/*
 * Transparent proxy support for Linux/iptables
 *
 * Copyright (c) 2006-2010 BalaBit IT Ltd.
 * Author: Balazs Scheidler, Krisztian Kovacs
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 */
#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 <linux/netfilter/xt_TPROXY.h>

enum nf_tproxy_lookup_t {
         NFT_LOOKUP_LISTENER,
         NFT_LOOKUP_ESTABLISHED,
};

static bool tproxy_sk_is_transparent(struct sock *sk)
{
        if (sk->sk_state != TCP_TIME_WAIT) {
                if (inet_sk(sk)->transparent)
                        return true;
                sock_put(sk);
        } else {
                if (inet_twsk(sk)->tw_transparent)
                        return true;
                inet_twsk_put(inet_twsk(sk));
        }
        return false;
}

static inline __be32
tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
{
        struct in_device *indev;
        __be32 laddr;

        if (user_laddr)
                return user_laddr;

        laddr = 0;
        rcu_read_lock();
        indev = __in_dev_get_rcu(skb->dev);
        for_primary_ifa(indev) {
                laddr = ifa->ifa_local;
                break;
        } endfor_ifa(indev);
        rcu_read_unlock();

        return laddr ? laddr : daddr;
}

/*
 * This is used when the user wants to intercept a connection matching
 * an explicit iptables rule. In this case the sockets are assumed
 * matching in preference order:
 *
 *   - match: if there's a fully established connection matching the
 *     _packet_ tuple, it is returned, assuming the redirection
 *     already took place and we process a packet belonging to an
 *     established connection
 *
 *   - match: if there's a listening socket matching the redirection
 *     (e.g. on-port & on-ip of the connection), it is returned,
 *     regardless if it was bound to 0.0.0.0 or an explicit
 *     address. The reasoning is that if there's an explicit rule, it
 *     does not really matter if the listener is bound to an interface
 *     or to 0. The user already stated that he wants redirection
 *     (since he added the rule).
 *
 * Please note that there's an overlap between what a TPROXY target
 * and a socket match will match. Normally if you have both rules the
 * "socket" match will be the first one, effectively all packets
 * belonging to established connections going through that one.
 */
static inline struct sock *
nf_tproxy_get_sock_v4(struct net *net, const u8 protocol,
                      const __be32 saddr, const __be32 daddr,
                      const __be16 sport, const __be16 dport,
                      const struct net_device *in,
                      const enum nf_tproxy_lookup_t lookup_type)
{
        struct sock *sk;

        switch (protocol) {
        case IPPROTO_TCP:
                switch (lookup_type) {
                case NFT_LOOKUP_LISTENER:
                        sk = inet_lookup_listener(net, &tcp_hashinfo,
                                                    saddr, sport,
                                                    daddr, dport,
                                                    in->ifindex);

                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        break;
                case NFT_LOOKUP_ESTABLISHED:
                        sk = inet_lookup_established(net, &tcp_hashinfo,
                                                    saddr, sport, daddr, dport,
                                                    in->ifindex);
                        break;
                default:
                        BUG();
                }
                break;
        case IPPROTO_UDP:
                sk = udp4_lib_lookup(net, saddr, sport, daddr, dport,
                                     in->ifindex);
                if (sk) {
                        int connected = (sk->sk_state == TCP_ESTABLISHED);
                        int wildcard = (inet_sk(sk)->inet_rcv_saddr == 0);

                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        if ((lookup_type == NFT_LOOKUP_ESTABLISHED && (!connected || wildcard)) ||
                            (lookup_type == NFT_LOOKUP_LISTENER && connected)) {
                                sock_put(sk);
                                sk = NULL;
                        }
                }
                break;
        default:
                WARN_ON(1);
                sk = NULL;
        }

        pr_debug("tproxy socket lookup: proto %u %08x:%u -> %08x:%u, lookup type: %d, sock %p\n",
                 protocol, ntohl(saddr), ntohs(sport), ntohl(daddr), ntohs(dport), lookup_type, sk);

        return sk;
}

#ifdef XT_TPROXY_HAVE_IPV6
static inline struct sock *
nf_tproxy_get_sock_v6(struct net *net, const u8 protocol,
                      const struct in6_addr *saddr, const struct in6_addr *daddr,
                      const __be16 sport, const __be16 dport,
                      const struct net_device *in,
                      const enum nf_tproxy_lookup_t lookup_type)
{
        struct sock *sk;

        switch (protocol) {
        case IPPROTO_TCP:
                switch (lookup_type) {
                case NFT_LOOKUP_LISTENER:
                        sk = inet6_lookup_listener(net, &tcp_hashinfo,
                                                   saddr, sport,
                                                   daddr, ntohs(dport),
                                                   in->ifindex);

