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                         struct nlmsghdr *nlh, struct nlattr *osf_attrs[])
  74 {
  75         struct xt_osf_user_finger *f;
  76         struct xt_osf_finger *kf = NULL, *sf;
  77         int err = 0;
  78
  79         if (!osf_attrs[OSF_ATTR_FINGER])
  80                 return -EINVAL;
  81
  82         if (!(nlh->nlmsg_flags & NLM_F_CREATE))
  83                 return -EINVAL;
  84
  85         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
  86
  87         kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
  88         if (!kf)
  89                 return -ENOMEM;
  90
  91         memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
  92
  93         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
  94                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
  95                         continue;
  96
  97                 kfree(kf);
  98                 kf = NULL;
  99
 100                 if (nlh->nlmsg_flags & NLM_F_EXCL)
 101                         err = -EEXIST;
 102                 break;
 103         }
 104
 105         /*
 106          * We are protected by nfnl mutex.
 107          */
 108         if (kf)
 109                 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
 110
 111         return err;
 112 }
 113
 114 static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb,
 115                         struct nlmsghdr *nlh, struct nlattr *osf_attrs[])
 116 {
 117         struct xt_osf_user_finger *f;
 118         struct xt_osf_finger *sf;
 119         int err = ENOENT;
 120
 121         if (!osf_attrs[OSF_ATTR_FINGER])
 122                 return -EINVAL;
 123
 124         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 125
 126         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
 127                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
 128                         continue;
 129
 130                 /*
 131                  * We are protected by nfnl mutex.
 132                  */
 133                 list_del_rcu(&sf->finger_entry);
 134                 call_rcu(&sf->rcu_head, xt_osf_finger_free_rcu);
 135
 136                 err = 0;
 137                 break;
 138         }
 139
 140         return err;
 141 }
 142
 143 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
 144         [OSF_MSG_ADD]   = {
 145                 .call           = xt_osf_add_callback,
 146                 .attr_count     = OSF_ATTR_MAX,
 147                 .policy         = xt_osf_policy,
 148         },
 149         [OSF_MSG_REMOVE]        = {
 150                 .call           = xt_osf_remove_callback,
 151                 .attr_count     = OSF_ATTR_MAX,
 152                 .policy         = xt_osf_policy,
 153         },
 154 };
 155
 156 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
 157         .name                   = "osf",
 158         .subsys_id              = NFNL_SUBSYS_OSF,
 159         .cb_count               = OSF_MSG_MAX,
 160         .cb                     = xt_osf_nfnetlink_callbacks,
 161 };
 162
 163 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
 164                             unsigned char f_ttl)
 165 {
 166         const struct iphdr *ip = ip_hdr(skb);
 167
 168         if (info->flags & XT_OSF_TTL) {
 169                 if (info->ttl == XT_OSF_TTL_TRUE)
 170                         return ip->ttl == f_ttl;
 171                 if (info->ttl == XT_OSF_TTL_NOCHECK)
 172                         return 1;
 173                 else if (ip->ttl <= f_ttl)
 174                         return 1;
 175                 else {
 176                         struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
 177                         int ret = 0;
 178
 179                         for_ifa(in_dev) {
 180                                 if (inet_ifa_match(ip->saddr, ifa)) {
 181                                         ret = (ip->ttl == f_ttl);
 182                                         break;
 183                                 }
 184                         }
 185                         endfor_ifa(in_dev);
 186
 187                         return ret;
 188                 }
 189         }
 190
 191         return ip->ttl == f_ttl;
 192 }
 193
 194 static bool xt_osf_match_packet(const struct sk_buff *skb,
 195                 const struct xt_match_param *p)
 196 {
 197         const struct xt_osf_info *info = p->matchinfo;
 198         const struct iphdr *ip = ip_hdr(skb);
 199         const struct tcphdr *tcp;
 200         struct tcphdr _tcph;
 201         int fmatch = FMATCH_WRONG, fcount = 0;
