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         if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 178                 module_put(h->me);
 179                 h = NULL;
 180         }
 181
 182         rcu_read_unlock();
 183
 184         return h;
 185 }
 186 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 187
 188 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 189 {
 190         refcount_dec(&helper->refcnt);
 191         module_put(helper->me);
 192 }
 193 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 194
 195 struct nf_conn_help *
 196 nf_ct_helper_ext_add(struct nf_conn *ct,
 197                      struct nf_conntrack_helper *helper, gfp_t gfp)
 198 {
 199         struct nf_conn_help *help;
 200
 201         help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 202         if (help)
 203                 INIT_HLIST_HEAD(&help->expectations);
 204         else
 205                 pr_debug("failed to add helper extension area");
 206         return help;
 207 }
 208 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 209
 210 static struct nf_conntrack_helper *
 211 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 212 {
 213         if (!net->ct.sysctl_auto_assign_helper) {
 214                 if (net->ct.auto_assign_helper_warned)
 215                         return NULL;
 216                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 217                         return NULL;
 218                 pr_info("nf_conntrack: default automatic helper assignment "
 219                         "has been turned off for security reasons and CT-based "
 220                         " firewall rule not found. Use the iptables CT target "
 221                         "to attach helpers instead.\n");
 222                 net->ct.auto_assign_helper_warned = 1;
 223                 return NULL;
 224         }
 225
 226         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 227 }
 228
 229
 230 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 231                               gfp_t flags)
 232 {
 233         struct nf_conntrack_helper *helper = NULL;
 234         struct nf_conn_help *help;
 235         struct net *net = nf_ct_net(ct);
 236
 237         /* We already got a helper explicitly attached. The function
 238          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 239          * the helper up again. Since now the user is in full control of
 240          * making consistent helper configurations, skip this automatic
 241          * re-lookup, otherwise we'll lose the helper.
 242          */
 243         if (test_bit(IPS_HELPER_BIT, &ct->status))
 244                 return 0;
 245
 246         if (tmpl != NULL) {
 247                 help = nfct_help(tmpl);
 248                 if (help != NULL) {
 249                         helper = help->helper;
 250                         set_bit(IPS_HELPER_BIT, &ct->status);
 251                 }
 252         }
 253
 254         help = nfct_help(ct);
 255
 256         if (helper == NULL) {
 257                 helper = nf_ct_lookup_helper(ct, net);
 258                 if (helper == NULL) {
 259                         if (help)
 260                                 RCU_INIT_POINTER(help->helper, NULL);
 261                         return 0;
 262                 }
 263         }
 264
 265         if (help == NULL) {
 266                 help = nf_ct_helper_ext_add(ct, helper, flags);
 267                 if (help == NULL)
 268                         return -ENOMEM;
 269         } else {
 270                 /* We only allow helper re-assignment of the same sort since
 271                  * we cannot reallocate the helper extension area.
 272                  */
 273                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 274
 275                 if (tmp && tmp->help != helper->help) {
 276                         RCU_INIT_POINTER(help->helper, NULL);
 277                         return 0;
 278                 }
 279         }
 280
 281         rcu_assign_pointer(help->helper, helper);
 282
 283         return 0;
 284 }
 285 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 286
 287 /* appropriate ct lock protecting must be taken by caller */
 288 static int unhelp(struct nf_conn *ct, void *me)
 289 {
 290         struct nf_conn_help *help = nfct_help(ct);
 291
 292         if (help && rcu_dereference_raw(help->helper) == me) {
 293                 nf_conntrack_event(IPCT_HELPER, ct);
 294                 RCU_INIT_POINTER(help->helper, NULL);
 295         }
 296
 297         /* We are not intended to delete this conntrack. */
 298         return 0;
 299 }
 300
 301 void nf_ct_helper_destroy(struct nf_conn *ct)
 302 {
 303         struct nf_conn_help *help = nfct_help(ct);
 304         struct nf_conntrack_helper *helper;
 305
 306         if (help) {
 307                 rcu_read_lock();
 308                 helper = rcu_dereference(help->helper);
 309                 if (helper && helper->destroy)
 310                         helper->destroy(ct);
 311                 rcu_read_unlock();
 312         }
 313 }
 314
 315 static LIST_HEAD(nf_ct_helper_expectfn_list);
 316
 317 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 318 {
 319         spin_lock_bh(&nf_conntrack_expect_lock);
 320         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 321         spin_unlock_bh(&nf_conntrack_expect_lock);
 322 }
 323 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 324
 325 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 326 {
 327         spin_lock_bh(&nf_conntrack_expect_lock);
 328         list_del_rcu(&n->head);
 329         spin_unlock_bh(&nf_conntrack_expect_lock);
 330 }
 331 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 332
 333 /* Caller should hold the rcu lock */
 334 struct nf_ct_helper_expectfn *
 335 nf_ct_helper_expectfn_find_by_name(const char *name)
 336 {
 337         struct nf_ct_helper_expectfn *cur;
 338         bool found = false;
 339
 340         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 341                 if (!strcmp(cur->name, name)) {
 342                         found = true;
 343                         break;
 344                 }
 345         }
 346         return found ? cur : NULL;
 347 }
 348 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 349
 350 /* Caller should hold the rcu lock */
 351 struct nf_ct_helper_expectfn *
 352 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 353 {
 354         struct nf_ct_helper_expectfn *cur;
 355         bool found = false;
 356
 357         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 358                 if (cur->expectfn == symbol) {
 359                         found = true;
 360                         break;
 361                 }
 362         }
 363         return found ? cur : NULL;
 364 }
 365 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 366
 367 __printf(3, 4)
 368 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 369                       const char *fmt, ...)
