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/capability.h>
23 #include <linux/if.h>
24 #include <linux/inetdevice.h>
25 #include <linux/ip.h>
26 #include <linux/list.h>
27 #include <linux/rculist.h>
28 #include <linux/skbuff.h>
29 #include <linux/slab.h>
30 #include <linux/tcp.h>
31
32 #include <net/ip.h>
33 #include <net/tcp.h>
34
35 #include <linux/netfilter/nfnetlink.h>
36 #include <linux/netfilter/x_tables.h>
37 #include <net/netfilter/nf_log.h>
38 #include <linux/netfilter/xt_osf.h>
39
40 struct xt_osf_finger {
41 struct rcu_head rcu_head;
42 struct list_head finger_entry;
43 struct xt_osf_user_finger finger;
44 };
45
46 enum osf_fmatch_states {
47 /* Packet does not match the fingerprint */
48 FMATCH_WRONG = 0,
49 /* Packet matches the fingerprint */
50 FMATCH_OK,
51 /* Options do not match the fingerprint, but header does */
52 FMATCH_OPT_WRONG,
53 };
54
55 /*
56 * Indexed by dont-fragment bit.
57 * It is the only constant value in the fingerprint.
58 */
59 static struct list_head xt_osf_fingers[2];
60
61 static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
62 [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) },
63 };
64
xt_osf_add_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])65 static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb,
66 const struct nlmsghdr *nlh,
67 const struct nlattr * const osf_attrs[])
68 {
69 struct xt_osf_user_finger *f;
70 struct xt_osf_finger *kf = NULL, *sf;
71 int err = 0;
72
73 if (!capable(CAP_NET_ADMIN))
74 return -EPERM;
75
76 if (!osf_attrs[OSF_ATTR_FINGER])
77 return -EINVAL;
78
79 if (!(nlh->nlmsg_flags & NLM_F_CREATE))
80 return -EINVAL;
81
82 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
83
84 kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
85 if (!kf)
86 return -ENOMEM;
87
88 memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
89
90 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
91 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
92 continue;
93
94 kfree(kf);
95 kf = NULL;
96
97 if (nlh->nlmsg_flags & NLM_F_EXCL)
98 err = -EEXIST;
99 break;
100 }
101
102 /*
103 * We are protected by nfnl mutex.
104 */
105 if (kf)
106 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
107
108 return err;
109 }
110
xt_osf_remove_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])111 static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
112 const struct nlmsghdr *nlh,
113 const struct nlattr * const osf_attrs[])
114 {
115 struct xt_osf_user_finger *f;
116 struct xt_osf_finger *sf;
117 int err = -ENOENT;
118
119 if (!capable(CAP_NET_ADMIN))
120 return -EPERM;
121
122 if (!osf_attrs[OSF_ATTR_FINGER])
123 return -EINVAL;
124
125 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
126
127 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
128 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
129 continue;
130
131 /*
132 * We are protected by nfnl mutex.
