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                             h->tuple.src.l3num == l3num &&
 143                             h->tuple.dst.protonum == protonum)
 144                                 return h;
 145                 }
 146         }
 147         return NULL;
 148 }
 149 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 150
 151 struct nf_conntrack_helper *
 152 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 153 {
 154         struct nf_conntrack_helper *h;
 155
 156         h = __nf_conntrack_helper_find(name, l3num, protonum);
 157 #ifdef CONFIG_MODULES
 158         if (h == NULL) {
 159                 if (request_module("nfct-helper-%s", name) == 0)
 160                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 161         }
 162 #endif
 163         if (h != NULL && !try_module_get(h->me))
 164                 h = NULL;
 165
 166         return h;
 167 }
 168 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 169
 170 struct nf_conn_help *
 171 nf_ct_helper_ext_add(struct nf_conn *ct,
 172                      struct nf_conntrack_helper *helper, gfp_t gfp)
 173 {
 174         struct nf_conn_help *help;
 175
 176         help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
 177                                     helper->data_len, gfp);
 178         if (help)
 179                 INIT_HLIST_HEAD(&help->expectations);
 180         else
 181                 pr_debug("failed to add helper extension area");
 182         return help;
 183 }
 184 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 185
 186 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 187                               gfp_t flags)
 188 {
 189         struct nf_conntrack_helper *helper = NULL;
 190         struct nf_conn_help *help;
 191         struct net *net = nf_ct_net(ct);
 192
 193         /* We already got a helper explicitly attached. The function
 194          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 195          * the helper up again. Since now the user is in full control of
 196          * making consistent helper configurations, skip this automatic
 197          * re-lookup, otherwise we'll lose the helper.
 198          */
 199         if (test_bit(IPS_HELPER_BIT, &ct->status))
 200                 return 0;
 201
 202         if (tmpl != NULL) {
 203                 help = nfct_help(tmpl);
 204                 if (help != NULL) {
 205                         helper = help->helper;
 206                         set_bit(IPS_HELPER_BIT, &ct->status);
 207                 }
 208         }
 209
 210         help = nfct_help(ct);
 211         if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
 212                 helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 213                 if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
 214                         pr_info("nf_conntrack: automatic helper "
 215                                 "assignment is deprecated and it will "
 216                                 "be removed soon. Use the iptables CT target "
 217                                 "to attach helpers instead.\n");
 218                         net->ct.auto_assign_helper_warned = true;
 219                 }
 220         }
 221
 222         if (helper == NULL) {
 223                 if (help)
 224                         RCU_INIT_POINTER(help->helper, NULL);
 225                 return 0;
 226         }
 227
 228         if (help == NULL) {
 229                 help = nf_ct_helper_ext_add(ct, helper, flags);
 230                 if (help == NULL)
 231                         return -ENOMEM;
 232         } else {
 233                 /* We only allow helper re-assignment of the same sort since
 234                  * we cannot reallocate the helper extension area.
 235                  */
 236                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 237
 238                 if (tmp && tmp->help != helper->help) {
 239                         RCU_INIT_POINTER(help->helper, NULL);
 240                         return 0;
 241                 }
 242         }
 243
 244         rcu_assign_pointer(help->helper, helper);
 245
 246         return 0;
 247 }
 248 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 249
 250 /* appropriate ct lock protecting must be taken by caller */
 251 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 252                          const struct nf_conntrack_helper *me)
 253 {
 254         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 255         struct nf_conn_help *help = nfct_help(ct);
 256
 257         if (help && rcu_dereference_raw(help->helper) == me) {
 258                 nf_conntrack_event(IPCT_HELPER, ct);
 259                 RCU_INIT_POINTER(help->helper, NULL);
 260         }
 261         return 0;
 262 }
 263
 264 void nf_ct_helper_destroy(struct nf_conn *ct)
 265 {
 266         struct nf_conn_help *help = nfct_help(ct);
 267         struct nf_conntrack_helper *helper;
 268
 269         if (help) {
 270                 rcu_read_lock();
 271                 helper = rcu_dereference(help->helper);
 272                 if (helper && helper->destroy)
 273                         helper->destroy(ct);
 274                 rcu_read_unlock();
 275         }
 276 }
 277
 278 static LIST_HEAD(nf_ct_helper_expectfn_list);
 279
 280 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 281 {
 282         spin_lock_bh(&nf_conntrack_expect_lock);
 283         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 284         spin_unlock_bh(&nf_conntrack_expect_lock);
 285 }
 286 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 287
 288 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 289 {
 290         spin_lock_bh(&nf_conntrack_expect_lock);
 291         list_del_rcu(&n->head);
 292         spin_unlock_bh(&nf_conntrack_expect_lock);
 293 }
 294 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 295
 296 struct nf_ct_helper_expectfn *
 297 nf_ct_helper_expectfn_find_by_name(const char *name)
 298 {
 299         struct nf_ct_helper_expectfn *cur;
 300         bool found = false;
 301
 302         rcu_read_lock();
 303         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 304                 if (!strcmp(cur->name, name)) {
 305                         found = true;
 306                         break;
 307                 }
 308         }
 309         rcu_read_unlock();
 310         return found ? cur : NULL;
 311 }
 312 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 313
 314 struct nf_ct_helper_expectfn *
 315 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 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 (cur->expectfn == symbol) {
 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_symbol);
 331
 332 __printf(3, 4)
 333 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 334                       const char *fmt, ...)
