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 /* appropriate ct lock protecting must be taken by caller */
 246 static int unhelp(struct nf_conn *ct, void *me)
 247 {
 248         struct nf_conn_help *help = nfct_help(ct);
 249
 250         if (help && rcu_dereference_raw(help->helper) == me) {
 251                 nf_conntrack_event(IPCT_HELPER, ct);
 252                 RCU_INIT_POINTER(help->helper, NULL);
 253         }
 254
 255         /* We are not intended to delete this conntrack. */
 256         return 0;
 257 }
 258
 259 void nf_ct_helper_destroy(struct nf_conn *ct)
 260 {
 261         struct nf_conn_help *help = nfct_help(ct);
 262         struct nf_conntrack_helper *helper;
 263
 264         if (help) {
 265                 rcu_read_lock();
 266                 helper = rcu_dereference(help->helper);
 267                 if (helper && helper->destroy)
 268                         helper->destroy(ct);
 269                 rcu_read_unlock();
 270         }
 271 }
 272
 273 static LIST_HEAD(nf_ct_helper_expectfn_list);
 274
 275 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 276 {
 277         spin_lock_bh(&nf_conntrack_expect_lock);
 278         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 279         spin_unlock_bh(&nf_conntrack_expect_lock);
 280 }
 281 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 282
 283 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 284 {
 285         spin_lock_bh(&nf_conntrack_expect_lock);
 286         list_del_rcu(&n->head);
 287         spin_unlock_bh(&nf_conntrack_expect_lock);
 288 }
 289 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 290
 291 /* Caller should hold the rcu lock */
 292 struct nf_ct_helper_expectfn *
 293 nf_ct_helper_expectfn_find_by_name(const char *name)
 294 {
 295         struct nf_ct_helper_expectfn *cur;
 296         bool found = false;
 297
 298         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 299                 if (!strcmp(cur->name, name)) {
 300                         found = true;
 301                         break;
 302                 }
 303         }
 304         return found ? cur : NULL;
 305 }
 306 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 307
 308 /* Caller should hold the rcu lock */
 309 struct nf_ct_helper_expectfn *
 310 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 311 {
 312         struct nf_ct_helper_expectfn *cur;
 313         bool found = false;
 314
 315         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 316                 if (cur->expectfn == symbol) {
 317                         found = true;
 318                         break;
 319                 }
 320         }
 321         return found ? cur : NULL;
 322 }
 323 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 324
 325 __printf(3, 4)
 326 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 327                       const char *fmt, ...)
 328 {
 329         const struct nf_conn_help *help;
 330         const struct nf_conntrack_helper *helper;
 331         struct va_format vaf;
 332         va_list args;
 333
 334         va_start(args, fmt);
 335
 336         vaf.fmt = fmt;
 337         vaf.va = &args;
 338
 339         /* Called from the helper function, this call never fails */
 340         help = nfct_help(ct);
 341
 342         /* rcu_read_lock()ed by nf_hook_thresh */
 343         helper = rcu_dereference(help->helper);
 344
 345         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 346                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 347
 348         va_end(args);
 349 }
 350 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 351
 352 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 353 {
 354         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 355         unsigned int h = helper_hash(&me->tuple);
 356         struct nf_conntrack_helper *cur;
 357         int ret = 0, i;
 358
 359         BUG_ON(me->expect_policy == NULL);
 360         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 361         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 362
 363         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 364                 return -EINVAL;
 365
 366         mutex_lock(&nf_ct_helper_mutex);
 367         for (i = 0; i < nf_ct_helper_hsize; i++) {
 368                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 369                         if (!strcmp(cur->name, me->name) &&
 370                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 371                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 372                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 373                                 ret = -EEXIST;
 374                                 goto out;
 375                         }
 376                 }
 377         }
 378
 379         /* avoid unpredictable behaviour for auto_assign_helper */
 380         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 381                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 382                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 383                                                      &mask)) {
 384                                 ret = -EEXIST;
 385                                 goto out;
 386                         }
 387                 }
 388         }
 389         refcount_set(&me->refcnt, 1);
 390         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 391         nf_ct_helper_count++;
 392 out:
 393         mutex_unlock(&nf_ct_helper_mutex);
 394         return ret;
 395 }
 396 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 397
 398 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 399 {
 400         struct nf_conn_help *help = nfct_help(exp->master);
 401         const struct nf_conntrack_helper *me = data;
 402         const struct nf_conntrack_helper *this;
 403
 404         if (exp->helper == me)
 405                 return true;
 406
 407         this = rcu_dereference_protected(help->helper,
 408                                          lockdep_is_held(&nf_conntrack_expect_lock));
 409         return this == me;
 410 }
 411
 412 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 413 {
 414         mutex_lock(&nf_ct_helper_mutex);
 415         hlist_del_rcu(&me->hnode);
 416         nf_ct_helper_count--;
 417         mutex_unlock(&nf_ct_helper_mutex);
 418
 419         /* Make sure every nothing is still using the helper unless its a
 420          * connection in the hash.
