net/netfilter/nf_conntrack_helper.c

   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 <[email protected]>
   6  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   7  * (C) 2006-2012 Patrick McHardy <[email protected]>
   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_conntrack_seqadj.h>
  30 #include <net/netfilter/nf_log.h>
  31 #include <net/ip.h>
  32
  33 static DEFINE_MUTEX(nf_ct_helper_mutex);
  34 struct hlist_head *nf_ct_helper_hash __read_mostly;
  35 EXPORT_SYMBOL_GPL(nf_ct_helper_hash);
  36 unsigned int nf_ct_helper_hsize __read_mostly;
  37 EXPORT_SYMBOL_GPL(nf_ct_helper_hsize);
  38 static unsigned int nf_ct_helper_count __read_mostly;
  39
  40 static DEFINE_MUTEX(nf_ct_nat_helpers_mutex);
  41 static struct list_head nf_ct_nat_helpers __read_mostly;
  42
  43 /* Stupid hash, but collision free for the default registrations of the
  44  * helpers currently in the kernel. */
  45 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  46 {
  47         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  48                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  49 }
  50
  51 struct nf_conntrack_helper *
  52 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  53 {
  54         struct nf_conntrack_helper *h;
  55         unsigned int i;
  56
  57         for (i = 0; i < nf_ct_helper_hsize; i++) {
  58                 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
  59                         if (strcmp(h->name, name))
  60                                 continue;
  61
  62                         if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
  63                             h->tuple.src.l3num != l3num)
  64                                 continue;
  65
  66                         if (h->tuple.dst.protonum == protonum)
  67                                 return h;
  68                 }
  69         }
  70         return NULL;
  71 }
  72 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  73
  74 struct nf_conntrack_helper *
  75 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  76 {
  77         struct nf_conntrack_helper *h;
  78
  79         rcu_read_lock();
  80
  81         h = __nf_conntrack_helper_find(name, l3num, protonum);
  82 #ifdef CONFIG_MODULES
  83         if (h == NULL) {
  84                 rcu_read_unlock();
  85                 if (request_module("nfct-helper-%s", name) == 0) {
  86                         rcu_read_lock();
  87                         h = __nf_conntrack_helper_find(name, l3num, protonum);
  88                 } else {
  89                         return h;
  90                 }
  91         }
  92 #endif
  93         if (h != NULL && !try_module_get(h->me))
  94                 h = NULL;
  95         if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
  96                 module_put(h->me);
  97                 h = NULL;
  98         }
  99
 100         rcu_read_unlock();
 101
 102         return h;
 103 }
 104 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 105
 106 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 107 {
 108         refcount_dec(&helper->refcnt);
 109         module_put(helper->me);
 110 }
 111 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 112
 113 static struct nf_conntrack_nat_helper *
 114 nf_conntrack_nat_helper_find(const char *mod_name)
 115 {
 116         struct nf_conntrack_nat_helper *cur;
 117         bool found = false;
 118
 119         list_for_each_entry_rcu(cur, &nf_ct_nat_helpers, list) {
 120                 if (!strcmp(cur->mod_name, mod_name)) {
 121                         found = true;
 122                         break;
 123                 }
 124         }
 125         return found ? cur : NULL;
 126 }
 127
 128 int
 129 nf_nat_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
 130 {
 131         struct nf_conntrack_helper *h;
 132         struct nf_conntrack_nat_helper *nat;
 133         char mod_name[NF_CT_HELPER_NAME_LEN];
 134         int ret = 0;
 135
 136         rcu_read_lock();
 137         h = __nf_conntrack_helper_find(name, l3num, protonum);
 138         if (!h) {
 139                 rcu_read_unlock();
 140                 return -ENOENT;
 141         }
 142
 143         nat = nf_conntrack_nat_helper_find(h->nat_mod_name);
 144         if (!nat) {
 145                 snprintf(mod_name, sizeof(mod_name), "%s", h->nat_mod_name);
 146                 rcu_read_unlock();
 147                 request_module("%s", mod_name);
 148
 149                 rcu_read_lock();
 150                 nat = nf_conntrack_nat_helper_find(mod_name);
 151                 if (!nat) {
 152                         rcu_read_unlock();
 153                         return -ENOENT;
 154                 }
 155         }
 156
 157         if (!try_module_get(nat->module))
 158                 ret = -ENOENT;
 159
 160         rcu_read_unlock();
 161         return ret;
 162 }
 163 EXPORT_SYMBOL_GPL(nf_nat_helper_try_module_get);
 164
 165 void nf_nat_helper_put(struct nf_conntrack_helper *helper)
 166 {
 167         struct nf_conntrack_nat_helper *nat;
 168
 169         nat = nf_conntrack_nat_helper_find(helper->nat_mod_name);
 170         if (WARN_ON_ONCE(!nat))
 171                 return;
 172
 173         module_put(nat->module);
 174 }
 175 EXPORT_SYMBOL_GPL(nf_nat_helper_put);
 176
 177 struct nf_conn_help *
 178 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 179 {
 180         struct nf_conn_help *help;
 181
 182         help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 183         if (help)
 184                 INIT_HLIST_HEAD(&help->expectations);
 185         else
 186                 pr_debug("failed to add helper extension area");
 187         return help;
 188 }
 189 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 190
 191 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 192                               gfp_t flags)
 193 {
 194         struct nf_conntrack_helper *helper = NULL;
 195         struct nf_conn_help *help;
 196
 197         /* We already got a helper explicitly attached. The function
 198          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 199          * the helper up again. Since now the user is in full control of
 200          * making consistent helper configurations, skip this automatic
 201          * re-lookup, otherwise we'll lose the helper.