                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        break;
                case NFT_LOOKUP_ESTABLISHED:
                        sk = __inet6_lookup_established(net, &tcp_hashinfo,
                                                        saddr, sport, daddr, ntohs(dport),
                                                        in->ifindex);
                        break;
                default:
                        BUG();
                }
                break;
        case IPPROTO_UDP:
                sk = udp6_lib_lookup(net, saddr, sport, daddr, dport,
                                     in->ifindex);
                if (sk) {
                        int connected = (sk->sk_state == TCP_ESTABLISHED);
                        int wildcard = ipv6_addr_any(&inet6_sk(sk)->rcv_saddr);

                        /* NOTE: we return listeners even if bound to
                         * 0.0.0.0, those are filtered out in
                         * xt_socket, since xt_TPROXY needs 0 bound
                         * listeners too
                         */
                        if ((lookup_type == NFT_LOOKUP_ESTABLISHED && (!connected || wildcard)) ||
                            (lookup_type == NFT_LOOKUP_LISTENER && connected)) {
                                sock_put(sk);
                                sk = NULL;
                        }
                }
                break;
        default:
                WARN_ON(1);
                sk = NULL;
        }

        pr_debug("tproxy socket lookup: proto %u %pI6:%u -> %pI6:%u, lookup type: %d, sock %p\n",
                 protocol, saddr, ntohs(sport), daddr, ntohs(dport), lookup_type, sk);

        return sk;
}
#endif

/**
 * tproxy_handle_time_wait4 - handle IPv4 TCP TIME_WAIT reopen redirections
 * @skb:        The skb being processed.
 * @laddr:      IPv4 address to redirect to or zero.
 * @lport:      TCP port to redirect to or zero.
 * @sk:         The TIME_WAIT TCP socket found by the lookup.
 *
 * We have to handle SYN packets arriving to TIME_WAIT sockets
 * differently: instead of reopening the connection we should rather
 * redirect the new connection to the proxy if there's a listener
 * socket present.
 *
 * tproxy_handle_time_wait4() consumes the socket reference passed in.
 *
 * Returns the listener socket if there's one, the TIME_WAIT socket if
 * no such listener is found, or NULL if the TCP header is incomplete.
 */
static struct sock *
tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport,
                        struct sock *sk)
{
        const struct iphdr *iph = ip_hdr(skb);
        struct tcphdr _hdr, *hp;

        hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
        if (hp == NULL) {
                inet_twsk_put(inet_twsk(sk));
                return NULL;
        }

        if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
                /* SYN to a TIME_WAIT socket, we'd rather redirect it
                 * to a listener socket if there's one */
                struct sock *sk2;

                sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
                                            iph->saddr, laddr ? laddr : iph->daddr,
                                            hp->source, lport ? lport : hp->dest,
                                            skb->dev, NFT_LOOKUP_LISTENER);
                if (sk2) {
                        inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
                        inet_twsk_put(inet_twsk(sk));
                        sk = sk2;
                }
        }

        return sk;
}

/* assign a socket to the skb -- consumes sk */
static void
nf_tproxy_assign_sock(struct sk_buff *skb, struct sock *sk)
{
        skb_orphan(skb);
        skb->sk = sk;
        skb->destructor = sock_edemux;
}

static unsigned int
tproxy_tg4(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(dev_net(skb->dev), iph->protocol,
                                   iph->saddr, iph->daddr,
                                   hp->source, hp->dest,
                                   skb->dev, NFT_LOOKUP_ESTABLISHED);

        laddr = 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 = tproxy_handle_time_wait4(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(dev_net(skb->dev), iph->protocol,
                                           iph->saddr, laddr,
                                           hp->source, lport,
                                           skb->dev, NFT_LOOKUP_LISTENER);

