net/ipv4/netfilter/nf_nat_sip.c

   1 /* SIP extension for NAT alteration.
   2  *
   3  * (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
   4  * based on RR's ip_nat_ftp.c and other modules.
   5  * (C) 2007 United Security Providers
   6  * (C) 2007, 2008 Patrick McHardy <kaber@trash.net>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/ip.h>
  16 #include <net/ip.h>
  17 #include <linux/udp.h>
  18 #include <linux/tcp.h>
  19
  20 #include <net/netfilter/nf_nat.h>
  21 #include <net/netfilter/nf_nat_helper.h>
  22 #include <net/netfilter/nf_nat_rule.h>
  23 #include <net/netfilter/nf_conntrack_helper.h>
  24 #include <net/netfilter/nf_conntrack_expect.h>
  25 #include <linux/netfilter/nf_conntrack_sip.h>
  26
  27 MODULE_LICENSE("GPL");
  28 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  29 MODULE_DESCRIPTION("SIP NAT helper");
  30 MODULE_ALIAS("ip_nat_sip");
  31
  32
  33 static unsigned int mangle_packet(struct sk_buff *skb, unsigned int dataoff,
  34                                   const char **dptr, unsigned int *datalen,
  35                                   unsigned int matchoff, unsigned int matchlen,
  36                                   const char *buffer, unsigned int buflen)
  37 {
  38         enum ip_conntrack_info ctinfo;
  39         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  40         struct tcphdr *th;
  41         unsigned int baseoff;
  42
  43         if (nf_ct_protonum(ct) == IPPROTO_TCP) {
  44                 th = (struct tcphdr *)(skb->data + ip_hdrlen(skb));
  45                 baseoff = ip_hdrlen(skb) + th->doff * 4;
  46                 matchoff += dataoff - baseoff;
  47
  48                 if (!__nf_nat_mangle_tcp_packet(skb, ct, ctinfo,
  49                                                 matchoff, matchlen,
  50                                                 buffer, buflen, false))
  51                         return 0;
  52         } else {
  53                 baseoff = ip_hdrlen(skb) + sizeof(struct udphdr);
  54                 matchoff += dataoff - baseoff;
  55
  56                 if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo,
  57                                               matchoff, matchlen,
  58                                               buffer, buflen))
  59                         return 0;
  60         }
  61
  62         /* Reload data pointer and adjust datalen value */
  63         *dptr = skb->data + dataoff;
  64         *datalen += buflen - matchlen;
  65         return 1;
  66 }
  67
  68 static int map_addr(struct sk_buff *skb, unsigned int dataoff,
  69                     const char **dptr, unsigned int *datalen,
  70                     unsigned int matchoff, unsigned int matchlen,
  71                     union nf_inet_addr *addr, __be16 port)
  72 {
  73         enum ip_conntrack_info ctinfo;
  74         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  75         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  76         char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  77         unsigned int buflen;
  78         __be32 newaddr;
  79         __be16 newport;
  80
  81         if (ct->tuplehash[dir].tuple.src.u3.ip == addr->ip &&
  82             ct->tuplehash[dir].tuple.src.u.udp.port == port) {
  83                 newaddr = ct->tuplehash[!dir].tuple.dst.u3.ip;
  84                 newport = ct->tuplehash[!dir].tuple.dst.u.udp.port;
  85         } else if (ct->tuplehash[dir].tuple.dst.u3.ip == addr->ip &&
  86                    ct->tuplehash[dir].tuple.dst.u.udp.port == port) {
  87                 newaddr = ct->tuplehash[!dir].tuple.src.u3.ip;
  88                 newport = ct->tuplehash[!dir].tuple.src.u.udp.port;
  89         } else
  90                 return 1;
  91
  92         if (newaddr == addr->ip && newport == port)
  93                 return 1;
  94
  95         buflen = sprintf(buffer, "%pI4:%u", &newaddr, ntohs(newport));
  96
  97         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
  98                              buffer, buflen);
  99 }
 100
 101 static int map_sip_addr(struct sk_buff *skb, unsigned int dataoff,
 102                         const char **dptr, unsigned int *datalen,
 103                         enum sip_header_types type)
 104 {
 105         enum ip_conntrack_info ctinfo;
 106         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 107         unsigned int matchlen, matchoff;
 108         union nf_inet_addr addr;
 109         __be16 port;
 110
 111         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen, type, NULL,
 112                                     &matchoff, &matchlen, &addr, &port) <= 0)
 113                 return 1;
 114         return map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 115                         &addr, port);
 116 }
 117
 118 static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
 119                                const char **dptr, unsigned int *datalen)
 120 {
 121         enum ip_conntrack_info ctinfo;
