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 *
   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
  32static DEFINE_MUTEX(nf_ct_helper_mutex);
  33struct hlist_head *nf_ct_helper_hash __read_mostly;
  34EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  35unsigned int nf_ct_helper_hsize __read_mostly;
  36EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  37static unsigned int nf_ct_helper_count __read_mostly;
  38
  39static bool nf_ct_auto_assign_helper __read_mostly = true;
  40module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  41MODULE_PARM_DESC(nf_conntrack_helper,
  42                 "Enable automatic conntrack helper assignment (default 1)");
  43
  44#ifdef CONFIG_SYSCTL
  45static struct ctl_table helper_sysctl_table[] = {
  46        {
  47                .procname       = "nf_conntrack_helper",
  48                .data           = &init_net.ct.sysctl_auto_assign_helper,
  49                .maxlen         = sizeof(unsigned int),
  50                .mode           = 0644,
  51                .proc_handler   = proc_dointvec,
  52        },
  53        {}
  54};
  55
  56static int nf_conntrack_helper_init_sysctl(struct net *net)
  57{
  58        struct ctl_table *table;
  59
  60        table = kmemdup(helper_sysctl_table, sizeof(helper_sysctl_table),
  61                        GFP_KERNEL);
  62        if (!table)
  63                goto out;
  64
  65        table[0].data = &net->ct.sysctl_auto_assign_helper;
  66
  67        net->ct.helper_sysctl_header =
  68                register_net_sysctl(net, "net/netfilter", table);
  69
  70        if (!net->ct.helper_sysctl_header) {
  71                pr_err("nf_conntrack_helper: can't register to sysctl.\n");
  72                goto out_register;
  73        }
  74        return 0;
  75
  76out_register:
  77        kfree(table);
  78out:
  79        return -ENOMEM;
  80}
  81
  82static void nf_conntrack_helper_fini_sysctl(struct net *net)
  83{
  84        struct ctl_table *table;
  85
  86        table = net->ct.helper_sysctl_header->ctl_table_arg;
  87        unregister_net_sysctl_table(net->ct.helper_sysctl_header);
  88        kfree(table);
  89}
  90#else
  91static int nf_conntrack_helper_init_sysctl(struct net *net)
  92{
  93        return 0;
  94}
  95
  96static void nf_conntrack_helper_fini_sysctl(struct net *net)
  97{
  98}
  99#endif /* CONFIG_SYSCTL */
 100
 101/* Stupid hash, but collision free for the default registrations of the
 102 * helpers currently in the kernel. */
 103static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 104{
 105        return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
 106                (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 107}
 108
 109static struct nf_conntrack_helper *
 110__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 111{
 112        struct nf_conntrack_helper *helper;
 113        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 114        struct hlist_node *n;
 115        unsigned int h;
 116
 117        if (!nf_ct_helper_count)
 118                return NULL;
 119
 120        h = helper_hash(tuple);
 121        hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
 122                if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
 123                        return helper;
 124        }
 125        return NULL;
 126}
 127
 128struct nf_conntrack_helper *
 129__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
 130{
 131        struct nf_conntrack_helper *h;
 132        struct hlist_node *n;
 133        unsigned int i;
 134
 135        for (i = 0; i < nf_ct_helper_hsize; i++) {
 136                hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
 137                        if (!strcmp(h->name, name) &&
 138                            h->tuple.src.l3num == l3num &&
 139                            h->tuple.dst.protonum == protonum)
 140                                return h;
 141                }
 142        }
 143        return NULL;
 144}
 145EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
 146
 147struct nf_conntrack_helper *
 148nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 149{
 150        struct nf_conntrack_helper *h;
 151
 152        h = __nf_conntrack_helper_find(name, l3num, protonum);
 153#ifdef CONFIG_MODULES
 154        if (h == NULL) {
 155                if (request_module("nfct-helper-%s", name) == 0)
 156                        h = __nf_conntrack_helper_find(name, l3num, protonum);
 157        }
 158#endif
 159        if (h != NULL && !try_module_get(h->me))
 160                h = NULL;
 161
 162        return h;
 163}
 164EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 165
 166struct nf_conn_help *
 167nf_ct_helper_ext_add(struct nf_conn *ct,
 168                     struct nf_conntrack_helper *helper, gfp_t gfp)
 169{
 170        struct nf_conn_help *help;
 171
 172        help = nf_ct_ext_add_length(ct, NF_CT_EXT_HELPER,
 173                                    helper->data_len, gfp);
 174        if (help)
 175                INIT_HLIST_HEAD(&help->expectations);
 176        else
 177                pr_debug("failed to add helper extension area");
 178        return help;
 179}
 180EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 181
 182int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 183                              gfp_t flags)
 184{
 185        struct nf_conntrack_helper *helper = NULL;
 186        struct nf_conn_help *help;
 187        struct net *net = nf_ct_net(ct);
 188        int ret = 0;
 189
 190        /* We already got a helper explicitly attached. The function
 191         * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 192         * the helper up again. Since now the user is in full control of
 193         * making consistent helper configurations, skip this automatic
 194         * re-lookup, otherwise we'll lose the helper.
