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  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  15  *
  16  * Limitations:
  17  *       - We blindly assume that control connections are always
  18  *         established in PNS->PAC direction.  This is a violation
  19  *         of RFC 2637
  20  *       - We can only support one single call within each session
  21  * TODO:
  22  *       - testing of incoming PPTP calls
  23  */
  24
  25 #include <linux/module.h>
  26 #include <linux/skbuff.h>
  27 #include <linux/in.h>
  28 #include <linux/tcp.h>
  29
  30 #include <net/netfilter/nf_conntrack.h>
  31 #include <net/netfilter/nf_conntrack_core.h>
  32 #include <net/netfilter/nf_conntrack_helper.h>
  33 #include <net/netfilter/nf_conntrack_zones.h>
  34 #include <linux/netfilter/nf_conntrack_proto_gre.h>
  35 #include <linux/netfilter/nf_conntrack_pptp.h>
  36
  37 #define NF_CT_PPTP_VERSION "3.1"
  38
  39 MODULE_LICENSE("GPL");
  40 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  41 MODULE_DESCRIPTION("Netfilter connection tracking helper module for PPTP");
  42 MODULE_ALIAS("ip_conntrack_pptp");
  43 MODULE_ALIAS_NFCT_HELPER("pptp");
  44
  45 static DEFINE_SPINLOCK(nf_pptp_lock);
  46
  47 int
  48 (*nf_nat_pptp_hook_outbound)(struct sk_buff *skb,
  49                              struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  50                              unsigned int protoff, struct PptpControlHeader *ctlh,
  51                              union pptp_ctrl_union *pptpReq) __read_mostly;
  52 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_outbound);
  53
  54 int
  55 (*nf_nat_pptp_hook_inbound)(struct sk_buff *skb,
  56                             struct nf_conn *ct, enum ip_conntrack_info ctinfo,
  57                             unsigned int protoff, struct PptpControlHeader *ctlh,
  58                             union pptp_ctrl_union *pptpReq) __read_mostly;
  59 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_inbound);
  60
  61 void
  62 (*nf_nat_pptp_hook_exp_gre)(struct nf_conntrack_expect *expect_orig,
  63                             struct nf_conntrack_expect *expect_reply)
  64                             __read_mostly;
  65 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_exp_gre);
  66
  67 void
  68 (*nf_nat_pptp_hook_expectfn)(struct nf_conn *ct,
  69                              struct nf_conntrack_expect *exp) __read_mostly;
  70 EXPORT_SYMBOL_GPL(nf_nat_pptp_hook_expectfn);
  71
  72 #if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)
  73 /* PptpControlMessageType names */
  74 const char *const pptp_msg_name[] = {
  75         "UNKNOWN_MESSAGE",
  76         "START_SESSION_REQUEST",
  77         "START_SESSION_REPLY",
  78         "STOP_SESSION_REQUEST",
  79         "STOP_SESSION_REPLY",
  80         "ECHO_REQUEST",
  81         "ECHO_REPLY",
  82         "OUT_CALL_REQUEST",
  83         "OUT_CALL_REPLY",
  84         "IN_CALL_REQUEST",
  85         "IN_CALL_REPLY",
  86         "IN_CALL_CONNECT",
  87         "CALL_CLEAR_REQUEST",
  88         "CALL_DISCONNECT_NOTIFY",
  89         "WAN_ERROR_NOTIFY",
  90         "SET_LINK_INFO"
  91 };
  92 EXPORT_SYMBOL(pptp_msg_name);
  93 #endif
  94
  95 #define SECS *HZ
  96 #define MINS * 60 SECS
  97 #define HOURS * 60 MINS
  98
  99 #define PPTP_GRE_TIMEOUT                (10 MINS)
 100 #define PPTP_GRE_STREAM_TIMEOUT         (5 HOURS)
 101
 102 static void pptp_expectfn(struct nf_conn *ct,
 103                          struct nf_conntrack_expect *exp)
 104 {
 105         struct net *net = nf_ct_net(ct);
 106         typeof(nf_nat_pptp_hook_expectfn) nf_nat_pptp_expectfn;
 107         pr_debug("increasing timeouts\n");
 108
 109         /* increase timeout of GRE data channel conntrack entry */
 110         ct->proto.gre.timeout        = PPTP_GRE_TIMEOUT;
 111         ct->proto.gre.stream_timeout = PPTP_GRE_STREAM_TIMEOUT;
 112
 113         /* Can you see how rusty this code is, compared with the pre-2.6.11
 114          * one? That's what happened to my shiny newnat of 2002 ;( -HW */
 115
 116         nf_nat_pptp_expectfn = rcu_dereference(nf_nat_pptp_hook_expectfn);
 117         if (nf_nat_pptp_expectfn && ct->master->status & IPS_NAT_MASK)
 118                 nf_nat_pptp_expectfn(ct, exp);
 119         else {
 120                 struct nf_conntrack_tuple inv_t;
 121                 struct nf_conntrack_expect *exp_other;
 122
