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 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
 197 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_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                 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
 386                 goto err_out_exit;
 387         }
 388
 389         err = xt_register_match(&xt_osf_match);
 390         if (err) {
 391                 pr_err("Failed to register OS fingerprint "
 392                        "matching module (%d)\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);