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