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_l4proto.h> 25 #include <net/netfilter/nf_conntrack_helper.h> 26 #include <net/netfilter/nf_conntrack_core.h> 27 #include <net/netfilter/nf_conntrack_extend.h> 28 #include <net/netfilter/nf_log.h> 29 30 static DEFINE_MUTEX(nf_ct_helper_mutex); 31 struct hlist_head *nf_ct_helper_hash __read_mostly; 32 EXPORT_SYMBOL_GPL(nf_ct_helper_hash); 33 unsigned int nf_ct_helper_hsize __read_mostly; 34 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize); 35 static unsigned int nf_ct_helper_count __read_mostly; 36 37 static bool nf_ct_auto_assign_helper __read_mostly = false; 38 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644); 39 MODULE_PARM_DESC(nf_conntrack_helper, 40 "Enable automatic conntrack helper assignment (default 0)"); 41 42 static DEFINE_MUTEX(nf_ct_nat_helpers_mutex); 43 static struct list_head nf_ct_nat_helpers __read_mostly; 44 45 /* Stupid hash, but collision free for the default registrations of the 46 * helpers currently in the kernel. */ 47 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple) 48 { 49 return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^ 50 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize; 51 } 52 53 static struct nf_conntrack_helper * 54 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple) 55 { 56 struct nf_conntrack_helper *helper; 57 struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) }; 58 unsigned int h; 59 60 if (!nf_ct_helper_count) 61 return NULL; 62 63 h = helper_hash(tuple); 64 hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) { 65 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask)) 66 return helper; 67 } 68 return NULL; 69 } 70 71 struct nf_conntrack_helper * 72 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum) 73 { 74 struct nf_conntrack_helper *h; 75 unsigned int i; 76 77 for (i = 0; i < nf_ct_helper_hsize; i++) { 78 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) { 79 if (strcmp(h->name, name)) 80 continue; 81 82 if (h->tuple.src.l3num != NFPROTO_UNSPEC && 83 h->tuple.src.l3num != l3num) 84 continue; 85 86 if (h->tuple.dst.protonum == protonum) 87 return h; 88 } 89 } 90 return NULL; 91 } 92 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find); 93 94 struct nf_conntrack_helper * 95 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum) 96 { 97 struct nf_conntrack_helper *h; 98 99 rcu_read_lock(); 100 101 h = __nf_conntrack_helper_find(name, l3num, protonum); 102 #ifdef CONFIG_MODULES 103 if (h == NULL) { 104 rcu_read_unlock(); 105 if (request_module("nfct-helper-%s", name) == 0) { 106 rcu_read_lock(); 107 h = __nf_conntrack_helper_find(name, l3num, protonum); 108 } else { 109 return h; 110 } 111 } 112 #endif 113 if (h != NULL && !try_module_get(h->me)) 114 h = NULL; 115 if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) { 116 module_put(h->me); 117 h = NULL; 118 } 119 120 rcu_read_unlock(); 121 122 return h; 123 } 124 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get); 125 126 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper) 127 { 128 refcount_dec(&helper->refcnt); 129 module_put(helper->me); 130 } 131 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put); 132 133 static struct nf_conntrack_nat_helper * 134 nf_conntrack_nat_helper_find(const char *mod_name) 135 { 136 struct nf_conntrack_nat_helper *cur; 137 bool found = false; 138 139 list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) { 140 if (!strcmp(cur->mod_name, mod_name)) { 141 found = true; 142 break; 143 } 144 } 145 return found ? cur : NULL; 146 } 147 148 int 149 nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum) 150 { 151 struct nf_conntrack_helper *h; 152 struct nf_conntrack_nat_helper *nat; 153 char mod_name[NF_CT_HELPER_NAME_LEN]; 154 int ret = 0; 155 156 rcu_read_lock(); 157 h = __nf_conntrack_helper_find(name, l3num, protonum); 158 if (!h) { 159 rcu_read_unlock(); 160 return -ENOENT; 161 } 162 163 nat = nf_conntrack_nat_helper_find(h->nat_mod_name); 164 if (!nat) { 165 snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name); 166 rcu_read_unlock(); 167 request_module(mod_name); 168 169 rcu_read_lock(); 170 nat = nf_conntrack_nat_helper_find(mod_name); 171 if (!nat) { 172 rcu_read_unlock(); 173 return -ENOENT; 174 } 175 } 176 177 if (!try_module_get(nat->module)) 178 ret = -ENOENT; 179 180 rcu_read_unlock(); 181 return ret; 182 } 183 EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get); 184 185 void nf_nat_helper_put(struct nf_conntrack_helper *helper) 186 { 187 struct nf_conntrack_nat_helper *nat; 188 189 nat = nf_conntrack_nat_helper_find(helper->nat_mod_name); 190 if (WARN_ON_ONCE(!nat)) 191 return; 192 193 module_put(nat->module); 194 } 195 EXPORT_SYMBOL_GPL(nf_nat_helper_put); 196 197 struct nf_conn_help * 198 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp) 199 { 200 struct nf_conn_help *help; 201 202 help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp); 203 if (help) 204 INIT_HLIST_HEAD(&help->expectations); 205 else 206 pr_debug("failed to add helper extension area"); 207 return help; 208 } 209 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add); 210 211 static struct nf_conntrack_helper * 212 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net) 213 { 214 if (!net->ct.sysctl_auto_assign_helper) { 215 if (net->ct.auto_assign_helper_warned) 216 return NULL; 217 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple)) 218 return NULL; 219 pr_info("nf_conntrack: default automatic helper assignment " 220 "has been turned off for security reasons and CT-based " 221 " firewall rule not found. Use the iptables CT target " 222 "to attach helpers instead.\n"); 223 net->ct.auto_assign_helper_warned = 1; 224 return NULL; 225 } 226 227 return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); 228 } 229 230 231 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, 232 gfp_t flags) 233 { 234 struct nf_conntrack_helper *helper = NULL; 235 struct nf_conn_help *help; 236 struct net *net = nf_ct_net(ct); 237 238 /* We already got a helper explicitly attached. The function 239 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking 240 * the helper up again. Since now the user is in full control of 241 * making consistent helper configurations, skip this automatic 242 * re-lookup, otherwise we'll lose the helper. 243 */ 244 if (test_bit(IPS_HELPER_BIT, &ct->status)) 245 return 0; 246 247 if (tmpl != NULL) { 248 help = nfct_help(tmpl); 249 if (help != NULL) { 250 helper = help->helper; 251 set_bit(IPS_HELPER_BIT, &ct->status); 252 } 253 } 254 255 help = nfct_help(ct); 256 257 if (helper == NULL) { 258 helper = nf_ct_lookup_helper(ct, net); 259 if (helper == NULL) { 260 if (help) 261 RCU_INIT_POINTER(help->helper, NULL); 262 return 0; 263 } 264 } 265 266 if (help == NULL) { 267 help = nf_ct_helper_ext_add(ct, flags); 268 if (help == NULL) 269 return -ENOMEM; 270 } else { 271 /* We only allow helper re-assignment of the same sort since 272 * we cannot reallocate the helper extension area. 273 */ 274 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper); 275 276 if (tmp && tmp->help != helper->help) { 277 RCU_INIT_POINTER(help->helper, NULL); 278 return 0; 279 } 280 } 281 282 rcu_assign_pointer(help->helper, helper); 283 284 return 0; 285 } 286 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper); 287 288 /* appropriate ct lock protecting must be taken by caller */ 289 static int unhelp(struct nf_conn *ct, void *me) 290 { 291 struct nf_conn_help *help = nfct_help(ct); 292 293 if (help && rcu_dereference_raw(help->helper) == me) { 294 nf_conntrack_event(IPCT_HELPER, ct); 295 RCU_INIT_POINTER(help->helper, NULL); 296 } 297 298 /* We are not intended to delete this conntrack. */ 299 return 0; 300 } 301 302 void nf_ct_helper_destroy(struct nf_conn *ct) 303 { 304 struct nf_conn_help *help = nfct_help(ct); 305 struct nf_conntrack_helper *helper; 306 307 if (help) { 308 rcu_read_lock(); 309 helper = rcu_dereference(help->helper); 310 if (helper && helper->destroy) 311 helper->destroy(ct); 312 rcu_read_unlock(); 