 370 {
 371         const struct nf_conn_help *help;
 372         const struct nf_conntrack_helper *helper;
 373         struct va_format vaf;
 374         va_list args;
 375
 376         va_start(args, fmt);
 377
 378         vaf.fmt = fmt;
 379         vaf.va = &args;
 380
 381         /* Called from the helper function, this call never fails */
 382         help = nfct_help(ct);
 383
 384         /* rcu_read_lock()ed by nf_hook_thresh */
 385         helper = rcu_dereference(help->helper);
 386
 387         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 388                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 389
 390         va_end(args);
 391 }
 392 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 393
 394 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 395 {
 396         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 397         unsigned int h = helper_hash(&me->tuple);
 398         struct nf_conntrack_helper *cur;
 399         int ret = 0, i;
 400
 401         BUG_ON(me->expect_policy == NULL);
 402         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 403         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 404
 405         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 406                 return -EINVAL;
 407
 408         mutex_lock(&nf_ct_helper_mutex);
 409         for (i = 0; i < nf_ct_helper_hsize; i++) {
 410                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 411                         if (!strcmp(cur->name, me->name) &&
 412                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 413                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 414                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 415                                 ret = -EEXIST;
 416                                 goto out;
 417                         }
 418                 }
 419         }
 420
 421         /* avoid unpredictable behaviour for auto_assign_helper */
 422         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 423                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 424                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 425                                                      &mask)) {
 426                                 ret = -EEXIST;
 427                                 goto out;
 428                         }
 429                 }
 430         }
 431         refcount_set(&me->refcnt, 1);
 432         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 433         nf_ct_helper_count++;
 434 out:
 435         mutex_unlock(&nf_ct_helper_mutex);
 436         return ret;
 437 }
 438 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 439
 440 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 441 {
 442         struct nf_conn_help *help = nfct_help(exp->master);
 443         const struct nf_conntrack_helper *me = data;
 444         const struct nf_conntrack_helper *this;
 445
 446         if (exp->helper == me)
 447                 return true;
 448
 449         this = rcu_dereference_protected(help->helper,
 450                                          lockdep_is_held(&nf_conntrack_expect_lock));
 451         return this == me;
 452 }
 453
 454 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 455 {
 456         mutex_lock(&nf_ct_helper_mutex);
 457         hlist_del_rcu(&me->hnode);
 458         nf_ct_helper_count--;
 459         mutex_unlock(&nf_ct_helper_mutex);
 460
 461         /* Make sure every nothing is still using the helper unless its a
 462          * connection in the hash.
 463          */
 464         synchronize_rcu();
 465
 466         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 467         nf_ct_iterate_destroy(unhelp, me);
 468
 469         /* Maybe someone has gotten the helper already when unhelp above.
 470          * So need to wait it.
 471          */
 472         synchronize_rcu();
 473 }
 474 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 475
 476 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 477                        u16 l3num, u16 protonum, const char *name,
 478                        u16 default_port, u16 spec_port, u32 id,
 479                        const struct nf_conntrack_expect_policy *exp_pol,
 480                        u32 expect_class_max,
 481                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 482                                    struct nf_conn *ct,
 483                                    enum ip_conntrack_info ctinfo),
 484                        int (*from_nlattr)(struct nlattr *attr,
 485                                           struct nf_conn *ct),
 486                        struct module *module)
 487 {
 488         helper->tuple.src.l3num = l3num;
 489         helper->tuple.dst.protonum = protonum;
 490         helper->tuple.src.u.all = htons(spec_port);
 491         helper->expect_policy = exp_pol;
 492         helper->expect_class_max = expect_class_max;
 493         helper->help = help;
 494         helper->from_nlattr = from_nlattr;
 495         helper->me = module;
 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 static const struct nf_ct_ext_type helper_extend = {
 533         .len    = sizeof(struct nf_conn_help),
 534         .align  = __alignof__(struct nf_conn_help),
 535         .id     = NF_CT_EXT_HELPER,
 536 };
 537
 538 int nf_conntrack_helper_pernet_init(struct net *net)
 539 {
 540         net->ct.auto_assign_helper_warned = false;
 541         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 542         return nf_conntrack_helper_init_sysctl(net);
 543 }
 544
 545 void nf_conntrack_helper_pernet_fini(struct net *net)
 546 {
 547         nf_conntrack_helper_fini_sysctl(net);
 548 }
 549
 550 int nf_conntrack_helper_init(void)
 551 {
 552         int ret;
 553         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 554         nf_ct_helper_hash =
 555                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 556         if (!nf_ct_helper_hash)
 557                 return -ENOMEM;
 558
 559         ret = nf_ct_extend_register(&helper_extend);
 560         if (ret < 0) {
 561                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 562                 goto out_extend;
 563         }
 564
 565         return 0;
 566 out_extend:
 567         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 568         return ret;
 569 }
 570
 571 void nf_conntrack_helper_fini(void)
 572 {
 573         nf_ct_extend_unregister(&helper_extend);
 574         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 575 }