net/netfilter/nf_conntrack_helper.c

   1 /* Helper handling for netfilter. */
   2
   3 /* (C) 1999-2001 Paul `Rusty' Russell
   4  * (C) 2002-2006 Netfilter Core Team <[email protected]>
   5  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   6  * (C) 2006-2012 Patrick McHardy <[email protected]>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License version 2 as
  10  * published by the Free Software Foundation.
  11  */
  12
  13 #include <linux/types.h>
  14 #include <linux/netfilter.h>
  15 #include <linux/module.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/vmalloc.h>
  18 #include <linux/stddef.h>
  19 #include <linux/random.h>
  20 #include <linux/err.h>
  21 #include <linux/kernel.h>
  22 #include <linux/netdevice.h>
  23 #include <linux/rculist.h>
  24 #include <linux/rtnetlink.h>
  25
  26 #include <net/netfilter/nf_conntrack.h>
  27 #include <net/netfilter/nf_conntrack_l4proto.h>
  28 #include <net/netfilter/nf_conntrack_helper.h>
  29 #include <net/netfilter/nf_conntrack_core.h>
  30 #include <net/netfilter/nf_conntrack_extend.h>
  31 #include <net/netfilter/nf_log.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 bool nf_ct_auto_assign_helper __read_mostly = false;
  41 module_param_named(nf_conntrack_helper, nf_ct_auto_assign_helper, bool, 0644);
  42 MODULE_PARM_DESC(nf_conntrack_helper,
  43                  "Enable automatic conntrack helper assignment (default 0)");
  44
  45 /* Stupid hash, but collision free for the default registrations of the
  46  * helpers currently in the kernel. */
  47 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
  48 {
  49         return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
  50                 (__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
  51 }
  52
  53 static struct nf_conntrack_helper *
  54 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
  55 {
  56         struct nf_conntrack_helper *helper;
  57         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
  58         unsigned int h;
  59
  60         if (!nf_ct_helper_count)
  61                 return NULL;
  62
  63         h = helper_hash(tuple);
  64         hlist_for_each_entry_rcu(helper, &nf_ct_helper_hash[h], hnode) {
  65                 if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
  66                         return helper;
  67         }
  68         return NULL;
  69 }
  70
  71 struct nf_conntrack_helper *
  72 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
  73 {
  74         struct nf_conntrack_helper *h;
  75         unsigned int i;
  76
  77         for (i = 0; i < nf_ct_helper_hsize; i++) {
  78                 hlist_for_each_entry_rcu(h, &nf_ct_helper_hash[i], hnode) {
  79                         if (strcmp(h->name, name))
  80                                 continue;
  81
  82                         if (h->tuple.src.l3num != NFPROTO_UNSPEC &&
  83                             h->tuple.src.l3num != l3num)
  84                                 continue;
  85
  86                         if (h->tuple.dst.protonum == protonum)
  87                                 return h;
  88                 }
  89         }
  90         return NULL;
  91 }
  92 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
  93
  94 struct nf_conntrack_helper *
  95 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
  96 {
  97         struct nf_conntrack_helper *h;
  98
  99         rcu_read_lock();
 100
 101         h = __nf_conntrack_helper_find(name, l3num, protonum);
 102 #ifdef CONFIG_MODULES
 103         if (h == NULL) {
 104                 rcu_read_unlock();
 105                 if (request_module("nfct-helper-%s", name) == 0) {
 106                         rcu_read_lock();
 107                         h = __nf_conntrack_helper_find(name, l3num, protonum);
 108                 } else {
 109                         return h;
 110                 }
 111         }
 112 #endif
 113         if (h != NULL && !try_module_get(h->me))
 114                 h = NULL;
 115         if (h != NULL && !refcount_inc_not_zero(&h->refcnt)) {
 116                 module_put(h->me);
 117                 h = NULL;
 118         }
 119
 120         rcu_read_unlock();
 121
 122         return h;
 123 }
 124 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
 125
 126 void nf_conntrack_helper_put(struct nf_conntrack_helper *helper)
 127 {
 128         refcount_dec(&helper->refcnt);
 129         module_put(helper->me);
 130 }
 131 EXPORT_SYMBOL_GPL(nf_conntrack_helper_put);
 132
 133 struct nf_conn_help *
 134 nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 135 {
 136         struct nf_conn_help *help;
 137
 138         help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
 139         if (help)
 140                 INIT_HLIST_HEAD(&help->expectations);
 141         else
 142                 pr_debug("failed to add helper extension area");
 143         return help;
 144 }
 145 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 146
 147 static struct nf_conntrack_helper *
 148 nf_ct_lookup_helper(struct nf_conn *ct, struct net *net)
 149 {
 150         if (!net->ct.sysctl_auto_assign_helper) {
 151                 if (net->ct.auto_assign_helper_warned)
 152                         return NULL;
 153                 if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple))
 154                         return NULL;
 155                 pr_info("nf_conntrack: default automatic helper assignment "
 156                         "has been turned off for security reasons and CT-based "
