/* SIP extension for UDP NAT alteration.
*
* (C) 2005 by Christian Hentschel <chentschel@arnet.com.ar>
* based on RR's ip_nat_ftp.c and other modules.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/ip.h>
#include <linux/udp.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_nat_rule.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <linux/netfilter/nf_conntrack_sip.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Christian Hentschel <chentschel@arnet.com.ar>");
MODULE_DESCRIPTION("SIP NAT helper");
MODULE_ALIAS("ip_nat_sip");
#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif
struct addr_map {
struct {
char src[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
char dst[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
unsigned int srclen, srciplen;
unsigned int dstlen, dstiplen;
} addr[IP_CT_DIR_MAX];
};
static void addr_map_init(struct nf_conn *ct, struct addr_map *map)
{
struct nf_conntrack_tuple *t;
enum ip_conntrack_dir dir;
unsigned int n;
for (dir = 0; dir < IP_CT_DIR_MAX; dir++) {
t = &ct->tuplehash[dir].tuple;
n = sprintf(map->addr[dir].src, "%u.%u.%u.%u",
NIPQUAD(t->src.u3.ip));
map->addr[dir].srciplen = n;
n += sprintf(map->addr[dir].src + n, ":%u",
ntohs(t->src.u.udp.port));
map->addr[dir].srclen = n;
n = sprintf(map->addr[dir].dst, "%u.%u.%u.%u",
NIPQUAD(t->dst.u3.ip));
map->addr[dir].dstiplen = n;
n += sprintf(map->addr[dir].dst + n, ":%u",
ntohs(t->dst.u.udp.port));
map->addr[dir].dstlen = n;
}
}
static int map_sip_addr(struct sk_buff **pskb, enum ip_conntrack_info ctinfo,
struct nf_conn *ct, const char **dptr, size_t dlen,
enum sip_header_pos pos, struct addr_map *map)
{
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
unsigned int matchlen, matchoff, addrlen;
char *addr;
if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
return 1;
if ((matchlen == map->addr[dir].srciplen ||
matchlen == map->addr[dir].srclen) &&
memcmp(*dptr + matchoff, map->addr[dir].src, matchlen) == 0) {
addr = map->addr[!dir].dst;
addrlen = map->addr[!dir].dstlen;
} else if ((matchlen == map->addr[dir].dstiplen ||
matchlen == map->addr[dir].dstlen) &&
memcmp(*dptr + matchoff, map->addr[dir].dst, matchlen) == 0) {
addr = map->addr[!dir].src;
addrlen = map->addr[!dir].srclen;
} else
return 1;
if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
matchoff, matchlen, addr, addrlen))
return 0;
*dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
return 1;
}
static unsigned int ip_nat_sip(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct nf_conn *ct,
const char **dptr)
{
enum sip_header_pos pos;
struct addr_map map;
int dataoff, datalen;
dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
datalen = (*pskb)->len - dataoff;
if (datalen < sizeof("SIP/2.0") - 1)
return NF_DROP;
addr_map_init(ct, &map);
/* Basic rules: requests and responses. */
if (strncmp(*dptr, "SIP/2.0", sizeof("SIP/2.0") - 1) != 0) {
/* 10.2: Constructing the REGISTER Request:
*
* The "userinfo" and "@" components of the SIP URI MUST NOT
* be present.
