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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, | |
39938324 PM |
73 | const struct nlmsghdr *nlh, |
74 | const struct nlattr * const osf_attrs[]) | |
11eeef41 EP |
75 | { |
76 | struct xt_osf_user_finger *f; | |
77 | struct xt_osf_finger *kf = NULL, *sf; | |
78 | int err = 0; | |
79 | ||
80 | if (!osf_attrs[OSF_ATTR_FINGER]) | |
81 | return -EINVAL; | |
82 | ||
83 | if (!(nlh->nlmsg_flags & NLM_F_CREATE)) | |
84 | return -EINVAL; | |
85 | ||
86 | f = nla_data(osf_attrs[OSF_ATTR_FINGER]); | |
87 | ||
88 | kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL); | |
89 | if (!kf) | |
90 | return -ENOMEM; | |
91 | ||
92 | memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger)); | |
93 | ||
94 | list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { | |
95 | if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) | |
96 | continue; | |
97 | ||
98 | kfree(kf); | |
99 | kf = NULL; | |
100 | ||
101 | if (nlh->nlmsg_flags & NLM_F_EXCL) | |
102 | err = -EEXIST; | |
103 | break; | |
104 | } | |
105 | ||
106 | /* | |
107 | * We are protected by nfnl mutex. | |
108 | */ | |
109 | if (kf) | |
110 | list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]); | |
111 | ||
112 | return err; | |
113 | } | |
114 | ||
115 | static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb, | |
39938324 PM |
116 | const struct nlmsghdr *nlh, |
117 | const struct nlattr * const osf_attrs[]) | |
11eeef41 EP |
118 | { |
119 | struct xt_osf_user_finger *f; | |
120 | struct xt_osf_finger *sf; | |
1c622ae6 | 121 | int err = -ENOENT; |
11eeef41 EP |
122 | |
123 | if (!osf_attrs[OSF_ATTR_FINGER]) | |
124 | return -EINVAL; | |
125 | ||
126 | f = nla_data(osf_attrs[OSF_ATTR_FINGER]); | |
127 | ||
128 | list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { | |
129 | if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) | |
130 | continue; | |
131 | ||
132 | /* | |
133 | * We are protected by nfnl mutex. | |
134 | */ | |
135 | list_del_rcu(&sf->finger_entry); | |
136 | call_rcu(&sf->rcu_head, xt_osf_finger_free_rcu); | |
137 | ||
138 | err = 0; | |
139 | break; | |
140 | } | |
141 | ||
142 | return err; | |
143 | } | |
144 | ||
145 | static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = { | |
146 | [OSF_MSG_ADD] = { | |
147 | .call = xt_osf_add_callback, | |
148 | .attr_count = OSF_ATTR_MAX, | |
149 | .policy = xt_osf_policy, | |
150 | }, | |
151 | [OSF_MSG_REMOVE] = { | |
152 | .call = xt_osf_remove_callback, | |
153 | .attr_count = OSF_ATTR_MAX, | |
154 | .policy = xt_osf_policy, | |
155 | }, | |
156 | }; | |
157 | ||
158 | static const struct nfnetlink_subsystem xt_osf_nfnetlink = { | |
159 | .name = "osf", | |
160 | .subsys_id = NFNL_SUBSYS_OSF, | |
161 | .cb_count = OSF_MSG_MAX, | |
162 | .cb = xt_osf_nfnetlink_callbacks, | |
163 | }; | |
164 | ||
165 | static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info, | |
166 | unsigned char f_ttl) | |
167 | { | |
168 | const struct iphdr *ip = ip_hdr(skb); | |
169 | ||
170 | if (info->flags & XT_OSF_TTL) { | |
171 | if (info->ttl == XT_OSF_TTL_TRUE) | |
172 | return ip->ttl == f_ttl; | |
173 | if (info->ttl == XT_OSF_TTL_NOCHECK) | |
174 | return 1; | |
175 | else if (ip->ttl <= f_ttl) | |
176 | return 1; | |
177 | else { | |
178 | struct in_device *in_dev = __in_dev_get_rcu(skb->dev); | |
179 | int ret = 0; | |
180 | ||
181 | for_ifa(in_dev) { | |
182 | if (inet_ifa_match(ip->saddr, ifa)) { | |
183 | ret = (ip->ttl == f_ttl); | |
184 | break; | |
185 | } | |
186 | } | |
187 | endfor_ifa(in_dev); | |
188 | ||
189 | return ret; | |