 157                         " firewall rule not found. Use the iptables CT target "
 158                         "to attach helpers instead.\n");
 159                 net->ct.auto_assign_helper_warned = 1;
 160                 return NULL;
 161         }
 162
 163         return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
 164 }
 165
 166
 167 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
 168                               gfp_t flags)
 169 {
 170         struct nf_conntrack_helper *helper = NULL;
 171         struct nf_conn_help *help;
 172         struct net *net = nf_ct_net(ct);
 173
 174         /* We already got a helper explicitly attached. The function
 175          * nf_conntrack_alter_reply - in case NAT is in use - asks for looking
 176          * the helper up again. Since now the user is in full control of
 177          * making consistent helper configurations, skip this automatic
 178          * re-lookup, otherwise we'll lose the helper.
 179          */
 180         if (test_bit(IPS_HELPER_BIT, &ct->status))
 181                 return 0;
 182
 183         if (tmpl != NULL) {
 184                 help = nfct_help(tmpl);
 185                 if (help != NULL) {
 186                         helper = help->helper;
 187                         set_bit(IPS_HELPER_BIT, &ct->status);
 188                 }
 189         }
 190
 191         help = nfct_help(ct);
 192
 193         if (helper == NULL) {
 194                 helper = nf_ct_lookup_helper(ct, net);
 195                 if (helper == NULL) {
 196                         if (help)
 197                                 RCU_INIT_POINTER(help->helper, NULL);
 198                         return 0;
 199                 }
 200         }
 201
 202         if (help == NULL) {
 203                 help = nf_ct_helper_ext_add(ct, flags);
 204                 if (help == NULL)
 205                         return -ENOMEM;
 206         } else {
 207                 /* We only allow helper re-assignment of the same sort since
 208                  * we cannot reallocate the helper extension area.
 209                  */
 210                 struct nf_conntrack_helper *tmp = rcu_dereference(help->helper);
 211
 212                 if (tmp && tmp->help != helper->help) {
 213                         RCU_INIT_POINTER(help->helper, NULL);
 214                         return 0;
 215                 }
 216         }
 217
 218         rcu_assign_pointer(help->helper, helper);
 219
 220         return 0;
 221 }
 222 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
 223
 224 /* appropriate ct lock protecting must be taken by caller */
 225 static int unhelp(struct nf_conn *ct, void *me)
 226 {
 227         struct nf_conn_help *help = nfct_help(ct);
 228
 229         if (help && rcu_dereference_raw(help->helper) == me) {
 230                 nf_conntrack_event(IPCT_HELPER, ct);
 231                 RCU_INIT_POINTER(help->helper, NULL);
 232         }
 233
 234         /* We are not intended to delete this conntrack. */
 235         return 0;
 236 }
 237
 238 void nf_ct_helper_destroy(struct nf_conn *ct)
 239 {
 240         struct nf_conn_help *help = nfct_help(ct);
 241         struct nf_conntrack_helper *helper;
 242
 243         if (help) {
 244                 rcu_read_lock();
 245                 helper = rcu_dereference(help->helper);
 246                 if (helper && helper->destroy)
 247                         helper->destroy(ct);
 248                 rcu_read_unlock();
 249         }
 250 }
 251
 252 static LIST_HEAD(nf_ct_helper_expectfn_list);
 253
 254 void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
 255 {
 256         spin_lock_bh(&nf_conntrack_expect_lock);
 257         list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
 258         spin_unlock_bh(&nf_conntrack_expect_lock);
 259 }
 260 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
 261
 262 void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
 263 {
 264         spin_lock_bh(&nf_conntrack_expect_lock);
 265         list_del_rcu(&n->head);
 266         spin_unlock_bh(&nf_conntrack_expect_lock);
 267 }
 268 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
 269
 270 /* Caller should hold the rcu lock */
 271 struct nf_ct_helper_expectfn *
 272 nf_ct_helper_expectfn_find_by_name(const char *name)
 273 {
 274         struct nf_ct_helper_expectfn *cur;
 275         bool found = false;
 276
 277         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 278                 if (!strcmp(cur->name, name)) {
 279                         found = true;
 280                         break;
 281                 }
 282         }
 283         return found ? cur : NULL;
 284 }
 285 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
 286
 287 /* Caller should hold the rcu lock */
 288 struct nf_ct_helper_expectfn *
 289 nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
 290 {
 291         struct nf_ct_helper_expectfn *cur;
 292         bool found = false;
 293
 294         list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
 295                 if (cur->expectfn == symbol) {
 296                         found = true;
 297                         break;
 298                 }
 299         }
 300         return found ? cur : NULL;
 301 }
 302 EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
 303
 304 __printf(3, 4)
 305 void nf_ct_helper_log(struct sk_buff *skb, const struct nf_conn *ct,
 306                       const char *fmt, ...)
