1 // SPDX-License-Identifier: GPL-2.0-only 2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 3 #include <linux/module.h> 4 #include <linux/kernel.h> 5 6 #include <linux/capability.h> 7 #include <linux/if.h> 8 #include <linux/inetdevice.h> 9 #include <linux/ip.h> 10 #include <linux/list.h> 11 #include <linux/rculist.h> 12 #include <linux/skbuff.h> 13 #include <linux/slab.h> 14 #include <linux/tcp.h> 15 16 #include <net/ip.h> 17 #include <net/tcp.h> 18 19 #include <linux/netfilter/nfnetlink.h> 20 #include <linux/netfilter/x_tables.h> 21 #include <net/netfilter/nf_log.h> 22 #include <linux/netfilter/nfnetlink_osf.h> 23 24 /* 25 * Indexed by dont-fragment bit. 26 * It is the only constant value in the fingerprint. 27 */ 28 struct list_head nf_osf_fingers[2]; 29 EXPORT_SYMBOL_GPL(nf_osf_fingers); 30 31 static inline int nf_osf_ttl(const struct sk_buff *skb, 32 int ttl_check, unsigned char f_ttl) 33 { 34 struct in_device *in_dev = __in_dev_get_rcu(skb->dev); 35 const struct iphdr *ip = ip_hdr(skb); 36 const struct in_ifaddr *ifa; 37 int ret = 0; 38 39 if (ttl_check == NF_OSF_TTL_TRUE) 40 return ip->ttl == f_ttl; 41 if (ttl_check == NF_OSF_TTL_NOCHECK) 42 return 1; 43 else if (ip->ttl <= f_ttl) 44 return 1; 45 46 in_dev_for_each_ifa_rcu(ifa, in_dev) { 47 if (inet_ifa_match(ip->saddr, ifa)) { 48 ret = (ip->ttl == f_ttl); 49 break; 50 } 51 } 52 53 return ret; 54 } 55 56 struct nf_osf_hdr_ctx { 57 bool df; 58 u16 window; 59 u16 totlen; 60 const unsigned char *optp; 61 unsigned int optsize; 62 }; 63 64 static bool nf_osf_match_one(const struct sk_buff *skb, 65 const struct nf_osf_user_finger *f, 66 int ttl_check, 67 struct nf_osf_hdr_ctx *ctx) 68 { 69 const __u8 *optpinit = ctx->optp; 70 unsigned int check_WSS = 0; 71 int fmatch = FMATCH_WRONG; 72 int foptsize, optnum; 73 u16 mss = 0; 74 75 if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl)) 76 return false; 77 78 /* 79 * Should not happen if userspace parser was written correctly. 80 */ 81 if (f->wss.wc >= OSF_WSS_MAX) 82 return false; 83 84 /* Check options */ 85 86 foptsize = 0; 87 for (optnum = 0; optnum < f->opt_num; ++optnum) 88 foptsize += f->opt[optnum].length; 89 90 if (foptsize > MAX_IPOPTLEN || 91 ctx->optsize > MAX_IPOPTLEN || 92 ctx->optsize != foptsize) 93 return false; 94 95 check_WSS = f->wss.wc; 96 97 for (optnum = 0; optnum < f->opt_num; ++optnum) { 98 if (f->opt[optnum].kind == *ctx->optp) { 99 __u32 len = f->opt[optnum].length; 100 const __u8 *optend = ctx->optp + len; 101 102 fmatch = FMATCH_OK; 103 104 switch (*ctx->optp) { 105 case OSFOPT_MSS: 106 mss = ctx->optp[3]; 107 mss <<= 8; 108 mss |= ctx->optp[2]; 109 110 mss = ntohs((__force __be16)mss); 111 break; 112 case OSFOPT_TS: 113 break; 114 } 115 116 ctx->optp = optend; 117 } else 118 fmatch = FMATCH_OPT_WRONG; 119 120 if (fmatch != FMATCH_OK) 121 break; 122 } 123 124 if (fmatch != FMATCH_OPT_WRONG) { 125 fmatch = FMATCH_WRONG; 126 127 switch (check_WSS) { 128 case OSF_WSS_PLAIN: 129 if (f->wss.val == 0 || ctx->window == f->wss.val) 130 fmatch = FMATCH_OK; 131 break; 132 case OSF_WSS_MSS: 133 /* 134 * Some smart modems decrease mangle MSS to 135 * SMART_MSS_2, so we check standard, decreased 136 * and the one provided in the fingerprint MSS 137 * values. 