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 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 <laforge@gnumonks.org>
  12  *
  13  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  14  *
  15  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  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 <laforge@gnumonks.org>");
  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 int
  49 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
  50                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  51                              unsigned int protoff, struct PptpControlHeader *ctlh,
  52                              union pptp_ctrl_union *pptpReq) __read_mostly;
  53 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
  54
  55 int
  56 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
  57                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  58                             unsigned int protoff, struct PptpControlHeader *ctlh,
  59                             union pptp_ctrl_union *pptpReq) __read_mostly;
  60 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
  61
  62 void
  63 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
  64                             struct nf_conntrack_expect *expect_reply)
  65                             __read_mostly;
  66 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
  67
  68 void
  69 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
  70                              struct nf_conntrack_expect *exp) __read_mostly;
  71 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
  72
  73 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
  74 /* PptpControlMessageType names */
  75 const char *const pptp_msg_name[] = {
  76         "UNKNOWN_MESSAGE",
  77         "START_SESSION_REQUEST",
  78         "START_SESSION_REPLY",
  79         "STOP_SESSION_REQUEST",
  80         "STOP_SESSION_REPLY",
  81         "ECHO_REQUEST",
  82         "ECHO_REPLY",
  83         "OUT_CALL_REQUEST",
  84         "OUT_CALL_REPLY",
  85         "IN_CALL_REQUEST",
  86         "IN_CALL_REPLY",
  87         "IN_CALL_CONNECT",
  88         "CALL_CLEAR_REQUEST",
  89         "CALL_DISCONNECT_NOTIFY",
  90         "WAN_ERROR_NOTIFY",
  91         "SET_LINK_INFO"
  92 };
  93 EXPORT_SYMBOL(pptp_msg_name);
  94 #endif
  95
  96 #define SECS *HZ
  97 #define MINS * 60 SECS
  98 #define HOURS * 60 MINS
  99
 100 #define PPTP_GRE_TIMEOUT                (10 MINS)
 101 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
 102
 103 static void pptp_expectfn(struct nf_conn *ct,
 104                          struct nf_conntrack_expect *exp)
 105 {
 106         struct net *net = nf_ct_net(ct);
 107         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
 108         pr_debug("increasing timeouts\n");
 109
 110         /* increase timeout of GRE data channel conntrack entry */
 111         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
 112         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
 113
 114         /* Can you see how rusty this code is, compared with the pre-2.6.11
 115          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
 116
 117         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
 118         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
 119                 nf_nat_pptp_expectfn(ct, exp);
 120         else {
 121                 struct nf_conntrack_tuple inv_t;
 122                 struct nf_conntrack_expect *exp_other;
 123
 124                 /* obviously this tuple inversion only works until you do NAT */
 125                 nf_ct_invert_tuple(&inv_t, &exp->tuple);
 126                 pr_debug("trying to unexpect other dir: ");
 127                 nf_ct_dump_tuple(&inv_t);
 128
 129                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
 130                 if (exp_other) {
 131                         /* delete other expectation.  */
 132                         pr_debug("found\n");
 133                         nf_ct_unexpect_related(exp_other);
 134                         nf_ct_expect_put(exp_other);
 135                 } else {
 136                         pr_debug("not found\n");
 137                 }
 138         }
 139 }
 140
 141 static int destroy_sibling_or_exp(struct net *net, struct nf_conn *ct,
 142                                   const struct nf_conntrack_tuple *t)
 143 {
 144         const struct nf_conntrack_tuple_hash *h;
 145         const struct nf_conntrack_zone *zone;
 146         struct nf_conntrack_expect *exp;
 147         struct nf_conn *sibling;
 148
 149         pr_debug("trying to timeout ct or exp for tuple ");
 150         nf_ct_dump_tuple(t);
 151
 152         zone = nf_ct_zone(ct);
 153         h = nf_conntrack_find_get(net, zone, t);
 154         if (h)  {
 155                 sibling = nf_ct_tuplehash_to_ctrack(h);
 156                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
 157                 sibling->proto.gre.timeout        = 0;