 307 {
 308         const struct nf_conn_help *help;
 309         const struct nf_conntrack_helper *helper;
 310         struct va_format vaf;
 311         va_list args;
 312
 313         va_start(args, fmt);
 314
 315         vaf.fmt = fmt;
 316         vaf.va = &args;
 317
 318         /* Called from the helper function, this call never fails */
 319         help = nfct_help(ct);
 320
 321         /* rcu_read_lock()ed by nf_hook_thresh */
 322         helper = rcu_dereference(help->helper);
 323
 324         nf_log_packet(nf_ct_net(ct), nf_ct_l3num(ct), 0, skb, NULL, NULL, NULL,
 325                       "nf_ct_%s: dropping packet: %pV ", helper->name, &vaf);
 326
 327         va_end(args);
 328 }
 329 EXPORT_SYMBOL_GPL(nf_ct_helper_log);
 330
 331 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 332 {
 333         struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
 334         unsigned int h = helper_hash(&me->tuple);
 335         struct nf_conntrack_helper *cur;
 336         int ret = 0, i;
 337
 338         BUG_ON(me->expect_policy == NULL);
 339         BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
 340         BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 341
 342         if (me->expect_policy->max_expected > NF_CT_EXPECT_MAX_CNT)
 343                 return -EINVAL;
 344
 345         mutex_lock(&nf_ct_helper_mutex);
 346         for (i = 0; i < nf_ct_helper_hsize; i++) {
 347                 hlist_for_each_entry(cur, &nf_ct_helper_hash[i], hnode) {
 348                         if (!strcmp(cur->name, me->name) &&
 349                             (cur->tuple.src.l3num == NFPROTO_UNSPEC ||
 350                              cur->tuple.src.l3num == me->tuple.src.l3num) &&
 351                             cur->tuple.dst.protonum == me->tuple.dst.protonum) {
 352                                 ret = -EEXIST;
 353                                 goto out;
 354                         }
 355                 }
 356         }
 357
 358         /* avoid unpredictable behaviour for auto_assign_helper */
 359         if (!(me->flags & NF_CT_HELPER_F_USERSPACE)) {
 360                 hlist_for_each_entry(cur, &nf_ct_helper_hash[h], hnode) {
 361                         if (nf_ct_tuple_src_mask_cmp(&cur->tuple, &me->tuple,
 362                                                      &mask)) {
 363                                 ret = -EEXIST;
 364                                 goto out;
 365                         }
 366                 }
 367         }
 368         refcount_set(&me->refcnt, 1);
 369         hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
 370         nf_ct_helper_count++;
 371 out:
 372         mutex_unlock(&nf_ct_helper_mutex);
 373         return ret;
 374 }
 375 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
 376
 377 static bool expect_iter_me(struct nf_conntrack_expect *exp, void *data)
 378 {
 379         struct nf_conn_help *help = nfct_help(exp->master);
 380         const struct nf_conntrack_helper *me = data;
 381         const struct nf_conntrack_helper *this;
 382
 383         if (exp->helper == me)
 384                 return true;
 385
 386         this = rcu_dereference_protected(help->helper,
 387                                          lockdep_is_held(&nf_conntrack_expect_lock));
 388         return this == me;
 389 }
 390
 391 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
 392 {
 393         mutex_lock(&nf_ct_helper_mutex);
 394         hlist_del_rcu(&me->hnode);
 395         nf_ct_helper_count--;
 396         mutex_unlock(&nf_ct_helper_mutex);
 397
 398         /* Make sure every nothing is still using the helper unless its a
 399          * connection in the hash.
