/*
 * 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/ip.h>
#include <linux/ipv6.h>
#include <linux/module.h>
#include <linux/skbuff.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>
#include <net/netfilter/nf_conntrack_count.h>

static bool
connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
{
        struct net *net = xt_net(par);
        const struct xt_connlimit_info *info = par->matchinfo;
        const struct nf_conntrack_zone *zone = &nf_ct_zone_dflt;
        enum ip_conntrack_info ctinfo;
        const struct nf_conn *ct;
        unsigned int connections;
        u32 key[5];

        ct = nf_ct_get(skb, &ctinfo);
        if (ct)
                zone = nf_ct_zone(ct);

        if (xt_family(par) == NFPROTO_IPV6) {
                const struct ipv6hdr *iph = ipv6_hdr(skb);
                union nf_inet_addr addr;
                unsigned int i;

                memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
                       &iph->daddr : &iph->saddr, sizeof(addr.ip6));

                for (i = 0; i < ARRAY_SIZE(addr.ip6); ++i)
                        addr.ip6[i] &= info->mask.ip6[i];
                memcpy(key, &addr, sizeof(addr.ip6));
                key[4] = zone->id;
        } else {
                const struct iphdr *iph = ip_hdr(skb);

                key[0] = (info->flags & XT_CONNLIMIT_DADDR) ?
                         (__force __u32)iph->daddr : (__force __u32)iph->saddr;
                key[0] &= (__force __u32)info->mask.ip;
                key[1] = zone->id;
        }

        connections = nf_conncount_count_skb(net, skb, xt_family(par), info->data, key);
        if (connections == 0)
                /* kmalloc failed or tuple couldn't be found, 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 keylen;
        int ret;

        keylen = sizeof(u32);
        if (par->family == NFPROTO_IPV6)
                keylen += sizeof(struct in6_addr);
        else
                keylen += sizeof(struct in_addr);

        ret = nf_ct_netns_get(par->net, par->family);
        if (ret < 0) {
                pr_info_ratelimited("cannot load conntrack support for proto=%u\n",
                                    par->family);
                return ret;
        }

        /* init private data */
        info->data = nf_conncount_init(par->net, keylen);
        if (IS_ERR(info->data))
                nf_ct_netns_put(par->net, par->family);

        return PTR_ERR_OR_ZERO(info->data);
}

static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
{
        const struct xt_connlimit_info *info = par->matchinfo;

        nf_conncount_destroy(par->net, info->data);
        nf_ct_netns_put(par->net, par->family);
}

static struct xt_match connlimit_mt_reg[] __read_mostly = {
        {
                .name       = "connlimit",
                .revision   = 1,
                .family     = NFPROTO_IPV4,
                .checkentry = connlimit_mt_check,
                .match      = connlimit_mt,
                .matchsize  = sizeof(struct xt_connlimit_info),
                .usersize   = offsetof(struct xt_connlimit_info, data),
                .destroy    = connlimit_mt_destroy,
                .me         = THIS_MODULE,
        },
#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
        {
                .name       = "connlimit",
                .revision   = 1,
                .family     = NFPROTO_IPV6,
                .checkentry = connlimit_mt_check,
                .match      = connlimit_mt,
                .matchsize  = sizeof(struct xt_connlimit_info),
                .usersize   = offsetof(struct xt_connlimit_info, data),
                .destroy    = connlimit_mt_destroy,
                .me         = THIS_MODULE,
        },
#endif
};

static int __init connlimit_mt_init(void)
{
        return xt_register_matches(connlimit_mt_reg, ARRAY_SIZE(connlimit_mt_reg));
}

static void __exit connlimit_mt_exit(void)
{
        xt_unregister_matches(connlimit_mt_reg, ARRAY_SIZE(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");