1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Helper handling for netfilter. */ 3 4 /* (C) 1999-2001 Paul `Rusty' Russell 5 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org> 6 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org> 7 * (C) 2006-2012 Patrick McHardy <kaber@trash.net> 8 */ 9 10 #include <linux/types.h> 11 #include <linux/netfilter.h> 12 #include <linux/module.h> 13 #include <linux/skbuff.h> 14 #include <linux/vmalloc.h> 15 #include <linux/stddef.h> 16 #include <linux/random.h> 17 #include <linux/err.h> 18 #include <linux/kernel.h> 19 #include <linux/netdevice.h> 20 #include <linux/rculist.h> 21 #include <linux/rtnetlink.h> 22 23 #include <net/netfilter/nf_conntrack.h> 24 #include <net/netfilter/nf_conntrack_core.h> 25 #include <net/netfilter/nf_conntrack_ecache.h> 26 #include <net/netfilter/nf_conntrack_extend.h> 27 #include <net/netfilter/nf_conntrack_helper.h> 28 #include <net/netfilter/nf_conntrack_l4proto.h> 29 #include <net/netfilter/nf_log.h> 30 31 static DEFINE_MUTEX(nf_ct_helper_mutex); 32 struct hlist_head *nf_ct_helper_hash __read_mostly; 33 EXPORT_SYMBOL_GPL(nf_ct_helper_hash); 34 unsigned int nf_ct_helper_hsize __read_mostly; 35 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize); 36 static unsigned int nf_ct_helper_count __read_mostly; 37 38 static bool nf_ct_auto_assign_helper __read_mostly = false; 39 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644); 40 MODULE_PARM_DESC(nf_conntrack_helper, 41 "Enable automatic conntrack helper assignment (default 0)"); 42 43 static DEFINE_MUTEX(nf_ct_nat_helpers_mutex); 44 static struct list_head nf_ct_nat_helpers __read_mostly; 45 46 /* Stupid hash, but collision free for the default registrations of the 47 * helpers currently in the kernel. */ 48 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple) 49 { 50 return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^ 51 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize; 52 } 53 54 static struct nf_conntrack_helper * 55 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple) 56 { 57 struct nf_conntrack_helper *helper; 58 struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) }; 59 unsigned int h; 60 61 if (!nf_ct_helper_count) 62 return NULL; 63 64 h = helper_hash(tuple); 65 hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) { 66 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask)) 67 return helper; 68 } 69 return NULL; 70 } 71 72 struct nf_conntrack_helper * 73 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum) 74 { 75 struct nf_conntrack_helper *h; 76 unsigned int i; 77 78 for (i = 0; i < nf_ct_helper_hsize; i++) { 79 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) { 80 if (strcmp(h->name, name)) 81 continue; 82 83 if (h->tuple.src.l3num != NFPROTO_UNSPEC && 84 h->tuple.src.l3num != l3num) 85 continue; 86 87 if (h->tuple.dst.protonum == protonum) 88 return h; 89 } 90 } 91 return NULL; 92 } 93 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find); 94 95 struct nf_conntrack_helper * 96 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum) 97 { 98 struct nf_conntrack_helper *h; 99 100 rcu_read_lock(); 101 102 h = __nf_conntrack_helper_find(name, l3num, protonum); 103 #ifdef CONFIG_MODULES 104 if (h == NULL) { 105 rcu_read_unlock(); 106 if (request_module("nfct-helper-%s", name) == 0) { 107 rcu_read_lock(); 108 h = __nf_conntrack_helper_find(name, l3num, protonum); 109 } else { 110 return h; 111 } 112 } 113 #endif 114 if (h != NULL && !try_module_get(h->me)) 115 h = NULL; 116 if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) { 117 module_put(h->me); 118 h = NULL; 119 } 120 121 rcu_read_unlock(); 122 123 return h; 124 } 125 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get); 126 127 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper) 128 { 129 refcount_dec(&helper->refcnt); 130 module_put(helper->me); 131 } 132 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put); 133 134 static struct nf_conntrack_nat_helper * 135 nf_conntrack_nat_helper_find(const char *mod_name) 136 { 137 struct nf_conntrack_nat_helper *cur; 138 bool found = false; 139 140 list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) { 141 if (!strcmp(cur->mod_name, mod_name)) { 142 found = true; 143 break; 144 } 145 } 146 return found ? cur : NULL; 147 } 148 149 int 150 nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum) 151 { 152 struct nf_conntrack_helper *h; 153 struct nf_conntrack_nat_helper *nat; 154 char mod_name[NF_CT_HELPER_NAME_LEN]; 155 int ret = 0; 156 157 rcu_read_lock(); 158 h = __nf_conntrack_helper_find(name, l3num, protonum); 159 if (!h) { 160 rcu_read_unlock(); 161 return -ENOENT; 162 } 163 164 nat = nf_conntrack_nat_helper_find(h->nat_mod_name); 165 if (!nat) { 166 snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name); 167 rcu_read_unlock(); 168 request_module(mod_name); 169 170 rcu_read_lock(); 171 nat = nf_conntrack_nat_helper_find(mod_name); 172 if (!nat) { 173 rcu_read_unlock(); 174 return -ENOENT; 175 } 176 } 177 178 if (!try_module_get(nat->module)) 179 ret = -ENOENT; 180 181 rcu_read_unlock(); 182 return ret; 183 } 184 EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get); 185 186 void nf_nat_helper_put(struct nf_conntrack_helper *helper) 187 { 188 struct nf_conntrack_nat_helper *nat; 189 190 nat = nf_conntrack_nat_helper_find(helper->nat_mod_name); 191 if (WARN_ON_ONCE(!nat)) 192 return; 193 194 module_put(nat->module); 195 } 196 EXPORT_SYMBOL_GPL(nf_nat_helper_put); 197 198 struct nf_conn_help * 199 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp) 200 { 201 struct nf_conn_help *help; 202 203 help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp); 204 if (help) 205 INIT_HLIST_HEAD(&help->expectations); 206 else 207 pr_debug("failed to add helper extension area"); 208 return help; 209 } 210 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add); 211 212 static struct nf_conntrack_helper * 213 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net) 214 { 215 if (!net->ct.sysctl_auto_assign_helper) { 216 if (net->ct.auto_assign_helper_warned) 217 return NULL; 218 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple)) 219 return NULL; 220 pr_info("nf_conntrack: default automatic helper assignment " 221 "has been turned off for security reasons and CT-based " 222 " firewall rule not found. Use the iptables CT target " 223 "to attach helpers instead.\n"); 224 net->ct.auto_assign_helper_warned = 1; 225 return NULL; 226 } 227 228 return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); 229 } 230 231 232 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, 233 gfp_t flags) 234 { 235 struct nf_conntrack_helper *helper = NULL; 236 struct nf_conn_help *help; 237 struct net *net = nf_ct_net(ct); 238 239 /* We already got a helper explicitly attached. The function 240 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking 241 * the helper up again. Since now the user is in full control of 242 * making consistent helper configurations, skip this automatic 243 * re-lookup, otherwise we'll lose the helper. 244 */ 245 if (test_bit(IPS_HELPER_BIT, &ct->status)) 246 return 0; 247 248 if (tmpl != NULL) { 249 help = nfct_help(tmpl); 250 if (help != NULL) { 251 helper = help->helper; 252 set_bit(IPS_HELPER_BIT, &ct->status); 253 } 254 } 255 256 help = nfct_help(ct); 257 258 if (helper == NULL) { 259 helper = nf_ct_lookup_helper(ct, net); 260 if (helper == NULL) { 261 if (help) 262 RCU_INIT_POINTER(help->helper, NULL); 263 return 0; 264 } 265 } 266 267 if (help == NULL) { 268 help = nf_ct_helper_ext_add(ct, flags); 269 if (help == NULL) 270 return -ENOMEM; 271 } else { 272 /* We only allow helper re-assignment of the same sort since 273 * we cannot reallocate the helper extension area. 274 */ 275 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper); 276 277 if (tmp && tmp->help != helper->help) { 278 RCU_INIT_POINTER(help->helper, NULL); 279 return 0; 280 } 281 } 282 283 rcu_assign_pointer(help->helper, helper); 284 285 return 0; 286 } 287 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper); 288 289 /* appropriate ct lock protecting must be taken by caller */ 290 static int unhelp(struct nf_conn *ct, void *me) 291 { 292 struct nf_conn_help *help = nfct_help(ct); 293 294 if (help && rcu_dereference_raw(help->helper) == me) { 295 nf_conntrack_event(IPCT_HELPER, ct); 296 RCU_INIT_POINTER(help->helper, NULL); 297 } 298 299 /* We are