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         else
  78                 return 0;
  79 }
  80
  81 static inline unsigned int
  82 same_source_net(const union nf_inet_addr *addr,
  83                 const union nf_inet_addr *mask,
  84                 const union nf_inet_addr *u3, unsigned int family)
  85 {
  86         if (family == AF_INET) {
  87                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  88         } else {
  89                 union nf_inet_addr lh, rh;
  90                 unsigned int i;
  91
  92                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  93                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  94                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  95                 }
  96
  97                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  98         }
  99 }
 100
 101 static int count_them(struct xt_connlimit_data *data,
 102                       const struct nf_conntrack_tuple *tuple,
 103                       const union nf_inet_addr *addr,
 104                       const union nf_inet_addr *mask,
 105                       const struct xt_match *match)
 106 {
 107         const struct nf_conntrack_tuple_hash *found;
 108         struct xt_connlimit_conn *conn;
 109         struct xt_connlimit_conn *tmp;
 110         const struct nf_conn *found_ct;
 111         struct list_head *hash;
 112         bool addit = true;
 113         int matches = 0;
 114
 115
 116         if (match->family == AF_INET6)
 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(&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                         list_del(&conn->list);
 154                         kfree(conn);
 155                         continue;
 156                 }
 157
 158                 if (same_source_net(addr, mask, &conn->tuple.src.u3,
 159                     match->family))
 160                         /* same source network -> be counted! */
 161                         ++matches;
 162         }
 163
 164         rcu_read_unlock();
 165
 166         if (addit) {
 167                 /* save the new connection in our list */
 168                 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
 169                 if (conn == NULL)
 170                         return -ENOMEM;
 171                 conn->tuple = *tuple;
 172                 list_add(&conn->list, hash);
 173                 ++matches;
 174         }
 175
 176         return matches;
 177 }
 178
 179 static bool
 180 connlimit_mt(const struct sk_buff *skb, const struct net_device *in,
 181              const struct net_device *out, const struct xt_match *match,
 182              const void *matchinfo, int offset, unsigned int protoff,
 183              bool *hotdrop)
 184 {
 185         const struct xt_connlimit_info *info = matchinfo;
 186         union nf_inet_addr addr;
 187         struct nf_conntrack_tuple tuple;
 188         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 189         enum ip_conntrack_info ctinfo;
 190         const struct nf_conn *ct;
 191         int connections;
 192
 193         ct = nf_ct_get(skb, &ctinfo);
 194         if (ct != NULL)
 195                 tuple_ptr = &ct->tuplehash[0].tuple;
 196         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 197                                     match->family, &tuple))
 198                 goto hotdrop;
 199
 200         if (match->family == AF_INET6) {
 201                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 202                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
 203         } else {
 204                 const struct iphdr *iph = ip_hdr(skb);
 205                 addr.ip = iph->saddr;
 206         }
 207
 208         spin_lock_bh(&info->data->lock);
 209         connections = count_them(info->data, tuple_ptr, &addr,
 210                                  &info->mask, match);
 211         spin_unlock_bh(&info->data->lock);
 212
 213         if (connections < 0) {
 214                 /* kmalloc failed, drop it entirely */
 215                 *hotdrop = true;
 216                 return false;
 217         }
 218
 219         return (connections > info->limit) ^ info->inverse;
 220
 221  hotdrop:
 222         *hotdrop = true;
 223         return false;
 224 }
 225
 226 static bool
 227 connlimit_mt_check(const char *tablename, const void *ip,
 228                    const struct xt_match *match, void *matchinfo,
 229                    unsigned int hook_mask)
 230 {
 231         struct xt_connlimit_info *info = matchinfo;
 232         unsigned int i;
 233
 234         if (nf_ct_l3proto_try_module_get(match->family) < 0) {
 235                 printk(KERN_WARNING "cannot load conntrack support for "
 236                        "address family %u\n", match->family);
 237                 return false;
 238         }
 239
 240         /* init private data */
 241         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 242         if (info->data == NULL) {
 243                 nf_ct_l3proto_module_put(match->family);
 244                 return false;
 245         }
 246
 247         spin_lock_init(&info->data->lock);
 248         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 249                 INIT_LIST_HEAD(&info->data->iphash[i]);
 250
 251         return true;
 252 }
 253
 254 static void
 255 connlimit_mt_destroy(const struct xt_match *match, void *matchinfo)
 256 {
 257         const struct xt_connlimit_info *info = matchinfo;
 258         struct xt_connlimit_conn *conn;
 259         struct xt_connlimit_conn *tmp;
 260         struct list_head *hash = info->data->iphash;
 261         unsigned int i;
 262
 263         nf_ct_l3proto_module_put(match->family);
 264
 265         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 266                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 267                         list_del(&conn->list);
 268                         kfree(conn);
 269                 }
 270         }
 271
 272         kfree(info->data);
 273 }
 274
 275 static struct xt_match connlimit_mt_reg[] __read_mostly = {
 276         {
 277                 .name       = "connlimit",
 278                 .family     = AF_INET,
 279                 .checkentry = connlimit_mt_check,
 280                 .match      = connlimit_mt,
 281                 .matchsize  = sizeof(struct xt_connlimit_info),
 282                 .destroy    = connlimit_mt_destroy,
 283                 .me         = THIS_MODULE,
 284         },
 285         {
 286                 .name       = "connlimit",
 287                 .family     = AF_INET6,
 288                 .checkentry = connlimit_mt_check,
 289                 .match      = connlimit_mt,
 290                 .matchsize  = sizeof(struct xt_connlimit_info),
 291                 .destroy    = connlimit_mt_destroy,
 292                 .me         = THIS_MODULE,
 293         },
 294 };
 295
 296 static int __init connlimit_mt_init(void)
 297 {
 298         return xt_register_matches(connlimit_mt_reg,
 299                ARRAY_SIZE(connlimit_mt_reg));
 300 }
 301
 302 static void __exit connlimit_mt_exit(void)
 303 {
 304         xt_unregister_matches(connlimit_mt_reg, ARRAY_SIZE(connlimit_mt_reg));
 305 }
 306
 307 module_init(connlimit_mt_init);
 308 module_exit(connlimit_mt_exit);
 309 MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
 310 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 311 MODULE_LICENSE("GPL");
 312 MODULE_ALIAS("ipt_connlimit");
 313 MODULE_ALIAS("ip6t_connlimit");