linux/net/netfilter/nf_conntrack_helper.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/* Helper handling for netfilter. */
   3
   4/* (C) 1999-2001 Paul `Rusty' Russell
   5 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   6 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   7 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   8 */
   9
  10#include <linux/types.h>
  11#include <linux/netfilter.h>
  12#include <linux/module.h>
  13#include <linux/skbuff.h>
  14#include <linux/vmalloc.h>
  15#include <linux/stddef.h>
  16#include <linux/random.h>
  17#include <linux/err.h>
  18#include <linux/kernel.h>
  19#include <linux/netdevice.h>
  20#include <linux/rculist.h>
  21#include <linux/rtnetlink.h>
  22
  23#include <net/netfilter/nf_conntrack.h>
  24#include <net/netfilter/nf_conntrack_core.h>
  25#include <net/netfilter/nf_conntrack_ecache.h>
  26#include <net/netfilter/nf_conntrack_extend.h>
  27#include <net/netfilter/nf_conntrack_helper.h>
  28#include <net/netfilter/nf_conntrack_l4proto.h>
  29#include <net/netfilter/nf_log.h>
  30
  31static DEFINE_MUTEX(nf_ct_helper_mutex);
  32struct hlist_head *nf_ct_helper_hash __read_mostly;
  33EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  34unsigned int nf_ct_helper_hsize __read_mostly;
  35EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  36static unsigned int nf_ct_helper_count __read_mostly;
  37
  38static bool nf_ct_auto_assign_helper __read_mostly = false;
  39module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  40MODULE_PARM_DESC(nf_conntrack_helper,
  41                 "Enable automatic conntrack helper assignment (default 0)");
  42
  43static DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
  44static struct list_head nf_ct_nat_helpers __read_mostly;
  45
  46/* Stupid hash, but collision free for the default registrations of the
  47 * helpers currently in the kernel. */
  48static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  49{
  50        return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  51                (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  52}
  53
  54static struct nf_conntrack_helper *
  55__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  56{
  57        struct nf_conntrack_helper *helper;
  58        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
  59        unsigned int h;
  60
  61        if (!nf_ct_helper_count)
  62                return NULL;
  63
  64        h = helper_hash(tuple);
  65        hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
  66                if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  67                        return helper;
  68        }
  69        return NULL;
  70}
  71
  72struct nf_conntrack_helper *
  73__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  74{
  75        struct nf_conntrack_helper *h;
  76        unsigned int i;
  77
  78        for (i = 0; i < nf_ct_helper_hsize; i++) {
  79                hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
  80                        if (strcmp(h->name, name))
  81                                continue;
  82
  83                        if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
  84                            h->tuple.src.l3num != l3num)
  85                                continue;
  86
  87                        if (h->tuple.dst.protonum == protonum)
  88                                return h;
  89                }
  90        }
  91        return NULL;
  92}
  93EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  94
  95struct nf_conntrack_helper *
  96nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  97{
  98        struct nf_conntrack_helper *h;
  99
 100        rcu_read_lock();
 101
 102        h = __nf_conntrack_helper_find(name, l3num, protonum);
 103#ifdef CONFIG_MODULES
 104        if (h == NULL) {
 105                rcu_read_unlock();
 106                if (request_module("nfct-helper-%s", name) == 0) {
 107                        rcu_read_lock();
 108                        h = __nf_conntrack_helper_find(name, l3num, protonum);
 109                } else {
 110                        return h;
 111                }
 112        }
 113#endif
 114        if (h != NULL && !try_module_get(h->me))
 115                h = NULL;
 116        if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 117                module_put(h->me);
 118                h = NULL;
 119        }
 120
 121        rcu_read_unlock();
 122
 123        return h;
 124}
 125EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 126
 127void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 128{
 129        refcount_dec(&helper->refcnt);
 130        module_put(helper->me);
 131}
 132EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 133
 134static struct nf_conntrack_nat_helper *
 135nf_conntrack_nat_helper_find(const char *mod_name)
 136{
