aboutsummaryrefslogtreecommitdiff
path: root/net/netfilter/xt_l2tp.c
blob: 8aee572771f2b698a2f8e12a226be7af71adbd04 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
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
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
/* Kernel module to match L2TP header parameters. */

/* (C) 2013      James Chapman <jchapman@katalix.com>
 *
 * 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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/if_ether.h>
#include <net/ip.h>
#include <linux/ipv6.h>
#include <net/ipv6.h>
#include <net/udp.h>
#include <linux/l2tp.h>

#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_tcpudp.h>
#include <linux/netfilter/xt_l2tp.h>

/* L2TP header masks */
#define L2TP_HDR_T_BIT	0x8000
#define L2TP_HDR_L_BIT	0x4000
#define L2TP_HDR_VER	0x000f

MODULE_LICENSE("GPL");
MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
MODULE_DESCRIPTION("Xtables: L2TP header match");
MODULE_ALIAS("ipt_l2tp");
MODULE_ALIAS("ip6t_l2tp");

/* The L2TP fields that can be matched */
struct l2tp_data {
	u32 tid;
	u32 sid;
	u8 type;
	u8 version;
};

union l2tp_val {
	__be16 val16[2];
	__be32 val32;
};

static bool l2tp_match(const struct xt_l2tp_info *info, struct l2tp_data *data)
{
	if ((info->flags & XT_L2TP_TYPE) && (info->type != data->type))
		return false;

	if ((info->flags & XT_L2TP_VERSION) && (info->version != data->version))
		return false;

	/* Check tid only for L2TPv3 control or any L2TPv2 packets */
	if ((info->flags & XT_L2TP_TID) &&
	    ((data->type == XT_L2TP_TYPE_CONTROL) || (data->version == 2)) &&
	    (info->tid != data->tid))
		return false;

	/* Check sid only for L2TP data packets */
	if ((info->flags & XT_L2TP_SID) && (data->type == XT_L2TP_TYPE_DATA) &&
	    (info->sid != data->sid))
		return false;

	return true;
}

/* Parse L2TP header fields when UDP encapsulation is used. Handles
 * L2TPv2 and L2TPv3. Note the L2TPv3 control and data packets have a
 * different format. See
 * RFC2661, Section 3.1, L2TPv2 Header Format
 * RFC3931, Section 3.2.1, L2TPv3 Control Message Header
 * RFC3931, Section 3.2.2, L2TPv3 Data Message Header
 * RFC3931, Section 4.1.2.1, L2TPv3 Session Header over UDP
 */
static bool l2tp_udp_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff)
{
	const struct xt_l2tp_info *info = par->matchinfo;
	int uhlen = sizeof(struct udphdr);
	int offs = thoff + uhlen;
	union l2tp_val *lh;
	union l2tp_val lhbuf;
	u16 flags;
	struct l2tp_data data = { 0, };

	if (par->fragoff != 0)
		return false;

	/* Extract L2TP header fields. The flags in the first 16 bits
	 * tell us where the other fields are.
	 */
	lh = skb_header_pointer(skb, offs, 2, &lhbuf);
	if (lh == NULL)
		return false;

	flags = ntohs(lh->val16[0]);
	if (flags & L2TP_HDR_T_BIT)
		data.type = XT_L2TP_TYPE_CONTROL;
	else
		data.type = XT_L2TP_TYPE_DATA;
	data.version = (u8) flags & L2TP_HDR_VER;

