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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 | |
16 | * along with this program; if not, write to the Free Software | |
17 | * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
18 | */ | |
19 | ||
20 | #include <linux/module.h> | |
21 | #include <linux/kernel.h> | |
22 | ||
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 | ||
65 | static void xt_osf_finger_free_rcu(struct rcu_head *rcu_head) | |
66 | { | |
67 | struct xt_osf_finger *f = container_of(rcu_head, struct xt_osf_finger, rcu_head); | |
68 | ||
69 | kfree(f); | |
70 | } | |
71 | ||
72 | static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb, | |
73 | struct nlmsghdr *nlh, struct nlattr *osf_attrs[]) | |
74 | { | |
75 | struct xt_osf_user_finger *f; | |
76 | struct xt_osf_finger *kf = NULL, *sf; | |
77 | int err = 0; | |
78 | ||
79 | if (!osf_attrs[OSF_ATTR_FINGER]) | |
80 | return -EINVAL; | |
81 | ||
82 | if (!(nlh->nlmsg_flags & NLM_F_CREATE)) | |
83 | return -EINVAL; | |
84 | ||
85 | f = nla_data(osf_attrs[OSF_ATTR_FINGER]); | |
86 | ||
87 | kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL); | |
88 | if (!kf) | |
89 | return -ENOMEM; | |
90 | ||
91 | memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger)); | |
92 | ||
93 | list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { | |
94 | if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) | |
95 | continue; | |
96 | ||
97 | kfree(kf); | |
98 | kf = NULL; | |
99 | ||
100 | if (nlh->nlmsg_flags & NLM_F_EXCL) | |
101 | err = -EEXIST; | |
102 | break; | |
103 | } | |
104 | ||
105 | /* | |
106 | * We are protected by nfnl mutex. | |
107 | */ | |
108 | if (kf) | |
109 | list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]); | |
110 | ||
111 | return err; | |
112 | } | |
113 | ||
114 | static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb, | |
115 | struct nlmsghdr *nlh, struct nlattr *osf_attrs[]) | |
116 | { | |
117 | struct xt_osf_user_finger *f; | |
118 | struct xt_osf_finger *sf; | |
119 | int err = ENOENT; | |
120 | ||
121 | if (!osf_attrs[OSF_ATTR_FINGER]) | |
122 | return -EINVAL; | |
123 | ||
124 | f = nla_data(osf_attrs[OSF_ATTR_FINGER]); | |
125 | ||
126 | list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { | |
127 | if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) | |
128 | continue; | |
129 | ||
130 | /* | |
131 | * We are protected by nfnl mutex. | |
132 | */ | |
133 | list_del_rcu(&sf->finger_entry); | |
134 | call_rcu(&sf->rcu_head, xt_osf_finger_free_rcu); | |
135 | ||
136 | err = 0; | |
137 | break; | |
138 | } | |
139 | ||
140 | return err; | |
141 | } | |
142 | ||
143 | static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = { | |
144 | [OSF_MSG_ADD] = { | |
145 | .call = xt_osf_add_callback, | |
146 | .attr_count = OSF_ATTR_MAX, | |
147 | .policy = xt_osf_policy, | |
148 | }, | |
149 | [OSF_MSG_REMOVE] = { | |
150 | .call = xt_osf_remove_callback, | |
151 | .attr_count = OSF_ATTR_MAX, | |
152 | .policy = xt_osf_policy, | |
153 | }, | |
154 | }; | |
155 | ||
156 | static const struct nfnetlink_subsystem xt_osf_nfnetlink = { | |
157 | .name = "osf", | |
158 | .subsys_id = NFNL_SUBSYS_OSF, | |
159 | .cb_count = OSF_MSG_MAX, | |
160 | .cb = xt_osf_nfnetlink_callbacks, | |
161 | }; | |
162 | ||
163 | static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info, | |
164 | unsigned char f_ttl) | |
165 | { | |
166 | const struct iphdr *ip = ip_hdr(skb); | |
167 | ||
168 | if (info->flags & XT_OSF_TTL) { | |
169 | if (info->ttl == XT_OSF_TTL_TRUE) | |
170 | return ip->ttl == f_ttl; | |
171 | if (info->ttl == XT_OSF_TTL_NOCHECK) | |
172 | return 1; | |
173 | else if (ip->ttl <= f_ttl) | |
174 | return 1; | |
175 | else { | |
176 | struct in_device *in_dev = __in_dev_get_rcu(skb->dev); | |
177 | int ret = 0; | |
