1 /* 2 * Copyright (c) 2003+ Evgeniy Polyakov <[email protected]> 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 struct netlink_ext_ack *extack) 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 net *net, struct sock *ctnl, 109 struct sk_buff *skb, 110 const struct nlmsghdr *nlh, 111 const struct nlattr * const osf_attrs[], 112 struct netlink_ext_ack *extack) 113 { 114 struct xt_osf_user_finger *f; 115 struct xt_osf_finger *sf; 116 int err = -ENOENT; 117 118 if (!osf_attrs[OSF_ATTR_FINGER]) 119 return -EINVAL; 120 121 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 122 123 list_for_each_entry(sf, &xt_osf_fingers[!!f->df], finger_entry) { 124 if (memcmp(&sf->finger, f, sizeof(struct xt_osf_user_finger))) 125 continue; 126 127 /* 128 * We are protected by nfnl mutex. 129 */ 130 list_del_rcu(&sf->finger_entry); 131 kfree_rcu(sf, rcu_head); 132 133 err = 0; 134 break; 135 } 136 137 return err; 138 } 139 140 static const struct nfnl_callback xt_osf_nfnetlink_callbacks[OSF_MSG_MAX] = { 141 [OSF_MSG_ADD] = { 142 .call = xt_osf_add_callback, 143 .attr_count = OSF_ATTR_MAX, 144 .policy = xt_osf_policy, 145 }, 146 [OSF_MSG_REMOVE] = { 147 .call = xt_osf_remove_callback, 148 .attr_count = OSF_ATTR_MAX, 149 .policy = xt_osf_policy, 150 }, 151 }; 152 153 static const struct nfnetlink_subsystem xt_osf_nfnetlink = { 154 .name = "osf", 155 .subsys_id = NFNL_SUBSYS_OSF, 156 .cb_count = OSF_MSG_MAX, 157 .cb = xt_osf_nfnetlink_callbacks, 158 }; 159 160 static inline int xt_osf_ttl(const struct sk_buff *skb, const struct xt_osf_info *info, 161 unsigned char f_ttl) 162 { 163 const struct iphdr *ip = ip_hdr(skb); 164 165 if (info->flags & XT_OSF_TTL) { 166 if (info->ttl == XT_OSF_TTL_TRUE) 167 return ip->ttl == f_ttl; 168 if (info->ttl == XT_OSF_TTL_NOCHECK) 169 return 1; 170 else if (ip->ttl <= f_ttl) 171 return 1; 172 else { 173 struct in_device *in_dev = __in_dev_get_rcu(skb->dev); 174 int ret = 0; 175 176 for_ifa(in_dev) { 177 if (inet_ifa_match(ip->saddr, ifa)) { 178 ret = (ip->ttl == f_ttl); 179 break; 180 } 181 } 182 endfor_ifa(in_dev); 183 184 return ret; 185 } 186 } 187 188 return ip->ttl == f_ttl; 189 } 190 191 static bool 192 xt_osf_match_packet(const struct sk_buff *skb, struct xt_action_param *p) 193 { 194 const struct xt_osf_info *info = p->matchinfo; 195 const struct iphdr *ip = ip_hdr(skb); 196 const struct tcphdr *tcp; 197 struct tcphdr _tcph; 198 int fmatch = FMATCH_WRONG, fcount = 0; 199 unsigned int optsize = 0, check_WSS = 0; 200 u16 window, totlen, mss = 0; 201 bool df; 202 const unsigned char *optp = NULL, *_optp = NULL; 203 unsigned char opts[MAX_IPOPTLEN]; 204 const struct xt_osf_finger *kf; 205 const struct xt_osf_user_finger *f; 206 struct net *net = xt_net(p); 207 208 if (!info) 209 return false; 210 211 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph); 212 if (!tcp) 213 return false; 214 215 if (!tcp->syn) 216 return false; 217 218 totlen = ntohs(ip->tot_len); 219 df = ntohs(ip->frag_off) & IP_DF; 220 window = ntohs(tcp->window); 221 222 if (tcp->doff * 4 > sizeof(struct tcphdr)) { 223 optsize = tcp->doff * 4 - sizeof(struct tcphdr); 224 225 _optp = optp = skb_header_pointer(skb, ip_hdrlen(skb) + 226 sizeof(struct tcphdr), optsize, opts); 227 } 228 229 list_for_each_entry_rcu(kf, &xt_osf_fingers[df], finger_entry) { 230 int foptsize, optnum; 231 232 f = &kf->finger; 233 234 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) 235 continue; 236 237 optp = _optp; 238 fmatch = FMATCH_WRONG; 239 240 if (totlen != f->ss || !xt_osf_ttl(skb, info, f->ttl)) 241 continue; 242 243 /* 244 * Should not happen if userspace parser was written correctly. 245 */ 246 if (f->wss.wc >= OSF_WSS_MAX) 247 continue; 248 249 /* Check options */ 250 251 foptsize = 0; 252 for (optnum = 0; optnum < f->opt_num; ++optnum) 253 foptsize += f->opt[optnum].length; 254 255 if (foptsize > MAX_IPOPTLEN || 256 optsize > MAX_IPOPTLEN || 257 optsize != foptsize) 258 continue; 259 260 check_WSS = f->wss.wc; 261 262 for (optnum = 0; optnum < f->opt_num; ++optnum) { 263 if (f->opt[optnum].kind == (*optp)) { 264 __u32 len = f->opt[optnum].length; 265 const __u8 *optend = optp + len; 266 267 fmatch = FMATCH_OK; 268 269 switch (*optp) { 270 case OSFOPT_MSS: 271 mss = optp[3]; 272 mss <<= 8; 273 mss |= optp[2]; 274 275 mss = ntohs((__force __be16)mss); 276 break; 277 case OSFOPT_TS: 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, xt_family(p), xt_hooknum(p), skb, 331 xt_in(p), xt_out(p), 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 } 342 343 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 <[email protected]>"); 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