	/* Now extract the L2TP tid/sid. These are in different places
	 * for L2TPv2 (rfc2661) and L2TPv3 (rfc3931). For L2TPv2, we
	 * must also check to see if the length field is present,
	 * since this affects the offsets into the packet of the
	 * tid/sid fields.
	 */
	if (data.version == 3) {
		lh = skb_header_pointer(skb, offs + 4, 4, &lhbuf);
		if (lh == NULL)
			return false;
		if (data.type == XT_L2TP_TYPE_CONTROL)
			data.tid = ntohl(lh->val32);
		else
			data.sid = ntohl(lh->val32);
	} else if (data.version == 2) {
		if (flags & L2TP_HDR_L_BIT)
			offs += 2;
		lh = skb_header_pointer(skb, offs + 2, 4, &lhbuf);
		if (lh == NULL)
			return false;
		data.tid = (u32) ntohs(lh->val16[0]);
		data.sid = (u32) ntohs(lh->val16[1]);
	} else
		return false;

	return l2tp_match(info, &data);
}

/* Parse L2TP header fields for IP encapsulation (no UDP header).
 * L2TPv3 data packets have a different form with IP encap. See
 * RC3931, Section 4.1.1.1, L2TPv3 Session Header over IP.
 * RC3931, Section 4.1.1.2, L2TPv3 Control and Data Traffic over IP.
 */
static bool l2tp_ip_mt(const struct sk_buff *skb, struct xt_action_param *par, u16 thoff)
{
	const struct xt_l2tp_info *info = par->matchinfo;
	union l2tp_val *lh;
	union l2tp_val lhbuf;
	struct l2tp_data data = { 0, };

	/* For IP encap, the L2TP sid is the first 32-bits. */
	lh = skb_header_pointer(skb, thoff, sizeof(lhbuf), &lhbuf);
	if (lh == NULL)
		return false;
	if (lh->val32 == 0) {
		/* Must be a control packet. The L2TP tid is further
		 * into the packet.
		 */
		data.type = XT_L2TP_TYPE_CONTROL;
		lh = skb_header_pointer(skb, thoff + 8, sizeof(lhbuf),
					&lhbuf);
		if (lh == NULL)
			return false;
		data.tid = ntohl(lh->val32);
	} else {
		data.sid = ntohl(lh->val32);
		data.type = XT_L2TP_TYPE_DATA;
	}

	data.version = 3;

	return l2tp_match(info, &data);
}

static bool l2tp_mt4(const struct sk_buff *skb, struct xt_action_param *par)
{
	struct iphdr *iph = ip_hdr(skb);
	u8 ipproto = iph->protocol;

	/* l2tp_mt_check4 already restricts the transport protocol */
	switch (ipproto) {
	case IPPROTO_UDP:
		return l2tp_udp_mt(skb, par, par->thoff);
	case IPPROTO_L2TP:
		return l2tp_ip_mt(skb, par, par->thoff);
	}

	return false;
}

#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static bool l2tp_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
	unsigned int thoff = 0;
	unsigned short fragoff = 0;
	int ipproto;

	ipproto = ipv6_find_hdr(skb, &thoff, -1, &fragoff, NULL);
	if (fragoff != 0)
		return false;

	/* l2tp_mt_check6 already restricts the transport protocol */
	switch (ipproto) {
	case IPPROTO_UDP:
		return l2tp_udp_mt(skb, par, thoff);
	case IPPROTO_L2TP:
		return l2tp_ip_mt(skb, par, thoff);
	}

	return false;
}
#endif

static int l2tp_mt_check(const struct xt_mtchk_param *par)
{
	const struct xt_l2tp_info *info = par->matchinfo;

	/* Check for invalid flags */
	if (info->flags & ~(XT_L2TP_TID | XT_L2TP_SID | XT_L2TP_VERSION |
			    XT_L2TP_TYPE)) {
		pr_info("unknown flags: %x\n", info->flags);
		return -EINVAL;
	}

	/* At least one of tid, sid or type=control must be specified */
	if ((!(info->flags & XT_L2TP_TID)) &&
	    (!(info->flags & XT_L2TP_SID)) &&
	    ((!(info->flags & XT_L2TP_TYPE)) ||
	     (info->type != XT_L2TP_TYPE_CONTROL))) {
		pr_info("invalid flags combination: %x\n", info->flags);
		return -EINVAL;
	}

