=========================================================================
Ubuntu Security Notice USN-4367-2
May 28, 2020

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

- Ubuntu 20.04 LTS

Summary:

USN-4367-1 introduced a regression in the Linux kernel.

Software Description:
- linux: Linux kernel

Details:

USN-4367-1 fixed vulnerabilities in the 5.4 Linux kernel. Unfortunately,
that update introduced a regression in overlayfs. This update corrects
the problem.

We apologize for the inconvenience.

Original advisory details:

 It was discovered that the btrfs implementation in the Linux kernel did not
 properly detect that a block was marked dirty in some situations. An
 attacker could use this to specially craft a file system image that, when
 unmounted, could cause a denial of service (system crash). (CVE-2019-19377)

 It was discovered that the linux kernel did not properly validate certain
 mount options to the tmpfs virtual memory file system. A local attacker
 with the ability to specify mount options could use this to cause a denial
 of service (system crash). (CVE-2020-11565)

 It was discovered that the block layer in the Linux kernel contained a race
 condition leading to a use-after-free vulnerability. A local attacker could
 possibly use this to cause a denial of service (system crash) or execute
 arbitrary code. (CVE-2020-12657)

Update instructions:

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

Ubuntu 20.04 LTS:
  linux-image-5.4.0-33-generic    5.4.0-33.37
  linux-image-5.4.0-33-generic-lpae  5.4.0-33.37
  linux-image-5.4.0-33-lowlatency  5.4.0-33.37
  linux-image-generic             5.4.0.33.38
  linux-image-generic-lpae        5.4.0.33.38
  linux-image-lowlatency          5.4.0.33.38
  linux-image-oem                 5.4.0.33.38
  linux-image-oem-osp1            5.4.0.33.38
  linux-image-virtual             5.4.0.33.38

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/4367-2
  https://usn.ubuntu.com/4367-1
  https://launchpad.net/bugs/1879690

Package Information:
  https://launchpad.net/ubuntu/+source/linux/5.4.0-33.37