A Linux kernel security update has been released for Ubuntu 18.04 LTS and 16.04 LTS.

USN-4318-1: Linux kernel vulnerabilities

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Ubuntu Security Notice USN-4318-1
April 06, 2020

linux, linux-hwe vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux: Linux kernel
- linux-hwe: Linux hardware enablement (HWE) kernel

Details:

Al Viro discovered that the vfs layer in the Linux kernel contained a use-
after-free vulnerability. A local attacker could use this to cause a denial
of service (system crash) or possibly expose sensitive information (kernel
memory). (CVE-2020-8428)

Gustavo Romero and Paul Mackerras discovered that the KVM implementation in
the Linux kernel for PowerPC processors did not properly keep guest state
separate from host state. A local attacker in a KVM guest could use this to
cause a denial of service (host system crash). (CVE-2020-8834)

Shijie Luo discovered that the ext4 file system implementation in the Linux
kernel did not properly check for a too-large journal size. An attacker
could use this to construct a malicious ext4 image that, when mounted,
could cause a denial of service (soft lockup). (CVE-2020-8992)

Update instructions:

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

Ubuntu 18.04 LTS:
linux-image-4.15.0-96-generic 4.15.0-96.97
linux-image-4.15.0-96-generic-lpae 4.15.0-96.97
linux-image-4.15.0-96-lowlatency 4.15.0-96.97
linux-image-generic 4.15.0.96.87
linux-image-generic-lpae 4.15.0.96.87
linux-image-lowlatency 4.15.0.96.87
linux-image-powerpc-e500mc 4.15.0.96.87
linux-image-powerpc-smp 4.15.0.96.87
linux-image-powerpc64-emb 4.15.0.96.87
linux-image-powerpc64-smp 4.15.0.96.87
linux-image-virtual 4.15.0.96.87

Ubuntu 16.04 LTS:
linux-image-4.15.0-96-generic 4.15.0-96.97~16.04.1
linux-image-4.15.0-96-generic-lpae 4.15.0-96.97~16.04.1
linux-image-4.15.0-96-lowlatency 4.15.0-96.97~16.04.1
linux-image-generic-hwe-16.04 4.15.0.96.104
linux-image-generic-lpae-hwe-16.04 4.15.0.96.104
linux-image-lowlatency-hwe-16.04 4.15.0.96.104
linux-image-oem 4.15.0.96.104
linux-image-virtual-hwe-16.04 4.15.0.96.104

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/4318-1
CVE-2020-8428, CVE-2020-8834, CVE-2020-8992

Package Information:
  https://launchpad.net/ubuntu/+source/linux/4.15.0-96.97
  https://launchpad.net/ubuntu/+source/linux-hwe/4.15.0-96.97~16.04.1