/*
   * Copyright (c) 2015 Pablo Neira Ayuso <pablo@netfilter.org>
   *
   * 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.
   */
  
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/netlink.h>
  #include <linux/netfilter.h>
  #include <linux/netfilter/nf_tables.h>

  #include <linux/ip.h>
  #include <linux/ipv6.h>

  #include <net/netfilter/nf_tables.h>
  #include <net/netfilter/nf_dup_netdev.h>

  #include <net/neighbour.h>
  #include <net/ip.h>

  
  struct nft_fwd_netdev {
  	enum nft_registers	sreg_dev:8;
  };
  
  static void nft_fwd_netdev_eval(const struct nft_expr *expr,
  				struct nft_regs *regs,
  				const struct nft_pktinfo *pkt)
  {
  	struct nft_fwd_netdev *priv = nft_expr_priv(expr);
  	int oif = regs->data[priv->sreg_dev];

  	nf_fwd_netdev_egress(pkt, oif);
  	regs->verdict.code = NF_STOLEN;

  }
  
  static const struct nla_policy nft_fwd_netdev_policy[NFTA_FWD_MAX + 1] = {
  	[NFTA_FWD_SREG_DEV]	= { .type = NLA_U32 },

  	[NFTA_FWD_SREG_ADDR]	= { .type = NLA_U32 },
  	[NFTA_FWD_NFPROTO]	= { .type = NLA_U32 },

  };
  
  static int nft_fwd_netdev_init(const struct nft_ctx *ctx,
  			       const struct nft_expr *expr,
  			       const struct nlattr * const tb[])
  {
  	struct nft_fwd_netdev *priv = nft_expr_priv(expr);
  
  	if (tb[NFTA_FWD_SREG_DEV] == NULL)
  		return -EINVAL;
  
  	priv->sreg_dev = nft_parse_register(tb[NFTA_FWD_SREG_DEV]);
  	return nft_validate_register_load(priv->sreg_dev, sizeof(int));
  }
  
  static const struct nft_expr_ops nft_fwd_netdev_ingress_ops;
  
  static int nft_fwd_netdev_dump(struct sk_buff *skb, const struct nft_expr *expr)
  {
  	struct nft_fwd_netdev *priv = nft_expr_priv(expr);
  
  	if (nft_dump_register(skb, NFTA_FWD_SREG_DEV, priv->sreg_dev))
  		goto nla_put_failure;
  
  	return 0;
  
  nla_put_failure:
  	return -1;
  }

  struct nft_fwd_neigh {
  	enum nft_registers	sreg_dev:8;
  	enum nft_registers	sreg_addr:8;
  	u8			nfproto;
  };
  
  static void nft_fwd_neigh_eval(const struct nft_expr *expr,
  			      struct nft_regs *regs,
  			      const struct nft_pktinfo *pkt)
  {
  	struct nft_fwd_neigh *priv = nft_expr_priv(expr);
  	void *addr = &regs->data[priv->sreg_addr];
  	int oif = regs->data[priv->sreg_dev];
  	unsigned int verdict = NF_STOLEN;
  	struct sk_buff *skb = pkt->skb;
  	struct net_device *dev;
  	int neigh_table;
  
  	switch (priv->nfproto) {
  	case NFPROTO_IPV4: {
  		struct iphdr *iph;
  
  		if (skb->protocol != htons(ETH_P_IP)) {
  			verdict = NFT_BREAK;
  			goto out;
  		}
  		if (skb_try_make_writable(skb, sizeof(*iph))) {
  			verdict = NF_DROP;
  			goto out;
  		}
  		iph = ip_hdr(skb);
  		ip_decrease_ttl(iph);
  		neigh_table = NEIGH_ARP_TABLE;
  		break;
  		}
  	case NFPROTO_IPV6: {
  		struct ipv6hdr *ip6h;
  
  		if (skb->protocol != htons(ETH_P_IPV6)) {
  			verdict = NFT_BREAK;
  			goto out;
  		}
  		if (skb_try_make_writable(skb, sizeof(*ip6h))) {
  			verdict = NF_DROP;
  			goto out;
  		}
  		ip6h = ipv6_hdr(skb);
  		ip6h->hop_limit--;
  		neigh_table = NEIGH_ND_TABLE;
  		break;
  		}
  	default:
  		verdict = NFT_BREAK;
  		goto out;
  	}
  
  	dev = dev_get_by_index_rcu(nft_net(pkt), oif);
  	if (dev == NULL)
  		return;
  
