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 bool found = false; 273 274 memset(&ctx, 0, sizeof(ctx)); 275 276 tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph); 277 if (!tcp) 278 return false; 279 280 list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { 281 f = &kf->finger; 282 if (!nf_osf_match_one(skb, f, ttl_check, &ctx)) 283 continue; 284 285 data->genre = f->genre; 286 data->version = f->version; 287 found = true; 288 break; 289 } 290 291 return found; 292 } 293 EXPORT_SYMBOL_GPL(nf_osf_find); 294 295 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = { 296 [OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) }, 297 }; 298 299 static int nfnl_osf_add_callback(struct sk_buff *skb, 300 const struct nfnl_info *info, 301 const struct nlattr * const osf_attrs[]) 302 { 303 struct nf_osf_user_finger *f; 304 struct nf_osf_finger *kf = NULL, *sf; 305 int err = 0; 306 307 if (!capable(CAP_NET_ADMIN)) 308 return -EPERM; 309 310 if (!osf_attrs[OSF_ATTR_FINGER]) 311 return -EINVAL; 312 313 if (!(info->nlh->nlmsg_flags & NLM_F_CREATE)) 314 return -EINVAL; 315 316 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 317 318 kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL); 319 if (!kf) 320 return -ENOMEM; 321 322 memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger)); 323 324 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 325 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 326 continue; 327 328 kfree(kf); 329 kf = NULL; 330 331 if (info->nlh->nlmsg_flags & NLM_F_EXCL) 332 err = -EEXIST; 333 break; 334 } 335 336 /* 337 * We are protected by nfnl mutex. 338 */ 339 if (kf) 340 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]); 341 342 return err; 343 } 344 345 static int nfnl_osf_remove_callback(struct sk_buff *skb, 346 const struct nfnl_info *info, 347 const struct nlattr * const osf_attrs[]) 348 { 349 struct nf_osf_user_finger *f; 350 struct nf_osf_finger *sf; 351 int err = -ENOENT; 352 353 if (!capable(CAP_NET_ADMIN)) 354 return -EPERM; 355 356 if (!osf_attrs[OSF_ATTR_FINGER]) 357 return -EINVAL; 358 359 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 360 361 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 362 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 363 continue; 364 365 /* 366 * We are protected by nfnl mutex. 367 */ 368 list_del_rcu(&sf->finger_entry); 369 kfree_rcu(sf, rcu_head); 370 371 err = 0; 372 break; 373 } 374 375 return err; 376 } 377 378 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = { 379 [OSF_MSG_ADD] = { 380 .call = nfnl_osf_add_callback, 381 .type = NFNL_CB_MUTEX, 382 .attr_count = OSF_ATTR_MAX, 383 .policy = nfnl_osf_policy, 384 }, 385 [OSF_MSG_REMOVE] = { 386 .call = nfnl_osf_remove_callback, 387 .type = NFNL_CB_MUTEX, 388 .attr_count = OSF_ATTR_MAX, 389 .policy = nfnl_osf_policy, 390 }, 391 }; 392 393 static const struct nfnetlink_subsystem nfnl_osf_subsys = { 394 .name = "osf", 395 .subsys_id = NFNL_SUBSYS_OSF, 396 .cb_count = OSF_MSG_MAX, 397 .cb = nfnl_osf_callbacks, 398 }; 399 400 static int __init nfnl_osf_init(void) 401 { 402 int err = -EINVAL; 403 int i; 404 405 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) 406 INIT_LIST_HEAD(&nf_osf_fingers[i]); 407 408 err = nfnetlink_subsys_register(&nfnl_osf_subsys); 409 if (err < 0) { 410 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); 411 goto err_out_exit; 412 } 413 return 0; 414 415 err_out_exit: 416 return err; 417 } 418 419 static void __exit nfnl_osf_fini(void) 420 { 421 struct nf_osf_finger *f; 422 int i; 423 424 nfnetlink_subsys_unregister(&nfnl_osf_subsys); 425 426 rcu_read_lock(); 427 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) { 428 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) { 429 list_del_rcu(&f->finger_entry); 430 kfree_rcu(f, rcu_head); 431 } 432 } 433 rcu_read_unlock(); 434 435 rcu_barrier(); 436 } 437 438 module_init(nfnl_osf_init); 439 module_exit(nfnl_osf_fini); 440 441 MODULE_LICENSE("GPL"); 442