net/netfilter/xt_connlimit.c

   1 /*
   2  * netfilter module to limit the number of parallel tcp
   3  * connections per IP address.
   4  *   (c) 2000 Gerd Knorr <kraxel@bytesex.org>
   5  *   Nov 2002: Martin Bene <martin.bene@icomedias.com>:
   6  *              only ignore TIME_WAIT or gone connections
   7  *   (C) CC Computer Consultants GmbH, 2007
   8  *
   9  * based on ...
  10  *
  11  * Kernel module to match connection tracking information.
  12  * GPL (C) 1999  Rusty Russell (rusty@rustcorp.com.au).
  13  */
  14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15 #include <linux/in.h>
  16 #include <linux/in6.h>
  17 #include <linux/ip.h>
  18 #include <linux/ipv6.h>
  19 #include <linux/jhash.h>
  20 #include <linux/slab.h>
  21 #include <linux/list.h>
  22 #include <linux/rbtree.h>
  23 #include <linux/module.h>
  24 #include <linux/random.h>
  25 #include <linux/skbuff.h>
  26 #include <linux/spinlock.h>
  27 #include <linux/netfilter/nf_conntrack_tcp.h>
  28 #include <linux/netfilter/x_tables.h>
  29 #include <linux/netfilter/xt_connlimit.h>
  30 #include <net/netfilter/nf_conntrack.h>
  31 #include <net/netfilter/nf_conntrack_core.h>
  32 #include <net/netfilter/nf_conntrack_tuple.h>
  33 #include <net/netfilter/nf_conntrack_zones.h>
  34
  35 #define CONNLIMIT_SLOTS         256U
  36
  37 #ifdef CONFIG_LOCKDEP
  38 #define CONNLIMIT_LOCK_SLOTS    8U
  39 #else
  40 #define CONNLIMIT_LOCK_SLOTS    256U
  41 #endif
  42
  43 #define CONNLIMIT_GC_MAX_NODES  8
  44
  45 /* we will save the tuples of all connections we care about */
  46 struct xt_connlimit_conn {
  47         struct hlist_node               node;
  48         struct nf_conntrack_tuple       tuple;
  49         union nf_inet_addr              addr;
  50 };
  51
  52 struct xt_connlimit_rb {
  53         struct rb_node node;
  54         struct hlist_head hhead; /* connections/hosts in same subnet */
  55         union nf_inet_addr addr; /* search key */
  56 };
  57
  58 static spinlock_t xt_connlimit_locks[CONNLIMIT_LOCK_SLOTS] __cacheline_aligned_in_smp;
  59
  60 struct xt_connlimit_data {
  61         struct rb_root climit_root4[CONNLIMIT_SLOTS];
  62         struct rb_root climit_root6[CONNLIMIT_SLOTS];
  63 };
  64
  65 static u_int32_t connlimit_rnd __read_mostly;
  66 static struct kmem_cache *connlimit_rb_cachep __read_mostly;
  67 static struct kmem_cache *connlimit_conn_cachep __read_mostly;
  68
  69 static inline unsigned int connlimit_iphash(__be32 addr)
  70 {
  71         return jhash_1word((__force __u32)addr,
  72                             connlimit_rnd) % CONNLIMIT_SLOTS;
  73 }
  74
  75 static inline unsigned int
  76 connlimit_iphash6(const union nf_inet_addr *addr,
  77                   const union nf_inet_addr *mask)
  78 {
  79         union nf_inet_addr res;
  80         unsigned int i;
  81
  82         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  83                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  84
  85         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6),
  86                        connlimit_rnd) % CONNLIMIT_SLOTS;
  87 }
  88
  89 static inline bool already_closed(const struct nf_conn *conn)
  90 {
  91         if (nf_ct_protonum(conn) == IPPROTO_TCP)
  92                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
  93                        conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
  94         else
  95                 return 0;
  96 }
  97
  98 static int
  99 same_source_net(const union nf_inet_addr *addr,
 100                 const union nf_inet_addr *mask,
 101                 const union nf_inet_addr *u3, u_int8_t family)
 102 {
 103         if (family == NFPROTO_IPV4) {
 104                 return ntohl(addr->ip & mask->ip) -
 105                        ntohl(u3->ip & mask->ip);
 106         } else {
 107                 union nf_inet_addr lh, rh;
 108                 unsigned int i;
 109
 110                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
 111                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
 112                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
 113                 }
 114
 115                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6));
 116         }
 117 }
 118
 119 static bool add_hlist(struct hlist_head *head,
 120                       const struct nf_conntrack_tuple *tuple,
 121                       const union nf_inet_addr *addr)
 122 {
 123         struct xt_connlimit_conn *conn;
 124
 125         conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
 126         if (conn == NULL)
 127                 return false;
 128         conn->tuple = *tuple;
 129         conn->addr = *addr;
 130         hlist_add_head(&conn->node, head);
 131         return true;
 132 }
 133
 134 static unsigned int check_hlist(struct net *net,
 135                                 struct hlist_head *head,
