#!/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() {
tmp=$(mktemp)
sbattach --detach $tmp $1 >/dev/null 2>/dev/null # that's ugly...
test "$(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 $1 >/dev/null 2>/dev/null
result=$?
if [ $result -eq 0 ]; then
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
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