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 } 190 191 return tcp; 192 } 193 194 bool 195 nf_osf_match(const struct sk_buff *skb, u_int8_t family, 196 int hooknum, struct net_device *in, struct net_device *out, 197 const struct nf_osf_info *info, struct net *net, 198 const struct list_head *nf_osf_fingers) 199 { 200 const struct iphdr *ip = ip_hdr(skb); 201 const struct nf_osf_user_finger *f; 202 unsigned char opts[MAX_IPOPTLEN]; 203 const struct nf_osf_finger *kf; 204 int fcount = 0, ttl_check; 205 int fmatch = FMATCH_WRONG; 206 struct nf_osf_hdr_ctx ctx; 207 const struct tcphdr *tcp; 208 struct tcphdr _tcph; 209 210 memset(&ctx, 0, sizeof(ctx)); 211 212 tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph); 213 if (!tcp) 214 return false; 215 216 ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : 0; 217 218 list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { 219 220 f = &kf->finger; 221 222 if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre)) 223 continue; 224 225 if (!nf_osf_match_one(skb, f, ttl_check, &ctx)) 226 continue; 227 228 fmatch = FMATCH_OK; 229 230 fcount++; 231 232 if (info->flags & NF_OSF_LOG) 233 nf_log_packet(net, family, hooknum, skb, 234 in, out, NULL, 235 "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n", 236 f->genre, f->version, f->subtype, 237 &ip->saddr, ntohs(tcp->source), 238 &ip->daddr, ntohs(tcp->dest), 239 f->ttl - ip->ttl); 240 241 if ((info->flags & NF_OSF_LOG) && 242 info->loglevel == NF_OSF_LOGLEVEL_FIRST) 243 break; 244 } 245 246 if (!fcount && (info->flags & NF_OSF_LOG)) 247 nf_log_packet(net, family, hooknum, skb, in, out, NULL, 248 "Remote OS is not known: %pI4:%u -> %pI4:%u\n", 249 &ip->saddr, ntohs(tcp->source), 250 &ip->daddr, ntohs(tcp->dest)); 251 252 if (fcount) 253 fmatch = FMATCH_OK; 254 255 return fmatch == FMATCH_OK; 256 } 257 EXPORT_SYMBOL_GPL(nf_osf_match); 258 259 bool nf_osf_find(const struct sk_buff *skb, 260 const struct list_head *nf_osf_fingers, 261 const int ttl_check, struct nf_osf_data *data) 262 { 263 const struct iphdr *ip = ip_hdr(skb); 264 const struct nf_osf_user_finger *f; 265 unsigned char opts[MAX_IPOPTLEN]; 266 const struct nf_osf_finger *kf; 267 struct nf_osf_hdr_ctx ctx; 268 const struct tcphdr *tcp; 269 struct tcphdr _tcph; 270 271 memset(&ctx, 0, sizeof(ctx)); 272 273 tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph); 274 if (!tcp) 275 return false; 276 277 list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) { 278 f = &kf->finger; 279 if (!nf_osf_match_one(skb, f, ttl_check, &ctx)) 280 continue; 281 282 data->genre = f->genre; 283 data->version = f->version; 284 break; 285 } 286 287 return true; 288 } 289 EXPORT_SYMBOL_GPL(nf_osf_find); 290 291 static const struct nla_policy nfnl_osf_policy[OSF_ATTR_MAX + 1] = { 292 [OSF_ATTR_FINGER] = { .len = sizeof(struct nf_osf_user_finger) }, 293 }; 294 295 static int nfnl_osf_add_callback(struct net *net, struct sock *ctnl, 296 struct sk_buff *skb, const struct nlmsghdr *nlh, 297 const struct nlattr * const osf_attrs[], 298 struct netlink_ext_ack *extack) 299 { 300 struct nf_osf_user_finger *f; 301 struct nf_osf_finger *kf = NULL, *sf; 302 int err = 0; 303 304 if (!capable(CAP_NET_ADMIN)) 305 return -EPERM; 306 307 if (!osf_attrs[OSF_ATTR_FINGER]) 308 return -EINVAL; 309 310 if (!