 335 {
 336         const struct nf_conn_help *help;
 337         const struct nf_conntrack_helper *helper;
 338         struct va_format vaf;
 339         va_list args;
 340
 341         va_start(args, fmt);
 342
 343         vaf.fmt = fmt;
 344         vaf.va = &args;
 345
 346         /* Called from the helper function, this call never fails */
 347         help = nfct_help(ct);
 348
 349         /* rcu_read_lock()ed by nf_hook_thresh */
 350         helper = rcu_dereference(help->helper);
 351
 352         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 353                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 354
 355         va_end(args);
 356 }
 357 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 358
 359 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 360 {
 361         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 362         unsigned int h = helper_hash(&me->tuple);
 363         struct nf_conntrack_helper *cur;
 364         int ret = 0;
 365
 366         BUG_ON(me->expect_policy == NULL);
 367         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 368         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 369
 370         mutex_lock(&nf_ct_helper_mutex);
 371         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 372                 if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple, &mask)) {
 373                         ret = -EEXIST;
 374                         goto out;
 375                 }
 376         }
 377         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 378         nf_ct_helper_count++;
 379 out:
 380         mutex_unlock(&nf_ct_helper_mutex);
 381         return ret;
 382 }
 383 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 384
 385 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 386                                              struct net *net)
 387 {
 388         struct nf_conntrack_tuple_hash *h;
 389         const struct hlist_nulls_node *nn;
 390         int cpu;
 391
 392         /* Get rid of expecteds, set helpers to NULL. */
 393         for_each_possible_cpu(cpu) {
 394                 struct ct_pcpu *pcpu = per_cpu_ptr(net->ct.pcpu_lists, cpu);
 395
 396                 spin_lock_bh(&pcpu->lock);
 397                 hlist_nulls_for_each_entry(h, nn, &pcpu->unconfirmed, hnnode)
 398                         unhelp(h, me);
 399                 spin_unlock_bh(&pcpu->lock);
 400         }
 401 }
 402
 403 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 404 {
 405         struct nf_conntrack_tuple_hash *h;
 406         struct nf_conntrack_expect *exp;
 407         const struct hlist_node *next;
 408         const struct hlist_nulls_node *nn;
 409         unsigned int last_hsize;
 410         spinlock_t *lock;
 411         struct net *net;
 412         unsigned int i;
 413
 414         mutex_lock(&nf_ct_helper_mutex);
 415         hlist_del_rcu(&me->hnode);
 416         nf_ct_helper_count--;
 417         mutex_unlock(&nf_ct_helper_mutex);
 418
 419         /* Make sure every nothing is still using the helper unless its a
 420          * connection in the hash.
