xt_TEE.c

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/*
 *  "TEE" target extension for Xtables
 *  Copyright © Sebastian Claßen, 2007
 *  Jan Engelhardt, 2007-2010
 *
 *  based on ipt_ROUTE.c from Cédric de Launois
 *  <[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 or later, as published by the Free Software Foundation.
 */
#include <linux/ip.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/route.h>
#include <linux/skbuff.h>
#include <linux/notifier.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/ip6_route.h>
#include <net/route.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter/xt_TEE.h>

#if IS_ENABLED(CONFIG_NF_CONNTRACK)
#   define WITH_CONNTRACK 1
#   include <net/netfilter/nf_conntrack.h>
#endif

struct xt_tee_priv {
    struct notifier_block   notifier;
    struct xt_tee_tginfo    *tginfo;
    int         oif;
};

static const union nf_inet_addr tee_zero_address;
static DEFINE_PER_CPU(bool, tee_active);

static struct net *pick_net(struct sk_buff *skb)
{
#ifdef CONFIG_NET_NS
    const struct dst_entry *dst;

    if (skb->dev != NULL)
        return dev_net(skb->dev);
    dst = skb_dst(skb);
    if (dst != NULL && dst->dev != NULL)
        return dev_net(dst->dev);
#endif
    return &init_net;
}

static bool
tee_tg_route4(struct sk_buff *skb, const struct xt_tee_tginfo *info)
{
    const struct iphdr *iph = ip_hdr(skb);
    struct net *net = pick_net(skb);
    struct rtable *rt;
    struct flowi4 fl4;

    memset(&fl4, 0, sizeof(fl4));
    if (info->priv) {
        if (info->priv->oif == -1)
            return false;
        fl4.flowi4_oif = info->priv->oif;
    }
    fl4.daddr = info->gw.ip;
    fl4.flowi4_tos = RT_TOS(iph->tos);
    fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
    fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
    rt = ip_route_output_key(net, &fl4);
    if (IS_ERR(rt))
        return false;

    skb_dst_drop(skb);
    skb_dst_set(skb, &rt->dst);
    skb->dev      = rt->dst.dev;
    skb->protocol = htons(ETH_P_IP);
    return true;
}

static unsigned int
tee_tg4(struct sk_buff *skb, const struct xt_action_param *par)
{
    const struct xt_tee_tginfo *info = par->targinfo;
    struct iphdr *iph;

    if (__this_cpu_read(tee_active))
        return XT_CONTINUE;
    /*
     * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
     * the original skb, which should continue on its way as if nothing has
     * happened. The copy should be independently delivered to the TEE
     * --gateway.
     */
    skb = pskb_copy(skb, GFP_ATOMIC);
    if (skb == NULL)
        return XT_CONTINUE;

#ifdef WITH_CONNTRACK
    /* Avoid counting cloned packets towards the original connection. */
    nf_conntrack_put(skb->nfct);
    skb->nfct     = &nf_ct_untracked_get()->ct_general;
    skb->nfctinfo = IP_CT_NEW;
    nf_conntrack_get(skb->nfct);
#endif
    /*
     * If we are in PREROUTING/INPUT, the checksum must be recalculated
     * since the length could have changed as a result of defragmentation.
     *
     * We also decrease the TTL to mitigate potential TEE loops
     * between two hosts.
     *
     * Set %IP_DF so that the original source is notified of a potentially
     * decreased MTU on the clone route. IPv6 does this too.
     */
    iph = ip_hdr(skb);
    iph->frag_off |= htons(IP_DF);
    if (par->hooknum == NF_INET_PRE_ROUTING ||
        par->hooknum == NF_INET_LOCAL_IN)
        --iph->ttl;
    ip_send_check(iph);

    if (tee_tg_route4(skb, info)) {
        __this_cpu_write(tee_active, true);
        ip_local_out(skb);
        __this_cpu_write(tee_active, false);
    } else {
        kfree_skb(skb);
    }
    return XT_CONTINUE;
}

#if IS_ENABLED(CONFIG_IPV6)
static bool
tee_tg_route6(struct sk_buff *skb, const struct xt_tee_tginfo *info)
{
    const struct ipv6hdr *iph = ipv6_hdr(skb);
    struct net *net = pick_net(skb);
    struct dst_entry *dst;
    struct flowi6 fl6;

    memset(&fl6, 0, sizeof(fl6));
    if (info->priv) {
        if (info->priv->oif == -1)
            return false;
        fl6.flowi6_oif = info->priv->oif;
    }
    fl6.daddr = info->gw.in6;
    fl6.flowlabel = ((iph->flow_lbl[0] & 0xF) << 16) |
               (iph->flow_lbl[1] << 8) | iph->flow_lbl[2];
    dst = ip6_route_output(net, NULL, &fl6);
    if (dst->error) {
        dst_release(dst);
        return false;
    }
    skb_dst_drop(skb);
    skb_dst_set(skb, dst);
    skb->dev      = dst->dev;
    skb->protocol = htons(ETH_P_IPV6);
    return true;
}

static unsigned int
tee_tg6(struct sk_buff *skb, const struct xt_action_param *par)
{
    const struct xt_tee_tginfo *info = par->targinfo;

    if (__this_cpu_read(tee_active))
        return XT_CONTINUE;
    skb = pskb_copy(skb, GFP_ATOMIC);
    if (skb == NULL)
        return XT_CONTINUE;