 158                 sibling->proto.gre.stream_timeout = 0;
 159                 nf_ct_kill(sibling);
 160                 nf_ct_put(sibling);
 161                 return 1;
 162         } else {
 163                 exp = nf_ct_expect_find_get(net, zone, t);
 164                 if (exp) {
 165                         pr_debug("unexpect_related of expect %p\n", exp);
 166                         nf_ct_unexpect_related(exp);
 167                         nf_ct_expect_put(exp);
 168                         return 1;
 169                 }
 170         }
 171         return 0;
 172 }
 173
 174 /* timeout GRE data connections */
 175 static void pptp_destroy_siblings(struct nf_conn *ct)
 176 {
 177         struct net *net = nf_ct_net(ct);
 178         const struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
 179         struct nf_conntrack_tuple t;
 180
 181         nf_ct_gre_keymap_destroy(ct);
 182
 183         /* try original (pns->pac) tuple */
 184         memcpy(&t, &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, sizeof(t));
 185         t.dst.protonum = IPPROTO_GRE;
 186         t.src.u.gre.key = ct_pptp_info->pns_call_id;
 187         t.dst.u.gre.key = ct_pptp_info->pac_call_id;
 188         if (!destroy_sibling_or_exp(net, ct, &t))
 189                 pr_debug("failed to timeout original pns->pac ct/exp\n");
 190
 191         /* try reply (pac->pns) tuple */
 192         memcpy(&t, &ct->tuplehash[IP_CT_DIR_REPLY].tuple, sizeof(t));
 193         t.dst.protonum = IPPROTO_GRE;
 194         t.src.u.gre.key = ct_pptp_info->pac_call_id;
 195         t.dst.u.gre.key = ct_pptp_info->pns_call_id;
 196         if (!destroy_sibling_or_exp(net, ct, &t))
 197                 pr_debug("failed to timeout reply pac->pns ct/exp\n");
 198 }
 199
 200 /* expect GRE connections (PNS->PAC and PAC->PNS direction) */
 201 static int exp_gre(struct nf_conn *ct, __be16 callid, __be16 peer_callid)
 202 {
 203         struct nf_conntrack_expect *exp_orig, *exp_reply;
 204         enum ip_conntrack_dir dir;
 205         int ret = 1;
 206         typeof(nf_nat_pptp_hook_exp_gre) nf_nat_pptp_exp_gre;
 207
 208         exp_orig = nf_ct_expect_alloc(ct);
 209         if (exp_orig == NULL)
 210                 goto out;
 211
 212         exp_reply = nf_ct_expect_alloc(ct);
 213         if (exp_reply == NULL)
 214                 goto out_put_orig;
 215
 216         /* original direction, PNS->PAC */
 217         dir = IP_CT_DIR_ORIGINAL;
 218         nf_ct_expect_init(exp_orig, NF_CT_EXPECT_CLASS_DEFAULT,
 219                           nf_ct_l3num(ct),
 220                           &ct->tuplehash[dir].tuple.src.u3,
 221                           &ct->tuplehash[dir].tuple.dst.u3,
 222                           IPPROTO_GRE, &peer_callid, &callid);
 223         exp_orig->expectfn = pptp_expectfn;
 224
 225         /* reply direction, PAC->PNS */
 226         dir = IP_CT_DIR_REPLY;
 227         nf_ct_expect_init(exp_reply, NF_CT_EXPECT_CLASS_DEFAULT,
 228                           nf_ct_l3num(ct),
 229                           &ct->tuplehash[dir].tuple.src.u3,
 230                           &ct->tuplehash[dir].tuple.dst.u3,
 231                           IPPROTO_GRE, &callid, &peer_callid);
 232         exp_reply->expectfn = pptp_expectfn;
 233
 234         nf_nat_pptp_exp_gre = rcu_dereference(nf_nat_pptp_hook_exp_gre);
 235         if (nf_nat_pptp_exp_gre && ct->status & IPS_NAT_MASK)
 236                 nf_nat_pptp_exp_gre(exp_orig, exp_reply);
 237         if (nf_ct_expect_related(exp_orig) != 0)
 238                 goto out_put_both;
 239         if (nf_ct_expect_related(exp_reply) != 0)
 240                 goto out_unexpect_orig;
 241
 242         /* Add GRE keymap entries */
 243         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_ORIGINAL, &exp_orig->tuple) != 0)
 244                 goto out_unexpect_both;
 245         if (nf_ct_gre_keymap_add(ct, IP_CT_DIR_REPLY, &exp_reply->tuple) != 0) {
 246                 nf_ct_gre_keymap_destroy(ct);
 247                 goto out_unexpect_both;
 248         }
 249         ret = 0;
 250
 251 out_put_both:
 252         nf_ct_expect_put(exp_reply);
 253 out_put_orig:
 254         nf_ct_expect_put(exp_orig);
 255 out:
 256         return ret;
 257
 258 out_unexpect_both:
 259         nf_ct_unexpect_related(exp_reply);
 260 out_unexpect_orig:
 261         nf_ct_unexpect_related(exp_orig);
 262         goto out_put_both;
 263 }
 264
 265 static int
 266 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
 267                  struct PptpControlHeader *ctlh,
 268                  union pptp_ctrl_union *pptpReq,
 269                  unsigned int reqlen,
 270                  struct nf_conn *ct,
 271                  enum ip_conntrack_info ctinfo)
 272 {
 273         struct nf_ct_pptp_master *info = nfct_help_data(ct);
 274         u_int16_t msg;
 275         __be16 cid = 0, pcid = 0;
 276         typeof(nf_nat_pptp_hook_inbound) nf_nat_pptp_inbound;
 277
 278         msg = ntohs(ctlh->messageType);
