// SPDX-License-Identifier: GPL-2.0-or-later

  /* IRC extension for TCP NAT alteration.
   *
   * (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
   * (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
   * based on a copy of RR's ip_nat_ftp.c

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/tcp.h>
  #include <linux/kernel.h>
  
  #include <net/netfilter/nf_nat.h>
  #include <net/netfilter/nf_nat_helper.h>

  #include <net/netfilter/nf_conntrack_helper.h>
  #include <net/netfilter/nf_conntrack_expect.h>
  #include <linux/netfilter/nf_conntrack_irc.h>

  #define NAT_HELPER_NAME "irc"

  MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  MODULE_DESCRIPTION("IRC (DCC) NAT helper");
  MODULE_LICENSE("GPL");

  MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  
  static struct nf_conntrack_nat_helper nat_helper_irc =
  	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);

  static unsigned int help(struct sk_buff *skb,

  			 enum ip_conntrack_info ctinfo,

  			 unsigned int protoff,

  			 unsigned int matchoff,
  			 unsigned int matchlen,
  			 struct nf_conntrack_expect *exp)
  {
  	char buffer[sizeof("4294967296 65635")];

  	struct nf_conn *ct = exp->master;
  	union nf_inet_addr newaddr;

  	u_int16_t port;

  	/* Reply comes from server. */

  	newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;

  	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  	exp->dir = IP_CT_DIR_REPLY;
  	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++) {

  		int ret;

  		exp->tuple.dst.u.tcp.port = htons(port);

  		ret = nf_ct_expect_related(exp, 0);

  		if (ret == 0)
  			break;
  		else if (ret != -EBUSY) {
  			port = 0;

  			break;

  		}

  	}

  	if (port == 0) {

  		nf_ct_helper_log(skb, ct, "all ports in use");

  		return NF_DROP;

  	}

  	/* strlen("\1DCC CHAT chat AAAAAAAA P\1
  ")=27
  	 * strlen("\1DCC SCHAT chat AAAAAAAA P\1
  ")=28
  	 * strlen("\1DCC SEND F AAAAAAAA P S\1
  ")=26
  	 * strlen("\1DCC MOVE F AAAAAAAA P S\1
  ")=26
  	 * strlen("\1DCC TSEND F AAAAAAAA P S\1
  ")=27
  	 *
  	 * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
  	 *                        255.255.255.255==4294967296, 10 digits)
  	 * P:         bound port (min 1 d, max 5d (65635))
  	 * F:         filename   (min 1 d )
  	 * S:         size       (min 1 d )
  	 * 0x01, 
  :  terminators
  	 */
  	/* AAA = "us", ie. where server normally talks to. */
  	snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);

  	pr_debug("inserting '%s' == %pI4, port %u
  ",

  		 buffer, &newaddr.ip, port);

  	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
  				      matchlen, buffer, strlen(buffer))) {

  		nf_ct_helper_log(skb, ct, "cannot mangle packet");

  		nf_ct_unexpect_related(exp);

  		return NF_DROP;

  	}

  	return NF_ACCEPT;

  }
  
  static void __exit nf_nat_irc_fini(void)
  {

  	nf_nat_helper_unregister(&nat_helper_irc);

  	RCU_INIT_POINTER(nf_nat_irc_hook, NULL);

  	synchronize_rcu();
  }
  
  static int __init nf_nat_irc_init(void)
  {

  	BUG_ON(nf_nat_irc_hook != NULL);

  	nf_nat_helper_register(&nat_helper_irc);

  	RCU_INIT_POINTER(nf_nat_irc_hook, help);

  	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, const struct kernel_param *kp)

  {

  	pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules
  ");

  	return 0;
  }
  module_param_call(ports, warn_set, NULL, NULL, 0);
  
  module_init(nf_nat_irc_init);
  module_exit(nf_nat_irc_fini);