  	skb->dev = dev;
  	neigh_xmit(neigh_table, dev, addr, skb);
  out:
  	regs->verdict.code = verdict;
  }
  
  static int nft_fwd_neigh_init(const struct nft_ctx *ctx,
  			      const struct nft_expr *expr,
  			      const struct nlattr * const tb[])
  {
  	struct nft_fwd_neigh *priv = nft_expr_priv(expr);
  	unsigned int addr_len;
  	int err;
  
  	if (!tb[NFTA_FWD_SREG_DEV] ||
  	    !tb[NFTA_FWD_SREG_ADDR] ||
  	    !tb[NFTA_FWD_NFPROTO])
  		return -EINVAL;
  
  	priv->sreg_dev = nft_parse_register(tb[NFTA_FWD_SREG_DEV]);
  	priv->sreg_addr = nft_parse_register(tb[NFTA_FWD_SREG_ADDR]);
  	priv->nfproto = ntohl(nla_get_be32(tb[NFTA_FWD_NFPROTO]));
  
  	switch (priv->nfproto) {
  	case NFPROTO_IPV4:
  		addr_len = sizeof(struct in_addr);
  		break;
  	case NFPROTO_IPV6:
  		addr_len = sizeof(struct in6_addr);
  		break;
  	default:
  		return -EOPNOTSUPP;
  	}
  
  	err = nft_validate_register_load(priv->sreg_dev, sizeof(int));
  	if (err < 0)
  		return err;
  
  	return nft_validate_register_load(priv->sreg_addr, addr_len);
  }
  
  static const struct nft_expr_ops nft_fwd_netdev_ingress_ops;
  
  static int nft_fwd_neigh_dump(struct sk_buff *skb, const struct nft_expr *expr)
  {
  	struct nft_fwd_neigh *priv = nft_expr_priv(expr);
  
  	if (nft_dump_register(skb, NFTA_FWD_SREG_DEV, priv->sreg_dev) ||
  	    nft_dump_register(skb, NFTA_FWD_SREG_ADDR, priv->sreg_addr) ||
  	    nla_put_be32(skb, NFTA_FWD_NFPROTO, htonl(priv->nfproto)))
  		goto nla_put_failure;
  
  	return 0;
  
  nla_put_failure:
  	return -1;
  }

  static struct nft_expr_type nft_fwd_netdev_type;

  static const struct nft_expr_ops nft_fwd_neigh_netdev_ops = {
  	.type		= &nft_fwd_netdev_type,
  	.size		= NFT_EXPR_SIZE(sizeof(struct nft_fwd_neigh)),
  	.eval		= nft_fwd_neigh_eval,
  	.init		= nft_fwd_neigh_init,
  	.dump		= nft_fwd_neigh_dump,
  };

  static const struct nft_expr_ops nft_fwd_netdev_ops = {
  	.type		= &nft_fwd_netdev_type,
  	.size		= NFT_EXPR_SIZE(sizeof(struct nft_fwd_netdev)),
  	.eval		= nft_fwd_netdev_eval,
  	.init		= nft_fwd_netdev_init,
  	.dump		= nft_fwd_netdev_dump,
  };

  static const struct nft_expr_ops *
  nft_fwd_select_ops(const struct nft_ctx *ctx,
  		   const struct nlattr * const tb[])
  {
  	if (tb[NFTA_FWD_SREG_ADDR])
  		return &nft_fwd_neigh_netdev_ops;
  	if (tb[NFTA_FWD_SREG_DEV])
  		return &nft_fwd_netdev_ops;
  
          return ERR_PTR(-EOPNOTSUPP);
  }

  static struct nft_expr_type nft_fwd_netdev_type __read_mostly = {
  	.family		= NFPROTO_NETDEV,
  	.name		= "fwd",

  	.select_ops	= nft_fwd_select_ops,

  	.policy		= nft_fwd_netdev_policy,
  	.maxattr	= NFTA_FWD_MAX,
  	.owner		= THIS_MODULE,
  };
  
  static int __init nft_fwd_netdev_module_init(void)
  {
  	return nft_register_expr(&nft_fwd_netdev_type);
  }
  
  static void __exit nft_fwd_netdev_module_exit(void)
  {
  	nft_unregister_expr(&nft_fwd_netdev_type);
  }
  
  module_init(nft_fwd_netdev_module_init);
  module_exit(nft_fwd_netdev_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
  MODULE_ALIAS_NFT_AF_EXPR(5, "fwd");