A Linux kernel regression update has been released for both Ubuntu 20.04 LTS and 20.10 to address a regression introduced by the USN-4576-1 update.

USN-4712-1: Linux kernel regression

=========================================================================
Ubuntu Security Notice USN-4712-1
January 28, 2021

linux regression
=========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.10
- Ubuntu 20.04 LTS

Summary:

USN-4576-1 introduced a regression in the Linux kernel.

Software Description:
- linux: Linux kernel

Details:

USN-4576-1 fixed a vulnerability in the overlay file system
implementation in the Linux kernel. Unfortunately, that fix introduced
a regression that could incorrectly deny access to overlay files in
some situations. This update fixes the problem.

We apologize for the inconvenience.

Original vulnerability details:

Giuseppe Scrivano discovered that the overlay file system in the Linux
kernel did not properly perform permission checks in some situations. A
local attacker could possibly use this to bypass intended restrictions and
gain read access to restricted files.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.10:
linux-image-5.8.0-41-generic 5.8.0-41.46
linux-image-5.8.0-41-generic-64k 5.8.0-41.46
linux-image-5.8.0-41-generic-lpae 5.8.0-41.46
linux-image-5.8.0-41-lowlatency 5.8.0-41.46
linux-image-generic 5.8.0.41.45
linux-image-generic-64k 5.8.0.41.45
linux-image-generic-lpae 5.8.0.41.45
linux-image-lowlatency 5.8.0.41.45
linux-image-oem-20.04 5.8.0.41.45
linux-image-virtual 5.8.0.41.45

Ubuntu 20.04 LTS:
linux-image-5.4.0-65-generic 5.4.0-65.73
linux-image-5.4.0-65-generic-lpae 5.4.0-65.73
linux-image-5.4.0-65-lowlatency 5.4.0-65.73
linux-image-generic 5.4.0.65.68
linux-image-generic-lpae 5.4.0.65.68
linux-image-lowlatency 5.4.0.65.68
linux-image-oem 5.4.0.65.68
linux-image-oem-osp1 5.4.0.65.68
linux-image-virtual 5.4.0.65.68

After a standard system update you need to reboot your computer to make
all the necessary changes.

ATTENTION: Due to an unavoidable ABI change the kernel updates have
been given a new version number, which requires you to recompile and
reinstall all third party kernel modules you might have installed.
Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual,
linux-powerpc), a standard system upgrade will automatically perform
this as well.

References:
https://usn.ubuntu.com/4712-1
https://bugs.launchpad.net/bugs/1900141, https://usn.ubuntu.com/usn/usn-4576-1

Package Information:
https://launchpad.net/ubuntu/+source/linux/5.8.0-41.46
https://launchpad.net/ubuntu/+source/linux/5.4.0-65.73