Loading...
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Copyright (c) 2003+ Evgeniy Polyakov <zbr@ioremap.net>
4 */
5#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
6#include <linux/module.h>
7#include <linux/kernel.h>
8
9#include <linux/capability.h>
10#include <linux/if.h>
11#include <linux/inetdevice.h>
12#include <linux/ip.h>
13#include <linux/list.h>
14#include <linux/rculist.h>
15#include <linux/skbuff.h>
16#include <linux/slab.h>
17#include <linux/tcp.h>
18
19#include <net/ip.h>
20#include <net/tcp.h>
21
22#include <linux/netfilter/nfnetlink.h>
23#include <linux/netfilter/x_tables.h>
24#include <net/netfilter/nf_log.h>
25#include <linux/netfilter/xt_osf.h>
26
27static bool
28xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
29{
30 return nf_osf_match(skb, xt_family(p), xt_hooknum(p), xt_in(p),
31 xt_out(p), p->matchinfo, xt_net(p), nf_osf_fingers);
32}
33
34static struct xt_match xt_osf_match = {
35 .name = "osf",
36 .revision = 0,
37 .family = NFPROTO_IPV4,
38 .proto = IPPROTO_TCP,
39 .hooks = (1 << NF_INET_LOCAL_IN) |
40 (1 << NF_INET_PRE_ROUTING) |
41 (1 << NF_INET_FORWARD),
42 .match = xt_osf_match_packet,
43 .matchsize = sizeof(struct xt_osf_info),
44 .me = THIS_MODULE,
45};
46
47static int __init xt_osf_init(void)
48{
49 int err;
50
51 err = xt_register_match(&xt_osf_match);
52 if (err) {
53 pr_err("Failed to register OS fingerprint "
54 "matching module (%d)\n", err);
55 return err;
56 }
57
58 return 0;
59}
60
61static void __exit xt_osf_fini(void)
62{
63 xt_unregister_match(&xt_osf_match);
64}
65
66module_init(xt_osf_init);
67module_exit(xt_osf_fini);
68
69MODULE_LICENSE("GPL");
70MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
71MODULE_DESCRIPTION("Passive OS fingerprint matching.");
72MODULE_ALIAS("ipt_osf");
73MODULE_ALIAS("ip6t_osf");
74MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
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 net *net, struct sock *ctnl,
65 struct sk_buff *skb, 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 net *net, struct sock *ctnl,
108 struct sk_buff *skb,
109 const struct nlmsghdr *nlh,
110 const struct nlattr * const osf_attrs[])
111{
112 struct xt_osf_user_finger *f;
113 struct xt_osf_finger *sf;
114 int err = -ENOENT;
115
116 if (!osf_attrs[OSF_ATTR_FINGER])
117 return -EINVAL;
118
119 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
120
121 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
122 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
123 continue;
124
125 /*
126 * We are protected by nfnl mutex.
127 */
128 list_del_rcu(&sf->finger_entry);
129 kfree_rcu(sf, rcu_head);
130
131 err = 0;
132 break;
133 }
134
135 return err;
136}
137
138static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
139 [OSF_MSG_ADD] = {
140 .call = xt_osf_add_callback,
141 .attr_count = OSF_ATTR_MAX,
142 .policy = xt_osf_policy,
143 },
144 [OSF_MSG_REMOVE] = {
145 .call = xt_osf_remove_callback,
146 .attr_count = OSF_ATTR_MAX,
147 .policy = xt_osf_policy,
148 },
149};
150
151static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
152 .name = "osf",
153 .subsys_id = NFNL_SUBSYS_OSF,
154 .cb_count = OSF_MSG_MAX,
155 .cb = xt_osf_nfnetlink_callbacks,
156};
157
158static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
159 unsigned char f_ttl)
160{
161 const struct iphdr *ip = ip_hdr(skb);
162
163 if (info->flags & XT_OSF_TTL) {
164 if (info->ttl == XT_OSF_TTL_TRUE)
165 return ip->ttl == f_ttl;
166 if (info->ttl == XT_OSF_TTL_NOCHECK)
167 return 1;
168 else if (ip->ttl <= f_ttl)
169 return 1;
170 else {
171 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
172 int ret = 0;
173
174 for_ifa(in_dev) {
175 if (inet_ifa_match(ip->saddr, ifa)) {
176 ret = (ip->ttl == f_ttl);
177 break;
178 }
179 }
180 endfor_ifa(in_dev);
181
182 return ret;
183 }
184 }
185
186 return ip->ttl == f_ttl;
187}
188
189static bool
190xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
191{
192 const struct xt_osf_info *info = p->matchinfo;
193 const struct iphdr *ip = ip_hdr(skb);
194 const struct tcphdr *tcp;
195 struct tcphdr _tcph;
196 int fmatch = FMATCH_WRONG, fcount = 0;
197 unsigned int optsize = 0, check_WSS = 0;
198 u16 window, totlen, mss = 0;
199 bool df;
200 const unsigned char *optp = NULL, *_optp = NULL;
201 unsigned char opts[MAX_IPOPTLEN];
202 const struct xt_osf_finger *kf;
203 const struct xt_osf_user_finger *f;
204 struct net *net = xt_net(p);
205
206 if (!info)
207 return false;
208
209 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
210 if (!tcp)
211 return false;
212
213 if (!tcp->syn)
214 return false;
215
216 totlen = ntohs(ip->tot_len);
217 df = ntohs(ip->frag_off) & IP_DF;
218 window = ntohs(tcp->window);
219
220 if (tcp->doff * 4 > sizeof(struct tcphdr)) {
221 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
222
223 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
224 sizeof(struct tcphdr), optsize, opts);
225 }
226
227 rcu_read_lock();
228 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
229 int foptsize, optnum;
230
231 f = &kf->finger;
232
233 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
234 continue;
235
236 optp = _optp;
237 fmatch = FMATCH_WRONG;
238
239 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
240 continue;
241
242 /*
243 * Should not happen if userspace parser was written correctly.
