genkernel: add keyctl support for loading LUKS passphrase into a keyring

cryptsetup LUKS2 format comes with an ability to automatically unlock
multiple devices (root, swap, etc.) sharing the same passphrase, without
retyping it for each of them, by loading it into the user keyring.

This commit adds such (optional) genkernel support for loading LUKS
passphrase into the user keyring on boot.

In the default mode of operation the newly added key is (possibly) used
only to unlock root and swap devices and is removed soon after that.
By providing appropriate kernel command line parameter the key can be left
in the keyring instead (with an optional timeout) for unlocking other LUKS
devices post-initramfs time.

Because one of the most common use cases of this functionality will be
having an encrypted swap for doing suspend to disk (hibernation) let's also
make sure that we don't unlock the root device when doing so is unnecessary
(when we are resuming the system from hibernation).

Since the security of a FDE passphrase is of paramount importance in this
solution significant care has been taken not to leak it accidentally:
* The passphrase is read directly by keyctl to avoid storing it in the
shell,

* If the passphrase is used only to unlock root and swap devices (which is
the default mode of operation) the init script will check whether its
removal from keyring has actually succeeded and, if not, reboot the system
rather than continue while leaving it exposed,

* keyutils includes a patch (already upstreamed) to wipe the passphrase
from memory when no longer needed.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>

9 files changed, 181 insertions, 3 deletions

diff --git a/defaults/initrd.scripts b/defaults/initrd.scripts
index 4932783..eb556d6 100644
--- a/defaults/initrd.scripts
+++ b/defaults/initrd.scripts
@@ -2108,6 +2108,54 @@ openLUKS() {
 	[ -d "${mntkey}" ] && run rmdir -p "${mntkey}" >/dev/null 2>&1
 }
 
+keyctl_keyadd() {
+	if [ -n "${KEYCTL_KEYDESC}" ]
+	then
+		if [ ! -x /bin/keyctl ]
+		then
+			bad_msg "keyctl program is missing. Was initramfs built without --keyctl parameter?"
+			exit 1
+		fi
+
+		# not using read to avoid secrets being left in memory
+		stty -echo
+		echo -n "Please type the key '${KEYCTL_KEYDESC}' for the user keyring then press Ctrl-D twice: "
+		KEYCTL_KEYID=`keyctl padd user "${KEYCTL_KEYDESC}" @u`
+		echo
+		stty echo
+
+		if [ -n "${KEYCTL_KEYID}" -a -n "${KEYCTL_KEYTIMEOUT}" ]
+		then
+			keyctl timeout "${KEYCTL_KEYID}" "${KEYCTL_KEYTIMEOUT}"
+		fi
+	fi
+}
+
+keyctl_keyremove() {
+	if [ -n "${KEYCTL_KEYID}" -a -z "${KEYCTL_KEYKEEP}" ]
+	then
+		if [ ! -x /bin/keyctl ]
+		then
+			bad_msg "keyctl program is missing. Was initramfs built without --keyctl parameter?"
+			exit 1
+		fi
+
+		keyctl revoke "${KEYCTL_KEYID}"
+		keyctl unlink "${KEYCTL_KEYID}" >/dev/null
+
+		# trust but verify
+		if keyctl show "${KEYCTL_KEYID}" >/dev/null 2>&1
+		then
+			# better reboot than leave the user passphrase accidentally exposed
+			bad_msg "unable to remove the newly added key from keyring, rebooting in 5 seconds for security"
+			sleep 5
+			reboot -f
+		fi
+
+		KEYCTL_KEYID=
+	fi
+}
+
 iface_name() {
 	local ifname="${1}"
 
@@ -2437,7 +2485,7 @@ ipv6_tentative() {
 	fi
 }
 
-start_LUKS() {
+start_LUKS_root() {
 	# if key is set but neither ssh enabled or key device is given, find
 	# the key device
 
@@ -2461,7 +2509,9 @@ start_LUKS() {
 			REAL_ROOT="/dev/mapper/root"
 		fi
 	fi
+}
 