190 | } | |
191 | } | |
192 | ||
193 | return ip->ttl == f_ttl; | |
194 | } | |
195 | ||
196 | static bool xt_osf_match_packet(const struct sk_buff *skb, | |
197 | const struct xt_match_param *p) | |
198 | { | |
199 | const struct xt_osf_info *info = p->matchinfo; | |
200 | const struct iphdr *ip = ip_hdr(skb); | |
201 | const struct tcphdr *tcp; | |
202 | struct tcphdr _tcph; | |
203 | int fmatch = FMATCH_WRONG, fcount = 0; | |
204 | unsigned int optsize = 0, check_WSS = 0; | |
205 | u16 window, totlen, mss = 0; | |
206 | bool df; | |
207 | const unsigned char *optp = NULL, *_optp = NULL; | |
208 | unsigned char opts[MAX_IPOPTLEN]; | |
209 | const struct xt_osf_finger *kf; | |
210 | const struct xt_osf_user_finger *f; | |
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(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) | |
aa6a03eb PM |
335 | nf_log_packet(p->family, p->hooknum, skb, |
336 | p->in, p->out, NULL, | |
11eeef41 EP |
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)) | |
aa6a03eb | 351 | nf_log_packet(p->family, p->hooknum, skb, p->in, p->out, NULL, |
11eeef41 EP |
352 | "Remote OS is not known: %pi4:%u -> %pi4:%u\n", |
353 | &ip->saddr, ntohs(tcp->source), | |
354 | &ip->daddr, ntohs(tcp->dest)); | |
355 | ||
356 | if (fcount) | |
357 | fmatch = FMATCH_OK; | |
358 | ||
359 | return fmatch == FMATCH_OK; | |
360 | } | |
361 | ||
362 | static struct xt_match xt_osf_match = { | |
363 | .name = "osf", | |
364 | .revision = 0, | |
365 | .family = NFPROTO_IPV4, | |
366 | .proto = IPPROTO_TCP, | |
367 | .hooks = (1 << NF_INET_LOCAL_IN) | | |
368 | (1 << NF_INET_PRE_ROUTING) | | |
369 | (1 << NF_INET_FORWARD), | |
370 | .match = xt_osf_match_packet, | |
371 | .matchsize = sizeof(struct xt_osf_info), | |
372 | .me = THIS_MODULE, | |
373 | }; | |
374 | ||
375 | static int __init xt_osf_init(void) | |
376 | { | |
377 | int err = -EINVAL; | |
378 | int i; | |
379 | ||
380 | for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) | |
381 | INIT_LIST_HEAD(&xt_osf_fingers[i]); | |
382 | ||
383 | err = nfnetlink_subsys_register(&xt_osf_nfnetlink); | |
384 | if (err < 0) { | |
385 | printk(KERN_ERR "Failed (%d) to register OSF nsfnetlink helper.\n", err); | |
386 | goto err_out_exit; | |
387 | } | |
388 | ||
389 | err = xt_register_match(&xt_osf_match); | |
390 | if (err) { | |
391 | printk(KERN_ERR "Failed (%d) to register OS fingerprint " | |
392 | "matching module.\n", err); | |
393 | goto err_out_remove; | |
394 | } | |
395 | ||
396 | return 0; | |
397 | ||
398 | err_out_remove: | |
399 | nfnetlink_subsys_unregister(&xt_osf_nfnetlink); | |
400 | err_out_exit: | |
401 | return err; | |
402 | } | |
403 | ||
404 | static void __exit xt_osf_fini(void) | |
405 | { | |
406 | struct xt_osf_finger *f; | |
407 | int i; | |
408 | ||
409 | nfnetlink_subsys_unregister(&xt_osf_nfnetlink); | |
410 | xt_unregister_match(&xt_osf_match); | |
411 | ||
412 | rcu_read_lock(); | |
413 | for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) { | |
414 | ||
415 | list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) { | |
416 | list_del_rcu(&f->finger_entry); | |
417 | call_rcu(&f->rcu_head, xt_osf_finger_free_rcu); | |
418 | } | |
419 | } | |
420 | rcu_read_unlock(); | |
421 | ||
422 | rcu_barrier(); | |
423 | } | |
424 | ||
425 | module_init(xt_osf_init); | |
426 | module_exit(xt_osf_fini); | |
427 | ||
428 | MODULE_LICENSE("GPL"); | |
429 | MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); | |
430 | MODULE_DESCRIPTION("Passive OS fingerprint matching."); | |
431 | MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); |