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
  46extern unsigned int nf_conntrack_net_id;
  47
  48/* Stupid hash, but collision free for the default registrations of the
  49 * helpers currently in the kernel. */
  50static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  51{
  52        return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  53                (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  54}
  55
  56static struct nf_conntrack_helper *
  57__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  58{
  59        struct nf_conntrack_helper *helper;
  60        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
  61        unsigned int h;
  62
  63        if (!nf_ct_helper_count)
  64                return NULL;
  65
  66        h = helper_hash(tuple);
  67        hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
  68                if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  69                        return helper;
  70        }
  71        return NULL;
  72}
  73
  74struct nf_conntrack_helper *
  75__nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  76{
  77        struct nf_conntrack_helper *h;
  78        unsigned int i;
  79
  80        for (i = 0; i < nf_ct_helper_hsize; i++) {
  81                hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
  82                        if (strcmp(h->name, name))
  83                                continue;
  84
  85                        if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
  86                            h->tuple.src.l3num != l3num)
  87                                continue;
  88
  89                        if (h->tuple.dst.protonum == protonum)
  90                                return h;
  91                }
  92        }
  93        return NULL;
  94}
  95EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  96
  97struct nf_conntrack_helper *
  98nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  99{
 100        struct nf_conntrack_helper *h;
 101
 102        rcu_read_lock();
 103
 104        h = __nf_conntrack_helper_find(name, l3num, protonum);
 105#ifdef CONFIG_MODULES
 106        if (h == NULL) {
 107                rcu_read_unlock();
 108                if (request_module("nfct-helper-%s", name) == 0) {
 109                        rcu_read_lock();
 110                        h = __nf_conntrack_helper_find(name, l3num, protonum);
 111                } else {
 112                        return h;
 113                }
 114        }
 115#endif
 116        if (h != NULL && !try_module_get(h->me))
 117                h = NULL;
 118        if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 119                module_put(h->me);
 120                h = NULL;
 121        }
 122
 123        rcu_read_unlock();
 124
 125        return h;
 126}
 127EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 128
 129void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 130{
 131        refcount_dec(&helper->refcnt);
 132        module_put(helper->me);
 133}
 134EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 135
 136static struct nf_conntrack_nat_helper *
 137nf_conntrack_nat_helper_find(const char *mod_name)
 138{
 139        struct nf_conntrack_nat_helper *cur;
 140        bool found = false;
 141
 142        list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
 143                if (!strcmp(cur->mod_name, mod_name)) {
 144                        found = true;
 145                        break;
 146                }
 147        }
 148        return found ? cur : NULL;
 149}
 150
 151int
 152nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 153{
 154        struct nf_conntrack_helper *h;
 155        struct nf_conntrack_nat_helper *nat;
 156        char mod_name[NF_CT_HELPER_NAME_LEN];
 157        int ret = 0;
 158
 159        rcu_read_lock();
 160        h = __nf_conntrack_helper_find(name, l3num, protonum);
 161        if (!h) {
 162                rcu_read_unlock();
 163                return -ENOENT;
 164        }
 165
 166        nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
 167        if (!nat) {
 168                snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
 169                rcu_read_unlock();
 170                request_module(mod_name);
 171
 172                rcu_read_lock();
 173                nat = nf_conntrack_nat_helper_find(mod_name);
 174                if (!nat) {
 175                        rcu_read_unlock();
 176                        return -ENOENT;
 177                }
 178        }
 179
 180        if (!try_module_get(nat->module))
 181                ret = -ENOENT;
 182
 183        rcu_read_unlock();
 184        return ret;
 185}
 186EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
 187
 188void nf_nat_helper_put(struct nf_conntrack_helper *helper)
 189{
 190        struct nf_conntrack_nat_helper *nat;
 191
 192        nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
 193        if (WARN_ON_ONCE(!nat))
 194                return;
 195