+start_LUKS_swap() {
 	if [ -n "${CRYPT_SWAP_KEY}" ]
 	then
 		# same for swap, but no need to sleep if root was unencrypted
diff --git a/defaults/linuxrc b/defaults/linuxrc
index 15fbf7c..5ee7804 100644
--- a/defaults/linuxrc
+++ b/defaults/linuxrc
@@ -272,6 +272,15 @@ do
 		swap_keydev_fstype=*)
 			CRYPT_SWAP_KEYDEV_FSTYPE=${x#*=}
 		;;
+		keyctl_keydesc=*)
+			KEYCTL_KEYDESC=${x#*=}
+		;;
+		keyctl_keytimeout=*)
+			KEYCTL_KEYTIMEOUT=${x#*=}
+		;;
+		keyctl_keykeep)
+			KEYCTL_KEYKEEP=1
+		;;
 		real_resume=*|resume=*)
 			REAL_RESUME=${x#*=}
 		;;
@@ -656,10 +665,23 @@ then
 	start_sshd
 fi
 
+keyctl_keyadd
+
 # Initialize LUKS root device except for livecd's
 if [ "${CDROOT}" != '1' ]
 then
-	start_LUKS
+	if ( [ -n "${CRYPT_SWAP_KEY}" ] && [ -z "${CRYPT_SWAP_KEYDEV}" ] ) || \
+	   ( [ -n "${CRYPT_SWAP_HEADER}" ] && [ -z "${CRYPT_SWAP_HEADERDEV}" ] )
+	then
+		# the swap key or header might be on the root fs so start it first in this case
+		start_LUKS_root
+		luks_root_started=1
+		start_LUKS_swap
+	else
+		# we don't need to start the root at all if we are resuming from suspend
+		start_LUKS_swap
+	fi
+
 	if [ "${NORESUME}" != '1' ] && [ -n "${REAL_RESUME}" ]
 	then
 		case "${REAL_RESUME}" in
@@ -691,6 +713,11 @@ then
 
 		do_resume
 	fi
+
+	if [ -z "${luks_root_started}" ]
+	then
+		start_LUKS_root
+	fi
 fi
 
 run mkdir -p "${NEW_ROOT}"
@@ -1060,7 +1087,8 @@ then
 		losetup /dev/loop0 "${CDROOT_PATH}/${LOOPEXT}${LOOP}"
 		test_success 'Preparing loop filesystem'
 
-		start_LUKS
+		start_LUKS_root
+		start_LUKS_swap
 
 		case ${LOOPTYPE} in
 			normal)
@@ -1302,6 +1330,8 @@ else
 	fi
 fi # if [ "${CDROOT}" = '1' ]
 
+keyctl_keyremove
+
 # Re-run to ensure $NEWROOT/etc/initramfs.mounts was processed at least once
 process_initramfs_mounts
 
diff --git a/defaults/software.sh b/defaults/software.sh
index ec2bacb..0dce9e1 100644
--- a/defaults/software.sh
+++ b/defaults/software.sh
@@ -128,6 +128,13 @@ GKPKG_JSON_C_SRCTAR="${GKPKG_JSON_C_SRCTAR:-${DISTDIR}/json-c-${GKPKG_JSON_C_PV}
 GKPKG_JSON_C_SRCDIR="${GKPKG_JSON_C_SRCDIR:-json-c-${GKPKG_JSON_C_PV}}"
 GKPKG_JSON_C_BINPKG="${GKPKG_JSON_C_BINPKG:-%%CACHE%%/json-c-${GKPKG_JSON_C_PV}-%%ARCH%%.tar.xz}"
 
+GKPKG_KEYUTILS_PN="keyutils"
+GKPKG_KEYUTILS_PV="${GKPKG_KEYUTILS_PV:-1.6.3}"
+GKPKG_KEYUTILS_DEPS=""
+GKPKG_KEYUTILS_SRCTAR="${GKPKG_KEYUTILS_SRCTAR:-${DISTDIR}/keyutils-${GKPKG_KEYUTILS_PV}.tar.gz}"
+GKPKG_KEYUTILS_SRCDIR="${GKPKG_KEYUTILS_SRCDIR:-keyutils-${GKPKG_KEYUTILS_PV}}"
+GKPKG_KEYUTILS_BINPKG="${GKPKG_KEYUTILS_BINPKG:-%%CACHE%%/keyutils-${GKPKG_KEYUTILS_PV}-%%ARCH%%.tar.xz}"
+
 GKPKG_KMOD_PN="kmod"
 GKPKG_KMOD_PV="${GKPKG_KMOD_PV:-VERSION_KMOD}"
 GKPKG_KMOD_DEPS="zlib xz zstd"
diff --git a/doc/genkernel.8.txt b/doc/genkernel.8.txt
index ba8fd0a..a5c0b92 100644
--- a/doc/genkernel.8.txt
+++ b/doc/genkernel.8.txt
@@ -468,6 +468,12 @@ system is able to load multiple initramfs.
     `gpg --symmetric -o /path/to/LUKS-key.gpg /path/to/LUKS-key` .
     After that, re-point the *root_key* argument to the new .gpg file.
 
