nf_nat_sip.c 8.79 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
/* 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>
14
#include <net/ip.h>
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
#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");

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,
88
				      matchoff, matchlen, addr, addrlen))
89
		return 0;
90
	*dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
91
92
93
94
95
96
97
98
99
100
101
102
103
	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;

104
	dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
	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,
149
				      matchoff, matchlen, buffer, bufflen))
150
151
152
		return 0;

	/* We need to reload this. Thanks Patrick. */
153
	*dptr = (*pskb)->data + ip_hdrlen(*pskb) + sizeof(struct udphdr);
154
155
156
157
158
159
160
161
162
163
164
165
	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;

166
	dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
167
168
169

	/* Get actual SDP lenght */
	if (ct_sip_get_info(ct, dptr, (*pskb)->len - dataoff, &matchoff,
170
			    &matchlen, POS_SDP_HEADER) > 0) {
171
172
173
174
175
176
177

		/* 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,
178
				    &matchlen, POS_CONTENT) > 0) {
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197

			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;

198
	dataoff = ip_hdrlen(*pskb) + sizeof(struct udphdr);
199
200
201
202

	/* 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,
203
			       buffer, bufflen, POS_OWNER_IP4))
204
205
206
		return 0;

	if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
207
			       buffer, bufflen, POS_CONNECTION_IP4))
208
209
210
211
212
		return 0;

	/* Mangle media port. */
	bufflen = sprintf(buffer, "%u", port);
	if (!mangle_sip_packet(pskb, ctinfo, ct, &dptr, (*pskb)->len - dataoff,
213
			       buffer, bufflen, POS_MEDIA))
214
215
216
217
218
		return 0;

	return mangle_content_len(pskb, ctinfo, ct, dptr);
}

219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
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);
}

242
243
244
245
246
247
248
249
250
251
252
253
254
/* 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;

	/* Connection will come from reply */
255
256
257
258
259
	if (ct->tuplehash[dir].tuple.src.u3.ip ==
	    ct->tuplehash[!dir].tuple.dst.u3.ip)
		newip = exp->tuple.dst.u3.ip;
	else
		newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
260

261
	exp->saved_ip = exp->tuple.dst.u3.ip;
262
263
264
265
266
267
	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. */
268
	exp->expectfn = ip_nat_sdp_expect;
269
270
271
272

	/* 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);
273
		if (nf_ct_expect_related(exp) == 0)
274
275
276
277
278
279
280
			break;
	}

	if (port == 0)
		return NF_DROP;

	if (!mangle_sdp(pskb, ctinfo, ct, newip, port, dptr)) {
281
		nf_ct_unexpect_related(exp);
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
		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);