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