 122         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 123         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 124         unsigned int coff, matchoff, matchlen;
 125         enum sip_header_types hdr;
 126         union nf_inet_addr addr;
 127         __be16 port;
 128         int request, in_header;
 129
 130         /* Basic rules: requests and responses. */
 131         if (strnicmp(*dptr, "SIP/2.0", strlen("SIP/2.0")) != 0) {
 132                 if (ct_sip_parse_request(ct, *dptr, *datalen,
 133                                          &matchoff, &matchlen,
 134                                          &addr, &port) > 0 &&
 135                     !map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 136                               &addr, port))
 137                         return NF_DROP;
 138                 request = 1;
 139         } else
 140                 request = 0;
 141
 142         if (nf_ct_protonum(ct) == IPPROTO_TCP)
 143                 hdr = SIP_HDR_VIA_TCP;
 144         else
 145                 hdr = SIP_HDR_VIA_UDP;
 146
 147         /* Translate topmost Via header and parameters */
 148         if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 149                                     hdr, NULL, &matchoff, &matchlen,
 150                                     &addr, &port) > 0) {
 151                 unsigned int matchend, poff, plen, buflen, n;
 152                 char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
 153
 154                 /* We're only interested in headers related to this
 155                  * connection */
 156                 if (request) {
 157                         if (addr.ip != ct->tuplehash[dir].tuple.src.u3.ip ||
 158                             port != ct->tuplehash[dir].tuple.src.u.udp.port)
 159                                 goto next;
 160                 } else {
 161                         if (addr.ip != ct->tuplehash[dir].tuple.dst.u3.ip ||
 162                             port != ct->tuplehash[dir].tuple.dst.u.udp.port)
 163                                 goto next;
 164                 }
 165
 166                 if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 167                               &addr, port))
 168                         return NF_DROP;
 169
 170                 matchend = matchoff + matchlen;
 171
 172                 /* The maddr= parameter (RFC 2361) specifies where to send
 173                  * the reply. */
 174                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 175                                                "maddr=", &poff, &plen,
 176                                                &addr) > 0 &&
 177                     addr.ip == ct->tuplehash[dir].tuple.src.u3.ip &&
 178                     addr.ip != ct->tuplehash[!dir].tuple.dst.u3.ip) {
 179                         buflen = sprintf(buffer, "%pI4",
 180                                         &ct->tuplehash[!dir].tuple.dst.u3.ip);
 181                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 182                                            poff, plen, buffer, buflen))
 183                                 return NF_DROP;
 184                 }
 185
 186                 /* The received= parameter (RFC 2361) contains the address
 187                  * from which the server received the request. */
 188                 if (ct_sip_parse_address_param(ct, *dptr, matchend, *datalen,
 189                                                "received=", &poff, &plen,
 190                                                &addr) > 0 &&
 191                     addr.ip == ct->tuplehash[dir].tuple.dst.u3.ip &&
 192                     addr.ip != ct->tuplehash[!dir].tuple.src.u3.ip) {
 193                         buflen = sprintf(buffer, "%pI4",
 194                                         &ct->tuplehash[!dir].tuple.src.u3.ip);
 195                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 196                                            poff, plen, buffer, buflen))
 197                                 return NF_DROP;
 198                 }
 199
 200                 /* The rport= parameter (RFC 3581) contains the port number
 201                  * from which the server received the request. */
 202                 if (ct_sip_parse_numerical_param(ct, *dptr, matchend, *datalen,
 203                                                  "rport=", &poff, &plen,
 204                                                  &n) > 0 &&
 205                     htons(n) == ct->tuplehash[dir].tuple.dst.u.udp.port &&
 206                     htons(n) != ct->tuplehash[!dir].tuple.src.u.udp.port) {
 207                         __be16 p = ct->tuplehash[!dir].tuple.src.u.udp.port;
 208                         buflen = sprintf(buffer, "%u", ntohs(p));
 209                         if (!mangle_packet(skb, dataoff, dptr, datalen,
 210                                            poff, plen, buffer, buflen))
 211                                 return NF_DROP;
 212                 }
 213         }
 214
 215 next:
 216         /* Translate Contact headers */
