linux/net/netfilter/nf_conntrack_helper.c
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   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
  34static DEFINE_MUTEX(nf_ct_helper_mutex);
  35struct hlist_head *nf_ct_helper_hash __read_mostly;
  36EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  37unsigned int nf_ct_helper_hsize __read_mostly;
  38EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  39static unsigned int nf_ct_helper_count __read_mostly;
  40
  41static bool nf_ct_auto_assign_helper __read_mostly = true;
  42module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  43MODULE_PARM_DESC(nf_conntrack_helper,
  44                 "Enable automatic conntrack helper assignment (default 1)");
  45
  46#ifdef CONFIG_SYSCTL
  47static 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
  58static 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
  82out_register:
  83        kfree(table);
  84out:
  85        return -ENOMEM;
  86}
  87
  88static 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
  97static int nf_conntrack_helper_init_sysctl(struct net *net)
  98{
  99        return 0;
 100}
 101
 102static 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. */
 109static 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
 115static 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
 133struct 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}
 149EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 150
 151struct nf_conntrack_helper *
 152nf_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}
 168EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 169
 170struct nf_conn_help *
 171nf_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}
 184EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 185
 186int __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);
 248out:
 249        return ret;
 250}
 251EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 252
 253static 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
 269void 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
 283static LIST_HEAD(nf_ct_helper_expectfn_list);
 284
 285void 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}
 291EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 292
 293void 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}
 299EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 300
 301struct nf_ct_helper_expectfn *
 302nf_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}
 317EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 318
 319struct nf_ct_helper_expectfn *
 320nf_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}
 335EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 336
 337__printf(3, 4)
 338void 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}
 362EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 363
 364int 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++;
 385out:
 386        mutex_unlock(&nf_ct_helper_mutex);
 387        return ret;
 388}
 389EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 390
 391static 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
 425void 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}
 446EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 447
 448static 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
 454int 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
 461void nf_conntrack_helper_pernet_fini(struct net *net)
 462{
 463        nf_conntrack_helper_fini_sysctl(net);
 464}
 465
 466int 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;
 482out_extend:
 483        nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 484        return ret;
 485}
 486
 487void 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}
 492
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