#!/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_