A Linux kernel regression update has been released for Ubuntu 14.04 ESM, 16.04 LTS, 18.04 LTS, and 20.04 LTS.

USN-4916-2: Linux kernel regression

=========================================================================
Ubuntu Security Notice USN-4916-2
April 21, 2021

linux, linux-aws, linux-gke-5.3, linux-hwe, linux-kvm, linux-lts-xenial,
linux-oem-5.6, linux-raspi2-5.3, linux-snapdragon regression
=========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 ESM

Summary:

USN-4916-1 introduced a regression in the Linux kernel.

Software Description:
- linux-oem-5.6: Linux kernel for OEM systems
- linux-gke-5.3: Linux kernel for Google Container Engine (GKE) systems
- linux-hwe: Linux hardware enablement (HWE) kernel
- linux-raspi2-5.3: Linux kernel for Raspberry Pi (V8) systems
- linux: Linux kernel
- linux-aws: Linux kernel for Amazon Web Services (AWS) systems
- linux-kvm: Linux kernel for cloud environments
- linux-snapdragon: Linux kernel for Qualcomm Snapdragon processors
- linux-lts-xenial: Linux hardware enablement kernel from Xenial for Trusty

Details:

USN-4916-1 fixed vulnerabilities in the Linux kernel. Unfortunately,
the fix for CVE-2021-3493 introduced a memory leak in some situations.
This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

It was discovered that the overlayfs implementation in the Linux kernel did
not properly validate the application of file system capabilities with
respect to user namespaces. A local attacker could use this to gain
elevated privileges. (CVE-2021-3493)

Piotr Krysiuk discovered that the BPF JIT compiler for x86 in the Linux
kernel did not properly validate computation of branch displacements in
some situations. A local attacker could use this to cause a denial of
service (system crash) or possibly execute arbitrary code. (CVE-2021-29154)

Update instructions:

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

Ubuntu 20.04 LTS:
linux-image-5.6.0-1055-oem 5.6.0-1055.59
linux-image-oem-20.04 5.6.0.1055.51

Ubuntu 18.04 LTS:
linux-image-5.3.0-1040-raspi2 5.3.0-1040.42
linux-image-5.3.0-1043-gke 5.3.0-1043.46
linux-image-5.3.0-74-generic 5.3.0-74.70
linux-image-5.3.0-74-lowlatency 5.3.0-74.70
linux-image-gke-5.3 5.3.0.1043.26
linux-image-gkeop-5.3 5.3.0.74.131
linux-image-raspi2-hwe-18.04 5.3.0.1040.29

Ubuntu 16.04 LTS:
linux-image-4.4.0-1093-kvm 4.4.0-1093.102
linux-image-4.4.0-1128-aws 4.4.0-1128.142
linux-image-4.4.0-1156-snapdragon 4.4.0-1156.166
linux-image-4.4.0-210-generic 4.4.0-210.242
linux-image-4.4.0-210-generic-lpae 4.4.0-210.242
linux-image-4.4.0-210-lowlatency 4.4.0-210.242
linux-image-4.4.0-210-powerpc-e500mc 4.4.0-210.242
linux-image-4.4.0-210-powerpc-smp 4.4.0-210.242
linux-image-4.4.0-210-powerpc64-emb 4.4.0-210.242
linux-image-4.4.0-210-powerpc64-smp 4.4.0-210.242
linux-image-aws 4.4.0.1128.133
linux-image-generic 4.4.0.210.216
linux-image-generic-lpae 4.4.0.210.216
linux-image-kvm 4.4.0.1093.91
linux-image-lowlatency 4.4.0.210.216
linux-image-powerpc-e500mc 4.4.0.210.216
linux-image-powerpc-smp 4.4.0.210.216
linux-image-powerpc64-emb 4.4.0.210.216
linux-image-powerpc64-smp 4.4.0.210.216
linux-image-snapdragon 4.4.0.1156.148
linux-image-virtual 4.4.0.210.216

Ubuntu 14.04 ESM:
linux-image-4.4.0-1092-aws 4.4.0-1092.96
linux-image-4.4.0-210-generic 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-generic-lpae 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-lowlatency 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-powerpc-e500mc 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-powerpc-smp 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-powerpc64-emb 4.4.0-210.242~14.04.1
linux-image-4.4.0-210-powerpc64-smp 4.4.0-210.242~14.04.1
linux-image-aws 4.4.0.1092.89
linux-image-generic-lpae-lts-xenial 4.4.0.210.183
linux-image-generic-lts-xenial 4.4.0.210.183
linux-image-lowlatency-lts-xenial 4.4.0.210.183
linux-image-powerpc-e500mc-lts-xenial 4.4.0.210.183
linux-image-powerpc-smp-lts-xenial 4.4.0.210.183
linux-image-powerpc64-emb-lts-xenial 4.4.0.210.183
linux-image-powerpc64-smp-lts-xenial 4.4.0.210.183
linux-image-virtual-lts-xenial 4.4.0.210.183

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-4916-2
  https://ubuntu.com/security/notices/USN-4916-1
  https://launchpad.net/bugs/1924611

Package Information:
  https://launchpad.net/ubuntu/+source/linux-oem-5.6/5.6.0-1055.59
  https://launchpad.net/ubuntu/+source/linux-gke-5.3/5.3.0-1043.46
  https://launchpad.net/ubuntu/+source/linux-hwe/5.3.0-74.70
  https://launchpad.net/ubuntu/+source/linux-raspi2-5.3/5.3.0-1040.42
  https://launchpad.net/ubuntu/+source/linux/4.4.0-210.242
  https://launchpad.net/ubuntu/+source/linux-aws/4.4.0-1128.142
  https://launchpad.net/ubuntu/+source/linux-kvm/4.4.0-1093.102
  https://launchpad.net/ubuntu/+source/linux-snapdragon/4.4.0-1156.166