A Linux kernel security update has been released for Ubuntu Linux 14.04 ESM and 16.04 LTS.

USN-4876-1: Linux kernel vulnerabilities

==========================================================================
Ubuntu Security Notice USN-4876-1
March 16, 2021

linux, linux-aws, linux-kvm, linux-lts-xenial, linux-raspi2,
linux-snapdragon vulnerabilities
==========================================================================

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

- Ubuntu 16.04 LTS
- Ubuntu 14.04 ESM

Summary:

Several security issues were fixed in the Linux kernel.

Software Description:
- linux: Linux kernel
- linux-aws: Linux kernel for Amazon Web Services (AWS) systems
- linux-kvm: Linux kernel for cloud environments
- linux-raspi2: Linux kernel for Raspberry Pi (V8) systems
- linux-snapdragon: Linux kernel for Qualcomm Snapdragon processors
- linux-lts-xenial: Linux hardware enablement kernel from Xenial for Trusty

Details:

Olivier Benjamin and Pawel Wieczorkiewicz discovered a race condition the
Xen paravirt block backend in the Linux kernel, leading to a use-after-free
vulnerability. An attacker in a guest VM could use this to cause a denial
of service in the host OS. (CVE-2020-29569)

It was discovered that the Marvell WiFi-Ex device driver in the Linux
kernel did not properly validate ad-hoc SSIDs. A local attacker could use
this to cause a denial of service (system crash) or possibly execute
arbitrary code. (CVE-2020-36158)

吴异 discovered that the NFS implementation in the Linux kernel did not
properly prevent access outside of an NFS export that is a subdirectory of
a file system. An attacker could possibly use this to bypass NFS access
restrictions. (CVE-2021-3178)

Update instructions:

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

Ubuntu 16.04 LTS:
linux-image-4.4.0-1089-kvm 4.4.0-1089.98
linux-image-4.4.0-1123-aws 4.4.0-1123.137
linux-image-4.4.0-1147-raspi2 4.4.0-1147.157
linux-image-4.4.0-1151-snapdragon 4.4.0-1151.161
linux-image-4.4.0-204-generic 4.4.0-204.236
linux-image-4.4.0-204-generic-lpae 4.4.0-204.236
linux-image-4.4.0-204-lowlatency 4.4.0-204.236
linux-image-4.4.0-204-powerpc-e500mc 4.4.0-204.236
linux-image-4.4.0-204-powerpc-smp 4.4.0-204.236
linux-image-4.4.0-204-powerpc64-emb 4.4.0-204.236
linux-image-4.4.0-204-powerpc64-smp 4.4.0-204.236
linux-image-aws 4.4.0.1123.128
linux-image-generic 4.4.0.204.210
linux-image-generic-lpae 4.4.0.204.210
linux-image-kvm 4.4.0.1089.87
linux-image-lowlatency 4.4.0.204.210
linux-image-powerpc-e500mc 4.4.0.204.210
linux-image-powerpc-smp 4.4.0.204.210
linux-image-powerpc64-emb 4.4.0.204.210
linux-image-powerpc64-smp 4.4.0.204.210
linux-image-raspi2 4.4.0.1147.147
linux-image-snapdragon 4.4.0.1151.143
linux-image-virtual 4.4.0.204.210

Ubuntu 14.04 ESM:
linux-image-4.4.0-1087-aws 4.4.0-1087.91
linux-image-4.4.0-204-generic 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-generic-lpae 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-lowlatency 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-powerpc-e500mc 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-powerpc-smp 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-powerpc64-emb 4.4.0-204.236~14.04.1
linux-image-4.4.0-204-powerpc64-smp 4.4.0-204.236~14.04.1
linux-image-aws 4.4.0.1087.84
linux-image-generic-lpae-lts-xenial 4.4.0.204.178
linux-image-generic-lts-xenial 4.4.0.204.178
linux-image-lowlatency-lts-xenial 4.4.0.204.178
linux-image-powerpc-e500mc-lts-xenial 4.4.0.204.178
linux-image-powerpc-smp-lts-xenial 4.4.0.204.178
linux-image-powerpc64-emb-lts-xenial 4.4.0.204.178
linux-image-powerpc64-smp-lts-xenial 4.4.0.204.178
linux-image-virtual-lts-xenial 4.4.0.204.178

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://ubuntu.com/security/notices/USN-4876-1
CVE-2020-29569, CVE-2020-36158, CVE-2021-3178

Package Information:
  https://launchpad.net/ubuntu/+source/linux/4.4.0-204.236
  https://launchpad.net/ubuntu/+source/linux-aws/4.4.0-1123.137
  https://launchpad.net/ubuntu/+source/linux-kvm/4.4.0-1089.98
  https://launchpad.net/ubuntu/+source/linux-raspi2/4.4.0-1147.157
  https://launchpad.net/ubuntu/+source/linux-snapdragon/4.4.0-1151.161