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 extern unsigned int nf_conntrack_net_id;
  47
  48 /* Stupid hash, but collision free for the default registrations of the
  49  * helpers currently in the kernel. */
  50 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  51 {
  52         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  53                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  54 }
  55
  56 static struct nf_conntrack_helper *
  57 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  58 {
  59         struct nf_conntrack_helper *helper;
  60         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
  61         unsigned int h;
  62
  63         if (!nf_ct_helper_count)
  64                 return NULL;
  65
  66         h = helper_hash(tuple);
  67         hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
  68                 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  69                         return helper;
  70         }
  71         return NULL;
  72 }
  73
  74 struct nf_conntrack_helper *
  75 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  76 {
  77         struct nf_conntrack_helper *h;
  78         unsigned int i;
  79
  80         for (i = 0; i < nf_ct_helper_hsize; i++) {
  81                 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
  82                         if (strcmp(h->name, name))
  83                                 continue;
  84
  85                         if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
  86                             h->tuple.src.l3num != l3num)
  87                                 continue;
  88
  89                         if (h->tuple.dst.protonum == protonum)
  90                                 return h;
  91                 }
  92         }
  93         return NULL;
  94 }
  95 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  96
  97 struct nf_conntrack_helper *
  98 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  99 {
 100         struct nf_conntrack_helper *h;
 101
 102         rcu_read_lock();
 103
 104         h = __nf_conntrack_helper_find(name, l3num, protonum);
 105 #ifdef CONFIG_MODULES
 106         if (h == NULL) {
 107                 rcu_read_unlock();
 108                 if (request_module("nfct-helper-%s", name) == 0) {
 109                         rcu_read_lock();
 110                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 111                 } else {
 112                         return h;
 113                 }
 114         }
 115 #endif
 116         if (h != NULL && !try_module_get(h->me))
 117                 h = NULL;
 118         if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 119                 module_put(h->me);
 120                 h = NULL;
 121         }
 122
 123         rcu_read_unlock();
 124
 125         return h;
 126 }
 127 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 128
 129 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 130 {
 131         refcount_dec(&helper->refcnt);
 132         module_put(helper->me);
 133 }
 134 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 135
 136 static struct nf_conntrack_nat_helper *
 137 nf_conntrack_nat_helper_find(const char *mod_name)
 138 {
 139         struct nf_conntrack_nat_helper *cur;
 140         bool found = false;
 141
 142         list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
 143                 if (!strcmp(cur->mod_name, mod_name)) {
 144                         found = true;
 145                         break;
 146                 }
 147         }
 148         return found ? cur : NULL;
 149 }
 150
 151 int
 152 nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 153 {
 154         struct nf_conntrack_helper *h;
 155         struct nf_conntrack_nat_helper *nat;
 156         char mod_name[NF_CT_HELPER_NAME_LEN];
 157         int ret = 0;
 158
 159         rcu_read_lock();
 160         h = __nf_conntrack_helper_find(name, l3num, protonum);
 161         if (!h) {
 162                 rcu_read_unlock();
 163                 return -ENOENT;
 164         }
 165
 166         nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
 167         if (!nat) {
 168                 snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
 169                 rcu_read_unlock();
 170                 request_module(mod_name);
 171
 172                 rcu_read_lock();
 173                 nat = nf_conntrack_nat_helper_find(mod_name);
 174                 if (!nat) {
 175                         rcu_read_unlock();
 176                         return -ENOENT;
 177                 }
 178         }
 179
 180         if (!try_module_get(nat->module))
 181                 ret = -ENOENT;
 182
 183         rcu_read_unlock();
 184         return ret;
 185 }
 186 EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
 187
 188 void nf_nat_helper_put(struct nf_conntrack_helper *helper)
 189 {
 190         struct nf_conntrack_nat_helper *nat;
 191
 192         nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
 193         if (WARN_ON_ONCE(!nat))
 194                 return;