138 */ 139 #define SMART_MSS_1 1460 140 #define SMART_MSS_2 1448 141 if (ctx->window == f->wss.val * mss || 142 ctx->window == f->wss.val * SMART_MSS_1 || 143 ctx->window == f->wss.val * SMART_MSS_2) 144 fmatch = FMATCH_OK; 145 break; 146 case OSF_WSS_MTU: 147 if (ctx->window == f->wss.val * (mss + 40) || 148 ctx->window == f->wss.val * (SMART_MSS_1 + 40) || 149 ctx->window == f->wss.val * (SMART_MSS_2 + 40)) 150 fmatch = FMATCH_OK; 151 break; 152 case OSF_WSS_MODULO: 153 if ((ctx->window % f->wss.val) == 0) 154 fmatch = FMATCH_OK; 155 break; 156 } 157 } 158 159 if (fmatch != FMATCH_OK) 160 ctx->optp = optpinit; 161 162 return fmatch == FMATCH_OK; 163 } 164 165 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx, 166 const struct sk_buff *skb, 167 const struct iphdr *ip, 168 unsigned char *opts, 169 struct tcphdr *_tcph) 170 { 171 const struct tcphdr *tcp; 172 173 tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), _tcph); 174 if (!tcp) 175 return NULL; 176 177 if (!tcp->syn) 178 return NULL; 179 180 ctx->totlen = ntohs(ip->tot_len); 181 ctx->df = ntohs(ip->frag_off) & IP_DF; 182 ctx->window = ntohs(tcp->window); 183 184 if (tcp->doff * 4 > sizeof(struct tcphdr)) { 185 ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr); 186 187 ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) + 188 sizeof(struct tcphdr), ctx->optsize, opts); 189 if (!ctx->optp) 190 return NULL; 191 } 192 193 return tcp; 194 } 195 196 bool 197 nf_osf_match(const struct sk_buff *skb, u_int8_t family, 198 int hooknum, struct net_device *in, struct net_device *out, 199 const struct nf_osf_info *info, struct net *net, 200 const struct list_head *nf_osf_fingers) 201 { 202 const struct iphdr *ip = ip_hdr(skb); 203 const struct nf_osf_user_finger *f; 204 unsigned char opts[MAX_IPOPTLEN]; 205 const struct nf_osf_finger *kf; 206 int fcount = 0, ttl_check; 207 int fmatch = FMATCH_WRONG; 208 struct nf_osf_hdr_ctx ctx; 209 const struct tcphdr *tcp; 210 struct tcphdr _tcph; 211 212 memset(&ctx, 0, sizeof(ctx)); 213 214 tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph); 215 if (!tcp) 216 return false; 217 218 ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0; 219 220 list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { 221 222 f = &kf->finger; 223 224 if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre)) 225 continue; 226 227 if (!nf_osf_match_one(skb, f, ttl_check, &ctx)) 228 continue; 229 230 fmatch = FMATCH_OK; 231 232 fcount++; 233 234 if (info->flags & NF_OSF_LOG) 235 nf_log_packet(net, family, hooknum, skb, 236 in, out, NULL, 237 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n", 238 f->genre, f->version, f->subtype, 239 &ip->saddr, ntohs(tcp->source), 240 &ip->daddr, ntohs(tcp->dest), 241 f->ttl - ip->ttl); 242 243 if ((info->flags & NF_OSF_LOG) && 244 info->loglevel == NF_OSF_LOGLEVEL_FIRST) 245 break; 246 } 247 248 if (!fcount && (info->flags & NF_OSF_LOG)) 249 nf_log_packet(net, family, hooknum, skb, in, out, NULL, 250 "Remote OS is not known: %pI4:%u -> %pI4:%u\n", 251 &ip->saddr, ntohs(tcp->source), 252 &ip->daddr, ntohs(tcp->dest)); 253 254 if (fcount) 255 fmatch = FMATCH_OK; 256 257 return fmatch == FMATCH_OK; 258 } 259 EXPORT_SYMBOL_GPL(nf_osf_match); 260 261 bool nf_osf_find(const struct sk_buff *skb, 262 const struct list_head *nf_osf_fingers, 263 const int ttl_check, struct nf_osf_data *data) 264 { 265 const struct iphdr *ip = ip_hdr(skb); 266 const struct nf_osf_user_finger *f; 267 unsigned char opts[MAX_IPOPTLEN]; 268 const struct nf_osf_finger *kf; 269 struct nf_osf_hdr_ctx ctx; 270 const struct tcphdr *tcp; 271 struct tcphdr _tcph; 272 273 memset(&ctx, 0, sizeof(ctx)); 274 275 tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph); 276 if (!tcp) 277 return false; 278 279 list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { 280 f = &kf->finger; 281 if (!nf_osf_match_one(skb, f, ttl_check, &ctx)) 282 continue; 283 284 