 279         pr_debug("inbound control message %s\n", pptp_msg_name[msg]);
 280
 281         switch (msg) {
 282         case PPTP_START_SESSION_REPLY:
 283                 /* server confirms new control session */
 284                 if (info->sstate < PPTP_SESSION_REQUESTED)
 285                         goto invalid;
 286                 if (pptpReq->srep.resultCode == PPTP_START_OK)
 287                         info->sstate = PPTP_SESSION_CONFIRMED;
 288                 else
 289                         info->sstate = PPTP_SESSION_ERROR;
 290                 break;
 291
 292         case PPTP_STOP_SESSION_REPLY:
 293                 /* server confirms end of control session */
 294                 if (info->sstate > PPTP_SESSION_STOPREQ)
 295                         goto invalid;
 296                 if (pptpReq->strep.resultCode == PPTP_STOP_OK)
 297                         info->sstate = PPTP_SESSION_NONE;
 298                 else
 299                         info->sstate = PPTP_SESSION_ERROR;
 300                 break;
 301
 302         case PPTP_OUT_CALL_REPLY:
 303                 /* server accepted call, we now expect GRE frames */
 304                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 305                         goto invalid;
 306                 if (info->cstate != PPTP_CALL_OUT_REQ &&
 307                     info->cstate != PPTP_CALL_OUT_CONF)
 308                         goto invalid;
 309
 310                 cid = pptpReq->ocack.callID;
 311                 pcid = pptpReq->ocack.peersCallID;
 312                 if (info->pns_call_id != pcid)
 313                         goto invalid;
 314                 pr_debug("%s, CID=%X, PCID=%X\n", pptp_msg_name[msg],
 315                          ntohs(cid), ntohs(pcid));
 316
 317                 if (pptpReq->ocack.resultCode == PPTP_OUTCALL_CONNECT) {
 318                         info->cstate = PPTP_CALL_OUT_CONF;
 319                         info->pac_call_id = cid;
 320                         exp_gre(ct, cid, pcid);
 321                 } else
 322                         info->cstate = PPTP_CALL_NONE;
 323                 break;
 324
 325         case PPTP_IN_CALL_REQUEST:
 326                 /* server tells us about incoming call request */
 327                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 328                         goto invalid;
 329
 330                 cid = pptpReq->icreq.callID;
 331                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 332                 info->cstate = PPTP_CALL_IN_REQ;
 333                 info->pac_call_id = cid;
 334                 break;
 335
 336         case PPTP_IN_CALL_CONNECT:
 337                 /* server tells us about incoming call established */
 338                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 339                         goto invalid;
 340                 if (info->cstate != PPTP_CALL_IN_REP &&
 341                     info->cstate != PPTP_CALL_IN_CONF)
 342                         goto invalid;
 343
 344                 pcid = pptpReq->iccon.peersCallID;
 345                 cid = info->pac_call_id;
 346
 347                 if (info->pns_call_id != pcid)
 348                         goto invalid;
 349
 350                 pr_debug("%s, PCID=%X\n", pptp_msg_name[msg], ntohs(pcid));
 351                 info->cstate = PPTP_CALL_IN_CONF;
 352
 353                 /* we expect a GRE connection from PAC to PNS */
 354                 exp_gre(ct, cid, pcid);
 355                 break;
 356
 357         case PPTP_CALL_DISCONNECT_NOTIFY:
 358                 /* server confirms disconnect */
 359                 cid = pptpReq->disc.callID;
 360                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 361                 info->cstate = PPTP_CALL_NONE;
 362
 363                 /* untrack this call id, unexpect GRE packets */
 364                 pptp_destroy_siblings(ct);
 365                 break;
 366
 367         case PPTP_WAN_ERROR_NOTIFY:
 368         case PPTP_SET_LINK_INFO:
 369         case PPTP_ECHO_REQUEST:
 370         case PPTP_ECHO_REPLY:
 371                 /* I don't have to explain these ;) */
 372                 break;
 373
 374         default:
 375                 goto invalid;
 376         }
 377
 378         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
 379         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
 380                 return nf_nat_pptp_inbound(skb, ct, ctinfo,
 381                                            protoff, ctlh, pptpReq);
 382         return NF_ACCEPT;
 383
 384 invalid:
 385         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 386                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 387                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 388                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 389                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 390         return NF_ACCEPT;
 391 }