 195
 196         module_put(nat->module);
 197 }
 198 EXPORT_SYMBOL_GPL(nf_nat_helper_put);
 199
 200 struct nf_conn_help *
 201 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 202 {
 203         struct nf_conn_help *help;
 204
 205         help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 206         if (help)
 207                 INIT_HLIST_HEAD(&help->expectations);
 208         else
 209                 pr_debug("failed to add helper extension area");
 210         return help;
 211 }
 212 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 213
 214 static struct nf_conntrack_helper *
 215 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 216 {
 217         struct nf_conntrack_net *cnet = net_generic(net, nf_conntrack_net_id);
 218
 219         if (!cnet->sysctl_auto_assign_helper) {
 220                 if (cnet->auto_assign_helper_warned)
 221                         return NULL;
 222                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 223                         return NULL;
 224                 pr_info("nf_conntrack: default automatic helper assignment "
 225                         "has been turned off for security reasons and CT-based "
 226                         "firewall rule not found. Use the iptables CT target "
 227                         "to attach helpers instead.\n");
 228                 cnet->auto_assign_helper_warned = true;
 229                 return NULL;
 230         }
 231
 232         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 233 }
 234
 235 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 236                               gfp_t flags)
 237 {
 238         struct nf_conntrack_helper *helper = NULL;
 239         struct nf_conn_help *help;
 240         struct net *net = nf_ct_net(ct);
 241
 242         /* We already got a helper explicitly attached. The function
 243          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 244          * the helper up again. Since now the user is in full control of
 245          * making consistent helper configurations, skip this automatic
 246          * re-lookup, otherwise we'll lose the helper.
 247          */
 248         if (test_bit(IPS_HELPER_BIT, &ct->status))
 249                 return 0;
 250
 251         if (tmpl != NULL) {
 252                 help = nfct_help(tmpl);
 253                 if (help != NULL) {
 254                         helper = help->helper;
 255                         set_bit(IPS_HELPER_BIT, &ct->status);
 256                 }
 257         }
 258
 259         help = nfct_help(ct);
 260
 261         if (helper == NULL) {
 262                 helper = nf_ct_lookup_helper(ct, net);
 263                 if (helper == NULL) {
 264                         if (help)
 265                                 RCU_INIT_POINTER(help->helper, NULL);
 266                         return 0;
 267                 }
 268         }
 269
 270         if (help == NULL) {
 271                 help = nf_ct_helper_ext_add(ct, flags);
 272                 if (help == NULL)
 273                         return -ENOMEM;
 274         } else {
 275                 /* We only allow helper re-assignment of the same sort since
 276                  * we cannot reallocate the helper extension area.
 277                  */
 278                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 279
 280                 if (tmp && tmp->help != helper->help) {
 281                         RCU_INIT_POINTER(help->helper, NULL);
 282                         return 0;
 283                 }
 284         }
 285
 286         rcu_assign_pointer(help->helper, helper);
 287
 288         return 0;
 289 }
 290 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 291
 292 /* appropriate ct lock protecting must be taken by caller */
 293 static int unhelp(struct nf_conn *ct, void *me)
 294 {
 295         struct nf_conn_help *help = nfct_help(ct);
 296
 297         if (help && rcu_dereference_raw(help->helper) == me) {
 298                 nf_conntrack_event(IPCT_HELPER, ct);
 299                 RCU_INIT_POINTER(help->helper, NULL);
 300         }
 301
 302         /* We are not intended to delete this conntrack. */
 303         return 0;
 304 }
 305
 306 void nf_ct_helper_destroy(struct nf_conn *ct)
 307 {
 308         struct nf_conn_help *help = nfct_help(ct);
 309         struct nf_conntrack_helper *helper;
 310
 311         if (help) {
 312                 rcu_read_lock();
 313                 helper = rcu_dereference(help->helper);
 314                 if (helper && helper->destroy)
 315                         helper->destroy(ct);
 316                 rcu_read_unlock();
 317         }
 318 }
 319
 320 static LIST_HEAD(nf_ct_helper_expectfn_list);
 321
 322 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 323 {
 324         spin_lock_bh(&nf_conntrack_expect_lock);
 325         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 326         spin_unlock_bh(&nf_conntrack_expect_lock);
 327 }
 328 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 329
 330 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 331 {
