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(ct, NF_CT_EXT_HELPER, gfp);
 191         if (help)
 192                 INIT_HLIST_HEAD(&help->expectations);
 193         else
 194                 pr_debug("failed to add helper extension area");
 195         return help;
 196 }
 197 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 198
 199 static struct nf_conntrack_helper *
 200 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 201 {
 202         if (!net->ct.sysctl_auto_assign_helper) {
 203                 if (net->ct.auto_assign_helper_warned)
 204                         return NULL;
 205                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 206                         return NULL;
 207                 pr_info("nf_conntrack: default automatic helper assignment "
 208                         "has been turned off for security reasons and CT-based "
 209                         " firewall rule not found. Use the iptables CT target "
 210                         "to attach helpers instead.\n");
 211                 net->ct.auto_assign_helper_warned = 1;
 212                 return NULL;
 213         }
 214
 215         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 216 }
 217
 218
 219 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 220                               gfp_t flags)
 221 {
 222         struct nf_conntrack_helper *helper = NULL;
 223         struct nf_conn_help *help;
 224         struct net *net = nf_ct_net(ct);
 225
 226         /* We already got a helper explicitly attached. The function
 227          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 228          * the helper up again. Since now the user is in full control of
 229          * making consistent helper configurations, skip this automatic
 230          * re-lookup, otherwise we'll lose the helper.
 231          */
 232         if (test_bit(IPS_HELPER_BIT, &ct->status))
 233                 return 0;
 234
 235         if (tmpl != NULL) {
 236                 help = nfct_help(tmpl);
 237                 if (help != NULL) {
 238                         helper = help->helper;
 239                         set_bit(IPS_HELPER_BIT, &ct->status);
 240                 }
 241         }
 242
 243         help = nfct_help(ct);
 244
 245         if (helper == NULL) {
 246                 helper = nf_ct_lookup_helper(ct, net);
 247                 if (helper == NULL) {
 248                         if (help)
 249                                 RCU_INIT_POINTER(help->helper, NULL);
 250                         return 0;
 251                 }
 252         }
 253
 254         if (help == NULL) {
 255                 help = nf_ct_helper_ext_add(ct, helper, flags);
 256                 if (help == NULL)
 257                         return -ENOMEM;
 258         } else {
 259                 /* We only allow helper re-assignment of the same sort since
 260                  * we cannot reallocate the helper extension area.
 261                  */
 262                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 263
 264                 if (tmp && tmp->help != helper->help) {
 265                         RCU_INIT_POINTER(help->helper, NULL);
 266                         return 0;
 267                 }
 268         }
 269
 270         rcu_assign_pointer(help->helper, helper);
 271
 272         return 0;
 273 }
 274 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 275
 276 /* appropriate ct lock protecting must be taken by caller */
 277 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 278                          const struct nf_conntrack_helper *me)
 279 {
 280         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 281         struct nf_conn_help *help = nfct_help(ct);
 282
 283         if (help && rcu_dereference_raw(help->helper) == me) {
 284                 nf_conntrack_event(IPCT_HELPER, ct);
 285                 RCU_INIT_POINTER(help->helper, NULL);
 286         }
 287         return 0;
 288 }
 289
 290 void nf_ct_helper_destroy(struct nf_conn *ct)
 291 {
 292         struct nf_conn_help *help = nfct_help(ct);
 293         struct nf_conntrack_helper *helper;
 294
 295         if (help) {
 296                 rcu_read_lock();
 297                 helper = rcu_dereference(help->helper);
 298                 if (helper && helper->destroy)
 299                         helper->destroy(ct);
 300                 rcu_read_unlock();
 301         }
 302 }
 303
 304 static LIST_HEAD(nf_ct_helper_expectfn_list);
 305
 306 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 307 {
 308         spin_lock_bh(&nf_conntrack_expect_lock);
 309         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 310         spin_unlock_bh(&nf_conntrack_expect_lock);
 311 }
 312 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 313
 314 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 315 {
 316         spin_lock_bh(&nf_conntrack_expect_lock);
 317         list_del_rcu(&n->head);
 318         spin_unlock_bh(&nf_conntrack_expect_lock);
 319 }
 320 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 321
 322 /* Caller should hold the rcu lock */
 323 struct nf_ct_helper_expectfn *
 324 nf_ct_helper_expectfn_find_by_name(const char *name)
 325 {
 326         struct nf_ct_helper_expectfn *cur;
 327         bool found = false;
 328
 329         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 330                 if (!strcmp(cur->name, name)) {
 331                         found = true;
 332                         break;
 333                 }
 334         }
 335         return found ? cur : NULL;
 336 }
 337 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 338
 339 /* Caller should hold the rcu lock */
 340 struct nf_ct_helper_expectfn *
 341 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 342 {
 343         struct nf_ct_helper_expectfn *cur;
 344         bool found = false;
 345
 346         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 347                 if (cur->expectfn == symbol) {
 348                         found = true;
 349                         break;
 350                 }
 351         }
 352         return found ? cur : NULL;
 353 }
 354 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 355
 356 __printf(3, 4)
 357 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 358                       const char *fmt, ...)
