=========================================================================
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