 196        module_put(nat->module);
 197}
 198EXPORT_SYMBOL_GPL(nf_nat_helper_put);
 199
 200struct nf_conn_help *
 201nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 202{
 203        struct nf_conn_help *help;
 204
 205        help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 206        if (help)
 207                INIT_HLIST_HEAD(&help->expectations);
 208        else
 209                pr_debug("failed to add helper extension area");
 210        return help;
 211}
 212EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 213
 214static struct nf_conntrack_helper *
 215nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 216{
 217        struct nf_conntrack_net *cnet = net_generic(net, nf_conntrack_net_id);
 218
 219        if (!cnet->sysctl_auto_assign_helper) {
 220                if (cnet->auto_assign_helper_warned)
 221                        return NULL;
 222                if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 223                        return NULL;
 224                pr_info("nf_conntrack: default automatic helper assignment "
 225                        "has been turned off for security reasons and CT-based "
 226                        "firewall rule not found. Use the iptables CT target "
 227                        "to attach helpers instead.\n");
 228                cnet->auto_assign_helper_warned = true;
 229                return NULL;
 230        }
 231
 232        return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 233}
 234
 235int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 236                              gfp_t flags)
 237{
 238        struct nf_conntrack_helper *helper = NULL;
 239        struct nf_conn_help *help;
 240        struct net *net = nf_ct_net(ct);
 241
 242        /* We already got a helper explicitly attached. The function
 243         * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 244         * the helper up again. Since now the user is in full control of
 245         * making consistent helper configurations, skip this automatic
 246         * re-lookup, otherwise we'll lose the helper.
 247         */
 248        if (test_bit(IPS_HELPER_BIT, &ct->status))
 249                return 0;
 250
 251        if (tmpl != NULL) {
 252                help = nfct_help(tmpl);
 253                if (help != NULL) {
 254                        helper = help->helper;
 255                        set_bit(IPS_HELPER_BIT, &ct->status);
 256                }
 257        }
 258
 259        help = nfct_help(ct);
 260
 261        if (helper == NULL) {
 262                helper = nf_ct_lookup_helper(ct, net);
 263                if (helper == NULL) {
 264                        if (help)
 265                                RCU_INIT_POINTER(help->helper, NULL);
 266                        return 0;
 267                }
 268        }
 269
 270        if (help == NULL) {
 271                help = nf_ct_helper_ext_add(ct, flags);
 272                if (help == NULL)
 273                        return -ENOMEM;
 274        } else {
 275                /* We only allow helper re-assignment of the same sort since
 276                 * we cannot reallocate the helper extension area.
 277                 */
 278                struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 279
 280                if (tmp && tmp->help != helper->help) {
 281                        RCU_INIT_POINTER(help->helper, NULL);
 282                        return 0;
 283                }
 284        }
 285
 286        rcu_assign_pointer(help->helper, helper);
 287
 288        return 0;
 289}
 290EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 291
 292/* appropriate ct lock protecting must be taken by caller */
 293static int unhelp(struct nf_conn *ct, void *me)
 294{
 295        struct nf_conn_help *help = nfct_help(ct);
 296
 297        if (help && rcu_dereference_raw(help->helper) == me) {
 298                nf_conntrack_event(IPCT_HELPER, ct);
 299                RCU_INIT_POINTER(help->helper, NULL);
 300        }
 301
 302        /* We are not intended to delete this conntrack. */
 303        return 0;
 304}
 305
 306void nf_ct_helper_destroy(struct nf_conn *ct)
 307{
 308        struct nf_conn_help *help = nfct_help(ct);
 309        struct nf_conntrack_helper *helper;
 310
 311        if (help) {
 312                rcu_read_lock();
 313                helper = rcu_dereference(help->helper);
 314                if (helper && helper->destroy)
 315                        helper->destroy(ct);
 316                rcu_read_unlock();
 317        }
 318}
 319
 320static LIST_HEAD(nf_ct_helper_expectfn_list);
 321
 322void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 323{
 324        spin_lock_bh(&nf_conntrack_expect_lock);
 325        list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 326        spin_unlock_bh(&nf_conntrack_expect_lock);
 327}
 328EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 329
 330void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 331{
 332        spin_lock_bh(&nf_conntrack_expect_lock);