 195         */
 196        if (test_bit(IPS_HELPER_BIT, &ct->status))
 197                return 0;
 198
 199        if (tmpl != NULL) {
 200                help = nfct_help(tmpl);
 201                if (help != NULL) {
 202                        helper = help->helper;
 203                        set_bit(IPS_HELPER_BIT, &ct->status);
 204                }
 205        }
 206
 207        help = nfct_help(ct);
 208        if (net->ct.sysctl_auto_assign_helper && helper == NULL) {
 209                helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 210                if (unlikely(!net->ct.auto_assign_helper_warned && helper)) {
 211                        pr_info("nf_conntrack: automatic helper "
 212                                "assignment is deprecated and it will "
 213                                "be removed soon. Use the iptables CT target "
 214                                "to attach helpers instead.\n");
 215                        net->ct.auto_assign_helper_warned = true;
 216                }
 217        }
 218
 219        if (helper == NULL) {
 220                if (help)
 221                        RCU_INIT_POINTER(help->helper, NULL);
 222                goto out;
 223        }
 224
 225        if (help == NULL) {
 226                help = nf_ct_helper_ext_add(ct, helper, flags);
 227                if (help == NULL) {
 228                        ret = -ENOMEM;
 229                        goto out;
 230                }
 231        } else {
 232                /* We only allow helper re-assignment of the same sort since
 233                 * we cannot reallocate the helper extension area.
 234                 */
 235                if (help->helper != helper) {
 236                        RCU_INIT_POINTER(help->helper, NULL);
 237                        goto out;
 238                }
 239        }
 240
 241        rcu_assign_pointer(help->helper, helper);
 242out:
 243        return ret;
 244}
 245EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 246
 247static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 248                         const struct nf_conntrack_helper *me)
 249{
 250        struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
 251        struct nf_conn_help *help = nfct_help(ct);
 252
 253        if (help && rcu_dereference_protected(
 254                        help->helper,
 255                        lockdep_is_held(&nf_conntrack_lock)
 256                        ) == me) {
 257                nf_conntrack_event(IPCT_HELPER, ct);
 258                RCU_INIT_POINTER(help->helper, NULL);
 259        }
 260        return 0;
 261}
 262
 263void nf_ct_helper_destroy(struct nf_conn *ct)
 264{
 265        struct nf_conn_help *help = nfct_help(ct);
 266        struct nf_conntrack_helper *helper;
 267
 268        if (help) {
 269                rcu_read_lock();
 270                helper = rcu_dereference(help->helper);
 271                if (helper && helper->destroy)
 272                        helper->destroy(ct);
 273                rcu_read_unlock();
 274        }
 275}
 276
 277static LIST_HEAD(nf_ct_helper_expectfn_list);
 278
 279void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 280{
 281        spin_lock_bh(&nf_conntrack_lock);
 282        list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 283        spin_unlock_bh(&nf_conntrack_lock);
 284}
 285EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 286
 287void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 288{
 289        spin_lock_bh(&nf_conntrack_lock);
 290        list_del_rcu(&n->head);
 291        spin_unlock_bh(&nf_conntrack_lock);
 292}
 293EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 294
 295struct nf_ct_helper_expectfn *
 296nf_ct_helper_expectfn_find_by_name(const char *name)
 297{
 298        struct nf_ct_helper_expectfn *cur;
 299        bool found = false;
 300
 301        rcu_read_lock();
 302        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 303                if (!strcmp(cur->name, name)) {
 304                        found = true;
 305                        break;
 306                }
 307        }
 308        rcu_read_unlock();
 309        return found ? cur : NULL;
 310}
 311EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 312
 313struct nf_ct_helper_expectfn *
 314nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 315{
 316        struct nf_ct_helper_expectfn *cur;
 317        bool found = false;
 318
 319        rcu_read_lock();
 320        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 321                if (cur->expectfn == symbol) {
 322                        found = true;
 323                        break;
 324                }
 325        }
 326        rcu_read_unlock();
 327        return found ? cur : NULL;
 328}
 329EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 330
 331int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 332{
 333        int ret = 0;