 217         coff = 0;
 218         in_header = 0;
 219         while (ct_sip_parse_header_uri(ct, *dptr, &coff, *datalen,
 220                                        SIP_HDR_CONTACT, &in_header,
 221                                        &matchoff, &matchlen,
 222                                        &addr, &port) > 0) {
 223                 if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 224                               &addr, port))
 225                         return NF_DROP;
 226         }
 227
 228         if (!map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_FROM) ||
 229             !map_sip_addr(skb, dataoff, dptr, datalen, SIP_HDR_TO))
 230                 return NF_DROP;
 231
 232         return NF_ACCEPT;
 233 }
 234
 235 static void ip_nat_sip_seq_adjust(struct sk_buff *skb, s16 off)
 236 {
 237         enum ip_conntrack_info ctinfo;
 238         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 239         const struct tcphdr *th;
 240
 241         if (nf_ct_protonum(ct) != IPPROTO_TCP || off == 0)
 242                 return;
 243
 244         th = (struct tcphdr *)(skb->data + ip_hdrlen(skb));
 245         nf_nat_set_seq_adjust(ct, ctinfo, th->seq, off);
 246 }
 247
 248 /* Handles expected signalling connections and media streams */
 249 static void ip_nat_sip_expected(struct nf_conn *ct,
 250                                 struct nf_conntrack_expect *exp)
 251 {
 252         struct nf_nat_range range;
 253
 254         /* This must be a fresh one. */
 255         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 256
 257         /* For DST manip, map port here to where it's expected. */
 258         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 259         range.min = range.max = exp->saved_proto;
 260         range.min_ip = range.max_ip = exp->saved_ip;
 261         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 262
 263         /* Change src to where master sends to, but only if the connection
 264          * actually came from the same source. */
 265         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip ==
 266             ct->master->tuplehash[exp->dir].tuple.src.u3.ip) {
 267                 range.flags = IP_NAT_RANGE_MAP_IPS;
 268                 range.min_ip = range.max_ip
 269                         = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 270                 nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
 271         }
 272 }
 273
 274 static unsigned int ip_nat_sip_expect(struct sk_buff *skb, unsigned int dataoff,
 275                                       const char **dptr, unsigned int *datalen,
 276                                       struct nf_conntrack_expect *exp,
 277                                       unsigned int matchoff,
 278                                       unsigned int matchlen)
 279 {
 280         enum ip_conntrack_info ctinfo;
 281         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 282         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 283         __be32 newip;
 284         u_int16_t port;
 285         char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
 286         unsigned buflen;
 287
 288         /* Connection will come from reply */
 289         if (ct->tuplehash[dir].tuple.src.u3.ip == ct->tuplehash[!dir].tuple.dst.u3.ip)
 290                 newip = exp->tuple.dst.u3.ip;
 291         else
 292                 newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 293
 294         /* If the signalling port matches the connection's source port in the
 295          * original direction, try to use the destination port in the opposite
 296          * direction. */
 297         if (exp->tuple.dst.u.udp.port ==
 298             ct->tuplehash[dir].tuple.src.u.udp.port)
 299                 port = ntohs(ct->tuplehash[!dir].tuple.dst.u.udp.port);
 300         else
 301                 port = ntohs(exp->tuple.dst.u.udp.port);
 302
 303         exp->saved_ip = exp->tuple.dst.u3.ip;
 304         exp->tuple.dst.u3.ip = newip;
 305         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 306         exp->dir = !dir;
 307         exp->expectfn = ip_nat_sip_expected;
 308
 309         for (; port != 0; port++) {
 310                 exp->tuple.dst.u.udp.port = htons(port);
 311                 if (nf_ct_expect_related(exp) == 0)
 312                         break;
 313         }
 314
 315         if (port == 0)
 316                 return NF_DROP;
 317
 318         if (exp->tuple.dst.u3.ip != exp->saved_ip ||
 319             exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
 320                 buflen = sprintf(buffer, "%pI4:%u", &newip, port);
 321                 if (!mangle_packet(skb, dataoff, dptr, datalen,
 322                                    matchoff, matchlen, buffer, buflen))
 323                         goto err;
 324         }
 325         return NF_ACCEPT;
 326
 327 err:
 328         nf_ct_unexpect_related(exp);
 329         return NF_DROP;
 330 }
 331
 332 static int mangle_content_len(struct sk_buff *skb, unsigned int dataoff,
