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. 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 (!nf_ct_helper_hash)
 364                 return -ENOENT;
 365
 366         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 367                 return -EINVAL;
 368
 369         mutex_lock(&nf_ct_helper_mutex);
 370         for (i = 0; i < nf_ct_helper_hsize; i++) {
 371                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 372                         if (!strcmp(cur->name, me->name) &&
 373                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 374                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 375                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 376                                 ret = -EEXIST;
 377                                 goto out;
 378                         }
 379                 }
 380         }
 381
 382         /* avoid unpredictable behaviour for auto_assign_helper */
 383         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 384                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 385                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 386                                                      &mask)) {
 387                                 ret = -EEXIST;
 388                                 goto out;
 389                         }
 390                 }
 391         }
 392         refcount_set(&me->refcnt, 1);
 393         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 394         nf_ct_helper_count++;
 395 out:
 396         mutex_unlock(&nf_ct_helper_mutex);
 397         return ret;
 398 }
 399 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 400
 401 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 402 {
 403         struct nf_conn_help *help = nfct_help(exp->master);
 404         const struct nf_conntrack_helper *me = data;
 405         const struct nf_conntrack_helper *this;
 406
 407         if (exp->helper == me)
 408                 return true;
 409
 410         this = rcu_dereference_protected(help->helper,
 411                                          lockdep_is_held(&nf_conntrack_expect_lock));
 412         return this == me;
 413 }
 414
 415 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 416 {
 417         mutex_lock(&nf_ct_helper_mutex);
 418         hlist_del_rcu(&me->hnode);
 419         nf_ct_helper_count--;
 420         mutex_unlock(&nf_ct_helper_mutex);
 421
 422         /* Make sure every nothing is still using the helper unless its a
 423          * connection in the hash.
 424          */
 425         synchronize_rcu();
 426
 427         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 428         nf_ct_iterate_destroy(unhelp, me);
 429 }
 430 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 431
 432 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 433                        u16 l3num, u16 protonum, const char *name,
 434                        u16 default_port, u16 spec_port, u32 id,
 435                        const struct nf_conntrack_expect_policy *exp_pol,
 436                        u32 expect_class_max,
 437                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 438                                    struct nf_conn *ct,
 439                                    enum ip_conntrack_info ctinfo),
 440                        int (*from_nlattr)(struct nlattr *attr,
 441                                           struct nf_conn *ct),
 442                        struct module *module)
 443 {
 444         helper->tuple.src.l3num = l3num;
 445         helper->tuple.dst.protonum = protonum;
 446         helper->tuple.src.u.all = htons(spec_port);
 447         helper->expect_policy = exp_pol;
 448         helper->expect_class_max = expect_class_max;
 449         helper->help = help;
 450         helper->from_nlattr = from_nlattr;
 451         helper->me = module;
 452         snprintf(helper->nat_mod_name, sizeof(helper->nat_mod_name),
 453                  NF_NAT_HELPER_PREFIX "%s", name);
 454
 455         if (spec_port == default_port)
 456                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 457         else
 458                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 459 }
 460 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 461
 462 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 463                                   unsigned int n)
 464 {
 465         unsigned int i;
 466         int err = 0;
 467
 468         for (i = 0; i < n; i++) {
 469                 err = nf_conntrack_helper_register(&helper[i]);
 470                 if (err < 0)
 471                         goto err;
 472         }
 473
 474         return err;
 475 err:
 476         if (i > 0)
 477                 nf_conntrack_helpers_unregister(helper, i);
 478         return err;
 479 }
 480 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 481
 482 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 483                                 unsigned int n)
 484 {
 485         while (n-- > 0)
 486                 nf_conntrack_helper_unregister(&helper[n]);
 487 }
 488 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 489
 490 void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat)
 491 {
 492         mutex_lock(&nf_ct_nat_helpers_mutex);
 493         list_add_rcu(&nat->list, &nf_ct_nat_helpers);
 494         mutex_unlock(&nf_ct_nat_helpers_mutex);
 495 }
 496 EXPORT_SYMBOL_GPL(nf_nat_helper_register);
 497
 498 void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat)
 499 {
 500         mutex_lock(&nf_ct_nat_helpers_mutex);
 501         list_del_rcu(&nat->list);
 502         mutex_unlock(&nf_ct_nat_helpers_mutex);
 503 }
 504 EXPORT_SYMBOL_GPL(nf_nat_helper_unregister);
 505
 506 int nf_conntrack_helper_init(void)
 507 {
 508         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 509         nf_ct_helper_hash =
 510                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 511         if (!nf_ct_helper_hash)
 512                 return -ENOMEM;
 513
 514         INIT_LIST_HEAD(&nf_ct_nat_helpers);
 515         return 0;
 516 }
 517
 518 void nf_conntrack_helper_fini(void)
 519 {
 520         kvfree(nf_ct_helper_hash);
 521         nf_ct_helper_hash = NULL;
 522 }