xt_connlimit.c

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/*
 * netfilter module to limit the number of parallel tcp
 * connections per IP address.
 *   (c) 2000 Gerd Knorr <[email protected]>
 *   Nov 2002: Martin Bene <[email protected]>:
 *      only ignore TIME_WAIT or gone connections
 *   (C) CC Computer Consultants GmbH, 2007
 *
 * based on ...
 *
 * Kernel module to match connection tracking information.
 * GPL (C) 1999  Rusty Russell ([email protected]).
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/in.h>
#include <linux/in6.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/jhash.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/netfilter/nf_conntrack_tcp.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_connlimit.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_conntrack_tuple.h>
#include <net/netfilter/nf_conntrack_zones.h>

/* we will save the tuples of all connections we care about */
struct xt_connlimit_conn {
    struct hlist_node       node;
    struct nf_conntrack_tuple   tuple;
    union nf_inet_addr      addr;
};

struct xt_connlimit_data {
    struct hlist_head   iphash[256];
    spinlock_t      lock;
};

static u_int32_t connlimit_rnd __read_mostly;

static inline unsigned int connlimit_iphash(__be32 addr)
{
    return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
}

static inline unsigned int
connlimit_iphash6(const union nf_inet_addr *addr,
                  const union nf_inet_addr *mask)
{
    union nf_inet_addr res;
    unsigned int i;

    for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
        res.ip6[i] = addr->ip6[i] & mask->ip6[i];

    return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
}

static inline bool already_closed(const struct nf_conn *conn)
{
    if (nf_ct_protonum(conn) == IPPROTO_TCP)
        return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
               conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
    else
        return 0;
}

static inline unsigned int
same_source_net(const union nf_inet_addr *addr,
        const union nf_inet_addr *mask,
        const union nf_inet_addr *u3, u_int8_t family)
{
    if (family == NFPROTO_IPV4) {
        return (addr->ip & mask->ip) == (u3->ip & mask->ip);
    } else {
        union nf_inet_addr lh, rh;
        unsigned int i;

        for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
            lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
            rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
        }

        return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
    }
}

static int count_them(struct net *net,
              struct xt_connlimit_data *data,
              const struct nf_conntrack_tuple *tuple,
              const union nf_inet_addr *addr,
              const union nf_inet_addr *mask,
              u_int8_t family)
{
    const struct nf_conntrack_tuple_hash *found;
    struct xt_connlimit_conn *conn;
    struct hlist_node *pos, *n;
    struct nf_conn *found_ct;
    struct hlist_head *hash;
    bool addit = true;
    int matches = 0;

    if (family == NFPROTO_IPV6)
        hash = &data->iphash[connlimit_iphash6(addr, mask)];
    else
        hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];

    rcu_read_lock();

    /* check the saved connections */
    hlist_for_each_entry_safe(conn, pos, n, hash, node) {
        found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
                         &conn->tuple);
        found_ct = NULL;

        if (found != NULL)
            found_ct = nf_ct_tuplehash_to_ctrack(found);

        if (found_ct != NULL &&
            nf_ct_tuple_equal(&conn->tuple, tuple) &&
            !already_closed(found_ct))
            /*
             * Just to be sure we have it only once in the list.
             * We should not see tuples twice unless someone hooks
             * this into a table without "-p tcp --syn".
             */
            addit = false;

        if (found == NULL) {
            /* this one is gone */
            hlist_del(&conn->node);
            kfree(conn);
            continue;
        }

        if (already_closed(found_ct)) {
            /*
             * we do not care about connections which are
             * closed already -> ditch it
             */
            nf_ct_put(found_ct);
            hlist_del(&conn->node);
            kfree(conn);
            continue;
        }

        if (same_source_net(addr, mask, &conn->addr, family))
            /* same source network -> be counted! */
            ++matches;
        nf_ct_put(found_ct);
    }

    rcu_read_unlock();