 136                                 const struct nf_conntrack_tuple *tuple,
 137                                 bool *addit)
 138 {
 139         const struct nf_conntrack_tuple_hash *found;
 140         struct xt_connlimit_conn *conn;
 141         struct hlist_node *n;
 142         struct nf_conn *found_ct;
 143         unsigned int length = 0;
 144
 145         *addit = true;
 146         rcu_read_lock();
 147
 148         /* check the saved connections */
 149         hlist_for_each_entry_safe(conn, n, head, node) {
 150                 found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
 151                                                  &conn->tuple);
 152                 if (found == NULL) {
 153                         hlist_del(&conn->node);
 154                         kmem_cache_free(connlimit_conn_cachep, conn);
 155                         continue;
 156                 }
 157
 158                 found_ct = nf_ct_tuplehash_to_ctrack(found);
 159
 160                 if (nf_ct_tuple_equal(&conn->tuple, tuple)) {
 161                         /*
 162                          * Just to be sure we have it only once in the list.
 163                          * We should not see tuples twice unless someone hooks
 164                          * this into a table without "-p tcp --syn".
 165                          */
 166                         *addit = false;
 167                 } else if (already_closed(found_ct)) {
 168                         /*
 169                          * we do not care about connections which are
 170                          * closed already -> ditch it
 171                          */
 172                         nf_ct_put(found_ct);
 173                         hlist_del(&conn->node);
 174                         kmem_cache_free(connlimit_conn_cachep, conn);
 175                         continue;
 176                 }
 177
 178                 nf_ct_put(found_ct);
 179                 length++;
 180         }
 181
 182         rcu_read_unlock();
 183
 184         return length;
 185 }
 186
 187 static void tree_nodes_free(struct rb_root *root,
 188                             struct xt_connlimit_rb *gc_nodes[],
 189                             unsigned int gc_count)
 190 {
 191         struct xt_connlimit_rb *rbconn;
 192
 193         while (gc_count) {
 194                 rbconn = gc_nodes[--gc_count];
 195                 rb_erase(&rbconn->node, root);
 196                 kmem_cache_free(connlimit_rb_cachep, rbconn);
 197         }
 198 }
 199
 200 static unsigned int
 201 count_tree(struct net *net, struct rb_root *root,
 202            const struct nf_conntrack_tuple *tuple,
 203            const union nf_inet_addr *addr, const union nf_inet_addr *mask,
 204            u8 family)
 205 {
 206         struct xt_connlimit_rb *gc_nodes[CONNLIMIT_GC_MAX_NODES];
 207         struct rb_node **rbnode, *parent;
 208         struct xt_connlimit_rb *rbconn;
 209         struct xt_connlimit_conn *conn;
 210         unsigned int gc_count;
 211         bool no_gc = false;
 212
 213  restart:
 214         gc_count = 0;
 215         parent = NULL;
 216         rbnode = &(root->rb_node);
 217         while (*rbnode) {
 218                 int diff;
 219                 bool addit;
 220
 221                 rbconn = container_of(*rbnode, struct xt_connlimit_rb, node);
 222
 223                 parent = *rbnode;
 224                 diff = same_source_net(addr, mask, &rbconn->addr, family);
 225                 if (diff < 0) {
 226                         rbnode = &((*rbnode)->rb_left);
 227                 } else if (diff > 0) {
 228                         rbnode = &((*rbnode)->rb_right);
 229                 } else {
 230                         /* same source network -> be counted! */
 231                         unsigned int count;
 232                         count = check_hlist(net, &rbconn->hhead, tuple, &addit);
 233
 234                         tree_nodes_free(root, gc_nodes, gc_count);
 235                         if (!addit)
 236                                 return count;
 237
 238                         if (!add_hlist(&rbconn->hhead, tuple, addr))
 239                                 return 0; /* hotdrop */
 240
 241                         return count + 1;
 242                 }
 243
 244                 if (no_gc || gc_count >= ARRAY_SIZE(gc_nodes))
 245                         continue;
 246
 247                 /* only used for GC on hhead, retval and 'addit' ignored */
 248                 check_hlist(net, &rbconn->hhead, tuple, &addit);
 249                 if (hlist_empty(&rbconn->hhead))
 250                         gc_nodes[gc_count++] = rbconn;
 251         }
 252
 253         if (gc_count) {
 254                 no_gc = true;
 255                 tree_nodes_free(root, gc_nodes, gc_count);
 256                 /* tree_node_free before new allocation permits
 257                  * allocator to re-use newly free'd object.
