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         h = __nf_conntrack_helper_find(name, l3num, protonum);
 162 #ifdef CONFIG_MODULES
 163         if (h == NULL) {
 164                 if (request_module("nfct-helper-%s", name) == 0)
 165                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 166         }
 167 #endif
 168         if (h != NULL && !try_module_get(h->me))
 169                 h = NULL;
 170
 171         return h;
 172 }
 173 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 174
 175 struct nf_conn_help *
 176 nf_ct_helper_ext_add(struct nf_conn *ct,
 177                      struct nf_conntrack_helper *helper, gfp_t gfp)
 178 {
 179         struct nf_conn_help *help;
 180
 181         help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
 182                                     helper->data_len, gfp);
 183         if (help)
 184                 INIT_HLIST_HEAD(&help->expectations);
 185         else
 186                 pr_debug("failed to add helper extension area");
 187         return help;
 188 }
 189 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 190
 191 static struct nf_conntrack_helper *
 192 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 193 {
 194         if (!net->ct.sysctl_auto_assign_helper) {
 195                 if (net->ct.auto_assign_helper_warned)
 196                         return NULL;
 197                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 198                         return NULL;
 199                 pr_info("nf_conntrack: default automatic helper assignment "
 200                         "has been turned off for security reasons and CT-based "
 201                         " firewall rule not found. Use the iptables CT target "
 202                         "to attach helpers instead.\n");
 203                 net->ct.auto_assign_helper_warned = 1;
 204                 return NULL;
 205         }
 206
 207         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 208 }
 209
 210
 211 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 212                               gfp_t flags)
 213 {
 214         struct nf_conntrack_helper *helper = NULL;
 215         struct nf_conn_help *help;
 216         struct net *net = nf_ct_net(ct);
 217
 218         /* We already got a helper explicitly attached. The function
 219          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 220          * the helper up again. Since now the user is in full control of
 221          * making consistent helper configurations, skip this automatic
 222          * re-lookup, otherwise we'll lose the helper.
 223          */
 224         if (test_bit(IPS_HELPER_BIT, &ct->status))
 225                 return 0;
 226
 227         if (tmpl != NULL) {
 228                 help = nfct_help(tmpl);
 229                 if (help != NULL) {
 230                         helper = help->helper;
 231                         set_bit(IPS_HELPER_BIT, &ct->status);
 232                 }
 233         }
 234
 235         help = nfct_help(ct);
 236
 237         if (helper == NULL) {
 238                 helper = nf_ct_lookup_helper(ct, net);
 239                 if (helper == NULL) {
 240                         if (help)
 241                                 RCU_INIT_POINTER(help->helper, NULL);
 242                         return 0;
 243                 }
 244         }
 245
 246         if (help == NULL) {
 247                 help = nf_ct_helper_ext_add(ct, helper, flags);
 248                 if (help == NULL)
 249                         return -ENOMEM;
 250         } else {
 251                 /* We only allow helper re-assignment of the same sort since
 252                  * we cannot reallocate the helper extension area.
 253                  */
 254                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 255
 256                 if (tmp && tmp->help != helper->help) {
 257                         RCU_INIT_POINTER(help->helper, NULL);
 258                         return 0;
 259                 }
 260         }
 261
 262         rcu_assign_pointer(help->helper, helper);
 263
 264         return 0;
 265 }
 266 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 267
 268 /* appropriate ct lock protecting must be taken by caller */
 269 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 270                          const struct nf_conntrack_helper *me)
 271 {
 272         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 273         struct nf_conn_help *help = nfct_help(ct);
 274
 275         if (help && rcu_dereference_raw(help->helper) == me) {
 276                 nf_conntrack_event(IPCT_HELPER, ct);
 277                 RCU_INIT_POINTER(help->helper, NULL);
 278         }
 279         return 0;
 280 }
 281
 282 void nf_ct_helper_destroy(struct nf_conn *ct)
 283 {
 284         struct nf_conn_help *help = nfct_help(ct);
 285         struct nf_conntrack_helper *helper;
 286
 287         if (help) {
 288                 rcu_read_lock();
 289                 helper = rcu_dereference(help->helper);
 290                 if (helper && helper->destroy)
 291                         helper->destroy(ct);
