 break;
 454
 455         default:
 456                 goto invalid;
 457         }
 458
 459         hook = rcu_dereference(nf_nat_pptp_hook);
 460         if (hook && ct->status & IPS_NAT_MASK)
 461                 return hook->outbound(skb, ct, ctinfo, protoff, ctlh, pptpReq);
 462         return NF_ACCEPT;
 463
 464 invalid:
 465         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 466                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 467                  pptp_msg_name(msg),
 468                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 469                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 470         return NF_ACCEPT;
 471 }
 472
 473 static const unsigned int pptp_msg_size[] = {
 474         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
 475         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
 476         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
 477         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
 478         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
 479         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
 480         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
 481         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
 482         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
 483         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
 484         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
 485         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
 486         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
 487 };
 488
 489 /* track caller id inside control connection, call expect_related */
 490 static int
 491 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
 492                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 493
 494 {
 495         int dir = CTINFO2DIR(ctinfo);
 496         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
 497         const struct tcphdr *tcph;
 498         struct tcphdr _tcph;
 499         const struct pptp_pkt_hdr *pptph;
 500         struct pptp_pkt_hdr _pptph;
 501         struct PptpControlHeader _ctlh, *ctlh;
 502         union pptp_ctrl_union _pptpReq, *pptpReq;
 503         unsigned int tcplen = skb->len - protoff;
 504         unsigned int datalen, reqlen, nexthdr_off;
 505         int oldsstate, oldcstate;
 506         int ret;
 507         u_int16_t msg;
 508
 509 #if IS_ENABLED(CONFIG_NF_NAT)
 510         if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
 511                 struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
 512
 513                 if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
 514                         return NF_DROP;
 515         }
 516 #endif
 517         /* don't do any tracking before tcp handshake complete */
 518         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 519                 return NF_ACCEPT;
 520
 521         nexthdr_off = protoff;
 522         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
 523         if (!tcph)
 524                 return NF_ACCEPT;
 525
 526         nexthdr_off += tcph->doff * 4;
 527         datalen = tcplen - tcph->doff * 4;
 528
 529         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
 530         if (!pptph) {
 531                 pr_debug("no full PPTP header, can't track\n");
 532                 return NF_ACCEPT;
 533         }
 534         nexthdr_off += sizeof(_pptph);
 535         datalen -= sizeof(_pptph);
 536
 537         /* if it's not a control message we can't do anything with it */
 538         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
 539             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
 540                 pr_debug("not a control packet\n");
 541                 return NF_ACCEPT;
 542         }
 543
 544         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
 545         if (!ctlh)
 546                 return NF_ACCEPT;
 547         nexthdr_off += sizeof(_ctlh);
 548         datalen -= sizeof(_ctlh);
 549
 550         reqlen = datalen;
 551         msg = ntohs(ctlh->messageType);
 552         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
 553                 return NF_ACCEPT;
 554         if (reqlen > sizeof(*pptpReq))
 555                 reqlen = sizeof(*pptpReq);
 556
 557         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
 558         if (!pptpReq)
 559                 return NF_ACCEPT;
 560
 561         oldsstate = info->sstate;
 562         oldcstate = info->cstate;
 563
 564         spin_lock_bh(&nf_pptp_lock);
 565
 566         /* FIXME: We just blindly assume that the control connection is always
 567          * established from PNS->PAC.  However, RFC makes no guarantee */
 568         if (dir == IP_CT_DIR_ORIGINAL)
 569                 /* client -> server (PNS -> PAC) */
 570                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 571                                         ctinfo);
 572         else
 573                 /* server -> client (PAC -> PNS) */
 574                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 575                                        ctinfo);
 576         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
 577                  oldsstate, info->sstate, oldcstate, info->cstate);
 578         spin_unlock_bh(&nf_pptp_lock);
 579
 580         return ret;
 581 }
 582
 583 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
 584         .max_expected   = 2,
 585         .timeout        = 5 * 60,
 586 };
 587
 588 /* control protocol helper */
 589 static struct nf_conntrack_helper pptp __read_mostly = {
 590         .name                   = "pptp",
 591         .me                     = THIS_MODULE,
 592         .tuple.src.l3num        = AF_INET,
 593         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
 594         .tuple.dst.protonum     = IPPROTO_TCP,
 595         .help                   = conntrack_pptp_help,
 596         .destroy                = pptp_destroy_siblings,
 597         .expect_policy          = &pptp_exp_policy,
 598 };
 599
 600 static int __init nf_conntrack_pptp_init(void)
 601 {
 602         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
 603
 604         return nf_conntrack_helper_register(&pptp);
 605 }
 606
 607 static void __exit nf_conntrack_pptp_fini(void)
 608 {
 609         nf_conntrack_helper_unregister(&pptp);
 610 }
 611
 612 module_init(nf_conntrack_pptp_init);
 613 module_exit(nf_conntrack_pptp_fini);