 359 {
 360         const struct nf_conn_help *help;
 361         const struct nf_conntrack_helper *helper;
 362         struct va_format vaf;
 363         va_list args;
 364
 365         va_start(args, fmt);
 366
 367         vaf.fmt = fmt;
 368         vaf.va = &args;
 369
 370         /* Called from the helper function, this call never fails */
 371         help = nfct_help(ct);
 372
 373         /* rcu_read_lock()ed by nf_hook_thresh */
 374         helper = rcu_dereference(help->helper);
 375
 376         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 377                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 378
 379         va_end(args);
 380 }
 381 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 382
 383 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 384 {
 385         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 386         unsigned int h = helper_hash(&me->tuple);
 387         struct nf_conntrack_helper *cur;
 388         int ret = 0, i;
 389
 390         BUG_ON(me->expect_policy == NULL);
 391         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 392         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 393
 394         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 395                 return -EINVAL;
 396
 397         mutex_lock(&nf_ct_helper_mutex);
 398         for (i = 0; i < nf_ct_helper_hsize; i++) {
 399                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 400                         if (!strcmp(cur->name, me->name) &&
 401                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 402                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 403                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 404                                 ret = -EEXIST;
 405                                 goto out;
 406                         }
 407                 }
 408         }
 409
 410         /* avoid unpredictable behaviour for auto_assign_helper */
 411         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 412                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 413                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 414                                                      &mask)) {
 415                                 ret = -EEXIST;
 416                                 goto out;
 417                         }
 418                 }
 419         }
 420         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 421         nf_ct_helper_count++;
 422 out:
 423         mutex_unlock(&nf_ct_helper_mutex);
 424         return ret;
 425 }
 426 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 427
 428 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 429                                              struct net *net)
 430 {
 431         struct nf_conntrack_tuple_hash *h;
 432         const struct hlist_nulls_node *nn;
 433         int cpu;
 434
 435         /* Get rid of expecteds, set helpers to NULL. */
 436         for_each_possible_cpu(cpu) {
 437                 struct ct_pcpu *pcpu = per_cpu_ptr(net->ct.pcpu_lists, cpu);
 438
 439                 spin_lock_bh(&pcpu->lock);
 440                 hlist_nulls_for_each_entry(h, nn, &pcpu->unconfirmed, hnnode)
 441                         unhelp(h, me);
 442                 spin_unlock_bh(&pcpu->lock);
 443         }
 444 }
 445
 446 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 447 {
 448         struct nf_conntrack_tuple_hash *h;
 449         struct nf_conntrack_expect *exp;
 450         const struct hlist_node *next;
 451         const struct hlist_nulls_node *nn;
 452         unsigned int last_hsize;
 453         spinlock_t *lock;
 454         struct net *net;
 455         unsigned int i;
 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         /* Get rid of expectations */
 468         spin_lock_bh(&nf_conntrack_expect_lock);
 469         for (i = 0; i < nf_ct_expect_hsize; i++) {
 470                 hlist_for_each_entry_safe(exp, next,
 471                                           &nf_ct_expect_hash[i], hnode) {
 472                         struct nf_conn_help *help = nfct_help(exp->master);
 473                         if ((rcu_dereference_protected(
 474                                         help->helper,
 475                                         lockdep_is_held(&nf_conntrack_expect_lock)
 476                                         ) == me || exp->helper == me))
 477                                 nf_ct_remove_expect(exp);
 478                 }
 479         }
 480         spin_unlock_bh(&nf_conntrack_expect_lock);
