summaryrefslogtreecommitdiff
path: root/net/netfilter/xt_osf.c
blob: 4e3c3affd2859060520e3717acf4d691fb16542f (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
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
/*
 * Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net>
 *
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/kernel.h>

#include <linux/if.h>
#include <linux/inetdevice.h>
#include <linux/ip.h>
#include <linux/list.h>
#include <linux/rculist.h>
#include <linux/skbuff.h>
#include <linux/slab.h>
#include <linux/tcp.h>

#include <net/ip.h>
#include <net/tcp.h>

#include <linux/netfilter/nfnetlink.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_log.h>
#include <linux/netfilter/xt_osf.h>

struct xt_osf_finger {
	struct rcu_head			rcu_head;
	struct list_head		finger_entry;
	struct xt_osf_user_finger	finger;
};

enum osf_fmatch_states {
	/* Packet does not match the fingerprint */
	FMATCH_WRONG = 0,
	/* Packet matches the fingerprint */
	FMATCH_OK,
	/* Options do not match the fingerprint, but header does */
	FMATCH_OPT_WRONG,
};

/*
 * Indexed by dont-fragment bit.
 * It is the only constant value in the fingerprint.
 */
static struct list_head xt_osf_fingers[2];

static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
	[OSF_ATTR_FINGER]	= { .len = sizeof(struct xt_osf_user_finger) },
};

static int xt_osf_add_callback(struct net *net, struct sock *ctnl,
			       struct sk_buff *skb, const struct nlmsghdr *nlh,
			       const struct nlattr * const osf_attrs[])
{
	struct xt_osf_user_finger *f;
	struct xt_osf_finger *kf = NULL, *sf;
	int err = 0;

	if (!osf_attrs[OSF_ATTR_FINGER])
		return -EINVAL;

	if (!(nlh->nlmsg_flags & NLM_F_CREATE))
		return -EINVAL;

	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);

	kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
	if (!kf)
		return -ENOMEM;

	memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));

	list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
		if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
			continue;

		kfree(kf);
		kf = NULL;

		if (nlh->nlmsg_flags & NLM_F_EXCL)
			err = -EEXIST;
		break;
	}

	/*
	 * We are protected by nfnl mutex.
	 */
	if (kf)
		list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);

	return err;
}

static int xt_osf_remove_callback(struct net *net, struct sock *ctnl,
				  struct sk_buff *skb,
				  const struct nlmsghdr *nlh,
				  const struct nlattr * const osf_attrs[])
{
	struct xt_osf_user_finger *f;
	struct xt_osf_finger *sf;
	int err = -ENOENT;

	if (!osf_attrs[OSF_ATTR_FINGER])
		return -EINVAL;

	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);

	list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
		if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
			continue;

		/*
		 * We are protected by nfnl mutex.
		 */
		list_del_rcu(&sf->finger_entry);
		kfree_rcu(sf, rcu_head);

		err = 0;
		break;
	}

	return err;
}

static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
	[OSF_MSG_ADD]	= {
		.call		= xt_osf_add_callback,
		.attr_count	= OSF_ATTR_MAX,
		.policy		= xt_osf_policy,
	},
	[OSF_MSG_REMOVE]	= {
		.call		= xt_osf_remove_callback,
		.attr_count	= OSF_ATTR_MAX,
		.policy		= xt_osf_policy,
	},
};

static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
	.name			= "osf",
	.subsys_id		= NFNL_SUBSYS_OSF,
	.cb_count		= OSF_MSG_MAX,
	.cb			= xt_osf_nfnetlink_callbacks,
};

static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
			    unsigned char f_ttl)
{
	const struct iphdr *ip = ip_hdr(skb);

	if (info->flags & XT_OSF_TTL) {
		if (info->ttl == XT_OSF_TTL_TRUE)
			return ip->ttl == f_ttl;
		if (info->ttl == XT_OSF_TTL_NOCHECK)
			return 1;
		else if (ip->ttl <= f_ttl)
			return 1;
		else {
			struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
			int ret = 0;

			for_ifa(in_dev) {
				if (inet_ifa_match(ip->saddr, ifa)) {
					ret = (ip->ttl == f_ttl);
					break;
				}
			}
			endfor_ifa(in_dev);

			return ret;
		}
	}

	return ip->ttl == f_ttl;
}

static bool
xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
{
	const struct xt_osf_info *info = p->matchinfo;
	const struct iphdr *ip = ip_hdr(skb);
	const struct tcphdr *tcp;
	struct tcphdr _tcph;
	int fmatch = FMATCH_WRONG, fcount = 0;
	unsigned int optsize = 0, check_WSS = 0;
	u16 window, totlen, mss = 0;
	bool df;
	const unsigned char *optp = NULL, *_optp = NULL;
	unsigned char opts[MAX_IPOPTLEN];
	const struct xt_osf_finger *kf;
	const struct xt_osf_user_finger *f;
	struct net *net = p->net;

	if (!info)
		return false;

	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
	if (!tcp)
		return false;

	if (!tcp->syn)
		return false;

	totlen = ntohs(ip->tot_len);
	df = ntohs(ip->frag_off) & IP_DF;
	window = ntohs(tcp->window);

	if (tcp->doff * 4 > sizeof(struct tcphdr)) {
		optsize = tcp->doff * 4 - sizeof(struct tcphdr);

