/*
   * xfrm4_mode_beet.c - BEET mode encapsulation for IPv4.
   *
   * Copyright (c) 2006 Diego Beltrami <diego.beltrami@gmail.com>
   *                    Miika Komu     <miika@iki.fi>
   *                    Herbert Xu     <herbert@gondor.apana.org.au>
   *                    Abhinav Pathak <abhinav.pathak@hiit.fi>
   *                    Jeff Ahrenholz <ahrenholz@gmail.com>
   */
  
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/stringify.h>
  #include <net/dst.h>
  #include <net/ip.h>
  #include <net/xfrm.h>

  static void xfrm4_beet_make_header(struct sk_buff *skb)
  {
  	struct iphdr *iph = ip_hdr(skb);
  
  	iph->ihl = 5;
  	iph->version = 4;
  
  	iph->protocol = XFRM_MODE_SKB_CB(skb)->protocol;
  	iph->tos = XFRM_MODE_SKB_CB(skb)->tos;
  
  	iph->id = XFRM_MODE_SKB_CB(skb)->id;
  	iph->frag_off = XFRM_MODE_SKB_CB(skb)->frag_off;
  	iph->ttl = XFRM_MODE_SKB_CB(skb)->ttl;
  }

  /* Add encapsulation header.
   *
   * The top IP header will be constructed per draft-nikander-esp-beet-mode-06.txt.

   */
  static int xfrm4_beet_output(struct xfrm_state *x, struct sk_buff *skb)
  {

  	struct ip_beet_phdr *ph;

  	struct iphdr *top_iph;

  	int hdrlen, optlen;

  	hdrlen = 0;

  	optlen = XFRM_MODE_SKB_CB(skb)->optlen;

  	if (unlikely(optlen))
  		hdrlen += IPV4_BEET_PHMAXLEN - (optlen & 4);

  	skb_set_network_header(skb, -x->props.header_len -
  			            hdrlen + (XFRM_MODE_SKB_CB(skb)->ihl - sizeof(*top_iph)));
  	if (x->sel.family != AF_INET6)
  		skb->network_header += IPV4_BEET_PHMAXLEN;

  	skb->mac_header = skb->network_header +
  			  offsetof(struct iphdr, protocol);

  	skb->transport_header = skb->network_header + sizeof(*top_iph);

  	xfrm4_beet_make_header(skb);

  	ph = (struct ip_beet_phdr *)
  		__skb_pull(skb, XFRM_MODE_SKB_CB(skb)->ihl - hdrlen);

  	top_iph = ip_hdr(skb);

  	if (unlikely(optlen)) {

  		BUG_ON(optlen < 0);

  		ph->padlen = 4 - (optlen & 4);

  		ph->hdrlen = optlen / 8;

  		ph->nexthdr = top_iph->protocol;

  		if (ph->padlen)
  			memset(ph + 1, IPOPT_NOP, ph->padlen);

  
  		top_iph->protocol = IPPROTO_BEETPH;
  		top_iph->ihl = sizeof(struct iphdr) / 4;
  	}
  
  	top_iph->saddr = x->props.saddr.a4;
  	top_iph->daddr = x->id.daddr.a4;
  
  	return 0;
  }
  
  static int xfrm4_beet_input(struct xfrm_state *x, struct sk_buff *skb)
  {

  	struct iphdr *iph;

  	int optlen = 0;

  	int err = -EINVAL;

  	if (unlikely(XFRM_MODE_SKB_CB(skb)->protocol == IPPROTO_BEETPH)) {

  		struct ip_beet_phdr *ph;

  		int phlen;

  
  		if (!pskb_may_pull(skb, sizeof(*ph)))
  			goto out;

  
  		ph = (struct ip_beet_phdr *)skb->data;

  		phlen = sizeof(*ph) + ph->padlen;

  		optlen = ph->hdrlen * 8 + (IPV4_BEET_PHMAXLEN - phlen);

  		if (optlen < 0 || optlen & 3 || optlen > 250)
  			goto out;

  		XFRM_MODE_SKB_CB(skb)->protocol = ph->nexthdr;

  		if (!pskb_may_pull(skb, phlen))

  			goto out;
  		__skb_pull(skb, phlen);

  	}

  	skb_push(skb, sizeof(*iph));
  	skb_reset_network_header(skb);
  
  	memmove(skb->data - skb->mac_len, skb_mac_header(skb),
  		skb->mac_len);
  	skb_set_mac_header(skb, -skb->mac_len);
  
  	xfrm4_beet_make_header(skb);

  	iph = ip_hdr(skb);

  
  	iph->ihl += optlen / 4;
  	iph->tot_len = htons(skb->len);

  	iph->daddr = x->sel.daddr.a4;
  	iph->saddr = x->sel.saddr.a4;

  	iph->check = 0;

  	iph->check = ip_fast_csum(skb_network_header(skb), iph->ihl);

  	err = 0;
  out:
  	return err;
  }
  
  static struct xfrm_mode xfrm4_beet_mode = {

  	.input2 = xfrm4_beet_input,
  	.input = xfrm_prepare_input,

  	.output2 = xfrm4_beet_output,
  	.output = xfrm4_prepare_output,

  	.owner = THIS_MODULE,
  	.encap = XFRM_MODE_BEET,

  	.flags = XFRM_MODE_FLAG_TUNNEL,

  };
  
  static int __init xfrm4_beet_init(void)
  {
  	return xfrm_register_mode(&xfrm4_beet_mode, AF_INET);
  }
  
  static void __exit xfrm4_beet_exit(void)
  {
  	int err;
  
  	err = xfrm_unregister_mode(&xfrm4_beet_mode, AF_INET);
  	BUG_ON(err);
  }
  
  module_init(xfrm4_beet_init);
  module_exit(xfrm4_beet_exit);
  MODULE_LICENSE("GPL");
  MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_BEET);