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 struct nf_conntrack_net *cnet = nf_ct_pernet(net); 216 217 if (!cnet->sysctl_auto_assign_helper) { 218 if (cnet->auto_assign_helper_warned) 219 return NULL; 220 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple)) 221 return NULL; 222 pr_info("nf_conntrack: default automatic helper assignment " 223 "has been turned off for security reasons and CT-based " 224 "firewall rule not found. Use the iptables CT target " 225 "to attach helpers instead.\n"); 226 cnet->auto_assign_helper_warned = true; 227 return NULL; 228 } 229 230 return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); 231 } 232 233 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, 234 gfp_t flags) 235 { 236 struct nf_conntrack_helper *helper = NULL; 237 struct nf_conn_help *help; 238 struct net *net = nf_ct_net(ct); 239 240 /* We already got a helper explicitly attached. The function 241 * nf_conntrack_alter_reply - in case NAT is in use - asks for looking 242 * the helper up again. Since now the user is in full control of 243 * making consistent helper configurations, skip this automatic 244 * re-lookup, otherwise we'll lose the helper. 245 */ 246 if (test_bit(IPS_HELPER_BIT, &ct->status)) 247 return 0; 248 249 if (tmpl != NULL) { 250 help = nfct_help(tmpl); 251 if (help != NULL) { 252 helper = help->helper; 253 set_bit(IPS_HELPER_BIT, &ct->status); 254 } 255 } 256 257 help = nfct_help(ct); 258 259 if (helper == NULL) { 260 helper = nf_ct_lookup_helper(ct, net); 261 if (helper == NULL) { 262 if (help) 263 RCU_INIT_POINTER(help->helper, NULL); 264 return 0; 265 } 266 } 267 268 if (help == NULL) { 269 help = nf_ct_helper_ext_add(ct, flags); 270 if (help == NULL) 271 return -ENOMEM; 272 } else { 273 /* We only allow helper re-assignment of the same sort since 274 * we cannot reallocate the helper extension area. 275 */ 276 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper); 277 278 if (tmp && tmp->help != helper->help) { 279 RCU_INIT_POINTER(help->helper, NULL); 280 return 0; 281 } 282 } 283 284 rcu_assign_pointer(help->helper, helper); 285 286 return 0; 287 } 288 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper); 289 290 /* appropriate ct lock protecting must be taken by caller */ 291 static int unhelp(struct nf_conn *ct, void *me) 292 { 293 struct nf_conn_help *help = nfct_help(ct); 294 295 if (help && rcu_dereference_raw(help->helper) == me) { 296 nf_conntrack_event(IPCT_HELPER, ct); 297 RCU_INIT_POINTER(help->helper, NULL); 298 } 299 300 /* We are not intended to delete this conntrack. */ 301 return 0; 302 } 303 304 void nf_ct_helper_destroy(struct nf_conn *ct) 305 { 306 struct nf_conn_help *help = nfct_help(ct); 307 struct nf_conntrack_helper *helper; 308 309 if (help) { 310 rcu_read_lock(); 311 helper = rcu_dereference(help->helper); 312 if (helper && helper->destroy) 313 helper->destroy(ct); 314 rcu_read_unlock(); 315 } 316 } 317 318 static LIST_HEAD(nf_ct_helper_expectfn_list); 319 320 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n) 321 { 322 spin_lock_bh(&nf_conntrack_expect_lock); 323 list_add_rcu(&n->head, &nf_ct_helper_expectfn_list); 324 spin_unlock_bh(&nf_conntrack_expect_lock); 325 } 326 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register); 327 328 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n) 329 { 330 spin_lock_bh(&nf_conntrack_expect_lock); 331 list_del_rcu(&n->head); 332 spin_unlock_bh(&nf_conntrack_expect_lock); 333 } 334 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister); 335 336 /* Caller should hold the rcu lock */ 337 struct nf_ct_helper_expectfn * 338 nf_ct_helper_expectfn_find_by_name(const char *name) 339 { 340 struct nf_ct_helper_expectfn *cur; 341 bool found = false; 342 343 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 344 if (!strcmp(cur->name, name)) { 345 found = true; 346 break; 347 } 348 } 349 return found ? cur : NULL; 350 } 351 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name); 352 353 /* Caller should hold the rcu lock */ 354 struct nf_ct_helper_expectfn * 355 nf_ct_helper_expectfn_find_by_symbol(const void *symbol) 356 { 357 struct nf_ct_helper_expectfn *cur; 358 bool found = false; 359 360 list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { 361 if (cur->expectfn == symbol) { 362 found = true; 363 break; 364 } 365 } 366 return found ? cur : NULL; 367 } 368 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol); 369 370 __printf(3, 4) 371 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct, 372 const char *fmt, ...) 