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_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 (e.g. nft_ct) */
 198         if (test_bit(IPS_HELPER_BIT, &ct->status))
 199                 return 0;
 200
 201         if (WARN_ON_ONCE(!tmpl))
 202                 return 0;
 203
 204         help = nfct_help(tmpl);
 205         if (help != NULL) {
 206                 helper = rcu_dereference(help->helper);
 207                 set_bit(IPS_HELPER_BIT, &ct->status);
 208         }
 209
 210         help = nfct_help(ct);
 211
 212         if (helper == NULL) {
 213                 if (help)
 214                         RCU_INIT_POINTER(help->helper, NULL);
 215                 return 0;
 216         }
 217
 218         if (help == NULL) {
 219                 help = nf_ct_helper_ext_add(ct, flags);
 220                 if (help == NULL)
 221                         return -ENOMEM;
 222         } else {
 223                 /* We only allow helper re-assignment of the same sort since
 224                  * we cannot reallocate the helper extension area.
 225                  */
 226                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 227
 228                 if (tmp && tmp->help != helper->help) {
 229                         RCU_INIT_POINTER(help->helper, NULL);
 230                         return 0;
 231                 }
 232         }
 233
 234         rcu_assign_pointer(help->helper, helper);
 235
 236         return 0;
 237 }
 238 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 239
 240 /* appropriate ct lock protecting must be taken by caller */
 241 static int unhelp(struct nf_conn *ct, void *me)
 242 {
 243         struct nf_conn_help *help = nfct_help(ct);
 244
 245         if (help && rcu_dereference_raw(help->helper) == me) {
 246                 nf_conntrack_event(IPCT_HELPER, ct);
 247                 RCU_INIT_POINTER(help->helper, NULL);
 248         }
 249
 250         /* We are not intended to delete this conntrack. */
 251         return 0;
 252 }
 253
 254 void nf_ct_helper_destroy(struct nf_conn *ct)
 255 {
 256         struct nf_conn_help *help = nfct_help(ct);
 257         struct nf_conntrack_helper *helper;
 258
 259         if (help) {
 260                 rcu_read_lock();
 261                 helper = rcu_dereference(help->helper);
 262                 if (helper && helper->destroy)
 263                         helper->destroy(ct);
 264                 rcu_read_unlock();
 265         }
 266 }
 267
 268 static LIST_HEAD(nf_ct_helper_expectfn_list);
 269
 270 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 271 {
 272         spin_lock_bh(&nf_conntrack_expect_lock);
 273         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 274         spin_unlock_bh(&nf_conntrack_expect_lock);
 275 }
 276 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 277
 278 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 279 {
 280         spin_lock_bh(&nf_conntrack_expect_lock);
 281         list_del_rcu(&n->head);
 282         spin_unlock_bh(&nf_conntrack_expect_lock);
 283 }
 284 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 285
 286 /* Caller should hold the rcu lock */
 287 struct nf_ct_helper_expectfn *
 288 nf_ct_helper_expectfn_find_by_name(const char *name)
 289 {
 290         struct nf_ct_helper_expectfn *cur;
 291         bool found = false;
 292
 293         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 294                 if (!strcmp(cur->name, name)) {
 295                         found = true;
 296                         break;
 297                 }
 298         }
 299         return found ? cur : NULL;
 300 }
 301 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 302
 303 /* Caller should hold the rcu lock */
 304 struct nf_ct_helper_expectfn *
 305 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 306 {
 307         struct nf_ct_helper_expectfn *cur;
 308         bool found = false;
 309
 310         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 311                 if (cur->expectfn == symbol) {
 312                         found = true;
 313                         break;
 314                 }
 315         }
 316         return found ? cur : NULL;
 317 }
 318 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 319
 320 __printf(3, 4)
 321 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 322                       const char *fmt, ...)
