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, see <http://www.gnu.org/licenses/>.
  17  */
  18 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  19 #include <linux/module.h>
  20 #include <linux/kernel.h>
  21
  22 #include <linux/capability.h>
  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 net *net, struct sock *ctnl,
  66                                struct sk_buff *skb, const struct nlmsghdr *nlh,
  67                                const struct nlattr * const osf_attrs[],
  68                                struct netlink_ext_ack *extack)
  69 {
  70         struct xt_osf_user_finger *f;
  71         struct xt_osf_finger *kf = NULL, *sf;
  72         int err = 0;
  73
  74         if (!capable(CAP_NET_ADMIN))
  75                 return -EPERM;
  76
  77         if (!osf_attrs[OSF_ATTR_FINGER])
  78                 return -EINVAL;
  79
  80         if (!(nlh->nlmsg_flags & NLM_F_CREATE))
  81                 return -EINVAL;
  82
  83         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
  84
  85         kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL);
  86         if (!kf)
  87                 return -ENOMEM;
  88
  89         memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger));
  90
  91         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
  92                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
  93                         continue;
  94
  95                 kfree(kf);
  96                 kf = NULL;
  97
  98                 if (nlh->nlmsg_flags & NLM_F_EXCL)
  99                         err = -EEXIST;
 100                 break;
 101         }
 102
 103         /*
 104          * We are protected by nfnl mutex.
 105          */
 106         if (kf)
 107                 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]);
 108
 109         return err;
 110 }
 111
 112 static int xt_osf_remove_callback(struct net *net, struct sock *ctnl,
 113                                   struct sk_buff *skb,
 114                                   const struct nlmsghdr *nlh,
 115                                   const struct nlattr * const osf_attrs[],
 116                                   struct netlink_ext_ack *extack)
 117 {
 118         struct xt_osf_user_finger *f;
 119         struct xt_osf_finger *sf;
 120         int err = -ENOENT;
 121
 122         if (!capable(CAP_NET_ADMIN))
 123                 return -EPERM;
 124
 125         if (!osf_attrs[OSF_ATTR_FINGER])
 126                 return -EINVAL;
 127
 128         f = nla_data(osf_attrs[OSF_ATTR_FINGER]);
 129
 130         list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) {
 131                 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger)))
 132                         continue;
 133
 134                 /*
 135                  * We are protected by nfnl mutex.
 136                  */
 137                 list_del_rcu(&sf->finger_entry);
 138                 kfree_rcu(sf, rcu_head);
 139
 140                 err = 0;
 141                 break;
 142         }
 143
 144         return err;
 145 }
 146
 147 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = {
 148         [OSF_MSG_ADD]   = {
 149                 .call           = xt_osf_add_callback,
 150                 .attr_count     = OSF_ATTR_MAX,
 151                 .policy         = xt_osf_policy,
 152         },
 153         [OSF_MSG_REMOVE]        = {
 154                 .call           = xt_osf_remove_callback,
 155                 .attr_count     = OSF_ATTR_MAX,
 156                 .policy         = xt_osf_policy,
 157         },
 158 };
 159
 160 static const struct nfnetlink_subsystem xt_osf_nfnetlink = {
 161         .name                   = "osf",
 162         .subsys_id              = NFNL_SUBSYS_OSF,
 163         .cb_count               = OSF_MSG_MAX,
 164         .cb                     = xt_osf_nfnetlink_callbacks,
 165 };
 166
 167 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info,
 168                             unsigned char f_ttl)
 169 {
 170         const struct iphdr *ip = ip_hdr(skb);
 171
 172         if (info->flags & XT_OSF_TTL) {
 173                 if (info->ttl == XT_OSF_TTL_TRUE)
 174                         return ip->ttl == f_ttl;
 175                 if (info->ttl == XT_OSF_TTL_NOCHECK)
 176                         return 1;
 177                 else if (ip->ttl <= f_ttl)
 178                         return 1;
 179                 else {
 180                         struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
 181                         int ret = 0;
 182
 183                         for_ifa(in_dev) {
 184                                 if (inet_ifa_match(ip->saddr, ifa)) {
 185                                         ret = (ip->ttl == f_ttl);
 186                                         break;
