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#!/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 "$@" >&2
exit 1
}
if [ -z "${CRYPTTAB_KEY:-}" ] || [ "$CRYPTTAB_KEY" = "none" ]; then
# store the passphrase in the key name used by systemd-ask-password
ID_="cryptsetup"
else
# the keyfile given from crypttab is used as identifier in the keyring
# including the prefix "cryptsetup:"
ID_="cryptsetup:$CRYPTTAB_KEY"
fi
TIMEOUT_='60'
ASKPASS_='/lib/cryptsetup/askpass'
PROMPT_="Caching passphrase for ${CRYPTTAB_NAME}: "
if ! KID_="$(keyctl search @u user "$ID_" 2>/dev/null)" || \
[ -z "$KID_" ] || [ "$CRYPTTAB_TRIED" -gt 0 ]; then
# key not found or wrong, ask the user
KEY_="$($ASKPASS_ "$PROMPT_")" || die "Error executing $ASKPASS_"
if [ -n "$KID_" ]; then
# I have cached wrong password and now i may use either `keyctl update`
# to update $KID_ or just unlink old key, and add new. With `update` i
# may hit "Key has expired", though. So i'll go "unlink and add" way.
keyctl unlink "$KID_" @u
KID_=""
fi
KID_="$(printf "%s" "$KEY_" | keyctl padd user "$ID_" @u)"
[ -n "$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 ${CRYPTTAB_NAME}." >&2
fi
keyctl pipe "$KID_"
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