A Linux kernel security update has been released for Ubuntu Linux 18.04 LTS and 20.04 LTS.

USN-4909-1: Linux kernel vulnerabilities

==========================================================================
Ubuntu Security Notice USN-4909-1
April 13, 2021

linux, linux-aws, linux-aws-5.4, linux-azure, linux-azure-5.4, linux-gcp,
linux-gcp-5.4, linux-gke-5.4, linux-gkeop, linux-gkeop-5.4, linux-hwe-5.4,
linux-kvm, linux-oracle, linux-oracle-5.4, linux-raspi, linux-raspi-5.4
vulnerabilities
==========================================================================

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

- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

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-azure: Linux kernel for Microsoft Azure Cloud systems
- linux-gcp: Linux kernel for Google Cloud Platform (GCP) systems
- linux-gkeop: Linux kernel for Google Container Engine (GKE) systems
- linux-kvm: Linux kernel for cloud environments
- linux-oracle: Linux kernel for Oracle Cloud systems
- linux-raspi: Linux kernel for Raspberry Pi (V8) systems
- linux-aws-5.4: Linux kernel for Amazon Web Services (AWS) systems
- linux-azure-5.4: Linux kernel for Microsoft Azure cloud systems
- linux-gcp-5.4: Linux kernel for Google Cloud Platform (GCP) systems
- linux-gke-5.4: Linux kernel for Google Container Engine (GKE) systems
- linux-gkeop-5.4: Linux kernel for Google Container Engine (GKE) systems
- linux-hwe-5.4: Linux hardware enablement (HWE) kernel
- linux-oracle-5.4: Linux kernel for Oracle Cloud systems
- linux-raspi-5.4: Linux kernel for Raspberry Pi (V8) systems

Details:

Loris Reiff discovered that the BPF implementation in the Linux kernel did
not properly validate attributes in the getsockopt BPF hook. A local
attacker could possibly use this to cause a denial of service (system
crash). (CVE-2021-20194)

Olivier Benjamin, Norbert Manthey, Martin Mazein, and Jan H. Schönherr
discovered that the Xen paravirtualization backend in the Linux kernel did
not properly propagate errors to frontend drivers in some situations. An
attacker in a guest VM could possibly use this to cause a denial of service
(host domain crash). (CVE-2021-26930)

Jan Beulich discovered that multiple Xen backends in the Linux kernel did
not properly handle certain error conditions under paravirtualization. An
attacker in a guest VM could possibly use this to cause a denial of service
(host domain crash). (CVE-2021-26931)

It was discovered that the network block device (nbd) driver in the Linux
kernel contained a use-after-free vulnerability during device setup. A
local attacker with access to the nbd device could use this to cause a
denial of service (system crash) or possibly execute arbitrary code.
(CVE-2021-3348)

Update instructions:

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

Ubuntu 20.04 LTS:
linux-image-5.4.0-1013-gkeop 5.4.0-1013.14
linux-image-5.4.0-1033-raspi 5.4.0-1033.36
linux-image-5.4.0-1037-kvm 5.4.0-1037.38
linux-image-5.4.0-1041-gcp 5.4.0-1041.44
linux-image-5.4.0-1042-oracle 5.4.0-1042.45
linux-image-5.4.0-1043-aws 5.4.0-1043.45
linux-image-5.4.0-1044-azure 5.4.0-1044.46
linux-image-5.4.0-71-generic 5.4.0-71.79
linux-image-5.4.0-71-generic-lpae 5.4.0-71.79
linux-image-5.4.0-71-lowlatency 5.4.0-71.79
linux-image-aws 5.4.0.1043.44
linux-image-azure 5.4.0.1044.42
linux-image-gcp 5.4.0.1041.50
linux-image-generic 5.4.0.71.74
linux-image-generic-lpae 5.4.0.71.74
linux-image-gkeop 5.4.0.1013.16
linux-image-gkeop-5.4 5.4.0.1013.16
linux-image-kvm 5.4.0.1037.35
linux-image-lowlatency 5.4.0.71.74
linux-image-oem 5.4.0.71.74
linux-image-oem-osp1 5.4.0.71.74
linux-image-oracle 5.4.0.1042.39
linux-image-raspi 5.4.0.1033.68
linux-image-raspi2 5.4.0.1033.68
linux-image-virtual 5.4.0.71.74

