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  *   Contact: <jengelh@computergmbh.de>
   9  *
  10  * based on ...
  11  *
  12  * Kernel module to match connection tracking information.
  13  * GPL (C) 1999  Rusty Russell (rusty@rustcorp.com.au).
  14  */
  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/list.h>
  21 #include <linux/module.h>
  22 #include <linux/random.h>
  23 #include <linux/skbuff.h>
  24 #include <linux/spinlock.h>
  25 #include <linux/netfilter/nf_conntrack_tcp.h>
  26 #include <linux/netfilter/x_tables.h>
  27 #include <linux/netfilter/xt_connlimit.h>
  28 #include <net/netfilter/nf_conntrack.h>
  29 #include <net/netfilter/nf_conntrack_core.h>
  30 #include <net/netfilter/nf_conntrack_tuple.h>
  31
  32 /* we will save the tuples of all connections we care about */
  33 struct xt_connlimit_conn {
  34         struct list_head list;
  35         struct nf_conntrack_tuple tuple;
  36 };
  37
  38 struct xt_connlimit_data {
  39         struct list_head iphash[256];
  40         spinlock_t lock;
  41 };
  42
  43 static u_int32_t connlimit_rnd;
  44 static bool connlimit_rnd_inited;
  45
  46 static inline unsigned int connlimit_iphash(__be32 addr)
  47 {
  48         if (unlikely(!connlimit_rnd_inited)) {
  49                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  50                 connlimit_rnd_inited = true;
  51         }
  52         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  53 }
  54
  55 static inline unsigned int
  56 connlimit_iphash6(const union nf_inet_addr *addr,
  57                   const union nf_inet_addr *mask)
  58 {
  59         union nf_inet_addr res;
  60         unsigned int i;
  61
  62         if (unlikely(!connlimit_rnd_inited)) {
  63                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  64                 connlimit_rnd_inited = true;
  65         }
  66
  67         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  68                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  69
  70         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
  71 }
  72
  73 static inline bool already_closed(const struct nf_conn *conn)
  74 {
  75         if (nf_ct_protonum(conn) == IPPROTO_TCP)
  76                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
  77                        conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
  78         else
  79                 return 0;
  80 }
  81
  82 static inline unsigned int
  83 same_source_net(const union nf_inet_addr *addr,
  84                 const union nf_inet_addr *mask,
  85                 const union nf_inet_addr *u3, u_int8_t family)
  86 {
  87         if (family == NFPROTO_IPV4) {
  88                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  89         } else {
  90                 union nf_inet_addr lh, rh;
  91                 unsigned int i;
  92
  93                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  94                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  95                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  96                 }
  97
  98                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  99         }
 100 }
 101
 102 static int count_them(struct xt_connlimit_data *data,
 103                       const struct nf_conntrack_tuple *tuple,
 104                       const union nf_inet_addr *addr,
 105                       const union nf_inet_addr *mask,
 106                       u_int8_t family)
 107 {
 108         const struct nf_conntrack_tuple_hash *found;
 109         struct xt_connlimit_conn *conn;
 110         struct xt_connlimit_conn *tmp;
 111         struct nf_conn *found_ct;
 112         struct list_head *hash;
 113         bool addit = true;
 114         int matches = 0;
 115
 116         if (family == NFPROTO_IPV6)
 117                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 118         else
 119                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 120
 121         rcu_read_lock();
 122
 123         /* check the saved connections */
 124         list_for_each_entry_safe(conn, tmp, hash, list) {
 125                 found    = nf_conntrack_find_get(&init_net, &conn->tuple);
 126                 found_ct = NULL;
 127
 128                 if (found != NULL)
 129                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 130
 131                 if (found_ct != NULL &&
 132                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 133                     !already_closed(found_ct))
 134                         /*
 135                          * Just to be sure we have it only once in the list.
 136                          * We should not see tuples twice unless someone hooks
 137                          * this into a table without "-p tcp --syn".