 123                 /* obviously this tuple inversion only works until you do NAT */
 124                 nf_ct_invert_tuplepr(&inv_t, &exp->tuple);
 125                 pr_debug("trying to unexpect other dir: ");
 126                 nf_ct_dump_tuple(&inv_t);
 127
 128                 exp_other = nf_ct_expect_find_get(net, nf_ct_zone(ct), &inv_t);
 129                 if (exp_other) {
 130                         /* delete other expectation.  */
 131                         pr_debug("found\n");
 132                         nf_ct_unexpect_related(exp_other);
 133                         nf_ct_expect_put(exp_other);
 134                 } else {
 135                         pr_debug("not found\n");
 136                 }
 137         }
 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         const struct nf_conntrack_zone *zone;
 145         struct nf_conntrack_expect *exp;
 146         struct nf_conn *sibling;
 147
 148         pr_debug("trying to timeout ct or exp for tuple ");
 149         nf_ct_dump_tuple(t);
 150
 151         zone = nf_ct_zone(ct);
 152         h = nf_conntrack_find_get(net, zone, t);
 153         if (h)  {
 154                 sibling = nf_ct_tuplehash_to_ctrack(h);
 155                 pr_debug("setting timeout of conntrack %p to 0\n", sibling);
 156                 sibling->proto.gre.timeout        = 0;
 157                 sibling->proto.gre.stream_timeout = 0;
 158                 nf_ct_kill(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_ct_pptp_master *ct_pptp_info = nfct_help_data(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 = ct_pptp_info->pns_call_id;
 186         t.dst.u.gre.key = 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 = ct_pptp_info->pac_call_id;
 194         t.dst.u.gre.key = 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 int
 265 pptp_inbound_pkt(struct sk_buff *skb, unsigned int protoff,
 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_data(ct);
 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_SET_LINK_INFO:
 368         case PPTP_ECHO_REQUEST:
 369         case PPTP_ECHO_REPLY:
 370                 /* I don't have to explain these ;) */
 371                 break;
 372
 373         default:
 374                 goto invalid;
 375         }
 376
 377         nf_nat_pptp_inbound = rcu_dereference(nf_nat_pptp_hook_inbound);
 378         if (nf_nat_pptp_inbound && ct->status & IPS_NAT_MASK)
 379                 return nf_nat_pptp_inbound(skb, ct, ctinfo,
 380                                            protoff, ctlh, pptpReq);
 381         return NF_ACCEPT;
 382
 383 invalid:
 384         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 385                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 386                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 387                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 388                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 389         return NF_ACCEPT;
 390 }
 391
 392 static int
 393 pptp_outbound_pkt(struct sk_buff *skb, unsigned int protoff,
 394                   struct PptpControlHeader *ctlh,
 395                   union pptp_ctrl_union *pptpReq,
 396                   unsigned int reqlen,
 397                   struct nf_conn *ct,
 398                   enum ip_conntrack_info ctinfo)
 399 {
 400         struct nf_ct_pptp_master *info = nfct_help_data(ct);
 401         u_int16_t msg;
 402         __be16 cid = 0, pcid = 0;
 403         typeof(nf_nat_pptp_hook_outbound) nf_nat_pptp_outbound;
 404
 405         msg = ntohs(ctlh->messageType);
 406         pr_debug("outbound control message %s\n", pptp_msg_name[msg]);
 407
 408         switch (msg) {
 409         case PPTP_START_SESSION_REQUEST:
 410                 /* client requests for new control session */
 411                 if (info->sstate != PPTP_SESSION_NONE)
 412                         goto invalid;
 413                 info->sstate = PPTP_SESSION_REQUESTED;
 414                 break;
 415
 416         case PPTP_STOP_SESSION_REQUEST:
 417                 /* client requests end of control session */
 418                 info->sstate = PPTP_SESSION_STOPREQ;
 419                 break;
 420
 421         case PPTP_OUT_CALL_REQUEST:
 422                 /* client initiating connection to server */
 423                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 424                         goto invalid;
 425                 info->cstate = PPTP_CALL_OUT_REQ;