#ifdef WITH_CONNTRACK
    nf_conntrack_put(skb->nfct);
    skb->nfct     = &nf_ct_untracked_get()->ct_general;
    skb->nfctinfo = IP_CT_NEW;
    nf_conntrack_get(skb->nfct);
#endif
    if (par->hooknum == NF_INET_PRE_ROUTING ||
        par->hooknum == NF_INET_LOCAL_IN) {
        struct ipv6hdr *iph = ipv6_hdr(skb);
        --iph->hop_limit;
    }
    if (tee_tg_route6(skb, info)) {
        __this_cpu_write(tee_active, true);
        ip6_local_out(skb);
        __this_cpu_write(tee_active, false);
    } else {
        kfree_skb(skb);
    }
    return XT_CONTINUE;
}
#endif

static int tee_netdev_event(struct notifier_block *this, unsigned long event,
                void *ptr)
{
    struct net_device *dev = ptr;
    struct xt_tee_priv *priv;

    priv = container_of(this, struct xt_tee_priv, notifier);
    switch (event) {
    case NETDEV_REGISTER:
        if (!strcmp(dev->name, priv->tginfo->oif))
            priv->oif = dev->ifindex;
        break;
    case NETDEV_UNREGISTER:
        if (dev->ifindex == priv->oif)
            priv->oif = -1;
        break;
    case NETDEV_CHANGENAME:
        if (!strcmp(dev->name, priv->tginfo->oif))
            priv->oif = dev->ifindex;
        else if (dev->ifindex == priv->oif)
            priv->oif = -1;
        break;
    }

    return NOTIFY_DONE;
}

static int tee_tg_check(const struct xt_tgchk_param *par)
{
    struct xt_tee_tginfo *info = par->targinfo;
    struct xt_tee_priv *priv;

    /* 0.0.0.0 and :: not allowed */
    if (memcmp(&info->gw, &tee_zero_address,
           sizeof(tee_zero_address)) == 0)
        return -EINVAL;

    if (info->oif[0]) {
        if (info->oif[sizeof(info->oif)-1] != '\0')
            return -EINVAL;

        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (priv == NULL)
            return -ENOMEM;

        priv->tginfo  = info;
        priv->oif     = -1;
        priv->notifier.notifier_call = tee_netdev_event;
        info->priv    = priv;

        register_netdevice_notifier(&priv->notifier);
    } else
        info->priv = NULL;

    return 0;
}

static void tee_tg_destroy(const struct xt_tgdtor_param *par)
{
    struct xt_tee_tginfo *info = par->targinfo;

    if (info->priv) {
        unregister_netdevice_notifier(&info->priv->notifier);
        kfree(info->priv);
    }
}

static struct xt_target tee_tg_reg[] __read_mostly = {
    {
        .name       = "TEE",
        .revision   = 1,
        .family     = NFPROTO_IPV4,
        .target     = tee_tg4,
        .targetsize = sizeof(struct xt_tee_tginfo),
        .checkentry = tee_tg_check,
        .destroy    = tee_tg_destroy,
        .me         = THIS_MODULE,
    },
#if IS_ENABLED(CONFIG_IPV6)
    {
        .name       = "TEE",
        .revision   = 1,
        .family     = NFPROTO_IPV6,
        .target     = tee_tg6,
        .targetsize = sizeof(struct xt_tee_tginfo),
        .checkentry = tee_tg_check,
        .destroy    = tee_tg_destroy,
        .me         = THIS_MODULE,
    },
#endif
};

static int __init tee_tg_init(void)
{
    return xt_register_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
}

static void __exit tee_tg_exit(void)
{
    xt_unregister_targets(tee_tg_reg, ARRAY_SIZE(tee_tg_reg));
}

module_init(tee_tg_init);
module_exit(tee_tg_exit);
MODULE_AUTHOR("Sebastian Claßen <[email protected]>");
MODULE_AUTHOR("Jan Engelhardt <[email protected]>");
MODULE_DESCRIPTION("Xtables: Reroute packet copy");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_TEE");
MODULE_ALIAS("ip6t_TEE");