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   1 /* SIP extension for UDP 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  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  */
  10
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/ip.h>
  14 #include <linux/udp.h>
  15
  16 #include <linux/netfilter_ipv4.h>
  17 #include <linux/netfilter_ipv4/ip_nat.h>
  18 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  19 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  20 #include <linux/netfilter_ipv4/ip_conntrack_sip.h>
  21
  22 MODULE_LICENSE("GPL");
  23 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  24 MODULE_DESCRIPTION("SIP NAT helper");
  25
  26 #if 0
  27 #define DEBUGP printk
  28 #else
  29 #define DEBUGP(format, args...)
  30 #endif
  31
  32 static unsigned int mangle_sip_packet(struct sk_buff **pskb,
  33                                       enum ip_conntrack_info ctinfo,
  34                                       struct ip_conntrack *ct,
  35                                       const char **dptr, size_t dlen,
  36                                       char *buffer, int bufflen,
  37                                       enum sip_header_pos pos)
  38 {
  39         unsigned int matchlen, matchoff;
  40
  41         if (ct_sip_get_info(*dptr, dlen, &matchoff, &matchlen, pos) <= 0)
  42                 return 0;
  43
  44         if (!ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
  45                                       matchoff, matchlen, buffer, bufflen))
  46                 return 0;
  47
  48         /* We need to reload this. Thanks Patrick. */
  49         *dptr = (*pskb)->data + (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
  50         return 1;
  51 }
  52
  53 static unsigned int ip_nat_sip(struct sk_buff **pskb,
  54                                enum ip_conntrack_info ctinfo,
  55                                struct ip_conntrack *ct,
  56                                const char **dptr)
  57 {
  58         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  59         char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  60         unsigned int bufflen, dataoff;
  61         __be32 ip;
  62         __be16 port;
  63
  64         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
  65
  66         ip   = ct->tuplehash[!dir].tuple.dst.ip;
  67         port = ct->tuplehash[!dir].tuple.dst.u.udp.port;
  68         bufflen = sprintf(buffer, "%u.%u.%u.%u:%u", NIPQUAD(ip), ntohs(port));
  69
  70         /* short packet ? */
  71         if (((*pskb)->len - dataoff) < (sizeof("SIP/2.0") - 1))
  72                 return 0;
  73
  74         /* Basic rules: requests and responses. */
  75         if (memcmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) == 0) {
  76                 const char *aux;
  77
  78                 if ((ctinfo) < IP_CT_IS_REPLY) {
  79                         mangle_sip_packet(pskb, ctinfo, ct, dptr,
  80                                           (*pskb)->len - dataoff,
  81                                           buffer, bufflen, POS_CONTACT);
  82                         return 1;
  83                 }
  84
  85                 if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
  86                                        (*pskb)->len - dataoff,
  87                                        buffer, bufflen, POS_VIA))
  88                         return 0;
  89
  90                 aux = ct_sip_search("CSeq:", *dptr, sizeof("CSeq:") - 1,
  91                                     (*pskb)->len - dataoff, 0);
  92                 if (!aux)
  93                         return 0;
  94
  95                 if (!ct_sip_search("REGISTER", aux, sizeof("REGISTER"),
  96                                    ct_sip_lnlen(aux,
  97                                                 *dptr + (*pskb)->len - dataoff),
  98                                    1))
  99                         return 1;
 100
 101                 return mangle_sip_packet(pskb, ctinfo, ct, dptr,
 102                                          (*pskb)->len - dataoff,
 103                                          buffer, bufflen, POS_CONTACT);
 104         }
 105         if ((ctinfo) < IP_CT_IS_REPLY) {
 106                 if (!mangle_sip_packet(pskb, ctinfo, ct, dptr,
 107                                        (*pskb)->len - dataoff,
 108                                        buffer, bufflen, POS_VIA))
 109                         return 0;
 110
 111                 /* Mangle Contact if exists only. - watch udp_nat_mangle()! */
 112                 mangle_sip_packet(pskb, ctinfo, ct, dptr, (*pskb)->len - dataoff,
 113                                   buffer, bufflen, POS_CONTACT);
 114                 return 1;
 115         }
 116         /* This mangle requests headers. */
 117         return mangle_sip_packet(pskb, ctinfo, ct, dptr,
 118                                  ct_sip_lnlen(*dptr,
 119                                               *dptr + (*pskb)->len - dataoff),
