From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Michael Chang via Grub-devel <grub-devel@gnu.org>

Date: Fri, 3 Dec 2021 16:13:28 +0800

Subject: [PATCH] grub-mkconfig: restore umask for grub.cfg

Since commit:

  ab2e53c8a grub-mkconfig: Honor a symlink when generating configuration

by grub-mkconfig

has inadvertently discarded umask for creating grub.cfg in the process

of grub-mkconfig. The resulting wrong permission (0644) would allow

unprivileged users to read grub's configuration file content. This

presents a low confidentiality risk as grub.cfg may contain non-secured

plain-text passwords.

This patch restores the missing umask and set the file mode of creation

to 0600 preventing unprivileged access.

Fixes: CVE-2021-3981

Signed-off-by: Michael Chang <mchang@suse.com>

---

 util/grub-mkconfig.in | 2 ++

 1 file changed, 2 insertions(+)

diff --git a/util/grub-mkconfig.in b/util/grub-mkconfig.in

index f55339a3f6..520a672cd2 100644

--- a/util/grub-mkconfig.in

+++ b/util/grub-mkconfig.in

@@ -311,7 +311,9 @@ and /etc/grub.d/* files or please file a bug report with

     exit 1

   else

     # none of the children aborted with error, install the new grub.cfg

+    oldumask=$(umask); umask 077

     cat ${grub_cfg}.new > ${grub_cfg}

+    umask $oldumask

     rm -f ${grub_cfg}.new

   fi

 fi