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/if.h> 23 #include <linux/inetdevice.h> 24 #include <linux/ip.h> 25 #include <linux/list.h> 26 #include <linux/rculist.h> 27 #include <linux/skbuff.h> 28 #include <linux/slab.h> 29 #include <linux/tcp.h> 30 31 #include <net/ip.h> 32 #include <net/tcp.h> 33 34 #include <linux/netfilter/nfnetlink.h> 35 #include <linux/netfilter/x_tables.h> 36 #include <net/netfilter/nf_log.h> 37 #include <linux/netfilter/xt_osf.h> 38 39 struct xt_osf_finger { 40 struct rcu_head rcu_head; 41 struct list_head finger_entry; 42 struct xt_osf_user_finger finger; 43 }; 44 45 enum osf_fmatch_states { 46 /* Packet does not match the fingerprint */ 47 FMATCH_WRONG = 0, 48 /* Packet matches the fingerprint */ 49 FMATCH_OK, 50 /* Options do not match the fingerprint, but header does */ 51 FMATCH_OPT_WRONG, 52 }; 53 54 /* 55 * Indexed by dont-fragment bit. 56 * It is the only constant value in the fingerprint. 57 */ 58 static struct list_head xt_osf_fingers[2]; 59 60 static const struct nla_policy xt_osf_policy[OSF_ATTR_MAX + 1] = { 61 [OSF_ATTR_FINGER] = { .len = sizeof(struct xt_osf_user_finger) }, 62 }; 63 64 static int xt_osf_add_callback(struct sock *ctnl, struct sk_buff *skb, 65 const struct nlmsghdr *nlh, 66 const struct nlattr * const osf_attrs[]) 67 { 68 struct xt_osf_user_finger *f; 69 struct xt_osf_finger *kf = NULL, *sf; 70 int err = 0; 71 72 if (!osf_attrs[OSF_ATTR_FINGER]) 73 return -EINVAL; 74 75 if (!(nlh->nlmsg_flags & NLM_F_CREATE)) 76 return -EINVAL; 77 78 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 79 80 kf = kmalloc(sizeof(struct xt_osf_finger), GFP_KERNEL); 81 if (!kf) 82 return -ENOMEM; 83 84 memcpy(&kf->finger, f, sizeof(struct xt_osf_user_finger)); 85 86 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { 87 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) 88 continue; 89 90 kfree(kf); 91 kf = NULL; 92 93 if (nlh->nlmsg_flags & NLM_F_EXCL) 94 err = -EEXIST; 95 break; 96 } 97 98 /* 99 * We are protected by nfnl mutex. 100 */ 101 if (kf) 102 list_add_tail_rcu(&kf->finger_entry, &xt_osf_fingers[!!f->df]); 103 104 return err; 105 } 106 107 static int xt_osf_remove_callback(struct sock *ctnl, struct sk_buff *skb, 108 const struct nlmsghdr *nlh, 109 const struct nlattr * const osf_attrs[]) 110 { 111 struct xt_osf_user_finger *f; 112 struct xt_osf_finger *sf; 113 int err = -ENOENT; 114 115 if (!osf_attrs[OSF_ATTR_FINGER]) 116 return -EINVAL; 117 118 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 119 120 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { 121 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) 122 continue; 123 124 /* 125 * We are protected by nfnl mutex. 126 */ 127 list_del_rcu(&sf->finger_entry); 128 kfree_rcu(sf, rcu_head); 129 130 err = 0; 131 break; 132 } 133 134 return err; 135 } 136 137 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = { 138 [OSF_MSG_ADD] = { 139 .call = xt_osf_add_callback, 140 .attr_count = OSF_ATTR_MAX, 141 .policy = xt_osf_policy, 142 }, 143 [OSF_MSG_REMOVE] = { 144 .call = xt_osf_remove_callback, 145 .attr_count = OSF_ATTR_MAX, 146 .policy = xt_osf_policy, 147 }, 148 }; 149 150 static const struct nfnetlink_subsystem xt_osf_nfnetlink = { 151 .name = "osf", 152 .subsys_id = NFNL_SUBSYS_OSF, 153 .cb_count = OSF_MSG_MAX, 154 .cb = xt_osf_nfnetlink_callbacks, 155 }; 156 157 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info, 158 unsigned char f_ttl) 159 { 160 const struct iphdr *ip = ip_hdr(skb); 161 162 if (info->flags & XT_OSF_TTL) { 163 if (info->ttl == XT_OSF_TTL_TRUE) 164 return ip->ttl == f_ttl; 165 if (info->ttl == XT_OSF_TTL_NOCHECK) 166 return 1; 167 else if (ip->ttl <= f_ttl) 168 return 1; 169 else { 