 334        struct nf_conntrack_helper *cur;
 335        struct hlist_node *n;
 336        unsigned int h = helper_hash(&me->tuple);
 337
 338        BUG_ON(me->expect_policy == NULL);
 339        BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 340        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 341
 342        mutex_lock(&nf_ct_helper_mutex);
 343        hlist_for_each_entry(cur, n, &nf_ct_helper_hash[h], hnode) {
 344                if (strncmp(cur->name, me->name, NF_CT_HELPER_NAME_LEN) == 0 &&
 345                    cur->tuple.src.l3num == me->tuple.src.l3num &&
 346                    cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 347                        ret = -EEXIST;
 348                        goto out;
 349                }
 350        }
 351        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 352        nf_ct_helper_count++;
 353out:
 354        mutex_unlock(&nf_ct_helper_mutex);
 355        return ret;
 356}
 357EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 358
 359static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
 360                                             struct net *net)
 361{
 362        struct nf_conntrack_tuple_hash *h;
 363        struct nf_conntrack_expect *exp;
 364        const struct hlist_node *n, *next;
 365        const struct hlist_nulls_node *nn;
 366        unsigned int i;
 367
 368        /* Get rid of expectations */
 369        for (i = 0; i < nf_ct_expect_hsize; i++) {
 370                hlist_for_each_entry_safe(exp, n, next,
 371                                          &net->ct.expect_hash[i], hnode) {
 372                        struct nf_conn_help *help = nfct_help(exp->master);
 373                        if ((rcu_dereference_protected(
 374                                        help->helper,
 375                                        lockdep_is_held(&nf_conntrack_lock)
 376                                        ) == me || exp->helper == me) &&
 377                            del_timer(&exp->timeout)) {
 378                                nf_ct_unlink_expect(exp);
 379                                nf_ct_expect_put(exp);
 380                        }
 381                }
 382        }
 383
 384        /* Get rid of expecteds, set helpers to NULL. */
 385        hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
 386                unhelp(h, me);
 387        for (i = 0; i < net->ct.htable_size; i++) {
 388                hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
 389                        unhelp(h, me);
 390        }
 391}
 392
 393void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 394{
 395        struct net *net;
 396
 397        mutex_lock(&nf_ct_helper_mutex);
 398        hlist_del_rcu(&me->hnode);
 399        nf_ct_helper_count--;
 400        mutex_unlock(&nf_ct_helper_mutex);
 401
 402        /* Make sure every nothing is still using the helper unless its a
 403         * connection in the hash.
 404         */
 405        synchronize_rcu();
 406
 407        rtnl_lock();
 408        spin_lock_bh(&nf_conntrack_lock);
 409        for_each_net(net)
 410                __nf_conntrack_helper_unregister(me, net);
 411        spin_unlock_bh(&nf_conntrack_lock);
 412        rtnl_unlock();
 413}
 414EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 415
 416static struct nf_ct_ext_type helper_extend __read_mostly = {
 417        .len    = sizeof(struct nf_conn_help),
 418        .align  = __alignof__(struct nf_conn_help),
 419        .id     = NF_CT_EXT_HELPER,
 420};
 421
 422int nf_conntrack_helper_init(struct net *net)
 423{
 424        int err;
 425
 426        net->ct.auto_assign_helper_warned = false;
 427        net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 428
 429        if (net_eq(net, &init_net)) {
 430                nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 431                nf_ct_helper_hash =
 432                        nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 433                if (!nf_ct_helper_hash)
 434                        return -ENOMEM;
 435
 436                err = nf_ct_extend_register(&helper_extend);
 437                if (err < 0)
 438                        goto err1;
 439        }
 440
 441        err = nf_conntrack_helper_init_sysctl(net);
 442        if (err < 0)
 443                goto out_sysctl;
 444
 445        return 0;
 446
 447out_sysctl:
 448        if (net_eq(net, &init_net))
 449                nf_ct_extend_unregister(&helper_extend);
 450err1:
 451        nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 452        return err;
 453}
 454
 455void nf_conntrack_helper_fini(struct net *net)
 456{
 457        nf_conntrack_helper_fini_sysctl(net);
 458        if (net_eq(net, &init_net)) {
 459                nf_ct_extend_unregister(&helper_extend);
 460                nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
 461        }
 462}
 463
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