373 { 374 const struct nf_conn_help *help; 375 const struct nf_conntrack_helper *helper; 376 struct va_format vaf; 377 va_list args; 378 379 va_start(args, fmt); 380 381 vaf.fmt = fmt; 382 vaf.va = &args; 383 384 /* Called from the helper function, this call never fails */ 385 help = nfct_help(ct); 386 387 /* rcu_read_lock()ed by nf_hook_thresh */ 388 helper = rcu_dereference(help->helper); 389 390 nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL, 391 "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf); 392 393 va_end(args); 394 } 395 EXPORT_SYMBOL_GPL(nf_ct_helper_log); 396 397 int nf_conntrack_helper_register(struct nf_conntrack_helper *me) 398 { 399 struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) }; 400 unsigned int h = helper_hash(&me->tuple); 401 struct nf_conntrack_helper *cur; 402 int ret = 0, i; 403 404 BUG_ON(me->expect_policy == NULL); 405 BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES); 406 BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1); 407 408 if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT) 409 return -EINVAL; 410 411 mutex_lock(&nf_ct_helper_mutex); 412 for (i = 0; i < nf_ct_helper_hsize; i++) { 413 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) { 414 if (!strcmp(cur->name, me->name) && 415 (cur->tuple.src.l3num == NFPROTO_UNSPEC || 416 cur->tuple.src.l3num == me->tuple.src.l3num) && 417 cur->tuple.dst.protonum == me->tuple.dst.protonum) { 418 ret = -EEXIST; 419 goto out; 420 } 421 } 422 } 423 424 /* avoid unpredictable behaviour for auto_assign_helper */ 425 if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) { 426 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) { 427 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, 428 &mask)) { 429 ret = -EEXIST; 430 goto out; 431 } 432 } 433 } 434 refcount_set(&me->refcnt, 1); 435 hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]); 436 nf_ct_helper_count++; 437 out: 438 mutex_unlock(&nf_ct_helper_mutex); 439 return ret; 440 } 441 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register); 442 443 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data) 444 { 445 struct nf_conn_help *help = nfct_help(exp->master); 446 const struct nf_conntrack_helper *me = data; 447 const struct nf_conntrack_helper *this; 448 449 if (exp->helper == me) 450 return true; 451 452 this = rcu_dereference_protected(help->helper, 453 lockdep_is_held(&nf_conntrack_expect_lock)); 454 return this == me; 455 } 456 457 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me) 458 { 459 mutex_lock(&nf_ct_helper_mutex); 460 hlist_del_rcu(&me->hnode); 461 nf_ct_helper_count--; 462 mutex_unlock(&nf_ct_helper_mutex); 463 464 /* Make sure every nothing is still using the helper unless its a 465 * connection in the hash. 466 */ 467 synchronize_rcu(); 468 469 nf_ct_expect_iterate_destroy(expect_iter_me, NULL); 470 nf_ct_iterate_destroy(unhelp, me); 471 } 472 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister); 473 474 void nf_ct_helper_init(struct nf_conntrack_helper *helper, 475 u16 l3num, u16 protonum, const char *name, 476 u16 default_port, u16 spec_port, u32 id, 477 const struct nf_conntrack_expect_policy *exp_pol, 478 u32 expect_class_max, 479 int (*help)(struct sk_buff *skb, unsigned int protoff, 480 struct nf_conn *ct, 481 enum ip_conntrack_info ctinfo), 482 int (*from_nlattr)(struct nlattr *attr, 483 struct nf_conn *ct), 484 struct module *module) 485 { 486 helper->tuple.src.l3num = l3num; 487 helper->tuple.dst.protonum = protonum; 488 helper->tuple.src.u.all = htons(spec_port); 489 helper->expect_policy = exp_pol; 490 helper->expect_class_max = expect_class_max; 491 helper->help = help; 492 helper->from_nlattr = from_nlattr; 493 helper->me = module; 494 snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name), 495 NF_NAT_HELPER_PREFIX "%s", name); 496 497 if (spec_port == default_port) 498 snprintf(helper->name, sizeof(helper->name), "%s", name); 499 else 500 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id); 501 } 502 EXPORT_SYMBOL_GPL(nf_ct_helper_init); 503 504 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper, 505 unsigned int n) 506 { 507 unsigned int i; 508 int err = 0; 509 510 for (i = 0; i < n; i++) { 511 err = nf_conntrack_helper_register(&helper[i]); 512 if (err < 0) 513 goto err; 514 } 515 516 return err; 517 err: 518 if (i > 0) 519 nf_conntrack_helpers_unregister(helper, i); 520 return err; 521 } 522 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register); 523 524 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper, 525 unsigned int n) 526 { 527 while (n-- > 0) 528 nf_conntrack_helper_unregister(&helper[n]); 529 } 530 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister); 531 532 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat) 533 { 534 mutex_lock(&nf_ct_nat_helpers_mutex); 535 list_add_rcu(&nat->list, &nf_ct_nat_helpers); 536 mutex_unlock(&nf_ct_nat_helpers_mutex); 537 } 538 EXPORT_SYMBOL_GPL(nf_nat_helper_register); 539 540 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat) 541 { 542 mutex_lock(&nf_ct_nat_helpers_mutex); 543 list_del_rcu(&nat->list); 544 mutex_unlock(&nf_ct_nat_helpers_mutex); 545 } 546 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister); 547 548 void nf_ct_set_auto_assign_helper_warned(struct net *net) 549 { 550 nf_ct_pernet(net)->auto_assign_helper_warned = true; 551 } 552 EXPORT_SYMBOL_GPL(nf_ct_set_auto_assign_helper_warned); 553 554 void nf_conntrack_helper_pernet_init(struct net *net) 555 { 556 struct nf_conntrack_net *cnet = nf_ct_pernet(net); 557 558 cnet->sysctl_auto_assign_helper = nf_ct_auto_assign_helper; 559 } 560 561 int nf_conntrack_helper_init(void) 562 { 563 nf_ct_helper_hsize = 1; /* gets rounded up to use one page */ 564 nf_ct_helper_hash = 565 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0); 566 if (!nf_ct_helper_hash) 567 return -ENOMEM; 568 569 INIT_LIST_HEAD(&nf_ct_nat_helpers); 570 return 0; 571 } 572 573 void nf_conntrack_helper_fini(void) 574 { 575 kvfree(nf_ct_helper_hash); 576 } 577