A Linux kernel security update has been released for Ubuntu Linux 20.04 LTS and 20.10.

USN-4910-1: Linux kernel vulnerabilities

==========================================================================
Ubuntu Security Notice USN-4910-1
April 13, 2021

linux, linux-aws, linux-azure, linux-gcp, linux-hwe-5.8, linux-kvm,
linux-oracle, linux-raspi vulnerabilities
==========================================================================

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

- Ubuntu 20.10
- Ubuntu 20.04 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-kvm: Linux kernel for cloud environments
- linux-oracle: Linux kernel for Oracle Cloud systems
- linux-raspi: Linux kernel for Raspberry Pi (V8) systems
- linux-hwe-5.8: Linux hardware enablement (HWE) kernel

Details:

Ryota Shiga discovered that the sockopt BPF hooks in the Linux kernel could
allow a user space program to probe for valid kernel addresses. A local
attacker could use this to ease exploitation of another kernel
vulnerability. (CVE-2021-20239)

It was discovered that the BPF verifier in the Linux kernel did not
properly handle signed add32 and sub integer overflows. A local attacker
could use this to cause a denial of service (system crash) or possibly
execute arbitrary code. (CVE-2021-20268)

It was discovered that the priority inheritance futex implementation in the
Linux kernel contained a race condition, leading to a use-after-free
vulnerability. A local attacker could use this to cause a denial of service
(system crash) or possibly execute arbitrary code. (CVE-2021-3347)

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)

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 20.10:
linux-image-5.8.0-1020-raspi 5.8.0-1020.23
linux-image-5.8.0-1020-raspi-nolpae 5.8.0-1020.23
linux-image-5.8.0-1023-kvm 5.8.0-1023.25
linux-image-5.8.0-1025-oracle 5.8.0-1025.26
linux-image-5.8.0-1027-azure 5.8.0-1027.29
linux-image-5.8.0-1027-gcp 5.8.0-1027.28
linux-image-5.8.0-1028-aws 5.8.0-1028.30
linux-image-5.8.0-49-generic 5.8.0-49.55
linux-image-5.8.0-49-generic-64k 5.8.0-49.55
linux-image-5.8.0-49-generic-lpae 5.8.0-49.55
linux-image-5.8.0-49-lowlatency 5.8.0-49.55
linux-image-aws 5.8.0.1028.30
linux-image-azure 5.8.0.1027.27
linux-image-gcp 5.8.0.1027.27
linux-image-generic 5.8.0.49.54
linux-image-generic-64k 5.8.0.49.54
linux-image-generic-lpae 5.8.0.49.54
linux-image-gke 5.8.0.1027.27
linux-image-kvm 5.8.0.1023.25
linux-image-lowlatency 5.8.0.49.54
linux-image-oem-20.04 5.8.0.49.54
linux-image-oracle 5.8.0.1025.24
linux-image-raspi 5.8.0.1020.23
linux-image-raspi-nolpae 5.8.0.1020.23
linux-image-virtual 5.8.0.49.54

Ubuntu 20.04 LTS:
linux-image-5.8.0-49-generic 5.8.0-49.55~20.04.1
linux-image-5.8.0-49-generic-64k 5.8.0-49.55~20.04.1
linux-image-5.8.0-49-generic-lpae 5.8.0-49.55~20.04.1
linux-image-5.8.0-49-lowlatency 5.8.0-49.55~20.04.1
linux-image-generic-64k-hwe-20.04 5.8.0.49.55~20.04.33
linux-image-generic-hwe-20.04 5.8.0.49.55~20.04.33
linux-image-generic-lpae-hwe-20.04 5.8.0.49.55~20.04.33
linux-image-lowlatency-hwe-20.04 5.8.0.49.55~20.04.33
linux-image-virtual-hwe-20.04 5.8.0.49.55~20.04.33

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-4910-1
CVE-2021-20239, CVE-2021-20268, CVE-2021-3178, CVE-2021-3347,
CVE-2021-3348

Package Information:
  https://launchpad.net/ubuntu/+source/linux/5.8.0-49.55
  https://launchpad.net/ubuntu/+source/linux-aws/5.8.0-1028.30
  https://launchpad.net/ubuntu/+source/linux-azure/5.8.0-1027.29
  https://launchpad.net/ubuntu/+source/linux-gcp/5.8.0-1027.28
  https://launchpad.net/ubuntu/+source/linux-kvm/5.8.0-1023.25
  https://launchpad.net/ubuntu/+source/linux-oracle/5.8.0-1025.26
  https://launchpad.net/ubuntu/+source/linux-raspi/5.8.0-1020.23
  https://launchpad.net/ubuntu/+source/linux-hwe-5.8/5.8.0-49.55~20.04.1