 333        list_del_rcu(&n->head);
 334        spin_unlock_bh(&nf_conntrack_expect_lock);
 335}
 336EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 337
 338/* Caller should hold the rcu lock */
 339struct nf_ct_helper_expectfn *
 340nf_ct_helper_expectfn_find_by_name(const char *name)
 341{
 342        struct nf_ct_helper_expectfn *cur;
 343        bool found = false;
 344
 345        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 346                if (!strcmp(cur->name, name)) {
 347                        found = true;
 348                        break;
 349                }
 350        }
 351        return found ? cur : NULL;
 352}
 353EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 354
 355/* Caller should hold the rcu lock */
 356struct nf_ct_helper_expectfn *
 357nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 358{
 359        struct nf_ct_helper_expectfn *cur;
 360        bool found = false;
 361
 362        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 363                if (cur->expectfn == symbol) {
 364                        found = true;
 365                        break;
 366                }
 367        }
 368        return found ? cur : NULL;
 369}
 370EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 371
 372__printf(3, 4)
 373void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 374                      const char *fmt, ...)
 375{
 376        const struct nf_conn_help *help;
 377        const struct nf_conntrack_helper *helper;
 378        struct va_format vaf;
 379        va_list args;
 380
 381        va_start(args, fmt);
 382
 383        vaf.fmt = fmt;
 384        vaf.va = &args;
 385
 386        /* Called from the helper function, this call never fails */
 387        help = nfct_help(ct);
 388
 389        /* rcu_read_lock()ed by nf_hook_thresh */
 390        helper = rcu_dereference(help->helper);
 391
 392        nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 393                      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 394
 395        va_end(args);
 396}
 397EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 398
 399int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 400{
 401        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 402        unsigned int h = helper_hash(&me->tuple);
 403        struct nf_conntrack_helper *cur;
 404        int ret = 0, i;
 405
 406        BUG_ON(me->expect_policy == NULL);
 407        BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 408        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 409
 410        if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 411                return -EINVAL;
 412
 413        mutex_lock(&nf_ct_helper_mutex);
 414        for (i = 0; i < nf_ct_helper_hsize; i++) {
 415                hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 416                        if (!strcmp(cur->name, me->name) &&
 417                            (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 418                             cur->tuple.src.l3num == me->tuple.src.l3num) &&
 419                            cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 420                                ret = -EEXIST;
 421                                goto out;
 422                        }
 423                }
 424        }
 425
 426        /* avoid unpredictable behaviour for auto_assign_helper */
 427        if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 428                hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 429                        if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 430                                                     &mask)) {
 431                                ret = -EEXIST;
 432                                goto out;
 433                        }
 434                }
 435        }
 436        refcount_set(&me->refcnt, 1);
 437        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 438        nf_ct_helper_count++;
 439out:
 440        mutex_unlock(&nf_ct_helper_mutex);
 441        return ret;
 442}
 443EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 444
 445static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 446{
 447        struct nf_conn_help *help = nfct_help(exp->master);
 448        const struct nf_conntrack_helper *me = data;
 449        const struct nf_conntrack_helper *this;
 450
 451        if (exp->helper == me)
 452                return true;
 453
 454        this = rcu_dereference_protected(help->helper,
 455                                         lockdep_is_held(&nf_conntrack_expect_lock));
 456        return this == me;
 457}
 458
 459void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 460{
 461        mutex_lock(&nf_ct_helper_mutex);
 462        hlist_del_rcu(&me->hnode);
 463        nf_ct_helper_count--;
 464        mutex_unlock(&nf_ct_helper_mutex);
 465
 466        /* Make sure every nothing is still using the helper unless its a
 467         * connection in the hash.
