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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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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
40struct xt_osf_finger {
41 struct rcu_head rcu_head;
42 struct list_head finger_entry;
43 struct xt_osf_user_finger finger;
44};
45
46enum 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 */
59static struct list_head xt_osf_fingers[2];
60
61static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
62 [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) },
63};
64
65static 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 (!osf_attrs[OSF_ATTR_FINGER])
74 return -EINVAL;
75
76 if (!(nlh->nlmsg_flags & NLM_F_CREATE))
77 return -EINVAL;
78
79 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
80
81 kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
82 if (!kf)
83 return -ENOMEM;
84
85 memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
86
87 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
88 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
89 continue;
90
91 kfree(kf);
92 kf = NULL;
93
94 if (nlh->nlmsg_flags & NLM_F_EXCL)
95 err = -EEXIST;
96 break;
97 }
98
99 /*
100 * We are protected by nfnl mutex.
101 */
102 if (kf)
103 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
104
105 return err;
106}
107
108static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
109 const struct nlmsghdr *nlh,
110 const struct nlattr * const osf_attrs[])
111{
112 struct xt_osf_user_finger *f;
113 struct xt_osf_finger *sf;
114 int err = -ENOENT;
115
116 if (!osf_attrs[OSF_ATTR_FINGER])
117 return -EINVAL;
118
119 f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
120
121 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
122 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
123 continue;
124
125 /*
126 * We are protected by nfnl mutex.
127 */
128 list_del_rcu(&sf->finger_entry);
129 kfree_rcu(sf, rcu_head);
130
131 err = 0;
132 break;
133 }
134
135 return err;
136}
137
138static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
139 [OSF_MSG_ADD] = {
140 .call = xt_osf_add_callback,
141 .attr_count = OSF_ATTR_MAX,
142 .policy = xt_osf_policy,
143 },
144 [OSF_MSG_REMOVE] = {
145 .call = xt_osf_remove_callback,
146 .attr_count = OSF_ATTR_MAX,
147 .policy = xt_osf_policy,
148 },
149};
150
151static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
152 .name = "osf",
153 .subsys_id = NFNL_SUBSYS_OSF,
154 .cb_count = OSF_MSG_MAX,
155 .cb = xt_osf_nfnetlink_callbacks,
156};
157
158static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
159 unsigned char f_ttl)
160{
161 const struct iphdr *ip = ip_hdr(skb);
162
163 if (info->flags & XT_OSF_TTL) {
164 if (info->ttl == XT_OSF_TTL_TRUE)
165 return ip->ttl == f_ttl;
166 if (info->ttl == XT_OSF_TTL_NOCHECK)
167 return 1;
168 else if (ip->ttl <= f_ttl)
169 return 1;
170 else {
171 struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
172 int ret = 0;
173
174 for_ifa(in_dev) {
175 if (inet_ifa_match(ip->saddr, ifa)) {
176 ret = (ip->ttl == f_ttl);
177 break;
178 }
179 }
180 endfor_ifa(in_dev);
181
182 return ret;
183 }
184 }
185
186 return ip->ttl == f_ttl;
187}
188
189static bool
190xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
191{
192 const struct xt_osf_info *info = p->matchinfo;
193 const struct iphdr *ip = ip_hdr(skb);
194 const struct tcphdr *tcp;
195 struct tcphdr _tcph;
196 int fmatch = FMATCH_WRONG, fcount = 0;
197 unsigned int optsize = 0, check_WSS = 0;
198 u16 window, totlen, mss = 0;
199 bool df;
200 const unsigned char *optp = NULL, *_optp = NULL;
201 unsigned char opts[MAX_IPOPTLEN];
202 const struct xt_osf_finger *kf;
203 const struct xt_osf_user_finger *f;
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
272 mss = ntohs(mss);
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)
328 nf_log_packet(p->family, p->hooknum, skb,
329 p->in, p->out, NULL,
330 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
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))
344 nf_log_packet(p->family, p->hooknum, skb, p->in, p->out, NULL,
345 "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
346 &ip->saddr, ntohs(tcp->source),
347 &ip->daddr, ntohs(tcp->dest));
348
349 if (fcount)
350 fmatch = FMATCH_OK;
351
352 return fmatch == FMATCH_OK;
353}
354
355static struct xt_match xt_osf_match = {
356 .name = "osf",
357 .revision = 0,
358 .family = NFPROTO_IPV4,
359 .proto = IPPROTO_TCP,
360 .hooks = (1 << NF_INET_LOCAL_IN) |
361 (1 << NF_INET_PRE_ROUTING) |
362 (1 << NF_INET_FORWARD),
363 .match = xt_osf_match_packet,
364 .matchsize = sizeof(struct xt_osf_info),
365 .me = THIS_MODULE,
366};
367
368static int __init xt_osf_init(void)
369{
370 int err = -EINVAL;
371 int i;
372
373 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
374 INIT_LIST_HEAD(&xt_osf_fingers[i]);
375
376 err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
377 if (err < 0) {
378 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
379 goto err_out_exit;
380 }
381
382 err = xt_register_match(&xt_osf_match);
383 if (err) {
384 pr_err("Failed to register OS fingerprint "
385 "matching module (%d)\n", err);
386 goto err_out_remove;
387 }
388
389 return 0;
390
391err_out_remove:
392 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
393err_out_exit:
394 return err;
395}
396
397static void __exit xt_osf_fini(void)
398{
399 struct xt_osf_finger *f;
400 int i;
401
402 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
403 xt_unregister_match(&xt_osf_match);
404
405 rcu_read_lock();
406 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
407
408 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
409 list_del_rcu(&f->finger_entry);
410 kfree_rcu(f, rcu_head);
411 }
412 }
413 rcu_read_unlock();
414
415 rcu_barrier();
416}
417
418module_init(xt_osf_init);
419module_exit(xt_osf_fini);
420
421MODULE_LICENSE("GPL");
422MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
423MODULE_DESCRIPTION("Passive OS fingerprint matching.");
424MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);