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 net *net, struct sock *ctnl, 65 struct sk_buff *skb, 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 net *net, struct sock *ctnl, 108 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 = xt_net(p); 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 int foptsize, optnum; 230 231 f = &kf->finger; 232 233 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) 234 continue; 235 236 optp = _optp; 237 fmatch = FMATCH_WRONG; 238 239 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl)) 240 continue; 241 242 /* 243 * Should not happen if userspace parser was written correctly. 244 */ 245 if (f->wss.wc >= OSF_WSS_MAX) 246 continue; 247 248 /* Check options */ 249 250 foptsize = 0; 251 for (optnum = 0; optnum < f->opt_num; ++optnum) 252 foptsize += f->opt[optnum].length; 253 254 if (foptsize > MAX_IPOPTLEN || 255 optsize > MAX_IPOPTLEN || 256 optsize != foptsize) 257 continue; 258 259 check_WSS = f->wss.wc; 260 261 for (optnum = 0; optnum < f->opt_num; ++optnum) { 262 if (f->opt[optnum].kind == (*optp)) { 263 __u32 len = f->opt[optnum].length; 264 const __u8 *optend = optp + len; 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 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, xt_family(p), xt_hooknum(p), skb, 330 xt_in(p), xt_out(p), 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 rcu_read_unlock(); 342 343 if (!fcount && (info->flags & XT_OSF_LOG)) 344 nf_log_packet(net, xt_family(p), xt_hooknum(p), skb, xt_in(p), 345 xt_out(p), NULL, 346 "Remote OS is not known: %pI4:%u -> %pI4:%u\n", 347 &ip->saddr, ntohs(tcp->source), 348 &ip->daddr, ntohs(tcp->dest)); 349 350 if (fcount) 351 fmatch = FMATCH_OK; 352 353 return fmatch == FMATCH_OK; 354 } 355 356 static struct xt_match xt_osf_match = { 357 .name = "osf", 358 .revision = 0, 359 .family = NFPROTO_IPV4, 360 .proto = IPPROTO_TCP, 361 .hooks = (1 << NF_INET_LOCAL_IN) | 362 (1 << NF_INET_PRE_ROUTING) | 363 (1 << NF_INET_FORWARD), 364 .match = xt_osf_match_packet, 365 .matchsize = sizeof(struct xt_osf_info), 366 .me = THIS_MODULE, 367 }; 368 369 static int __init xt_osf_init(void) 370 { 371 int err = -EINVAL; 372 int i; 373 374 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) 375 INIT_LIST_HEAD(&xt_osf_fingers[i]); 376 377 err = nfnetlink_subsys_register(&xt_osf_nfnetlink); 378 if (err < 0) { 379 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); 380 goto err_out_exit; 381 } 382 383 err = xt_register_match(&xt_osf_match); 384 if (err) { 385 pr_err("Failed to register OS fingerprint " 386 "matching module (%d)\n", err); 387 goto err_out_remove; 388 } 389 390 return 0; 391 392 err_out_remove: 393 nfnetlink_subsys_unregister(&xt_osf_nfnetlink); 394 err_out_exit: 395 return err; 396 } 397 398 static void __exit xt_osf_fini(void) 399 { 400 struct xt_osf_finger *f; 401 int i; 402 403 nfnetlink_subsys_unregister(&xt_osf_nfnetlink); 404 xt_unregister_match(&xt_osf_match); 405 406 rcu_read_lock(); 407 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) { 408 409 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) { 410 list_del_rcu(&f->finger_entry); 411 kfree_rcu(f, rcu_head); 412 } 413 } 414 rcu_read_unlock(); 415 416 rcu_barrier(); 417 } 418 419 module_init(xt_osf_init); 420 module_exit(xt_osf_fini); 421 422 MODULE_LICENSE("GPL"); 423 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); 424 MODULE_DESCRIPTION("Passive OS fingerprint matching."); 425 MODULE_ALIAS("ipt_osf"); 426 MODULE_ALIAS("ip6t_osf"); 427 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); 428