USN-4712-1: Linux kernel regression

2 February 2021

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

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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.

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Ubuntu Pro provides ten-year security coverage to 25,000+ packages in Main and Universe repositories, and it is free for up to five machines.

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Update instructions

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

Ubuntu 20.10
Ubuntu 20.04
Ubuntu 18.04

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

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