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  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/types.h>
  13 #include <linux/netfilter.h>
  14 #include <linux/module.h>
  15 #include <linux/skbuff.h>
  16 #include <linux/vmalloc.h>
  17 #include <linux/stddef.h>
  18 #include <linux/random.h>
  19 #include <linux/err.h>
  20 #include <linux/kernel.h>
  21 #include <linux/netdevice.h>
  22 #include <linux/rculist.h>
  23 #include <linux/rtnetlink.h>
  24
  25 #include <net/netfilter/nf_conntrack.h>
  26 #include <net/netfilter/nf_conntrack_l3proto.h>
  27 #include <net/netfilter/nf_conntrack_l4proto.h>
  28 #include <net/netfilter/nf_conntrack_helper.h>
  29 #include <net/netfilter/nf_conntrack_core.h>
  30 #include <net/netfilter/nf_conntrack_extend.h>
  31 #include <net/netfilter/nf_log.h>
  32
  33 static DEFINE_MUTEX(nf_ct_helper_mutex);
  34 struct hlist_head *nf_ct_helper_hash __read_mostly;
  35 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  36 unsigned int nf_ct_helper_hsize __read_mostly;
  37 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  38 static unsigned int nf_ct_helper_count __read_mostly;
  39
  40 static bool nf_ct_auto_assign_helper __read_mostly = true;
  41 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  42 MODULE_PARM_DESC(nf_conntrack_helper,
  43                  "Enable automatic conntrack helper assignment (default 1)");
  44
  45 #ifdef CONFIG_SYSCTL
  46 static struct ctl_table helper_sysctl_table[] = {
  47         {
  48                 .procname       = "nf_conntrack_helper",
  49                 .data           = &init_net.ct.sysctl_auto_assign_helper,
  50                 .maxlen         = sizeof(unsigned int),
  51                 .mode           = 0644,
  52                 .proc_handler   = proc_dointvec,
  53         },
  54         {}
  55 };
  56
  57 static int nf_conntrack_helper_init_sysctl(struct net *net)
  58 {
  59         struct ctl_table *table;
  60
  61         table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
  62                         GFP_KERNEL);
  63         if (!table)
  64                 goto out;
  65
  66         table[0].data = &net->ct.sysctl_auto_assign_helper;
  67
  68         /* Don't export sysctls to unprivileged users */
  69         if (net->user_ns != &init_user_ns)
  70                 table[0].procname = NULL;
  71
  72         net->ct.helper_sysctl_header =
  73                 register_net_sysctl(net, "net/netfilter", table);
  74
  75         if (!net->ct.helper_sysctl_header) {
  76                 pr_err("nf_conntrack_helper: can't register to sysctl.\n");
  77                 goto out_register;
  78         }
  79         return 0;
  80
  81 out_register:
  82         kfree(table);
  83 out:
  84         return -ENOMEM;
  85 }
  86
  87 static void nf_conntrack_helper_fini_sysctl(struct net *net)
  88 {
  89         struct ctl_table *table;
  90
  91         table = net->ct.helper_sysctl_header->ctl_table_arg;
  92         unregister_net_sysctl_table(net->ct.helper_sysctl_header);
  93         kfree(table);
  94 }
  95 #else
  96 static int nf_conntrack_helper_init_sysctl(struct net *net)
  97 {
  98         return 0;
  99 }
 100
 101 static void nf_conntrack_helper_fini_sysctl(struct net *net)
 102 {
 103 }
 104 #endif /* CONFIG_SYSCTL */
 105
 106 /* Stupid hash, but collision free for the default registrations of the
 107  * helpers currently in the kernel. */
 108 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 109 {
 110         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
 111                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 112 }
 113
 114 static struct nf_conntrack_helper *
 115 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 116 {
 117         struct nf_conntrack_helper *helper;
 118         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 119         unsigned int h;
 120
 121         if (!nf_ct_helper_count)
 122                 return NULL;
 123
 124         h = helper_hash(tuple);
 125         hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
 126                 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
 127                         return helper;
 128         }
 129         return NULL;
 130 }
 131
 132 struct nf_conntrack_helper *
 133 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
 134 {
 135         struct nf_conntrack_helper *h;
 136         unsigned int i;
 137
 138         for (i = 0; i < nf_ct_helper_hsize; i++) {
 139                 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
 140                         if (!strcmp(h->name, name) &&
 141                             h->tuple.src.l3num == l3num &&
 142                             h->tuple.dst.protonum == protonum)
 143                                 return h;
 144                 }
 145         }
 146         return NULL;
 147 }
 148 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 149
 150 struct nf_conntrack_helper *
 151 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 152 {
 153         struct nf_conntrack_helper *h;
 154
 155         h = __nf_conntrack_helper_find(name, l3num, protonum);
 156 #ifdef CONFIG_MODULES
 157         if (h == NULL) {
