netfilter: nf_nat: better error handling of nf_ct_expect_related() in helpers
[linux-2.6.git] / 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                 int ret;
311
312                 exp->tuple.dst.u.udp.port = htons(port);
313                 ret = nf_ct_expect_related(exp);
314                 if (ret == 0)
315                         break;
316                 else if (ret != -EBUSY) {
317                         port = 0;
318                         break;
319                 }
320         }
321
322         if (port == 0)
323                 return NF_DROP;
324
325         if (exp->tuple.dst.u3.ip != exp->saved_ip ||
326             exp->tuple.dst.u.udp.port != exp->saved_proto.udp.port) {
327                 buflen = sprintf(buffer, "%pI4:%u", &newip, port);
328                 if (!mangle_packet(skb, dataoff, dptr, datalen,
329                                    matchoff, matchlen, buffer, buflen))
330                         goto err;
331         }
332         return NF_ACCEPT;
333
334 err:
335         nf_ct_unexpect_related(exp);
336         return NF_DROP;
337 }
338
339 static int mangle_content_len(struct sk_buff *skb, unsigned int dataoff,
340                               const char **dptr, unsigned int *datalen)
341 {
342         enum ip_conntrack_info ctinfo;
343         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
344         unsigned int matchoff, matchlen;
345         char buffer[sizeof("65536")];
346         int buflen, c_len;
347
348         /* Get actual SDP length */
349         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,
350                                   SDP_HDR_VERSION, SDP_HDR_UNSPEC,
351                                   &matchoff, &matchlen) <= 0)
352                 return 0;
353         c_len = *datalen - matchoff + strlen("v=");
354
355         /* Now, update SDP length */
356         if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH,
357                               &matchoff, &matchlen) <= 0)
358                 return 0;
359
360         buflen = sprintf(buffer, "%u", c_len);
361         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
362                              buffer, buflen);
363 }
364
365 static int mangle_sdp_packet(struct sk_buff *skb, unsigned int dataoff,
366                              const char **dptr, unsigned int *datalen,
367                              unsigned int sdpoff,
368                              enum sdp_header_types type,
369                              enum sdp_header_types term,
370                              char *buffer, int buflen)
371 {
372         enum ip_conntrack_info ctinfo;
373         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
374         unsigned int matchlen, matchoff;
375
376         if (ct_sip_get_sdp_header(ct, *dptr, sdpoff, *datalen, type, term,
377                                   &matchoff, &matchlen) <= 0)
378                 return -ENOENT;
379         return mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
380                              buffer, buflen) ? 0 : -EINVAL;
381 }
382
383 static unsigned int ip_nat_sdp_addr(struct sk_buff *skb, unsigned int dataoff,
384                                     const char **dptr, unsigned int *datalen,
385                                     unsigned int sdpoff,
386                                     enum sdp_header_types type,
387                                     enum sdp_header_types term,
388                                     const union nf_inet_addr *addr)
389 {
390         char buffer[sizeof("nnn.nnn.nnn.nnn")];
391         unsigned int buflen;
392
393         buflen = sprintf(buffer, "%pI4", &addr->ip);
394         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff, type, term,
395                               buffer, buflen))
396                 return 0;
397
398         return mangle_content_len(skb, dataoff, dptr, datalen);
399 }
400
401 static unsigned int ip_nat_sdp_port(struct sk_buff *skb, unsigned int dataoff,
402                                     const char **dptr, unsigned int *datalen,
403                                     unsigned int matchoff,
404                                     unsigned int matchlen,
405                                     u_int16_t port)
406 {
407         char buffer[sizeof("nnnnn")];
408         unsigned int buflen;
409
410         buflen = sprintf(buffer, "%u", port);
411         if (!mangle_packet(skb, dataoff, dptr, datalen, matchoff, matchlen,
412                            buffer, buflen))
413                 return 0;
414
415         return mangle_content_len(skb, dataoff, dptr, datalen);
416 }
417
418 static unsigned int ip_nat_sdp_session(struct sk_buff *skb, unsigned int dataoff,
419                                        const char **dptr, unsigned int *datalen,
420                                        unsigned int sdpoff,
421                                        const union nf_inet_addr *addr)
422 {
423         char buffer[sizeof("nnn.nnn.nnn.nnn")];
424         unsigned int buflen;
425
426         /* Mangle session description owner and contact addresses */
427         buflen = sprintf(buffer, "%pI4", &addr->ip);
428         if (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
429                                SDP_HDR_OWNER_IP4, SDP_HDR_MEDIA,
430                                buffer, buflen))
431                 return 0;
432
433         switch (mangle_sdp_packet(skb, dataoff, dptr, datalen, sdpoff,
434                                   SDP_HDR_CONNECTION_IP4, SDP_HDR_MEDIA,
435                                   buffer, buflen)) {
436         case 0:
437         /*
438          * RFC 2327:
439          *
440          * Session description
441          *
442          * c=* (connection information - not required if included in all media)
443          */
444         case -ENOENT:
445                 break;
446         default:
447                 return 0;
448         }
449
450         return mangle_content_len(skb, dataoff, dptr, datalen);
451 }
452
453 /* So, this packet has hit the connection tracking matching code.
