net/netfilter/nf_conntrack_helper.c

   1 /* Helper handling for netfilter. */
   2
   3 /* (C) 1999-2001 Paul `Rusty' Russell
   4  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   5  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   6  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/types.h>
  14 #include <linux/netfilter.h>
  15 #include <linux/module.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/vmalloc.h>
  18 #include <linux/stddef.h>
  19 #include <linux/random.h>
  20 #include <linux/err.h>
  21 #include <linux/kernel.h>
  22 #include <linux/netdevice.h>
  23 #include <linux/rculist.h>
  24 #include <linux/rtnetlink.h>
  25
  26 #include <net/netfilter/nf_conntrack.h>
  27 #include <net/netfilter/nf_conntrack_l4proto.h>
  28 #include <net/netfilter/nf_conntrack_helper.h>
  29 #include <net/netfilter/nf_conntrack_core.h>
  30 #include <net/netfilter/nf_conntrack_extend.h>
  31 #include <net/netfilter/nf_log.h>
  32
  33 static DEFINE_MUTEX(nf_ct_helper_mutex);
  34 struct hlist_head *nf_ct_helper_hash __read_mostly;
  35 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  36 unsigned int nf_ct_helper_hsize __read_mostly;
  37 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  38 static unsigned int nf_ct_helper_count __read_mostly;
  39
  40 static bool nf_ct_auto_assign_helper __read_mostly = false;
  41 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  42 MODULE_PARM_DESC(nf_conntrack_helper,
  43                  "Enable automatic conntrack helper assignment (default 0)");
  44
  45 static DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
  46 static struct list_head nf_ct_nat_helpers __read_mostly;
  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         if (!net->ct.sysctl_auto_assign_helper) {
 218                 if (net->ct.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                 net->ct.auto_assign_helper_warned = 1;
 227                 return NULL;
 228         }
 229
 230         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 231 }
 232
 233
 234 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 235                               gfp_t flags)
 236 {
 237         struct nf_conntrack_helper *helper = NULL;
 238         struct nf_conn_help *help;
 239         struct net *net = nf_ct_net(ct);
 240
 241         /* We already got a helper explicitly attached. The function
 242          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 243          * the helper up again. Since now the user is in full control of
 244          * making consistent helper configurations, skip this automatic
 245          * re-lookup, otherwise we'll lose the helper.
 246          */
 247         if (test_bit(IPS_HELPER_BIT, &ct->status))
 248                 return 0;
 249
 250         if (tmpl != NULL) {
 251                 help = nfct_help(tmpl);
 252                 if (help != NULL) {
 253                         helper = help->helper;
 254                         set_bit(IPS_HELPER_BIT, &ct->status);
 255                 }
 256         }
 257
 258         help = nfct_help(ct);
 259
 260         if (helper == NULL) {
 261                 helper = nf_ct_lookup_helper(ct, net);
 262                 if (helper == NULL) {
 263                         if (help)
 264                                 RCU_INIT_POINTER(help->helper, NULL);
 265                         return 0;
 266                 }
 267         }
 268
 269         if (help == NULL) {
 270                 help = nf_ct_helper_ext_add(ct, flags);
 271                 if (help == NULL)
 272                         return -ENOMEM;
 273         } else {
 274                 /* We only allow helper re-assignment of the same sort since
 275                  * we cannot reallocate the helper extension area.
