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

USN-4425-1: Linux kernel vulnerabilities

=========================================================================
Ubuntu Security Notice USN-4425-1
July 21, 2020

linux, linux-aws, linux-gcp, linux-hwe-5.4, linux-kvm, linux-oracle,
linux-raspi-5.4, linux-riscv 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-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-riscv: Linux kernel for RISC-V systems
- linux-hwe-5.4: Linux hardware enablement (HWE) kernel
- linux-raspi-5.4: Linux kernel for Raspberry Pi (V8) systems

Details:

It was discovered that the network block device (nbd) implementation in the
Linux kernel did not properly check for error conditions in some
situations. An attacker could possibly use this to cause a denial of
service (system crash). (CVE-2019-16089)

It was discovered that the kernel->user space relay implementation in the
Linux kernel did not properly check return values in some situations. A
local attacker could possibly use this to cause a denial of service (system
crash). (CVE-2019-19462)

Mauricio Faria de Oliveira discovered that the aufs implementation in the
Linux kernel improperly managed inode reference counts in the
vfsub_dentry_open() method. A local attacker could use this vulnerability
to cause a denial of service. (CVE-2020-11935)

Jason A. Donenfeld discovered that the ACPI implementation in the Linux
kernel did not properly restrict loading ACPI tables via configfs. A
privileged attacker could use this to bypass Secure Boot lockdown
restrictions and execute arbitrary code in the kernel. (CVE-2020-15780)

Update instructions:

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

Ubuntu 20.04 LTS:
linux-image-5.4.0-1020-aws 5.4.0-1020.20
linux-image-5.4.0-1021-gcp 5.4.0-1021.21
linux-image-5.4.0-1021-oracle 5.4.0-1021.21
linux-image-5.4.0-30-generic 5.4.0-30.34
linux-image-5.4.0-42-generic 5.4.0-42.46
linux-image-5.4.0-42-generic-lpae 5.4.0-42.46
linux-image-5.4.0-42-lowlatency 5.4.0-42.46
linux-image-aws 5.4.0.1020.21
linux-image-gcp 5.4.0.1021.19
linux-image-generic 5.4.0.30.37
linux-image-generic-lpae 5.4.0.42.45
linux-image-gke 5.4.0.1021.19
linux-image-kvm 5.4.0.1020.19
linux-image-lowlatency 5.4.0.42.45
linux-image-oem 5.4.0.42.45
linux-image-oem-osp1 5.4.0.42.45
linux-image-oracle 5.4.0.1021.19
linux-image-virtual 5.4.0.30.37

Ubuntu 18.04 LTS:
linux-image-5.4.0-1015-raspi 5.4.0-1015.15~18.04.1
linux-image-5.4.0-42-generic 5.4.0-42.46~18.04.1
linux-image-5.4.0-42-generic-lpae 5.4.0-42.46~18.04.1
linux-image-5.4.0-42-lowlatency 5.4.0-42.46~18.04.1
linux-image-generic-hwe-18.04 5.4.0.42.46~18.04.35
linux-image-generic-lpae-hwe-18.04 5.4.0.42.46~18.04.35
linux-image-gkeop-5.4 5.4.0.42.46~18.04.35
linux-image-lowlatency-hwe-18.04 5.4.0.42.46~18.04.35
linux-image-raspi-hwe-18.04 5.4.0.1015.19
linux-image-snapdragon-hwe-18.04 5.4.0.42.46~18.04.35
linux-image-virtual-hwe-18.04 5.4.0.42.46~18.04.35

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/4425-1
CVE-2019-16089, CVE-2019-19462, CVE-2020-11935, CVE-2020-15780

Package Information:
  https://launchpad.net/ubuntu/+source/linux/5.4.0-42.46
  https://launchpad.net/ubuntu/+source/linux-aws/5.4.0-1020.20
  https://launchpad.net/ubuntu/+source/linux-gcp/5.4.0-1021.21
  https://launchpad.net/ubuntu/+source/linux-kvm/5.4.0-1020.20
  https://launchpad.net/ubuntu/+source/linux-oracle/5.4.0-1021.21
  https://launchpad.net/ubuntu/+source/linux-riscv/5.4.0-30.34
  https://launchpad.net/ubuntu/+source/linux-hwe-5.4/5.4.0-42.46~18.04.1
  https://launchpad.net/ubuntu/+source/linux-raspi-5.4/5.4.0-1015.15~18.04.1