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/module.h>
  23 #include <linux/random.h>
  24 #include <linux/skbuff.h>
  25 #include <linux/spinlock.h>
  26 #include <linux/netfilter/nf_conntrack_tcp.h>
  27 #include <linux/netfilter/x_tables.h>
  28 #include <linux/netfilter/xt_connlimit.h>
  29 #include <net/netfilter/nf_conntrack.h>
  30 #include <net/netfilter/nf_conntrack_core.h>
  31 #include <net/netfilter/nf_conntrack_tuple.h>
  32 #include <net/netfilter/nf_conntrack_zones.h>
  33
  34 /* we will save the tuples of all connections we care about */
  35 struct xt_connlimit_conn {
  36         struct hlist_node               node;
  37         struct nf_conntrack_tuple       tuple;
  38         union nf_inet_addr              addr;
  39 };
  40
  41 struct xt_connlimit_data {
  42         struct hlist_head       iphash[256];
  43         spinlock_t              lock;
  44 };
  45
  46 static u_int32_t connlimit_rnd __read_mostly;
  47
  48 static inline unsigned int connlimit_iphash(__be32 addr)
  49 {
  50         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  51 }
  52
  53 static inline unsigned int
  54 connlimit_iphash6(const union nf_inet_addr *addr,
  55                   const union nf_inet_addr *mask)
  56 {
  57         union nf_inet_addr res;
  58         unsigned int i;
  59
  60         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  61                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  62
  63         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
  64 }
  65
  66 static inline bool already_closed(const struct nf_conn *conn)
  67 {
  68         if (nf_ct_protonum(conn) == IPPROTO_TCP)
  69                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
  70                        conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
  71         else
  72                 return 0;
  73 }
  74
  75 static inline unsigned int
  76 same_source_net(const union nf_inet_addr *addr,
  77                 const union nf_inet_addr *mask,
  78                 const union nf_inet_addr *u3, u_int8_t family)
  79 {
  80         if (family == NFPROTO_IPV4) {
  81                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  82         } else {
  83                 union nf_inet_addr lh, rh;
  84                 unsigned int i;
  85
  86                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  87                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  88                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  89                 }
  90
  91                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  92         }
  93 }
  94
  95 static int count_them(struct net *net,
  96                       struct xt_connlimit_data *data,
  97                       const struct nf_conntrack_tuple *tuple,
  98                       const union nf_inet_addr *addr,
  99                       const union nf_inet_addr *mask,
 100                       u_int8_t family)
 101 {
 102         const struct nf_conntrack_tuple_hash *found;
 103         struct xt_connlimit_conn *conn;
 104         struct hlist_node *pos, *n;
 105         struct nf_conn *found_ct;
 106         struct hlist_head *hash;
 107         bool addit = true;
 108         int matches = 0;
 109
 110         if (family == NFPROTO_IPV6)
 111                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 112         else
 113                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 114
 115         rcu_read_lock();
 116
 117         /* check the saved connections */
 118         hlist_for_each_entry_safe(conn, pos, n, hash, node) {
 119                 found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
 120                                                  &conn->tuple);
 121                 found_ct = NULL;
 122
 123                 if (found != NULL)
 124                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 125
 126                 if (found_ct != NULL &&
 127                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 128                     !already_closed(found_ct))
 129                         /*
 130                          * Just to be sure we have it only once in the list.
 131                          * We should not see tuples twice unless someone hooks
 132                          * this into a table without "-p tcp --syn".
