OwlCyberSecurity - MANAGER

Edit File: grub-check-signatures

#!/bin/sh

set -e

. /usr/share/debconf/confmodule

# Check if we are on an EFI system
efivars=/sys/firmware/efi/efivars
secureboot_var=SecureBoot-8be4df61-93ca-11d2-aa0d-00e098032b8c
moksbstatert_var=MokSBStateRT-605dab50-e046-4300-abb6-3dd810dd8b23
tmpdir=$(mktemp -d)

on_secure_boot() {
	# Validate any queued actions before we go try to do them.
	local moksbstatert=0

if ! [ -d $efivars ]; then
		return 1
	fi

if ! [ -f $efivars/$secureboot_var ] \
		|| [ "$(od -An -t u1 $efivars/$secureboot_var | awk '{ print $NF }')" -ne 1 ]
	then
		return 1
	fi

if [ -f /proc/sys/kernel/moksbstate_disabled ]; then
		moksbstatert=$(cat /proc/sys/kernel/moksbstate_disabled 2>/dev/null || echo 0)
	elif [ -f $efivars/$moksbstatert_var ]; then
		# MokSBStateRT set to 1 means validation is disabled
		moksbstatert=$(od -An -t u1 $efivars/$moksbstatert_var | \
					   awk '{ print $NF; }')
	fi

if [ $moksbstatert -eq 1 ]; then
		return 1
	fi

return 0
}

# Retrieve the keys we do trust from PK, DB, KEK, and MokList.
extract_known_keys() {
	# Make the Canonical CA cert available for validation too; in case
	# MokListRT is empty due to a bug.
	cp /usr/share/grub/canonical-uefi-ca.crt $tmpdir

# Extract known UEFI certs from firmware variables
	( cd $tmpdir; \
		mokutil --export --db >/dev/null 2>/dev/null; \
		mokutil --export --mok >/dev/null 2>/dev/null; )
	find $tmpdir -name "*.der" -exec openssl x509 -inform der -in {} -outform pem -out {}.crt  \;
}

# Check if a given kernel image is signed
is_signed() {
	kernel=$1
	tmp=$(mktemp)
	kernel_tmp=$(mktemp)
	if zcat $kernel > $kernel_tmp 2>/dev/null; then
		kernel=$kernel_tmp
	fi
	sbattach --detach $tmp $kernel >/dev/null 2>/dev/null 	# that's ugly...
	test "$(wc -c < $tmp)" -ge 16	# Just _some_ minimum size
	result=$?
	if [ $result -eq 0 ]; then
		sig_subject=$(openssl pkcs7 -inform der -in $tmp -print_certs | openssl x509 -noout -text | grep Subject: )
	fi
	rm $tmp
	if [ $result -eq 0 ]; then
		for crtfile in $tmpdir/*.crt; do
			sbverify --cert $crtfile $kernel >/dev/null 2>/dev/null
			result=$?
			if [ $result -eq 0 ]; then
				rm "$kernel_tmp"
				return $result;
			fi
		done
		echo "$1 is signed, but using an unknown key:" >&2
		echo "$sig_subject" >&2
	else
		echo "$1 is unsigned." >&2
	fi
	rm "$kernel_tmp"
	return $result
}

# Check that our current kernel and every newer one is signed
find_unsigned() {
	uname_r="$(uname -r)"
	for kernel in $(ls -1 /boot/vmlinuz-* | sort -V -r); do
		# no kernels :(
		if [ "$kernel" = "/boot/vmlinuz-*" ]; then
			break
		fi
		this_uname_r="$(echo "$kernel" | sed -r 's#^/boot/vmlinuz-(.*)#\1#; s#\.efi\.signed$##')"
		if dpkg --compare-versions "$this_uname_r" lt "$uname_r"; then
			continue
		fi
		if [ -e "$kernel.efi.signed" ]; then
			continue
		fi
		if ! is_signed $kernel; then
			echo "$this_uname_r"
		fi
	done
}

# Only reached from show_warning
error() {
	echo "E: Your kernels are not signed with a key known to your firmware. This system will fail to boot in a Secure Boot environment." >&2
	exit 1
}

# Either shows a debconf note or prints an error with error() above if
# that fails
show_warning() {
	# kernels should be an indented list of one version per line
	escaped="$(printf "%s" "$unsigned" | sed "s#^#     #" | debconf-escape -e )"
	db_capb escape
	db_settitle grub2/unsigned_kernels_title || error
	db_fset grub2/unsigned_kernels seen 0 || error
	db_subst grub2/unsigned_kernels unsigned_versions "$escaped" || error
	db_input critical grub2/unsigned_kernels || error
	db_go || error
	error
}

if on_secure_boot; then
	extract_known_keys
	unsigned="$(find_unsigned)"
	if [ -n "$unsigned" ]; then
		show_warning "$unsigned"
	fi
	rm -rf "$tmpdir"
fi