Unlock encrypted root partition over SSH

This commit add a new feature for Debian-based distributions to unlock
encrypted root partition over SSH.  This feature is very handy on
headless NAS or VPS cloud servers.  To use this feature, you will need
to install the dropbear-initramfs package.

Reviewed-By: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-By: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Andrey Prokopenko <job@terem.fr>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #10027

contrib/initramfs/Makefile.am

@@ -1,5 +1,8 @@
 initrddir = /usr/share/initramfs-tools
 
+dist_initrd_SCRIPTS = \
+       zfsunlock
+
 SUBDIRS = conf.d conf-hooks.d hooks scripts
 
 EXTRA_DIST = \

contrib/initramfs/README.initramfs.markdown

@@ -72,3 +72,15 @@ The following kernel command line arguments are supported:
 * `zfsdebug=(on,yes,1)`: Show extra debugging information
 * `zfsforce=(on,yes,1)`: Force import the pool
 * `rollback=(on,yes,1)`: Rollback to (instead of clone) the snapshot
+
+### Unlocking a ZFS encrypted root over SSH
+
+To use this feature:
+
+1. Install the `dropbear-initramfs` package.  You may wish to uninstall the
+   `cryptsetup-initramfs` package to avoid warnings.
+2. Add your SSH key(s) to `/etc/dropbear-initramfs/authorized_keys`.  Note
+   that Dropbear does not support ed25519 keys; use RSA (2048-bit or more)
+   instead.
+3. Rebuild the initramfs with your keys: `update-initramfs -u`
+4. During the system boot, login via SSH and run: `zfsunlock`

contrib/initramfs/hooks/.gitignore

@@ -1 +1,2 @@
 zfs
+zfsunlock

contrib/initramfs/hooks/Makefile.am

@@ -1,10 +1,12 @@
 hooksdir = /usr/share/initramfs-tools/hooks
 
 hooks_SCRIPTS = \
-	zfs
+	zfs \
+	zfsunlock
 
 EXTRA_DIST = \
-	$(top_srcdir)/contrib/initramfs/hooks/zfs.in
+	$(top_srcdir)/contrib/initramfs/hooks/zfs.in \
+	$(top_srcdir)/contrib/initramfs/hooks/zfsunlock.in
 
 $(hooks_SCRIPTS):%:%.in Makefile
 	-$(SED) -e 's,@sbindir\@,$(sbindir),g' \

contrib/initramfs/hooks/zfs.in

@@ -21,6 +21,7 @@ COPY_FILE_LIST="$COPY_FILE_LIST @udevruledir@/69-vdev.rules"
 # These prerequisites are provided by the base system.
 COPY_EXEC_LIST="$COPY_EXEC_LIST /usr/bin/dirname /bin/hostname /sbin/blkid"
 COPY_EXEC_LIST="$COPY_EXEC_LIST /usr/bin/env"
+COPY_EXEC_LIST="$COPY_EXEC_LIST $(which systemd-ask-password)"
 
 # Explicitly specify all kernel modules because automatic dependency resolution
 # is unreliable on many systems.

contrib/initramfs/hooks/zfsunlock.in

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+PREREQ="dropbear"
+
+prereqs() {
+    echo "$PREREQ"
+}
+
+case "$1" in
+    prereqs)
+        prereqs
+        exit 0
+    ;;
+esac
+
+. /usr/share/initramfs-tools/hook-functions
+
+copy_exec /usr/share/initramfs-tools/zfsunlock /usr/bin

contrib/initramfs/scripts/zfs

@@ -405,6 +405,8 @@ decrypt_fs()
 		ENCRYPTIONROOT="$(get_fs_value "${fs}" encryptionroot)"
 		KEYLOCATION="$(get_fs_value "${ENCRYPTIONROOT}" keylocation)"
 
+		echo "${ENCRYPTIONROOT}" > /run/zfs_fs_name
+
 		# If root dataset is encrypted...
 		if ! [ "${ENCRYPTIONROOT}" = "-" ]; then
 			KEYSTATUS="$(get_fs_value "${ENCRYPTIONROOT}" keystatus)"
@@ -418,6 +420,7 @@ decrypt_fs()
 