 137        struct nf_conntrack_nat_helper *cur;
 138        bool found = false;
 139
 140        list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
 141                if (!strcmp(cur->mod_name, mod_name)) {
 142                        found = true;
 143                        break;
 144                }
 145        }
 146        return found ? cur : NULL;
 147}
 148
 149int
 150nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 151{
 152        struct nf_conntrack_helper *h;
 153        struct nf_conntrack_nat_helper *nat;
 154        char mod_name[NF_CT_HELPER_NAME_LEN];
 155        int ret = 0;
 156
 157        rcu_read_lock();
 158        h = __nf_conntrack_helper_find(name, l3num, protonum);
 159        if (!h) {
 160                rcu_read_unlock();
 161                return -ENOENT;
 162        }
 163
 164        nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
 165        if (!nat) {
 166                snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
 167                rcu_read_unlock();
 168                request_module(mod_name);
 169
 170                rcu_read_lock();
 171                nat = nf_conntrack_nat_helper_find(mod_name);
 172                if (!nat) {
 173                        rcu_read_unlock();
 174                        return -ENOENT;
 175                }
 176        }
 177
 178        if (!try_module_get(nat->module))
 179                ret = -ENOENT;
 180
 181        rcu_read_unlock();
 182        return ret;
 183}
 184EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
 185
 186void nf_nat_helper_put(struct nf_conntrack_helper *helper)
 187{
 188        struct nf_conntrack_nat_helper *nat;
 189
 190        nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
 191        if (WARN_ON_ONCE(!nat))
 192                return;
 193
 194        module_put(nat->module);
 195}
 196EXPORT_SYMBOL_GPL(nf_nat_helper_put);
 197
 198struct nf_conn_help *
 199nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 200{
 201        struct nf_conn_help *help;
 202
 203        help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 204        if (help)
 205                INIT_HLIST_HEAD(&help->expectations);
 206        else
 207                pr_debug("failed to add helper extension area");
 208        return help;
 209}
 210EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 211
 212static struct nf_conntrack_helper *
 213nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 214{
 215        if (!net->ct.sysctl_auto_assign_helper) {
 216                if (net->ct.auto_assign_helper_warned)
 217                        return NULL;
 218                if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 219                        return NULL;
 220                pr_info("nf_conntrack: default automatic helper assignment "
 221                        "has been turned off for security reasons and CT-based "
 222                        " firewall rule not found. Use the iptables CT target "
 223                        "to attach helpers instead.\n");
 224                net->ct.auto_assign_helper_warned = 1;
 225                return NULL;
 226        }
 227
 228        return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 229}
 230
 231
 232int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 233                              gfp_t flags)
 234{
 235        struct nf_conntrack_helper *helper = NULL;
 236        struct nf_conn_help *help;
 237        struct net *net = nf_ct_net(ct);
 238
 239        /* We already got a helper explicitly attached. The function
 240         * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 241         * the helper up again. Since now the user is in full control of
 242         * making consistent helper configurations, skip this automatic
 243         * re-lookup, otherwise we'll lose the helper.
 244         */
 245        if (test_bit(IPS_HELPER_BIT, &ct->status))
 246                return 0;
 247
 248        if (tmpl != NULL) {
 249                help = nfct_help(tmpl);
 250                if (help != NULL) {
 251                        helper = help->helper;
 252                        set_bit(IPS_HELPER_BIT, &ct->status);
 253                }
 254        }
 255
 256        help = nfct_help(ct);
 257
 258        if (helper == NULL) {
 259                helper = nf_ct_lookup_helper(ct, net);
 260                if (helper == NULL) {
 261                        if (help)
 262                                RCU_INIT_POINTER(help->helper, NULL);
 263                        return 0;
 264                }
 265        }
 266
 267        if (help == NULL) {
 268                help = nf_ct_helper_ext_add(ct, flags);
 269                if (help == NULL)
 270                        return -ENOMEM;
 271        } else {
 272                /* We only allow helper re-assignment of the same sort since
 273                 * we cannot reallocate the helper extension area.
