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_add_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])65 static 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
xt_osf_remove_callback(struct sock * ctnl,struct sk_buff * skb,const struct nlmsghdr * nlh,const struct nlattr * const osf_attrs[])108 static 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
138 static 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
151 static 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
xt_osf_ttl(const struct sk_buff * skb,const struct xt_osf_info * info,unsigned char f_ttl)158 static 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
189 static bool
xt_osf_match_packet(const struct sk_buff * skb,struct xt_action_param * p)190 xt_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 struct net *net = dev_net(p->in ? p->in : p->out);
205
206 if (!info)
207 return false;
208
209 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
210 if (!tcp)
211 return false;
212
213 if (!tcp->syn)
214 return false;
215
216 totlen = ntohs(ip->tot_len);
217 df = ntohs(ip->frag_off) & IP_DF;
218 window = ntohs(tcp->window);
219
220 if (tcp->doff * 4 > sizeof(struct tcphdr)) {
221 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
222
223 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
224 sizeof(struct tcphdr), optsize, opts);
225 }
226
227 rcu_read_lock();
228 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
229 f = &kf->finger;
230
231 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
232 continue;
233
234 optp = _optp;
235 fmatch = FMATCH_WRONG;
236
237 if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) {
238 int foptsize, optnum;
239
240 /*
241 * Should not happen if userspace parser was written correctly.
242 */
243 if (f->wss.wc >= OSF_WSS_MAX)
244 continue;
245
246 /* Check options */
247
248 foptsize = 0;
249 for (optnum = 0; optnum < f->opt_num; ++optnum)
250 foptsize += f->opt[optnum].length;
251
252 if (foptsize > MAX_IPOPTLEN ||
253 optsize > MAX_IPOPTLEN ||
254 optsize != foptsize)
255 continue;
256
257 check_WSS = f->wss.wc;
258
259 for (optnum = 0; optnum < f->opt_num; ++optnum) {
260 if (f->opt[optnum].kind == (*optp)) {
261 __u32 len = f->opt[optnum].length;
262 const __u8 *optend = optp + len;
263 int loop_cont = 0;
264
265 fmatch = FMATCH_OK;
266
267 switch (*optp) {
268 case OSFOPT_MSS:
269 mss = optp[3];
270 mss <<= 8;
271 mss |= optp[2];
272
273 mss = ntohs((__force __be16)mss);
274 break;
275 case OSFOPT_TS:
276 loop_cont = 1;
277 break;
278 }
279
280 optp = optend;
281 } else
282 fmatch = FMATCH_OPT_WRONG;
283
284 if (fmatch != FMATCH_OK)
285 break;
286 }
287
288 if (fmatch != FMATCH_OPT_WRONG) {
289 fmatch = FMATCH_WRONG;
290
291 switch (check_WSS) {
292 case OSF_WSS_PLAIN:
293 if (f->wss.val == 0 || window == f->wss.val)
294 fmatch = FMATCH_OK;
295 break;
296 case OSF_WSS_MSS:
297 /*
298 * Some smart modems decrease mangle MSS to
299 * SMART_MSS_2, so we check standard, decreased
300 * and the one provided in the fingerprint MSS
301 * values.
302 */
303 #define SMART_MSS_1 1460
304 #define SMART_MSS_2 1448
305 if (window == f->wss.val * mss ||
306 window == f->wss.val * SMART_MSS_1 ||
307 window == f->wss.val * SMART_MSS_2)
308 fmatch = FMATCH_OK;
309 break;
310 case OSF_WSS_MTU:
311 if (window == f->wss.val * (mss + 40) ||
312 window == f->wss.val * (SMART_MSS_1 + 40) ||
313 window == f->wss.val * (SMART_MSS_2 + 40))
314 fmatch = FMATCH_OK;
315 break;
316 case OSF_WSS_MODULO:
317 if ((window % f->wss.val) == 0)
318 fmatch = FMATCH_OK;
319 break;
320 }
321 }
322
323 if (fmatch != FMATCH_OK)
324 continue;
325
326 fcount++;
327
328 if (info->flags & XT_OSF_LOG)
329 nf_log_packet(net, p->family, p->hooknum, skb,
330 p->in, p->out, NULL,
331 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
332 f->genre, f->version, f->subtype,
333 &ip->saddr, ntohs(tcp->source),
334 &ip->daddr, ntohs(tcp->dest),
335 f->ttl - ip->ttl);
336
337 if ((info->flags & XT_OSF_LOG) &&
338 info->loglevel == XT_OSF_LOGLEVEL_FIRST)
339 break;
340 }
341 }
342 rcu_read_unlock();
343
344 if (!fcount && (info->flags & XT_OSF_LOG))
345 nf_log_packet(net, p->family, p->hooknum, skb, p->in,
346 p->out, NULL,
347 "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
348 &ip->saddr, ntohs(tcp->source),
349 &ip->daddr, ntohs(tcp->dest));
350
351 if (fcount)
352 fmatch = FMATCH_OK;
353
354 return fmatch == FMATCH_OK;
355 }
356
357 static struct xt_match xt_osf_match = {
358 .name = "osf",
359 .revision = 0,
360 .family = NFPROTO_IPV4,
361 .proto = IPPROTO_TCP,
362 .hooks = (1 << NF_INET_LOCAL_IN) |
363 (1 << NF_INET_PRE_ROUTING) |
364 (1 << NF_INET_FORWARD),
365 .match = xt_osf_match_packet,
366 .matchsize = sizeof(struct xt_osf_info),
367 .me = THIS_MODULE,
368 };
369
xt_osf_init(void)370 static int __init xt_osf_init(void)
371 {
372 int err = -EINVAL;
373 int i;
374
375 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
376 INIT_LIST_HEAD(&xt_osf_fingers[i]);
377
378 err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
379 if (err < 0) {
380 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
381 goto err_out_exit;
382 }
383
384 err = xt_register_match(&xt_osf_match);
385 if (err) {
386 pr_err("Failed to register OS fingerprint "
387 "matching module (%d)\n", err);
388 goto err_out_remove;
389 }
390
391 return 0;
392
393 err_out_remove:
394 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
395 err_out_exit:
396 return err;
397 }
398
xt_osf_fini(void)399 static void __exit xt_osf_fini(void)
400 {
401 struct xt_osf_finger *f;
402 int i;
403
404 nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
405 xt_unregister_match(&xt_osf_match);
406
407 rcu_read_lock();
408 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
409
410 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
411 list_del_rcu(&f->finger_entry);
412 kfree_rcu(f, rcu_head);
413 }
414 }
415 rcu_read_unlock();
416
417 rcu_barrier();
418 }
419
420 module_init(xt_osf_init);
421 module_exit(xt_osf_fini);
422
423 MODULE_LICENSE("GPL");
424 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
425 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
426 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
427