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 *
   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 */
  35struct xt_connlimit_conn {
  36        struct hlist_node               node;
  37        struct nf_conntrack_tuple       tuple;
  38        union nf_inet_addr              addr;
  39};
  40
  41struct xt_connlimit_data {
  42        struct hlist_head       iphash[256];
  43        spinlock_t              lock;
  44};
  45
  46static u_int32_t connlimit_rnd __read_mostly;
  47
  48static inline unsigned int connlimit_iphash(__be32 addr)
  49{
  50        return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  51}
  52
  53static inline unsigned int
  54connlimit_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
  66static 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
  75static inline unsigned int
  76same_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
  95static 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 hlist_node *n;
 105        struct nf_conn *found_ct;
 106        struct hlist_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        hlist_for_each_entry_safe(conn, n, hash, node) {
 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                        hlist_del(&conn->node);
 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                        hlist_del(&conn->node);
 150                        kfree(conn);
 151                        continue;
 152                }
 153
 154                if (same_source_net(addr, mask, &conn->addr, 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 = kmalloc(sizeof(*conn), GFP_ATOMIC);
 165                if (conn == NULL)
 166                        return -ENOMEM;
 167                conn->tuple = *tuple;
 168                conn->addr = *addr;
 169                hlist_add_head(&conn->node, hash);
 170                ++matches;
 171        }
 172
 173        return matches;
 174}
 175
 176static bool
 177connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 178{
 179        struct net *net = dev_net(par->in ? par->in : par->out);
 180        const struct xt_connlimit_info *info = par->matchinfo;
 181        union nf_inet_addr addr;
 182        struct nf_conntrack_tuple tuple;
 183        const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 184        enum ip_conntrack_info ctinfo;
 185        const struct nf_conn *ct;
 186        int connections;
 187
 188        ct = nf_ct_get(skb, &ctinfo);
 189        if (ct != NULL)
 190                tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 191        else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 192                                    par->family, &tuple))
 193                goto hotdrop;
 194
 195        if (par->family == NFPROTO_IPV6) {
 196                const struct ipv6hdr *iph = ipv6_hdr(skb);
 197                memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
 198                       &iph->daddr : &iph->saddr, sizeof(addr.ip6));
 199        } else {
 200                const struct iphdr *iph = ip_hdr(skb);
 201                addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
 202                          iph->daddr : iph->saddr;
 203        }
 204
 205        spin_lock_bh(&info->data->lock);
 206        connections = count_them(net, info->data, tuple_ptr, &addr,
 207                                 &info->mask, par->family);
 208        spin_unlock_bh(&info->data->lock);
 209
 210        if (connections < 0)
 211                /* kmalloc failed, drop it entirely */
 212                goto hotdrop;
 213
 214        return (connections > info->limit) ^
 215               !!(info->flags & XT_CONNLIMIT_INVERT);
 216
 217 hotdrop:
 218        par->hotdrop = true;
 219        return false;
 220}
 221
 222static int connlimit_mt_check(const struct xt_mtchk_param *par)
 223{
 224        struct xt_connlimit_info *info = par->matchinfo;
 225        unsigned int i;
 226        int ret;
 227
 228        if (unlikely(!connlimit_rnd)) {
 229                u_int32_t rand;
 230
 231                do {
 232                        get_random_bytes(&rand, sizeof(rand));
 233                } while (!rand);
 234                cmpxchg(&connlimit_rnd, 0, rand);
 235        }
 236        ret = nf_ct_l3proto_try_module_get(par->family);
 237        if (ret < 0) {
 238                pr_info("cannot load conntrack support for "
 239                        "address family %u\n", par->family);
 240                return ret;
 241        }
 242
 243        /* init private data */
 244        info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 245        if (info->data == NULL) {
 246                nf_ct_l3proto_module_put(par->family);
 247                return -ENOMEM;
 248        }
 249
 250        spin_lock_init(&info->data->lock);
 251        for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 252                INIT_HLIST_HEAD(&info->data->iphash[i]);
 253
 254        return 0;
 255}
 256
 257static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 258{
 259        const struct xt_connlimit_info *info = par->matchinfo;
 260        struct xt_connlimit_conn *conn;
 261        struct hlist_node *n;
 262        struct hlist_head *hash = info->data->iphash;
 263        unsigned int i;
 264
 265        nf_ct_l3proto_module_put(par->family);
 266
 267        for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 268                hlist_for_each_entry_safe(conn, n, &hash[i], node) {
 269                        hlist_del(&conn->node);
 270                        kfree(conn);
 271                }
 272        }
 273
 274        kfree(info->data);
 275}
 276
 277static struct xt_match connlimit_mt_reg __read_mostly = {
 278        .name       = "connlimit",
 279        .revision   = 1,
 280        .family     = NFPROTO_UNSPEC,
 281        .checkentry = connlimit_mt_check,
 282        .match      = connlimit_mt,
 283        .matchsize  = sizeof(struct xt_connlimit_info),
 284        .destroy    = connlimit_mt_destroy,
 285        .me         = THIS_MODULE,
 286};
 287
 288static int __init connlimit_mt_init(void)
 289{
 290        return xt_register_match(&connlimit_mt_reg);
 291}
 292
 293static void __exit connlimit_mt_exit(void)
 294{
 295        xt_unregister_match(&connlimit_mt_reg);
 296}
 297
 298module_init(connlimit_mt_init);
 299module_exit(connlimit_mt_exit);
 300MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 301MODULE_DESCRIPTION("Xtables: Number of connections matching");
 302MODULE_LICENSE("GPL");
 303MODULE_ALIAS("ipt_connlimit");
 304MODULE_ALIAS("ip6t_connlimit");
 305
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