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
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
xt_osf_finger_free_rcu(struct rcu_head * rcu_head)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
xt_osf_add_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])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
xt_osf_remove_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])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
xt_osf_ttl(const struct sk_buff * skb,const struct xt_osf_info * info,unsigned char f_ttl)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,struct xt_action_param * p)197 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_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
xt_osf_init(void)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 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
386 goto err_out_exit;
387 }
388
389 err = xt_register_match(&xt_osf_match);
390 if (err) {
391 pr_err("Failed to register OS fingerprint "
392 "matching module (%d)\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
xt_osf_fini(void)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