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