// SPDX-License-Identifier: GPL-2.0-only
/*
 * Transparent proxy support for Linux/iptables
 *
 * Copyright (c) 2006-2010 BalaBit IT Ltd.
 * Author: Balazs Scheidler, Krisztian Kovacs
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <net/tcp.h>
#include <net/inet_sock.h>
#include <net/inet_hashtables.h>
#include <linux/inetdevice.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>

#include <net/netfilter/ipv4/nf_defrag_ipv4.h>

#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
#define XT_TPROXY_HAVE_IPV6 1
#include <net/if_inet6.h>
#include <net/addrconf.h>
#include <net/inet6_hashtables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
#endif

#include <net/netfilter/nf_tproxy.h>
#include <linux/netfilter/xt_TPROXY.h>

static unsigned int
tproxy_tg4(struct net *net, struct sk_buff *skb, __be32 laddr, __be16 lport,
           u_int32_t mark_mask, u_int32_t mark_value)
{
        const struct iphdr *iph = ip_hdr(skb);
        struct udphdr _hdr, *hp;
        struct sock *sk;

        hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
        if (hp == NULL)
                return NF_DROP;

        /* check if there's an ongoing connection on the packet
         * addresses, this happens if the redirect already happened
         * and the current packet belongs to an already established
         * connection */
        sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
                                   iph->saddr, iph->daddr,
                                   hp->source, hp->dest,
                                   skb->dev, NF_TPROXY_LOOKUP_ESTABLISHED);

        laddr = nf_tproxy_laddr4(skb, laddr, iph->daddr);
        if (!lport)
                lport = hp->dest;

        /* UDP has no TCP_TIME_WAIT state, so we never enter here */
        if (sk && sk->sk_state == TCP_TIME_WAIT)
                /* reopening a TIME_WAIT connection needs special handling */
                sk = nf_tproxy_handle_time_wait4(net, skb, laddr, lport, sk);
        else if (!sk)
                /* no, there's no established connection, check if
                 * there's a listener on the redirected addr/port */
                sk = nf_tproxy_get_sock_v4(net, skb, iph->protocol,
                                           iph->saddr, laddr,
                                           hp->source, lport,
                                           skb->dev, NF_TPROXY_LOOKUP_LISTENER);

        /* NOTE: assign_sock consumes our sk reference */
        if (sk && nf_tproxy_sk_is_transparent(sk)) {
                /* This should be in a separate target, but we don't do multiple
                   targets on the same rule yet */
                skb->mark = (skb->mark & ~mark_mask) ^ mark_value;
                nf_tproxy_assign_sock(skb, sk);
                return NF_ACCEPT;
        }

        return NF_DROP;
}

static unsigned int
tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
{
        const struct xt_tproxy_target_info *tgi = par->targinfo;

        return tproxy_tg4(xt_net(par), skb, tgi->laddr, tgi->lport,
                          tgi->mark_mask, tgi->mark_value);
}

static unsigned int
tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
{
        const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

        return tproxy_tg4(xt_net(par), skb, tgi->laddr.ip, tgi->lport,
                          tgi->mark_mask, tgi->mark_value);
}

#ifdef XT_TPROXY_HAVE_IPV6

static unsigned int
tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
{
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
        struct udphdr _hdr, *hp;
        struct sock *sk;
        const struct in6_addr *laddr;
        __be16 lport;
        int thoff = 0;
        int tproto;

        tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
        if (tproto < 0)
                return NF_DROP;

        hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
        if (!hp)
                return NF_DROP;

        /* check if there's an ongoing connection on the packet
         * addresses, this happens if the redirect already happened
         * and the current packet belongs to an already established
         * connection */
        sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff, tproto,
                                   &iph->saddr, &iph->daddr,
                                   hp->source, hp->dest,
                                   xt_in(par), NF_TPROXY_LOOKUP_ESTABLISHED);

        laddr = nf_tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
        lport = tgi->lport ? tgi->lport : hp->dest;

