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Linux/net/netfilter/xt_osf.c

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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, see <http://www.gnu.org/licenses/>.
 17  */
 18 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 19 #include <linux/module.h>
 20 #include <linux/kernel.h>
 21 
 22 #include <linux/if.h>
 23 #include <linux/inetdevice.h>
 24 #include <linux/ip.h>
 25 #include <linux/list.h>
 26 #include <linux/rculist.h>
 27 #include <linux/skbuff.h>
 28 #include <linux/slab.h>
 29 #include <linux/tcp.h>
 30 
 31 #include <net/ip.h>
 32 #include <net/tcp.h>
 33 
 34 #include <linux/netfilter/nfnetlink.h>
 35 #include <linux/netfilter/x_tables.h>
 36 #include <net/netfilter/nf_log.h>
 37 #include <linux/netfilter/xt_osf.h>
 38 
 39 struct xt_osf_finger {
 40         struct rcu_head                 rcu_head;
 41         struct list_head                finger_entry;
 42         struct xt_osf_user_finger       finger;
 43 };
 44 
 45 enum osf_fmatch_states {
 46         /* Packet does not match the fingerprint */
 47         FMATCH_WRONG = 0,
 48         /* Packet matches the fingerprint */
 49         FMATCH_OK,
 50         /* Options do not match the fingerprint, but header does */
 51         FMATCH_OPT_WRONG,
 52 };
 53 
 54 /*
 55  * Indexed by dont-fragment bit.
 56  * It is the only constant value in the fingerprint.
 57  */
 58 static struct list_head xt_osf_fingers[2];
 59 
 60 static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = {
 61         [OSF_ATTR_FINGER]       = { .len = sizeof(struct xt_osf_user_finger) },
 62 };
 63 
 64 static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb,
 65                                const struct nlmsghdr *nlh,
 66                                const struct nlattr * const osf_attrs[])
 67 {
 68         struct xt_osf_user_finger *f;
 69         struct xt_osf_finger *kf = NULL, *sf;
 70         int err = 0;
 71 
 72         if (!osf_attrs[OSF_ATTR_FINGER])
 73                 return -EINVAL;
 74 
 75         if (!(nlh->nlmsg_flags & NLM_F_CREATE))
 76                 return -EINVAL;
 77 
 78         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 79 
 80         kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
 81         if (!kf)
 82                 return -ENOMEM;
 83 
 84         memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
 85 
 86         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
 87                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
 88                         continue;
 89 
 90                 kfree(kf);
 91                 kf = NULL;
 92 
 93                 if (nlh->nlmsg_flags & NLM_F_EXCL)
 94                         err = -EEXIST;
 95                 break;
 96         }
 97 
 98         /*
 99          * We are protected by nfnl mutex.
100          */
101         if (kf)
102                 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
103 
104         return err;
105 }
106 
107 static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
108                                   const struct nlmsghdr *nlh,
109                                   const struct nlattr * const osf_attrs[])
110 {
111         struct xt_osf_user_finger *f;
112         struct xt_osf_finger *sf;
113         int err = -ENOENT;
114 
115         if (!osf_attrs[OSF_ATTR_FINGER])
116                 return -EINVAL;
117 
118         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
119 
120         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
121                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
122                         continue;
123 
124                 /*
125                  * We are protected by nfnl mutex.
126                  */
127                 list_del_rcu(&sf->finger_entry);
128                 kfree_rcu(sf, rcu_head);
129 
130                 err = 0;
131                 break;
132         }
133 
134         return err;
135 }
136 
137 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
138         [OSF_MSG_ADD]   = {
139                 .call           = xt_osf_add_callback,
140                 .attr_count     = OSF_ATTR_MAX,
141                 .policy         = xt_osf_policy,
142         },
143         [OSF_MSG_REMOVE]        = {
144                 .call           = xt_osf_remove_callback,
145                 .attr_count     = OSF_ATTR_MAX,
146                 .policy         = xt_osf_policy,
147         },
148 };
149 
150 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
151         .name                   = "osf",
152         .subsys_id              = NFNL_SUBSYS_OSF,
153         .cb_count               = OSF_MSG_MAX,
154         .cb                     = xt_osf_nfnetlink_callbacks,
155 };
156 
157 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
158                             unsigned char f_ttl)
159 {
160         const struct iphdr *ip = ip_hdr(skb);
161 
162         if (info->flags & XT_OSF_TTL) {
163                 if (info->ttl == XT_OSF_TTL_TRUE)
164                         return ip->ttl == f_ttl;
165                 if (info->ttl == XT_OSF_TTL_NOCHECK)
166                         return 1;
167                 else if (ip->ttl <= f_ttl)
168                         return 1;
169                 else {
170                         struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
171                         int ret = 0;
172 
173                         for_ifa(in_dev) {
174                                 if (inet_ifa_match(ip->saddr, ifa)) {
175                                         ret = (ip->ttl == f_ttl);
176                                         break;
177                                 }
178                         }
179                         endfor_ifa(in_dev);
180 
181                         return ret;
182                 }
183         }
184 
185         return ip->ttl == f_ttl;
186 }
187 
188 static bool
189 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
190 {
191         const struct xt_osf_info *info = p->matchinfo;
192         const struct iphdr *ip = ip_hdr(skb);
193         const struct tcphdr *tcp;
194         struct tcphdr _tcph;
195         int fmatch = FMATCH_WRONG, fcount = 0;
196         unsigned int optsize = 0, check_WSS = 0;
197         u16 window, totlen, mss = 0;
198         bool df;
199         const unsigned char *optp = NULL, *_optp = NULL;
200         unsigned char opts[MAX_IPOPTLEN];
201         const struct xt_osf_finger *kf;
202         const struct xt_osf_user_finger *f;
203         struct net *net = dev_net(p->in ? p->in : p->out);
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                 int foptsize, optnum;
229 
230                 f = &kf->finger;
231 
232                 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
233                         continue;
234 
235                 optp = _optp;
236                 fmatch = FMATCH_WRONG;
237 
238                 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
239                         continue;
240 
241                 /*
242                  * Should not happen if userspace parser was written correctly.