(nlh->nlmsg_flags & NLM_F_CREATE)) 311 return -EINVAL; 312 313 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 314 315 kf = kmalloc(sizeof(struct nf_osf_finger), GFP_KERNEL); 316 if (!kf) 317 return -ENOMEM; 318 319 memcpy(&kf->finger, f, sizeof(struct nf_osf_user_finger)); 320 321 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 322 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 323 continue; 324 325 kfree(kf); 326 kf = NULL; 327 328 if (nlh->nlmsg_flags & NLM_F_EXCL) 329 err = -EEXIST; 330 break; 331 } 332 333 /* 334 * We are protected by nfnl mutex. 335 */ 336 if (kf) 337 list_add_tail_rcu(&kf->finger_entry, &nf_osf_fingers[!!f->df]); 338 339 return err; 340 } 341 342 static int nfnl_osf_remove_callback(struct net *net, struct sock *ctnl, 343 struct sk_buff *skb, 344 const struct nlmsghdr *nlh, 345 const struct nlattr * const osf_attrs[], 346 struct netlink_ext_ack *extack) 347 { 348 struct nf_osf_user_finger *f; 349 struct nf_osf_finger *sf; 350 int err = -ENOENT; 351 352 if (!capable(CAP_NET_ADMIN)) 353 return -EPERM; 354 355 if (!osf_attrs[OSF_ATTR_FINGER]) 356 return -EINVAL; 357 358 f = nla_data(osf_attrs[OSF_ATTR_FINGER]); 359 360 list_for_each_entry(sf, &nf_osf_fingers[!!f->df], finger_entry) { 361 if (memcmp(&sf->finger, f, sizeof(struct nf_osf_user_finger))) 362 continue; 363 364 /* 365 * We are protected by nfnl mutex. 366 */ 367 list_del_rcu(&sf->finger_entry); 368 kfree_rcu(sf, rcu_head); 369 370 err = 0; 371 break; 372 } 373 374 return err; 375 } 376 377 static const struct nfnl_callback nfnl_osf_callbacks[OSF_MSG_MAX] = { 378 [OSF_MSG_ADD] = { 379 .call = nfnl_osf_add_callback, 380 .attr_count = OSF_ATTR_MAX, 381 .policy = nfnl_osf_policy, 382 }, 383 [OSF_MSG_REMOVE] = { 384 .call = nfnl_osf_remove_callback, 385 .attr_count = OSF_ATTR_MAX, 386 .policy = nfnl_osf_policy, 387 }, 388 }; 389 390 static const struct nfnetlink_subsystem nfnl_osf_subsys = { 391 .name = "osf", 392 .subsys_id = NFNL_SUBSYS_OSF, 393 .cb_count = OSF_MSG_MAX, 394 .cb = nfnl_osf_callbacks, 395 }; 396 397 static int __init nfnl_osf_init(void) 398 { 399 int err = -EINVAL; 400 int i; 401 402 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) 403 INIT_LIST_HEAD(&nf_osf_fingers[i]); 404 405 err = nfnetlink_subsys_register(&nfnl_osf_subsys); 406 if (err < 0) { 407 pr_err("Failed to register OSF nsfnetlink helper (%d)\n", err); 408 goto err_out_exit; 409 } 410 return 0; 411 412 err_out_exit: 413 return err; 414 } 415 416 static void __exit nfnl_osf_fini(void) 417 { 418 struct nf_osf_finger *f; 419 int i; 420 421 nfnetlink_subsys_unregister(&nfnl_osf_subsys); 422 423 rcu_read_lock(); 424 for (i = 0; i < ARRAY_SIZE(nf_osf_fingers); ++i) { 425 list_for_each_entry_rcu(f, &nf_osf_fingers[i], finger_entry) { 426 list_del_rcu(&f->finger_entry); 427 kfree_rcu(f, rcu_head); 428 } 429 } 430 rcu_read_unlock(); 431 432 rcu_barrier(); 433 } 434 435 module_init(nfnl_osf_init); 436 module_exit(nfnl_osf_fini); 437 438 MODULE_LICENSE("GPL"); 439