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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 | const struct nlmsghdr *nlh, |
74 | const struct nlattr * const osf_attrs[]) |
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, |
116 | const struct nlmsghdr *nlh, |
117 | const struct nlattr * const osf_attrs[]) |
118 | { |
119 | struct xt_osf_user_finger *f; |
120 | struct xt_osf_finger *sf; |
121 | int err = -ENOENT; |
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) |
335 | nf_log_packet(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(p->family, p->hooknum, skb, p->in, p->out, NULL, |
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); |
432 |
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