 258                  *
 259                  * This is a rare event; in most cases we will find
 260                  * existing node to re-use. (or gc_count is 0).
 261                  */
 262                 goto restart;
 263         }
 264
 265         /* no match, need to insert new node */
 266         rbconn = kmem_cache_alloc(connlimit_rb_cachep, GFP_ATOMIC);
 267         if (rbconn == NULL)
 268                 return 0;
 269
 270         conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
 271         if (conn == NULL) {
 272                 kmem_cache_free(connlimit_rb_cachep, rbconn);
 273                 return 0;
 274         }
 275
 276         conn->tuple = *tuple;
 277         conn->addr = *addr;
 278         rbconn->addr = *addr;
 279
 280         INIT_HLIST_HEAD(&rbconn->hhead);
 281         hlist_add_head(&conn->node, &rbconn->hhead);
 282
 283         rb_link_node(&rbconn->node, parent, rbnode);
 284         rb_insert_color(&rbconn->node, root);
 285         return 1;
 286 }
 287
 288 static int count_them(struct net *net,
 289                       struct xt_connlimit_data *data,
 290                       const struct nf_conntrack_tuple *tuple,
 291                       const union nf_inet_addr *addr,
 292                       const union nf_inet_addr *mask,
 293                       u_int8_t family)
 294 {
 295         struct rb_root *root;
 296         int count;
 297         u32 hash;
 298
 299         if (family == NFPROTO_IPV6) {
 300                 hash = connlimit_iphash6(addr, mask);
 301                 root = &data->climit_root6[hash];
 302         } else {
 303                 hash = connlimit_iphash(addr->ip & mask->ip);
 304                 root = &data->climit_root4[hash];
 305         }
 306
 307         spin_lock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
 308
 309         count = count_tree(net, root, tuple, addr, mask, family);
 310
 311         spin_unlock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
 312
 313         return count;
 314 }
 315
 316 static bool
 317 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 318 {
 319         struct net *net = dev_net(par->in ? par->in : par->out);
 320         const struct xt_connlimit_info *info = par->matchinfo;
 321         union nf_inet_addr addr;
 322         struct nf_conntrack_tuple tuple;
 323         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 324         enum ip_conntrack_info ctinfo;
 325         const struct nf_conn *ct;
 326         unsigned int connections;
 327
 328         ct = nf_ct_get(skb, &ctinfo);
 329         if (ct != NULL)
 330                 tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 331         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 332                                     par->family, &tuple))
 333                 goto hotdrop;
 334
 335         if (par->family == NFPROTO_IPV6) {
 336                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 337                 memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
 338                        &iph->daddr : &iph->saddr, sizeof(addr.ip6));
 339         } else {
 340                 const struct iphdr *iph = ip_hdr(skb);
 341                 addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
 342                           iph->daddr : iph->saddr;
 343         }
 344
 345         connections = count_them(net, info->data, tuple_ptr, &addr,
 346                                  &info->mask, par->family);
 347         if (connections == 0)
 348                 /* kmalloc failed, drop it entirely */
 349                 goto hotdrop;
 350
 351         return (connections > info->limit) ^
 352                !!(info->flags & XT_CONNLIMIT_INVERT);
 353
 354  hotdrop:
 355         par->hotdrop = true;
 356         return false;
 357 }
 358
 359 static int connlimit_mt_check(const struct xt_mtchk_param *par)
 360 {
 361         struct xt_connlimit_info *info = par->matchinfo;
 362         unsigned int i;
 363         int ret;
 364
 365         if (unlikely(!connlimit_rnd)) {
 366                 u_int32_t rand;
 367
 368                 do {
 369                         get_random_bytes(&rand, sizeof(rand));
 370                 } while (!rand);
 371                 cmpxchg(&connlimit_rnd, 0, rand);