    if (addit) {
        /* save the new connection in our list */
        conn = kmalloc(sizeof(*conn), GFP_ATOMIC);
        if (conn == NULL)
            return -ENOMEM;
        conn->tuple = *tuple;
        conn->addr = *addr;
        hlist_add_head(&conn->node, hash);
        ++matches;
    }

    return matches;
}

static bool
connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
    struct net *net = dev_net(par->in ? par->in : par->out);
    const struct xt_connlimit_info *info = par->matchinfo;
    union nf_inet_addr addr;
    struct nf_conntrack_tuple tuple;
    const struct nf_conntrack_tuple *tuple_ptr = &tuple;
    enum ip_conntrack_info ctinfo;
    const struct nf_conn *ct;
    int connections;

    ct = nf_ct_get(skb, &ctinfo);
    if (ct != NULL)
        tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
    else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
                    par->family, &tuple))
        goto hotdrop;

    if (par->family == NFPROTO_IPV6) {
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
               &iph->daddr : &iph->saddr, sizeof(addr.ip6));
    } else {
        const struct iphdr *iph = ip_hdr(skb);
        addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
              iph->daddr : iph->saddr;
    }

    spin_lock_bh(&info->data->lock);
    connections = count_them(net, info->data, tuple_ptr, &addr,
                             &info->mask, par->family);
    spin_unlock_bh(&info->data->lock);

    if (connections < 0)
        /* kmalloc failed, drop it entirely */
        goto hotdrop;

    return (connections > info->limit) ^
           !!(info->flags & XT_CONNLIMIT_INVERT);

 hotdrop:
    par->hotdrop = true;
    return false;
}

static int connlimit_mt_check(const struct xt_mtchk_param *par)
{
    struct xt_connlimit_info *info = par->matchinfo;
    unsigned int i;
    int ret;

    if (unlikely(!connlimit_rnd)) {
        u_int32_t rand;

        do {
            get_random_bytes(&rand, sizeof(rand));
        } while (!rand);
        cmpxchg(&connlimit_rnd, 0, rand);
    }
    ret = nf_ct_l3proto_try_module_get(par->family);
    if (ret < 0) {
        pr_info("cannot load conntrack support for "
            "address family %u\n", par->family);
        return ret;
    }

    /* init private data */
    info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
    if (info->data == NULL) {
        nf_ct_l3proto_module_put(par->family);
        return -ENOMEM;
    }

    spin_lock_init(&info->data->lock);
    for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
        INIT_HLIST_HEAD(&info->data->iphash[i]);

    return 0;
}

static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
{
    const struct xt_connlimit_info *info = par->matchinfo;
    struct xt_connlimit_conn *conn;
    struct hlist_node *pos, *n;
    struct hlist_head *hash = info->data->iphash;
    unsigned int i;

    nf_ct_l3proto_module_put(par->family);

    for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
        hlist_for_each_entry_safe(conn, pos, n, &hash[i], node) {
            hlist_del(&conn->node);
            kfree(conn);
        }
    }

    kfree(info->data);
}

static struct xt_match connlimit_mt_reg __read_mostly = {
    .name       = "connlimit",
    .revision   = 1,
    .family     = NFPROTO_UNSPEC,
    .checkentry = connlimit_mt_check,
    .match      = connlimit_mt,
    .matchsize  = sizeof(struct xt_connlimit_info),
    .destroy    = connlimit_mt_destroy,
    .me         = THIS_MODULE,
};

static int __init connlimit_mt_init(void)
{
    return xt_register_match(&connlimit_mt_reg);
}

static void __exit connlimit_mt_exit(void)
{
    xt_unregister_match(&connlimit_mt_reg);
}

module_init(connlimit_mt_init);
module_exit(connlimit_mt_exit);
MODULE_AUTHOR("Jan Engelhardt <[email protected]>");
MODULE_DESCRIPTION("Xtables: Number of connections matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_connlimit");
MODULE_ALIAS("ip6t_connlimit");