        /* UDP has no TCP_TIME_WAIT state, so we never enter here */
        if (sk && sk->sk_state == TCP_TIME_WAIT) {
                const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
                /* reopening a TIME_WAIT connection needs special handling */
                sk = nf_tproxy_handle_time_wait6(skb, tproto, thoff,
                                              xt_net(par),
                                              &tgi->laddr.in6,
                                              tgi->lport,
                                              sk);
        }
        else if (!sk)
                /* no there's no established connection, check if
                 * there's a listener on the redirected addr/port */
                sk = nf_tproxy_get_sock_v6(xt_net(par), skb, thoff,
                                           tproto, &iph->saddr, laddr,
                                           hp->source, lport,
                                           xt_in(par), NF_TPROXY_LOOKUP_LISTENER);

        /* NOTE: assign_sock consumes our sk reference */
        if (sk && nf_tproxy_sk_is_transparent(sk)) {
                /* This should be in a separate target, but we don't do multiple
                   targets on the same rule yet */
                skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
                nf_tproxy_assign_sock(skb, sk);
                return NF_ACCEPT;
        }

        return NF_DROP;
}

static int tproxy_tg6_check(const struct xt_tgchk_param *par)
{
        const struct ip6t_ip6 *i = par->entryinfo;
        int err;

        err = nf_defrag_ipv6_enable(par->net);
        if (err)
                return err;

        if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP) &&
            !(i->invflags & IP6T_INV_PROTO))
                return 0;

        pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
        return -EINVAL;
}

static void tproxy_tg6_destroy(const struct xt_tgdtor_param *par)
{
        nf_defrag_ipv6_disable(par->net);
}
#endif

static int tproxy_tg4_check(const struct xt_tgchk_param *par)
{
        const struct ipt_ip *i = par->entryinfo;
        int err;

        err = nf_defrag_ipv4_enable(par->net);
        if (err)
                return err;

        if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
            && !(i->invflags & IPT_INV_PROTO))
                return 0;

        pr_info_ratelimited("Can be used only with -p tcp or -p udp\n");
        return -EINVAL;
}

static void tproxy_tg4_destroy(const struct xt_tgdtor_param *par)
{
        nf_defrag_ipv4_disable(par->net);
}

static struct xt_target tproxy_tg_reg[] __read_mostly = {
        {
                .name           = "TPROXY",
                .family         = NFPROTO_IPV4,
                .table          = "mangle",
                .target         = tproxy_tg4_v0,
                .revision       = 0,
                .targetsize     = sizeof(struct xt_tproxy_target_info),
                .checkentry     = tproxy_tg4_check,
                .destroy        = tproxy_tg4_destroy,
                .hooks          = 1 << NF_INET_PRE_ROUTING,
                .me             = THIS_MODULE,
        },
        {
                .name           = "TPROXY",
                .family         = NFPROTO_IPV4,
                .table          = "mangle",
                .target         = tproxy_tg4_v1,
                .revision       = 1,
                .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
                .checkentry     = tproxy_tg4_check,
                .destroy        = tproxy_tg4_destroy,
                .hooks          = 1 << NF_INET_PRE_ROUTING,
                .me             = THIS_MODULE,
        },
#ifdef XT_TPROXY_HAVE_IPV6
        {
                .name           = "TPROXY",
                .family         = NFPROTO_IPV6,
                .table          = "mangle",
                .target         = tproxy_tg6_v1,
                .revision       = 1,
                .targetsize     = sizeof(struct xt_tproxy_target_info_v1),
                .checkentry     = tproxy_tg6_check,
                .destroy        = tproxy_tg6_destroy,
                .hooks          = 1 << NF_INET_PRE_ROUTING,
                .me             = THIS_MODULE,
        },
#endif

};

static int __init tproxy_tg_init(void)
{
        return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
}

static void __exit tproxy_tg_exit(void)
{
        xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
}

module_init(tproxy_tg_init);
module_exit(tproxy_tg_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
MODULE_ALIAS("ipt_TPROXY");
MODULE_ALIAS("ip6t_TPROXY");