 372         }
 373         ret = nf_ct_l3proto_try_module_get(par->family);
 374         if (ret < 0) {
 375                 pr_info("cannot load conntrack support for "
 376                         "address family %u\n", par->family);
 377                 return ret;
 378         }
 379
 380         /* init private data */
 381         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 382         if (info->data == NULL) {
 383                 nf_ct_l3proto_module_put(par->family);
 384                 return -ENOMEM;
 385         }
 386
 387         for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
 388                 info->data->climit_root4[i] = RB_ROOT;
 389         for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
 390                 info->data->climit_root6[i] = RB_ROOT;
 391
 392         return 0;
 393 }
 394
 395 static void destroy_tree(struct rb_root *r)
 396 {
 397         struct xt_connlimit_conn *conn;
 398         struct xt_connlimit_rb *rbconn;
 399         struct hlist_node *n;
 400         struct rb_node *node;
 401
 402         while ((node = rb_first(r)) != NULL) {
 403                 rbconn = container_of(node, struct xt_connlimit_rb, node);
 404
 405                 rb_erase(node, r);
 406
 407                 hlist_for_each_entry_safe(conn, n, &rbconn->hhead, node)
 408                         kmem_cache_free(connlimit_conn_cachep, conn);
 409
 410                 kmem_cache_free(connlimit_rb_cachep, rbconn);
 411         }
 412 }
 413
 414 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 415 {
 416         const struct xt_connlimit_info *info = par->matchinfo;
 417         unsigned int i;
 418
 419         nf_ct_l3proto_module_put(par->family);
 420
 421         for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
 422                 destroy_tree(&info->data->climit_root4[i]);
 423         for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
 424                 destroy_tree(&info->data->climit_root6[i]);
 425
 426         kfree(info->data);
 427 }
 428
 429 static struct xt_match connlimit_mt_reg __read_mostly = {
 430         .name       = "connlimit",
 431         .revision   = 1,
 432         .family     = NFPROTO_UNSPEC,
 433         .checkentry = connlimit_mt_check,
 434         .match      = connlimit_mt,
 435         .matchsize  = sizeof(struct xt_connlimit_info),
 436         .destroy    = connlimit_mt_destroy,
 437         .me         = THIS_MODULE,
 438 };
 439
 440 static int __init connlimit_mt_init(void)
 441 {
 442         int ret, i;
 443
 444         BUILD_BUG_ON(CONNLIMIT_LOCK_SLOTS > CONNLIMIT_SLOTS);
 445         BUILD_BUG_ON((CONNLIMIT_SLOTS % CONNLIMIT_LOCK_SLOTS) != 0);
 446
 447         for (i = 0; i < CONNLIMIT_LOCK_SLOTS; ++i)
 448                 spin_lock_init(&xt_connlimit_locks[i]);
 449
 450         connlimit_conn_cachep = kmem_cache_create("xt_connlimit_conn",
 451                                            sizeof(struct xt_connlimit_conn),
 452                                            0, 0, NULL);
 453         if (!connlimit_conn_cachep)
 454                 return -ENOMEM;
 455
 456         connlimit_rb_cachep = kmem_cache_create("xt_connlimit_rb",
 457                                            sizeof(struct xt_connlimit_rb),
 458                                            0, 0, NULL);
 459         if (!connlimit_rb_cachep) {
 460                 kmem_cache_destroy(connlimit_conn_cachep);
 461                 return -ENOMEM;
 462         }
 463         ret = xt_register_match(&connlimit_mt_reg);
 464         if (ret != 0) {
 465                 kmem_cache_destroy(connlimit_conn_cachep);
 466                 kmem_cache_destroy(connlimit_rb_cachep);
 467         }
 468         return ret;
 469 }
 470
 471 static void __exit connlimit_mt_exit(void)
 472 {
 473         xt_unregister_match(&connlimit_mt_reg);
 474         kmem_cache_destroy(connlimit_conn_cachep);
 475         kmem_cache_destroy(connlimit_rb_cachep);
 476 }
 477
 478 module_init(connlimit_mt_init);
 479 module_exit(connlimit_mt_exit);
 480 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 481 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 482 MODULE_LICENSE("GPL");
 483 MODULE_ALIAS("ipt_connlimit");
 484 MODULE_ALIAS("ip6t_connlimit");