base-files: introduce sysupgrade signature chain verification

Verify ucert signature chains in sysupgrade images in case ucert is
installed and $CHECK_IMAGE_SIGNARURE = 1.
Also make sure ucert host binary is present and generate a self-signed
ucert in case $TOPDIR/key-build.ucert is missing.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/base-files/Makefile

@@ -12,11 +12,11 @@ include $(INCLUDE_DIR)/version.mk
 include $(INCLUDE_DIR)/feeds.mk
 
 PKG_NAME:=base-files
-PKG_RELEASE:=194
+PKG_RELEASE:=195
 PKG_FLAGS:=nonshared
 
 PKG_FILE_DEPENDS:=$(PLATFORM_DIR)/ $(GENERIC_PLATFORM_DIR)/base-files/
-PKG_BUILD_DEPENDS:=usign/host
+PKG_BUILD_DEPENDS:=usign/host ucert/host
 PKG_LICENSE:=GPL-2.0
 
 # Extend depends from version.mk
@@ -102,6 +102,9 @@ ifdef CONFIG_SIGNED_PACKAGES
 	[ -s $(BUILD_KEY) -a -s $(BUILD_KEY).pub ] || \
 		$(STAGING_DIR_HOST)/bin/usign -G -s $(BUILD_KEY) -p $(BUILD_KEY).pub -c "Local build key"
 
+	[ -s $(BUILD_KEY).ucert ] || \
+		$(STAGING_DIR_HOST)/bin/ucert -I -c $(BUILD_KEY).ucert -p $(BUILD_KEY).pub -s $(BUILD_KEY)
+
   endef
 
   define Package/base-files/install-key

package/base-files/files/lib/upgrade/fwtool.sh

@@ -1,3 +1,28 @@
+fwtool_check_signature() {
+	[ $# -gt 1 ] && return 1
+
+	[ ! -x /usr/bin/ucert ] && {
+		if [ "$REQUIRE_IMAGE_SIGNATURE" = 1 ]; then
+			return 1
+		else
+			return 0
+		fi
+	}
+
+	if ! fwtool -q -t -s /tmp/sysupgrade.ucert "$1"; then
+		echo "Image signature not found"
+		[ "$REQUIRE_IMAGE_SIGNATURE" = 1 -a "$FORCE" != 1 ] && {
+			echo "Use sysupgrade -F to override this check when downgrading or flashing to vendor firmware"
+		}
+		[ "$REQUIRE_IMAGE_SIGNATURE" = 1 ] && return 1
+		return 0
+	fi
+
+	ucert -V -m "$1" -c "/tmp/sysupgrade.ucert" -P /etc/opkg/keys
+
+	return $?
+}
+
 fwtool_check_image() {
 	[ $# -gt 1 ] && return 1
 

package/base-files/files/sbin/sysupgrade

@@ -136,7 +136,7 @@ add_overlayfiles() {
 }
 
 # hooks
-sysupgrade_image_check="fwtool_check_image platform_check_image"
+sysupgrade_image_check="fwtool_check_signature fwtool_check_image platform_check_image"
 
 if [ $SAVE_OVERLAY = 1 ]; then
 	[ ! -d /overlay/upper/etc ] && {