313 } 314 } 315 316 static LIST_HEAD(nf_ct_helper_expectfn_list); 317 318 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n) 319 { 320 spin_lock_bh(&nf_conntrack_expect_lock); 321 list_add_rcu(&n->head, &nf_ct_helper_expectfn_list); 322 spin_unlock_bh(&nf_conntrack_expect_lock); 323 } 324 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register); 325 326 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n) 327 { 328 spin_lock_bh(&nf_conntrack_expect_lock); 329 list_del_rcu(&n->head); 330 spin_unlock_bh(&nf_conntrack_expect_lock); 331 } 332 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister); 333 334 /* Caller should hold the rcu lock */ 335 struct nf_ct_helper_expectfn * 336 nf_ct_helper_expectfn_find_by_name(const char *name) 337 { 338 struct nf_ct_helper_expectfn *cur; 339 bool found = false; 340 341 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 342 if (!strcmp(cur->name, name)) { 343 found = true; 344 break; 345 } 346 } 347 return found ? cur : NULL; 348 } 349 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name); 350 351 /* Caller should hold the rcu lock */ 352 struct nf_ct_helper_expectfn * 353 nf_ct_helper_expectfn_find_by_symbol(const void *symbol) 354 { 355 struct nf_ct_helper_expectfn *cur; 356 bool found = false; 357 358 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 359 if (cur->expectfn == symbol) { 360 found = true; 361 break; 362 } 363 } 364 return found ? cur : NULL; 365 } 366 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol); 367 368 __printf(3, 4) 369 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct, 370 const char *fmt, ...) 371 { 372 const struct nf_conn_help *help; 373 const struct nf_conntrack_helper *helper; 374 struct va_format vaf; 375 va_list args; 376 377 va_start(args, fmt); 378 379 vaf.fmt = fmt; 380 vaf.va = &args; 381 382 /* Called from the helper function, this call never fails */ 383 help = nfct_help(ct); 384 385 /* rcu_read_lock()ed by nf_hook_thresh */ 386 helper = rcu_dereference(help->helper); 387 388 nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL, 389 "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf); 390 391 va_end(args); 392 } 393 EXPORT_SYMBOL_GPL(nf_ct_helper_log); 394 395 int nf_conntrack_helper_register(struct nf_conntrack_helper *me) 396 { 397 struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) }; 398 unsigned int h = helper_hash(&me->tuple); 399 struct nf_conntrack_helper *cur; 400 int ret = 0, i; 401 402 BUG_ON(me->expect_policy == NULL); 403 BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES); 404 BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1); 405 406 if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT) 407 return -EINVAL; 408 409 mutex_lock(&nf_ct_helper_mutex); 410 for (i = 0; i < nf_ct_helper_hsize; i++) { 411 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) { 412 if (!strcmp(cur->name, me->name) && 413 (cur->tuple.src.l3num == NFPROTO_UNSPEC || 414 cur->tuple.src.l3num == me->tuple.src.l3num) && 415 cur->tuple.dst.protonum == me->tuple.dst.protonum) { 416 ret = -EEXIST; 417 goto out; 418 } 419 } 420 } 421 422 /* avoid unpredictable behaviour for auto_assign_helper */ 423 if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) { 424 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) { 425 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, 426 &mask)) { 427 ret = -EEXIST; 428 goto out; 429 } 430 } 431 } 432 refcount_set(&me->refcnt, 1); 433 hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]); 434 nf_ct_helper_count++; 435 out: 436 mutex_unlock(&nf_ct_helper_mutex); 437 return ret; 438 } 439 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register); 440 441 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data) 442 { 443 struct nf_conn_help *help = nfct_help(exp->master); 444 const struct nf_conntrack_helper *me = data; 445 const struct nf_conntrack_helper *this; 446 447 if (exp->helper == me) 448 return true; 449 450 this = rcu_dereference_protected(help->helper, 451 lockdep_is_held(&nf_conntrack_expect_lock)); 452 return this == me; 453 } 454 455 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me) 456 { 457 mutex_lock(&nf_ct_helper_mutex); 458 hlist_del_rcu(&me->hnode); 459 nf_ct_helper_count--; 460 mutex_unlock(&nf_ct_helper_mutex); 461 462 /* Make sure every nothing is still using the helper unless its a 463 * connection in the hash. 464 */ 465 synchronize_rcu(); 466 467 nf_ct_expect_iterate_destroy(expect_iter_me, NULL); 468 nf_ct_iterate_destroy(unhelp, me); 469 470 /* Maybe someone has gotten the helper already when unhelp above. 