1/*
2 * Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net>
3 *
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, see <http://www.gnu.org/licenses/>.
17 */
18#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
19#include <linux/module.h>
20#include <linux/kernel.h>
21
22#include <linux/if.h>
23#include <linux/inetdevice.h>
24#include <linux/ip.h>
25#include <linux/list.h>
26#include <linux/rculist.h>
27#include <linux/skbuff.h>
28#include <linux/slab.h>
29#include <linux/tcp.h>
30
31#include <net/ip.h>
32#include <net/tcp.h>
33
34#include <linux/netfilter/nfnetlink.h>
35#include <linux/netfilter/x_tables.h>
36#include <net/netfilter/nf_log.h>
37#include <linux/netfilter/xt_osf.h>
38
39struct xt_osf_finger {
40	struct rcu_head			rcu_head;
41	struct list_head		finger_entry;
42	struct xt_osf_user_finger	finger;
43};
44
45enum osf_fmatch_states {
46	/* Packet does not match the fingerprint */
47	FMATCH_WRONG = 0,
48	/* Packet matches the fingerprint */
49	FMATCH_OK,
50	/* Options do not match the fingerprint, but header does */
51	FMATCH_OPT_WRONG,
52};
53
54/*
55 * Indexed by dont-fragment bit.
56 * It is the only constant value in the fingerprint.
57 */
58static struct list_head xt_osf_fingers[2];
59
60static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
61	[OSF_ATTR_FINGER]	= { .len = sizeof(struct xt_osf_user_finger) },
62};
63
64static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb,
65			       const struct nlmsghdr *nlh,
66			       const struct nlattr * const osf_attrs[])
67{
68	struct xt_osf_user_finger *f;
69	struct xt_osf_finger *kf = NULL, *sf;
70	int err = 0;
71
72	if (!osf_attrs[OSF_ATTR_FINGER])
73		return -EINVAL;
74
75	if (!(nlh->nlmsg_flags & NLM_F_CREATE))
76		return -EINVAL;
77
78	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
79
80	kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
81	if (!kf)
82		return -ENOMEM;
83
84	memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
85
86	list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
87		if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
88			continue;
89
90		kfree(kf);
91		kf = NULL;
92
93		if (nlh->nlmsg_flags & NLM_F_EXCL)
94			err = -EEXIST;
95		break;
96	}
97
98	/*
99	 * We are protected by nfnl mutex.
100	 */
101	if (kf)
102		list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
103
104	return err;
105}
106
107static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
108				  const struct nlmsghdr *nlh,
109				  const struct nlattr * const osf_attrs[])
110{
111	struct xt_osf_user_finger *f;
112	struct xt_osf_finger *sf;
113	int err = -ENOENT;
114
115	if (!osf_attrs[OSF_ATTR_FINGER])
116		return -EINVAL;
117
118	f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
119
120	list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
121		if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
122			continue;
123
124		/*
125		 * We are protected by nfnl mutex.
