linux/net/netfilter/nf_conntrack_helper.c
<<
>>
Prefs
   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        struct nf_conntrack_net *cnet = nf_ct_pernet(net);
 216
 217        if (!cnet->sysctl_auto_assign_helper) {
 218                if (cnet->auto_assign_helper_warned)
 219                        return NULL;
 220                if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 221                        return NULL;
 222                pr_info("nf_conntrack: default automatic helper assignment "
 223                        "has been turned off for security reasons and CT-based "
 224                        "firewall rule not found. Use the iptables CT target "
 225                        "to attach helpers instead.\n");
 226                cnet->auto_assign_helper_warned = true;
 227                return NULL;
 228        }
 229
 230        return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 231}
 232
 233int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 234                              gfp_t flags)
 235{
 236        struct nf_conntrack_helper *helper = NULL;
 237        struct nf_conn_help *help;
 238        struct net *net = nf_ct_net(ct);
 239
 240        /* We already got a helper explicitly attached. The function
 241         * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 242         * the helper up again. Since now the user is in full control of
 243         * making consistent helper configurations, skip this automatic
 244         * re-lookup, otherwise we'll lose the helper.
 245         */
 246        if (test_bit(IPS_HELPER_BIT, &ct->status))
 247                return 0;
 248
 249        if (tmpl != NULL) {
 250                help = nfct_help(tmpl);
 251                if (help != NULL) {
 252                        helper = help->helper;
 253                        set_bit(IPS_HELPER_BIT, &ct->status);
 254                }
 255        }
 256
 257        help = nfct_help(ct);
 258
 259        if (helper == NULL) {
 260                helper = nf_ct_lookup_helper(ct, net);
 261                if (helper == NULL) {
 262                        if (help)
 263                                RCU_INIT_POINTER(help->helper, NULL);
 264                        return 0;
 265                }
 266        }
 267
 268        if (help == NULL) {
 269                help = nf_ct_helper_ext_add(ct, flags);
 270                if (help == NULL)
 271                        return -ENOMEM;
 272        } else {
 273                /* We only allow helper re-assignment of the same sort since
 274                 * we cannot reallocate the helper extension area.
 275                 */
 276                struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 277
 278                if (tmp && tmp->help != helper->help) {
 279                        RCU_INIT_POINTER(help->helper, NULL);
 280                        return 0;
 281                }
 282        }
 283
 284        rcu_assign_pointer(help->helper, helper);
 285
 286        return 0;
 287}
 288EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 289
 290/* appropriate ct lock protecting must be taken by caller */
 291static int unhelp(struct nf_conn *ct, void *me)
 292{
 293        struct nf_conn_help *help = nfct_help(ct);
 294
 295        if (help && rcu_dereference_raw(help->helper) == me) {
 296                nf_conntrack_event(IPCT_HELPER, ct);
 297                RCU_INIT_POINTER(help->helper, NULL);
 298        }
 299
 300        /* We are not intended to delete this conntrack. */
 301        return 0;
 302}
 303
 304void nf_ct_helper_destroy(struct nf_conn *ct)
 305{
 306        struct nf_conn_help *help = nfct_help(ct);
 307        struct nf_conntrack_helper *helper;
 308
 309        if (help) {
 310                rcu_read_lock();
 311                helper = rcu_dereference(help->helper);
 312                if (helper && helper->destroy)
 313                        helper->destroy(ct);
 314                rcu_read_unlock();
 315        }
 316}
 317
 318static LIST_HEAD(nf_ct_helper_expectfn_list);
 319
 320void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 321{
 322        spin_lock_bh(&nf_conntrack_expect_lock);
 323        list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 324        spin_unlock_bh(&nf_conntrack_expect_lock);
 325}
 326EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 327
 328void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 329{
 330        spin_lock_bh(&nf_conntrack_expect_lock);
 331        list_del_rcu(&n->head);
 332        spin_unlock_bh(&nf_conntrack_expect_lock);
 333}
 334EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 335
 336/* Caller should hold the rcu lock */
 337struct nf_ct_helper_expectfn *
 338nf_ct_helper_expectfn_find_by_name(const char *name)
 339{
 340        struct nf_ct_helper_expectfn *cur;
 341        bool found = false;
 342
 343        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 344                if (!strcmp(cur->name, name)) {
 345                        found = true;
 346                        break;
 347                }
 348        }
 349        return found ? cur : NULL;
 350}
 351EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 352
 353/* Caller should hold the rcu lock */
 354struct nf_ct_helper_expectfn *
 355nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 356{
 357        struct nf_ct_helper_expectfn *cur;
 358        bool found = false;
 359
 360        list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 361                if (cur->expectfn == symbol) {
 362                        found = true;
 363                        break;
 364                }
 365        }
 366        return found ? cur : NULL;
 367}
 368EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 369
 370__printf(3, 4)
 371void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 372                      const char *fmt, ...)
