xt_REDIRECT.c

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/*
 * (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 * Copyright (c) 2011 Patrick McHardy <[email protected]>
 *
 * 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.
 *
 * Based on Rusty Russell's IPv4 REDIRECT target. Development of IPv6
 * NAT funded by Astaro.
 */

#include <linux/if.h>
#include <linux/inetdevice.h>
#include <linux/ip.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/netfilter.h>
#include <linux/types.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv6.h>
#include <linux/netfilter/x_tables.h>
#include <net/addrconf.h>
#include <net/checksum.h>
#include <net/protocol.h>
#include <net/netfilter/nf_nat.h>

static const struct in6_addr loopback_addr = IN6ADDR_LOOPBACK_INIT;

static unsigned int
redirect_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
    const struct nf_nat_range *range = par->targinfo;
    struct nf_nat_range newrange;
    struct in6_addr newdst;
    enum ip_conntrack_info ctinfo;
    struct nf_conn *ct;

    ct = nf_ct_get(skb, &ctinfo);
    if (par->hooknum == NF_INET_LOCAL_OUT)
        newdst = loopback_addr;
    else {
        struct inet6_dev *idev;
        struct inet6_ifaddr *ifa;
        bool addr = false;

        rcu_read_lock();
        idev = __in6_dev_get(skb->dev);
        if (idev != NULL) {
            list_for_each_entry(ifa, &idev->addr_list, if_list) {
                newdst = ifa->addr;
                addr = true;
                break;
            }
        }
        rcu_read_unlock();

        if (!addr)
            return NF_DROP;
    }

    newrange.flags      = range->flags | NF_NAT_RANGE_MAP_IPS;
    newrange.min_addr.in6   = newdst;
    newrange.max_addr.in6   = newdst;
    newrange.min_proto  = range->min_proto;
    newrange.max_proto  = range->max_proto;

    return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_DST);
}

static int redirect_tg6_checkentry(const struct xt_tgchk_param *par)
{
    const struct nf_nat_range *range = par->targinfo;

    if (range->flags & NF_NAT_RANGE_MAP_IPS)
        return -EINVAL;
    return 0;
}

/* FIXME: Take multiple ranges --RR */
static int redirect_tg4_check(const struct xt_tgchk_param *par)
{
    const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;

    if (mr->range[0].flags & NF_NAT_RANGE_MAP_IPS) {
        pr_debug("bad MAP_IPS.\n");
        return -EINVAL;
    }
    if (mr->rangesize != 1) {
        pr_debug("bad rangesize %u.\n", mr->rangesize);
        return -EINVAL;
    }
    return 0;
}

static unsigned int
redirect_tg4(struct sk_buff *skb, const struct xt_action_param *par)
{
    struct nf_conn *ct;
    enum ip_conntrack_info ctinfo;
    __be32 newdst;
    const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;
    struct nf_nat_range newrange;

    NF_CT_ASSERT(par->hooknum == NF_INET_PRE_ROUTING ||
             par->hooknum == NF_INET_LOCAL_OUT);

    ct = nf_ct_get(skb, &ctinfo);
    NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED));

    /* Local packets: make them go to loopback */
    if (par->hooknum == NF_INET_LOCAL_OUT)
        newdst = htonl(0x7F000001);
    else {
        struct in_device *indev;
        struct in_ifaddr *ifa;

        newdst = 0;

        rcu_read_lock();
        indev = __in_dev_get_rcu(skb->dev);
        if (indev && (ifa = indev->ifa_list))
            newdst = ifa->ifa_local;
        rcu_read_unlock();

        if (!newdst)
            return NF_DROP;
    }

    /* Transfer from original range. */
    memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
    memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
    newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
    newrange.min_addr.ip = newdst;
    newrange.max_addr.ip = newdst;
    newrange.min_proto   = mr->range[0].min;
    newrange.max_proto   = mr->range[0].max;

    /* Hand modified range to generic setup. */
    return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_DST);
}

static struct xt_target redirect_tg_reg[] __read_mostly = {
    {
        .name       = "REDIRECT",
        .family     = NFPROTO_IPV6,
        .revision   = 0,
        .table      = "nat",
        .checkentry = redirect_tg6_checkentry,
        .target     = redirect_tg6,
        .targetsize = sizeof(struct nf_nat_range),
        .hooks      = (1 << NF_INET_PRE_ROUTING) |
                      (1 << NF_INET_LOCAL_OUT),
        .me         = THIS_MODULE,
    },
    {
        .name       = "REDIRECT",
        .family     = NFPROTO_IPV4,
        .revision   = 0,
        .table      = "nat",
        .target     = redirect_tg4,
        .checkentry = redirect_tg4_check,
        .targetsize = sizeof(struct nf_nat_ipv4_multi_range_compat),
        .hooks      = (1 << NF_INET_PRE_ROUTING) |
                      (1 << NF_INET_LOCAL_OUT),
        .me         = THIS_MODULE,
    },
};

static int __init redirect_tg_init(void)
{
    return xt_register_targets(redirect_tg_reg,
                   ARRAY_SIZE(redirect_tg_reg));
}

static void __exit redirect_tg_exit(void)
{
    xt_unregister_targets(redirect_tg_reg, ARRAY_SIZE(redirect_tg_reg));
}

module_init(redirect_tg_init);
module_exit(redirect_tg_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Patrick McHardy <[email protected]>");
MODULE_DESCRIPTION("Xtables: Connection redirection to localhost");
MODULE_ALIAS("ip6t_REDIRECT");
MODULE_ALIAS("ipt_REDIRECT");