ubuntu-cpc: secure esp mountpoint (LP: #1881006)

Change mount option for ubuntu-cpc images from "defaults" to
"umask=0077". ESP partitions might contain sensitive data and
non-root users shouldn't have read access on it.

debian/changelog

@@ -1,3 +1,12 @@
+livecd-rootfs (2.408.68) UNRELEASED; urgency=medium
+
+  * ubuntu-cpc: secure esp mountpoint (LP: #1881006)
+    Change mount option for ubuntu-cpc images from "defaults" to "umask=0077"
+    ESP partitions might contain sensitive data and non-root users shouldn't
+    have read access on it.
+
+ -- Gauthier Jolly <gauthier.jolly@canonical.com>  Wed, 17 Mar 2021 16:55:37 +0000
+
 livecd-rootfs (2.408.67) xenial; urgency=medium
 
   * Revert "esp: install grub in ubuntu bootloader id path, instead of

live-build/ubuntu-cpc/hooks.d/base/disk-image-uefi.binary

@@ -49,7 +49,7 @@ create_and_mount_uefi_partition() {
     mount "${uefi_dev}" "$mountpoint"/boot/efi
 
     cat << EOF >> "mountpoint/etc/fstab"
-LABEL=UEFI	/boot/efi	vfat	defaults	0 1
+LABEL=UEFI	/boot/efi	vfat	umask=0077	0 1
 EOF
 }