 187                                 }
 188                         }
 189                         endfor_ifa(in_dev);
 190
 191                         return ret;
 192                 }
 193         }
 194
 195         return ip->ttl == f_ttl;
 196 }
 197
 198 static bool
 199 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p)
 200 {
 201         const struct xt_osf_info *info = p->matchinfo;
 202         const struct iphdr *ip = ip_hdr(skb);
 203         const struct tcphdr *tcp;
 204         struct tcphdr _tcph;
 205         int fmatch = FMATCH_WRONG, fcount = 0;
 206         unsigned int optsize = 0, check_WSS = 0;
 207         u16 window, totlen, mss = 0;
 208         bool df;
 209         const unsigned char *optp = NULL, *_optp = NULL;
 210         unsigned char opts[MAX_IPOPTLEN];
 211         const struct xt_osf_finger *kf;
 212         const struct xt_osf_user_finger *f;
 213         struct net *net = xt_net(p);
 214
 215         if (!info)
 216                 return false;
 217
 218         tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
 219         if (!tcp)
 220                 return false;
 221
 222         if (!tcp->syn)
 223                 return false;
 224
 225         totlen = ntohs(ip->tot_len);
 226         df = ntohs(ip->frag_off) & IP_DF;
 227         window = ntohs(tcp->window);
 228
 229         if (tcp->doff * 4 > sizeof(struct tcphdr)) {
 230                 optsize = tcp->doff * 4 - sizeof(struct tcphdr);
 231
 232                 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) +
 233                                 sizeof(struct tcphdr), optsize, opts);
 234         }
 235
 236         list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) {
 237                 int foptsize, optnum;
 238
 239                 f = &kf->finger;
 240
 241                 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre))
 242                         continue;
 243
 244                 optp = _optp;
 245                 fmatch = FMATCH_WRONG;
 246
 247                 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl))
 248                         continue;
 249
 250                 /*
 251                  * Should not happen if userspace parser was written correctly.
 252                  */
 253                 if (f->wss.wc >= OSF_WSS_MAX)
 254                         continue;
 255
 256                 /* Check options */
 257
 258                 foptsize = 0;
 259                 for (optnum = 0; optnum < f->opt_num; ++optnum)
 260                         foptsize += f->opt[optnum].length;
 261
 262                 if (foptsize > MAX_IPOPTLEN ||
 263                     optsize > MAX_IPOPTLEN ||
 264                     optsize != foptsize)
 265                         continue;
 266
 267                 check_WSS = f->wss.wc;
 268
 269                 for (optnum = 0; optnum < f->opt_num; ++optnum) {
 270                         if (f->opt[optnum].kind == (*optp)) {
 271                                 __u32 len = f->opt[optnum].length;
 272                                 const __u8 *optend = optp + len;
 273
 274                                 fmatch = FMATCH_OK;
 275
 276                                 switch (*optp) {
 277                                 case OSFOPT_MSS:
 278                                         mss = optp[3];
 279                                         mss <<= 8;
 280                                         mss |= optp[2];
 281
 282                                         mss = ntohs((__force __be16)mss);
 283                                         break;
 284                                 case OSFOPT_TS:
 285                                         break;
 286                                 }
 287
 288                                 optp = optend;
 289                         } else
 290                                 fmatch = FMATCH_OPT_WRONG;
 291
 292                         if (fmatch != FMATCH_OK)
 293                                 break;
 294                 }
 295
 296                 if (fmatch != FMATCH_OPT_WRONG) {
 297                         fmatch = FMATCH_WRONG;
 298
 299                         switch (check_WSS) {
 300                         case OSF_WSS_PLAIN:
 301                                 if (f->wss.val == 0 || window == f->wss.val)
 302                                         fmatch = FMATCH_OK;
 303                                 break;
 304                         case OSF_WSS_MSS:
 305                                 /*
 306                                  * Some smart modems decrease mangle MSS to
 307                                  * SMART_MSS_2, so we check standard, decreased
 308                                  * and the one provided in the fingerprint MSS
 309                                  * values.