 468         */
 469        synchronize_rcu();
 470
 471        nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 472        nf_ct_iterate_destroy(unhelp, me);
 473
 474        /* Maybe someone has gotten the helper already when unhelp above.
 475         * So need to wait it.
 476         */
 477        synchronize_rcu();
 478}
 479EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 480
 481void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 482                       u16 l3num, u16 protonum, const char *name,
 483                       u16 default_port, u16 spec_port, u32 id,
 484                       const struct nf_conntrack_expect_policy *exp_pol,
 485                       u32 expect_class_max,
 486                       int (*help)(struct sk_buff *skb, unsigned int protoff,
 487                                   struct nf_conn *ct,
 488                                   enum ip_conntrack_info ctinfo),
 489                       int (*from_nlattr)(struct nlattr *attr,
 490                                          struct nf_conn *ct),
 491                       struct module *module)
 492{
 493        helper->tuple.src.l3num = l3num;
 494        helper->tuple.dst.protonum = protonum;
 495        helper->tuple.src.u.all = htons(spec_port);
 496        helper->expect_policy = exp_pol;
 497        helper->expect_class_max = expect_class_max;
 498        helper->help = help;
 499        helper->from_nlattr = from_nlattr;
 500        helper->me = module;
 501        snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 502                 NF_NAT_HELPER_PREFIX "%s", name);
 503
 504        if (spec_port == default_port)
 505                snprintf(helper->name, sizeof(helper->name), "%s", name);
 506        else
 507                snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 508}
 509EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 510
 511int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 512                                  unsigned int n)
 513{
 514        unsigned int i;
 515        int err = 0;
 516
 517        for (i = 0; i < n; i++) {
 518                err = nf_conntrack_helper_register(&helper[i]);
 519                if (err < 0)
 520                        goto err;
 521        }
 522
 523        return err;
 524err:
 525        if (i > 0)
 526                nf_conntrack_helpers_unregister(helper, i);
 527        return err;
 528}
 529EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 530
 531void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 532                                unsigned int n)
 533{
 534        while (n-- > 0)
 535                nf_conntrack_helper_unregister(&helper[n]);
 536}
 537EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 538
 539void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 540{
 541        mutex_lock(&nf_ct_nat_helpers_mutex);
 542        list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 543        mutex_unlock(&nf_ct_nat_helpers_mutex);
 544}
 545EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 546
 547void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 548{
 549        mutex_lock(&nf_ct_nat_helpers_mutex);
 550        list_del_rcu(&nat->list);
 551        mutex_unlock(&nf_ct_nat_helpers_mutex);
 552}
 553EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 554
 555static const struct nf_ct_ext_type helper_extend = {
 556        .len    = sizeof(struct nf_conn_help),
 557        .align  = __alignof__(struct nf_conn_help),
 558        .id     = NF_CT_EXT_HELPER,
 559};
 560
 561void nf_conntrack_helper_pernet_init(struct net *net)
 562{
 563        struct nf_conntrack_net *cnet = net_generic(net, nf_conntrack_net_id);
 564
 565        cnet->sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 566}
 567
 568int nf_conntrack_helper_init(void)
 569{
 570        int ret;
 571        nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 572        nf_ct_helper_hash =
 573                nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 574        if (!nf_ct_helper_hash)
 575                return -ENOMEM;
 576
 577        ret = nf_ct_extend_register(&helper_extend);
 578        if (ret < 0) {
 579                pr_err("nf_ct_helper: Unable to register helper extension.\n");
 580                goto out_extend;
 581        }
 582
 583        INIT_LIST_HEAD(&nf_ct_nat_helpers);
 584        return 0;
 585out_extend:
 586        kvfree(nf_ct_helper_hash);
 587        return ret;
 588}
 589
 590void nf_conntrack_helper_fini(void)
 591{
 592        nf_ct_extend_unregister(&helper_extend);
 593        kvfree(nf_ct_helper_hash);
 594}
 595