net/ipv4/netfilter/nf_nat_sip.c

   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 <net/ip.h>
  15 #include <linux/udp.h>
  16
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_helper.h>
  19 #include <net/netfilter/nf_nat_rule.h>
  20 #include <net/netfilter/nf_conntrack_helper.h>
  21 #include <net/netfilter/nf_conntrack_expect.h>
  22 #include <linux/netfilter/nf_conntrack_sip.h>
  23
  24 MODULE_LICENSE("GPL");
  25 MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
  26 MODULE_DESCRIPTION("SIP NAT helper");
  27 MODULE_ALIAS("ip_nat_sip");
  28
  29 struct addr_map {
  30         struct {
  31                 char            src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  32                 char            dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
  33                 unsigned int    srclen, srciplen;
  34                 unsigned int    dstlen, dstiplen;
  35         } addr[IP_CT_DIR_MAX];
  36 };
  37
  38 static void addr_map_init(const struct nf_conn *ct, struct addr_map *map)
  39 {
  40         const struct nf_conntrack_tuple *t;
  41         enum ip_conntrack_dir dir;
  42         unsigned int n;
  43
  44         for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
  45                 t = &ct->tuplehash[dir].tuple;
  46
  47                 n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
  48                             NIPQUAD(t->src.u3.ip));
  49                 map->addr[dir].srciplen = n;
  50                 n += sprintf(map->addr[dir].src + n, ":%u",
  51                              ntohs(t->src.u.udp.port));
  52                 map->addr[dir].srclen = n;
  53
  54                 n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
  55                             NIPQUAD(t->dst.u3.ip));
  56                 map->addr[dir].dstiplen = n;
  57                 n += sprintf(map->addr[dir].dst + n, ":%u",
  58                              ntohs(t->dst.u.udp.port));
  59                 map->addr[dir].dstlen = n;
  60         }
  61 }
  62
  63 static unsigned int mangle_packet(struct sk_buff *skb,
  64                                   const char **dptr, unsigned int *datalen,
  65                                   unsigned int matchoff, unsigned int matchlen,
  66                                   const char *buffer, unsigned int buflen)
  67 {
  68         enum ip_conntrack_info ctinfo;
  69         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  70
  71         if (!nf_nat_mangle_udp_packet(skb, ct, ctinfo, matchoff, matchlen,
  72                                       buffer, buflen))
  73                 return 0;
  74
  75         /* Reload data pointer and adjust datalen value */
  76         *dptr = skb->data + ip_hdrlen(skb) + sizeof(struct udphdr);
  77         *datalen += buflen - matchlen;
  78         return 1;
  79 }
  80
  81 static int map_addr(struct sk_buff *skb,
  82                     const char **dptr, unsigned int *datalen,
  83                     unsigned int matchoff, unsigned int matchlen,
  84                     struct addr_map *map)
  85 {
  86         enum ip_conntrack_info ctinfo;
  87         struct nf_conn *ct __maybe_unused = nf_ct_get(skb, &ctinfo);
  88         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
  89         unsigned int addrlen;
  90         char *addr;
  91
  92         if ((matchlen == map->addr[dir].srciplen ||
  93              matchlen == map->addr[dir].srclen) &&
  94             strncmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
  95                 addr    = map->addr[!dir].dst;
  96                 addrlen = map->addr[!dir].dstlen;
  97         } else if ((matchlen == map->addr[dir].dstiplen ||
  98                     matchlen == map->addr[dir].dstlen) &&
  99                    strncmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
 100                 addr    = map->addr[!dir].src;
 101                 addrlen = map->addr[!dir].srclen;
 102         } else
 103                 return 1;
 104
 105         return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
 106                              addr, addrlen);
 107 }
 108
 109 static int map_sip_addr(struct sk_buff *skb,
 110                         const char **dptr, unsigned int *datalen,
 111                         enum sip_header_types type, struct addr_map *map)
 112 {
 113         enum ip_conntrack_info ctinfo;
 114         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 115         unsigned int matchlen, matchoff;
 116
 117         if (ct_sip_get_header(ct, *dptr, 0, *datalen, type,
 118                               &matchoff, &matchlen) <= 0)
 119                 return 1;
 120         return map_addr(skb, dptr, datalen, matchoff, matchlen, map);
 121 }
 122
 123 static unsigned int ip_nat_sip(struct sk_buff *skb,
 124                                const char **dptr, unsigned int *datalen)
 125 {
 126         enum ip_conntrack_info ctinfo;
 127         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 128         struct addr_map map;
 129         unsigned int matchoff, matchlen;
 130
 131         if (*datalen < strlen("SIP/2.0"))
 132                 return NF_ACCEPT;
 133
 134         addr_map_init(ct, &map);
 135
 136         /* Basic rules: requests and responses. */
 137         if (strnicmp(*dptr, "SIP/2.0", strlen("SIP/2.0")) != 0) {
 138                 if (ct_sip_parse_request(ct, *dptr, *datalen,
 139                                          &matchoff, &matchlen) > 0 &&
 140                     !map_addr(skb, dptr, datalen, matchoff, matchlen, &map))
 141                         return NF_DROP;
 142         }
 143
 144         if (!map_sip_addr(skb, dptr, datalen, SIP_HDR_FROM, &map) ||
 145             !map_sip_addr(skb, dptr, datalen, SIP_HDR_TO, &map) ||
 146             !map_sip_addr(skb, dptr, datalen, SIP_HDR_VIA, &map) ||
 147             !map_sip_addr(skb, dptr, datalen, SIP_HDR_CONTACT, &map))
 148                 return NF_DROP;
 149         return NF_ACCEPT;
 150 }
 151
 152 static int mangle_content_len(struct sk_buff *skb,
 153                               const char **dptr, unsigned int *datalen)
 154 {
 155         enum ip_conntrack_info ctinfo;
