/*
 * netfilter module to limit the number of parallel tcp
 * connections per IP address.
 *   (c) 2000 Gerd Knorr <kraxel@bytesex.org>
 *   Nov 2002: Martin Bene <martin.bene@icomedias.com>:
 *              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 (rusty@rustcorp.com.au).
 */
#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 list_head list;
        struct nf_conntrack_tuple tuple;
};

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

static u_int32_t connlimit_rnd __read_mostly;
static bool connlimit_rnd_inited __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 xt_connlimit_conn *tmp;
        struct nf_conn *found_ct;
        struct list_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 */
        list_for_each_entry_safe(conn, tmp, hash, list) {
                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 */
                        list_del(&conn->list);
                        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);
                        list_del(&conn->list);
                        kfree(conn);
                        continue;
                }

                if (same_source_net(addr, mask, &conn->tuple.src.u3, 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 = kzalloc(sizeof(*conn), GFP_ATOMIC);
                if (conn == NULL)
                        return -ENOMEM;
                conn->tuple = *tuple;
                list_add(&conn->list, 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[0].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, &iph->saddr, sizeof(iph->saddr));
        } else {
                const struct iphdr *iph = ip_hdr(skb);
                addr.ip = 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 */
                par->hotdrop = true;
                return false;
        }

        return (connections > info->limit) ^ info->inverse;

 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_inited)) {
                get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
                connlimit_rnd_inited = true;
        }
        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_LIST_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 xt_connlimit_conn *tmp;
        struct list_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) {
                list_for_each_entry_safe(conn, tmp, &hash[i], list) {
                        list_del(&conn->list);
                        kfree(conn);
                }
        }

        kfree(info->data);
}

static struct xt_match connlimit_mt_reg __read_mostly = {
        .name       = "connlimit",
        .revision   = 0,
        .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 <jengelh@medozas.de>");
MODULE_DESCRIPTION("Xtables: Number of connections matching");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_connlimit");
MODULE_ALIAS("ip6t_connlimit");