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
  32 static DEFINE_MUTEX(nf_ct_helper_mutex);
  33 static struct hlist_head *nf_ct_helper_hash __read_mostly;
  34 static unsigned int nf_ct_helper_hsize __read_mostly;
  35 static unsigned int nf_ct_helper_count __read_mostly;
  36
  37 static bool nf_ct_auto_assign_helper __read_mostly = true;
  38 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  39 MODULE_PARM_DESC(nf_conntrack_helper,
  40                  "Enable automatic conntrack helper assignment (default 1)");
  41
  42 #ifdef CONFIG_SYSCTL
  43 static struct ctl_table helper_sysctl_table[] = {
  44         {
  45                 .procname       = "nf_conntrack_helper",
  46                 .data           = &init_net.ct.sysctl_auto_assign_helper,
  47                 .maxlen         = sizeof(unsigned int),
  48                 .mode           = 0644,
  49                 .proc_handler   = proc_dointvec,
  50         },
  51         {}
  52 };
  53
  54 static int nf_conntrack_helper_init_sysctl(struct net *net)
  55 {
  56         struct ctl_table *table;
  57
  58         table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
  59                         GFP_KERNEL);
  60         if (!table)
  61                 goto out;
  62
  63         table[0].data = &net->ct.sysctl_auto_assign_helper;
  64
  65         net->ct.helper_sysctl_header =
  66                 register_net_sysctl(net, "net/netfilter", table);
  67
  68         if (!net->ct.helper_sysctl_header) {
  69                 pr_err("nf_conntrack_helper: can't register to sysctl.\n");
  70                 goto out_register;
  71         }
  72         return 0;
  73
  74 out_register:
  75         kfree(table);
  76 out:
  77         return -ENOMEM;
  78 }
  79
  80 static void nf_conntrack_helper_fini_sysctl(struct net *net)
  81 {
  82         struct ctl_table *table;
  83
  84         table = net->ct.helper_sysctl_header->ctl_table_arg;
  85         unregister_net_sysctl_table(net->ct.helper_sysctl_header);
  86         kfree(table);
  87 }
  88 #else
  89 static int nf_conntrack_helper_init_sysctl(struct net *net)
  90 {
  91         return 0;
  92 }
  93
  94 static void nf_conntrack_helper_fini_sysctl(struct net *net)
  95 {
  96 }
  97 #endif /* CONFIG_SYSCTL */
  98
  99 /* Stupid hash, but collision free for the default registrations of the
 100  * helpers currently in the kernel. */
 101 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 102 {
 103         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
 104                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 105 }
 106
 107 static struct nf_conntrack_helper *
 108 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 109 {
 110         struct nf_conntrack_helper *helper;
 111         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 112         struct hlist_node *n;
 113         unsigned int h;
 114
 115         if (!nf_ct_helper_count)
 116                 return NULL;
 117
 118         h = helper_hash(tuple);
 119         hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
 120                 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
 121                         return helper;
 122         }
 123         return NULL;
 124 }
 125
 126 struct nf_conntrack_helper *
 127 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
 128 {
 129         struct nf_conntrack_helper *h;
 130         struct hlist_node *n;
 131         unsigned int i;
 132
 133         for (i = 0; i < nf_ct_helper_hsize; i++) {
 134                 hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
 135                         if (!strcmp(h->name, name) &&
 136                             h->tuple.src.l3num == l3num &&
 137                             h->tuple.dst.protonum == protonum)
 138                                 return h;
 139                 }
 140         }
 141         return NULL;
 142 }
 143 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 144
 145 struct nf_conntrack_helper *
 146 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 147 {
 148         struct nf_conntrack_helper *h;
 149
 150         h = __nf_conntrack_helper_find(name, l3num, protonum);
 151 #ifdef CONFIG_MODULES
 152         if (h == NULL) {
 153                 if (request_module("nfct-helper-%s", name) == 0)
 154                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 155         }
 156 #endif
 157         if (h != NULL && !try_module_get(h->me))
 158                 h = NULL;
 159
 160         return h;
 161 }
 162 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 163
 164 struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 165 {
 166         struct nf_conn_help *help;
 167
 168         help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 169         if (help)
 170                 INIT_HLIST_HEAD(&help->expectations);
 171         else
 172                 pr_debug("failed to add helper extension area");
 173         return help;
 174 }
 175 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 176
 177 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 178                               gfp_t flags)
 179 {
 180         struct nf_conntrack_helper *helper = NULL;
 181         struct nf_conn_help *help;
 182         struct net *net = nf_ct_net(ct);
 183         int ret = 0;
 184
 185         /* We already got a helper explicitly attached. The function
 186          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 187          * the helper up again. Since now the user is in full control of
 188          * making consistent helper configurations, skip this automatic
 189          * re-lookup, otherwise we'll lose the helper.
