/*
   * DCCP NAT protocol helper
   *

   * Copyright (c) 2005, 2006, 2008 Patrick McHardy <kaber@trash.net>

   *
   * 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/skbuff.h>

  #include <linux/dccp.h>
  
  #include <net/netfilter/nf_conntrack.h>
  #include <net/netfilter/nf_nat.h>

  #include <net/netfilter/nf_nat_l3proto.h>
  #include <net/netfilter/nf_nat_l4proto.h>

  
  static u_int16_t dccp_port_rover;

  static void

  dccp_unique_tuple(const struct nf_nat_l3proto *l3proto,
  		  struct nf_conntrack_tuple *tuple,

  		  const struct nf_nat_range2 *range,

  		  enum nf_nat_manip_type maniptype,
  		  const struct nf_conn *ct)
  {

  	nf_nat_l4proto_unique_tuple(l3proto, tuple, range, maniptype, ct,
  				    &dccp_port_rover);

  }

  static bool

  dccp_manip_pkt(struct sk_buff *skb,

  	       const struct nf_nat_l3proto *l3proto,
  	       unsigned int iphdroff, unsigned int hdroff,

  	       const struct nf_conntrack_tuple *tuple,
  	       enum nf_nat_manip_type maniptype)
  {

  	struct dccp_hdr *hdr;

  	__be16 *portptr, oldport, newport;
  	int hdrsize = 8; /* DCCP connection tracking guarantees this much */
  
  	if (skb->len >= hdroff + sizeof(struct dccp_hdr))
  		hdrsize = sizeof(struct dccp_hdr);
  
  	if (!skb_make_writable(skb, hdroff + hdrsize))

  		return false;

  	hdr = (struct dccp_hdr *)(skb->data + hdroff);

  	if (maniptype == NF_NAT_MANIP_SRC) {

  		newport = tuple->src.u.dccp.port;
  		portptr = &hdr->dccph_sport;
  	} else {

  		newport = tuple->dst.u.dccp.port;
  		portptr = &hdr->dccph_dport;
  	}
  
  	oldport = *portptr;
  	*portptr = newport;
  
  	if (hdrsize < sizeof(*hdr))

  		return true;

  	l3proto->csum_update(skb, iphdroff, &hdr->dccph_checksum,
  			     tuple, maniptype);

  	inet_proto_csum_replace2(&hdr->dccph_checksum, skb, oldport, newport,

  				 false);

  	return true;

  }

  const struct nf_nat_l4proto nf_nat_l4proto_dccp = {

  	.l4proto		= IPPROTO_DCCP,

  	.manip_pkt		= dccp_manip_pkt,

  	.in_range		= nf_nat_l4proto_in_range,

  	.unique_tuple		= dccp_unique_tuple,

  #if IS_ENABLED(CONFIG_NF_CT_NETLINK)

  	.nlattr_to_range	= nf_nat_l4proto_nlattr_to_range,

  #endif
  };