 332         spin_lock_bh(&nf_conntrack_expect_lock);
 333         list_del_rcu(&n->head);
 334         spin_unlock_bh(&nf_conntrack_expect_lock);
 335 }
 336 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 337
 338 /* Caller should hold the rcu lock */
 339 struct nf_ct_helper_expectfn *
 340 nf_ct_helper_expectfn_find_by_name(const char *name)
 341 {
 342         struct nf_ct_helper_expectfn *cur;
 343         bool found = false;
 344
 345         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 346                 if (!strcmp(cur->name, name)) {
 347                         found = true;
 348                         break;
 349                 }
 350         }
 351         return found ? cur : NULL;
 352 }
 353 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 354
 355 /* Caller should hold the rcu lock */
 356 struct nf_ct_helper_expectfn *
 357 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 358 {
 359         struct nf_ct_helper_expectfn *cur;
 360         bool found = false;
 361
 362         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 363                 if (cur->expectfn == symbol) {
 364                         found = true;
 365                         break;
 366                 }
 367         }
 368         return found ? cur : NULL;
 369 }
 370 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 371
 372 __printf(3, 4)
 373 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 374                       const char *fmt, ...)
 375 {
 376         const struct nf_conn_help *help;
 377         const struct nf_conntrack_helper *helper;
 378         struct va_format vaf;
 379         va_list args;
 380
 381         va_start(args, fmt);
 382
 383         vaf.fmt = fmt;
 384         vaf.va = &args;
 385
 386         /* Called from the helper function, this call never fails */
 387         help = nfct_help(ct);
 388
 389         /* rcu_read_lock()ed by nf_hook_thresh */
 390         helper = rcu_dereference(help->helper);
 391
 392         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 393                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 394
 395         va_end(args);
 396 }
 397 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 398
 399 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 400 {
 401         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 402         unsigned int h = helper_hash(&me->tuple);
 403         struct nf_conntrack_helper *cur;
 404         int ret = 0, i;
 405
 406         BUG_ON(me->expect_policy == NULL);
 407         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 408         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 409
 410         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 411                 return -EINVAL;
 412
 413         mutex_lock(&nf_ct_helper_mutex);
 414         for (i = 0; i < nf_ct_helper_hsize; i++) {
 415                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 416                         if (!strcmp(cur->name, me->name) &&
 417                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 418                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 419                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 420                                 ret = -EEXIST;
 421                                 goto out;
 422                         }
 423                 }
 424         }
 425
 426         /* avoid unpredictable behaviour for auto_assign_helper */
 427         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 428                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 429                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 430                                                      &mask)) {
 431                                 ret = -EEXIST;
 432                                 goto out;
 433                         }
 434                 }
 435         }
 436         refcount_set(&me->refcnt, 1);
 437         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 438         nf_ct_helper_count++;
 439 out:
 440         mutex_unlock(&nf_ct_helper_mutex);
 441         return ret;
 442 }
 443 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 444
 445 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 446 {
 447         struct nf_conn_help *help = nfct_help(exp->master);
 448         const struct nf_conntrack_helper *me = data;
 449         const struct nf_conntrack_helper *this;
 450
 451         if (exp->helper == me)
 452                 return true;
 453
 454         this = rcu_dereference_protected(help->helper,
 455                                          lockdep_is_held(&nf_conntrack_expect_lock));
 456         return this == me;
 457 }
 458
 459 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 460 {
 461         mutex_lock(&nf_ct_helper_mutex);
 462         hlist_del_rcu(&me->hnode);
 463         nf_ct_helper_count--;
 464         mutex_unlock(&nf_ct_helper_mutex);
 465
 466         /* Make sure every nothing is still using the helper unless its a
 467          * connection in the hash.