133 */
134 list_del_rcu(&sf->finger_entry);
135 kfree_rcu(sf, rcu_head);
136
137 err = 0;
138 break;
139 }
140
141 return err;
142 }
143
144 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
145 [OSF_MSG_ADD] = {
146 .call = xt_osf_add_callback,
147 .attr_count = OSF_ATTR_MAX,
148 .policy = xt_osf_policy,
149 },
150 [OSF_MSG_REMOVE] = {
151 .call = xt_osf_remove_callback,
152 .attr_count = OSF_ATTR_MAX,
153 .policy = xt_osf_policy,
154 },
155 };
156
157 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
158 .name = "osf",
159 .subsys_id = NFNL_SUBSYS_OSF,
160 .cb_count = OSF_MSG_MAX,
161 .cb = xt_osf_nfnetlink_callbacks,
162 };
163
xt_osf_ttl(const struct sk_buff * skb,const struct xt_osf_info * info,unsigned char f_ttl)164 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
165 unsigned char f_ttl)
166 {
167 const struct iphdr *ip = ip_hdr(skb);
168
169 if (info->flags & XT_OSF_TTL) {
170 if (info->ttl == XT_OSF_TTL_TRUE)
171 return ip->ttl == f_ttl;
172 if (info->ttl == XT_OSF_TTL_NOCHECK)
173 return 1;
174 else if (ip->ttl <= f_ttl)
175 return 1;
176 else {
177 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
178 int ret = 0;
179
180 for_ifa(in_dev) {
181 if (inet_ifa_match(ip->saddr, ifa)) {
182 ret = (ip->ttl == f_ttl);
183 break;
184 }
185 }
186 endfor_ifa(in_dev);
187
188 return ret;
189 }
190 }
191
192 return ip->ttl == f_ttl;
193 }
194
195 static bool
xt_osf_match_packet(const struct sk_buff * skb,struct xt_action_param * p)196 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
197 {
198 const struct xt_osf_info *info = p->matchinfo;
199 const struct iphdr *ip = ip_hdr(skb);
200 const struct tcphdr *tcp;
201 struct tcphdr _tcph;
202 int fmatch = FMATCH_WRONG, fcount = 0;
203 unsigned int optsize = 0, check_WSS = 0;
204 u16 window, totlen, mss = 0;
205 bool df;
206 const unsigned char *optp = NULL, *_optp = NULL;
207 unsigned char opts[MAX_IPOPTLEN];
208 const struct xt_osf_finger *kf;
209 const struct xt_osf_user_finger *f;
210 struct net *net = dev_net(p->in ? p->in : p->out);
211
212 if (!info)
213 return false;
214
215 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
216 if (!tcp)
217 return false;
218
219 if (!tcp->syn)
220 return false;
221
222 totlen = ntohs(ip->tot_len);
223 df = ntohs(ip->frag_off) & IP_DF;
224 window = ntohs(tcp->window);
225
226 if (tcp->doff * 4 > sizeof(struct tcphdr)) {
227 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
228
229 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
230 sizeof(struct tcphdr), optsize, opts);
231 }
232
233 rcu_read_lock();
234 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
235 f = &kf->finger;
236
237 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
238 continue;
239
240 optp = _optp;
241 fmatch = FMATCH_WRONG;
242
243 if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) {
244 int foptsize, optnum;
245
246 /*
247 * Should not happen if userspace parser was written correctly.
248 */
249 if (f->wss.wc >= OSF_WSS_MAX)
250 continue;
251
252 /* Check options */
253
254 foptsize = 0;
255 for (optnum = 0; optnum < f->opt_num; ++optnum)
256 foptsize += f->opt[optnum].length;
257
258 if (foptsize > MAX_IPOPTLEN ||
259 optsize > MAX_IPOPTLEN ||
260 optsize != foptsize)
261 continue;
262
263 check_WSS = f->wss.wc;
264
265 for (optnum = 0; optnum < f->opt_num; ++optnum) {
266 if (f->opt[optnum].kind == (*optp)) {
267 __u32 len = f->opt[optnum].length;
268 const __u8 *optend = optp + len;
269 int loop_cont = 0;
270
271 fmatch = FMATCH_OK;
272
273 switch (*optp) {
274 case OSFOPT_MSS:
275 mss = optp[3];
276 mss <<= 8;
277 mss |= optp[2];
278
279 mss = ntohs((__force __be16)mss);
280 break;
281 case OSFOPT_TS:
282 loop_cont = 1;
283 break;
284 }
285
286 optp = optend;
287 } else
288 fmatch = FMATCH_OPT_WRONG;
289
290 if (fmatch != FMATCH_OK)
291 break;
292 }
293
294 if (fmatch != FMATCH_OPT_WRONG) {
295 fmatch = FMATCH_WRONG;
296
297 switch (check_WSS) {
298 case OSF_WSS_PLAIN:
299 if (f->wss.val == 0 || window == f->wss.val)
300 fmatch = FMATCH_OK;
301 break;
302 case OSF_WSS_MSS:
303 /*
304 * Some smart modems decrease mangle MSS to
305 * SMART_MSS_2, so we check standard, decreased
306 * and the one provided in the fingerprint MSS
307 * values.