 274                 */
 275                struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 276
 277                if (tmp && tmp->help != helper->help) {
 278                        RCU_INIT_POINTER(help->helper, NULL);
 279                        return 0;
 280                }
 281        }
 282
 283        rcu_assign_pointer(help->helper, helper);
 284
 285        return 0;
 286}
 287EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 288
 289/* appropriate ct lock protecting must be taken by caller */
 290static int unhelp(struct nf_conn *ct, void *me)
 291{
 292        struct nf_conn_help *help = nfct_help(ct);
 293
 294        if (help && rcu_dereference_raw(help->helper) == me) {
 295                nf_conntrack_event(IPCT_HELPER, ct);
 296                RCU_INIT_POINTER(help->helper, NULL);
 297        }
 298
 299        /* We are not intended to delete this conntrack. */
 300        return 0;
 301}
 302
 303void nf_ct_helper_destroy(struct nf_conn *ct)
 304{
 305        struct nf_conn_help *help = nfct_help(ct);
 306        struct nf_conntrack_helper *helper;
 307
 308        if (help) {
 309                rcu_read_lock();
 310                helper = rcu_dereference(help->helper);
 311                if (helper && helper->destroy)
 312                        helper->destroy(ct);
 313                rcu_read_unlock();
 314        }
 315}
 316
 317static LIST_HEAD(nf_ct_helper_expectfn_list);
 318
 319void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 320{
 321        spin_lock_bh(&nf_conntrack_expect_lock);
 322        list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 323        spin_unlock_bh(&nf_conntrack_expect_lock);
 324}
 325EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 326
 327void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 328{
 329        spin_lock_bh(&nf_conntrack_expect_lock);
 330        list_del_rcu(&n->head);
 331        spin_unlock_bh(&nf_conntrack_expect_lock);
 332}
 333EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 334
 335/* Caller should hold the rcu lock */
 336struct nf_ct_helper_expectfn *
 337nf_ct_helper_expectfn_find_by_name(const char *name)
 338{
 339        struct nf_ct_helper_expectfn *cur;
 340        bool found = false;
 341
 342        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 343                if (!strcmp(cur->name, name)) {
 344                        found = true;
 345                        break;
 346                }
 347        }
 348        return found ? cur : NULL;
 349}
 350EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 351
 352/* Caller should hold the rcu lock */
 353struct nf_ct_helper_expectfn *
 354nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 355{
 356        struct nf_ct_helper_expectfn *cur;
 357        bool found = false;
 358
 359        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 360                if (cur->expectfn == symbol) {
 361                        found = true;
 362                        break;
 363                }
 364        }
 365        return found ? cur : NULL;
 366}
 367EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 368
 369__printf(3, 4)
 370void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 371                      const char *fmt, ...)
 372{
 373        const struct nf_conn_help *help;
 374        const struct nf_conntrack_helper *helper;
 375        struct va_format vaf;
 376        va_list args;
 377
 378        va_start(args, fmt);
 379
 380        vaf.fmt = fmt;
 381        vaf.va = &args;
 382
 383        /* Called from the helper function, this call never fails */
 384        help = nfct_help(ct);
 385
 386        /* rcu_read_lock()ed by nf_hook_thresh */
 387        helper = rcu_dereference(help->helper);
 388
 389        nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 390                      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 391
 392        va_end(args);
 393}
 394EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 395
 396int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 397{
 398        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 399        unsigned int h = helper_hash(&me->tuple);
 400        struct nf_conntrack_helper *cur;
 401        int ret = 0, i;
 402
 403        BUG_ON(me->expect_policy == NULL);
 404        BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 405        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 406
 407        if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 408                return -EINVAL;
 409
 410        mutex_lock(&nf_ct_helper_mutex);
 411        for (i = 0; i < nf_ct_helper_hsize; i++) {
 412                hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 413                        if (!strcmp(cur->name, me->name) &&
 414                            (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 415                             cur->tuple.src.l3num == me->tuple.src.l3num) &&
 416                            cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 417                                ret = -EEXIST;
 418                                goto out;
 419                        }
 420                }
 421        }
 422
 423        /* avoid unpredictable behaviour for auto_assign_helper */
 424        if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 425                hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 426                        if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 427                                                     &mask)) {
 428                                ret = -EEXIST;
 429                                goto out;
 430                        }
 431                }
 432        }
 433        refcount_set(&me->refcnt, 1);
 434        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 435        nf_ct_helper_count++;
 436out:
 437        mutex_unlock(&nf_ct_helper_mutex);
 438        return ret;
 439}
 440EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 441
 442static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 443{
 444        struct nf_conn_help *help = nfct_help(exp->master);
 445        const struct nf_conntrack_helper *me = data;
 446        const struct nf_conntrack_helper *this;
 447
 448        if (exp->helper == me)
 449                return true;
 450
 451        this = rcu_dereference_protected(help->helper,
 452                                         lockdep_is_held(&nf_conntrack_expect_lock));
 453        return this == me;
 454}
 455
 456void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 457{
 458        mutex_lock(&nf_ct_helper_mutex);
 459        hlist_del_rcu(&me->hnode);
 460        nf_ct_helper_count--;
 461        mutex_unlock(&nf_ct_helper_mutex);
 462
 463        /* Make sure every nothing is still using the helper unless its a
 464         * connection in the hash.