244 */
245 if (f->wss.wc >= OSF_WSS_MAX)
246 continue;
247
248 /* Check options */
249
250 foptsize = 0;
251 for (optnum = 0; optnum < f->opt_num; ++optnum)
252 foptsize += f->opt[optnum].length;
253
254 if (foptsize > MAX_IPOPTLEN ||
255 optsize > MAX_IPOPTLEN ||
256 optsize != foptsize)
257 continue;
258
259 check_WSS = f->wss.wc;
260
261 for (optnum = 0; optnum < f->opt_num; ++optnum) {
262 if (f->opt[optnum].kind == (*optp)) {
263 __u32 len = f->opt[optnum].length;
264 const __u8 *optend = optp + len;
265
266 fmatch = FMATCH_OK;
267
268 switch (*optp) {
269 case OSFOPT_MSS:
270 mss = optp[3];
271 mss <<= 8;
272 mss |= optp[2];
273
274 mss = ntohs((__force __be16)mss);
275 break;
276 case OSFOPT_TS:
277 break;
278 }
279
280 optp = optend;
281 } else
282 fmatch = FMATCH_OPT_WRONG;
283
284 if (fmatch != FMATCH_OK)
285 break;
286 }
287
288 if (fmatch != FMATCH_OPT_WRONG) {
289 fmatch = FMATCH_WRONG;
290
291 switch (check_WSS) {
292 case OSF_WSS_PLAIN:
293 if (f->wss.val == 0 || window == f->wss.val)
294 fmatch = FMATCH_OK;
295 break;
296 case OSF_WSS_MSS:
297 /*
298 * Some smart modems decrease mangle MSS to
299 * SMART_MSS_2, so we check standard, decreased
300 * and the one provided in the fingerprint MSS
301 * values.
302 */
303#define SMART_MSS_1 1460
304#define SMART_MSS_2 1448
305 if (window == f->wss.val * mss ||
306 window == f->wss.val * SMART_MSS_1 ||
307 window == f->wss.val * SMART_MSS_2)
308 fmatch = FMATCH_OK;
309 break;
310 case OSF_WSS_MTU:
311 if (window == f->wss.val * (mss + 40) ||
312 window == f->wss.val * (SMART_MSS_1 + 40) ||
313 window == f->wss.val * (SMART_MSS_2 + 40))
314 fmatch = FMATCH_OK;
315 break;
316 case OSF_WSS_MODULO:
317 if ((window % f->wss.val) == 0)
318 fmatch = FMATCH_OK;
319 break;
320 }
321 }
322
323 if (fmatch != FMATCH_OK)
324 continue;
325
326 fcount++;
327
328 if (info->flags & XT_OSF_LOG)
329 nf_log_packet(net, xt_family(p), xt_hooknum(p), skb,
330 xt_in(p), xt_out(p), NULL,
331 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
332 f->genre, f->version, f->subtype,
333 &ip->saddr, ntohs(tcp->source),
334 &ip->daddr, ntohs(tcp->dest),
335 f->ttl - ip->ttl);
336
337 if ((info->flags & XT_OSF_LOG) &&
338 info->loglevel == XT_OSF_LOGLEVEL_FIRST)
339 break;
340 }
341 rcu_read_unlock();
342
343 if (!fcount && (info->flags & XT_OSF_LOG))
344 nf_log_packet(net, xt_family(p), xt_hooknum(p), skb, xt_in(p),
345 xt_out(p), 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);