 373{
 374        const struct nf_conn_help *help;
 375        const struct nf_conntrack_helper *helper;
 376        struct va_format vaf;
 377        va_list args;
 378
 379        va_start(args, fmt);
 380
 381        vaf.fmt = fmt;
 382        vaf.va = &args;
 383
 384        /* Called from the helper function, this call never fails */
 385        help = nfct_help(ct);
 386
 387        /* rcu_read_lock()ed by nf_hook_thresh */
 388        helper = rcu_dereference(help->helper);
 389
 390        nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 391                      "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 392
 393        va_end(args);
 394}
 395EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 396
 397int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 398{
 399        struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 400        unsigned int h = helper_hash(&me->tuple);
 401        struct nf_conntrack_helper *cur;
 402        int ret = 0, i;
 403
 404        BUG_ON(me->expect_policy == NULL);
 405        BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 406        BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 407
 408        if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 409                return -EINVAL;
 410
 411        mutex_lock(&nf_ct_helper_mutex);
 412        for (i = 0; i < nf_ct_helper_hsize; i++) {
 413                hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 414                        if (!strcmp(cur->name, me->name) &&
 415                            (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 416                             cur->tuple.src.l3num == me->tuple.src.l3num) &&
 417                            cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 418                                ret = -EEXIST;
 419                                goto out;
 420                        }
 421                }
 422        }
 423
 424        /* avoid unpredictable behaviour for auto_assign_helper */
 425        if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 426                hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 427                        if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 428                                                     &mask)) {
 429                                ret = -EEXIST;
 430                                goto out;
 431                        }
 432                }
 433        }
 434        refcount_set(&me->refcnt, 1);
 435        hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 436        nf_ct_helper_count++;
 437out:
 438        mutex_unlock(&nf_ct_helper_mutex);
 439        return ret;
 440}
 441EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 442
 443static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 444{
 445        struct nf_conn_help *help = nfct_help(exp->master);
 446        const struct nf_conntrack_helper *me = data;
 447        const struct nf_conntrack_helper *this;
 448
 449        if (exp->helper == me)
 450                return true;
 451
 452        this = rcu_dereference_protected(help->helper,
 453                                         lockdep_is_held(&nf_conntrack_expect_lock));
 454        return this == me;
 455}
 456
 457void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 458{
 459        mutex_lock(&nf_ct_helper_mutex);
 460        hlist_del_rcu(&me->hnode);
 461        nf_ct_helper_count--;
 462        mutex_unlock(&nf_ct_helper_mutex);
 463
 464        /* Make sure every nothing is still using the helper unless its a
 465         * connection in the hash.
 466         */
 467        synchronize_rcu();
 468
 469        nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 470        nf_ct_iterate_destroy(unhelp, me);
 471
 472        /* Maybe someone has gotten the helper already when unhelp above.
 473         * So need to wait it.
 474         */
 475        synchronize_rcu();
 476}
 477EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 478
 479void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 480                       u16 l3num, u16 protonum, const char *name,
 481                       u16 default_port, u16 spec_port, u32 id,
 482                       const struct nf_conntrack_expect_policy *exp_pol,
 483                       u32 expect_class_max,
 484                       int (*help)(struct sk_buff *skb, unsigned int protoff,
 485                                   struct nf_conn *ct,
 486                                   enum ip_conntrack_info ctinfo),
 487                       int (*from_nlattr)(struct nlattr *attr,
 488                                          struct nf_conn *ct),
 489                       struct module *module)
 490{
 491        helper->tuple.src.l3num = l3num;
 492        helper->tuple.dst.protonum = protonum;
 493        helper->tuple.src.u.all = htons(spec_port);
 494        helper->expect_policy = exp_pol;
 495        helper->expect_class_max = expect_class_max;
 496        helper->help = help;
 497        helper->from_nlattr = from_nlattr;
 498        helper->me = module;
 499        snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 500                 NF_NAT_HELPER_PREFIX "%s", name);
 501
 502        if (spec_port == default_port)
 503                snprintf(helper->name, sizeof(helper->name), "%s", name);
 504        else
 505                snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 506}
 507EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 508
 509int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 510                                  unsigned int n)
 511{
 512        unsigned int i;
 513        int err = 0;
 514
 515        for (i = 0; i < n; i++) {
 516                err = nf_conntrack_helper_register(&helper[i]);
 517                if (err < 0)
 518                        goto err;
 519        }
 520
 521        return err;
 522err:
 523        if (i > 0)
 524                nf_conntrack_helpers_unregister(helper, i);
 525        return err;
 526}
 527EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 528
 529void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 530                                unsigned int n)
 531{
 532        while (n-- > 0)
 533                nf_conntrack_helper_unregister(&helper[n]);
 534}
 535EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 536
 537void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 538{
 539        mutex_lock(&nf_ct_nat_helpers_mutex);
 540        list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 541        mutex_unlock(&nf_ct_nat_helpers_mutex);
 542}
 543EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 544
 545void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 546{
 547        mutex_lock(&nf_ct_nat_helpers_mutex);
 548        list_del_rcu(&nat->list);
 549        mutex_unlock(&nf_ct_nat_helpers_mutex);
 550}
 551EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 552
 553static const struct nf_ct_ext_type helper_extend = {
 554        .len    = sizeof(struct nf_conn_help),
 555        .align  = __alignof__(struct nf_conn_help),
 556        .id     = NF_CT_EXT_HELPER,
 557};
 558
 559void nf_conntrack_helper_pernet_init(struct net *net)
 560{
 561        struct nf_conntrack_net *cnet = nf_ct_pernet(net);
 562
 563        cnet->sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 564}
 565
 566int nf_conntrack_helper_init(void)
 567{
 568        int ret;
 569        nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 570        nf_ct_helper_hash =
 571                nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 572        if (!nf_ct_helper_hash)
 573                return -ENOMEM;
 574
 575        ret = nf_ct_extend_register(&helper_extend);
 576        if (ret < 0) {
 577                pr_err("nf_ct_helper: Unable to register helper extension.\n");
 578                goto out_extend;
 579        }
 580
 581        INIT_LIST_HEAD(&nf_ct_nat_helpers);
 582        return 0;
 583out_extend:
 584        kvfree(nf_ct_helper_hash);
 585        return ret;
 586}
 587
 588void nf_conntrack_helper_fini(void)
 589{
 590        nf_ct_extend_unregister(&helper_extend);
 591        kvfree(nf_ct_helper_hash);
 592}
 593
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.