 333                               const char **dptr, unsigned int *datalen)
 334 {
 335         enum ip_conntrack_info ctinfo;
 336         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 337         unsigned int matchoff, matchlen;
 338         char buffer[sizeof("65536")];
 339         int buflen, c_len;
 340
 341         /* Get actual SDP length */
 342         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,
 343                                   SDP_HDR_VERSION, SDP_HDR_UNSPEC,
 344                                   &matchoff, &matchlen) <= 0)
 345                 return 0;
 346         c_len = *datalen - matchoff + strlen("v=");
 347
 348         /* Now, update SDP length */
 349         if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH,
 350                               &matchoff, &matchlen) <= 0)
 351                 return 0;
 352
 353         buflen = sprintf(buffer, "%u", c_len);
 354         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 355                              buffer, buflen);
 356 }
 357
 358 static int mangle_sdp_packet(struct sk_buff *skb, unsigned int dataoff,
 359                              const char **dptr, unsigned int *datalen,
 360                              unsigned int sdpoff,
 361                              enum sdp_header_types type,
 362                              enum sdp_header_types term,
 363                              char *buffer, int buflen)
 364 {
 365         enum ip_conntrack_info ctinfo;
 366         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 367         unsigned int matchlen, matchoff;
 368
 369         if (ct_sip_get_sdp_header(ct, *dptr, sdpoff, *datalen, type, term,
 370                                   &matchoff, &matchlen) <= 0)
 371                 return -ENOENT;
 372         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 373                              buffer, buflen) ? 0 : -EINVAL;
 374 }
 375
 376 static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, unsigned int dataoff,
 377                                     const char **dptr, unsigned int *datalen,
 378                                     unsigned int sdpoff,
 379                                     enum sdp_header_types type,
 380                                     enum sdp_header_types term,
 381                                     const union nf_inet_addr *addr)
 382 {
 383         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 384         unsigned int buflen;
 385
 386         buflen = sprintf(buffer, "%pI4", &addr->ip);
 387         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff, type, term,
 388                               buffer, buflen))
 389                 return 0;
 390
 391         return mangle_content_len(skb, dataoff, dptr, datalen);
 392 }
 393
 394 static unsigned int ip_nat_sdp_port(struct sk_buff *skb, unsigned int dataoff,
 395                                     const char **dptr, unsigned int *datalen,
 396                                     unsigned int matchoff,
 397                                     unsigned int matchlen,
 398                                     u_int16_t port)
 399 {
 400         char buffer[sizeof("nnnnn")];
 401         unsigned int buflen;
 402
 403         buflen = sprintf(buffer, "%u", port);
 404         if (!mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
 405                            buffer, buflen))
 406                 return 0;
 407
 408         return mangle_content_len(skb, dataoff, dptr, datalen);
 409 }
 410
 411 static unsigned int ip_nat_sdp_session(struct sk_buff *skb, unsigned int dataoff,
 412                                        const char **dptr, unsigned int *datalen,
 413                                        unsigned int sdpoff,
 414                                        const union nf_inet_addr *addr)
 415 {
 416         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 417         unsigned int buflen;
 418
 419         /* Mangle session description owner and contact addresses */
 420         buflen = sprintf(buffer, "%pI4", &addr->ip);
 421         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 422                                SDP_HDR_OWNER_IP4, SDP_HDR_MEDIA,
 423                                buffer, buflen))
 424                 return 0;
 425
 426         switch (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
 427                                   SDP_HDR_CONNECTION_IP4, SDP_HDR_MEDIA,
 428                                   buffer, buflen)) {
 429         case 0:
 430         /*
 431          * RFC 2327:
 432          *
 433          * Session description
 434          *
 435          * c=* (connection information - not required if included in all media)
 436          */
 437         case -ENOENT:
 438                 break;
 439         default:
 440                 return 0;
 441         }
 442
 443         return mangle_content_len(skb, dataoff, dptr, datalen);
 444 }
 445
 446 /* So, this packet has hit the connection tracking matching code.
