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 list_head list;
  37         struct nf_conntrack_tuple tuple;
  38 };
  39
  40 struct xt_connlimit_data {
  41         struct list_head iphash[256];
  42         spinlock_t lock;
  43 };
  44
  45 static u_int32_t connlimit_rnd __read_mostly;
  46 static bool connlimit_rnd_inited __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 xt_connlimit_conn *tmp;
 105         struct nf_conn *found_ct;
 106         struct list_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         list_for_each_entry_safe(conn, tmp, hash, list) {
 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                         list_del(&conn->list);
 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                         list_del(&conn->list);
 150                         kfree(conn);
 151                         continue;
 152                 }
 153
 154                 if (same_source_net(addr, mask, &conn->tuple.src.u3, 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 = kzalloc(sizeof(*conn), GFP_ATOMIC);
 165                 if (conn == NULL)
 166                         return -ENOMEM;
 167                 conn->tuple = *tuple;
 168                 list_add(&conn->list, hash);
 169                 ++matches;
 170         }
 171
 172         return matches;
 173 }
 174
 175 static bool
 176 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 177 {
 178         struct net *net = dev_net(par->in ? par->in : par->out);
 179         const struct xt_connlimit_info *info = par->matchinfo;
 180         union nf_inet_addr addr;
 181         struct nf_conntrack_tuple tuple;
 182         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 183         enum ip_conntrack_info ctinfo;
 184         const struct nf_conn *ct;
 185         int connections;
 186
 187         ct = nf_ct_get(skb, &ctinfo);
 188         if (ct != NULL)
 189                 tuple_ptr = &ct->tuplehash[0].tuple;
 190         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 191                                     par->family, &tuple))
 192                 goto hotdrop;
 193
 194         if (par->family == NFPROTO_IPV6) {
 195                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 196                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
 197         } else {
 198                 const struct iphdr *iph = ip_hdr(skb);
 199                 addr.ip = iph->saddr;
 200         }
 201
 202         spin_lock_bh(&info->data->lock);
 203         connections = count_them(net, info->data, tuple_ptr, &addr,
 204                                  &info->mask, par->family);
 205         spin_unlock_bh(&info->data->lock);
 206
 207         if (connections < 0) {
 208                 /* kmalloc failed, drop it entirely */
 209                 par->hotdrop = true;
 210                 return false;
 211         }
 212
 213         return (connections > info->limit) ^ info->inverse;
 214
 215  hotdrop:
 216         par->hotdrop = true;
 217         return false;
 218 }
 219
 220 static int connlimit_mt_check(const struct xt_mtchk_param *par)
 221 {
 222         struct xt_connlimit_info *info = par->matchinfo;
 223         unsigned int i;
 224         int ret;
 225
 226         if (unlikely(!connlimit_rnd_inited)) {
 227                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
 228                 connlimit_rnd_inited = true;
 229         }
 230         ret = nf_ct_l3proto_try_module_get(par->family);
 231         if (ret < 0) {
 232                 pr_info("cannot load conntrack support for "
 233                         "address family %u\n", par->family);
 234                 return ret;
 235         }
 236
 237         /* init private data */
 238         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 239         if (info->data == NULL) {
 240                 nf_ct_l3proto_module_put(par->family);
 241                 return -ENOMEM;
 242         }
 243
 244         spin_lock_init(&info->data->lock);
 245         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 246                 INIT_LIST_HEAD(&info->data->iphash[i]);
 247
 248         return 0;
 249 }
 250
 251 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 252 {
 253         const struct xt_connlimit_info *info = par->matchinfo;
 254         struct xt_connlimit_conn *conn;
 255         struct xt_connlimit_conn *tmp;
 256         struct list_head *hash = info->data->iphash;
 257         unsigned int i;
 258
 259         nf_ct_l3proto_module_put(par->family);
 260
 261         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 262                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 263                         list_del(&conn->list);
 264                         kfree(conn);
 265                 }
 266         }
 267
 268         kfree(info->data);
 269 }
 270
 271 static struct xt_match connlimit_mt_reg __read_mostly = {
 272         .name       = "connlimit",
 273         .revision   = 0,
 274         .family     = NFPROTO_UNSPEC,
 275         .checkentry = connlimit_mt_check,
 276         .match      = connlimit_mt,
 277         .matchsize  = sizeof(struct xt_connlimit_info),
 278         .destroy    = connlimit_mt_destroy,
 279         .me         = THIS_MODULE,
 280 };
 281
 282 static int __init connlimit_mt_init(void)
 283 {
 284         return xt_register_match(&connlimit_mt_reg);
 285 }
 286
 287 static void __exit connlimit_mt_exit(void)
 288 {
 289         xt_unregister_match(&connlimit_mt_reg);
 290 }
 291
 292 module_init(connlimit_mt_init);
 293 module_exit(connlimit_mt_exit);
 294 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 295 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 296 MODULE_LICENSE("GPL");
 297 MODULE_ALIAS("ipt_connlimit");
 298 MODULE_ALIAS("ip6t_connlimit");