 158                 if (request_module("nfct-helper-%s", name) == 0)
 159                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 160         }
 161 #endif
 162         if (h != NULL && !try_module_get(h->me))
 163                 h = NULL;
 164
 165         return h;
 166 }
 167 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 168
 169 struct nf_conn_help *
 170 nf_ct_helper_ext_add(struct nf_conn *ct,
 171                      struct nf_conntrack_helper *helper, gfp_t gfp)
 172 {
 173         struct nf_conn_help *help;
 174
 175         help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
 176                                     helper->data_len, gfp);
 177         if (help)
 178                 INIT_HLIST_HEAD(&help->expectations);
 179         else
 180                 pr_debug("failed to add helper extension area");
 181         return help;
 182 }
 183 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 184
 185 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 186                               gfp_t flags)
 187 {
 188         struct nf_conntrack_helper *helper = NULL;
 189         struct nf_conn_help *help;
 190         struct net *net = nf_ct_net(ct);
 191         int ret = 0;
 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                 goto out;
 226         }
 227
 228         if (help == NULL) {
 229                 help = nf_ct_helper_ext_add(ct, helper, flags);
 230                 if (help == NULL) {
 231                         ret = -ENOMEM;
 232                         goto out;
 233                 }
 234         } else {
 235                 /* We only allow helper re-assignment of the same sort since
 236                  * we cannot reallocate the helper extension area.
 237                  */
 238                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 239
 240                 if (tmp && tmp->help != helper->help) {
 241                         RCU_INIT_POINTER(help->helper, NULL);
 242                         goto out;
 243                 }
 244         }
 245
 246         rcu_assign_pointer(help->helper, helper);
 247 out:
 248         return ret;
 249 }
 250 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 251
 252 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 253                          const struct nf_conntrack_helper *me)
 254 {
 255         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 256         struct nf_conn_help *help = nfct_help(ct);
 257
 258         if (help && rcu_dereference_protected(
 259                         help->helper,
 260                         lockdep_is_held(&nf_conntrack_lock)
 261                         ) == me) {
 262                 nf_conntrack_event(IPCT_HELPER, ct);
 263                 RCU_INIT_POINTER(help->helper, NULL);
 264         }
 265         return 0;
 266 }
 267
 268 void nf_ct_helper_destroy(struct nf_conn *ct)
 269 {
 270         struct nf_conn_help *help = nfct_help(ct);
 271         struct nf_conntrack_helper *helper;
 272
 273         if (help) {
 274                 rcu_read_lock();
 275                 helper = rcu_dereference(help->helper);
 276                 if (helper && helper->destroy)
 277                         helper->destroy(ct);
 278                 rcu_read_unlock();
 279         }
 280 }
 281
 282 static LIST_HEAD(nf_ct_helper_expectfn_list);
 283
 284 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 285 {
 286         spin_lock_bh(&nf_conntrack_lock);
 287         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 288         spin_unlock_bh(&nf_conntrack_lock);
 289 }
 290 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 291
 292 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 293 {
 294         spin_lock_bh(&nf_conntrack_lock);
 295         list_del_rcu(&n->head);
 296         spin_unlock_bh(&nf_conntrack_lock);
 297 }
 298 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 299
 300 struct nf_ct_helper_expectfn *
 301 nf_ct_helper_expectfn_find_by_name(const char *name)
 302 {
 303         struct nf_ct_helper_expectfn *cur;
 304         bool found = false;
 305
 306         rcu_read_lock();
 307         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 308                 if (!strcmp(cur->name, name)) {
 309                         found = true;
 310                         break;
 311                 }
 312         }
 313         rcu_read_unlock();
 314         return found ? cur : NULL;
 315 }
 316 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 317
 318 struct nf_ct_helper_expectfn *
 319 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 320 {
 321         struct nf_ct_helper_expectfn *cur;
 322         bool found = false;
 323
 324         rcu_read_lock();
 325         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 326                 if (cur->expectfn == symbol) {
 327                         found = true;
 328                         break;
 329                 }
 330         }
 331         rcu_read_unlock();
 332         return found ? cur : NULL;
 333 }
 334 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 335
 336 __printf(3, 4)
 337 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 338                       const char *fmt, ...)