*/
if (datalen >= sizeof("REGISTER") - 1 &&
strncmp(*dptr, "REGISTER", sizeof("REGISTER") - 1) == 0)
pos = POS_REG_REQ_URI;
else
pos = POS_REQ_URI;
if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, pos, &map))
return NF_DROP;
}
if (!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_FROM, &map) ||
!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_TO, &map) ||
!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_VIA, &map) ||
!map_sip_addr(pskb, ctinfo, ct, dptr, datalen, POS_CONTACT, &map))
return NF_DROP;
return NF_ACCEPT;
}
static unsigned int mangle_sip_packet(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct nf_conn *ct,
const char **dptr, size_t dlen,
char *buffer, int bufflen,
enum sip_header_pos pos)
{
unsigned int matchlen, matchoff;
if (ct_sip_get_info(ct, *dptr, dlen, &matchoff, &matchlen, pos) <= 0)
return 0;
if (!nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
matchoff, matchlen, buffer, bufflen))
return 0;
/* We need to reload this. Thanks Patrick. */
*dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
return 1;
}
static int mangle_content_len(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct nf_conn *ct,
const char *dptr)
{
unsigned int dataoff, matchoff, matchlen;
char buffer[sizeof("65536")];
int bufflen;
dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
/* Get actual SDP lenght */
if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
&matchlen, POS_SDP_HEADER) > 0) {
/* since ct_sip_get_info() give us a pointer passing 'v='
we need to add 2 bytes in this count. */
int c_len = (*pskb)->len - dataoff - matchoff + 2;
/* Now, update SDP length */
if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
&matchlen, POS_CONTENT) > 0) {
bufflen = sprintf(buffer, "%u", c_len);
return nf_nat_mangle_udp_packet(pskb, ct, ctinfo,
matchoff, matchlen,
buffer, bufflen);
}
}
return 0;
}
static unsigned int mangle_sdp(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct nf_conn *ct,
__be32 newip, u_int16_t port,
const char *dptr)
{
char buffer[sizeof("nnn.nnn.nnn.nnn")];
unsigned int dataoff, bufflen;
dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
/* Mangle owner and contact info. */
bufflen = sprintf(buffer, "%u.%u.%u.%u", NIPQUAD(newip));
if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
buffer, bufflen, POS_OWNER_IP4))
return 0;
if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
buffer, bufflen, POS_CONNECTION_IP4))
return 0;
/* Mangle media port. */
bufflen = sprintf(buffer, "%u", port);
if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
buffer, bufflen, POS_MEDIA))
return 0;
return mangle_content_len(pskb, ctinfo, ct, dptr);
}
static void ip_nat_sdp_expect(struct nf_conn *ct,
struct nf_conntrack_expect *exp)
{
struct nf_nat_range range;
/* This must be a fresh one. */
BUG_ON(ct->status & IPS_NAT_DONE_MASK);
/* Change src to where master sends to */
range.flags = IP_NAT_RANGE_MAP_IPS;
range.min_ip = range.max_ip
= ct->master->tuplehash[!exp->dir].tuple.dst.u3.ip;
/* hook doesn't matter, but it has to do source manip */
nf_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
/* For DST manip, map port here to where it's expected. */
range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
range.min = range.max = exp->saved_proto;
range.min_ip = range.max_ip = exp->saved_ip;
/* hook doesn't matter, but it has to do destination manip */
nf_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
}
/* So, this packet has hit the connection tracking matching code.
Mangle it, and change the expectation to match the new version. */
static unsigned int ip_nat_sdp(struct sk_buff **pskb,
enum ip_conntrack_info ctinfo,
struct nf_conntrack_expect *exp,
const char *dptr)
{
struct nf_conn *ct = exp->master;
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
__be32 newip;
u_int16_t port;
DEBUGP("ip_nat_sdp():\n");
/* Connection will come from reply */
newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
exp->saved_ip = exp->tuple.dst.u3.ip;
exp->tuple.dst.u3.ip = newip;
exp->saved_proto.udp.port = exp->tuple.dst.u.udp.port;
exp->dir = !dir;
/* When you see the packet, we need to NAT it the same as the
this one. */
exp->expectfn = ip_nat_sdp_expect;
/* Try to get same port: if not, try to change it. */
for (port = ntohs(exp->saved_proto.udp.port); port != 0; port++) {
exp->tuple.dst.u.udp.port = htons(port);
if (nf_conntrack_expect_related(exp) == 0)
break;
}
if (port == 0)
return NF_DROP;
if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
nf_conntrack_unexpect_related(exp);
return NF_DROP;
}
return NF_ACCEPT;
}
static void __exit nf_nat_sip_fini(void)
{
rcu_assign_pointer(nf_nat_sip_hook, NULL);
rcu_assign_pointer(nf_nat_sdp_hook, NULL);
synchronize_rcu();
}
static int __init nf_nat_sip_init(void)
{
BUG_ON(rcu_dereference(nf_nat_sip_hook));
BUG_ON(rcu_dereference(nf_nat_sdp_hook));
rcu_assign_pointer(nf_nat_sip_hook, ip_nat_sip);
rcu_assign_pointer(nf_nat_sdp_hook, ip_nat_sdp);
return 0;
}
module_init(nf_nat_sip_init);
module_exit(nf_nat_sip_fini);