 202          */
 203         if (test_bit(IPS_HELPER_BIT, &ct->status))
 204                 return 0;
 205
 206         if (WARN_ON_ONCE(!tmpl))
 207                 return 0;
 208
 209         help = nfct_help(tmpl);
 210         if (help != NULL) {
 211                 helper = rcu_dereference(help->helper);
 212                 set_bit(IPS_HELPER_BIT, &ct->status);
 213         }
 214
 215         help = nfct_help(ct);
 216
 217         if (helper == NULL) {
 218                 if (help)
 219                         RCU_INIT_POINTER(help->helper, NULL);
 220                 return 0;
 221         }
 222
 223         if (help == NULL) {
 224                 help = nf_ct_helper_ext_add(ct, flags);
 225                 if (help == NULL)
 226                         return -ENOMEM;
 227         } else {
 228                 /* We only allow helper re-assignment of the same sort since
 229                  * we cannot reallocate the helper extension area.
 230                  */
 231                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 232
 233                 if (tmp && tmp->help != helper->help) {
 234                         RCU_INIT_POINTER(help->helper, NULL);
 235                         return 0;
 236                 }
 237         }
 238
 239         rcu_assign_pointer(help->helper, helper);
 240
 241         return 0;
 242 }
 243 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 244
 245 /* 'skb' should already be pulled to nh_ofs. */
 246 int nf_ct_helper(struct sk_buff *skb, struct nf_conn *ct,
 247                  enum ip_conntrack_info ctinfo, u16 proto)
 248 {
 249         const struct nf_conntrack_helper *helper;
 250         const struct nf_conn_help *help;
 251         unsigned int protoff;
 252         int err;
 253
 254         if (ctinfo == IP_CT_RELATED_REPLY)
 255                 return NF_ACCEPT;
 256
 257         help = nfct_help(ct);
 258         if (!help)
 259                 return NF_ACCEPT;
 260
 261         helper = rcu_dereference(help->helper);
 262         if (!helper)
 263                 return NF_ACCEPT;
 264
 265         if (helper->tuple.src.l3num != NFPROTO_UNSPEC &&
 266             helper->tuple.src.l3num != proto)
 267                 return NF_ACCEPT;
 268
 269         switch (proto) {
 270         case NFPROTO_IPV4:
 271                 protoff = ip_hdrlen(skb);
 272                 proto = ip_hdr(skb)->protocol;
 273                 break;
 274         case NFPROTO_IPV6: {
 275                 u8 nexthdr = ipv6_hdr(skb)->nexthdr;
 276                 __be16 frag_off;
 277                 int ofs;
 278
 279                 ofs = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr,
 280                                        &frag_off);
 281                 if (ofs < 0 || (frag_off & htons(~0x7)) != 0) {
 282                         pr_debug("proto header not found\n");
 283                         return NF_ACCEPT;
 284                 }
 285                 protoff = ofs;
 286                 proto = nexthdr;
 287                 break;
 288         }
 289         default:
 290                 WARN_ONCE(1, "helper invoked on non-IP family!");
 291                 return NF_DROP;
 292         }
 293
 294         if (helper->tuple.dst.protonum != proto)
 295                 return NF_ACCEPT;
 296
 297         err = helper->help(skb, protoff, ct, ctinfo);
 298         if (err != NF_ACCEPT)
 299                 return err;
 300
 301         /* Adjust seqs after helper.  This is needed due to some helpers (e.g.,
 302          * FTP with NAT) adusting the TCP payload size when mangling IP
 303          * addresses and/or port numbers in the text-based control connection.