 421          */
 422         synchronize_rcu();
 423
 424         /* Get rid of expectations */
 425         spin_lock_bh(&nf_conntrack_expect_lock);
 426         for (i = 0; i < nf_ct_expect_hsize; i++) {
 427                 hlist_for_each_entry_safe(exp, next,
 428                                           &nf_ct_expect_hash[i], hnode) {
 429                         struct nf_conn_help *help = nfct_help(exp->master);
 430                         if ((rcu_dereference_protected(
 431                                         help->helper,
 432                                         lockdep_is_held(&nf_conntrack_expect_lock)
 433                                         ) == me || exp->helper == me) &&
 434                             del_timer(&exp->timeout)) {
 435                                 nf_ct_unlink_expect(exp);
 436                                 nf_ct_expect_put(exp);
 437                         }
 438                 }
 439         }
 440         spin_unlock_bh(&nf_conntrack_expect_lock);
 441
 442         rtnl_lock();
 443         for_each_net(net)
 444                 __nf_conntrack_helper_unregister(me, net);
 445         rtnl_unlock();
 446
 447         local_bh_disable();
 448 restart:
 449         last_hsize = nf_conntrack_htable_size;
 450         for (i = 0; i < last_hsize; i++) {
 451                 lock = &nf_conntrack_locks[i % CONNTRACK_LOCKS];
 452                 nf_conntrack_lock(lock);
 453                 if (last_hsize != nf_conntrack_htable_size) {
 454                         spin_unlock(lock);
 455                         goto restart;
 456                 }
 457                 hlist_nulls_for_each_entry(h, nn, &nf_conntrack_hash[i], hnnode)
 458                         unhelp(h, me);
 459                 spin_unlock(lock);
 460         }
 461         local_bh_enable();
 462 }
 463 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 464
 465 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 466                        u16 l3num, u16 protonum, const char *name,
 467                        u16 default_port, u16 spec_port, u32 id,
 468                        const struct nf_conntrack_expect_policy *exp_pol,
 469                        u32 expect_class_max, u32 data_len,
 470                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 471                                    struct nf_conn *ct,
 472                                    enum ip_conntrack_info ctinfo),
 473                        int (*from_nlattr)(struct nlattr *attr,
 474                                           struct nf_conn *ct),
 475                        struct module *module)
 476 {
 477         helper->tuple.src.l3num = l3num;
 478         helper->tuple.dst.protonum = protonum;
 479         helper->tuple.src.u.all = htons(spec_port);
 480         helper->expect_policy = exp_pol;
 481         helper->expect_class_max = expect_class_max;
 482         helper->data_len = data_len;
 483         helper->help = help;
 484         helper->from_nlattr = from_nlattr;
 485         helper->me = module;
 486
 487         if (spec_port == default_port)
 488                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 489         else
 490                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 491 }
 492 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 493
 494 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 495                                   unsigned int n)
 496 {
 497         unsigned int i;
 498         int err = 0;
 499
 500         for (i = 0; i < n; i++) {
 501                 err = nf_conntrack_helper_register(&helper[i]);
 502                 if (err < 0)
 503                         goto err;
 504         }
 505
 506         return err;
 507 err:
 508         if (i > 0)
 509                 nf_conntrack_helpers_unregister(helper, i);
 510         return err;
 511 }
 512 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 513
 514 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 515                                 unsigned int n)
 516 {
 517         while (n-- > 0)
 518                 nf_conntrack_helper_unregister(&helper[n]);
 519 }
 520 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 521
 522 static struct nf_ct_ext_type helper_extend __read_mostly = {
 523         .len    = sizeof(struct nf_conn_help),
 524         .align  = __alignof__(struct nf_conn_help),
 525         .id     = NF_CT_EXT_HELPER,
 526 };
 527
 528 int nf_conntrack_helper_pernet_init(struct net *net)
 529 {
 530         net->ct.auto_assign_helper_warned = false;
 531         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 532         return nf_conntrack_helper_init_sysctl(net);
 533 }
 534
 535 void nf_conntrack_helper_pernet_fini(struct net *net)
 536 {
 537         nf_conntrack_helper_fini_sysctl(net);
 538 }
 539
 540 int nf_conntrack_helper_init(void)
 541 {
 542         int ret;
 543         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 544         nf_ct_helper_hash =
 545                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 546         if (!nf_ct_helper_hash)
 547                 return -ENOMEM;
 548
 549         ret = nf_ct_extend_register(&helper_extend);
 550         if (ret < 0) {
 551                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 552                 goto out_extend;
 553         }
 554
 555         return 0;
 556 out_extend:
 557         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 558         return ret;
 559 }
 560
 561 void nf_conntrack_helper_fini(void)
 562 {
 563         nf_ct_extend_unregister(&helper_extend);
 564         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 565 }