Ubuntu 18.04 LTS:
linux-image-5.4.0-1013-gkeop 5.4.0-1013.14~18.04.1
linux-image-5.4.0-1033-raspi 5.4.0-1033.36~18.04.1
linux-image-5.4.0-1040-gke 5.4.0-1040.42~18.04.1
linux-image-5.4.0-1041-gcp 5.4.0-1041.44~18.04.1
linux-image-5.4.0-1042-oracle 5.4.0-1042.45~18.04.1
linux-image-5.4.0-1043-aws 5.4.0-1043.45~18.04.1
linux-image-5.4.0-1044-azure 5.4.0-1044.46~18.04.1
linux-image-5.4.0-71-generic 5.4.0-71.79~18.04.1
linux-image-5.4.0-71-generic-lpae 5.4.0-71.79~18.04.1
linux-image-5.4.0-71-lowlatency 5.4.0-71.79~18.04.1
linux-image-aws 5.4.0.1043.26
linux-image-azure 5.4.0.1044.24
linux-image-gcp 5.4.0.1041.28
linux-image-generic-hwe-18.04 5.4.0.71.79~18.04.64
linux-image-generic-lpae-hwe-18.04 5.4.0.71.79~18.04.64
linux-image-gke-5.4 5.4.0.1040.42~18.04.7
linux-image-gkeop-5.4 5.4.0.1013.14~18.04.14
linux-image-lowlatency-hwe-18.04 5.4.0.71.79~18.04.64
linux-image-oem 5.4.0.71.79~18.04.64
linux-image-oem-osp1 5.4.0.71.79~18.04.64
linux-image-oracle 5.4.0.1042.45~18.04.24
linux-image-raspi-hwe-18.04 5.4.0.1033.35
linux-image-snapdragon-hwe-18.04 5.4.0.71.79~18.04.64
linux-image-virtual-hwe-18.04 5.4.0.71.79~18.04.64

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-4909-1
CVE-2021-20194, CVE-2021-26930, CVE-2021-26931, CVE-2021-3348

Package Information:
  https://launchpad.net/ubuntu/+source/linux/5.4.0-71.79
  https://launchpad.net/ubuntu/+source/linux-aws/5.4.0-1043.45
  https://launchpad.net/ubuntu/+source/linux-azure/5.4.0-1044.46
  https://launchpad.net/ubuntu/+source/linux-gcp/5.4.0-1041.44
  https://launchpad.net/ubuntu/+source/linux-gkeop/5.4.0-1013.14
  https://launchpad.net/ubuntu/+source/linux-kvm/5.4.0-1037.38
  https://launchpad.net/ubuntu/+source/linux-oracle/5.4.0-1042.45
  https://launchpad.net/ubuntu/+source/linux-raspi/5.4.0-1033.36
  https://launchpad.net/ubuntu/+source/linux-aws-5.4/5.4.0-1043.45~18.04.1
  https://launchpad.net/ubuntu/+source/linux-azure-5.4/5.4.0-1044.46~18.04.1
  https://launchpad.net/ubuntu/+source/linux-gcp-5.4/5.4.0-1041.44~18.04.1
  https://launchpad.net/ubuntu/+source/linux-gke-5.4/5.4.0-1040.42~18.04.1
  https://launchpad.net/ubuntu/+source/linux-gkeop-5.4/5.4.0-1013.14~18.04.1
  https://launchpad.net/ubuntu/+source/linux-hwe-5.4/5.4.0-71.79~18.04.1
  https://launchpad.net/ubuntu/+source/linux-oracle-5.4/5.4.0-1042.45~18.04.1
  https://launchpad.net/ubuntu/+source/linux-raspi-5.4/5.4.0-1033.36~18.04.1