 323 {
 324         const struct nf_conn_help *help;
 325         const struct nf_conntrack_helper *helper;
 326         struct va_format vaf;
 327         va_list args;
 328
 329         va_start(args, fmt);
 330
 331         vaf.fmt = fmt;
 332         vaf.va = &args;
 333
 334         /* Called from the helper function, this call never fails */
 335         help = nfct_help(ct);
 336
 337         /* rcu_read_lock()ed by nf_hook_thresh */
 338         helper = rcu_dereference(help->helper);
 339
 340         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 341                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 342
 343         va_end(args);
 344 }
 345 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 346
 347 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 348 {
 349         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 350         unsigned int h = helper_hash(&me->tuple);
 351         struct nf_conntrack_helper *cur;
 352         int ret = 0, i;
 353
 354         BUG_ON(me->expect_policy == NULL);
 355         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 356         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 357
 358         if (!nf_ct_helper_hash)
 359                 return -ENOENT;
 360
 361         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 362                 return -EINVAL;
 363
 364         mutex_lock(&nf_ct_helper_mutex);
 365         for (i = 0; i < nf_ct_helper_hsize; i++) {
 366                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 367                         if (!strcmp(cur->name, me->name) &&
 368                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 369                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 370                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 371                                 ret = -EEXIST;
 372                                 goto out;
 373                         }
 374                 }
 375         }
 376
 377         /* avoid unpredictable behaviour for auto_assign_helper */
 378         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 379                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 380                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 381                                                      &mask)) {
 382                                 ret = -EEXIST;
 383                                 goto out;
 384                         }
 385                 }
 386         }
 387         refcount_set(&me->refcnt, 1);
 388         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 389         nf_ct_helper_count++;
 390 out:
 391         mutex_unlock(&nf_ct_helper_mutex);
 392         return ret;
 393 }
 394 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 395
 396 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 397 {
 398         struct nf_conn_help *help = nfct_help(exp->master);
 399         const struct nf_conntrack_helper *me = data;
 400         const struct nf_conntrack_helper *this;
 401
 402         if (exp->helper == me)
 403                 return true;
 404
 405         this = rcu_dereference_protected(help->helper,
 406                                          lockdep_is_held(&nf_conntrack_expect_lock));
 407         return this == me;
 408 }
 409
 410 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 411 {
 412         mutex_lock(&nf_ct_helper_mutex);
 413         hlist_del_rcu(&me->hnode);
 414         nf_ct_helper_count--;
 415         mutex_unlock(&nf_ct_helper_mutex);
 416
 417         /* Make sure every nothing is still using the helper unless its a
 418          * connection in the hash.
 419          */
 420         synchronize_rcu();
 421
 422         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 423         nf_ct_iterate_destroy(unhelp, me);
 424 }
 425 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 426
 427 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 428                        u16 l3num, u16 protonum, const char *name,
 429                        u16 default_port, u16 spec_port, u32 id,
 430                        const struct nf_conntrack_expect_policy *exp_pol,
 431                        u32 expect_class_max,
 432                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 433                                    struct nf_conn *ct,
 434                                    enum ip_conntrack_info ctinfo),
 435                        int (*from_nlattr)(struct nlattr *attr,
 436                                           struct nf_conn *ct),
 437                        struct module *module)
 438 {
 439         helper->tuple.src.l3num = l3num;
 440         helper->tuple.dst.protonum = protonum;
 441         helper->tuple.src.u.all = htons(spec_port);
 442         helper->expect_policy = exp_pol;
 443         helper->expect_class_max = expect_class_max;
 444         helper->help = help;
 445         helper->from_nlattr = from_nlattr;
 446         helper->me = module;
 447         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 448                  NF_NAT_HELPER_PREFIX "%s", name);
 449
 450         if (spec_port == default_port)
 451                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 452         else
 453                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 454 }
 455 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 456
 457 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 458                                   unsigned int n)
 459 {
 460         unsigned int i;
 461         int err = 0;
 462
 463         for (i = 0; i < n; i++) {
 464                 err = nf_conntrack_helper_register(&helper[i]);
 465                 if (err < 0)
 466                         goto err;
 467         }
 468
 469         return err;
 470 err:
 471         if (i > 0)
 472                 nf_conntrack_helpers_unregister(helper, i);
 473         return err;
 474 }
 475 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 476
 477 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 478                                 unsigned int n)
 479 {
 480         while (n-- > 0)
 481                 nf_conntrack_helper_unregister(&helper[n]);
 482 }
 483 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 484
 485 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 486 {
 487         mutex_lock(&nf_ct_nat_helpers_mutex);
 488         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 489         mutex_unlock(&nf_ct_nat_helpers_mutex);
 490 }
 491 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 492
 493 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 494 {
 495         mutex_lock(&nf_ct_nat_helpers_mutex);
 496         list_del_rcu(&nat->list);
 497         mutex_unlock(&nf_ct_nat_helpers_mutex);
 498 }
 499 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 500
 501 int nf_conntrack_helper_init(void)
 502 {
 503         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 504         nf_ct_helper_hash =
 505                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 506         if (!nf_ct_helper_hash)
 507                 return -ENOMEM;
 508
 509         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 510         return 0;
 511 }
 512
 513 void nf_conntrack_helper_fini(void)
 514 {
 515         kvfree(nf_ct_helper_hash);
 516         nf_ct_helper_hash = NULL;
 517 }