 339 {
 340         const struct nf_conn_help *help;
 341         const struct nf_conntrack_helper *helper;
 342
 343         /* Called from the helper function, this call never fails */
 344         help = nfct_help(ct);
 345
 346         /* rcu_read_lock()ed by nf_hook_slow */
 347         helper = rcu_dereference(help->helper);
 348
 349         nf_log_packet(nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 350                       "nf_ct_%s: dropping packet: %s ", helper->name, fmt);
 351 }
 352 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 353
 354 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 355 {
 356         int ret = 0;
 357         struct nf_conntrack_helper *cur;
 358         unsigned int h = helper_hash(&me->tuple);
 359
 360         BUG_ON(me->expect_policy == NULL);
 361         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 362         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 363
 364         mutex_lock(&nf_ct_helper_mutex);
 365         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 366                 if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
 367                     cur->tuple.src.l3num == me->tuple.src.l3num &&
 368                     cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 369                         ret = -EEXIST;
 370                         goto out;
 371                 }
 372         }
 373         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 374         nf_ct_helper_count++;
 375 out:
 376         mutex_unlock(&nf_ct_helper_mutex);
 377         return ret;
 378 }
 379 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 380
 381 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 382                                              struct net *net)
 383 {
 384         struct nf_conntrack_tuple_hash *h;
 385         struct nf_conntrack_expect *exp;
 386         const struct hlist_node *next;
 387         const struct hlist_nulls_node *nn;
 388         unsigned int i;
 389
 390         /* Get rid of expectations */
 391         for (i = 0; i < nf_ct_expect_hsize; i++) {
 392                 hlist_for_each_entry_safe(exp, next,
 393                                           &net->ct.expect_hash[i], hnode) {
 394                         struct nf_conn_help *help = nfct_help(exp->master);
 395                         if ((rcu_dereference_protected(
 396                                         help->helper,
 397                                         lockdep_is_held(&nf_conntrack_lock)
 398                                         ) == me || exp->helper == me) &&
 399                             del_timer(&exp->timeout)) {
 400                                 nf_ct_unlink_expect(exp);
 401                                 nf_ct_expect_put(exp);
 402                         }
 403                 }
 404         }
 405
 406         /* Get rid of expecteds, set helpers to NULL. */
 407         hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
 408                 unhelp(h, me);
 409         for (i = 0; i < net->ct.htable_size; i++) {
 410                 hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
 411                         unhelp(h, me);
 412         }
 413 }
 414
 415 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 416 {
 417         struct net *net;
 418
 419         mutex_lock(&nf_ct_helper_mutex);
 420         hlist_del_rcu(&me->hnode);
 421         nf_ct_helper_count--;
 422         mutex_unlock(&nf_ct_helper_mutex);
 423
 424         /* Make sure every nothing is still using the helper unless its a
 425          * connection in the hash.
 426          */
 427         synchronize_rcu();
 428
 429         rtnl_lock();
 430         spin_lock_bh(&nf_conntrack_lock);
 431         for_each_net(net)
 432                 __nf_conntrack_helper_unregister(me, net);
 433         spin_unlock_bh(&nf_conntrack_lock);
 434         rtnl_unlock();
 435 }
 436 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 437
 438 static struct nf_ct_ext_type helper_extend __read_mostly = {
 439         .len    = sizeof(struct nf_conn_help),
 440         .align  = __alignof__(struct nf_conn_help),
 441         .id     = NF_CT_EXT_HELPER,
 442 };
 443
 444 int nf_conntrack_helper_pernet_init(struct net *net)
 445 {
 446         net->ct.auto_assign_helper_warned = false;
 447         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 448         return nf_conntrack_helper_init_sysctl(net);
 449 }
 450
 451 void nf_conntrack_helper_pernet_fini(struct net *net)
 452 {
 453         nf_conntrack_helper_fini_sysctl(net);
 454 }
 455
 456 int nf_conntrack_helper_init(void)
 457 {
 458         int ret;
 459         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 460         nf_ct_helper_hash =
 461                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 462         if (!nf_ct_helper_hash)
 463                 return -ENOMEM;
 464
 465         ret = nf_ct_extend_register(&helper_extend);
 466         if (ret < 0) {
 467                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 468                 goto out_extend;
 469         }
 470
 471         return 0;
 472 out_extend:
 473         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 474         return ret;
 475 }
 476
 477 void nf_conntrack_helper_fini(void)
 478 {
 479         nf_ct_extend_unregister(&helper_extend);
 480         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 481 }