net/netfilter/nf_conntrack_helper.c

   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 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 }