 310                                  */
 311 #define SMART_MSS_1     1460
 312 #define SMART_MSS_2     1448
 313                                 if (window == f->wss.val * mss ||
 314                                     window == f->wss.val * SMART_MSS_1 ||
 315                                     window == f->wss.val * SMART_MSS_2)
 316                                         fmatch = FMATCH_OK;
 317                                 break;
 318                         case OSF_WSS_MTU:
 319                                 if (window == f->wss.val * (mss + 40) ||
 320                                     window == f->wss.val * (SMART_MSS_1 + 40) ||
 321                                     window == f->wss.val * (SMART_MSS_2 + 40))
 322                                         fmatch = FMATCH_OK;
 323                                 break;
 324                         case OSF_WSS_MODULO:
 325                                 if ((window % f->wss.val) == 0)
 326                                         fmatch = FMATCH_OK;
 327                                 break;
 328                         }
 329                 }
 330
 331                 if (fmatch != FMATCH_OK)
 332                         continue;
 333
 334                 fcount++;
 335
 336                 if (info->flags & XT_OSF_LOG)
 337                         nf_log_packet(net, xt_family(p), xt_hooknum(p), skb,
 338                                       xt_in(p), xt_out(p), NULL,
 339                                       "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
 340                                       f->genre, f->version, f->subtype,
 341                                       &ip->saddr, ntohs(tcp->source),
 342                                       &ip->daddr, ntohs(tcp->dest),
 343                                       f->ttl - ip->ttl);
 344
 345                 if ((info->flags & XT_OSF_LOG) &&
 346                     info->loglevel == XT_OSF_LOGLEVEL_FIRST)
 347                         break;
 348         }
 349
 350         if (!fcount && (info->flags & XT_OSF_LOG))
 351                 nf_log_packet(net, xt_family(p), xt_hooknum(p), skb, xt_in(p),
 352                               xt_out(p), NULL,
 353                         "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
 354                                 &ip->saddr, ntohs(tcp->source),
 355                                 &ip->daddr, ntohs(tcp->dest));
 356
 357         if (fcount)
 358                 fmatch = FMATCH_OK;
 359
 360         return fmatch == FMATCH_OK;
 361 }
 362
 363 static struct xt_match xt_osf_match = {
 364         .name           = "osf",
 365         .revision       = 0,
 366         .family         = NFPROTO_IPV4,
 367         .proto          = IPPROTO_TCP,
 368         .hooks          = (1 << NF_INET_LOCAL_IN) |
 369                                 (1 << NF_INET_PRE_ROUTING) |
 370                                 (1 << NF_INET_FORWARD),
 371         .match          = xt_osf_match_packet,
 372         .matchsize      = sizeof(struct xt_osf_info),
 373         .me             = THIS_MODULE,
 374 };
 375
 376 static int __init xt_osf_init(void)
 377 {
 378         int err = -EINVAL;
 379         int i;
 380
 381         for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i)
 382                 INIT_LIST_HEAD(&xt_osf_fingers[i]);
 383
 384         err = nfnetlink_subsys_register(&xt_osf_nfnetlink);
 385         if (err < 0) {
 386                 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err);
 387                 goto err_out_exit;
 388         }
 389
 390         err = xt_register_match(&xt_osf_match);
 391         if (err) {
 392                 pr_err("Failed to register OS fingerprint "
 393                        "matching module (%d)\n", err);
 394                 goto err_out_remove;
 395         }
 396
 397         return 0;
 398
 399 err_out_remove:
 400         nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
 401 err_out_exit:
 402         return err;
 403 }
 404
 405 static void __exit xt_osf_fini(void)
 406 {
 407         struct xt_osf_finger *f;
 408         int i;
 409
 410         nfnetlink_subsys_unregister(&xt_osf_nfnetlink);
 411         xt_unregister_match(&xt_osf_match);
 412
 413         rcu_read_lock();
 414         for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) {
 415
 416                 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) {
 417                         list_del_rcu(&f->finger_entry);
 418                         kfree_rcu(f, rcu_head);
 419                 }
 420         }
 421         rcu_read_unlock();
 422
 423         rcu_barrier();
 424 }
 425
 426 module_init(xt_osf_init);
 427 module_exit(xt_osf_fini);
 428
 429 MODULE_LICENSE("GPL");
 430 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>");
 431 MODULE_DESCRIPTION("Passive OS fingerprint matching.");
 432 MODULE_ALIAS("ipt_osf");
 433 MODULE_ALIAS("ip6t_osf");
 434 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF);