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_l3proto.h>
  28 #include <net/netfilter/nf_conntrack_l4proto.h>
  29 #include <net/netfilter/nf_conntrack_helper.h>
  30 #include <net/netfilter/nf_conntrack_core.h>
  31 #include <net/netfilter/nf_conntrack_extend.h>
  32 #include <net/netfilter/nf_log.h>
  33
  34 static DEFINE_MUTEX(nf_ct_helper_mutex);
  35 struct hlist_head *nf_ct_helper_hash __read_mostly;
  36 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  37 unsigned int nf_ct_helper_hsize __read_mostly;
  38 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  39 static unsigned int nf_ct_helper_count __read_mostly;
  40
  41 static bool nf_ct_auto_assign_helper __read_mostly = false;
  42 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  43 MODULE_PARM_DESC(nf_conntrack_helper,
  44                  "Enable automatic conntrack helper assignment (default 0)");
  45
  46 #ifdef CONFIG_SYSCTL
  47 static struct ctl_table helper_sysctl_table[] = {
  48         {
  49                 .procname       = "nf_conntrack_helper",
  50                 .data           = &init_net.ct.sysctl_auto_assign_helper,
  51                 .maxlen         = sizeof(unsigned int),
  52                 .mode           = 0644,
  53                 .proc_handler   = proc_dointvec,
  54         },
  55         {}
  56 };
  57
  58 static int nf_conntrack_helper_init_sysctl(struct net *net)
  59 {
  60         struct ctl_table *table;
  61
  62         table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
  63                         GFP_KERNEL);
  64         if (!table)
  65                 goto out;
  66
  67         table[0].data = &net->ct.sysctl_auto_assign_helper;
  68
  69         /* Don't export sysctls to unprivileged users */
  70         if (net->user_ns != &init_user_ns)
  71                 table[0].procname = NULL;
  72
  73         net->ct.helper_sysctl_header =
  74                 register_net_sysctl(net, "net/netfilter", table);
  75
  76         if (!net->ct.helper_sysctl_header) {
  77                 pr_err("nf_conntrack_helper: can't register to sysctl.\n");
  78                 goto out_register;
  79         }
  80         return 0;
  81
  82 out_register:
  83         kfree(table);
  84 out:
  85         return -ENOMEM;
  86 }
  87
  88 static void nf_conntrack_helper_fini_sysctl(struct net *net)
  89 {
  90         struct ctl_table *table;
  91
  92         table = net->ct.helper_sysctl_header->ctl_table_arg;
  93         unregister_net_sysctl_table(net->ct.helper_sysctl_header);
  94         kfree(table);
  95 }
  96 #else
  97 static int nf_conntrack_helper_init_sysctl(struct net *net)
  98 {
  99         return 0;
 100 }
 101
 102 static void nf_conntrack_helper_fini_sysctl(struct net *net)
 103 {
 104 }
 105 #endif /* CONFIG_SYSCTL */
 106
 107 /* Stupid hash, but collision free for the default registrations of the
 108  * helpers currently in the kernel. */
 109 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 110 {
 111         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
 112                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 113 }
 114
 115 static struct nf_conntrack_helper *
 116 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 117 {
 118         struct nf_conntrack_helper *helper;
 119         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 120         unsigned int h;
 121
 122         if (!nf_ct_helper_count)
 123                 return NULL;
 124
 125         h = helper_hash(tuple);
 126         hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
 127                 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
 128                         return helper;
 129         }
 130         return NULL;
 131 }
 132
 133 struct nf_conntrack_helper *
 134 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
 135 {
 136         struct nf_conntrack_helper *h;
 137         unsigned int i;
 138
 139         for (i = 0; i < nf_ct_helper_hsize; i++) {
 140                 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
 141                         if (strcmp(h->name, name))
 142                                 continue;
 143
 144                         if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
 145                             h->tuple.src.l3num != l3num)
 146                                 continue;
 147
 148                         if (h->tuple.dst.protonum == protonum)
 149                                 return h;
 150                 }
 151         }
 152         return NULL;
 153 }
 154 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 155
 156 struct nf_conntrack_helper *
 157 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 158 {
 159         struct nf_conntrack_helper *h;
 160
 161         rcu_read_lock();
 162
 163         h = __nf_conntrack_helper_find(name, l3num, protonum);
 164 #ifdef CONFIG_MODULES
 165         if (h == NULL) {
 166                 rcu_read_unlock();
 167                 if (request_module("nfct-helper-%s", name) == 0) {
 168                         rcu_read_lock();
 169                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 170                 } else {
 171                         return h;
 172                 }
 173         }
 174 #endif
 175         if (h != NULL && !try_module_get(h->me))
 176                 h = NULL;
 177
 178         rcu_read_unlock();
 179
 180         return h;
 181 }
 182 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 183
 184 struct nf_conn_help *
 185 nf_ct_helper_ext_add(struct nf_conn *ct,
 186                      struct nf_conntrack_helper *helper, gfp_t gfp)
 187 {
 188         struct nf_conn_help *help;
 189
 190         help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
 191                                     helper->data_len, gfp);
 192         if (help)
 193                 INIT_HLIST_HEAD(&help->expectations);
 194         else
 195                 pr_debug("failed to add helper extension area");
 196         return help;
 197 }
 198 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 199
 200 static struct nf_conntrack_helper *
 201 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 202 {
 203         if (!net->ct.sysctl_auto_assign_helper) {
 204                 if (net->ct.auto_assign_helper_warned)
 205                         return NULL;
 206                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 207                         return NULL;
 208                 pr_info("nf_conntrack: default automatic helper assignment "
 209                         "has been turned off for security reasons and CT-based "
 210                         " firewall rule not found. Use the iptables CT target "
 211                         "to attach helpers instead.\n");
 212                 net->ct.auto_assign_helper_warned = 1;
 213                 return NULL;
 214         }
 215
 216         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 217 }
 218
 219
 220 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 221                               gfp_t flags)
 222 {
 223         struct nf_conntrack_helper *helper = NULL;
 224         struct nf_conn_help *help;
 225         struct net *net = nf_ct_net(ct);
 226
 227         /* We already got a helper explicitly attached. The function
 228          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 229          * the helper up again. Since now the user is in full control of
 230          * making consistent helper configurations, skip this automatic
 231          * re-lookup, otherwise we'll lose the helper.
 232          */
 233         if (test_bit(IPS_HELPER_BIT, &ct->status))
 234                 return 0;
 235
 236         if (tmpl != NULL) {
 237                 help = nfct_help(tmpl);
 238                 if (help != NULL) {
 239                         helper = help->helper;
 240                         set_bit(IPS_HELPER_BIT, &ct->status);
 241                 }
 242         }
 243
 244         help = nfct_help(ct);
 245
 246         if (helper == NULL) {
 247                 helper = nf_ct_lookup_helper(ct, net);
 248                 if (helper == NULL) {
 249                         if (help)
 250                                 RCU_INIT_POINTER(help->helper, NULL);
 251                         return 0;
 252                 }
 253         }
 254
 255         if (help == NULL) {
 256                 help = nf_ct_helper_ext_add(ct, helper, flags);
 257                 if (help == NULL)
 258                         return -ENOMEM;
 259         } else {
 260                 /* We only allow helper re-assignment of the same sort since
 261                  * we cannot reallocate the helper extension area.
 262                  */
 263                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 264
 265                 if (tmp && tmp->help != helper->help) {
 266                         RCU_INIT_POINTER(help->helper, NULL);
 267                         return 0;
 268                 }
 269         }
 270
 271         rcu_assign_pointer(help->helper, helper);
 272
 273         return 0;
 274 }
 275 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 276
 277 /* appropriate ct lock protecting must be taken by caller */
 278 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 279                          const struct nf_conntrack_helper *me)
 280 {
 281         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 282         struct nf_conn_help *help = nfct_help(ct);
 283
 284         if (help && rcu_dereference_raw(help->helper) == me) {
 285                 nf_conntrack_event(IPCT_HELPER, ct);
 286                 RCU_INIT_POINTER(help->helper, NULL);
 287         }
 288         return 0;
 289 }
 290
 291 void nf_ct_helper_destroy(struct nf_conn *ct)
 292 {
 293         struct nf_conn_help *help = nfct_help(ct);
 294         struct nf_conntrack_helper *helper;
 295
 296         if (help) {
 297                 rcu_read_lock();
 298                 helper = rcu_dereference(help->helper);
 299                 if (helper && helper->destroy)
 300                         helper->destroy(ct);
 301                 rcu_read_unlock();
 302         }
 303 }
 304
 305 static LIST_HEAD(nf_ct_helper_expectfn_list);
 306
 307 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 308 {
 309         spin_lock_bh(&nf_conntrack_expect_lock);
 310         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 311         spin_unlock_bh(&nf_conntrack_expect_lock);
 312 }
 313 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 314
 315 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 316 {
 317         spin_lock_bh(&nf_conntrack_expect_lock);
 318         list_del_rcu(&n->head);
 319         spin_unlock_bh(&nf_conntrack_expect_lock);
 320 }
 321 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 322
 323 /* Caller should hold the rcu lock */
 324 struct nf_ct_helper_expectfn *
 325 nf_ct_helper_expectfn_find_by_name(const char *name)
 326 {
 327         struct nf_ct_helper_expectfn *cur;
 328         bool found = false;
 329
 330         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 331                 if (!strcmp(cur->name, name)) {
 332                         found = true;
 333                         break;
 334                 }
 335         }
 336         return found ? cur : NULL;
 337 }
 338 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 339
 340 /* Caller should hold the rcu lock */
 341 struct nf_ct_helper_expectfn *
 342 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 343 {
 344         struct nf_ct_helper_expectfn *cur;
 345         bool found = false;
 346
 347         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 348                 if (cur->expectfn == symbol) {
 349                         found = true;
 350                         break;
 351                 }
 352         }
 353         return found ? cur : NULL;
 354 }
 355 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 356
 357 __printf(3, 4)
 358 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 359                       const char *fmt, ...)
 360 {
 361         const struct nf_conn_help *help;
 362         const struct nf_conntrack_helper *helper;
 363         struct va_format vaf;
 364         va_list args;
 365
 366         va_start(args, fmt);
 367
 368         vaf.fmt = fmt;
 369         vaf.va = &args;
 370
 371         /* Called from the helper function, this call never fails */
 372         help = nfct_help(ct);
 373
 374         /* rcu_read_lock()ed by nf_hook_thresh */
 375         helper = rcu_dereference(help->helper);
 376
 377         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 378                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 379
 380         va_end(args);
 381 }
 382 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 383
 384 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 385 {
 386         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 387         unsigned int h = helper_hash(&me->tuple);
 388         struct nf_conntrack_helper *cur;
 389         int ret = 0;
 390
 391         BUG_ON(me->expect_policy == NULL);
 392         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 393         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 394
 395         mutex_lock(&nf_ct_helper_mutex);
 396         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 397                 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, &mask)) {
 398                         ret = -EEXIST;
 399                         goto out;
 400                 }
 401         }
 402         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 403         nf_ct_helper_count++;
 404 out:
 405         mutex_unlock(&nf_ct_helper_mutex);
 406         return ret;
 407 }
 408 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 409
 410 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 411                                              struct net *net)
 412 {
 413         struct nf_conntrack_tuple_hash *h;
 414         const struct hlist_nulls_node *nn;
 415         int cpu;
 416
 417         /* Get rid of expecteds, set helpers to NULL. */
 418         for_each_possible_cpu(cpu) {
 419                 struct ct_pcpu *pcpu = per_cpu_ptr(net->ct.pcpu_lists, cpu);
 420
 421                 spin_lock_bh(&pcpu->lock);
 422                 hlist_nulls_for_each_entry(h, nn, &pcpu->unconfirmed, hnnode)
 423                         unhelp(h, me);
 424                 spin_unlock_bh(&pcpu->lock);
 425         }
 426 }
 427
 428 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 429 {
 430         struct nf_conntrack_tuple_hash *h;
 431         struct nf_conntrack_expect *exp;
 432         const struct hlist_node *next;
 433         const struct hlist_nulls_node *nn;
 434         unsigned int last_hsize;
 435         spinlock_t *lock;
 436         struct net *net;
 437         unsigned int i;
 438
 439         mutex_lock(&nf_ct_helper_mutex);
 440         hlist_del_rcu(&me->hnode);
 441         nf_ct_helper_count--;
 442         mutex_unlock(&nf_ct_helper_mutex);
 443
 444         /* Make sure every nothing is still using the helper unless its a
 445          * connection in the hash.
 446          */
 447         synchronize_rcu();
 448
 449         /* Get rid of expectations */
 450         spin_lock_bh(&nf_conntrack_expect_lock);
 451         for (i = 0; i < nf_ct_expect_hsize; i++) {
 452                 hlist_for_each_entry_safe(exp, next,
 453                                           &nf_ct_expect_hash[i], hnode) {
 454                         struct nf_conn_help *help = nfct_help(exp->master);
 455                         if ((rcu_dereference_protected(
 456                                         help->helper,
 457                                         lockdep_is_held(&nf_conntrack_expect_lock)
 458                                         ) == me || exp->helper == me) &&
 459                             del_timer(&exp->timeout)) {
 460                                 nf_ct_unlink_expect(exp);
 461                                 nf_ct_expect_put(exp);
 462                         }
 463                 }
 464         }
 465         spin_unlock_bh(&nf_conntrack_expect_lock);
 466
 467         rtnl_lock();
 468         for_each_net(net)
 469                 __nf_conntrack_helper_unregister(me, net);
 470         rtnl_unlock();
 471
 472         local_bh_disable();
 473 restart:
 474         last_hsize = nf_conntrack_htable_size;
 475         for (i = 0; i < last_hsize; i++) {
 476                 lock = &nf_conntrack_locks[i % CONNTRACK_LOCKS];
 477                 nf_conntrack_lock(lock);
 478                 if (last_hsize != nf_conntrack_htable_size) {
 479                         spin_unlock(lock);
 480                         goto restart;
 481                 }
 482                 hlist_nulls_for_each_entry(h, nn, &nf_conntrack_hash[i], hnnode)
 483                         unhelp(h, me);
 484                 spin_unlock(lock);
 485         }
 486         local_bh_enable();
 487 }
 488 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 489
 490 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 491                        u16 l3num, u16 protonum, const char *name,
 492                        u16 default_port, u16 spec_port, u32 id,
 493                        const struct nf_conntrack_expect_policy *exp_pol,
 494                        u32 expect_class_max, u32 data_len,
 495                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 496                                    struct nf_conn *ct,
 497                                    enum ip_conntrack_info ctinfo),
 498                        int (*from_nlattr)(struct nlattr *attr,
 499                                           struct nf_conn *ct),
 500                        struct module *module)
 501 {
 502         helper->tuple.src.l3num = l3num;
 503         helper->tuple.dst.protonum = protonum;
 504         helper->tuple.src.u.all = htons(spec_port);
 505         helper->expect_policy = exp_pol;
 506         helper->expect_class_max = expect_class_max;
 507         helper->data_len = data_len;
 508         helper->help = help;
 509         helper->from_nlattr = from_nlattr;
 510         helper->me = module;
 511
 512         if (spec_port == default_port)
 513                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 514         else
 515                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 516 }
 517 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 518
 519 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 520                                   unsigned int n)
 521 {
 522         unsigned int i;
 523         int err = 0;
 524
 525         for (i = 0; i < n; i++) {
 526                 err = nf_conntrack_helper_register(&helper[i]);
 527                 if (err < 0)
 528                         goto err;
 529         }
 530
 531         return err;
 532 err:
 533         if (i > 0)
 534                 nf_conntrack_helpers_unregister(helper, i);
 535         return err;
 536 }
 537 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 538
 539 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 540                                 unsigned int n)
 541 {
 542         while (n-- > 0)
 543                 nf_conntrack_helper_unregister(&helper[n]);
 544 }
 545 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 546
 547 static struct nf_ct_ext_type helper_extend __read_mostly = {
 548         .len    = sizeof(struct nf_conn_help),
 549         .align  = __alignof__(struct nf_conn_help),
 550         .id     = NF_CT_EXT_HELPER,
 551 };
 552
 553 int nf_conntrack_helper_pernet_init(struct net *net)
 554 {
 555         net->ct.auto_assign_helper_warned = false;
 556         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 557         return nf_conntrack_helper_init_sysctl(net);
 558 }
 559
 560 void nf_conntrack_helper_pernet_fini(struct net *net)
 561 {
 562         nf_conntrack_helper_fini_sysctl(net);
 563 }
 564
 565 int nf_conntrack_helper_init(void)
 566 {
 567         int ret;
 568         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 569         nf_ct_helper_hash =
 570                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 571         if (!nf_ct_helper_hash)
 572                 return -ENOMEM;
 573
 574         ret = nf_ct_extend_register(&helper_extend);
 575         if (ret < 0) {
 576                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 577                 goto out_extend;
 578         }
 579
 580         return 0;
 581 out_extend:
 582         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 583         return ret;
 584 }
 585
 586 void nf_conntrack_helper_fini(void)
 587 {
 588         nf_ct_extend_unregister(&helper_extend);
 589         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 590 }