 			# Prompt with plymouth, if active
 			elif [ -e /bin/plymouth ] && /bin/plymouth --ping 2>/dev/null; then
+				echo "plymouth" > /run/zfs_console_askpwd_cmd
 				while [ $TRY_COUNT -gt 0 ]; do
 					plymouth ask-for-password --prompt "Encrypted ZFS password for ${ENCRYPTIONROOT}" | \
 						$ZFS load-key "${ENCRYPTIONROOT}" && break
@@ -426,6 +429,7 @@ decrypt_fs()
 
 			# Prompt with systemd, if active 
 			elif [ -e /run/systemd/system ]; then
+				echo "systemd-ask-password" > /run/zfs_console_askpwd_cmd
 				while [ $TRY_COUNT -gt 0 ]; do
 					systemd-ask-password "Encrypted ZFS password for ${ENCRYPTIONROOT}" --no-tty | \
 						$ZFS load-key "${ENCRYPTIONROOT}" && break
@@ -434,7 +438,8 @@ decrypt_fs()
 
 			# Prompt with ZFS tty, otherwise
 			else
-				# Setting "printk" temporarily to "7" will allow prompt even if kernel option "quiet"
+				# Temporarily setting "printk" to "7" allows the prompt to appear even when the "quiet" kernel option has been used
+				echo "load-key" > /run/zfs_console_askpwd_cmd
 				storeprintk="$(awk '{print $1}' /proc/sys/kernel/printk)"
 				echo 7 > /proc/sys/kernel/printk
 				$ZFS load-key "${ENCRYPTIONROOT}"
@@ -964,6 +969,11 @@ mountroot()
 		mount_fs "$fs"
 	done
 
+	touch /run/zfs_unlock_complete
+	if [ -e /run/zfs_unlock_complete_notify ]; then
+		read zfs_unlock_complete_notify < /run/zfs_unlock_complete_notify
+	fi
+
 	# ------------
 	# Debugging information
 	if [ -n "${ZFS_DEBUG}" ]

contrib/initramfs/zfsunlock

@@ -0,0 +1,42 @@
+#!/bin/sh
+
+set -eu
+if [ ! -e /run/zfs_fs_name ]; then
+	echo "Wait for the root pool to be imported or press Ctrl-C to exit."
+fi
+while [ ! -e /run/zfs_fs_name ]; do
+	if [ -e /run/zfs_unlock_complete ]; then
+		exit 0
+	fi
+	sleep 0.5
+done
+echo
+echo "Unlocking encrypted ZFS filesystems..."
+echo "Enter the password or press Ctrl-C to exit."
+echo
+zfs_fs_name=""
+if [ ! -e /run/zfs_unlock_complete_notify ]; then
+	mkfifo /run/zfs_unlock_complete_notify
+fi
+while [ ! -e /run/zfs_unlock_complete ]; do
+	zfs_fs_name=$(cat /run/zfs_fs_name)
+	zfs_console_askpwd_cmd=$(cat /run/zfs_console_askpwd_cmd)
+	systemd-ask-password "Encrypted ZFS password for ${zfs_fs_name}:" | \
+		/sbin/zfs load-key "$zfs_fs_name" || true
+	if [ "$(/sbin/zfs get -H -ovalue keystatus "$zfs_fs_name" 2> /dev/null)" = "available" ]; then
+		echo "Password for $zfs_fs_name accepted."
+		zfs_console_askpwd_pid=$(ps a -o pid= -o args | grep -v grep | grep "$zfs_console_askpwd_cmd" | cut -d ' ' -f3 | sort -n | head -n1)
+		if [ -n "$zfs_console_askpwd_pid" ]; then
+			kill "$zfs_console_askpwd_pid"
+		fi
+		# Wait for another filesystem to unlock.
+		while [ "$(cat /run/zfs_fs_name)" = "$zfs_fs_name" ] && [ ! -e /run/zfs_unlock_complete ]; do
+			sleep 0.5
+		done
+	else
+		echo "Wrong password.  Try again."
+	fi
+done
+echo "Unlocking complete.  Resuming boot sequence..."
+echo "Please reconnect in a while."
+echo "ok" > /run/zfs_unlock_complete_notify