 292                 rcu_read_unlock();
 293         }
 294 }
 295
 296 static LIST_HEAD(nf_ct_helper_expectfn_list);
 297
 298 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 299 {
 300         spin_lock_bh(&nf_conntrack_expect_lock);
 301         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 302         spin_unlock_bh(&nf_conntrack_expect_lock);
 303 }
 304 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 305
 306 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 307 {
 308         spin_lock_bh(&nf_conntrack_expect_lock);
 309         list_del_rcu(&n->head);
 310         spin_unlock_bh(&nf_conntrack_expect_lock);
 311 }
 312 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 313
 314 struct nf_ct_helper_expectfn *
 315 nf_ct_helper_expectfn_find_by_name(const char *name)
 316 {
 317         struct nf_ct_helper_expectfn *cur;
 318         bool found = false;
 319
 320         rcu_read_lock();
 321         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 322                 if (!strcmp(cur->name, name)) {
 323                         found = true;
 324                         break;
 325                 }
 326         }
 327         rcu_read_unlock();
 328         return found ? cur : NULL;
 329 }
 330 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 331
 332 struct nf_ct_helper_expectfn *
 333 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 334 {
 335         struct nf_ct_helper_expectfn *cur;
 336         bool found = false;
 337
 338         rcu_read_lock();
 339         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 340                 if (cur->expectfn == symbol) {
 341                         found = true;
 342                         break;
 343                 }
 344         }
 345         rcu_read_unlock();
 346         return found ? cur : NULL;
 347 }
 348 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 349
 350 __printf(3, 4)
 351 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 352                       const char *fmt, ...)
 353 {
 354         const struct nf_conn_help *help;
 355         const struct nf_conntrack_helper *helper;
 356         struct va_format vaf;
 357         va_list args;
 358
 359         va_start(args, fmt);
 360
 361         vaf.fmt = fmt;
 362         vaf.va = &args;
 363
 364         /* Called from the helper function, this call never fails */
 365         help = nfct_help(ct);
 366
 367         /* rcu_read_lock()ed by nf_hook_thresh */
 368         helper = rcu_dereference(help->helper);
 369
 370         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 371                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 372
 373         va_end(args);
 374 }
 375 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 376
 377 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 378 {
 379         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 380         unsigned int h = helper_hash(&me->tuple);
 381         struct nf_conntrack_helper *cur;
 382         int ret = 0;
 383
 384         BUG_ON(me->expect_policy == NULL);
 385         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 386         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 387
 388         mutex_lock(&nf_ct_helper_mutex);
 389         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 390                 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, &mask)) {
 391                         ret = -EEXIST;
 392                         goto out;
 393                 }
 394         }
 395         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 396         nf_ct_helper_count++;
 397 out:
 398         mutex_unlock(&nf_ct_helper_mutex);
 399         return ret;
 400 }
 401 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 402
 403 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 404                                              struct net *net)
 405 {
 406         struct nf_conntrack_tuple_hash *h;
 407         const struct hlist_nulls_node *nn;
 408         int cpu;
 409
 410         /* Get rid of expecteds, set helpers to NULL. */
 411         for_each_possible_cpu(cpu) {
 412                 struct ct_pcpu *pcpu = per_cpu_ptr(net->ct.pcpu_lists, cpu);
 413
 414                 spin_lock_bh(&pcpu->lock);
 415                 hlist_nulls_for_each_entry(h, nn, &pcpu->unconfirmed, hnnode)
 416                         unhelp(h, me);
 417                 spin_unlock_bh(&pcpu->lock);
 418         }
 419 }
 420
 421 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 422 {
 423         struct nf_conntrack_tuple_hash *h;
 424         struct nf_conntrack_expect *exp;
 425         const struct hlist_node *next;
 426         const struct hlist_nulls_node *nn;
 427         unsigned int last_hsize;
 428         spinlock_t *lock;
 429         struct net *net;
 430         unsigned int i;
 431
 432         mutex_lock(&nf_ct_helper_mutex);
 433         hlist_del_rcu(&me->hnode);
 434         nf_ct_helper_count--;
 435         mutex_unlock(&nf_ct_helper_mutex);
 436
 437         /* Make sure every nothing is still using the helper unless its a
 438          * connection in the hash.