 468          */
 469         synchronize_rcu();
 470
 471         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 472         nf_ct_iterate_destroy(unhelp, me);
 473
 474         /* Maybe someone has gotten the helper already when unhelp above.
 475          * So need to wait it.
 476          */
 477         synchronize_rcu();
 478 }
 479 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 480
 481 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 482                        u16 l3num, u16 protonum, const char *name,
 483                        u16 default_port, u16 spec_port, u32 id,
 484                        const struct nf_conntrack_expect_policy *exp_pol,
 485                        u32 expect_class_max,
 486                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 487                                    struct nf_conn *ct,
 488                                    enum ip_conntrack_info ctinfo),
 489                        int (*from_nlattr)(struct nlattr *attr,
 490                                           struct nf_conn *ct),
 491                        struct module *module)
 492 {
 493         helper->tuple.src.l3num = l3num;
 494         helper->tuple.dst.protonum = protonum;
 495         helper->tuple.src.u.all = htons(spec_port);
 496         helper->expect_policy = exp_pol;
 497         helper->expect_class_max = expect_class_max;
 498         helper->help = help;
 499         helper->from_nlattr = from_nlattr;
 500         helper->me = module;
 501         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 502                  NF_NAT_HELPER_PREFIX "%s", name);
 503
 504         if (spec_port == default_port)
 505                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 506         else
 507                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 508 }
 509 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 510
 511 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 512                                   unsigned int n)
 513 {
 514         unsigned int i;
 515         int err = 0;
 516
 517         for (i = 0; i < n; i++) {
 518                 err = nf_conntrack_helper_register(&helper[i]);
 519                 if (err < 0)
 520                         goto err;
 521         }
 522
 523         return err;
 524 err:
 525         if (i > 0)
 526                 nf_conntrack_helpers_unregister(helper, i);
 527         return err;
 528 }
 529 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 530
 531 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 532                                 unsigned int n)
 533 {
 534         while (n-- > 0)
 535                 nf_conntrack_helper_unregister(&helper[n]);
 536 }
 537 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 538
 539 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 540 {
 541         mutex_lock(&nf_ct_nat_helpers_mutex);
 542         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 543         mutex_unlock(&nf_ct_nat_helpers_mutex);
 544 }
 545 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 546
 547 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 548 {
 549         mutex_lock(&nf_ct_nat_helpers_mutex);
 550         list_del_rcu(&nat->list);
 551         mutex_unlock(&nf_ct_nat_helpers_mutex);
 552 }
 553 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 554
 555 static const struct nf_ct_ext_type helper_extend = {
 556         .len    = sizeof(struct nf_conn_help),
 557         .align  = __alignof__(struct nf_conn_help),
 558         .id     = NF_CT_EXT_HELPER,
 559 };
 560
 561 void nf_conntrack_helper_pernet_init(struct net *net)
 562 {
 563         struct nf_conntrack_net *cnet = net_generic(net, nf_conntrack_net_id);
 564
 565         cnet->sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 566 }
 567
 568 int nf_conntrack_helper_init(void)
 569 {
 570         int ret;
 571         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 572         nf_ct_helper_hash =
 573                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 574         if (!nf_ct_helper_hash)
 575                 return -ENOMEM;
 576
 577         ret = nf_ct_extend_register(&helper_extend);
 578         if (ret < 0) {
 579                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 580                 goto out_extend;
 581         }
 582
 583         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 584         return 0;
 585 out_extend:
 586         kvfree(nf_ct_helper_hash);
 587         return ret;
 588 }
 589
 590 void nf_conntrack_helper_fini(void)
 591 {
 592         nf_ct_extend_unregister(&helper_extend);
 593         kvfree(nf_ct_helper_hash);
 594 }