 202         unsigned int optsize = 0, check_WSS = 0;
 203         u16 window, totlen, mss = 0;
 204         bool df;
 205         const unsigned char *optp = NULL, *_optp = NULL;
 206         unsigned char opts[MAX_IPOPTLEN];
 207         const struct xt_osf_finger *kf;
 208         const struct xt_osf_user_finger *f;
 209
 210         if (!info)
 211                 return false;
 212
 213         tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
 214         if (!tcp)
 215                 return false;
 216
 217         if (!tcp->syn)
 218                 return false;
 219
 220         totlen = ntohs(ip->tot_len);
 221         df = ntohs(ip->frag_off) & IP_DF;
 222         window = ntohs(tcp->window);
 223
 224         if (tcp->doff * 4 > sizeof(struct tcphdr)) {
 225                 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
 226
 227                 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
 228                                 sizeof(struct tcphdr), optsize, opts);
 229         }
 230
 231         rcu_read_lock();
 232         list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
 233                 f = &kf->finger;
 234
 235                 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
 236                         continue;
 237
 238                 optp = _optp;
 239                 fmatch = FMATCH_WRONG;
 240
 241                 if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) {
 242                         int foptsize, optnum;
 243
 244                         /*
 245                          * Should not happen if userspace parser was written correctly.
 246                          */
 247                         if (f->wss.wc >= OSF_WSS_MAX)
 248                                 continue;
 249
 250                         /* Check options */
 251
 252                         foptsize = 0;
 253                         for (optnum = 0; optnum < f->opt_num; ++optnum)
 254                                 foptsize += f->opt[optnum].length;
 255
 256                         if (foptsize > MAX_IPOPTLEN ||
 257                                 optsize > MAX_IPOPTLEN ||
 258                                 optsize != foptsize)
 259                                 continue;
 260
 261                         check_WSS = f->wss.wc;
 262
 263                         for (optnum = 0; optnum < f->opt_num; ++optnum) {
 264                                 if (f->opt[optnum].kind == (*optp)) {
 265                                         __u32 len = f->opt[optnum].length;
 266                                         const __u8 *optend = optp + len;
 267                                         int loop_cont = 0;
 268
 269                                         fmatch = FMATCH_OK;
 270
 271                                         switch (*optp) {
 272                                         case OSFOPT_MSS:
 273                                                 mss = optp[3];
 274                                                 mss <<= 8;
 275                                                 mss |= optp[2];
 276
 277                                                 mss = ntohs(mss);
 278                                                 break;
 279                                         case OSFOPT_TS:
 280                                                 loop_cont = 1;
 281                                                 break;
 282                                         }
 283
 284                                         optp = optend;
 285                                 } else
 286                                         fmatch = FMATCH_OPT_WRONG;
 287
 288                                 if (fmatch != FMATCH_OK)
 289                                         break;
 290                         }
 291
 292                         if (fmatch != FMATCH_OPT_WRONG) {
 293                                 fmatch = FMATCH_WRONG;
 294
 295                                 switch (check_WSS) {
 296                                 case OSF_WSS_PLAIN:
 297                                         if (f->wss.val == 0 || window == f->wss.val)
 298                                                 fmatch = FMATCH_OK;
 299                                         break;
 300                                 case OSF_WSS_MSS:
 301                                         /*
 302                                          * Some smart modems decrease mangle MSS to
 303                                          * SMART_MSS_2, so we check standard, decreased
 304                                          * and the one provided in the fingerprint MSS
 305                                          * values.
