/*
 * natd - Network Address Translation Daemon for FreeBSD.
 *
 * This software is provided free of charge, with no
 * warranty of any kind, either expressed or implied.
 * Use at your own risk.
 *
 * You may copy, modify and distribute this software (icmp.c) freely.
 *
 * Ari Suutari <suutari@iki.fi>
 *
 * $FreeBSD: src/sbin/natd/icmp.c,v 1.6 1999/08/28 00:13:45 peter Exp $
 * $DragonFly: src/sbin/natd/icmp.c,v 1.5 2005/06/07 20:21:23 swildner Exp $
 */

#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

#include <errno.h>
#include <signal.h>

#include <netdb.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>

#include <alias.h>

#include "natd.h"

int
SendNeedFragIcmp(int sock, struct ip *failedDgram, int mtu)
{
	char			icmpBuf[IP_MAXPACKET];
	struct ip*		ip;
	struct icmp*		icmp;
	int			icmpLen;
	int			failBytes;
	int			failHdrLen;
	struct sockaddr_in	addr;
	int			wrote;
	struct in_addr		swap;
/*
 * Don't send error if packet is
 * not the first fragment.
 */
	if (ntohs(failedDgram->ip_off) & ~(IP_MF | IP_DF))
		return 0;
/*
 * Dont respond if failed datagram is ICMP.
 */
	if (failedDgram->ip_p == IPPROTO_ICMP)
		return 0;
/*
 * Start building the message.
 */
	ip   = (struct ip *)icmpBuf;
	icmp = (struct icmp *)(icmpBuf + sizeof(struct ip));
/*
 * Complete ICMP part.
 */
	icmp->icmp_type		= ICMP_UNREACH;
	icmp->icmp_code		= ICMP_UNREACH_NEEDFRAG;
	icmp->icmp_cksum	= 0;
	icmp->icmp_void		= 0;
	icmp->icmp_nextmtu	= htons(mtu);
/*
 * Copy header + 64 bits of original datagram.
 */
	failHdrLen = (failedDgram->ip_hl << 2);
	failBytes  = failedDgram->ip_len - failHdrLen;
	if (failBytes > 8)
		failBytes = 8;

	failBytes += failHdrLen;
	icmpLen	   = ICMP_MINLEN + failBytes;

	memcpy(&icmp->icmp_ip, failedDgram, failBytes);
/*
 * Calculate checksum.
 */
	icmp->icmp_cksum = PacketAliasInternetChecksum((u_short *)icmp,
						       icmpLen);
/*
 * Add IP header using old IP header as template.
 */
	memcpy(ip, failedDgram, sizeof(struct ip));

	ip->ip_v	= 4;
	ip->ip_hl	= 5;
	ip->ip_len	= htons(sizeof(struct ip) + icmpLen);
	ip->ip_p	= IPPROTO_ICMP;
	ip->ip_tos	= 0;

	swap = ip->ip_dst;
	ip->ip_dst = ip->ip_src;
	ip->ip_src = swap;

	PacketAliasIn((char *)ip, IP_MAXPACKET);

	addr.sin_family		= AF_INET;
	addr.sin_addr		= ip->ip_dst;
	addr.sin_port		= 0;
/*
 * Put packet into processing queue.
 */
	wrote = sendto(sock,
		       icmp,
		       icmpLen,
		       0,
		       (struct sockaddr *)&addr,
	    	       sizeof addr);

	if (wrote != icmpLen)
		Warn("Cannot send ICMP message.");

	return 1;
}