#!/bin/sh
#Hashes all files in /boot to check them during early boot
#Exit codes: 0 = success, 1 = checksum mbr mismatch, 2 = checksum /boot mismatch,
#3 = checksum mbr/boot mismatch, 4 = not root, 5 = no hasher found, 6 = wrong usage,
#7 = write error, 8 = dd error

VERSION="0.7.1"
PATH="/bin:/usr/bin:/sbin:/usr/sbin"

DIGEST_FILE="/var/lib/hashboot.digest"
LOG_FILE="/tmp/hashboot.log"
MBR_DEVICE="/dev/sda"
MBR_TMP="/tmp/mbr"
BACKUP_FILE="/var/cache/boot-backup.tar.gz"
HASHER=""
BOOT_MOUNTED=0

#Umount /boot if we mounted it, exit with given exit code
function die
{
    if [ ${BOOT_MOUNTED} -gt 0 ]
    then
        umount /boot
    fi

    exit ${1}
}


#If we're not root: exit
if [ ${UID} -ne 0 ]
then
    echo "You have to be root" >&2
    die 4
fi

#Try different hashers, use the most secure
HASHER=$(/usr/bin/which --skip-dot sha512sum 2> /dev/null)
test -z ${HASHER} && HASHER=$(/usr/bin/which --skip-dot sha384sum 2> /dev/null)
test -z ${HASHER} && HASHER=$(/usr/bin/which --skip-dot sha256sum 2> /dev/null)
test -z ${HASHER} && HASHER=$(/usr/bin/which --skip-dot sha224sum 2> /dev/null)
#It gets insecure below here, but better than nothing?
test -z ${HASHER} && HASHER=$(/usr/bin/which --skip-dot sha1sum 2> /dev/null)
test -z ${HASHER} && HASHER=$(/usr/bin/which --skip-dot md5sum 2> /dev/null)
#If we found no hasher: exit
if [ -z ${HASHER} ]
then
    echo "No hash calculator found" >&2
    die 5
fi

#If /boot is in fstab but not mounted: mount, mark as mounted
if grep -q '/boot.*noauto' /etc/fstab && ! grep -q /boot /etc/mtab
then
    mount /boot
    BOOT_MOUNTED=1
fi

if [ "${1}" == "index" ]
then
    #Write header
    echo "#hashboot ${VERSION} - Algorithm: $(basename ${HASHER})" > ${DIGEST_FILE}
    #Write MBR of MBR_DEVICE to ${DIGEST_FILE}
    dd if=/dev/sda of=${MBR_TMP} bs=1M count=1 status=noxfer || die 8
    #Write hashes of all regular files to ${DIGEST_FILE}
    ${HASHER} ${MBR_TMP} > ${DIGEST_FILE}
    find /boot -type f -exec ${HASHER} --binary {} >> ${DIGEST_FILE} +
    if [ $? == 0 ]
    then
        echo "List of hashes written to ${DIGEST_FILE}"
    else
        echo "Error writing ${DIGEST_FILE}" >&2
        die 7
    fi
    #Backup of good files
    tar -czpPf ${BACKUP_FILE} ${MBR_TMP} /boot ${DIGEST_FILE}
    if [ $? == 0 ]
    then
        echo "Backup written to ${BACKUP_FILE}"
    else
        echo "Error writing ${BACKUP_FILE}" >&2
        die 7
    fi
elif [ "${1}" == "check" ]
then
    COUNTER=0
    dd if=/dev/sda of=${MBR_TMP} bs=1M count=1 status=noxfer || die 8
    if $(grep ${MBR_TMP} ${DIGEST_FILE} | ${HASHER} --check --warn --quiet --strict > ${LOG_FILE})
    then
        echo "MBR ok"
    else
        echo "    !! TIME TO PANIK: MBR WAS MODIFIED !!"
        COUNTER=$((COUNTER + 1))
    fi
    if $(grep -v ${MBR_TMP} ${DIGEST_FILE} | ${HASHER} --check --warn --quiet --strict >> ${LOG_FILE})
    then
        echo "/boot ok"
        die 0
    else
        echo "    !! TIME TO PANIK: AT LEAST 1 FILE WAS MODIFIED !!"
        COUNTER=$((COUNTER + 2))
        die $COUNTER
    fi
elif [ "${1}" == "recover" ]
then
    echo "Restoring files from backup... (type yes or no for each file)"

    #For each failed file: ask if it should be recovered from backup
    for file in $(cut -d: -f1 ${LOG_FILE})
    do
        tar -xzpPvwf ${BACKUP_FILE} ${file}
        [ $? != 0 ] && echo "Error restoring ${file} from backup, continuing"
        # If the MBR is to be recovered, ask if it really should be copied to /dev/sda.
        # Should be no problem to do it automatically, but it is untested and would
        # be really bad if there is an error.
        if [ "$file" == ${MBR_TMP} ]
        then
            echo "Backup of MBR copied to ${MBR_TMP}, copy it to /dev/sda? (DANGEROUS) [y/N] "
            read -r yesno
            if [ "${yesno}" == "y" ]
            then
                cp ${MBR_TMP} /dev/sda
            else
                echo "MBR not recovered, you can copy it manually with:"
                echo "cp ${MBR_TMP} /dev/sda"
            fi
        fi
    done
else
    echo "Usage: ${0} index|check|recover" >&2
    die 6
fi

die 0