+*--*[*no-*]*keyctl*::
+    Includes or excludes support for keyutils keyctl.
+    This way a LUKS passphrase can be loaded into a keyring at boot time
+    to unlock multiple devices (root, swap, etc.) without retyping it for each
+    one.
+
 *--*[*no-*]*b2sum*::
     Includes or excludes b2sum in the initramfs.
     When enabled, this will compile coreutils' b2sum for you.
@@ -737,6 +743,24 @@ recognized by the kernel itself.
 *swap_keydev_fstype*=<...>::
     Used filesystem for *swap_keydev*. See *rootfstype* for more details.
 
+*keyctl_keydesc*=<...>::
+    Load a passphrase into a keyring at boot time under the key name provided
+    as an argument to this option.
+    This way multiple devices (root, swap, etc.) can be unlocked without
+    retyping the passphrase for each one.
+    You'll need to add this key name as a keyring token to every LUKS device
+    that it is supposed to unlock - have a look at cryptsetup 'token add'
+    operation.
+
+*keyctl_keykeep*::
+    Don't remove the newly added key before starting the real init.
+    Useful if you want to utilize it to unlock LUKS devices post-initramfs.
+
+*keyctl_keytimeout*=<...>::
+    Enable a timeout (in seconds) for the newly added key.
+    This option normally only makes sense when used together with the
+    *keyctl_keykeep* option.
+
 *crypt_silent*::
     Set this to silent all the output related to the cryptographic
     software,  and in case your encrypted device isn't open with the
diff --git a/gen_cmdline.sh b/gen_cmdline.sh
index e53de69..0cba7d1 100755
--- a/gen_cmdline.sh
+++ b/gen_cmdline.sh
@@ -181,6 +181,8 @@ longusage() {
   echo "	--no-luks		Exclude LUKS support"
   echo "	--gpg			Include GPG-armored LUKS key support"
   echo "	--no-gpg		Exclude GPG-armored LUKS key support"
+  echo "	--keyctl		Include keyctl support for loading LUKS passphrase into a keyring"
+  echo "	--no-keyctl		Exclude keyctl support for loading LUKS passphrase into a keyring"
   echo "	--b2sum			Include b2sum"
   echo "	--no-b2sum		Exclude b2sum"
   echo "	--busybox		Include busybox"
@@ -837,6 +839,10 @@ parse_cmdline() {
 			CMD_GPG=$(parse_optbool "$*")
 			print_info 3 "CMD_GPG: ${CMD_GPG}"
 			;;
+		--keyctl|--no-keyctl)
+			CMD_KEYCTL=$(parse_optbool "$*")
+			print_info 3 "CMD_KEYCTL: ${CMD_KEYCTL}"
+			;;
 		--firmware|--no-firmware)
 			CMD_FIRMWARE=$(parse_optbool "$*")
 			print_info 3 "CMD_FIRMWARE: ${CMD_FIRMWARE}"
diff --git a/gen_determineargs.sh b/gen_determineargs.sh
index 07b2202..ef69414 100755
--- a/gen_determineargs.sh
+++ b/gen_determineargs.sh
@@ -433,6 +433,7 @@ determine_real_args() {
 	set_config_with_override STRING REAL_ROOT                             CMD_REAL_ROOT
 	set_config_with_override BOOL   LUKS                                  CMD_LUKS                                  "no"
 	set_config_with_override BOOL   GPG                                   CMD_GPG                                   "no"
+	set_config_with_override BOOL   KEYCTL                                CMD_KEYCTL                                "no"
 	set_config_with_override BOOL   MDADM                                 CMD_MDADM                                 "no"
 	set_config_with_override STRING MDADM_CONFIG                          CMD_MDADM_CONFIG
 	set_config_with_override BOOL   E2FSPROGS                             CMD_E2FSPROGS                             "no"
@@ -1099,6 +1100,7 @@ determine_real_args() {
 			FEATURES_REQUIRING_BUSYBOX+=( KEYMAP )
 			FEATURES_REQUIRING_BUSYBOX+=( LVM )
 			FEATURES_REQUIRING_BUSYBOX+=( LUKS )
+			FEATURES_REQUIRING_BUSYBOX+=( KEYCTL )
 			FEATURES_REQUIRING_BUSYBOX+=( MDADM )
 			FEATURES_REQUIRING_BUSYBOX+=( MULTIPATH )
 			FEATURES_REQUIRING_BUSYBOX+=( SPLASH )
diff --git a/gen_initramfs.sh b/gen_initramfs.sh
index 0b74f4c..227badd 100755
--- a/gen_initramfs.sh
+++ b/gen_initramfs.sh
@@ -484,6 +484,7 @@ append_base_layout() {
 	isTrue "${ZFS}" && build_parameters+=( --zfs ) || build_parameters+=( --no-zfs )
 	isTrue "${SPLASH}" && build_parameters+=( --splash ) || build_parameters+=( --no-splash )
 	isTrue "${STRACE}" && build_parameters+=( --strace ) || build_parameters+=( --no-strace )
+	isTrue "${KEYCTL}" && build_parameters+=( --keyctl ) || build_parameters+=( --no-keyctl )
 	isTrue "${GPG}" && build_parameters+=( --gpg ) || build_parameters+=( --no-gpg )
 	isTrue "${LUKS}" && build_parameters+=( --luks ) || build_parameters+=( --no-luks )
 	isTrue "${FIRMWARE}" && build_parameters+=( --firmware ) || build_parameters+=( --no-firmware )
@@ -901,6 +902,33 @@ append_iscsi() {
 	fi
 }
 
