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Filename : cryptroot-unlock
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#!/bin/busybox ash

# Remotely unlock encrypted volumes.
#
# Copyright © 2015-2018 Guilhem Moulin <guilhem@debian.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

set -ue
PATH=/sbin:/bin

TIMEOUT=10
PASSFIFO=/lib/cryptsetup/passfifo
ASKPASS=/lib/cryptsetup/askpass
UNLOCK_ALL=n

[ -f /lib/cryptsetup/functions ] || return 0
. /lib/cryptsetup/functions
TABFILE="/cryptroot/crypttab"
unset -v IFS

if [ ! -f "$TABFILE" ] || [ "$TABFILE" -ot "/proc/1" ]; then
	# Too early, init-top/cryptroot hasn't finished yet
	echo "Try again later" >&2
	exit 1
fi

# Print the list of PIDs the executed command of which is $exe.
pgrep_exe() {
	local exe pid
	exe="$(readlink -f -- "$1" 2>/dev/null)" && [ -f "$exe" ] || return 0
	ps | awk '{print $1, $5}' | while read LINE; do
		set $LINE
		local pid=$1
		local cmd=$(readlink -f -- "$2")
		if [ "$cmd" == "$exe" ]; then
			echo $pid
			break
		fi
	done
}

# Return 0 if $pid has a file descriptor pointing to $name, and 1
# otherwise.
in_fds() {
	local pid="$1" name fd
	name="$(readlink -f -- "$2" 2>/dev/null)" && [ -e "$name" ] || return 1
	for fd in $(find "/proc/$pid/fd" -type l); do
		[ "$(readlink -f "$fd")" != "$name" ] || return 0
	done
	return 1
}

# Print the PID of the askpass process with a file descriptor opened to
# /lib/cryptsetup/passfifo.
get_askpass_pid() {
	local pid
	for pid in $(pgrep_exe "$ASKPASS"); do
		if in_fds "$pid" "$PASSFIFO"; then
			echo "$pid"
			return 0
		fi
	done
	return 1
}

# Print the number of configured crypt devices that have not been unlocked yet.
count_locked_devices() {
	local COUNT=0
	crypttab_foreach_entry count_locked_devices_callback
	printf '%d\n' "$COUNT"
}
count_locked_devices_callback() {
	dm_blkdevname "$CRYPTTAB_NAME" >/dev/null || COUNT=$(( $COUNT + 1 ))
}

# Wait for askpass, then set $PID (resp. $BIRTH) to the PID (resp.
# birth date) of the cryptsetup process with same $CRYPTTAB_NAME.
wait_for_prompt() {
	local pid timer num_locked_devices=-1 n

	# wait for the fifo
	while :; do
		n=$(count_locked_devices)
		if [ $n -eq 0 ]; then
			# all configured devices have been unlocked, we're done
			exit 0
		elif [ $num_locked_devices -lt 0 ] || [ $n -lt $num_locked_devices ]; then
			# reset $timer if a device was unlocked (for instance using
			# a keyscript) while we were waiting
			timer=$(( 10 * $TIMEOUT ))
		fi
		num_locked_devices=$n

		if pid=$(get_askpass_pid) && [ -p "$PASSFIFO" ]; then
			break
		fi

		sleep 0.1
		timer=$(( $timer - 1 ))
		if [ $timer -le 0 ]; then
			echo "Error: Timeout reached while waiting for askpass." >&2
			exit 1
		fi
	done

	# find the cryptsetup process with same $CRYPTTAB_NAME
	local o v
	for o in NAME TRIED OPTION_tries; do
		if v="$(tr '\0' '\n' < "/proc/$pid/environ" | grep -m1 "^CRYPTTAB_$o=")"; then
			eval "CRYPTTAB_$o"="\${v#CRYPTTAB_$o=}"
		else
			eval unset -v "CRYPTTAB_$o"
		fi
	done
	if [ -z "${CRYPTTAB_NAME:+x}" ] || [ -z "${CRYPTTAB_TRIED:+x}" ]; then
		return 1
	fi
	if ( ! crypttab_find_entry --quiet "$CRYPTTAB_NAME" ); then
		# use a subshell to avoid polluting our enironment
		echo "Error: Refusing to process unknown device $CRYPTTAB_NAME" >&2
		exit 1
	fi

	for pid in $(pgrep_exe "/sbin/cryptsetup"); do
		if tr '\0' '\n' < "/proc/$pid/environ" | grep -Fxq "CRYPTTAB_NAME=$CRYPTTAB_NAME"; then
			PID=$pid
			BIRTH=$(stat -c"%Z" "/proc/$PID" 2>/dev/null) || break
			return 0
		fi
	done

	PID=
	BIRTH=
	return 1
}

# Wait until $PID no longer exists or has a birth date greater that
# $BIRTH (ie was reallocated).  Then return with exit value 0 if
# /dev/mapper/$CRYPTTAB_NAME exists, and with exit value 1 if the
# maximum number of tries exceeded.  Otherwise (if the unlocking
# failed), return with value 1.
wait_for_answer() {
	local timer=$(( 10 * $TIMEOUT )) b
	while [ -d "/proc/$PID" ] && b=$(stat -c"%Z" "/proc/$PID" 2>/dev/null) && [ $b -le $BIRTH ]; do
		sleep 0.1
		timer=$(( $timer - 1 ))
		if [ $timer -le 0 ]; then
			echo "Error: Timeout reached while waiting for PID $PID." >&2
			exit 1
		fi
	done

	if dm_blkdevname "$CRYPTTAB_NAME" >/dev/null; then
		echo "cryptsetup: $CRYPTTAB_NAME set up successfully" >&2
		[ "$UNLOCK_ALL" = y ] && return 0 || exit 0
	elif [ $(( ${CRYPTTAB_TRIED:-0} + 1 )) -ge ${CRYPTTAB_OPTION_tries:-3} ] &&
			[ ${CRYPTTAB_OPTION_tries:-3} -gt 0 ]; then
		echo "cryptsetup: maximum number of tries exceeded for $CRYPTTAB_NAME" >&2
		exit 1
	else
		echo "cryptsetup: cryptsetup failed, bad password or options?" >&2
		return 1
	fi
}


if [ -t 0 ] && [ -x "$ASKPASS" ]; then
	# interactive mode on a TTY: keep trying until all configured devices have
	# been unlocked or the maximum number of tries exceeded
	UNLOCK_ALL=y
	while :; do
		# note: if the script is not killed before pivot_root it should
		# exit on its own once $TIMEOUT is reached
		if ! wait_for_prompt; then
			usleep 100000
			continue
		fi
		read -rs -p "Please unlock disk $CRYPTTAB_NAME: "; echo
		printf '%s' "$REPLY" >"$PASSFIFO"
		wait_for_answer || true
	done
else
	# non-interactive mode: slurp the passphrase from stdin and exit
	wait_for_prompt || exit 1
	echo "Please unlock disk $CRYPTTAB_NAME"
	cat >"$PASSFIFO"
	wait_for_answer || exit 1
fi

# vim: set filetype=sh :