 426                 /* track PNS call id */
 427                 cid = pptpReq->ocreq.callID;
 428                 pr_debug("%s, CID=%X\n", pptp_msg_name[msg], ntohs(cid));
 429                 info->pns_call_id = cid;
 430                 break;
 431
 432         case PPTP_IN_CALL_REPLY:
 433                 /* client answers incoming call */
 434                 if (info->cstate != PPTP_CALL_IN_REQ &&
 435                     info->cstate != PPTP_CALL_IN_REP)
 436                         goto invalid;
 437
 438                 cid = pptpReq->icack.callID;
 439                 pcid = pptpReq->icack.peersCallID;
 440                 if (info->pac_call_id != pcid)
 441                         goto invalid;
 442                 pr_debug("%s, CID=%X PCID=%X\n", pptp_msg_name[msg],
 443                          ntohs(cid), ntohs(pcid));
 444
 445                 if (pptpReq->icack.resultCode == PPTP_INCALL_ACCEPT) {
 446                         /* part two of the three-way handshake */
 447                         info->cstate = PPTP_CALL_IN_REP;
 448                         info->pns_call_id = cid;
 449                 } else
 450                         info->cstate = PPTP_CALL_NONE;
 451                 break;
 452
 453         case PPTP_CALL_CLEAR_REQUEST:
 454                 /* client requests hangup of call */
 455                 if (info->sstate != PPTP_SESSION_CONFIRMED)
 456                         goto invalid;
 457                 /* FUTURE: iterate over all calls and check if
 458                  * call ID is valid.  We don't do this without newnat,
 459                  * because we only know about last call */
 460                 info->cstate = PPTP_CALL_CLEAR_REQ;
 461                 break;
 462
 463         case PPTP_SET_LINK_INFO:
 464         case PPTP_ECHO_REQUEST:
 465         case PPTP_ECHO_REPLY:
 466                 /* I don't have to explain these ;) */
 467                 break;
 468
 469         default:
 470                 goto invalid;
 471         }
 472
 473         nf_nat_pptp_outbound = rcu_dereference(nf_nat_pptp_hook_outbound);
 474         if (nf_nat_pptp_outbound && ct->status & IPS_NAT_MASK)
 475                 return nf_nat_pptp_outbound(skb, ct, ctinfo,
 476                                             protoff, ctlh, pptpReq);
 477         return NF_ACCEPT;
 478
 479 invalid:
 480         pr_debug("invalid %s: type=%d cid=%u pcid=%u "
 481                  "cstate=%d sstate=%d pns_cid=%u pac_cid=%u\n",
 482                  msg <= PPTP_MSG_MAX ? pptp_msg_name[msg] : pptp_msg_name[0],
 483                  msg, ntohs(cid), ntohs(pcid),  info->cstate, info->sstate,
 484                  ntohs(info->pns_call_id), ntohs(info->pac_call_id));
 485         return NF_ACCEPT;
 486 }
 487
 488 static const unsigned int pptp_msg_size[] = {
 489         [PPTP_START_SESSION_REQUEST]  = sizeof(struct PptpStartSessionRequest),
 490         [PPTP_START_SESSION_REPLY]    = sizeof(struct PptpStartSessionReply),
 491         [PPTP_STOP_SESSION_REQUEST]   = sizeof(struct PptpStopSessionRequest),
 492         [PPTP_STOP_SESSION_REPLY]     = sizeof(struct PptpStopSessionReply),
 493         [PPTP_OUT_CALL_REQUEST]       = sizeof(struct PptpOutCallRequest),
 494         [PPTP_OUT_CALL_REPLY]         = sizeof(struct PptpOutCallReply),
 495         [PPTP_IN_CALL_REQUEST]        = sizeof(struct PptpInCallRequest),
 496         [PPTP_IN_CALL_REPLY]          = sizeof(struct PptpInCallReply),
 497         [PPTP_IN_CALL_CONNECT]        = sizeof(struct PptpInCallConnected),
 498         [PPTP_CALL_CLEAR_REQUEST]     = sizeof(struct PptpClearCallRequest),
 499         [PPTP_CALL_DISCONNECT_NOTIFY] = sizeof(struct PptpCallDisconnectNotify),
 500         [PPTP_WAN_ERROR_NOTIFY]       = sizeof(struct PptpWanErrorNotify),
 501         [PPTP_SET_LINK_INFO]          = sizeof(struct PptpSetLinkInfo),
 502 };
 503
 504 /* track caller id inside control connection, call expect_related */
 505 static int
 506 conntrack_pptp_help(struct sk_buff *skb, unsigned int protoff,
 507                     struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 508
 509 {
 510         int dir = CTINFO2DIR(ctinfo);
 511         const struct nf_ct_pptp_master *info = nfct_help_data(ct);
 512         const struct tcphdr *tcph;
 513         struct tcphdr _tcph;
 514         const struct pptp_pkt_hdr *pptph;
 515         struct pptp_pkt_hdr _pptph;
 516         struct PptpControlHeader _ctlh, *ctlh;