 304          */
 305         if (test_bit(IPS_SEQ_ADJUST_BIT, &ct->status) &&
 306             !nf_ct_seq_adjust(skb, ct, ctinfo, protoff))
 307                 return NF_DROP;
 308         return NF_ACCEPT;
 309 }
 310 EXPORT_SYMBOL_GPL(nf_ct_helper);
 311
 312 int nf_ct_add_helper(struct nf_conn *ct, const char *name, u8 family,
 313                      u8 proto, bool nat, struct nf_conntrack_helper **hp)
 314 {
 315         struct nf_conntrack_helper *helper;
 316         struct nf_conn_help *help;
 317         int ret = 0;
 318
 319         helper = nf_conntrack_helper_try_module_get(name, family, proto);
 320         if (!helper)
 321                 return -EINVAL;
 322
 323         help = nf_ct_helper_ext_add(ct, GFP_KERNEL);
 324         if (!help) {
 325                 nf_conntrack_helper_put(helper);
 326                 return -ENOMEM;
 327         }
 328 #if IS_ENABLED(CONFIG_NF_NAT)
 329         if (nat) {
 330                 ret = nf_nat_helper_try_module_get(name, family, proto);
 331                 if (ret) {
 332                         nf_conntrack_helper_put(helper);
 333                         return ret;
 334                 }
 335         }
 336 #endif
 337         rcu_assign_pointer(help->helper, helper);
 338         *hp = helper;
 339         return ret;
 340 }
 341 EXPORT_SYMBOL_GPL(nf_ct_add_helper);
 342
 343 /* appropriate ct lock protecting must be taken by caller */
 344 static int unhelp(struct nf_conn *ct, void *me)
 345 {
 346         struct nf_conn_help *help = nfct_help(ct);
 347
 348         if (help && rcu_dereference_raw(help->helper) == me) {
 349                 nf_conntrack_event(IPCT_HELPER, ct);
 350                 RCU_INIT_POINTER(help->helper, NULL);
 351         }
 352
 353         /* We are not intended to delete this conntrack. */
 354         return 0;
 355 }
 356
 357 void nf_ct_helper_destroy(struct nf_conn *ct)
 358 {
 359         struct nf_conn_help *help = nfct_help(ct);
 360         struct nf_conntrack_helper *helper;
 361
 362         if (help) {
 363                 rcu_read_lock();
 364                 helper = rcu_dereference(help->helper);
 365                 if (helper && helper->destroy)
 366                         helper->destroy(ct);
 367                 rcu_read_unlock();
 368         }
 369 }
 370
 371 static LIST_HEAD(nf_ct_helper_expectfn_list);
 372
 373 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 374 {
 375         spin_lock_bh(&nf_conntrack_expect_lock);
 376         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 377         spin_unlock_bh(&nf_conntrack_expect_lock);
 378 }
 379 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 380
 381 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 382 {
 383         spin_lock_bh(&nf_conntrack_expect_lock);
 384         list_del_rcu(&n->head);
 385         spin_unlock_bh(&nf_conntrack_expect_lock);
 386 }
 387 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 388
 389 /* Caller should hold the rcu lock */
 390 struct nf_ct_helper_expectfn *
 391 nf_ct_helper_expectfn_find_by_name(const char *name)
 392 {
 393         struct nf_ct_helper_expectfn *cur;
 394         bool found = false;
 395
 396         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 397                 if (!strcmp(cur->name, name)) {
 398                         found = true;
 399                         break;
 400                 }
 401         }
 402         return found ? cur : NULL;
 403 }
 404 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 405
 406 /* Caller should hold the rcu lock */
 407 struct nf_ct_helper_expectfn *
 408 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 409 {
 410         struct nf_ct_helper_expectfn *cur;
 411         bool found = false;
 412
 413         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 414                 if (cur->expectfn == symbol) {
 415                         found = true;
 416                         break;
 417                 }
 418         }
 419         return found ? cur : NULL;
 420 }
 421 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 422
 423 __printf(3, 4)
 424 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 425                       const char *fmt, ...)