 120                                  buffer, bufflen, POS_REQ_HEADER);
 121 }
 122
 123 static int mangle_content_len(struct sk_buff **pskb,
 124                               enum ip_conntrack_info ctinfo,
 125                               struct ip_conntrack *ct,
 126                               const char *dptr)
 127 {
 128         unsigned int dataoff, matchoff, matchlen;
 129         char buffer[sizeof("65536")];
 130         int bufflen;
 131
 132         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
 133
 134         /* Get actual SDP lenght */
 135         if (ct_sip_get_info(dptr, (*pskb)->len - dataoff, &matchoff,
 136                             &matchlen, POS_SDP_HEADER) > 0) {
 137
 138                 /* since ct_sip_get_info() give us a pointer passing 'v='
 139                    we need to add 2 bytes in this count. */
 140                 int c_len = (*pskb)->len - dataoff - matchoff + 2;
 141
 142                 /* Now, update SDP lenght */
 143                 if (ct_sip_get_info(dptr, (*pskb)->len - dataoff, &matchoff,
 144                                     &matchlen, POS_CONTENT) > 0) {
 145
 146                         bufflen = sprintf(buffer, "%u", c_len);
 147
 148                         return ip_nat_mangle_udp_packet(pskb, ct, ctinfo,
 149                                                         matchoff, matchlen,
 150                                                         buffer, bufflen);
 151                 }
 152         }
 153         return 0;
 154 }
 155
 156 static unsigned int mangle_sdp(struct sk_buff **pskb,
 157                                enum ip_conntrack_info ctinfo,
 158                                struct ip_conntrack *ct,
 159                                __be32 newip, u_int16_t port,
 160                                const char *dptr)
 161 {
 162         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 163         unsigned int dataoff, bufflen;
 164
 165         dataoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct udphdr);
 166
 167         /* Mangle owner and contact info. */
 168         bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
 169         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 170                                buffer, bufflen, POS_OWNER))
 171                 return 0;
 172
 173         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 174                                buffer, bufflen, POS_CONNECTION))
 175                 return 0;
 176
 177         /* Mangle media port. */
 178         bufflen = sprintf(buffer, "%u", port);
 179         if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
 180                                buffer, bufflen, POS_MEDIA))
 181                 return 0;
 182
 183         return mangle_content_len(pskb, ctinfo, ct, dptr);
 184 }
 185
 186 /* So, this packet has hit the connection tracking matching code.
 187    Mangle it, and change the expectation to match the new version. */
 188 static unsigned int ip_nat_sdp(struct sk_buff **pskb,
 189                                enum ip_conntrack_info ctinfo,
 190                                struct ip_conntrack_expect *exp,
 191                                const char *dptr)
 192 {
 193         struct ip_conntrack *ct = exp->master;
 194         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 195         __be32 newip;
 196         u_int16_t port;
 197
 198         DEBUGP("ip_nat_sdp():\n");
 199
 200         /* Connection will come from reply */
 201         newip = ct->tuplehash[!dir].tuple.dst.ip;
 202
 203         exp->tuple.dst.ip = newip;
 204         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 205         exp->dir = !dir;
 206
 207         /* When you see the packet, we need to NAT it the same as the
 208            this one. */
 209         exp->expectfn = ip_nat_follow_master;
 210
 211         /* Try to get same port: if not, try to change it. */
 212         for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) {
 213                 exp->tuple.dst.u.udp.port = htons(port);
 214                 if (ip_conntrack_expect_related(exp) == 0)
 215                         break;
 216         }
 217
 218         if (port == 0)
 219                 return NF_DROP;
 220
 221         if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
 222                 ip_conntrack_unexpect_related(exp);
 223                 return NF_DROP;
 224         }
 225         return NF_ACCEPT;
 226 }
 227
 228 static void __exit fini(void)
 229 {
 230         rcu_assign_pointer(ip_nat_sip_hook, NULL);
 231         rcu_assign_pointer(ip_nat_sdp_hook, NULL);
 232         synchronize_rcu();
 233 }
 234
 235 static int __init init(void)
 236 {
 237         BUG_ON(rcu_dereference(ip_nat_sip_hook));
 238         BUG_ON(rcu_dereference(ip_nat_sdp_hook));
 239         rcu_assign_pointer(ip_nat_sip_hook, ip_nat_sip);
 240         rcu_assign_pointer(ip_nat_sdp_hook, ip_nat_sdp);
 241         return 0;
 242 }
 243
 244 module_init(init);
 245 module_exit(fini);