text: /* FTP extension for TCP NAT alteration. */
  
  /* (C) 1999-2001 Paul `Rusty' Russell
   * (C) 2002-2006 Netfilter Core Team <coreteam@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/module.h>
  #include <linux/moduleparam.h>
  #include <linux/ip.h>
  #include <linux/tcp.h>
  #include <linux/netfilter_ipv4.h>
  #include <net/netfilter/nf_nat.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_ftp.h>
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  MODULE_DESCRIPTION("ftp NAT helper");
  MODULE_ALIAS("ip_nat_ftp");
  
  #if 0
  #define DEBUGP printk
  #else
  #define DEBUGP(format, args...)
  #endif
  
  /* FIXME: Time out? --RR */
  
  static int
  mangle_rfc959_packet(struct sk_buff *skb,
  		     __be32 newip,
  		     u_int16_t port,
  		     unsigned int matchoff,
  		     unsigned int matchlen,
  		     struct nf_conn *ct,
  		     enum ip_conntrack_info ctinfo)
  {
  	char buffer[sizeof("nnn,nnn,nnn,nnn,nnn,nnn")];
  
  	sprintf(buffer, "%u,%u,%u,%u,%u,%u",
  		NIPQUAD(newip), port>>8, port&0xFF);
  
  	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  
  	return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  					matchlen, buffer, strlen(buffer));
  }
  
  /* |1|132.235.1.2|6275| */
  static int
  mangle_eprt_packet(struct sk_buff *skb,
  		   __be32 newip,
  		   u_int16_t port,
  		   unsigned int matchoff,
  		   unsigned int matchlen,
  		   struct nf_conn *ct,
  		   enum ip_conntrack_info ctinfo)
  {
  	char buffer[sizeof("|1|255.255.255.255|65535|")];
  
  	sprintf(buffer, "|1|%u.%u.%u.%u|%u|", NIPQUAD(newip), port);
  
  	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  
  	return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  					matchlen, buffer, strlen(buffer));
  }
  
  /* |1|132.235.1.2|6275| */
  static int
  mangle_epsv_packet(struct sk_buff *skb,
  		   __be32 newip,
  		   u_int16_t port,
  		   unsigned int matchoff,
  		   unsigned int matchlen,
  		   struct nf_conn *ct,
  		   enum ip_conntrack_info ctinfo)
  {
  	char buffer[sizeof("|||65535|")];
  
  	sprintf(buffer, "|||%u|", port);
  
  	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
  
  	return nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
  					matchlen, buffer, strlen(buffer));
  }
  
  static int (*mangle[])(struct sk_buff *, __be32, u_int16_t,
  		       unsigned int, unsigned int, struct nf_conn *,
  		       enum ip_conntrack_info)
  = {
  	[NF_CT_FTP_PORT] = mangle_rfc959_packet,
  	[NF_CT_FTP_PASV] = mangle_rfc959_packet,
  	[NF_CT_FTP_EPRT] = mangle_eprt_packet,
  	[NF_CT_FTP_EPSV] = mangle_epsv_packet
  };
  
  /* So, this packet has hit the connection tracking matching code.
     Mangle it, and change the expectation to match the new version. */
  static unsigned int nf_nat_ftp(struct sk_buff *skb,
  			       enum ip_conntrack_info ctinfo,
  			       enum nf_ct_ftp_type type,
  			       unsigned int matchoff,
  			       unsigned int matchlen,
  			       struct nf_conntrack_expect *exp)
  {
  	__be32 newip;
  	u_int16_t port;
  	int dir = CTINFO2DIR(ctinfo);
  	struct nf_conn *ct = exp->master;
  
  	DEBUGP("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
  
  	/* Connection will come from wherever this packet goes, hence !dir */
  	newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
  	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  	exp->dir = !dir;
  
  	/* When you see the packet, we need to NAT it the same as the
  	 * this one. */
  	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;
  
  	if (!mangle[type](skb, newip, port, matchoff, matchlen, ct, ctinfo)) {
  		nf_conntrack_unexpect_related(exp);
  		return NF_DROP;
  	}
  	return NF_ACCEPT;
  }
  
  static void __exit nf_nat_ftp_fini(void)
  {
  	rcu_assign_pointer(nf_nat_ftp_hook, NULL);
  	synchronize_rcu();
  }
  
  static int __init nf_nat_ftp_init(void)
  {
  	BUG_ON(rcu_dereference(nf_nat_ftp_hook));
  	rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
  	return 0;
  }
  
  /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
  static int warn_set(const char *val, struct kernel_param *kp)
  {
  	printk(KERN_INFO KBUILD_MODNAME
  	       ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
  	return 0;
  }
  module_param_call(ports, warn_set, NULL, NULL, 0);
  
  module_init(nf_nat_ftp_init);
  module_exit(nf_nat_ftp_fini);
  