126		 */
127		list_del_rcu(&sf->finger_entry);
128		kfree_rcu(sf, rcu_head);
129
130		err = 0;
131		break;
132	}
133
134	return err;
135}
136
137static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
138	[OSF_MSG_ADD]	= {
139		.call		= xt_osf_add_callback,
140		.attr_count	= OSF_ATTR_MAX,
141		.policy		= xt_osf_policy,
142	},
143	[OSF_MSG_REMOVE]	= {
144		.call		= xt_osf_remove_callback,
145		.attr_count	= OSF_ATTR_MAX,
146		.policy		= xt_osf_policy,
147	},
148};
149
150static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
151	.name			= "osf",
152	.subsys_id		= NFNL_SUBSYS_OSF,
153	.cb_count		= OSF_MSG_MAX,
154	.cb			= xt_osf_nfnetlink_callbacks,
155};
156
157static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
158			    unsigned char f_ttl)
159{
160	const struct iphdr *ip = ip_hdr(skb);
161
162	if (info->flags & XT_OSF_TTL) {
163		if (info->ttl == XT_OSF_TTL_TRUE)
164			return ip->ttl == f_ttl;
165		if (info->ttl == XT_OSF_TTL_NOCHECK)
166			return 1;
167		else if (ip->ttl <= f_ttl)
168			return 1;
169		else {
170			struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
171			int ret = 0;
172
173			for_ifa(in_dev) {
174				if (inet_ifa_match(ip->saddr, ifa)) {
175					ret = (ip->ttl == f_ttl);
176					break;
177				}
178			}
179			endfor_ifa(in_dev);
180
181			return ret;
182		}
183	}
184
185	return ip->ttl == f_ttl;
186}
187
188static bool
189xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
190{
191	const struct xt_osf_info *info = p->matchinfo;
192	const struct iphdr *ip = ip_hdr(skb);
193	const struct tcphdr *tcp;
194	struct tcphdr _tcph;
195	int fmatch = FMATCH_WRONG, fcount = 0;
196	unsigned int optsize = 0, check_WSS = 0;
197	u16 window, totlen, mss = 0;
198	bool df;
199	const unsigned char *optp = NULL, *_optp = NULL;
200	unsigned char opts[MAX_IPOPTLEN];
201	const struct xt_osf_finger *kf;
202	const struct xt_osf_user_finger *f;
203	struct net *net = dev_net(p->in ? p->in : p->out);
204
205	if (!info)
206		return false;
207
208	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
209	if (!tcp)
210		return false;
211
212	if (!tcp->syn)
213		return false;
214
215	totlen = ntohs(ip->tot_len);
216	df = ntohs(ip->frag_off) & IP_DF;
217	window = ntohs(tcp->window);
218
219	if (tcp->doff * 4 > sizeof(struct tcphdr)) {
220		optsize = tcp->doff * 4 - sizeof(struct tcphdr);
221
222		_optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
223				sizeof(struct tcphdr), optsize, opts);
224	}
225
226	rcu_read_lock();
227	list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
228		f = &kf->finger;
229
230		if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
231			continue;
232
233		optp = _optp;
234		fmatch = FMATCH_WRONG;
235
236		if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) {
237			int foptsize, optnum;
238
239			/*
240			 * Should not happen if userspace parser was written correctly.
241			 */
242			if (f->wss.wc >= OSF_WSS_MAX)
243				continue;
244
245			/* Check options */
246
247			foptsize = 0;
248			for (optnum = 0; optnum < f->opt_num; ++optnum)
249				foptsize += f->opt[optnum].length;
250
251			if (foptsize > MAX_IPOPTLEN ||
252				optsize > MAX_IPOPTLEN ||
253				optsize != foptsize)
254				continue;
255
256			check_WSS = f->wss.wc;
257
258			for (optnum = 0; optnum < f->opt_num; ++optnum) {
259				if (f->opt[optnum].kind == (*optp)) {
260					__u32 len = f->opt[optnum].length;
261					const __u8 *optend = optp + len;
262					int loop_cont = 0;
263
264					fmatch = FMATCH_OK;
265
266					switch (*optp) {
267					case OSFOPT_MSS:
268						mss = optp[3];
269						mss <<= 8;
270						mss |= optp[2];
271
272						mss = ntohs((__force __be16)mss);
273						break;
274					case OSFOPT_TS:
275						loop_cont = 1;
276						break;
277					}
278
279					optp = optend;
280				} else
281					fmatch = FMATCH_OPT_WRONG;
282
283				if (fmatch != FMATCH_OK)
284					break;
285			}
286
287			if (fmatch != FMATCH_OPT_WRONG) {
288				fmatch = FMATCH_WRONG;
289
290				switch (check_WSS) {
291				case OSF_WSS_PLAIN:
292					if (f->wss.val == 0 || window == f->wss.val)
293						fmatch = FMATCH_OK;
294					break;
295				case OSF_WSS_MSS:
296					/*
297					 * Some smart modems decrease mangle MSS to
298					 * SMART_MSS_2, so we check standard, decreased
299					 * and the one provided in the fingerprint MSS
300					 * values.