 439          */
 440         synchronize_rcu();
 441
 442         /* Get rid of expectations */
 443         spin_lock_bh(&nf_conntrack_expect_lock);
 444         for (i = 0; i < nf_ct_expect_hsize; i++) {
 445                 hlist_for_each_entry_safe(exp, next,
 446                                           &nf_ct_expect_hash[i], hnode) {
 447                         struct nf_conn_help *help = nfct_help(exp->master);
 448                         if ((rcu_dereference_protected(
 449                                         help->helper,
 450                                         lockdep_is_held(&nf_conntrack_expect_lock)
 451                                         ) == me || exp->helper == me) &&
 452                             del_timer(&exp->timeout)) {
 453                                 nf_ct_unlink_expect(exp);
 454                                 nf_ct_expect_put(exp);
 455                         }
 456                 }
 457         }
 458         spin_unlock_bh(&nf_conntrack_expect_lock);
 459
 460         rtnl_lock();
 461         for_each_net(net)
 462                 __nf_conntrack_helper_unregister(me, net);
 463         rtnl_unlock();
 464
 465         local_bh_disable();
 466 restart:
 467         last_hsize = nf_conntrack_htable_size;
 468         for (i = 0; i < last_hsize; i++) {
 469                 lock = &nf_conntrack_locks[i % CONNTRACK_LOCKS];
 470                 nf_conntrack_lock(lock);
 471                 if (last_hsize != nf_conntrack_htable_size) {
 472                         spin_unlock(lock);
 473                         goto restart;
 474                 }
 475                 hlist_nulls_for_each_entry(h, nn, &nf_conntrack_hash[i], hnnode)
 476                         unhelp(h, me);
 477                 spin_unlock(lock);
 478         }
 479         local_bh_enable();
 480 }
 481 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 482
 483 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 484                        u16 l3num, u16 protonum, const char *name,
 485                        u16 default_port, u16 spec_port, u32 id,
 486                        const struct nf_conntrack_expect_policy *exp_pol,
 487                        u32 expect_class_max, u32 data_len,
 488                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 489                                    struct nf_conn *ct,
 490                                    enum ip_conntrack_info ctinfo),
 491                        int (*from_nlattr)(struct nlattr *attr,
 492                                           struct nf_conn *ct),
 493                        struct module *module)
 494 {
 495         helper->tuple.src.l3num = l3num;
 496         helper->tuple.dst.protonum = protonum;
 497         helper->tuple.src.u.all = htons(spec_port);
 498         helper->expect_policy = exp_pol;
 499         helper->expect_class_max = expect_class_max;
 500         helper->data_len = data_len;
 501         helper->help = help;
 502         helper->from_nlattr = from_nlattr;
 503         helper->me = module;
 504
 505         if (spec_port == default_port)
 506                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 507         else
 508                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 509 }
 510 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 511
 512 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 513                                   unsigned int n)
 514 {
 515         unsigned int i;
 516         int err = 0;
 517
 518         for (i = 0; i < n; i++) {
 519                 err = nf_conntrack_helper_register(&helper[i]);
 520                 if (err < 0)
 521                         goto err;
 522         }
 523
 524         return err;
 525 err:
 526         if (i > 0)
 527                 nf_conntrack_helpers_unregister(helper, i);
 528         return err;
 529 }
 530 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 531
 532 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 533                                 unsigned int n)
 534 {
 535         while (n-- > 0)
 536                 nf_conntrack_helper_unregister(&helper[n]);
 537 }
 538 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 539
 540 static struct nf_ct_ext_type helper_extend __read_mostly = {
 541         .len    = sizeof(struct nf_conn_help),
 542         .align  = __alignof__(struct nf_conn_help),
 543         .id     = NF_CT_EXT_HELPER,
 544 };
 545
 546 int nf_conntrack_helper_pernet_init(struct net *net)
 547 {
 548         net->ct.auto_assign_helper_warned = false;
 549         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 550         return nf_conntrack_helper_init_sysctl(net);
 551 }
 552
 553 void nf_conntrack_helper_pernet_fini(struct net *net)
 554 {
 555         nf_conntrack_helper_fini_sysctl(net);
 556 }
 557
 558 int nf_conntrack_helper_init(void)
 559 {
 560         int ret;
 561         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 562         nf_ct_helper_hash =
 563                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 564         if (!nf_ct_helper_hash)
 565                 return -ENOMEM;
 566
 567         ret = nf_ct_extend_register(&helper_extend);
 568         if (ret < 0) {
 569                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 570                 goto out_extend;
 571         }
 572
 573         return 0;
 574 out_extend:
 575         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 576         return ret;
 577 }
 578
 579 void nf_conntrack_helper_fini(void)
 580 {
 581         nf_ct_extend_unregister(&helper_extend);
 582         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 583 }