 517         union pptp_ctrl_union _pptpReq, *pptpReq;
 518         unsigned int tcplen = skb->len - protoff;
 519         unsigned int datalen, reqlen, nexthdr_off;
 520         int oldsstate, oldcstate;
 521         int ret;
 522         u_int16_t msg;
 523
 524 #if IS_ENABLED(CONFIG_NF_NAT)
 525         if (!nf_ct_is_confirmed(ct) && (ct->status & IPS_NAT_MASK)) {
 526                 struct nf_conn_nat *nat = nf_ct_ext_find(ct, NF_CT_EXT_NAT);
 527
 528                 if (!nat && !nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC))
 529                         return NF_DROP;
 530         }
 531 #endif
 532         /* don't do any tracking before tcp handshake complete */
 533         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 534                 return NF_ACCEPT;
 535
 536         nexthdr_off = protoff;
 537         tcph = skb_header_pointer(skb, nexthdr_off, sizeof(_tcph), &_tcph);
 538         BUG_ON(!tcph);
 539         nexthdr_off += tcph->doff * 4;
 540         datalen = tcplen - tcph->doff * 4;
 541
 542         pptph = skb_header_pointer(skb, nexthdr_off, sizeof(_pptph), &_pptph);
 543         if (!pptph) {
 544                 pr_debug("no full PPTP header, can't track\n");
 545                 return NF_ACCEPT;
 546         }
 547         nexthdr_off += sizeof(_pptph);
 548         datalen -= sizeof(_pptph);
 549
 550         /* if it's not a control message we can't do anything with it */
 551         if (ntohs(pptph->packetType) != PPTP_PACKET_CONTROL ||
 552             ntohl(pptph->magicCookie) != PPTP_MAGIC_COOKIE) {
 553                 pr_debug("not a control packet\n");
 554                 return NF_ACCEPT;
 555         }
 556
 557         ctlh = skb_header_pointer(skb, nexthdr_off, sizeof(_ctlh), &_ctlh);
 558         if (!ctlh)
 559                 return NF_ACCEPT;
 560         nexthdr_off += sizeof(_ctlh);
 561         datalen -= sizeof(_ctlh);
 562
 563         reqlen = datalen;
 564         msg = ntohs(ctlh->messageType);
 565         if (msg > 0 && msg <= PPTP_MSG_MAX && reqlen < pptp_msg_size[msg])
 566                 return NF_ACCEPT;
 567         if (reqlen > sizeof(*pptpReq))
 568                 reqlen = sizeof(*pptpReq);
 569
 570         pptpReq = skb_header_pointer(skb, nexthdr_off, reqlen, &_pptpReq);
 571         if (!pptpReq)
 572                 return NF_ACCEPT;
 573
 574         oldsstate = info->sstate;
 575         oldcstate = info->cstate;
 576
 577         spin_lock_bh(&nf_pptp_lock);
 578
 579         /* FIXME: We just blindly assume that the control connection is always
 580          * established from PNS->PAC.  However, RFC makes no guarantee */
 581         if (dir == IP_CT_DIR_ORIGINAL)
 582                 /* client -> server (PNS -> PAC) */
 583                 ret = pptp_outbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 584                                         ctinfo);
 585         else
 586                 /* server -> client (PAC -> PNS) */
 587                 ret = pptp_inbound_pkt(skb, protoff, ctlh, pptpReq, reqlen, ct,
 588                                        ctinfo);
 589         pr_debug("sstate: %d->%d, cstate: %d->%d\n",
 590                  oldsstate, info->sstate, oldcstate, info->cstate);
 591         spin_unlock_bh(&nf_pptp_lock);
 592
 593         return ret;
 594 }
 595
 596 static const struct nf_conntrack_expect_policy pptp_exp_policy = {
 597         .max_expected   = 2,
 598         .timeout        = 5 * 60,
 599 };
 600
 601 /* control protocol helper */
 602 static struct nf_conntrack_helper pptp __read_mostly = {
 603         .name                   = "pptp",
 604         .me                     = THIS_MODULE,
 605         .tuple.src.l3num        = AF_INET,
 606         .tuple.src.u.tcp.port   = cpu_to_be16(PPTP_CONTROL_PORT),
 607         .tuple.dst.protonum     = IPPROTO_TCP,
 608         .help                   = conntrack_pptp_help,
 609         .destroy                = pptp_destroy_siblings,
 610         .expect_policy          = &pptp_exp_policy,
 611 };
 612
 613 static int __init nf_conntrack_pptp_init(void)
 614 {
 615         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_pptp_master));
 616
 617         return nf_conntrack_helper_register(&pptp);
 618 }
 619
 620 static void __exit nf_conntrack_pptp_fini(void)
 621 {
 622         nf_conntrack_helper_unregister(&pptp);
 623 }
 624
 625 module_init(nf_conntrack_pptp_init);
 626 module_exit(nf_conntrack_pptp_fini);