 306                                          */
 307 #define SMART_MSS_1     1460
 308 #define SMART_MSS_2     1448
 309                                         if (window == f->wss.val * mss ||
 310                                             window == f->wss.val * SMART_MSS_1 ||
 311                                             window == f->wss.val * SMART_MSS_2)
 312                                                 fmatch = FMATCH_OK;
 313                                         break;
 314                                 case OSF_WSS_MTU:
 315                                         if (window == f->wss.val * (mss + 40) ||
 316                                             window == f->wss.val * (SMART_MSS_1 + 40) ||
 317                                             window == f->wss.val * (SMART_MSS_2 + 40))
 318                                                 fmatch = FMATCH_OK;
 319                                         break;
 320                                 case OSF_WSS_MODULO:
 321                                         if ((window % f->wss.val) == 0)
 322                                                 fmatch = FMATCH_OK;
 323                                         break;
 324                                 }
 325                         }
 326
 327                         if (fmatch != FMATCH_OK)
 328                                 continue;
 329
 330                         fcount++;
 331
 332                         if (info->flags & XT_OSF_LOG)
 333                                 nf_log_packet(p->hooknum, 0, skb, p->in, p->out, NULL,
 334                                         "%s [%s:%s] : %pi4:%d -> %pi4:%d hops=%d\n",
 335                                         f->genre, f->version, f->subtype,
 336                                         &ip->saddr, ntohs(tcp->source),
 337                                         &ip->daddr, ntohs(tcp->dest),
 338                                         f->ttl - ip->ttl);
 339
 340                         if ((info->flags & XT_OSF_LOG) &&
 341                             info->loglevel == XT_OSF_LOGLEVEL_FIRST)
 342                                 break;
 343                 }
 344         }
 345         rcu_read_unlock();
 346
 347         if (!fcount && (info->flags & XT_OSF_LOG))
 348                 nf_log_packet(p->hooknum, 0, skb, p->in, p->out, NULL,
 349                         "Remote OS is not known: %pi4:%u -> %pi4:%u\n",
 350                                 &ip->saddr, ntohs(tcp->source),
 351                                 &ip->daddr, ntohs(tcp->dest));
 352
 353         if (fcount)
 354                 fmatch = FMATCH_OK;
 355
 356         return fmatch == FMATCH_OK;
 357 }
 358
 359 static struct xt_match xt_osf_match = {
 360         .name           = "osf",
 361         .revision       = 0,
 362         .family         = NFPROTO_IPV4,
 363         .proto          = IPPROTO_TCP,
 364         .hooks          = (1 << NF_INET_LOCAL_IN) |
 365                                 (1 << NF_INET_PRE_ROUTING) |
 366                                 (1 << NF_INET_FORWARD),
 367         .match          = xt_osf_match_packet,
 368         .matchsize      = sizeof(struct xt_osf_info),
 369         .me             = THIS_MODULE,
 370 };
 371
 372 static int __init xt_osf_init(void)
 373 {
 374         int err = -EINVAL;
 375         int i;
 376
 377         for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
 378                 INIT_LIST_HEAD(&xt_osf_fingers[i]);
 379
 380         err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
 381         if (err < 0) {
 382                 printk(KERN_ERR "Failed (%d) to register OSF nsfnetlink helper.\n", err);
 383                 goto err_out_exit;
 384         }
 385
 386         err = xt_register_match(&xt_osf_match);
 387         if (err) {
 388                 printk(KERN_ERR "Failed (%d) to register OS fingerprint "
 389                                 "matching module.\n", err);
 390                 goto err_out_remove;
 391         }
 392
 393         return 0;
 394
 395 err_out_remove:
 396         nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
 397 err_out_exit:
 398         return err;
 399 }
 400
 401 static void __exit xt_osf_fini(void)
 402 {
 403         struct xt_osf_finger *f;
 404         int i;
 405
 406         nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
 407         xt_unregister_match(&xt_osf_match);
 408
 409         rcu_read_lock();
 410         for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
 411
 412                 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
 413                         list_del_rcu(&f->finger_entry);
 414                         call_rcu(&f->rcu_head, xt_osf_finger_free_rcu);
 415                 }
 416         }
 417         rcu_read_unlock();
 418
 419         rcu_barrier();
 420 }
 421
 422 module_init(xt_osf_init);
 423 module_exit(xt_osf_fini);
 424
 425 MODULE_LICENSE("GPL");
 426 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
 427 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
 428 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);