 133                          */
 134                         addit = false;
 135
 136                 if (found == NULL) {
 137                         /* this one is gone */
 138                         hlist_del(&conn->node);
 139                         kfree(conn);
 140                         continue;
 141                 }
 142
 143                 if (already_closed(found_ct)) {
 144                         /*
 145                          * we do not care about connections which are
 146                          * closed already -> ditch it
 147                          */
 148                         nf_ct_put(found_ct);
 149                         hlist_del(&conn->node);
 150                         kfree(conn);
 151                         continue;
 152                 }
 153
 154                 if (same_source_net(addr, mask, &conn->addr, family))
 155                         /* same source network -> be counted! */
 156                         ++matches;
 157                 nf_ct_put(found_ct);
 158         }
 159
 160         rcu_read_unlock();
 161
 162         if (addit) {
 163                 /* save the new connection in our list */
 164                 conn = kmalloc(sizeof(*conn), GFP_ATOMIC);
 165                 if (conn == NULL)
 166                         return -ENOMEM;
 167                 conn->tuple = *tuple;
 168                 conn->addr = *addr;
 169                 hlist_add_head(&conn->node, hash);
 170                 ++matches;
 171         }
 172
 173         return matches;
 174 }
 175
 176 static bool
 177 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 178 {
 179         struct net *net = dev_net(par->in ? par->in : par->out);
 180         const struct xt_connlimit_info *info = par->matchinfo;
 181         union nf_inet_addr addr;
 182         struct nf_conntrack_tuple tuple;
 183         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 184         enum ip_conntrack_info ctinfo;
 185         const struct nf_conn *ct;
 186         int connections;
 187
 188         ct = nf_ct_get(skb, &ctinfo);
 189         if (ct != NULL)
 190                 tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 191         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 192                                     par->family, &tuple))
 193                 goto hotdrop;
 194
 195         if (par->family == NFPROTO_IPV6) {
 196                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 197                 memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
 198                        &iph->daddr : &iph->saddr, sizeof(addr.ip6));
 199         } else {
 200                 const struct iphdr *iph = ip_hdr(skb);
 201                 addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
 202                           iph->daddr : iph->saddr;
 203         }
 204
 205         spin_lock_bh(&info->data->lock);
 206         connections = count_them(net, info->data, tuple_ptr, &addr,
 207                                  &info->mask, par->family);
 208         spin_unlock_bh(&info->data->lock);
 209
 210         if (connections < 0)
 211                 /* kmalloc failed, drop it entirely */
 212                 goto hotdrop;
 213
 214         return (connections > info->limit) ^
 215                !!(info->flags & XT_CONNLIMIT_INVERT);
 216
 217  hotdrop:
 218         par->hotdrop = true;
 219         return false;
 220 }
 221
 222 static int connlimit_mt_check(const struct xt_mtchk_param *par)
 223 {
 224         struct xt_connlimit_info *info = par->matchinfo;
 225         unsigned int i;
 226         int ret;
 227
 228         if (unlikely(!connlimit_rnd)) {
 229                 u_int32_t rand;
 230
 231                 do {
 232                         get_random_bytes(&rand, sizeof(rand));
 233                 } while (!rand);
 234                 cmpxchg(&connlimit_rnd, 0, rand);
 235         }
 236         ret = nf_ct_l3proto_try_module_get(par->family);
 237         if (ret < 0) {
 238                 pr_info("cannot load conntrack support for "
 239                         "address family %u\n", par->family);
 240                 return ret;
 241         }
 242
 243         /* init private data */
 244         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 245         if (info->data == NULL) {
 246                 nf_ct_l3proto_module_put(par->family);
 247                 return -ENOMEM;
 248         }
 249
 250         spin_lock_init(&info->data->lock);
 251         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 252                 INIT_HLIST_HEAD(&info->data->iphash[i]);
 253
 254         return 0;
 255 }
 256
 257 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 258 {
 259         const struct xt_connlimit_info *info = par->matchinfo;
 260         struct xt_connlimit_conn *conn;
 261         struct hlist_node *pos, *n;
 262         struct hlist_head *hash = info->data->iphash;
 263         unsigned int i;
 264
 265         nf_ct_l3proto_module_put(par->family);
 266
 267         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 268                 hlist_for_each_entry_safe(conn, pos, n, &hash[i], node) {
 269                         hlist_del(&conn->node);
 270                         kfree(conn);
 271                 }
 272         }
 273
 274         kfree(info->data);
 275 }
 276
 277 static struct xt_match connlimit_mt_reg __read_mostly = {
 278         .name       = "connlimit",
 279         .revision   = 1,
 280         .family     = NFPROTO_UNSPEC,
 281         .checkentry = connlimit_mt_check,
 282         .match      = connlimit_mt,
 283         .matchsize  = sizeof(struct xt_connlimit_info),
 284         .destroy    = connlimit_mt_destroy,
 285         .me         = THIS_MODULE,
 286 };
 287
 288 static int __init connlimit_mt_init(void)
 289 {
 290         return xt_register_match(&connlimit_mt_reg);
 291 }
 292
 293 static void __exit connlimit_mt_exit(void)
 294 {
 295         xt_unregister_match(&connlimit_mt_reg);
 296 }
 297
 298 module_init(connlimit_mt_init);
 299 module_exit(connlimit_mt_exit);
 300 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 301 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 302 MODULE_LICENSE("GPL");
 303 MODULE_ALIAS("ipt_connlimit");
 304 MODULE_ALIAS("ip6t_connlimit");