 465         */
 466        synchronize_rcu();
 467
 468        nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 469        nf_ct_iterate_destroy(unhelp, me);
 470
 471        /* Maybe someone has gotten the helper already when unhelp above.
 472         * So need to wait it.
 473         */
 474        synchronize_rcu();
 475}
 476EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 477
 478void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 479                       u16 l3num, u16 protonum, const char *name,
 480                       u16 default_port, u16 spec_port, u32 id,
 481                       const struct nf_conntrack_expect_policy *exp_pol,
 482                       u32 expect_class_max,
 483                       int (*help)(struct sk_buff *skb, unsigned int protoff,
 484                                   struct nf_conn *ct,
 485                                   enum ip_conntrack_info ctinfo),
 486                       int (*from_nlattr)(struct nlattr *attr,
 487                                          struct nf_conn *ct),
 488                       struct module *module)
 489{
 490        helper->tuple.src.l3num = l3num;
 491        helper->tuple.dst.protonum = protonum;
 492        helper->tuple.src.u.all = htons(spec_port);
 493        helper->expect_policy = exp_pol;
 494        helper->expect_class_max = expect_class_max;
 495        helper->help = help;
 496        helper->from_nlattr = from_nlattr;
 497        helper->me = module;
 498        snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 499                 NF_NAT_HELPER_PREFIX "%s", name);
 500
 501        if (spec_port == default_port)
 502                snprintf(helper->name, sizeof(helper->name), "%s", name);
 503        else
 504                snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 505}
 506EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 507
 508int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 509                                  unsigned int n)
 510{
 511        unsigned int i;
 512        int err = 0;
 513
 514        for (i = 0; i < n; i++) {
 515                err = nf_conntrack_helper_register(&helper[i]);
 516                if (err < 0)
 517                        goto err;
 518        }
 519
 520        return err;
 521err:
 522        if (i > 0)
 523                nf_conntrack_helpers_unregister(helper, i);
 524        return err;
 525}
 526EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 527
 528void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 529                                unsigned int n)
 530{
 531        while (n-- > 0)
 532                nf_conntrack_helper_unregister(&helper[n]);
 533}
 534EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 535
 536void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 537{
 538        mutex_lock(&nf_ct_nat_helpers_mutex);
 539        list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 540        mutex_unlock(&nf_ct_nat_helpers_mutex);
 541}
 542EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 543
 544void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 545{
 546        mutex_lock(&nf_ct_nat_helpers_mutex);
 547        list_del_rcu(&nat->list);
 548        mutex_unlock(&nf_ct_nat_helpers_mutex);
 549}
 550EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 551
 552static const struct nf_ct_ext_type helper_extend = {
 553        .len    = sizeof(struct nf_conn_help),
 554        .align  = __alignof__(struct nf_conn_help),
 555        .id     = NF_CT_EXT_HELPER,
 556};
 557
 558void nf_conntrack_helper_pernet_init(struct net *net)
 559{
 560        net->ct.auto_assign_helper_warned = false;
 561        net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 562}
 563
 564int nf_conntrack_helper_init(void)
 565{
 566        int ret;
 567        nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 568        nf_ct_helper_hash =
 569                nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 570        if (!nf_ct_helper_hash)
 571                return -ENOMEM;
 572
 573        ret = nf_ct_extend_register(&helper_extend);
 574        if (ret < 0) {
 575                pr_err("nf_ct_helper: Unable to register helper extension.\n");
 576                goto out_extend;
 577        }
 578
 579        INIT_LIST_HEAD(&nf_ct_nat_helpers);
 580        return 0;
 581out_extend:
 582        kvfree(nf_ct_helper_hash);
 583        return ret;
 584}
 585
 586void nf_conntrack_helper_fini(void)
 587{
 588        nf_ct_extend_unregister(&helper_extend);
 589        kvfree(nf_ct_helper_hash);
 590}
 591