 276                  */
 277                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 278
 279                 if (tmp && tmp->help != helper->help) {
 280                         RCU_INIT_POINTER(help->helper, NULL);
 281                         return 0;
 282                 }
 283         }
 284
 285         rcu_assign_pointer(help->helper, helper);
 286
 287         return 0;
 288 }
 289 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 290
 291 /* appropriate ct lock protecting must be taken by caller */
 292 static int unhelp(struct nf_conn *ct, void *me)
 293 {
 294         struct nf_conn_help *help = nfct_help(ct);
 295
 296         if (help && rcu_dereference_raw(help->helper) == me) {
 297                 nf_conntrack_event(IPCT_HELPER, ct);
 298                 RCU_INIT_POINTER(help->helper, NULL);
 299         }
 300
 301         /* We are not intended to delete this conntrack. */
 302         return 0;
 303 }
 304
 305 void nf_ct_helper_destroy(struct nf_conn *ct)
 306 {
 307         struct nf_conn_help *help = nfct_help(ct);
 308         struct nf_conntrack_helper *helper;
 309
 310         if (help) {
 311                 rcu_read_lock();
 312                 helper = rcu_dereference(help->helper);
 313                 if (helper && helper->destroy)
 314                         helper->destroy(ct);
 315                 rcu_read_unlock();
 316         }
 317 }
 318
 319 static LIST_HEAD(nf_ct_helper_expectfn_list);
 320
 321 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 322 {
 323         spin_lock_bh(&nf_conntrack_expect_lock);
 324         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 325         spin_unlock_bh(&nf_conntrack_expect_lock);
 326 }
 327 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 328
 329 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 330 {
 331         spin_lock_bh(&nf_conntrack_expect_lock);
 332         list_del_rcu(&n->head);
 333         spin_unlock_bh(&nf_conntrack_expect_lock);
 334 }
 335 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 336
 337 /* Caller should hold the rcu lock */
 338 struct nf_ct_helper_expectfn *
 339 nf_ct_helper_expectfn_find_by_name(const char *name)
 340 {
 341         struct nf_ct_helper_expectfn *cur;
 342         bool found = false;
 343
 344         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 345                 if (!strcmp(cur->name, name)) {
 346                         found = true;
 347                         break;
 348                 }
 349         }
 350         return found ? cur : NULL;
 351 }
 352 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 353
 354 /* Caller should hold the rcu lock */
 355 struct nf_ct_helper_expectfn *
 356 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 357 {
 358         struct nf_ct_helper_expectfn *cur;
 359         bool found = false;
 360
 361         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 362                 if (cur->expectfn == symbol) {
 363                         found = true;
 364                         break;
 365                 }
 366         }
 367         return found ? cur : NULL;
 368 }
 369 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 370
 371 __printf(3, 4)
 372 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 373                       const char *fmt, ...)
 374 {
 375         const struct nf_conn_help *help;
 376         const struct nf_conntrack_helper *helper;
 377         struct va_format vaf;
 378         va_list args;
 379
 380         va_start(args, fmt);
 381
 382         vaf.fmt = fmt;
 383         vaf.va = &args;
 384
 385         /* Called from the helper function, this call never fails */
 386         help = nfct_help(ct);
 387
 388         /* rcu_read_lock()ed by nf_hook_thresh */
 389         helper = rcu_dereference(help->helper);
 390
 391         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 392                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 393
 394         va_end(args);
 395 }
 396 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 397
 398 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 399 {
 400         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 401         unsigned int h = helper_hash(&me->tuple);
 402         struct nf_conntrack_helper *cur;
 403         int ret = 0, i;
 404
 405         BUG_ON(me->expect_policy == NULL);
 406         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 407         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 408
 409         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 410                 return -EINVAL;
 411
 412         mutex_lock(&nf_ct_helper_mutex);
 413         for (i = 0; i < nf_ct_helper_hsize; i++) {
 414                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 415                         if (!strcmp(cur->name, me->name) &&
 416                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 417                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 418                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 419                                 ret = -EEXIST;
 420                                 goto out;
 421                         }
 422                 }
 423         }
 424
 425         /* avoid unpredictable behaviour for auto_assign_helper */
 426         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 427                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 428                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 429                                                      &mask)) {
 430                                 ret = -EEXIST;
 431                                 goto out;
 432                         }
 433                 }
 434         }
 435         refcount_set(&me->refcnt, 1);
 436         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 437         nf_ct_helper_count++;
 438 out:
 439         mutex_unlock(&nf_ct_helper_mutex);
 440         return ret;
 441 }
 442 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 443
 444 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 445 {
 446         struct nf_conn_help *help = nfct_help(exp->master);
 447         const struct nf_conntrack_helper *me = data;
 448         const struct nf_conntrack_helper *this;
 449
 450         if (exp->helper == me)
 451                 return true;
 452
 453         this = rcu_dereference_protected(help->helper,
 454                                          lockdep_is_held(&nf_conntrack_expect_lock));
 455         return this == me;
 456 }
 457
 458 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 459 {
 460         mutex_lock(&nf_ct_helper_mutex);
 461         hlist_del_rcu(&me->hnode);
 462         nf_ct_helper_count--;
 463         mutex_unlock(&nf_ct_helper_mutex);
 464
 465         /* Make sure every nothing is still using the helper unless its a
 466          * connection in the hash.
 467          */
 468         synchronize_rcu();
 469
 470         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 471         nf_ct_iterate_destroy(unhelp, me);
 472
 473         /* Maybe someone has gotten the helper already when unhelp above.
 474          * So need to wait it.
 475          */
 476         synchronize_rcu();
 477 }
 478 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 479
 480 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 481                        u16 l3num, u16 protonum, const char *name,
 482                        u16 default_port, u16 spec_port, u32 id,
 483                        const struct nf_conntrack_expect_policy *exp_pol,
 484                        u32 expect_class_max,
 485                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 486                                    struct nf_conn *ct,
 487                                    enum ip_conntrack_info ctinfo),
 488                        int (*from_nlattr)(struct nlattr *attr,
 489                                           struct nf_conn *ct),
 490                        struct module *module)
 491 {
 492         helper->tuple.src.l3num = l3num;
 493         helper->tuple.dst.protonum = protonum;
 494         helper->tuple.src.u.all = htons(spec_port);
 495         helper->expect_policy = exp_pol;
 496         helper->expect_class_max = expect_class_max;
 497         helper->help = help;
 498         helper->from_nlattr = from_nlattr;
 499         helper->me = module;
 500         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 501                  NF_NAT_HELPER_PREFIX "%s", name);
 502
 503         if (spec_port == default_port)
 504                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 505         else
 506                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 507 }
 508 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 509
 510 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 511                                   unsigned int n)
 512 {
 513         unsigned int i;
 514         int err = 0;
 515
 516         for (i = 0; i < n; i++) {
 517                 err = nf_conntrack_helper_register(&helper[i]);
 518                 if (err < 0)
 519                         goto err;
 520         }
 521
 522         return err;
 523 err:
 524         if (i > 0)
 525                 nf_conntrack_helpers_unregister(helper, i);
 526         return err;
 527 }
 528 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 529
 530 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 531                                 unsigned int n)
 532 {
 533         while (n-- > 0)
 534                 nf_conntrack_helper_unregister(&helper[n]);
 535 }
 536 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 537
 538 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 539 {
 540         mutex_lock(&nf_ct_nat_helpers_mutex);
 541         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 542         mutex_unlock(&nf_ct_nat_helpers_mutex);
 543 }
 544 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 545
 546 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 547 {
 548         mutex_lock(&nf_ct_nat_helpers_mutex);
 549         list_del_rcu(&nat->list);
 550         mutex_unlock(&nf_ct_nat_helpers_mutex);
 551 }
 552 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 553
 554 static const struct nf_ct_ext_type helper_extend = {
 555         .len    = sizeof(struct nf_conn_help),
 556         .align  = __alignof__(struct nf_conn_help),
 557         .id     = NF_CT_EXT_HELPER,
 558 };
 559
 560 void nf_conntrack_helper_pernet_init(struct net *net)
 561 {
 562         net->ct.auto_assign_helper_warned = false;
 563         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 564 }
 565
 566 int nf_conntrack_helper_init(void)
 567 {
 568         int ret;
 569         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 570         nf_ct_helper_hash =
 571                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 572         if (!nf_ct_helper_hash)
 573                 return -ENOMEM;
 574
 575         ret = nf_ct_extend_register(&helper_extend);
 576         if (ret < 0) {
 577                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 578                 goto out_extend;
 579         }
 580
 581         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 582         return 0;
 583 out_extend:
 584         kvfree(nf_ct_helper_hash);
 585         return ret;
 586 }
 587
 588 void nf_conntrack_helper_fini(void)
 589 {
 590         nf_ct_extend_unregister(&helper_extend);
 591         kvfree(nf_ct_helper_hash);
 592 }