        /* NOTE: assign_sock consumes our sk reference */
        if (sk && 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;

                pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
                         iph->protocol, &iph->daddr, ntohs(hp->dest),
                         &laddr, ntohs(lport), skb->mark);

                nf_tproxy_assign_sock(skb, sk);
                return NF_ACCEPT;
        }

        pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
                 iph->protocol, &iph->saddr, ntohs(hp->source),
                 &iph->daddr, ntohs(hp->dest), skb->mark);
        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(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(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value);
}

#ifdef XT_TPROXY_HAVE_IPV6

static inline const struct in6_addr *
tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr,
              const struct in6_addr *daddr)
{
        struct inet6_dev *indev;
        struct inet6_ifaddr *ifa;
        struct in6_addr *laddr;

        if (!ipv6_addr_any(user_laddr))
                return user_laddr;
        laddr = NULL;

        rcu_read_lock();
        indev = __in6_dev_get(skb->dev);
        if (indev)
                list_for_each_entry(ifa, &indev->addr_list, if_list) {
                        if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED))
                                continue;

                        laddr = &ifa->addr;
                        break;
                }
        rcu_read_unlock();

        return laddr ? laddr : daddr;
}

/**
 * tproxy_handle_time_wait6 - handle IPv6 TCP TIME_WAIT reopen redirections
 * @skb:        The skb being processed.
 * @tproto:     Transport protocol.
 * @thoff:      Transport protocol header offset.
 * @par:        Iptables target parameters.
 * @sk:         The TIME_WAIT TCP socket found by the lookup.
 *
 * We have to handle SYN packets arriving to TIME_WAIT sockets
 * differently: instead of reopening the connection we should rather
 * redirect the new connection to the proxy if there's a listener
 * socket present.
 *
 * tproxy_handle_time_wait6() consumes the socket reference passed in.
 *
 * Returns the listener socket if there's one, the TIME_WAIT socket if
 * no such listener is found, or NULL if the TCP header is incomplete.
 */
static struct sock *
tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
                         const struct xt_action_param *par,
                         struct sock *sk)
{
        const struct ipv6hdr *iph = ipv6_hdr(skb);
        struct tcphdr _hdr, *hp;
        const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

        hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
        if (hp == NULL) {
                inet_twsk_put(inet_twsk(sk));
                return NULL;
        }

        if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
                /* SYN to a TIME_WAIT socket, we'd rather redirect it
                 * to a listener socket if there's one */
                struct sock *sk2;

                sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
                                            &iph->saddr,
                                            tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr),
                                            hp->source,
                                            tgi->lport ? tgi->lport : hp->dest,
                                            skb->dev, NFT_LOOKUP_LISTENER);
                if (sk2) {
                        inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
                        inet_twsk_put(inet_twsk(sk));
                        sk = sk2;
                }
        }

        return sk;
}

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) {
                pr_debug("unable to find transport header in IPv6 packet, dropping\n");
                return NF_DROP;
        }

        hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
        if (hp == NULL) {
                pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
                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(dev_net(skb->dev), tproto,
                                   &iph->saddr, &iph->daddr,
                                   hp->source, hp->dest,
                                   par->in, NFT_LOOKUP_ESTABLISHED);

        laddr = 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)
                /* reopening a TIME_WAIT connection needs special handling */
                sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, 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(dev_net(skb->dev), tproto,
                                           &iph->saddr, laddr,
                                           hp->source, lport,
                                           par->in, NFT_LOOKUP_LISTENER);

        /* NOTE: assign_sock consumes our sk reference */
        if (sk && 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;

                pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
                         tproto, &iph->saddr, ntohs(hp->source),
                         laddr, ntohs(lport), skb->mark);

                nf_tproxy_assign_sock(skb, sk);
                return NF_ACCEPT;
        }

        pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
                 tproto, &iph->saddr, ntohs(hp->source),
                 &iph->daddr, ntohs(hp->dest), skb->mark);

        return NF_DROP;
}

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

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

        pr_info("Can be used only in combination with "
                "either -p tcp or -p udp\n");
        return -EINVAL;
}
#endif

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

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

        pr_info("Can be used only in combination with "
                "either -p tcp or -p udp\n");
        return -EINVAL;
}

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,
                .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,
                .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,
                .hooks          = 1 << NF_INET_PRE_ROUTING,
                .me             = THIS_MODULE,
        },
#endif

};

static int __init tproxy_tg_init(void)
{
        nf_defrag_ipv4_enable();
#ifdef XT_TPROXY_HAVE_IPV6
        nf_defrag_ipv6_enable();
#endif

        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");