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 = true;
  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 1)");
  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         int ret = 0;
 193
 194         /* We already got a helper explicitly attached. The function
 195          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 196          * the helper up again. Since now the user is in full control of
 197          * making consistent helper configurations, skip this automatic
 198          * re-lookup, otherwise we'll lose the helper.
 199          */
 200         if (test_bit(IPS_HELPER_BIT, &ct->status))
 201                 return 0;
 202
 203         if (tmpl != NULL) {
 204                 help = nfct_help(tmpl);
 205                 if (help != NULL) {
 206                         helper = help->helper;
 207                         set_bit(IPS_HELPER_BIT, &ct->status);
 208                 }
 209         }
 210
 211         help = nfct_help(ct);
 212         if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
 213                 helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 214                 if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
 215                         pr_info("nf_conntrack: automatic helper "
 216                                 "assignment is deprecated and it will "
 217                                 "be removed soon. Use the iptables CT target "
 218                                 "to attach helpers instead.\n");
 219                         net->ct.auto_assign_helper_warned = true;
 220                 }
 221         }
 222
 223         if (helper == NULL) {
 224                 if (help)
 225                         RCU_INIT_POINTER(help->helper, NULL);
 226                 goto out;
 227         }
 228
 229         if (help == NULL) {
 230                 help = nf_ct_helper_ext_add(ct, helper, flags);
 231                 if (help == NULL) {
 232                         ret = -ENOMEM;
 233                         goto out;
 234                 }
 235         } else {
 236                 /* We only allow helper re-assignment of the same sort since
 237                  * we cannot reallocate the helper extension area.
 238                  */
 239                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 240
 241                 if (tmp && tmp->help != helper->help) {
 242                         RCU_INIT_POINTER(help->helper, NULL);
 243                         goto out;
 244                 }
 245         }
 246
 247         rcu_assign_pointer(help->helper, helper);
 248 out:
 249         return ret;
 250 }
 251 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 252
 253 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 254                          const struct nf_conntrack_helper *me)
 255 {
 256         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 257         struct nf_conn_help *help = nfct_help(ct);
 258
 259         if (help && rcu_dereference_protected(
 260                         help->helper,
 261                         lockdep_is_held(&nf_conntrack_lock)
 262                         ) == me) {
 263                 nf_conntrack_event(IPCT_HELPER, ct);
 264                 RCU_INIT_POINTER(help->helper, NULL);
 265         }
 266         return 0;
 267 }
 268
 269 void nf_ct_helper_destroy(struct nf_conn *ct)
 270 {
 271         struct nf_conn_help *help = nfct_help(ct);
 272         struct nf_conntrack_helper *helper;
 273
 274         if (help) {
 275                 rcu_read_lock();
 276                 helper = rcu_dereference(help->helper);
 277                 if (helper && helper->destroy)
 278                         helper->destroy(ct);
 279                 rcu_read_unlock();
 280         }
 281 }
 282
 283 static LIST_HEAD(nf_ct_helper_expectfn_list);
 284
 285 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 286 {
 287         spin_lock_bh(&nf_conntrack_lock);
 288         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 289         spin_unlock_bh(&nf_conntrack_lock);
 290 }
 291 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 292
 293 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 294 {
 295         spin_lock_bh(&nf_conntrack_lock);
 296         list_del_rcu(&n->head);
 297         spin_unlock_bh(&nf_conntrack_lock);
 298 }
 299 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 300
 301 struct nf_ct_helper_expectfn *
 302 nf_ct_helper_expectfn_find_by_name(const char *name)
 303 {
 304         struct nf_ct_helper_expectfn *cur;
 305         bool found = false;
 306
 307         rcu_read_lock();
 308         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 309                 if (!strcmp(cur->name, name)) {
 310                         found = true;
 311                         break;
 312                 }
 313         }
 314         rcu_read_unlock();
 315         return found ? cur : NULL;
 316 }
 317 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 318
 319 struct nf_ct_helper_expectfn *
 320 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 321 {
 322         struct nf_ct_helper_expectfn *cur;
 323         bool found = false;
 324
 325         rcu_read_lock();
 326         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 327                 if (cur->expectfn == symbol) {
 328                         found = true;
 329                         break;
 330                 }
 331         }
 332         rcu_read_unlock();
 333         return found ? cur : NULL;
 334 }
 335 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 336
 337 __printf(3, 4)
 338 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 339                       const char *fmt, ...)