 392
 393 static int
 394 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
 395                   struct PptpControlHeader *ctlh,
 396                   union pptp_ctrl_union *pptpReq,
 397                   unsigned int reqlen,
 398                   struct nf_conn *ct,
 399                   enum ip_conntrack_info ctinfo)
 400 {
 401         struct nf_ct_pptp_master *info = nfct_help_data(ct);
 402         u_int16_t msg;
 403         __be16 cid = 0, pcid = 0;
 404         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
 405
 406         msg = ntohs(ctlh->messageType);
 407         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
 408
 409         switch (msg) {
 410         case PPTP_START_SESSION_REQUEST:
 411                 /* client requests for new control session */
 412                 if (info->sstate != PPTP_SESSION_NONE)
 413                         goto invalid;
 414                 info->sstate = PPTP_SESSION_REQUESTED;
 415                 break;
 416
 417         case PPTP_STOP_SESSION_REQUEST:
 418                 /* client requests end of control session */
 419                 info->sstate = PPTP_SESSION_STOPREQ;
 420                 break;
 421
 422         case PPTP_OUT_CALL_REQUEST:
 423                 /* client initiating connection to server */
 424                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 425                         goto invalid;
 426                 info->cstate = PPTP_CALL_OUT_REQ;
 427                 /* track PNS call id */
 428                 cid = pptpReq->ocreq.callID;
 429                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 430                 info->pns_call_id = cid;
 431                 break;
 432
 433         case PPTP_IN_CALL_REPLY:
 434                 /* client answers incoming call */
 435                 if (info->cstate != PPTP_CALL_IN_REQ &&
 436                     info->cstate != PPTP_CALL_IN_REP)
 437                         goto invalid;
 438
 439                 cid = pptpReq->icack.callID;
 440                 pcid = pptpReq->icack.peersCallID;
 441                 if (info->pac_call_id != pcid)
 442                         goto invalid;
 443                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
 444                          ntohs(cid), ntohs(pcid));
 445
 446                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
 447                         /* part two of the three-way handshake */
 448                         info->cstate = PPTP_CALL_IN_REP;
 449                         info->pns_call_id = cid;
 450                 } else
 451                         info->cstate = PPTP_CALL_NONE;
 452                 break;
 453
 454         case PPTP_CALL_CLEAR_REQUEST:
 455                 /* client requests hangup of call */
 456                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 457                         goto invalid;
 458                 /* FUTURE: iterate over all calls and check if
 459                  * call ID is valid.  We don't do this without newnat,
 460                  * because we only know about last call */
 461                 info->cstate = PPTP_CALL_CLEAR_REQ;
 462                 break;
 463
 464         case PPTP_SET_LINK_INFO:
 465         case PPTP_ECHO_REQUEST:
 466         case PPTP_ECHO_REPLY:
 467                 /* I don't have to explain these ;) */
 468                 break;
 469
 470         default:
 471                 goto invalid;
 472         }
 473
 474         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
 475         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
 476                 return nf_nat_pptp_outbound(skb, ct, ctinfo,
 477                                             protoff, ctlh, pptpReq);
 478         return NF_ACCEPT;
 479
 480 invalid:
 481         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 482                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 483                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 484                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 485                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 486         return NF_ACCEPT;
 487 }
 488
 489 static const unsigned int pptp_msg_size[] = {
 490         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
 491         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
 492         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
 493         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
 494         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
 495         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
 496         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
 497         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
 498         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
 499         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
 500         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