 400          */
 401         synchronize_rcu();
 402
 403         nf_ct_expect_iterate_destroy(expect_iter_me, NULL);
 404         nf_ct_iterate_destroy(unhelp, me);
 405
 406         /* Maybe someone has gotten the helper already when unhelp above.
 407          * So need to wait it.
 408          */
 409         synchronize_rcu();
 410 }
 411 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
 412
 413 void nf_ct_helper_init(struct nf_conntrack_helper *helper,
 414                        u16 l3num, u16 protonum, const char *name,
 415                        u16 default_port, u16 spec_port, u32 id,
 416                        const struct nf_conntrack_expect_policy *exp_pol,
 417                        u32 expect_class_max,
 418                        int (*help)(struct sk_buff *skb, unsigned int protoff,
 419                                    struct nf_conn *ct,
 420                                    enum ip_conntrack_info ctinfo),
 421                        int (*from_nlattr)(struct nlattr *attr,
 422                                           struct nf_conn *ct),
 423                        struct module *module)
 424 {
 425         helper->tuple.src.l3num = l3num;
 426         helper->tuple.dst.protonum = protonum;
 427         helper->tuple.src.u.all = htons(spec_port);
 428         helper->expect_policy = exp_pol;
 429         helper->expect_class_max = expect_class_max;
 430         helper->help = help;
 431         helper->from_nlattr = from_nlattr;
 432         helper->me = module;
 433
 434         if (spec_port == default_port)
 435                 snprintf(helper->name, sizeof(helper->name), "%s", name);
 436         else
 437                 snprintf(helper->name, sizeof(helper->name), "%s-%u", name, id);
 438 }
 439 EXPORT_SYMBOL_GPL(nf_ct_helper_init);
 440
 441 int nf_conntrack_helpers_register(struct nf_conntrack_helper *helper,
 442                                   unsigned int n)
 443 {
 444         unsigned int i;
 445         int err = 0;
 446
 447         for (i = 0; i < n; i++) {
 448                 err = nf_conntrack_helper_register(&helper[i]);
 449                 if (err < 0)
 450                         goto err;
 451         }
 452
 453         return err;
 454 err:
 455         if (i > 0)
 456                 nf_conntrack_helpers_unregister(helper, i);
 457         return err;
 458 }
 459 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_register);
 460
 461 void nf_conntrack_helpers_unregister(struct nf_conntrack_helper *helper,
 462                                 unsigned int n)
 463 {
 464         while (n-- > 0)
 465                 nf_conntrack_helper_unregister(&helper[n]);
 466 }
 467 EXPORT_SYMBOL_GPL(nf_conntrack_helpers_unregister);
 468
 469 static const struct nf_ct_ext_type helper_extend = {
 470         .len    = sizeof(struct nf_conn_help),
 471         .align  = __alignof__(struct nf_conn_help),
 472         .id     = NF_CT_EXT_HELPER,
 473 };
 474
 475 void nf_conntrack_helper_pernet_init(struct net *net)
 476 {
 477         net->ct.auto_assign_helper_warned = false;
 478         net->ct.sysctl_auto_assign_helper = nf_ct_auto_assign_helper;
 479 }
 480
 481 int nf_conntrack_helper_init(void)
 482 {
 483         int ret;
 484         nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
 485         nf_ct_helper_hash =
 486                 nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
 487         if (!nf_ct_helper_hash)
 488                 return -ENOMEM;
 489
 490         ret = nf_ct_extend_register(&helper_extend);
 491         if (ret < 0) {
 492                 pr_err("nf_ct_helper: Unable to register helper extension.\n");
 493                 goto out_extend;
 494         }
 495
 496         return 0;
 497 out_extend:
 498         kvfree(nf_ct_helper_hash);
 499         return ret;
 500 }
 501
 502 void nf_conntrack_helper_fini(void)
 503 {
 504         nf_ct_extend_unregister(&helper_extend);
 505         kvfree(nf_ct_helper_hash);
 506 }