text: /* Amanda extension for TCP NAT alteration.
   * (C) 2002 by Brian J. Murrell <netfilter@interlinx.bc.ca>
   * based on a copy of HW's ip_nat_irc.c as well as other modules
   *
   * 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.
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/skbuff.h>
  #include <linux/udp.h>
  
  #include <net/netfilter/nf_nat_helper.h>
  #include <net/netfilter/nf_nat_rule.h>
  #include <net/netfilter/nf_conntrack_helper.h>
  #include <net/netfilter/nf_conntrack_expect.h>
  #include <linux/netfilter/nf_conntrack_amanda.h>
  
  MODULE_AUTHOR("Brian J. Murrell <netfilter@interlinx.bc.ca>");
  MODULE_DESCRIPTION("Amanda NAT helper");
  MODULE_LICENSE("GPL");
  MODULE_ALIAS("ip_nat_amanda");
  
  static unsigned int help(struct sk_buff **pskb,
  			 enum ip_conntrack_info ctinfo,
  			 unsigned int matchoff,
  			 unsigned int matchlen,
  			 struct nf_conntrack_expect *exp)
  {
  	char buffer[sizeof("65535")];
  	u_int16_t port;
  	unsigned int ret;
  
  	/* Connection comes from client. */
  	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  	exp->dir = IP_CT_DIR_ORIGINAL;
  
  	/* When you see the packet, we need to NAT it the same as the
  	 * this one (ie. same IP: it will be TCP and master is UDP). */
  	exp->expectfn = nf_nat_follow_master;
  
  	/* Try to get same port: if not, try to change it. */
  	for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  		exp->tuple.dst.u.tcp.port = htons(port);
  		if (nf_conntrack_expect_related(exp) == 0)
  			break;
  	}
  
  	if (port == 0)
  		return NF_DROP;
  
  	sprintf(buffer, "%u", port);
  	ret = nf_nat_mangle_udp_packet(pskb, exp->master, ctinfo,
  				       matchoff, matchlen,
  				       buffer, strlen(buffer));
  	if (ret != NF_ACCEPT)
  		nf_conntrack_unexpect_related(exp);
  	return ret;
  }
  
  static void __exit nf_nat_amanda_fini(void)
  {
  	rcu_assign_pointer(nf_nat_amanda_hook, NULL);
  	synchronize_rcu();
  }
  
  static int __init nf_nat_amanda_init(void)
  {
  	BUG_ON(rcu_dereference(nf_nat_amanda_hook));
  	rcu_assign_pointer(nf_nat_amanda_hook, help);
  	return 0;
  }
  
  module_init(nf_nat_amanda_init);
  module_exit(nf_nat_amanda_fini);
  