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