 190          */
 191         if (test_bit(IPS_HELPER_BIT, &ct->status))
 192                 return 0;
 193
 194         if (tmpl != NULL) {
 195                 help = nfct_help(tmpl);
 196                 if (help != NULL) {
 197                         helper = help->helper;
 198                         set_bit(IPS_HELPER_BIT, &ct->status);
 199                 }
 200         }
 201
 202         help = nfct_help(ct);
 203         if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
 204                 helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 205                 if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
 206                         pr_info("nf_conntrack: automatic helper "
 207                                 "assignment is deprecated and it will "
 208                                 "be removed soon. Use the iptables CT target "
 209                                 "to attach helpers instead.\n");
 210                         net->ct.auto_assign_helper_warned = true;
 211                 }
 212         }
 213
 214         if (helper == NULL) {
 215                 if (help)
 216                         RCU_INIT_POINTER(help->helper, NULL);
 217                 goto out;
 218         }
 219
 220         if (help == NULL) {
 221                 help = nf_ct_helper_ext_add(ct, flags);
 222                 if (help == NULL) {
 223                         ret = -ENOMEM;
 224                         goto out;
 225                 }
 226         } else {
 227                 memset(&help->help, 0, sizeof(help->help));
 228         }
 229
 230         rcu_assign_pointer(help->helper, helper);
 231 out:
 232         return ret;
 233 }
 234 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 235
 236 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 237                          const struct nf_conntrack_helper *me)
 238 {
 239         struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 240         struct nf_conn_help *help = nfct_help(ct);
 241
 242         if (help && rcu_dereference_protected(
 243                         help->helper,
 244                         lockdep_is_held(&nf_conntrack_lock)
 245                         ) == me) {
 246                 nf_conntrack_event(IPCT_HELPER, ct);
 247                 RCU_INIT_POINTER(help->helper, NULL);
 248         }
 249         return 0;
 250 }
 251
 252 void nf_ct_helper_destroy(struct nf_conn *ct)
 253 {
 254         struct nf_conn_help *help = nfct_help(ct);
 255         struct nf_conntrack_helper *helper;
 256
 257         if (help) {
 258                 rcu_read_lock();
 259                 helper = rcu_dereference(help->helper);
 260                 if (helper && helper->destroy)
 261                         helper->destroy(ct);
 262                 rcu_read_unlock();
 263         }
 264 }
 265
 266 static LIST_HEAD(nf_ct_helper_expectfn_list);
 267
 268 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 269 {
 270         spin_lock_bh(&nf_conntrack_lock);
 271         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 272         spin_unlock_bh(&nf_conntrack_lock);
 273 }
 274 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 275
 276 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 277 {
 278         spin_lock_bh(&nf_conntrack_lock);
 279         list_del_rcu(&n->head);
 280         spin_unlock_bh(&nf_conntrack_lock);
 281 }
 282 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 283
 284 struct nf_ct_helper_expectfn *
 285 nf_ct_helper_expectfn_find_by_name(const char *name)
 286 {
 287         struct nf_ct_helper_expectfn *cur;
 288         bool found = false;
 289
 290         rcu_read_lock();
 291         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 292                 if (!strcmp(cur->name, name)) {
 293                         found = true;
 294                         break;
 295                 }
 296         }
 297         rcu_read_unlock();
 298         return found ? cur : NULL;
 299 }
 300 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 301
 302 struct nf_ct_helper_expectfn *
 303 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 304 {
 305         struct nf_ct_helper_expectfn *cur;
 306         bool found = false;
 307
 308         rcu_read_lock();
 309         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 310                 if (cur->expectfn == symbol) {
 311                         found = true;
 312                         break;
 313                 }
 314         }
 315         rcu_read_unlock();
 316         return found ? cur : NULL;
 317 }