454    Mangle it, and change the expectation to match the new version. */
455 static unsigned int ip_nat_sdp_media(struct sk_buff *skb, unsigned int dataoff,
456                                      const char **dptr, unsigned int *datalen,
457                                      struct nf_conntrack_expect *rtp_exp,
458                                      struct nf_conntrack_expect *rtcp_exp,
459                                      unsigned int mediaoff,
460                                      unsigned int medialen,
461                                      union nf_inet_addr *rtp_addr)
462 {
463         enum ip_conntrack_info ctinfo;
464         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
465         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
466         u_int16_t port;
467
468         /* Connection will come from reply */
469         if (ct->tuplehash[dir].tuple.src.u3.ip ==
470             ct->tuplehash[!dir].tuple.dst.u3.ip)
471                 rtp_addr->ip = rtp_exp->tuple.dst.u3.ip;
472         else
473                 rtp_addr->ip = ct->tuplehash[!dir].tuple.dst.u3.ip;
474
475         rtp_exp->saved_ip = rtp_exp->tuple.dst.u3.ip;
476         rtp_exp->tuple.dst.u3.ip = rtp_addr->ip;
477         rtp_exp->saved_proto.udp.port = rtp_exp->tuple.dst.u.udp.port;
478         rtp_exp->dir = !dir;
479         rtp_exp->expectfn = ip_nat_sip_expected;
480
481         rtcp_exp->saved_ip = rtcp_exp->tuple.dst.u3.ip;
482         rtcp_exp->tuple.dst.u3.ip = rtp_addr->ip;
483         rtcp_exp->saved_proto.udp.port = rtcp_exp->tuple.dst.u.udp.port;
484         rtcp_exp->dir = !dir;
485         rtcp_exp->expectfn = ip_nat_sip_expected;
486
487         /* Try to get same pair of ports: if not, try to change them. */
488         for (port = ntohs(rtp_exp->tuple.dst.u.udp.port);
489              port != 0; port += 2) {
490                 int ret;
491
492                 rtp_exp->tuple.dst.u.udp.port = htons(port);
493                 ret = nf_ct_expect_related(rtp_exp);
494                 if (ret == -EBUSY)
495                         continue;
496                 else if (ret < 0) {
497                         port = 0;
498                         break;
499                 }
500                 rtcp_exp->tuple.dst.u.udp.port = htons(port + 1);
501                 ret = nf_ct_expect_related(rtcp_exp);
502                 if (ret == 0)
503                         break;
504                 else if (ret != -EBUSY) {
505                         nf_ct_unexpect_related(rtp_exp);
506                         port = 0;
507                         break;
508                 }
509         }
510
511         if (port == 0)
512                 goto err1;
513
514         /* Update media port. */
515         if (rtp_exp->tuple.dst.u.udp.port != rtp_exp->saved_proto.udp.port &&
516             !ip_nat_sdp_port(skb, dataoff, dptr, datalen,
517                              mediaoff, medialen, port))
518                 goto err2;
519
520         return NF_ACCEPT;
521
522 err2:
523         nf_ct_unexpect_related(rtp_exp);
524         nf_ct_unexpect_related(rtcp_exp);
525 err1:
526         return NF_DROP;
527 }
528
529 static void __exit nf_nat_sip_fini(void)
530 {
531         rcu_assign_pointer(nf_nat_sip_hook, NULL);
532         rcu_assign_pointer(nf_nat_sip_seq_adjust_hook, NULL);
533         rcu_assign_pointer(nf_nat_sip_expect_hook, NULL);
534         rcu_assign_pointer(nf_nat_sdp_addr_hook, NULL);
535         rcu_assign_pointer(nf_nat_sdp_port_hook, NULL);
536         rcu_assign_pointer(nf_nat_sdp_session_hook, NULL);
537         rcu_assign_pointer(nf_nat_sdp_media_hook, NULL);
538         synchronize_rcu();
539 }
540
541 static int __init nf_nat_sip_init(void)
542 {
543         BUG_ON(nf_nat_sip_hook != NULL);
544         BUG_ON(nf_nat_sip_seq_adjust_hook != NULL);
545         BUG_ON(nf_nat_sip_expect_hook != NULL);
546         BUG_ON(nf_nat_sdp_addr_hook != NULL);
547         BUG_ON(nf_nat_sdp_port_hook != NULL);
548         BUG_ON(nf_nat_sdp_session_hook != NULL);
549         BUG_ON(nf_nat_sdp_media_hook != NULL);
550         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
551         rcu_assign_pointer(nf_nat_sip_seq_adjust_hook, ip_nat_sip_seq_adjust);
552         rcu_assign_pointer(nf_nat_sip_expect_hook, ip_nat_sip_expect);
553         rcu_assign_pointer(nf_nat_sdp_addr_hook, ip_nat_sdp_addr);
554         rcu_assign_pointer(nf_nat_sdp_port_hook, ip_nat_sdp_port);
555         rcu_assign_pointer(nf_nat_sdp_session_hook, ip_nat_sdp_session);
556         rcu_assign_pointer(nf_nat_sdp_media_hook, ip_nat_sdp_media);
557         return 0;
558 }
559
560 module_init(nf_nat_sip_init);
561 module_exit(nf_nat_sip_fini);