178 | ||
179 | for_ifa(in_dev) { | |
180 | if (inet_ifa_match(ip->saddr, ifa)) { | |
181 | ret = (ip->ttl == f_ttl); | |
182 | break; | |
183 | } | |
184 | } | |
185 | endfor_ifa(in_dev); | |
186 | ||
187 | return ret; | |
188 | } | |
189 | } | |
190 | ||
191 | return ip->ttl == f_ttl; | |
192 | } | |
193 | ||
194 | static bool xt_osf_match_packet(const struct sk_buff *skb, | |
195 | const struct xt_match_param *p) | |
196 | { | |
197 | const struct xt_osf_info *info = p->matchinfo; | |
198 | const struct iphdr *ip = ip_hdr(skb); | |
199 | const struct tcphdr *tcp; | |
200 | struct tcphdr _tcph; | |
201 | int fmatch = FMATCH_WRONG, fcount = 0; | |
202 | unsigned int optsize = 0, check_WSS = 0; | |
203 | u16 window, totlen, mss = 0; | |
204 | bool df; | |
205 | const unsigned char *optp = NULL, *_optp = NULL; | |
206 | unsigned char opts[MAX_IPOPTLEN]; | |
207 | const struct xt_osf_finger *kf; | |
208 | const struct xt_osf_user_finger *f; | |
209 | ||
210 | if (!info) | |
211 | return false; | |
212 | ||
213 | tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph); | |
214 | if (!tcp) | |
215 | return false; | |
216 | ||
217 | if (!tcp->syn) | |
218 | return false; | |
219 | ||
220 | totlen = ntohs(ip->tot_len); | |
221 | df = ntohs(ip->frag_off) & IP_DF; | |
222 | window = ntohs(tcp->window); | |
223 | ||
224 | if (tcp->doff * 4 > sizeof(struct tcphdr)) { | |
225 | optsize = tcp->doff * 4 - sizeof(struct tcphdr); | |
226 | ||
227 | _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) + | |
228 | sizeof(struct tcphdr), optsize, opts); | |
229 | } | |
230 | ||
231 | rcu_read_lock(); | |
232 | list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) { | |
233 | f = &kf->finger; | |
234 | ||
235 | if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) | |
236 | continue; | |
237 | ||
238 | optp = _optp; | |
239 | fmatch = FMATCH_WRONG; | |
240 | ||
241 | if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) { | |
242 | int foptsize, optnum; | |
243 | ||
244 | /* | |
245 | * Should not happen if userspace parser was written correctly. | |
246 | */ | |
247 | if (f->wss.wc >= OSF_WSS_MAX) | |
248 | continue; | |
249 | ||
250 | /* Check options */ | |
251 | ||
252 | foptsize = 0; | |
253 | for (optnum = 0; optnum < f->opt_num; ++optnum) | |
254 | foptsize += f->opt[optnum].length; | |
255 | ||
256 | if (foptsize > MAX_IPOPTLEN || | |
257 | optsize > MAX_IPOPTLEN || | |
258 | optsize != foptsize) | |
259 | continue; | |
260 | ||
261 | check_WSS = f->wss.wc; | |
262 | ||
263 | for (optnum = 0; optnum < f->opt_num; ++optnum) { | |
264 | if (f->opt[optnum].kind == (*optp)) { | |
265 | __u32 len = f->opt[optnum].length; | |
266 | const __u8 *optend = optp + len; | |
267 | int loop_cont = 0; | |
268 | ||
269 | fmatch = FMATCH_OK; | |
270 | ||
271 | switch (*optp) { | |
272 | case OSFOPT_MSS: | |
273 | mss = optp[3]; | |
274 | mss <<= 8; | |
275 | mss |= optp[2]; | |
276 | ||
277 | mss = ntohs(mss); | |
278 | break; | |
279 | case OSFOPT_TS: | |
280 | loop_cont = 1; | |
281 | break; | |
282 | } | |
283 | ||
284 | optp = optend; | |
285 | } else | |
286 | fmatch = FMATCH_OPT_WRONG; | |
287 | ||
288 | if (fmatch != FMATCH_OK) | |
289 | break; | |
290 | } | |
291 | ||
292 | if (fmatch != FMATCH_OPT_WRONG) { | |
293 | fmatch = FMATCH_WRONG; | |
294 | ||
295 | switch (check_WSS) { | |
296 | case OSF_WSS_PLAIN: | |
297 | if (f->wss.val == 0 || window == f->wss.val) | |
298 | fmatch = FMATCH_OK; | |
299 | break; | |
300 | case OSF_WSS_MSS: | |
301 | /* | |
302 | * Some smart modems decrease mangle MSS to | |
303 | * SMART_MSS_2, so we check standard, decreased | |
304 | * and the one provided in the fingerprint MSS | |
305 | * values. | |
306 | */ | |
307 | #define SMART_MSS_1 1460 | |
308 | #define SMART_MSS_2 1448 | |
309 | if (window == f->wss.val * mss || | |