		_optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
				sizeof(struct tcphdr), optsize, opts);
	}

	rcu_read_lock();
	list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
		int foptsize, optnum;

		f = &kf->finger;

		if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
			continue;

		optp = _optp;
		fmatch = FMATCH_WRONG;

		if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
			continue;

		/*
		 * Should not happen if userspace parser was written correctly.
		 */
		if (f->wss.wc >= OSF_WSS_MAX)
			continue;

		/* Check options */

		foptsize = 0;
		for (optnum = 0; optnum < f->opt_num; ++optnum)
			foptsize += f->opt[optnum].length;

		if (foptsize > MAX_IPOPTLEN ||
		    optsize > MAX_IPOPTLEN ||
		    optsize != foptsize)
			continue;

		check_WSS = f->wss.wc;

		for (optnum = 0; optnum < f->opt_num; ++optnum) {
			if (f->opt[optnum].kind == (*optp)) {
				__u32 len = f->opt[optnum].length;
				const __u8 *optend = optp + len;
				int loop_cont = 0;

				fmatch = FMATCH_OK;

				switch (*optp) {
				case OSFOPT_MSS:
					mss = optp[3];
					mss <<= 8;
					mss |= optp[2];

					mss = ntohs((__force __be16)mss);
					break;
				case OSFOPT_TS:
					loop_cont = 1;
					break;
				}

				optp = optend;
			} else
				fmatch = FMATCH_OPT_WRONG;

			if (fmatch != FMATCH_OK)
				break;
		}

		if (fmatch != FMATCH_OPT_WRONG) {
			fmatch = FMATCH_WRONG;

			switch (check_WSS) {
			case OSF_WSS_PLAIN:
				if (f->wss.val == 0 || window == f->wss.val)
					fmatch = FMATCH_OK;
				break;
			case OSF_WSS_MSS:
				/*
				 * Some smart modems decrease mangle MSS to
				 * SMART_MSS_2, so we check standard, decreased
				 * and the one provided in the fingerprint MSS
				 * values.
				 */
#define SMART_MSS_1	1460
#define SMART_MSS_2	1448
				if (window == f->wss.val * mss ||
				    window == f->wss.val * SMART_MSS_1 ||
				    window == f->wss.val * SMART_MSS_2)
					fmatch = FMATCH_OK;
				break;
			case OSF_WSS_MTU:
				if (window == f->wss.val * (mss + 40) ||
				    window == f->wss.val * (SMART_MSS_1 + 40) ||
				    window == f->wss.val * (SMART_MSS_2 + 40))
					fmatch = FMATCH_OK;
				break;
			case OSF_WSS_MODULO:
				if ((window % f->wss.val) == 0)
					fmatch = FMATCH_OK;
				break;
			}
		}

		if (fmatch != FMATCH_OK)
			continue;

		fcount++;

		if (info->flags & XT_OSF_LOG)
			nf_log_packet(net, p->family, p->hooknum, skb,
				      p->in, p->out, NULL,
				      "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
				      f->genre, f->version, f->subtype,
				      &ip->saddr, ntohs(tcp->source),
				      &ip->daddr, ntohs(tcp->dest),
				      f->ttl - ip->ttl);

		if ((info->flags & XT_OSF_LOG) &&
		    info->loglevel == XT_OSF_LOGLEVEL_FIRST)
			break;
	}
	rcu_read_unlock();

	if (!fcount && (info->flags & XT_OSF_LOG))
		nf_log_packet(net, p->family, p->hooknum, skb, p->in,
			      p->out, NULL,
			"Remote OS is not known: %pI4:%u -> %pI4:%u\n",
				&ip->saddr, ntohs(tcp->source),
				&ip->daddr, ntohs(tcp->dest));

	if (fcount)
		fmatch = FMATCH_OK;

	return fmatch == FMATCH_OK;
}

static struct xt_match xt_osf_match = {
	.name 		= "osf",
	.revision	= 0,
	.family		= NFPROTO_IPV4,
	.proto		= IPPROTO_TCP,
	.hooks      	= (1 << NF_INET_LOCAL_IN) |
				(1 << NF_INET_PRE_ROUTING) |
				(1 << NF_INET_FORWARD),
	.match 		= xt_osf_match_packet,
	.matchsize	= sizeof(struct xt_osf_info),
	.me		= THIS_MODULE,
};

static int __init xt_osf_init(void)
{
	int err = -EINVAL;
	int i;

	for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
		INIT_LIST_HEAD(&xt_osf_fingers[i]);

	err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
	if (err < 0) {
		pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
		goto err_out_exit;
	}

	err = xt_register_match(&xt_osf_match);
	if (err) {
		pr_err("Failed to register OS fingerprint "
		       "matching module (%d)\n", err);
		goto err_out_remove;
	}

	return 0;

err_out_remove:
	nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
err_out_exit:
	return err;
}

static void __exit xt_osf_fini(void)
{
	struct xt_osf_finger *f;
	int i;

	nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
	xt_unregister_match(&xt_osf_match);

	rcu_read_lock();
	for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {

		list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
			list_del_rcu(&f->finger_entry);
			kfree_rcu(f, rcu_head);
		}
	}
	rcu_read_unlock();

	rcu_barrier();
}

module_init(xt_osf_init);
module_exit(xt_osf_fini);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
MODULE_DESCRIPTION("Passive OS fingerprint matching.");
MODULE_ALIAS("ipt_osf");
MODULE_ALIAS("ip6t_osf");
MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);