/*
 * 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;
}