310 | window == f->wss.val * SMART_MSS_1 || | |
311 | window == f->wss.val * SMART_MSS_2) | |
312 | fmatch = FMATCH_OK; | |
313 | break; | |
314 | case OSF_WSS_MTU: | |
315 | if (window == f->wss.val * (mss + 40) || | |
316 | window == f->wss.val * (SMART_MSS_1 + 40) || | |
317 | window == f->wss.val * (SMART_MSS_2 + 40)) | |
318 | fmatch = FMATCH_OK; | |
319 | break; | |
320 | case OSF_WSS_MODULO: | |
321 | if ((window % f->wss.val) == 0) | |
322 | fmatch = FMATCH_OK; | |
323 | break; | |
324 | } | |
325 | } | |
326 | ||
327 | if (fmatch != FMATCH_OK) | |
328 | continue; | |
329 | ||
330 | fcount++; | |
331 | ||
332 | if (info->flags & XT_OSF_LOG) | |
aa6a03eb PM |
333 | nf_log_packet(p->family, p->hooknum, skb, |
334 | p->in, p->out, NULL, | |
11eeef41 EP |
335 | "%s [%s:%s] : %pi4:%d -> %pi4:%d hops=%d\n", |
336 | f->genre, f->version, f->subtype, | |
337 | &ip->saddr, ntohs(tcp->source), | |
338 | &ip->daddr, ntohs(tcp->dest), | |
339 | f->ttl - ip->ttl); | |
340 | ||
341 | if ((info->flags & XT_OSF_LOG) && | |
342 | info->loglevel == XT_OSF_LOGLEVEL_FIRST) | |
343 | break; | |
344 | } | |
345 | } | |
346 | rcu_read_unlock(); | |
347 | ||
348 | if (!fcount && (info->flags & XT_OSF_LOG)) | |
aa6a03eb | 349 | nf_log_packet(p->family, p->hooknum, skb, p->in, p->out, NULL, |
11eeef41 EP |
350 | "Remote OS is not known: %pi4:%u -> %pi4:%u\n", |
351 | &ip->saddr, ntohs(tcp->source), | |
352 | &ip->daddr, ntohs(tcp->dest)); | |
353 | ||
354 | if (fcount) | |
355 | fmatch = FMATCH_OK; | |
356 | ||
357 | return fmatch == FMATCH_OK; | |
358 | } | |
359 | ||
360 | static struct xt_match xt_osf_match = { | |
361 | .name = "osf", | |
362 | .revision = 0, | |
363 | .family = NFPROTO_IPV4, | |
364 | .proto = IPPROTO_TCP, | |
365 | .hooks = (1 << NF_INET_LOCAL_IN) | | |
366 | (1 << NF_INET_PRE_ROUTING) | | |
367 | (1 << NF_INET_FORWARD), | |
368 | .match = xt_osf_match_packet, | |
369 | .matchsize = sizeof(struct xt_osf_info), | |
370 | .me = THIS_MODULE, | |
371 | }; | |
372 | ||
373 | static int __init xt_osf_init(void) | |
374 | { | |
375 | int err = -EINVAL; | |
376 | int i; | |
377 | ||
378 | for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) | |
379 | INIT_LIST_HEAD(&xt_osf_fingers[i]); | |
380 | ||
381 | err = nfnetlink_subsys_register(&xt_osf_nfnetlink); | |
382 | if (err < 0) { | |
383 | printk(KERN_ERR "Failed (%d) to register OSF nsfnetlink helper.\n", err); | |
384 | goto err_out_exit; | |
385 | } | |
386 | ||
387 | err = xt_register_match(&xt_osf_match); | |
388 | if (err) { | |
389 | printk(KERN_ERR "Failed (%d) to register OS fingerprint " | |
390 | "matching module.\n", err); | |
391 | goto err_out_remove; | |
392 | } | |
393 | ||
394 | return 0; | |
395 | ||
396 | err_out_remove: | |
397 | nfnetlink_subsys_unregister(&xt_osf_nfnetlink); | |
398 | err_out_exit: | |
399 | return err; | |
400 | } | |
401 | ||
402 | static void __exit xt_osf_fini(void) | |
403 | { | |
404 | struct xt_osf_finger *f; | |
405 | int i; | |
406 | ||
407 | nfnetlink_subsys_unregister(&xt_osf_nfnetlink); | |
408 | xt_unregister_match(&xt_osf_match); | |
409 | ||
410 | rcu_read_lock(); | |
411 | for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) { | |
412 | ||
413 | list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) { | |
414 | list_del_rcu(&f->finger_entry); | |
415 | call_rcu(&f->rcu_head, xt_osf_finger_free_rcu); | |
416 | } | |
417 | } | |
418 | rcu_read_unlock(); | |
419 | ||
420 | rcu_barrier(); | |
421 | } | |
422 | ||
423 | module_init(xt_osf_init); | |
424 | module_exit(xt_osf_fini); | |
425 | ||
426 | MODULE_LICENSE("GPL"); | |
427 | MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); | |
428 | MODULE_DESCRIPTION("Passive OS fingerprint matching."); | |
429 | MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); |