xt_TPROXY.c

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/*
 * 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/inet_sock.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 <linux/netfilter_ipv6/ip6_tables.h>
#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
#endif

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

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;
}

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;
}

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;
}

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");