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