#!/bin/sh
# decrypt_keyctl - to use in /etc/crypttab as keyscript
#  Allows to cache passwords for cryptdevices for 60s
#  The same password is used for for cryptdevices with the same identifier.
#  The keyfile parameter, which is the third field from /etc/crypttab, is
#  used as identifier in this keyscript.
#
# sample crypttab entries:
# test1   /dev/sda1    test_pw         luks,keyscript=decrypt_keyctl
# test2   /dev/sda2    test_pw         luks,keyscript=decrypt_keyctl
# test3   /dev/sda3    test_other_pw   luks,keyscript=decrypt_keyctl
#
#  test1 and test2 have the same identifier thus test2 does not need a password
#  typed in manually

die()
{
    echo "$@" >&2
    exit 1
}

# the keyfile given from crypttab is used as identifier in the keyring
# including the prefix "cryptkey-"
ID_="cryptkey-$1"
TIMEOUT_='60'
ASKPASS_='/lib/cryptsetup/askpass'
STTY_='/bin/stty'
PW_READER_='undefined'
PROMPT_="Caching passphrase for ${CRYPTTAB_SOURCE}: "

test -x "$STTY_" && PW_READER_='stty'           # 1. backup method
test -x "$ASKPASS_" && PW_READER_='askpass'     # prefered method

KID_=$(keyctl search @u user "$ID_" 2>/dev/null)
if [ $? -ne 0 ] || [ -z "$KID_" ]; then
    # key not found, ask the user
    case "$PW_READER_" in
        askpass)
            KEY_=$($ASKPASS_ "$PROMPT_") || die "Error executing $ASKPASS_"
            ;;
        stty) # disable echoing with stty
            $STTY_ -echo
            if ! read -r KEY_; then
                $STTY_ echo
                die "Error reading key from /dev/stdin"
            else
                $STTY_ echo
                echo >&2
            fi
            ;;
        *)  # first try to read the posix way, then at least give the user a chance
            echo -n "$PROMPT_" >&2
            if ! read -res KEY_; then
                echo
                echo "ERROR: Can not disable echoing, YOUR PASSWORD WILL BE VISIBLE!" >&2
                echo "This can be fixed if you add either $ASKPASS_" >&2
                echo "or $STTY_ to your initramfs" >&2
                echo -n "$PROMPT_" >&2
                if ! read -r KEY_; then
                    die "Error reading key from /dev/stdin"
                else
                    echo >&2
                fi
            else
                echo >&2
            fi
            ;;
    esac
    KID_=$(echo -n "$KEY_" |keyctl padd user "$ID_" @u)
    [ -z "$KID_" ] && die "Error adding passphrase to kernel keyring"
    if ! keyctl timeout $KID_ $TIMEOUT_; then
        keyctl unlink $KID_ @u
        die "Error setting timeout on key ($KID_), removing"
    fi
else
    echo "Using cached passphrase for ${CRYPTTAB_SOURCE}." >&2
fi
keyctl pipe $KID_