/*
   *	"TEE" target extension for Xtables
   *	Copyright © Sebastian Claßen, 2007
   *	Jan Engelhardt, 2007-2010
   *
   *	based on ipt_ROUTE.c from Cédric de Launois
   *	<delaunois@info.ucl.be>
   *
   *	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 = netdev_notifier_info_to_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 <sebastian.classen@freenet.ag>");
  MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
  MODULE_DESCRIPTION("Xtables: Reroute packet copy");
  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ipt_TEE");
  MODULE_ALIAS("ip6t_TEE");