 421          */
 422         synchronize_rcu();
 423
 424         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 425         nf_ct_iterate_destroy(unhelp, me);
 426 }
 427 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 428
 429 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 430                        u16 l3num, u16 protonum, const char *name,
 431                        u16 default_port, u16 spec_port, u32 id,
 432                        const struct nf_conntrack_expect_policy *exp_pol,
 433                        u32 expect_class_max,
 434                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 435                                    struct nf_conn *ct,
 436                                    enum ip_conntrack_info ctinfo),
 437                        int (*from_nlattr)(struct nlattr *attr,
 438                                           struct nf_conn *ct),
 439                        struct module *module)
 440 {
 441         helper->tuple.src.l3num = l3num;
 442         helper->tuple.dst.protonum = protonum;
 443         helper->tuple.src.u.all = htons(spec_port);
 444         helper->expect_policy = exp_pol;
 445         helper->expect_class_max = expect_class_max;
 446         helper->help = help;
 447         helper->from_nlattr = from_nlattr;
 448         helper->me = module;
 449         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 450                  NF_NAT_HELPER_PREFIX "%s", name);
 451
 452         if (spec_port == default_port)
 453                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 454         else
 455                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 456 }
 457 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 458
 459 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 460                                   unsigned int n)
 461 {
 462         unsigned int i;
 463         int err = 0;
 464
 465         for (i = 0; i < n; i++) {
 466                 err = nf_conntrack_helper_register(&helper[i]);
 467                 if (err < 0)
 468                         goto err;
 469         }
 470
 471         return err;
 472 err:
 473         if (i > 0)
 474                 nf_conntrack_helpers_unregister(helper, i);
 475         return err;
 476 }
 477 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 478
 479 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 480                                 unsigned int n)
 481 {
 482         while (n-- > 0)
 483                 nf_conntrack_helper_unregister(&helper[n]);
 484 }
 485 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 486
 487 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 488 {
 489         mutex_lock(&nf_ct_nat_helpers_mutex);
 490         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 491         mutex_unlock(&nf_ct_nat_helpers_mutex);
 492 }
 493 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 494
 495 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 496 {
 497         mutex_lock(&nf_ct_nat_helpers_mutex);
 498         list_del_rcu(&nat->list);
 499         mutex_unlock(&nf_ct_nat_helpers_mutex);
 500 }
 501 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 502
 503 int nf_conntrack_helper_init(void)
 504 {
 505         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 506         nf_ct_helper_hash =
 507                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 508         if (!nf_ct_helper_hash)
 509                 return -ENOMEM;
 510
 511         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 512         return 0;
 513 }
 514
 515 void nf_conntrack_helper_fini(void)
 516 {
 517         kvfree(nf_ct_helper_hash);
 518 }