 318 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 319
 320 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 321 {
 322         unsigned int h = helper_hash(&me->tuple);
 323
 324         BUG_ON(me->expect_policy == NULL);
 325         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 326         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 327
 328         mutex_lock(&nf_ct_helper_mutex);
 329         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 330         nf_ct_helper_count++;
 331         mutex_unlock(&nf_ct_helper_mutex);
 332
 333         return 0;
 334 }
 335 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 336
 337 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 338                                              struct net *net)
 339 {
 340         struct nf_conntrack_tuple_hash *h;
 341         struct nf_conntrack_expect *exp;
 342         const struct hlist_node *n, *next;
 343         const struct hlist_nulls_node *nn;
 344         unsigned int i;
 345
 346         /* Get rid of expectations */
 347         for (i = 0; i < nf_ct_expect_hsize; i++) {
 348                 hlist_for_each_entry_safe(exp, n, next,
 349                                           &net->ct.expect_hash[i], hnode) {
 350                         struct nf_conn_help *help = nfct_help(exp->master);
 351                         if ((rcu_dereference_protected(
 352                                         help->helper,
 353                                         lockdep_is_held(&nf_conntrack_lock)
 354                                         ) == me || exp->helper == me) &&
 355                             del_timer(&exp->timeout)) {
 356                                 nf_ct_unlink_expect(exp);
 357                                 nf_ct_expect_put(exp);
 358                         }
 359                 }
 360         }
 361
 362         /* Get rid of expecteds, set helpers to NULL. */
 363         hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
 364                 unhelp(h, me);
 365         for (i = 0; i < net->ct.htable_size; i++) {
 366                 hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
 367                         unhelp(h, me);
 368         }
 369 }
 370
 371 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 372 {
 373         struct net *net;
 374
 375         mutex_lock(&nf_ct_helper_mutex);
 376         hlist_del_rcu(&me->hnode);
 377         nf_ct_helper_count--;
 378         mutex_unlock(&nf_ct_helper_mutex);
 379
 380         /* Make sure every nothing is still using the helper unless its a
 381          * connection in the hash.
 382          */
 383         synchronize_rcu();
 384
 385         rtnl_lock();
 386         spin_lock_bh(&nf_conntrack_lock);
 387         for_each_net(net)
 388                 __nf_conntrack_helper_unregister(me, net);
 389         spin_unlock_bh(&nf_conntrack_lock);
 390         rtnl_unlock();
 391 }
 392 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 393
 394 static struct nf_ct_ext_type helper_extend __read_mostly = {
 395         .len    = sizeof(struct nf_conn_help),
 396         .align  = __alignof__(struct nf_conn_help),
 397         .id     = NF_CT_EXT_HELPER,
 398 };
 399
 400 int nf_conntrack_helper_init(struct net *net)
 401 {
 402         int err;
 403
 404         net->ct.auto_assign_helper_warned = false;
 405         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 406
 407         if (net_eq(net, &init_net)) {
 408                 nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 409                 nf_ct_helper_hash =
 410                         nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 411                 if (!nf_ct_helper_hash)
 412                         return -ENOMEM;
 413
 414                 err = nf_ct_extend_register(&helper_extend);
 415                 if (err < 0)
 416                         goto err1;
 417         }
 418
 419         err = nf_conntrack_helper_init_sysctl(net);
 420         if (err < 0)
 421                 goto out_sysctl;
 422
 423         return 0;
 424
 425 out_sysctl:
 426         if (net_eq(net, &init_net))
 427                 nf_ct_extend_unregister(&helper_extend);
 428 err1:
 429         nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 430         return err;
 431 }
 432
 433 void nf_conntrack_helper_fini(struct net *net)
 434 {
 435         nf_conntrack_helper_fini_sysctl(net);
 436         if (net_eq(net, &init_net)) {
 437                 nf_ct_extend_unregister(&helper_extend);
 438                 nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 439         }
 440 }