 501         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
 502         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
 503 };
 504
 505 /* track caller id inside control connection, call expect_related */
 506 static int
 507 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
 508                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 509
 510 {
 511         int dir = CTINFO2DIR(ctinfo);
 512         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
 513         const struct tcphdr *tcph;
 514         struct tcphdr _tcph;
 515         const struct pptp_pkt_hdr *pptph;
 516         struct pptp_pkt_hdr _pptph;
 517         struct PptpControlHeader _ctlh, *ctlh;
 518         union pptp_ctrl_union _pptpReq, *pptpReq;
 519         unsigned int tcplen = skb->len - protoff;
 520         unsigned int datalen, reqlen, nexthdr_off;
 521         int oldsstate, oldcstate;
 522         int ret;
 523         u_int16_t msg;
 524
 525 #if IS_ENABLED(CONFIG_NF_NAT)
 526         if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
 527                 struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
 528
 529                 if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
 530                         return NF_DROP;
 531         }
 532 #endif
 533         /* don't do any tracking before tcp handshake complete */
 534         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 535                 return NF_ACCEPT;
 536
 537         nexthdr_off = protoff;
 538         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
 539         BUG_ON(!tcph);
 540         nexthdr_off += tcph->doff * 4;
 541         datalen = tcplen - tcph->doff * 4;
 542
 543         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
 544         if (!pptph) {
 545                 pr_debug("no full PPTP header, can't track\n");
 546                 return NF_ACCEPT;
 547         }
 548         nexthdr_off += sizeof(_pptph);
 549         datalen -= sizeof(_pptph);
 550
 551         /* if it's not a control message we can't do anything with it */
 552         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
 553             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
 554                 pr_debug("not a control packet\n");
 555                 return NF_ACCEPT;
 556         }
 557
 558         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
 559         if (!ctlh)
 560                 return NF_ACCEPT;
 561         nexthdr_off += sizeof(_ctlh);
 562         datalen -= sizeof(_ctlh);
 563
 564         reqlen = datalen;
 565         msg = ntohs(ctlh->messageType);
 566         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
 567                 return NF_ACCEPT;
 568         if (reqlen > sizeof(*pptpReq))
 569                 reqlen = sizeof(*pptpReq);
 570
 571         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
 572         if (!pptpReq)
 573                 return NF_ACCEPT;
 574
 575         oldsstate = info->sstate;
 576         oldcstate = info->cstate;
 577
 578         spin_lock_bh(&nf_pptp_lock);
 579
 580         /* FIXME: We just blindly assume that the control connection is always
 581          * established from PNS->PAC.  However, RFC makes no guarantee */
 582         if (dir == IP_CT_DIR_ORIGINAL)
 583                 /* client -> server (PNS -> PAC) */
 584                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 585                                         ctinfo);
 586         else
 587                 /* server -> client (PAC -> PNS) */
 588                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 589                                        ctinfo);
 590         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
 591                  oldsstate, info->sstate, oldcstate, info->cstate);
 592         spin_unlock_bh(&nf_pptp_lock);
 593
 594         return ret;
 595 }
 596
 597 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
 598         .max_expected   = 2,
 599         .timeout        = 5 * 60,
 600 };
 601
 602 /* control protocol helper */
 603 static struct nf_conntrack_helper pptp __read_mostly = {
 604         .name                   = "pptp",
 605         .me                     = THIS_MODULE,
 606         .tuple.src.l3num        = AF_INET,
 607         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
 608         .tuple.dst.protonum     = IPPROTO_TCP,
 609         .help                   = conntrack_pptp_help,
 610         .destroy                = pptp_destroy_siblings,
 611         .expect_policy          = &pptp_exp_policy,
 612 };
 613
 614 static int __init nf_conntrack_pptp_init(void)
 615 {
 616         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
 617
 618         return nf_conntrack_helper_register(&pptp);
 619 }
 620
 621 static void __exit nf_conntrack_pptp_fini(void)
 622 {
 623         nf_conntrack_helper_unregister(&pptp);
 624 }
 625
 626 module_init(nf_conntrack_pptp_init);
 627 module_exit(nf_conntrack_pptp_fini);