 426 {
 427         const struct nf_conn_help *help;
 428         const struct nf_conntrack_helper *helper;
 429         struct va_format vaf;
 430         va_list args;
 431
 432         va_start(args, fmt);
 433
 434         vaf.fmt = fmt;
 435         vaf.va = &args;
 436
 437         /* Called from the helper function, this call never fails */
 438         help = nfct_help(ct);
 439
 440         /* rcu_read_lock()ed by nf_hook_thresh */
 441         helper = rcu_dereference(help->helper);
 442
 443         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 444                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 445
 446         va_end(args);
 447 }
 448 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 449
 450 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 451 {
 452         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 453         unsigned int h = helper_hash(&me->tuple);
 454         struct nf_conntrack_helper *cur;
 455         int ret = 0, i;
 456
 457         BUG_ON(me->expect_policy == NULL);
 458         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 459         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 460
 461         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 462                 return -EINVAL;
 463
 464         mutex_lock(&nf_ct_helper_mutex);
 465         for (i = 0; i < nf_ct_helper_hsize; i++) {
 466                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 467                         if (!strcmp(cur->name, me->name) &&
 468                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 469                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 470                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 471                                 ret = -EEXIST;
 472                                 goto out;
 473                         }
 474                 }
 475         }
 476
 477         /* avoid unpredictable behaviour for auto_assign_helper */
 478         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 479                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 480                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 481                                                      &mask)) {
 482                                 ret = -EEXIST;
 483                                 goto out;
 484                         }
 485                 }
 486         }
 487         refcount_set(&me->refcnt, 1);
 488         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 489         nf_ct_helper_count++;
 490 out:
 491         mutex_unlock(&nf_ct_helper_mutex);
 492         return ret;
 493 }
 494 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 495
 496 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 497 {
 498         struct nf_conn_help *help = nfct_help(exp->master);
 499         const struct nf_conntrack_helper *me = data;
 500         const struct nf_conntrack_helper *this;
 501
 502         if (exp->helper == me)
 503                 return true;
 504
 505         this = rcu_dereference_protected(help->helper,
 506                                          lockdep_is_held(&nf_conntrack_expect_lock));
 507         return this == me;
 508 }
 509
 510 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 511 {
 512         mutex_lock(&nf_ct_helper_mutex);
 513         hlist_del_rcu(&me->hnode);
 514         nf_ct_helper_count--;
 515         mutex_unlock(&nf_ct_helper_mutex);
 516
 517         /* Make sure every nothing is still using the helper unless its a
 518          * connection in the hash.
 519          */
 520         synchronize_rcu();
 521
 522         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 523         nf_ct_iterate_destroy(unhelp, me);
 524 }
 525 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 526
 527 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 528                        u16 l3num, u16 protonum, const char *name,
 529                        u16 default_port, u16 spec_port, u32 id,
 530                        const struct nf_conntrack_expect_policy *exp_pol,
 531                        u32 expect_class_max,
 532                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 533                                    struct nf_conn *ct,
 534                                    enum ip_conntrack_info ctinfo),
 535                        int (*from_nlattr)(struct nlattr *attr,
 536                                           struct nf_conn *ct),
 537                        struct module *module)
 538 {
 539         helper->tuple.src.l3num = l3num;
 540         helper->tuple.dst.protonum = protonum;
 541         helper->tuple.src.u.all = htons(spec_port);
 542         helper->expect_policy = exp_pol;
 543         helper->expect_class_max = expect_class_max;
 544         helper->help = help;
 545         helper->from_nlattr = from_nlattr;
 546         helper->me = module;
 547         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 548                  NF_NAT_HELPER_PREFIX "%s", name);
 549
 550         if (spec_port == default_port)
 551                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 552         else
 553                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 554 }
 555 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 556
 557 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 558                                   unsigned int n)
 559 {
 560         unsigned int i;
 561         int err = 0;
 562
 563         for (i = 0; i < n; i++) {
 564                 err = nf_conntrack_helper_register(&helper[i]);
 565                 if (err < 0)
 566                         goto err;
 567         }
 568
 569         return err;
 570 err:
 571         if (i > 0)
 572                 nf_conntrack_helpers_unregister(helper, i);
 573         return err;
 574 }
 575 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 576
 577 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 578                                 unsigned int n)
 579 {
 580         while (n-- > 0)
 581                 nf_conntrack_helper_unregister(&helper[n]);
 582 }
 583 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 584
 585 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 586 {
 587         mutex_lock(&nf_ct_nat_helpers_mutex);
 588         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 589         mutex_unlock(&nf_ct_nat_helpers_mutex);
 590 }
 591 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 592
 593 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 594 {
 595         mutex_lock(&nf_ct_nat_helpers_mutex);
 596         list_del_rcu(&nat->list);
 597         mutex_unlock(&nf_ct_nat_helpers_mutex);
 598 }
 599 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 600
 601 int nf_conntrack_helper_init(void)
 602 {
 603         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 604         nf_ct_helper_hash =
 605                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 606         if (!nf_ct_helper_hash)
 607                 return -ENOMEM;
 608
 609         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 610         return 0;
 611 }
 612
 613 void nf_conntrack_helper_fini(void)
 614 {
 615         kvfree(nf_ct_helper_hash);
 616 }