471 * So need to wait it. 472 */ 473 synchronize_rcu(); 474 } 475 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister); 476 477 void nf_ct_helper_init(struct nf_conntrack_helper *helper, 478 u16 l3num, u16 protonum, const char *name, 479 u16 default_port, u16 spec_port, u32 id, 480 const struct nf_conntrack_expect_policy *exp_pol, 481 u32 expect_class_max, 482 int (*help)(struct sk_buff *skb, unsigned int protoff, 483 struct nf_conn *ct, 484 enum ip_conntrack_info ctinfo), 485 int (*from_nlattr)(struct nlattr *attr, 486 struct nf_conn *ct), 487 struct module *module) 488 { 489 helper->tuple.src.l3num = l3num; 490 helper->tuple.dst.protonum = protonum; 491 helper->tuple.src.u.all = htons(spec_port); 492 helper->expect_policy = exp_pol; 493 helper->expect_class_max = expect_class_max; 494 helper->help = help; 495 helper->from_nlattr = from_nlattr; 496 helper->me = module; 497 snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name), 498 NF_NAT_HELPER_PREFIX "%s", name); 499 500 if (spec_port == default_port) 501 snprintf(helper->name, sizeof(helper->name), "%s", name); 502 else 503 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id); 504 } 505 EXPORT_SYMBOL_GPL(nf_ct_helper_init); 506 507 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper, 508 unsigned int n) 509 { 510 unsigned int i; 511 int err = 0; 512 513 for (i = 0; i < n; i++) { 514 err = nf_conntrack_helper_register(&helper[i]); 515 if (err < 0) 516 goto err; 517 } 518 519 return err; 520 err: 521 if (i > 0) 522 nf_conntrack_helpers_unregister(helper, i); 523 return err; 524 } 525 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register); 526 527 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper, 528 unsigned int n) 529 { 530 while (n-- > 0) 531 nf_conntrack_helper_unregister(&helper[n]); 532 } 533 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister); 534 535 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat) 536 { 537 mutex_lock(&nf_ct_nat_helpers_mutex); 538 list_add_rcu(&nat->list, &nf_ct_nat_helpers); 539 mutex_unlock(&nf_ct_nat_helpers_mutex); 540 } 541 EXPORT_SYMBOL_GPL(nf_nat_helper_register); 542 543 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat) 544 { 545 mutex_lock(&nf_ct_nat_helpers_mutex); 546 list_del_rcu(&nat->list); 547 mutex_unlock(&nf_ct_nat_helpers_mutex); 548 } 549 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister); 550 551 static const struct nf_ct_ext_type helper_extend = { 552 .len = sizeof(struct nf_conn_help), 553 .align = __alignof__(struct nf_conn_help), 554 .id = NF_CT_EXT_HELPER, 555 }; 556 557 void nf_conntrack_helper_pernet_init(struct net *net) 558 { 559 net->ct.auto_assign_helper_warned = false; 560 net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper; 561 } 562 563 int nf_conntrack_helper_init(void) 564 { 565 int ret; 566 nf_ct_helper_hsize = 1; /* gets rounded up to use one page */ 567 nf_ct_helper_hash = 568 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0); 569 if (!nf_ct_helper_hash) 570 return -ENOMEM; 571 572 ret = nf_ct_extend_register(&helper_extend); 573 if (ret < 0) { 574 pr_err("nf_ct_helper: Unable to register helper extension.\n"); 575 goto out_extend; 576 } 577 578 INIT_LIST_HEAD(&nf_ct_nat_helpers); 579 return 0; 580 out_extend: 581 kvfree(nf_ct_helper_hash); 582 return ret; 583 } 584 585 void nf_conntrack_helper_fini(void) 586 { 587 nf_ct_extend_unregister(&helper_extend); 588 kvfree(nf_ct_helper_hash); 589 } 590