	/* If version 2 is specified, check that incompatible params
	 * are not supplied
	 */
	if (info->flags & XT_L2TP_VERSION) {
		if ((info->version < 2) || (info->version > 3)) {
			pr_info("wrong L2TP version: %u\n", info->version);
			return -EINVAL;
		}

		if (info->version == 2) {
			if ((info->flags & XT_L2TP_TID) &&
			    (info->tid > 0xffff)) {
				pr_info("v2 tid > 0xffff: %u\n", info->tid);
				return -EINVAL;
			}
			if ((info->flags & XT_L2TP_SID) &&
			    (info->sid > 0xffff)) {
				pr_info("v2 sid > 0xffff: %u\n", info->sid);
				return -EINVAL;
			}
		}
	}

	return 0;
}

static int l2tp_mt_check4(const struct xt_mtchk_param *par)
{
	const struct xt_l2tp_info *info = par->matchinfo;
	const struct ipt_entry *e = par->entryinfo;
	const struct ipt_ip *ip = &e->ip;
	int ret;

	ret = l2tp_mt_check(par);
	if (ret != 0)
		return ret;

	if ((ip->proto != IPPROTO_UDP) &&
	    (ip->proto != IPPROTO_L2TP)) {
		pr_info("missing protocol rule (udp|l2tpip)\n");
		return -EINVAL;
	}

	if ((ip->proto == IPPROTO_L2TP) &&
	    (info->version == 2)) {
		pr_info("v2 doesn't support IP mode\n");
		return -EINVAL;
	}

	return 0;
}

#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
static int l2tp_mt_check6(const struct xt_mtchk_param *par)
{
	const struct xt_l2tp_info *info = par->matchinfo;
	const struct ip6t_entry *e = par->entryinfo;
	const struct ip6t_ip6 *ip = &e->ipv6;
	int ret;

	ret = l2tp_mt_check(par);
	if (ret != 0)
		return ret;

	if ((ip->proto != IPPROTO_UDP) &&
	    (ip->proto != IPPROTO_L2TP)) {
		pr_info("missing protocol rule (udp|l2tpip)\n");
		return -EINVAL;
	}

	if ((ip->proto == IPPROTO_L2TP) &&
	    (info->version == 2)) {
		pr_info("v2 doesn't support IP mode\n");
		return -EINVAL;
	}

	return 0;
}
#endif

static struct xt_match l2tp_mt_reg[] __read_mostly = {
	{
		.name      = "l2tp",
		.revision  = 0,
		.family    = NFPROTO_IPV4,
		.match     = l2tp_mt4,
		.matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)),
		.checkentry = l2tp_mt_check4,
		.hooks     = ((1 << NF_INET_PRE_ROUTING) |
			      (1 << NF_INET_LOCAL_IN) |
			      (1 << NF_INET_LOCAL_OUT) |
			      (1 << NF_INET_FORWARD)),
		.me        = THIS_MODULE,
	},
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
	{
		.name      = "l2tp",
		.revision  = 0,
		.family    = NFPROTO_IPV6,
		.match     = l2tp_mt6,
		.matchsize = XT_ALIGN(sizeof(struct xt_l2tp_info)),
		.checkentry = l2tp_mt_check6,
		.hooks     = ((1 << NF_INET_PRE_ROUTING) |
			      (1 << NF_INET_LOCAL_IN) |
			      (1 << NF_INET_LOCAL_OUT) |
			      (1 << NF_INET_FORWARD)),
		.me        = THIS_MODULE,
	},
#endif
};

static int __init l2tp_mt_init(void)
{
	return xt_register_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg));
}

static void __exit l2tp_mt_exit(void)
{
	xt_unregister_matches(&l2tp_mt_reg[0], ARRAY_SIZE(l2tp_mt_reg));
}

module_init(l2tp_mt_init);
module_exit(l2tp_mt_exit);