 481
 482         rtnl_lock();
 483         for_each_net(net)
 484                 __nf_conntrack_helper_unregister(me, net);
 485         rtnl_unlock();
 486
 487         local_bh_disable();
 488 restart:
 489         last_hsize = nf_conntrack_htable_size;
 490         for (i = 0; i < last_hsize; i++) {
 491                 lock = &nf_conntrack_locks[i % CONNTRACK_LOCKS];
 492                 nf_conntrack_lock(lock);
 493                 if (last_hsize != nf_conntrack_htable_size) {
 494                         spin_unlock(lock);
 495                         goto restart;
 496                 }
 497                 hlist_nulls_for_each_entry(h, nn, &nf_conntrack_hash[i], hnnode)
 498                         unhelp(h, me);
 499                 spin_unlock(lock);
 500         }
 501         local_bh_enable();
 502 }
 503 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 504
 505 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 506                        u16 l3num, u16 protonum, const char *name,
 507                        u16 default_port, u16 spec_port, u32 id,
 508                        const struct nf_conntrack_expect_policy *exp_pol,
 509                        u32 expect_class_max,
 510                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 511                                    struct nf_conn *ct,
 512                                    enum ip_conntrack_info ctinfo),
 513                        int (*from_nlattr)(struct nlattr *attr,
 514                                           struct nf_conn *ct),
 515                        struct module *module)
 516 {
 517         helper->tuple.src.l3num = l3num;
 518         helper->tuple.dst.protonum = protonum;
 519         helper->tuple.src.u.all = htons(spec_port);
 520         helper->expect_policy = exp_pol;
 521         helper->expect_class_max = expect_class_max;
 522         helper->help = help;
 523         helper->from_nlattr = from_nlattr;
 524         helper->me = module;
 525
 526         if (spec_port == default_port)
 527                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 528         else
 529                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 530 }
 531 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 532
 533 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 534                                   unsigned int n)
 535 {
 536         unsigned int i;
 537         int err = 0;
 538
 539         for (i = 0; i < n; i++) {
 540                 err = nf_conntrack_helper_register(&helper[i]);
 541                 if (err < 0)
 542                         goto err;
 543         }
 544
 545         return err;
 546 err:
 547         if (i > 0)
 548                 nf_conntrack_helpers_unregister(helper, i);
 549         return err;
 550 }
 551 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 552
 553 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 554                                 unsigned int n)
 555 {
 556         while (n-- > 0)
 557                 nf_conntrack_helper_unregister(&helper[n]);
 558 }
 559 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 560
 561 static const struct nf_ct_ext_type helper_extend = {
 562         .len    = sizeof(struct nf_conn_help),
 563         .align  = __alignof__(struct nf_conn_help),
 564         .id     = NF_CT_EXT_HELPER,
 565 };
 566
 567 int nf_conntrack_helper_pernet_init(struct net *net)
 568 {
 569         net->ct.auto_assign_helper_warned = false;
 570         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 571         return nf_conntrack_helper_init_sysctl(net);
 572 }
 573
 574 void nf_conntrack_helper_pernet_fini(struct net *net)
 575 {
 576         nf_conntrack_helper_fini_sysctl(net);
 577 }
 578
 579 int nf_conntrack_helper_init(void)
 580 {
 581         int ret;
 582         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 583         nf_ct_helper_hash =
 584                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 585         if (!nf_ct_helper_hash)
 586                 return -ENOMEM;
 587
 588         ret = nf_ct_extend_register(&helper_extend);
 589         if (ret < 0) {
 590                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 591                 goto out_extend;
 592         }
 593
 594         return 0;
 595 out_extend:
 596         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 597         return ret;
 598 }
 599
 600 void nf_conntrack_helper_fini(void)
 601 {
 602         nf_ct_extend_unregister(&helper_extend);
 603         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 604 }