 447    Mangle it, and change the expectation to match the new version. */
 448 static unsigned int ip_nat_sdp_media(struct sk_buff *skb, unsigned int dataoff,
 449                                      const char **dptr, unsigned int *datalen,
 450                                      struct nf_conntrack_expect *rtp_exp,
 451                                      struct nf_conntrack_expect *rtcp_exp,
 452                                      unsigned int mediaoff,
 453                                      unsigned int medialen,
 454                                      union nf_inet_addr *rtp_addr)
 455 {
 456         enum ip_conntrack_info ctinfo;
 457         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 458         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 459         u_int16_t port;
 460
 461         /* Connection will come from reply */
 462         if (ct->tuplehash[dir].tuple.src.u3.ip ==
 463             ct->tuplehash[!dir].tuple.dst.u3.ip)
 464                 rtp_addr->ip = rtp_exp->tuple.dst.u3.ip;
 465         else
 466                 rtp_addr->ip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 467
 468         rtp_exp->saved_ip = rtp_exp->tuple.dst.u3.ip;
 469         rtp_exp->tuple.dst.u3.ip = rtp_addr->ip;
 470         rtp_exp->saved_proto.udp.port = rtp_exp->tuple.dst.u.udp.port;
 471         rtp_exp->dir = !dir;
 472         rtp_exp->expectfn = ip_nat_sip_expected;
 473
 474         rtcp_exp->saved_ip = rtcp_exp->tuple.dst.u3.ip;
 475         rtcp_exp->tuple.dst.u3.ip = rtp_addr->ip;
 476         rtcp_exp->saved_proto.udp.port = rtcp_exp->tuple.dst.u.udp.port;
 477         rtcp_exp->dir = !dir;
 478         rtcp_exp->expectfn = ip_nat_sip_expected;
 479
 480         /* Try to get same pair of ports: if not, try to change them. */
 481         for (port = ntohs(rtp_exp->tuple.dst.u.udp.port);
 482              port != 0; port += 2) {
 483                 rtp_exp->tuple.dst.u.udp.port = htons(port);
 484                 if (nf_ct_expect_related(rtp_exp) != 0)
 485                         continue;
 486                 rtcp_exp->tuple.dst.u.udp.port = htons(port + 1);
 487                 if (nf_ct_expect_related(rtcp_exp) == 0)
 488                         break;
 489                 nf_ct_unexpect_related(rtp_exp);
 490         }
 491
 492         if (port == 0)
 493                 goto err1;
 494
 495         /* Update media port. */
 496         if (rtp_exp->tuple.dst.u.udp.port != rtp_exp->saved_proto.udp.port &&
 497             !ip_nat_sdp_port(skb, dataoff, dptr, datalen,
 498                              mediaoff, medialen, port))
 499                 goto err2;
 500
 501         return NF_ACCEPT;
 502
 503 err2:
 504         nf_ct_unexpect_related(rtp_exp);
 505         nf_ct_unexpect_related(rtcp_exp);
 506 err1:
 507         return NF_DROP;
 508 }
 509
 510 static void __exit nf_nat_sip_fini(void)
 511 {
 512         rcu_assign_pointer(nf_nat_sip_hook, NULL);
 513         rcu_assign_pointer(nf_nat_sip_seq_adjust_hook, NULL);
 514         rcu_assign_pointer(nf_nat_sip_expect_hook, NULL);
 515         rcu_assign_pointer(nf_nat_sdp_addr_hook, NULL);
 516         rcu_assign_pointer(nf_nat_sdp_port_hook, NULL);
 517         rcu_assign_pointer(nf_nat_sdp_session_hook, NULL);
 518         rcu_assign_pointer(nf_nat_sdp_media_hook, NULL);
 519         synchronize_rcu();
 520 }
 521
 522 static int __init nf_nat_sip_init(void)
 523 {
 524         BUG_ON(nf_nat_sip_hook != NULL);
 525         BUG_ON(nf_nat_sip_seq_adjust_hook != NULL);
 526         BUG_ON(nf_nat_sip_expect_hook != NULL);
 527         BUG_ON(nf_nat_sdp_addr_hook != NULL);
 528         BUG_ON(nf_nat_sdp_port_hook != NULL);
 529         BUG_ON(nf_nat_sdp_session_hook != NULL);
 530         BUG_ON(nf_nat_sdp_media_hook != NULL);
 531         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 532         rcu_assign_pointer(nf_nat_sip_seq_adjust_hook, ip_nat_sip_seq_adjust);
 533         rcu_assign_pointer(nf_nat_sip_expect_hook, ip_nat_sip_expect);
 534         rcu_assign_pointer(nf_nat_sdp_addr_hook, ip_nat_sdp_addr);
 535         rcu_assign_pointer(nf_nat_sdp_port_hook, ip_nat_sdp_port);
 536         rcu_assign_pointer(nf_nat_sdp_session_hook, ip_nat_sdp_session);
 537         rcu_assign_pointer(nf_nat_sdp_media_hook, ip_nat_sdp_media);
 538         return 0;
 539 }
 540
 541 module_init(nf_nat_sip_init);
 542 module_exit(nf_nat_sip_fini);