+append_keyutils() {
+	local PN=keyutils
+	local TDIR="${TEMP}/initramfs-${PN}-temp"
+	if [ -d "${TDIR}" ]
+	then
+		rm -r "${TDIR}" || gen_die "Failed to clean out existing '${TDIR}'!"
+	fi
+
+	populate_binpkg ${PN}
+
+	mkdir "${TDIR}" || gen_die "Failed to create '${TDIR}'!"
+
+	unpack "$(get_gkpkg_binpkg "${PN}")" "${TDIR}"
+
+	cd "${TDIR}" || gen_die "Failed to chdir to '${TDIR}'!"
+
+	log_future_cpio_content
+	find . -print0 | "${CPIO_COMMAND}" ${CPIO_ARGS} --append -F "${CPIO_ARCHIVE}" \
+		|| gen_die "Failed to append ${PN} to cpio!"
+
+	cd "${TEMP}" || die "Failed to chdir to '${TEMP}'!"
+	if isTrue "${CLEANUP}"
+	then
+		rm -rf "${TDIR}"
+	fi
+}
+
 append_lvm() {
 	local PN=lvm
 	local TDIR="${TEMP}/initramfs-${PN}-temp"
@@ -2050,6 +2078,7 @@ create_initramfs() {
 	append_data 'e2fsprogs' "${E2FSPROGS}"
 	append_data 'gpg' "${GPG}"
 	append_data 'iscsi' "${ISCSI}"
+	append_data 'keyutils' "${KEYCTL}"
 	append_data 'luks' "${LUKS}"
 	append_data 'lvm' "${LVM}"
 	append_data 'bcache' "${BCACHE}"
diff --git a/genkernel.conf b/genkernel.conf
index 7d10496..7045e18 100644
--- a/genkernel.conf
+++ b/genkernel.conf
@@ -80,6 +80,9 @@ NOCOLOR="false"
 # Add GnuPG support
 #GPG="no"
 
+# Add keyctl support for loading LUKS passphrase into a keyring
+#KEYCTL="no"
+
 # Add in early microcode support: this sets the kernel options for early microcode loading
 # Possible values: empty/"no", "all", "intel", "amd"
 #MICROCODE="all"
diff --git a/gkbuilds/keyutils.gkbuild b/gkbuilds/keyutils.gkbuild
new file mode 100644
index 0000000..dc232be
--- /dev/null
+++ b/gkbuilds/keyutils.gkbuild
@@ -0,0 +1,27 @@
+# Copyright 1999-2019 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+src_prepare() {
+	default
+
+	sed -i \
+		-e "1iRPATH = -static" \
+		-e 's:-Werror::' \
+		-e '/^NO_SOLIB/d' \
+		Makefile || die
+}
+
+src_compile() {
+	export NO_SOLIB=1
+
+	gkmake keyctl
+}
+
+src_install() {
+	mkdir "${D}"/bin || die "Failed to create '${D}/bin'!"
+	cp -a keyctl "${D}"/bin/ \
+		|| die "Failed to copy '${S}/keyctl'!"
+
+	"${STRIP}" --strip-all "${D}"/bin/keyctl \
+		|| die "Failed to strip keyctl!"
+}