308 */
309 #define SMART_MSS_1 1460
310 #define SMART_MSS_2 1448
311 if (window == f->wss.val * mss ||
312 window == f->wss.val * SMART_MSS_1 ||
313 window == f->wss.val * SMART_MSS_2)
314 fmatch = FMATCH_OK;
315 break;
316 case OSF_WSS_MTU:
317 if (window == f->wss.val * (mss + 40) ||
318 window == f->wss.val * (SMART_MSS_1 + 40) ||
319 window == f->wss.val * (SMART_MSS_2 + 40))
320 fmatch = FMATCH_OK;
321 break;
322 case OSF_WSS_MODULO:
323 if ((window % f->wss.val) == 0)
324 fmatch = FMATCH_OK;
325 break;
326 }
327 }
328
329 if (fmatch != FMATCH_OK)
330 continue;
331
332 fcount++;
333
334 if (info->flags & XT_OSF_LOG)
335 nf_log_packet(net, p->family, p->hooknum, skb,
336 p->in, p->out, NULL,
337 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
338 f->genre, f->version, f->subtype,
339 &ip->saddr, ntohs(tcp->source),
340 &ip->daddr, ntohs(tcp->dest),
341 f->ttl - ip->ttl);
342
343 if ((info->flags & XT_OSF_LOG) &&
344 info->loglevel == XT_OSF_LOGLEVEL_FIRST)
345 break;
346 }
347 }
348 rcu_read_unlock();
349
350 if (!fcount && (info->flags & XT_OSF_LOG))
351 nf_log_packet(net, p->family, p->hooknum, skb, p->in,
352 p->out, NULL,
353 "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
354 &ip->saddr, ntohs(tcp->source),
355 &ip->daddr, ntohs(tcp->dest));
356
357 if (fcount)
358 fmatch = FMATCH_OK;
359
360 return fmatch == FMATCH_OK;
361 }
362
363 static struct xt_match xt_osf_match = {
364 .name = "osf",
365 .revision = 0,
366 .family = NFPROTO_IPV4,
367 .proto = IPPROTO_TCP,
368 .hooks = (1 << NF_INET_LOCAL_IN) |
369 (1 << NF_INET_PRE_ROUTING) |
370 (1 << NF_INET_FORWARD),
371 .match = xt_osf_match_packet,
372 .matchsize = sizeof(struct xt_osf_info),
373 .me = THIS_MODULE,
374 };
375
xt_osf_init(void)376 static int __init xt_osf_init(void)
377 {
378 int err = -EINVAL;
379 int i;
380
381 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
382 INIT_LIST_HEAD(&xt_osf_fingers[i]);
383
384 err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
385 if (err < 0) {
386 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
387 goto err_out_exit;
388 }
389
390 err = xt_register_match(&xt_osf_match);
391 if (err) {
392 pr_err("Failed to register OS fingerprint "
393 "matching module (%d)\n", err);
394 goto err_out_remove;
395 }
396
397 return 0;
398
399 err_out_remove:
400 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
401 err_out_exit:
402 return err;
403 }
404
xt_osf_fini(void)405 static void __exit xt_osf_fini(void)
406 {
407 struct xt_osf_finger *f;
408 int i;
409
410 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
411 xt_unregister_match(&xt_osf_match);
412
413 rcu_read_lock();
414 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
415
416 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
417 list_del_rcu(&f->finger_entry);
418 kfree_rcu(f, rcu_head);
419 }
420 }
421 rcu_read_unlock();
422
423 rcu_barrier();
424 }
425
426 module_init(xt_osf_init);
427 module_exit(xt_osf_fini);
428
429 MODULE_LICENSE("GPL");
430 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
431 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
432 MODULE_ALIAS("ipt_osf");
433 MODULE_ALIAS("ip6t_osf");
434 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
435