summaryrefslogtreecommitdiffstats
path: root/net/netfilter/nfnetlink_osf.c
blob: 916a3c7f9eafe78b6a5507ae6bb5ac39f42e6ba7 (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
430
431
432
433
434
435
436
437
438
// SPDX-License-Identifier: GPL-2.0-only
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/kernel.h>

#include <linux/capability.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/nfnetlink_osf.h>

/*
 * Indexed by dont-fragment bit.
 * It is the only constant value in the fingerprint.
 */
struct list_head nf_osf_fingers[2];
EXPORT_SYMBOL_GPL(nf_osf_fingers);

static inline int nf_osf_ttl(const struct sk_buff *skb,
			     int ttl_check, unsigned char f_ttl)
{
	struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
	const struct iphdr *ip = ip_hdr(skb);
	const struct in_ifaddr *ifa;
	int ret = 0;

	if (ttl_check == NF_OSF_TTL_TRUE)
		return ip->ttl == f_ttl;
	if (ttl_check == NF_OSF_TTL_NOCHECK)
		return 1;
	else if (ip->ttl <= f_ttl)
		return 1;

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

	return ret;
}

struct nf_osf_hdr_ctx {
	bool			df;
	u16			window;
	u16			totlen;
	const unsigned char	*optp;
	unsigned int		optsize;
};

static bool nf_osf_match_one(const struct sk_buff *skb,
			     const struct nf_osf_user_finger *f,
			     int ttl_check,
			     struct nf_osf_hdr_ctx *ctx)
{
	const __u8 *optpinit = ctx->optp;
	unsigned int check_WSS = 0;
	int fmatch = FMATCH_WRONG;
	int foptsize, optnum;
	u16 mss = 0;

	if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
		return false;

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

	/* Check options */

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

	if (foptsize > MAX_IPOPTLEN ||
	    ctx->optsize > MAX_IPOPTLEN ||
	    ctx->optsize != foptsize)
		return false;

	check_WSS = f->wss.wc;

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

			fmatch = FMATCH_OK;

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

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

			ctx->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 || ctx->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 (ctx->window == f->wss.val * mss ||
			    ctx->window == f->wss.val * SMART_MSS_1 ||
			    ctx->window == f->wss.val * SMART_MSS_2)
				fmatch = FMATCH_OK;
			break;
		case OSF_WSS_MTU:
			if (ctx->window == f->wss.val * (mss + 40) ||
			    ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
			    ctx->window == f->wss.val * (SMART_MSS_2 + 40))
				fmatch = FMATCH_OK;
			break;
		case OSF_WSS_MODULO:
			if ((ctx->window % f->wss.val) == 0)
				fmatch = FMATCH_OK;
			break;
		}
	}

	if (fmatch != FMATCH_OK)
		ctx->optp = optpinit;

	return fmatch == FMATCH_OK;
}

static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
						const struct sk_buff *skb,
						const struct iphdr *ip,
						unsigned char *opts,
						struct tcphdr *_tcph)
{
	const struct tcphdr *tcp;

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

	if (!tcp->syn)
		return NULL;

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

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

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

	return tcp;
}

bool
nf_osf_match(const struct sk_buff *skb, u_int8_t family,
	     int hooknum, struct net_device *in, struct net_device *out,
	     const struct nf_osf_info *info, struct net *net,
	     const struct list_head *nf_osf_fingers)
{
	const struct iphdr *ip = ip_hdr(skb);
	const struct nf_osf_user_finger *f;
	unsigned char opts[MAX_IPOPTLEN];
	const struct nf_osf_finger *kf;
	int fcount = 0, ttl_check;
	int fmatch = FMATCH_WRONG;
	struct nf_osf_hdr_ctx ctx;
	const struct tcphdr *tcp;
	struct tcphdr _tcph;

	memset(&ctx, 0, sizeof(ctx));

	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
	if (!tcp)
		return false;

	ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0;

	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {

		f = &kf->finger;

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

		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
			continue;

		fmatch = FMATCH_OK;

		fcount++;

		if (info->flags & NF_OSF_LOG)
			nf_log_packet(net, family, hooknum, skb,
				      in, 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 & NF_OSF_LOG) &&
		    info->loglevel == NF_OSF_LOGLEVEL_FIRST)
			break;
	}

	if (!fcount && (info->flags & NF_OSF_LOG))
		nf_log_packet(net, family, hooknum, skb, in, 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;
}
EXPORT_SYMBOL_GPL(nf_osf_match);

bool nf_osf_find(const struct sk_buff *skb,
		 const struct list_head *nf_osf_fingers,
		 const int ttl_check, struct nf_osf_data *data)
{
	const struct iphdr *ip = ip_hdr(skb);
	const struct nf_osf_user_finger *f;
	unsigned char opts[MAX_IPOPTLEN];
	const struct nf_osf_finger *kf;
	struct nf_osf_hdr_ctx ctx;
	const struct tcphdr *tcp;
	struct tcphdr _tcph;

	memset(&ctx, 0, sizeof(ctx));

	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
	if (!tcp)
		return false;

	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
		f = &kf->finger;
		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
			continue;

		data->genre = f->genre;
		data->version = f->version;
		break;
	}

	return true;
}
EXPORT_SYMBOL_GPL(nf_osf_find);

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

static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl,
				 struct sk_buff *skb, const struct nlmsghdr *nlh,
				 const struct nlattr * const osf_attrs[],
				 struct netlink_ext_ack *extack)
{
	struct nf_osf_user_finger *f;
	struct nf_osf_finger *kf = NULL, *sf;
	int err = 0;

	if (!capable(CAP_NET_ADMIN))
		return -EPERM;

	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 nf_osf_finger), GFP_KERNEL);
	if (!kf)
		return -ENOMEM;

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

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

	return err;
}

static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl,
				    struct sk_buff *skb,
				    const struct nlmsghdr *nlh,
				    const struct nlattr * const osf_attrs[],
				    struct netlink_ext_ack *extack)
{
	struct nf_osf_user_finger *f;
	struct nf_osf_finger *sf;
	int err = -ENOENT;

	if (!capable(CAP_NET_ADMIN))
		return -EPERM;

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

	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);

	list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) {
		if (memcmp(&sf->finger, f, sizeof(struct nf_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 nfnl_osf_callbacks[OSF_MSG_MAX] = {
	[OSF_MSG_ADD]	= {
		.call		= nfnl_osf_add_callback,
		.attr_count	= OSF_ATTR_MAX,
		.policy		= nfnl_osf_policy,
	},
	[OSF_MSG_REMOVE]	= {
		.call		= nfnl_osf_remove_callback,
		.attr_count	= OSF_ATTR_MAX,
		.policy		= nfnl_osf_policy,
	},
};

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

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

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

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

err_out_exit:
	return err;
}

static void __exit nfnl_osf_fini(void)
{
	struct nf_osf_finger *f;
	int i;

	nfnetlink_subsys_unregister(&nfnl_osf_subsys);

	rcu_read_lock();
	for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) {
		list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) {
			list_del_rcu(&f->finger_entry);
			kfree_rcu(f, rcu_head);
		}
	}
	rcu_read_unlock();

	rcu_barrier();
}

module_init(nfnl_osf_init);
module_exit(nfnl_osf_fini);

MODULE_LICENSE("GPL");