170 struct in_device *in_dev = __in_dev_get_rcu(skb->dev); 171 int ret = 0; 172 173 for_ifa(in_dev) { 174 if (inet_ifa_match(ip->saddr, ifa)) { 175 ret = (ip->ttl == f_ttl); 176 break; 177 } 178 } 179 endfor_ifa(in_dev); 180 181 return ret; 182 } 183 } 184 185 return ip->ttl == f_ttl; 186 } 187 188 static bool 189 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p) 190 { 191 const struct xt_osf_info *info = p->matchinfo; 192 const struct iphdr *ip = ip_hdr(skb); 193 const struct tcphdr *tcp; 194 struct tcphdr _tcph; 195 int fmatch = FMATCH_WRONG, fcount = 0; 196 unsigned int optsize = 0, check_WSS = 0; 197 u16 window, totlen, mss = 0; 198 bool df; 199 const unsigned char *optp = NULL, *_optp = NULL; 200 unsigned char opts[MAX_IPOPTLEN]; 201 const struct xt_osf_finger *kf; 202 const struct xt_osf_user_finger *f; 203 struct net *net = dev_net(p->in ? p->in : p->out); 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 int foptsize, optnum; 229 230 f = &kf->finger; 231 232 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) 233 continue; 234 235 optp = _optp; 236 fmatch = FMATCH_WRONG; 237 238 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl)) 239 continue; 240 241 /* 242 * Should not happen if userspace parser was written correctly. 243 */ 244 if (f->wss.wc >= OSF_WSS_MAX) 245 continue; 246 247 /* Check options */ 248 249 foptsize = 0; 250 for (optnum = 0; optnum < f->opt_num; ++optnum) 251 foptsize += f->opt[optnum].length; 252 253 if (foptsize > MAX_IPOPTLEN || 254 optsize > MAX_IPOPTLEN || 255 optsize != foptsize) 256 continue; 257 258 check_WSS = f->wss.wc; 259 260 for (optnum = 0; optnum < f->opt_num; ++optnum) { 261 if (f->opt[optnum].kind == (*optp)) { 262 __u32 len = f->opt[optnum].length; 263 const __u8 *optend = optp + len; 264 int loop_cont = 0; 265 266 fmatch = FMATCH_OK; 267 268 switch (*optp) { 269 case OSFOPT_MSS: 270 mss = optp[3]; 271 mss <<= 8; 272 mss |= optp[2]; 273 274 mss = ntohs((__force __be16)mss); 275 break; 276 case OSFOPT_TS: 277 loop_cont = 1; 278 break; 279 } 280 281 optp = optend; 282 } else 283 fmatch = FMATCH_OPT_WRONG; 284 285 if (fmatch != FMATCH_OK) 286 break; 287 } 288 289 if (fmatch != FMATCH_OPT_WRONG) { 290 fmatch = FMATCH_WRONG; 291 292 switch (check_WSS) { 293 case OSF_WSS_PLAIN: 294 if (f->wss.val == 0 || window == f->wss.val) 295 fmatch = FMATCH_OK; 296 break; 297 case OSF_WSS_MSS: 298 /* 299 * Some smart modems decrease mangle MSS to 300 * SMART_MSS_2, so we check standard, decreased 301 * and the one provided in the fingerprint MSS 302 * values. 303 */ 304 #define SMART_MSS_1 1460 305 #define SMART_MSS_2 1448 306 if (window == f->wss.val * mss || 307 window == f->wss.val * SMART_MSS_1 || 308 window == f->wss.val * SMART_MSS_2) 309 fmatch = FMATCH_OK; 310 break; 311 case OSF_WSS_MTU: 312 if (window == f->wss.val * (mss + 40) || 313 window == f->wss.val * (SMART_MSS_1 + 40) || 314 window == f->wss.val * (SMART_MSS_2 + 40)) 315 fmatch = FMATCH_OK; 316 break; 317 case OSF_WSS_MODULO: 318 if ((window % f->wss.val) == 0) 319 fmatch = FMATCH_OK; 320 break; 321 } 322 } 323 324 if (fmatch != FMATCH_OK) 325 continue; 326 327 fcount++; 328 329 if (info->flags & XT_OSF_LOG) 330 nf_log_packet(net, p->family, p->hooknum, skb, 331 p->in, p->out, NULL, 332 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n", 333 f->genre, f->version, f->subtype, 334 &ip->saddr, ntohs(tcp->source), 335 &ip->daddr, ntohs(tcp->dest), 336 f->ttl - ip->ttl); 337 338 if ((info->flags & XT_OSF_LOG) && 339 info->loglevel == XT_OSF_LOGLEVEL_FIRST) 340 break; 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("ipt_osf"); 427 MODULE_ALIAS("ip6t_osf"); 428 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); 429