 138                          */
 139                         addit = false;
 140
 141                 if (found == NULL) {
 142                         /* this one is gone */
 143                         list_del(&conn->list);
 144                         kfree(conn);
 145                         continue;
 146                 }
 147
 148                 if (already_closed(found_ct)) {
 149                         /*
 150                          * we do not care about connections which are
 151                          * closed already -> ditch it
 152                          */
 153                         nf_ct_put(found_ct);
 154                         list_del(&conn->list);
 155                         kfree(conn);
 156                         continue;
 157                 }
 158
 159                 if (same_source_net(addr, mask, &conn->tuple.src.u3, family))
 160                         /* same source network -> be counted! */
 161                         ++matches;
 162                 nf_ct_put(found_ct);
 163         }
 164
 165         rcu_read_unlock();
 166
 167         if (addit) {
 168                 /* save the new connection in our list */
 169                 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
 170                 if (conn == NULL)
 171                         return -ENOMEM;
 172                 conn->tuple = *tuple;
 173                 list_add(&conn->list, hash);
 174                 ++matches;
 175         }
 176
 177         return matches;
 178 }
 179
 180 static bool
 181 connlimit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
 182 {
 183         const struct xt_connlimit_info *info = par->matchinfo;
 184         union nf_inet_addr addr;
 185         struct nf_conntrack_tuple tuple;
 186         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 187         enum ip_conntrack_info ctinfo;
 188         const struct nf_conn *ct;
 189         int connections;
 190
 191         ct = nf_ct_get(skb, &ctinfo);
 192         if (ct != NULL)
 193                 tuple_ptr = &ct->tuplehash[0].tuple;
 194         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 195                                     par->family, &tuple))
 196                 goto hotdrop;
 197
 198         if (par->family == NFPROTO_IPV6) {
 199                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 200                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
 201         } else {
 202                 const struct iphdr *iph = ip_hdr(skb);
 203                 addr.ip = iph->saddr;
 204         }
 205
 206         spin_lock_bh(&info->data->lock);
 207         connections = count_them(info->data, tuple_ptr, &addr,
 208                                  &info->mask, par->family);
 209         spin_unlock_bh(&info->data->lock);
 210
 211         if (connections < 0) {
 212                 /* kmalloc failed, drop it entirely */
 213                 *par->hotdrop = true;
 214                 return false;
 215         }
 216
 217         return (connections > info->limit) ^ info->inverse;
 218
 219  hotdrop:
 220         *par->hotdrop = true;
 221         return false;
 222 }
 223
 224 static bool connlimit_mt_check(const struct xt_mtchk_param *par)
 225 {
 226         struct xt_connlimit_info *info = par->matchinfo;
 227         unsigned int i;
 228
 229         if (nf_ct_l3proto_try_module_get(par->family) < 0) {
 230                 printk(KERN_WARNING "cannot load conntrack support for "
 231                        "address family %u\n", par->family);
 232                 return false;
 233         }
 234
 235         /* init private data */
 236         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 237         if (info->data == NULL) {
 238                 nf_ct_l3proto_module_put(par->family);
 239                 return false;
 240         }
 241
 242         spin_lock_init(&info->data->lock);
 243         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 244                 INIT_LIST_HEAD(&info->data->iphash[i]);
 245
 246         return true;
 247 }
 248
 249 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 250 {
 251         const struct xt_connlimit_info *info = par->matchinfo;
 252         struct xt_connlimit_conn *conn;
 253         struct xt_connlimit_conn *tmp;
 254         struct list_head *hash = info->data->iphash;
 255         unsigned int i;
 256
 257         nf_ct_l3proto_module_put(par->family);
 258
 259         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 260                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 261                         list_del(&conn->list);
 262                         kfree(conn);
 263                 }
 264         }
 265
 266         kfree(info->data);
 267 }
 268
 269 static struct xt_match connlimit_mt_reg __read_mostly = {
 270         .name       = "connlimit",
 271         .revision   = 0,
 272         .family     = NFPROTO_UNSPEC,
 273         .checkentry = connlimit_mt_check,
 274         .match      = connlimit_mt,
 275         .matchsize  = sizeof(struct xt_connlimit_info),
 276         .destroy    = connlimit_mt_destroy,
 277         .me         = THIS_MODULE,
 278 };
 279
 280 static int __init connlimit_mt_init(void)
 281 {
 282         return xt_register_match(&connlimit_mt_reg);
 283 }
 284
 285 static void __exit connlimit_mt_exit(void)
 286 {
 287         xt_unregister_match(&connlimit_mt_reg);
 288 }
 289
 290 module_init(connlimit_mt_init);
 291 module_exit(connlimit_mt_exit);
 292 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 293 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 294 MODULE_LICENSE("GPL");
 295 MODULE_ALIAS("ipt_connlimit");
 296 MODULE_ALIAS("ip6t_connlimit");