/* 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");

/* FIXME: Time out? --RR */

static int nf_nat_ftp_fmt_cmd(enum nf_ct_ftp_type type,
			      char *buffer, size_t buflen,
			      __be32 addr, u16 port)
{
	switch (type) {
	case NF_CT_FTP_PORT:
	case NF_CT_FTP_PASV:
		return snprintf(buffer, buflen, "%u,%u,%u,%u,%u,%u",
				((unsigned char *)&addr)[0],
				((unsigned char *)&addr)[1],
				((unsigned char *)&addr)[2],
				((unsigned char *)&addr)[3],
				port >> 8,
				port & 0xFF);
	case NF_CT_FTP_EPRT:
		return snprintf(buffer, buflen, "|1|%pI4|%u|", &addr, port);
	case NF_CT_FTP_EPSV:
		return snprintf(buffer, buflen, "|||%u|", port);
	}

	return 0;
}

/* 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;
	char buffer[sizeof("|1|255.255.255.255|65535|")];
	unsigned int buflen;

	pr_debug("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_ct_expect_related(exp) == 0)
			break;
	}

	if (port == 0)
		return NF_DROP;

	buflen = nf_nat_ftp_fmt_cmd(type, buffer, sizeof(buffer), newip, port);
	if (!buflen)
		goto out;

	pr_debug("calling nf_nat_mangle_tcp_packet\n");

	if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, matchoff,
				      matchlen, buffer, buflen))
		goto out;

	return NF_ACCEPT;

out:
	nf_ct_unexpect_related(exp);
	return NF_DROP;
}

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(nf_nat_ftp_hook != NULL);
	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);