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; 204 205 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 f = &kf->finger; 229 230 if (!(info->flags & XT_OSF_LOG) && strcmp(info->genre, f->genre)) 231 continue; 232 233 optp = _optp; 234 fmatch = FMATCH_WRONG; 235 236 if (totlen == f->ss && xt_osf_ttl(skb, info, f->ttl)) { 237 int foptsize, optnum; 238 239 /* 240 * Should not happen if userspace parser was written correctly. 241 */ 242 if (f->wss.wc >= OSF_WSS_MAX) 243 continue; 244 245 /* Check options */ 246 247 foptsize = 0; 248 for (optnum = 0; optnum < f->opt_num; ++optnum) 249 foptsize += f->opt[optnum].length; 250 251 if (foptsize > MAX_IPOPTLEN || 252 optsize > MAX_IPOPTLEN || 253 optsize != foptsize) 254 continue; 255 256 check_WSS = f->wss.wc; 257 258 for (optnum = 0; optnum < f->opt_num; ++optnum) { 259 if (f->opt[optnum].kind == (*optp)) { 260 __u32 len = f->opt[optnum].length; 261 const __u8 *optend = optp + len; 262 int loop_cont = 0; 263 264 fmatch = FMATCH_OK; 265 266 switch (*optp) { 267 case OSFOPT_MSS: 268 mss = optp[3]; 269 mss <<= 8; 270 mss |= optp[2]; 271 272 mss = ntohs((__force __be16)mss); 273 break; 274 case OSFOPT_TS: 275 loop_cont = 1; 276 break; 277 } 278 279 optp = optend; 280 } else 281 fmatch = FMATCH_OPT_WRONG; 282 283 if (fmatch != FMATCH_OK) 284 break; 285 } 286 287 if (fmatch != FMATCH_OPT_WRONG) { 288 fmatch = FMATCH_WRONG; 289 290 switch (check_WSS) { 291 case OSF_WSS_PLAIN: 292 if (f->wss.val == 0 || window == f->wss.val) 293 fmatch = FMATCH_OK; 294 break; 295 case OSF_WSS_MSS: 296 /* 297 * Some smart modems decrease mangle MSS to 298 * SMART_MSS_2, so we check standard, decreased 299 * and the one provided in the fingerprint MSS 300 * values. 301 */ 302 #define SMART_MSS_1 1460 303 #define SMART_MSS_2 1448 304 if (window == f->wss.val * mss || 305 window == f->wss.val * SMART_MSS_1 || 306 window == f->wss.val * SMART_MSS_2) 307 fmatch = FMATCH_OK; 308 break; 309 case OSF_WSS_MTU: 310 if (window == f->wss.val * (mss + 40) || 311 window == f->wss.val * (SMART_MSS_1 + 40) || 312 window == f->wss.val * (SMART_MSS_2 + 40)) 313 fmatch = FMATCH_OK; 314 break; 315 case OSF_WSS_MODULO: 316 if ((window % f->wss.val) == 0) 317 fmatch = FMATCH_OK; 318 break; 319 } 320 } 321 322 if (fmatch != FMATCH_OK) 323 continue; 324 325 fcount++; 326 327 if (info->flags & XT_OSF_LOG) 328 nf_log_packet(p->family, p->hooknum, skb, 329 p->in, p->out, NULL, 330 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n", 331 f->genre, f->version, f->subtype, 332 &ip->saddr, ntohs(tcp->source), 333 &ip->daddr, ntohs(tcp->dest), 334 f->ttl - ip->ttl); 335 336 if ((info->flags & XT_OSF_LOG) && 337 info->loglevel == XT_OSF_LOGLEVEL_FIRST) 338 break; 339 } 340 } 341 rcu_read_unlock(); 342 343 if (!fcount && (info->flags & XT_OSF_LOG)) 344 nf_log_packet(p->family, p->hooknum, skb, p->in, p->out, NULL, 345 "Remote OS is not known: %pI4:%u -> %pI4:%u\n", 346 &ip->saddr, ntohs(tcp->source), 347 &ip->daddr, ntohs(tcp->dest)); 348 349 if (fcount) 350 fmatch = FMATCH_OK; 351 352 return fmatch == FMATCH_OK; 353 } 354 355 static struct xt_match xt_osf_match = { 356 .name = "osf", 357 .revision = 0, 358 .family = NFPROTO_IPV4, 359 .proto = IPPROTO_TCP, 360 .hooks = (1 << NF_INET_LOCAL_IN) | 361 (1 << NF_INET_PRE_ROUTING) | 362 (1 << NF_INET_FORWARD), 363 .match = xt_osf_match_packet, 364 .matchsize = sizeof(struct xt_osf_info), 365 .me = THIS_MODULE, 366 }; 367 368 static int __init xt_osf_init(void) 369 { 370 int err = -EINVAL; 371 int i; 372 373 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) 374 INIT_LIST_HEAD(&xt_osf_fingers[i]); 375 376 err = nfnetlink_subsys_register(&xt_osf_nfnetlink); 377 if (err < 0) { 378 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); 379 goto err_out_exit; 380 } 381 382 err = xt_register_match(&xt_osf_match); 383 if (err) { 384 pr_err("Failed to register OS fingerprint " 385 "matching module (%d)\n", err); 386 goto err_out_remove; 387 } 388 389 return 0; 390 391 err_out_remove: 392 nfnetlink_subsys_unregister(&xt_osf_nfnetlink); 393 err_out_exit: 394 return err; 395 } 396 397 static void __exit xt_osf_fini(void) 398 { 399 struct xt_osf_finger *f; 400 int i; 401 402 nfnetlink_subsys_unregister(&xt_osf_nfnetlink); 403 xt_unregister_match(&xt_osf_match); 404 405 rcu_read_lock(); 406 for (i=0; i<ARRAY_SIZE(xt_osf_fingers); ++i) { 407 408 list_for_each_entry_rcu(f, &xt_osf_fingers[i], finger_entry) { 409 list_del_rcu(&f->finger_entry); 410 kfree_rcu(f, rcu_head); 411 } 412 } 413 rcu_read_unlock(); 414 415 rcu_barrier(); 416 } 417 418 module_init(xt_osf_init); 419 module_exit(xt_osf_fini); 420 421 MODULE_LICENSE("GPL"); 422 MODULE_AUTHOR("Evgeniy Polyakov <zbr@ioremap.net>"); 423 MODULE_DESCRIPTION("Passive OS fingerprint matching."); 424 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_OSF); 425