#include <linux/ip.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_TPROXY.h>

struct xt_target * tproxy = NULL;
static unsigned int simple_tproxy(void *priv,
                struct sk_buff *skb,
                const struct nf_hook_state *state)
{
        struct xt_action_param par = {
                .state    = state,
                .targinfo = (struct xt_tproxy_target_info_v1 []) {{
                        /* --tproxy-mask=0/0 */
                        .mark_value = 0,
                        .mark_mask  = 0,
                        /* --on-ip=127.0.0.1 */
                        .laddr      = (union nf_inet_addr) { .ip = INADDR_LOOPBACK },
                        /* --on-port=1234    */
                        .lport      = htons(1234),
                },},
        };

        /* -d 192.0.2.0/24 -p tcp */
        if ((ipv4_is_test_192(ip_hdr(skb)->daddr)
             && ip_hdr(skb)->protocol == IPPROTO_TCP))
                return tproxy->target(skb, &par);

        return NF_ACCEPT;
}

static struct nf_hook_ops tproxy_ops __read_mostly = {
        .hook           = simple_tproxy,
        .pf             = NFPROTO_IPV4,
        .hooknum        = NF_INET_PRE_ROUTING,
        .priority       = (NF_IP_PRI_MANGLE+1), /* after normal mangle matches */
};

static int __init simple_tproxy_init(void)
{
        tproxy = xt_request_find_target(NFPROTO_IPV4, "TPROXY", 1);
        if (tproxy)
                return nf_register_hook(&tproxy_ops);

        return 0;
}

module_init(simple_tproxy_init);