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 static bool connlimit_rnd_inited __read_mostly;
  48
  49 static inline unsigned int connlimit_iphash(__be32 addr)
  50 {
  51         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  52 }
  53
  54 static inline unsigned int
  55 connlimit_iphash6(const union nf_inet_addr *addr,
  56                   const union nf_inet_addr *mask)
  57 {
  58         union nf_inet_addr res;
  59         unsigned int i;
  60
  61         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  62                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  63
  64         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
  65 }
  66
  67 static inline bool already_closed(const struct nf_conn *conn)
  68 {
  69         if (nf_ct_protonum(conn) == IPPROTO_TCP)
  70                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
  71                        conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
  72         else
  73                 return 0;
  74 }
  75
  76 static inline unsigned int
  77 same_source_net(const union nf_inet_addr *addr,
  78                 const union nf_inet_addr *mask,
  79                 const union nf_inet_addr *u3, u_int8_t family)
  80 {
  81         if (family == NFPROTO_IPV4) {
  82                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  83         } else {
  84                 union nf_inet_addr lh, rh;
  85                 unsigned int i;
  86
  87                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  88                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  89                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  90                 }
  91
  92                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  93         }
  94 }
  95
  96 static int count_them(struct net *net,
  97                       struct xt_connlimit_data *data,
  98                       const struct nf_conntrack_tuple *tuple,
  99                       const union nf_inet_addr *addr,
 100                       const union nf_inet_addr *mask,
 101                       u_int8_t family)
 102 {
 103         const struct nf_conntrack_tuple_hash *found;
 104         struct xt_connlimit_conn *conn;
 105         struct hlist_node *pos, *n;
 106         struct nf_conn *found_ct;
 107         struct hlist_head *hash;
 108         bool addit = true;
 109         int matches = 0;
 110
 111         if (family == NFPROTO_IPV6)
 112                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 113         else
 114                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 115
 116         rcu_read_lock();
 117
 118         /* check the saved connections */
 119         hlist_for_each_entry_safe(conn, pos, n, hash, node) {
 120                 found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
 121                                                  &conn->tuple);
 122                 found_ct = NULL;
 123
 124                 if (found != NULL)
 125                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 126
 127                 if (found_ct != NULL &&
 128                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 129                     !already_closed(found_ct))
 130                         /*
 131                          * Just to be sure we have it only once in the list.
 132                          * We should not see tuples twice unless someone hooks
 133                          * this into a table without "-p tcp --syn".
 134                          */
 135                         addit = false;
 136
 137                 if (found == NULL) {
 138                         /* this one is gone */
 139                         hlist_del(&conn->node);
 140                         kfree(conn);
 141                         continue;
 142                 }
 143
 144                 if (already_closed(found_ct)) {
 145                         /*
 146                          * we do not care about connections which are
 147                          * closed already -> ditch it
 148                          */
 149                         nf_ct_put(found_ct);
 150                         hlist_del(&conn->node);
 151                         kfree(conn);
 152                         continue;
 153                 }
 154
 155                 if (same_source_net(addr, mask, &conn->addr, family))
 156                         /* same source network -> be counted! */
 157                         ++matches;
 158                 nf_ct_put(found_ct);
 159         }
 160
 161         rcu_read_unlock();
 162
 163         if (addit) {
 164                 /* save the new connection in our list */
 165                 conn = kmalloc(sizeof(*conn), GFP_ATOMIC);
 166                 if (conn == NULL)
 167                         return -ENOMEM;
 168                 conn->tuple = *tuple;
 169                 conn->addr = *addr;
 170                 hlist_add_head(&conn->node, hash);
 171                 ++matches;
 172         }
 173
 174         return matches;
 175 }
 176
 177 static bool
 178 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 179 {
 180         struct net *net = dev_net(par->in ? par->in : par->out);
 181         const struct xt_connlimit_info *info = par->matchinfo;
 182         union nf_inet_addr addr;
 183         struct nf_conntrack_tuple tuple;
 184         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 185         enum ip_conntrack_info ctinfo;
 186         const struct nf_conn *ct;
 187         int connections;
 188
 189         ct = nf_ct_get(skb, &ctinfo);
 190         if (ct != NULL)
 191                 tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 192         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 193                                     par->family, &tuple))
 194                 goto hotdrop;
 195
 196         if (par->family == NFPROTO_IPV6) {
 197                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 198                 memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
 199                        &iph->daddr : &iph->saddr, sizeof(addr.ip6));
 200         } else {
 201                 const struct iphdr *iph = ip_hdr(skb);
 202                 addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
 203                           iph->daddr : iph->saddr;
 204         }
 205
 206         spin_lock_bh(&info->data->lock);
 207         connections = count_them(net, 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                 goto hotdrop;
 214
 215         return (connections > info->limit) ^
 216                !!(info->flags & XT_CONNLIMIT_INVERT);
 217
 218  hotdrop:
 219         par->hotdrop = true;
 220         return false;
 221 }
 222
 223 static int connlimit_mt_check(const struct xt_mtchk_param *par)
 224 {
 225         struct xt_connlimit_info *info = par->matchinfo;
 226         unsigned int i;
 227         int ret;
 228
 229         if (unlikely(!connlimit_rnd_inited)) {
 230                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
 231                 connlimit_rnd_inited = true;
 232         }
 233         ret = nf_ct_l3proto_try_module_get(par->family);
 234         if (ret < 0) {
 235                 pr_info("cannot load conntrack support for "
 236                         "address family %u\n", par->family);
 237                 return ret;
 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(par->family);
 244                 return -ENOMEM;
 245         }
 246
 247         spin_lock_init(&info->data->lock);
 248         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 249                 INIT_HLIST_HEAD(&info->data->iphash[i]);
 250
 251         return 0;
 252 }
 253
 254 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 255 {
 256         const struct xt_connlimit_info *info = par->matchinfo;
 257         struct xt_connlimit_conn *conn;
 258         struct hlist_node *pos, *n;
 259         struct hlist_head *hash = info->data->iphash;
 260         unsigned int i;
 261
 262         nf_ct_l3proto_module_put(par->family);
 263
 264         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 265                 hlist_for_each_entry_safe(conn, pos, n, &hash[i], node) {
 266                         hlist_del(&conn->node);
 267                         kfree(conn);
 268                 }
 269         }
 270
 271         kfree(info->data);
 272 }
 273
 274 static struct xt_match connlimit_mt_reg[] __read_mostly = {
 275         {
 276                 .name       = "connlimit",
 277                 .revision   = 0,
 278                 .family     = NFPROTO_UNSPEC,
 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                 .revision   = 1,
 288                 .family     = NFPROTO_UNSPEC,
 289                 .checkentry = connlimit_mt_check,
 290                 .match      = connlimit_mt,
 291                 .matchsize  = sizeof(struct xt_connlimit_info),
 292                 .destroy    = connlimit_mt_destroy,
 293                 .me         = THIS_MODULE,
 294         },
 295 };
 296
 297 static int __init connlimit_mt_init(void)
 298 {
 299         return xt_register_matches(connlimit_mt_reg,
 300                ARRAY_SIZE(connlimit_mt_reg));
 301 }
 302
 303 static void __exit connlimit_mt_exit(void)
 304 {
 305         xt_unregister_matches(connlimit_mt_reg, ARRAY_SIZE(connlimit_mt_reg));
 306 }
 307
 308 module_init(connlimit_mt_init);
 309 module_exit(connlimit_mt_exit);
 310 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 311 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 312 MODULE_LICENSE("GPL");
 313 MODULE_ALIAS("ipt_connlimit");
 314 MODULE_ALIAS("ip6t_connlimit");