243                  */
244                 if (f->wss.wc >= OSF_WSS_MAX)
245                         continue;
246 
247                 /* Check options */
248 
249                 foptsize = 0;
250                 for (optnum = 0; optnum < f->opt_num; ++optnum)
251                         foptsize += f->opt[optnum].length;
252 
253                 if (foptsize > MAX_IPOPTLEN ||
254                     optsize > MAX_IPOPTLEN ||
255                     optsize != foptsize)
256                         continue;
257 
258                 check_WSS = f->wss.wc;
259 
260                 for (optnum = 0; optnum < f->opt_num; ++optnum) {
261                         if (f->opt[optnum].kind == (*optp)) {
262                                 __u32 len = f->opt[optnum].length;
263                                 const __u8 *optend = optp + len;
264                                 int loop_cont = 0;
265 
266                                 fmatch = FMATCH_OK;
267 
268                                 switch (*optp) {
269                                 case OSFOPT_MSS:
270                                         mss = optp[3];
271                                         mss <<= 8;
272                                         mss |= optp[2];
273 
274                                         mss = ntohs((__force __be16)mss);
275                                         break;
276                                 case OSFOPT_TS:
277                                         loop_cont = 1;
278                                         break;
279                                 }
280 
281                                 optp = optend;
282                         } else
283                                 fmatch = FMATCH_OPT_WRONG;
284 
285                         if (fmatch != FMATCH_OK)
286                                 break;
287                 }
288 
289                 if (fmatch != FMATCH_OPT_WRONG) {
290                         fmatch = FMATCH_WRONG;
291 
292                         switch (check_WSS) {
293                         case OSF_WSS_PLAIN:
294                                 if (f->wss.val == 0 || window == f->wss.val)
295                                         fmatch = FMATCH_OK;
296                                 break;
297                         case OSF_WSS_MSS:
298                                 /*
299                                  * Some smart modems decrease mangle MSS to
300                                  * SMART_MSS_2, so we check standard, decreased
301                                  * and the one provided in the fingerprint MSS
302                                  * values.
303                                  */
304 #define SMART_MSS_1     1460
305 #define SMART_MSS_2     1448
306                                 if (window == f->wss.val * mss ||
307                                     window == f->wss.val * SMART_MSS_1 ||
308                                     window == f->wss.val * SMART_MSS_2)
309                                         fmatch = FMATCH_OK;
310                                 break;
311                         case OSF_WSS_MTU:
312                                 if (window == f->wss.val * (mss + 40) ||
313                                     window == f->wss.val * (SMART_MSS_1 + 40) ||
314                                     window == f->wss.val * (SMART_MSS_2 + 40))
315                                         fmatch = FMATCH_OK;
316                                 break;
317                         case OSF_WSS_MODULO:
318                                 if ((window % f->wss.val) == 0)
319                                         fmatch = FMATCH_OK;
320                                 break;
321                         }
322                 }
323 
324                 if (fmatch != FMATCH_OK)
325                         continue;
326 
327                 fcount++;
328 
329                 if (info->flags & XT_OSF_LOG)
330                         nf_log_packet(net, p->family, p->hooknum, skb,
331                                       p->in, p->out, NULL,
332                                       "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
333                                       f->genre, f->version, f->subtype,
334                                       &ip->saddr, ntohs(tcp->source),
335                                       &ip->daddr, ntohs(tcp->dest),
336                                       f->ttl - ip->ttl);
337 
338                 if ((info->flags & XT_OSF_LOG) &&
339                     info->loglevel == XT_OSF_LOGLEVEL_FIRST)
340                         break;
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 
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 
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("ipt_osf");
427 MODULE_ALIAS("ip6t_osf");
428 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
429 

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