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