data->genre = f->genre; 285 data->version = f->version; 286 break; 287 } 288 289 return true; 290 } 291 EXPORT_SYMBOL_GPL(nf_osf_find); 292 293 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = { 294 [OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) }, 295 }; 296 297 static int nfnl_osf_add_callback(struct sk_buff *skb, 298 const struct nfnl_info *info, 299 const struct nlattr * const osf_attrs[]) 300 { 301 struct nf_osf_user_finger *f; 302 struct nf_osf_finger *kf = NULL, *sf; 303 int err = 0; 304 305 if (!capable(CAP_NET_ADMIN)) 306 return -EPERM; 307 308 if (!osf_attrs[OSF_ATTR_FINGER]) 309 return -EINVAL; 310 311 if (!(info->nlh->nlmsg_flags & NLM_F_CREATE)) 312 return -EINVAL; 313 314 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 315 316 kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL); 317 if (!kf) 318 return -ENOMEM; 319 320 memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger)); 321 322 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 323 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 324 continue; 325 326 kfree(kf); 327 kf = NULL; 328 329 if (info->nlh->nlmsg_flags & NLM_F_EXCL) 330 err = -EEXIST; 331 break; 332 } 333 334 /* 335 * We are protected by nfnl mutex. 336 */ 337 if (kf) 338 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]); 339 340 return err; 341 } 342 343 static int nfnl_osf_remove_callback(struct sk_buff *skb, 344 const struct nfnl_info *info, 345 const struct nlattr * const osf_attrs[]) 346 { 347 struct nf_osf_user_finger *f; 348 struct nf_osf_finger *sf; 349 int err = -ENOENT; 350 351 if (!capable(CAP_NET_ADMIN)) 352 return -EPERM; 353 354 if (!osf_attrs[OSF_ATTR_FINGER]) 355 return -EINVAL; 356 357 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 358 359 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 360 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 361 continue; 362 363 /* 364 * We are protected by nfnl mutex. 365 */ 366 list_del_rcu(&sf->finger_entry); 367 kfree_rcu(sf, rcu_head); 368 369 err = 0; 370 break; 371 } 372 373 return err; 374 } 375 376 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = { 377 [OSF_MSG_ADD] = { 378 .call = nfnl_osf_add_callback, 379 .type = NFNL_CB_MUTEX, 380 .attr_count = OSF_ATTR_MAX, 381 .policy = nfnl_osf_policy, 382 }, 383 [OSF_MSG_REMOVE] = { 384 .call = nfnl_osf_remove_callback, 385 .type = NFNL_CB_MUTEX, 386 .attr_count = OSF_ATTR_MAX, 387 .policy = nfnl_osf_policy, 388 }, 389 }; 390 391 static const struct nfnetlink_subsystem nfnl_osf_subsys = { 392 .name = "osf", 393 .subsys_id = NFNL_SUBSYS_OSF, 394 .cb_count = OSF_MSG_MAX, 395 .cb = nfnl_osf_callbacks, 396 }; 397 398 static int __init nfnl_osf_init(void) 399 { 400 int err = -EINVAL; 401 int i; 402 403 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) 404 INIT_LIST_HEAD(&nf_osf_fingers[i]); 405 406 err = nfnetlink_subsys_register(&nfnl_osf_subsys); 407 if (err < 0) { 408 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); 409 goto err_out_exit; 410 } 411 return 0; 412 413 err_out_exit: 414 return err; 415 } 416 417 static void __exit nfnl_osf_fini(void) 418 { 419 struct nf_osf_finger *f; 420 int i; 421 422 nfnetlink_subsys_unregister(&nfnl_osf_subsys); 423 424 rcu_read_lock(); 425 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) { 426 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) { 427 list_del_rcu(&f->finger_entry); 428 kfree_rcu(f, rcu_head); 429 } 430 } 431 rcu_read_unlock(); 432 433 rcu_barrier(); 434 } 435 436 module_init(nfnl_osf_init); 437 module_exit(nfnl_osf_fini); 438 439 MODULE_LICENSE("GPL"); 440