/*
   * IP Payload Compression Protocol (IPComp) - RFC3173.
   *
   * Copyright (c) 2003 James Morris <jmorris@intercode.com.au>
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License as published by the Free

   * Software Foundation; either version 2 of the License, or (at your option)

   * any later version.
   *
   * Todo:
   *   - Tunable compression parameters.
   *   - Compression stats.
   *   - Adaptive compression.
   */

  #include <linux/module.h>

  #include <linux/err.h>

  #include <linux/rtnetlink.h>
  #include <net/ip.h>
  #include <net/xfrm.h>
  #include <net/icmp.h>
  #include <net/ipcomp.h>

  #include <net/protocol.h>

  #include <net/sock.h>

  static int ipcomp4_err(struct sk_buff *skb, u32 info)

  {

  	struct net *net = dev_net(skb->dev);

  	__be32 spi;

  	const struct iphdr *iph = (const struct iphdr *)skb->data;

  	struct ip_comp_hdr *ipch = (struct ip_comp_hdr *)(skb->data+(iph->ihl<<2));
  	struct xfrm_state *x;

  	switch (icmp_hdr(skb)->type) {
  	case ICMP_DEST_UNREACH:
  		if (icmp_hdr(skb)->code != ICMP_FRAG_NEEDED)

  			return 0;

  	case ICMP_REDIRECT:
  		break;
  	default:

  		return 0;

  	}

  	spi = htonl(ntohs(ipch->cpi));

  	x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,

  			      spi, IPPROTO_COMP, AF_INET);

  	if (!x)

  		return 0;

  	if (icmp_hdr(skb)->type == ICMP_DEST_UNREACH)

  		ipv4_update_pmtu(skb, net, info, 0, 0, IPPROTO_COMP, 0);

  	else

  		ipv4_redirect(skb, net, 0, 0, IPPROTO_COMP, 0);

  	xfrm_state_put(x);

  
  	return 0;

  }

  /* We always hold one tunnel user reference to indicate a tunnel */

  static struct xfrm_state *ipcomp_tunnel_create(struct xfrm_state *x)
  {

  	struct net *net = xs_net(x);

  	struct xfrm_state *t;

  	t = xfrm_state_alloc(net);

  	if (!t)

  		goto out;
  
  	t->id.proto = IPPROTO_IPIP;
  	t->id.spi = x->props.saddr.a4;
  	t->id.daddr.a4 = x->id.daddr.a4;
  	memcpy(&t->sel, &x->sel, sizeof(t->sel));
  	t->props.family = AF_INET;

  	t->props.mode = x->props.mode;

  	t->props.saddr.a4 = x->props.saddr.a4;
  	t->props.flags = x->props.flags;

  	t->props.extra_flags = x->props.extra_flags;

  	memcpy(&t->mark, &x->mark, sizeof(t->mark));

  
  	if (xfrm_init_state(t))

  		goto error;

  	atomic_set(&t->tunnel_users, 1);
  out:
  	return t;
  
  error:
  	t->km.state = XFRM_STATE_DEAD;
  	xfrm_state_put(t);
  	t = NULL;
  	goto out;
  }
  
  /*

   * Must be protected by xfrm_cfg_mutex.  State and tunnel user references are

   * always incremented on success.
   */
  static int ipcomp_tunnel_attach(struct xfrm_state *x)
  {

  	struct net *net = xs_net(x);

  	int err = 0;
  	struct xfrm_state *t;

  	u32 mark = x->mark.v & x->mark.m;

  	t = xfrm_state_lookup(net, mark, (xfrm_address_t *)&x->id.daddr.a4,

  			      x->props.saddr.a4, IPPROTO_IPIP, AF_INET);

  	if (!t) {
  		t = ipcomp_tunnel_create(x);
  		if (!t) {
  			err = -EINVAL;
  			goto out;
  		}
  		xfrm_state_insert(t);
  		xfrm_state_hold(t);
  	}
  	x->tunnel = t;
  	atomic_inc(&t->tunnel_users);
  out:
  	return err;
  }

  static int ipcomp4_init_state(struct xfrm_state *x)

  {

  	int err = -EINVAL;

  	x->props.header_len = 0;
  	switch (x->props.mode) {
  	case XFRM_MODE_TRANSPORT:
  		break;
  	case XFRM_MODE_TUNNEL:
  		x->props.header_len += sizeof(struct iphdr);
  		break;
  	default:
  		goto out;
  	}

  	err = ipcomp_init_state(x);
  	if (err)

  		goto out;

  	if (x->props.mode == XFRM_MODE_TUNNEL) {

  		err = ipcomp_tunnel_attach(x);
  		if (err)

  			goto out;

  	}

  	err = 0;
  out:
  	return err;

  }

  static int ipcomp4_rcv_cb(struct sk_buff *skb, int err)
  {
  	return 0;
  }

  static const struct xfrm_type ipcomp_type = {

  	.description	= "IPCOMP4",
  	.owner		= THIS_MODULE,
  	.proto	     	= IPPROTO_COMP,

  	.init_state	= ipcomp4_init_state,

  	.destructor	= ipcomp_destroy,
  	.input		= ipcomp_input,
  	.output		= ipcomp_output
  };

  static struct xfrm4_protocol ipcomp4_protocol = {

  	.handler	=	xfrm4_rcv,

  	.input_handler	=	xfrm_input,
  	.cb_handler	=	ipcomp4_rcv_cb,

  	.err_handler	=	ipcomp4_err,

  	.priority	=	0,

  };
  
  static int __init ipcomp4_init(void)
  {
  	if (xfrm_register_type(&ipcomp_type, AF_INET) < 0) {

  		pr_info("%s: can't add xfrm type
  ", __func__);

  		return -EAGAIN;
  	}

  	if (xfrm4_protocol_register(&ipcomp4_protocol, IPPROTO_COMP) < 0) {

  		pr_info("%s: can't add protocol
  ", __func__);

  		xfrm_unregister_type(&ipcomp_type, AF_INET);
  		return -EAGAIN;
  	}
  	return 0;
  }
  
  static void __exit ipcomp4_fini(void)
  {

  	if (xfrm4_protocol_deregister(&ipcomp4_protocol, IPPROTO_COMP) < 0)

  		pr_info("%s: can't remove protocol
  ", __func__);

  	if (xfrm_unregister_type(&ipcomp_type, AF_INET) < 0)

  		pr_info("%s: can't remove xfrm type
  ", __func__);

  }
  
  module_init(ipcomp4_init);
  module_exit(ipcomp4_fini);
  
  MODULE_LICENSE("GPL");

  MODULE_DESCRIPTION("IP Payload Compression Protocol (IPComp/IPv4) - RFC3173");

  MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");

  MODULE_ALIAS_XFRM_TYPE(AF_INET, XFRM_PROTO_COMP);