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TOMOYO Linux Cross Reference
Linux/net/netfilter/xt_osf.c

Version: ~ [ linux-5.8-rc3 ] ~ [ linux-5.7.5 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.48 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.129 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.185 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.228 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.228 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.85 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
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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 
 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 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 
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 
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
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 
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_NFNL_SUBSYS(NFNL_SUBSYS_OSF);
427 

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