 340 {
 341         const struct nf_conn_help *help;
 342         const struct nf_conntrack_helper *helper;
 343         struct va_format vaf;
 344         va_list args;
 345
 346         va_start(args, fmt);
 347
 348         vaf.fmt = fmt;
 349         vaf.va = &args;
 350
 351         /* Called from the helper function, this call never fails */
 352         help = nfct_help(ct);
 353
 354         /* rcu_read_lock()ed by nf_hook_slow */
 355         helper = rcu_dereference(help->helper);
 356
 357         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 358                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 359
 360         va_end(args);
 361 }
 362 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 363
 364 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 365 {
 366         int ret = 0;
 367         struct nf_conntrack_helper *cur;
 368         unsigned int h = helper_hash(&me->tuple);
 369
 370         BUG_ON(me->expect_policy == NULL);
 371         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 372         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 373
 374         mutex_lock(&nf_ct_helper_mutex);
 375         hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 376                 if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
 377                     cur->tuple.src.l3num == me->tuple.src.l3num &&
 378                     cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 379                         ret = -EEXIST;
 380                         goto out;
 381                 }
 382         }
 383         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 384         nf_ct_helper_count++;
 385 out:
 386         mutex_unlock(&nf_ct_helper_mutex);
 387         return ret;
 388 }
 389 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 390
 391 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 392                                              struct net *net)
 393 {
 394         struct nf_conntrack_tuple_hash *h;
 395         struct nf_conntrack_expect *exp;
 396         const struct hlist_node *next;
 397         const struct hlist_nulls_node *nn;
 398         unsigned int i;
 399
 400         /* Get rid of expectations */
 401         for (i = 0; i < nf_ct_expect_hsize; i++) {
 402                 hlist_for_each_entry_safe(exp, next,
 403                                           &net->ct.expect_hash[i], hnode) {
 404                         struct nf_conn_help *help = nfct_help(exp->master);
 405                         if ((rcu_dereference_protected(
 406                                         help->helper,
 407                                         lockdep_is_held(&nf_conntrack_lock)
 408                                         ) == me || exp->helper == me) &&
 409                             del_timer(&exp->timeout)) {
 410                                 nf_ct_unlink_expect(exp);
 411                                 nf_ct_expect_put(exp);
 412                         }
 413                 }
 414         }
 415
 416         /* Get rid of expecteds, set helpers to NULL. */
 417         hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
 418                 unhelp(h, me);
 419         for (i = 0; i < net->ct.htable_size; i++) {
 420                 hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
 421                         unhelp(h, me);
 422         }
 423 }
 424
 425 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 426 {
 427         struct net *net;
 428
 429         mutex_lock(&nf_ct_helper_mutex);
 430         hlist_del_rcu(&me->hnode);
 431         nf_ct_helper_count--;
 432         mutex_unlock(&nf_ct_helper_mutex);
 433
 434         /* Make sure every nothing is still using the helper unless its a
 435          * connection in the hash.
 436          */
 437         synchronize_rcu();
 438
 439         rtnl_lock();
 440         spin_lock_bh(&nf_conntrack_lock);
 441         for_each_net(net)
 442                 __nf_conntrack_helper_unregister(me, net);
 443         spin_unlock_bh(&nf_conntrack_lock);
 444         rtnl_unlock();
 445 }
 446 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 447
 448 static struct nf_ct_ext_type helper_extend __read_mostly = {
 449         .len    = sizeof(struct nf_conn_help),
 450         .align  = __alignof__(struct nf_conn_help),
 451         .id     = NF_CT_EXT_HELPER,
 452 };
 453
 454 int nf_conntrack_helper_pernet_init(struct net *net)
 455 {
 456         net->ct.auto_assign_helper_warned = false;
 457         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 458         return nf_conntrack_helper_init_sysctl(net);
 459 }
 460
 461 void nf_conntrack_helper_pernet_fini(struct net *net)
 462 {
 463         nf_conntrack_helper_fini_sysctl(net);
 464 }
 465
 466 int nf_conntrack_helper_init(void)
 467 {
 468         int ret;
 469         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 470         nf_ct_helper_hash =
 471                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 472         if (!nf_ct_helper_hash)
 473                 return -ENOMEM;
 474
 475         ret = nf_ct_extend_register(&helper_extend);
 476         if (ret < 0) {
 477                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 478                 goto out_extend;
 479         }
 480
 481         return 0;
 482 out_extend:
 483         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 484         return ret;
 485 }
 486
 487 void nf_conntrack_helper_fini(void)
 488 {
 489         nf_ct_extend_unregister(&helper_extend);
 490         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 491 }