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11eeef41 EP |
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 | |
e664eabd | 16 | * along with this program; if not, see <http://www.gnu.org/licenses/>. |
11eeef41 | 17 | */ |
8bee4bad | 18 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
11eeef41 EP |
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 | ||
39 | struct xt_osf_finger { | |
40 | struct rcu_head rcu_head; | |
41 | struct list_head finger_entry; | |
42 | struct xt_osf_user_finger finger; | |
43 | }; | |
44 | ||
45 | enum 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 | */ | |
58 | static struct list_head xt_osf_fingers[2]; | |
59 | ||
60 | static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = { | |
61 | [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) }, | |
62 | }; | |
63 | ||
11eeef41 | 64 | static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb, |
39938324 PM |
65 | const struct nlmsghdr *nlh, |
66 | const struct nlattr * const osf_attrs[]) | |
11eeef41 EP |
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 | ||
107 | static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb, | |
39938324 PM |
108 | const struct nlmsghdr *nlh, |
109 | const struct nlattr * const osf_attrs[]) | |
11eeef41 EP |
110 | { |
111 | struct xt_osf_user_finger *f; | |
112 | struct xt_osf_finger *sf; | |
d667b9cf | 113 | int err = -ENOENT; |
11eeef41 EP |
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); | |
88b4a034 | 128 | kfree_rcu(sf, rcu_head); |
11eeef41 EP |
129 | |
130 | err = 0; | |
131 | break; | |
132 | } | |
133 | ||
134 | return err; | |
135 | } | |
136 | ||
137 | static 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 | ||
150 | static 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 | ||
157 | static 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 | ||
4b560b44 | 188 | static bool |
62fc8051 | 189 | xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p) |
11eeef41 EP |
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; | |
30e0c6a6 | 203 | struct net *net = dev_net(p->in ? p->in : p->out); |
11eeef41 EP |
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 | ||
fe31d1a8 | 272 | mss = ntohs((__force __be16)mss); |
11eeef41 EP |
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) | |
30e0c6a6 | 328 | nf_log_packet(net, p->family, p->hooknum, skb, |
aa6a03eb | 329 | p->in, p->out, NULL, |
7f635d0d | 330 | "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n", |
11eeef41 EP |
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)) | |
30e0c6a6 G |
344 | nf_log_packet(net, p->family, p->hooknum, skb, p->in, |
345 | p->out, NULL, | |
7f635d0d | 346 | "Remote OS is not known: %pI4:%u -> %pI4:%u\n", |
11eeef41 EP |
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 | ||
356 | static 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 | ||
369 | static 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) { | |
8bee4bad | 379 | pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); |
11eeef41 EP |
380 | goto err_out_exit; |
381 | } | |
382 | ||
383 | err = xt_register_match(&xt_osf_match); | |
384 | if (err) { | |
8bee4bad JE |
385 | pr_err("Failed to register OS fingerprint " |
386 | "matching module (%d)\n", err); | |
11eeef41 EP |
387 | goto err_out_remove; |
388 | } | |
389 | ||
390 | return 0; | |
391 | ||
392 | err_out_remove: | |
393 | nfnetlink_subsys_unregister(&xt_osf_nfnetlink); | |
394 | err_out_exit: | |
395 | return err; | |
396 | } | |
397 | ||
398 | static 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); | |
88b4a034 | 411 | kfree_rcu(f, rcu_head); |
11eeef41 EP |
412 | } |
413 | } | |
414 | rcu_read_unlock(); | |
415 | ||
416 | rcu_barrier(); | |
417 | } | |
418 | ||
419 | module_init(xt_osf_init); | |
420 | module_exit(xt_osf_fini); | |
421 | ||
422 | MODULE_LICENSE("GPL"); | |
423 | MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); | |
424 | MODULE_DESCRIPTION("Passive OS fingerprint matching."); | |
b8ddd9ea KT |
425 | MODULE_ALIAS("ipt_osf"); |
426 | MODULE_ALIAS("ip6t_osf"); | |
11eeef41 | 427 | MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); |