 156         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 157         unsigned int matchoff, matchlen;
 158         char buffer[sizeof("65536")];
 159         int buflen, c_len;
 160
 161         /* Get actual SDP length */
 162         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen,
 163                                   SDP_HDR_VERSION, SDP_HDR_UNSPEC,
 164                                   &matchoff, &matchlen) <= 0)
 165                 return 0;
 166         c_len = *datalen - matchoff + strlen("v=");
 167
 168         /* Now, update SDP length */
 169         if (ct_sip_get_header(ct, *dptr, 0, *datalen, SIP_HDR_CONTENT_LENGTH,
 170                               &matchoff, &matchlen) <= 0)
 171                 return 0;
 172
 173         buflen = sprintf(buffer, "%u", c_len);
 174         return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
 175                              buffer, buflen);
 176 }
 177
 178 static unsigned mangle_sdp_packet(struct sk_buff *skb,
 179                                   const char **dptr, unsigned int *datalen,
 180                                   enum sdp_header_types type,
 181                                   char *buffer, int buflen)
 182 {
 183         enum ip_conntrack_info ctinfo;
 184         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 185         unsigned int matchlen, matchoff;
 186
 187         if (ct_sip_get_sdp_header(ct, *dptr, 0, *datalen, type, SDP_HDR_UNSPEC,
 188                                   &matchoff, &matchlen) <= 0)
 189                 return 0;
 190         return mangle_packet(skb, dptr, datalen, matchoff, matchlen,
 191                              buffer, buflen);
 192 }
 193
 194 static unsigned int mangle_sdp(struct sk_buff *skb,
 195                                enum ip_conntrack_info ctinfo,
 196                                struct nf_conn *ct,
 197                                __be32 newip, u_int16_t port,
 198                                const char **dptr, unsigned int *datalen)
 199 {
 200         char buffer[sizeof("nnn.nnn.nnn.nnn")];
 201         unsigned int bufflen;
 202
 203         /* Mangle owner and contact info. */
 204         bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
 205         if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_OWNER_IP4,
 206                                buffer, bufflen))
 207                 return 0;
 208
 209         if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_CONNECTION_IP4,
 210                                buffer, bufflen))
 211                 return 0;
 212
 213         /* Mangle media port. */
 214         bufflen = sprintf(buffer, "%u", port);
 215         if (!mangle_sdp_packet(skb, dptr, datalen, SDP_HDR_MEDIA,
 216                                buffer, bufflen))
 217                 return 0;
 218
 219         return mangle_content_len(skb, dptr, datalen);
 220 }
 221
 222 static void ip_nat_sdp_expect(struct nf_conn *ct,
 223                               struct nf_conntrack_expect *exp)
 224 {
 225         struct nf_nat_range range;
 226
 227         /* This must be a fresh one. */
 228         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 229
 230         /* For DST manip, map port here to where it's expected. */
 231         range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
 232         range.min = range.max = exp->saved_proto;
 233         range.min_ip = range.max_ip = exp->saved_ip;
 234         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_DST);
 235
 236         /* Change src to where master sends to */
 237         range.flags = IP_NAT_RANGE_MAP_IPS;
 238         range.min_ip = range.max_ip
 239                 = ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
 240         nf_nat_setup_info(ct, &range, IP_NAT_MANIP_SRC);
 241 }
 242
 243 /* So, this packet has hit the connection tracking matching code.
 244    Mangle it, and change the expectation to match the new version. */
 245 static unsigned int ip_nat_sdp(struct sk_buff *skb,
 246                                const char **dptr, unsigned int *datalen,
 247                                struct nf_conntrack_expect *exp)
 248 {
 249         enum ip_conntrack_info ctinfo;
 250         struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
 251         enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 252         __be32 newip;
 253         u_int16_t port;
 254
 255         /* Connection will come from reply */
 256         if (ct->tuplehash[dir].tuple.src.u3.ip ==
 257             ct->tuplehash[!dir].tuple.dst.u3.ip)
 258                 newip = exp->tuple.dst.u3.ip;
 259         else
 260                 newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
 261
 262         exp->saved_ip = exp->tuple.dst.u3.ip;
 263         exp->tuple.dst.u3.ip = newip;
 264         exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
 265         exp->dir = !dir;
 266
 267         /* When you see the packet, we need to NAT it the same as the
 268            this one. */
 269         exp->expectfn = ip_nat_sdp_expect;
 270
 271         /* Try to get same port: if not, try to change it. */
 272         for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) {
 273                 exp->tuple.dst.u.udp.port = htons(port);
 274                 if (nf_ct_expect_related(exp) == 0)
 275                         break;
 276         }
 277
 278         if (port == 0)
 279                 return NF_DROP;
 280
 281         if (!mangle_sdp(skb, ctinfo, ct, newip, port, dptr, datalen)) {
 282                 nf_ct_unexpect_related(exp);
 283                 return NF_DROP;
 284         }
 285         return NF_ACCEPT;
 286 }
 287
 288 static void __exit nf_nat_sip_fini(void)
 289 {
 290         rcu_assign_pointer(nf_nat_sip_hook, NULL);
 291         rcu_assign_pointer(nf_nat_sdp_hook, NULL);
 292         synchronize_rcu();
 293 }
 294
 295 static int __init nf_nat_sip_init(void)
 296 {
 297         BUG_ON(nf_nat_sip_hook != NULL);
 298         BUG_ON(nf_nat_sdp_hook != NULL);
 299         rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
 300         rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
 301         return 0;
 302 }
 303
 304 module_init(nf_nat_sip_init);
 305 module_exit(nf_nat_sip_fini);