not intended to delete this conntrack. */ 300 return 0; 301 } 302 303 void nf_ct_helper_destroy(struct nf_conn *ct) 304 { 305 struct nf_conn_help *help = nfct_help(ct); 306 struct nf_conntrack_helper *helper; 307 308 if (help) { 309 rcu_read_lock(); 310 helper = rcu_dereference(help->helper); 311 if (helper && helper->destroy) 312 helper->destroy(ct); 313 rcu_read_unlock(); 314 } 315 } 316 317 static LIST_HEAD(nf_ct_helper_expectfn_list); 318 319 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n) 320 { 321 spin_lock_bh(&nf_conntrack_expect_lock); 322 list_add_rcu(&n->head, &nf_ct_helper_expectfn_list); 323 spin_unlock_bh(&nf_conntrack_expect_lock); 324 } 325 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register); 326 327 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n) 328 { 329 spin_lock_bh(&nf_conntrack_expect_lock); 330 list_del_rcu(&n->head); 331 spin_unlock_bh(&nf_conntrack_expect_lock); 332 } 333 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister); 334 335 /* Caller should hold the rcu lock */ 336 struct nf_ct_helper_expectfn * 337 nf_ct_helper_expectfn_find_by_name(const char *name) 338 { 339 struct nf_ct_helper_expectfn *cur; 340 bool found = false; 341 342 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 343 if (!strcmp(cur->name, name)) { 344 found = true; 345 break; 346 } 347 } 348 return found ? cur : NULL; 349 } 350 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name); 351 352 /* Caller should hold the rcu lock */ 353 struct nf_ct_helper_expectfn * 354 nf_ct_helper_expectfn_find_by_symbol(const void *symbol) 355 { 356 struct nf_ct_helper_expectfn *cur; 357 bool found = false; 358 359 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 360 if (cur->expectfn == symbol) { 361 found = true; 362 break; 363 } 364 } 365 return found ? cur : NULL; 366 } 367 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol); 368 369 __printf(3, 4) 370 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct, 371 const char *fmt, ...) 372 { 373 const struct nf_conn_help *help; 374 const struct nf_conntrack_helper *helper; 375 struct va_format vaf; 376 va_list args; 377 378 va_start(args, fmt); 379 380 vaf.fmt = fmt; 381 vaf.va = &args; 382 383 /* Called from the helper function, this call never fails */ 384 help = nfct_help(ct); 385 386 /* rcu_read_lock()ed by nf_hook_thresh */ 387 helper = rcu_dereference(help->helper); 388 389 nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL, 390 "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf); 391 392 va_end(args); 393 } 394 EXPORT_SYMBOL_GPL(nf_ct_helper_log); 395 396 int nf_conntrack_helper_register(struct nf_conntrack_helper *me) 397 { 398 struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) }; 399 unsigned int h = helper_hash(&me->tuple); 400 struct nf_conntrack_helper *cur; 401 int ret = 0, i; 402 403 BUG_ON(me->expect_policy == NULL); 404 BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES); 405 BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1); 406 407 if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT) 408 return -EINVAL; 409 410 mutex_lock(&nf_ct_helper_mutex); 411 for (i = 0; i < nf_ct_helper_hsize; i++) { 412 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) { 413 if (!strcmp(cur->name, me->name) && 414 (cur->tuple.src.l3num == NFPROTO_UNSPEC || 415 cur->tuple.src.l3num == me->tuple.src.l3num) && 416 cur->tuple.dst.protonum == me->tuple.dst.protonum) { 417 ret = -EEXIST; 418 goto out; 419 } 420 } 421 } 422 423 /* avoid unpredictable behaviour for auto_assign_helper */ 424 if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) { 425 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) { 426 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, 427 &mask)) { 428 ret = -EEXIST; 429 goto out; 430 } 431 } 432 } 433 refcount_set(&me->refcnt, 1); 434 hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]); 435 nf_ct_helper_count++; 436 out: 437 mutex_unlock(&nf_ct_helper_mutex); 438 return ret; 439 } 440 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register); 441 442 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data) 443 { 444 struct nf_conn_help *help = nfct_help(exp->master); 445 const struct