netfilter: don't use INIT_RCU_HEAD()
[linux-2.6.git] / net / netfilter / xt_osf.c
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);