301					 */
302#define SMART_MSS_1	1460
303#define SMART_MSS_2	1448
304					if (window == f->wss.val * mss ||
305					    window == f->wss.val * SMART_MSS_1 ||
306					    window == f->wss.val * SMART_MSS_2)
307						fmatch = FMATCH_OK;
308					break;
309				case OSF_WSS_MTU:
310					if (window == f->wss.val * (mss + 40) ||
311					    window == f->wss.val * (SMART_MSS_1 + 40) ||
312					    window == f->wss.val * (SMART_MSS_2 + 40))
313						fmatch = FMATCH_OK;
314					break;
315				case OSF_WSS_MODULO:
316					if ((window % f->wss.val) == 0)
317						fmatch = FMATCH_OK;
318					break;
319				}
320			}
321
322			if (fmatch != FMATCH_OK)
323				continue;
324
325			fcount++;
326
327			if (info->flags & XT_OSF_LOG)
328				nf_log_packet(net, p->family, p->hooknum, skb,
329					p->in, p->out, NULL,
330					"%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
331					f->genre, f->version, f->subtype,
332					&ip->saddr, ntohs(tcp->source),
333					&ip->daddr, ntohs(tcp->dest),
334					f->ttl - ip->ttl);
335
336			if ((info->flags & XT_OSF_LOG) &&
337			    info->loglevel == XT_OSF_LOGLEVEL_FIRST)
338				break;
339		}
340	}
341	rcu_read_unlock();
342
343	if (!fcount && (info->flags & XT_OSF_LOG))
344		nf_log_packet(net, p->family, p->hooknum, skb, p->in,
345			      p->out, NULL,
346			"Remote OS is not known: %pI4:%u -> %pI4:%u\n",
347				&ip->saddr, ntohs(tcp->source),
348				&ip->daddr, ntohs(tcp->dest));
349
350	if (fcount)
351		fmatch = FMATCH_OK;
352
353	return fmatch == FMATCH_OK;
354}
355
356static struct xt_match xt_osf_match = {
357	.name 		= "osf",
358	.revision	= 0,
359	.family		= NFPROTO_IPV4,
360	.proto		= IPPROTO_TCP,
361	.hooks      	= (1 << NF_INET_LOCAL_IN) |
362				(1 << NF_INET_PRE_ROUTING) |
363				(1 << NF_INET_FORWARD),
364	.match 		= xt_osf_match_packet,
365	.matchsize	= sizeof(struct xt_osf_info),
366	.me		= THIS_MODULE,
367};
368
369static int __init xt_osf_init(void)
370{
371	int err = -EINVAL;
372	int i;
373
374	for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
375		INIT_LIST_HEAD(&xt_osf_fingers[i]);
376
377	err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
378	if (err < 0) {
379		pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
380		goto err_out_exit;
381	}
382
383	err = xt_register_match(&xt_osf_match);
384	if (err) {
385		pr_err("Failed to register OS fingerprint "
386		       "matching module (%d)\n", err);
387		goto err_out_remove;
388	}
389
390	return 0;
391
392err_out_remove:
393	nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
394err_out_exit:
395	return err;
396}
397
398static void __exit xt_osf_fini(void)
399{
400	struct xt_osf_finger *f;
401	int i;
402
403	nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
404	xt_unregister_match(&xt_osf_match);
405
406	rcu_read_lock();
407	for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
408
409		list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
410			list_del_rcu(&f->finger_entry);
411			kfree_rcu(f, rcu_head);
412		}
413	}
414	rcu_read_unlock();
415
416	rcu_barrier();
417}
418
419module_init(xt_osf_init);
420module_exit(xt_osf_fini);
421
422MODULE_LICENSE("GPL");
423MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
424MODULE_DESCRIPTION("Passive OS fingerprint matching.");
425MODULE_ALIAS("ipt_osf");
426MODULE_ALIAS("ip6t_osf");
427MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
428