nf_conntrack_helper *me = data; 446 const struct nf_conntrack_helper *this; 447 448 if (exp->helper == me) 449 return true; 450 451 this = rcu_dereference_protected(help->helper, 452 lockdep_is_held(&nf_conntrack_expect_lock)); 453 return this == me; 454 } 455 456 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me) 457 { 458 mutex_lock(&nf_ct_helper_mutex); 459 hlist_del_rcu(&me->hnode); 460 nf_ct_helper_count--; 461 mutex_unlock(&nf_ct_helper_mutex); 462 463 /* Make sure every nothing is still using the helper unless its a 464 * connection in the hash. 465 */ 466 synchronize_rcu(); 467 468 nf_ct_expect_iterate_destroy(expect_iter_me, NULL); 469 nf_ct_iterate_destroy(unhelp, me); 470 471 /* Maybe someone has gotten the helper already when unhelp above. 472 * So need to wait it. 473 */ 474 synchronize_rcu(); 475 } 476 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister); 477 478 void nf_ct_helper_init(struct nf_conntrack_helper *helper, 479 u16 l3num, u16 protonum, const char *name, 480 u16 default_port, u16 spec_port, u32 id, 481 const struct nf_conntrack_expect_policy *exp_pol, 482 u32 expect_class_max, 483 int (*help)(struct sk_buff *skb, unsigned int protoff, 484 struct nf_conn *ct, 485 enum ip_conntrack_info ctinfo), 486 int (*from_nlattr)(struct nlattr *attr, 487 struct nf_conn *ct), 488 struct module *module) 489 { 490 helper->tuple.src.l3num = l3num; 491 helper->tuple.dst.protonum = protonum; 492 helper->tuple.src.u.all = htons(spec_port); 493 helper->expect_policy = exp_pol; 494 helper->expect_class_max = expect_class_max; 495 helper->help = help; 496 helper->from_nlattr = from_nlattr; 497 helper->me = module; 498 snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name), 499 NF_NAT_HELPER_PREFIX "%s", name); 500 501 if (spec_port == default_port) 502 snprintf(helper->name, sizeof(helper->name), "%s", name); 503 else 504 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id); 505 } 506 EXPORT_SYMBOL_GPL(nf_ct_helper_init); 507 508 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper, 509 unsigned int n) 510 { 511 unsigned int i; 512 int err = 0; 513 514 for (i = 0; i < n; i++) { 515 err = nf_conntrack_helper_register(&helper[i]); 516 if (err < 0) 517 goto err; 518 } 519 520 return err; 521 err: 522 if (i > 0) 523 nf_conntrack_helpers_unregister(helper, i); 524 return err; 525 } 526 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register); 527 528 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper, 529 unsigned int n) 530 { 531 while (n-- > 0) 532 nf_conntrack_helper_unregister(&helper[n]); 533 } 534 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister); 535 536 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat) 537 { 538 mutex_lock(&nf_ct_nat_helpers_mutex); 539 list_add_rcu(&nat->list, &nf_ct_nat_helpers); 540 mutex_unlock(&nf_ct_nat_helpers_mutex); 541 } 542 EXPORT_SYMBOL_GPL(nf_nat_helper_register); 543 544 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat) 545 { 546 mutex_lock(&nf_ct_nat_helpers_mutex); 547 list_del_rcu(&nat->list); 548 mutex_unlock(&nf_ct_nat_helpers_mutex); 549 } 550 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister); 551 552 static const struct nf_ct_ext_type helper_extend = { 553 .len = sizeof(struct nf_conn_help), 554 .align = __alignof__(struct nf_conn_help), 555 .id = NF_CT_EXT_HELPER, 556 }; 557 558 void nf_conntrack_helper_pernet_init(struct net *net) 559 { 560 net->ct.auto_assign_helper_warned = false; 561 net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper; 562 } 563 564 int nf_conntrack_helper_init(void) 565 { 566 int ret; 567 nf_ct_helper_hsize = 1; /* gets rounded up to use one page */ 568 nf_ct_helper_hash = 569 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0); 570 if (!nf_ct_helper_hash) 571 return -ENOMEM; 572 573 ret = nf_ct_extend_register(&helper_extend); 574 if (ret < 0) { 575 pr_err("nf_ct_helper: Unable to register helper extension.\n"); 576 goto out_extend; 577 } 578 579 INIT_LIST_HEAD(&nf_ct_nat_helpers); 580 return 0; 581 out_extend: 582 kvfree(nf_ct_helper_hash); 583 return ret; 584 } 585 586 void nf_conntrack_helper_fini(void) 587 { 588 nf_ct_extend_unregister(&helper_extend); 589 kvfree(nf_ct_helper_hash); 590 } 591