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         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);