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

USN-4576-1: Linux kernel vulnerabilities

=========================================================================
Ubuntu Security Notice USN-4576-1
October 14, 2020

linux, linux-aws, linux-aws-5.4, linux-azure, linux-azure-5.4, linux-gcp,
linux-gcp-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-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-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:

Hador Manor discovered that the DCCP protocol implementation in the Linux
kernel improperly handled socket reuse, 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-2020-16119)

Jay Shin discovered that the ext4 file system implementation in the Linux
kernel did not properly handle directory access with broken indexing,
leading to an out-of-bounds read vulnerability. A local attacker could use
this to cause a denial of service (system crash). (CVE-2020-14314)

David Alan Gilbert discovered that the XFS file system implementation in
the Linux kernel did not properly perform metadata validation in some
circumstances. A local attacker could use this to cause a denial of
service. (CVE-2020-14385)

Giuseppe Scrivano discovered that the overlay file system in the Linux
kernel did not properly perform permission checks in some situations. A
local attacker could possibly use this to bypass intended restrictions and
gain read access to restricted files. (CVE-2020-16120)

It was discovered that a race condition existed in the hugetlb sysctl
implementation in the Linux kernel. A privileged attacker could use this to
cause a denial of service (system crash). (CVE-2020-25285)

It was discovered that the block layer subsystem in the Linux kernel did
not properly handle zero-length requests. A local attacker could use this
to cause a denial of service. (CVE-2020-25641)

Update instructions:

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

Ubuntu 20.04 LTS:
linux-image-5.4.0-1021-raspi 5.4.0-1021.24
linux-image-5.4.0-1026-kvm 5.4.0-1026.27
linux-image-5.4.0-1028-aws 5.4.0-1028.29
linux-image-5.4.0-1028-gcp 5.4.0-1028.29
linux-image-5.4.0-1028-oracle 5.4.0-1028.29
linux-image-5.4.0-1031-azure 5.4.0-1031.32
linux-image-5.4.0-51-generic 5.4.0-51.56
linux-image-5.4.0-51-generic-lpae 5.4.0-51.56
linux-image-5.4.0-51-lowlatency 5.4.0-51.56
linux-image-aws 5.4.0.1028.29
linux-image-azure 5.4.0.1031.29
linux-image-gcp 5.4.0.1028.36
linux-image-generic 5.4.0.51.54
linux-image-generic-hwe-20.04 5.4.0.51.54
linux-image-generic-lpae 5.4.0.51.54
linux-image-generic-lpae-hwe-20.04 5.4.0.51.54
linux-image-gke 5.4.0.1028.36
linux-image-kvm 5.4.0.1026.24
linux-image-lowlatency 5.4.0.51.54
linux-image-lowlatency-hwe-20.04 5.4.0.51.54
linux-image-oem 5.4.0.51.54
linux-image-oem-osp1 5.4.0.51.54
linux-image-oracle 5.4.0.1028.25
linux-image-raspi 5.4.0.1021.56
linux-image-raspi2 5.4.0.1021.56
linux-image-virtual 5.4.0.51.54
linux-image-virtual-hwe-20.04 5.4.0.51.54

Ubuntu 18.04 LTS:
linux-image-5.4.0-1021-raspi 5.4.0-1021.24~18.04.1
linux-image-5.4.0-1028-aws 5.4.0-1028.29~18.04.1
linux-image-5.4.0-1028-gcp 5.4.0-1028.29~18.04.1
linux-image-5.4.0-1028-oracle 5.4.0-1028.29~18.04.1
linux-image-5.4.0-1031-azure 5.4.0-1031.32~18.04.1
linux-image-5.4.0-51-generic 5.4.0-51.56~18.04.1
linux-image-5.4.0-51-generic-lpae 5.4.0-51.56~18.04.1
linux-image-5.4.0-51-lowlatency 5.4.0-51.56~18.04.1
linux-image-aws 5.4.0.1028.13
linux-image-azure 5.4.0.1031.13
linux-image-gcp 5.4.0.1028.16
linux-image-generic-hwe-18.04 5.4.0.51.56~18.04.45
linux-image-generic-lpae-hwe-18.04 5.4.0.51.56~18.04.45
linux-image-lowlatency-hwe-18.04 5.4.0.51.56~18.04.45
linux-image-oracle 5.4.0.1028.12
linux-image-raspi-hwe-18.04 5.4.0.1021.25
linux-image-snapdragon-hwe-18.04 5.4.0.51.56~18.04.45
linux-image-virtual-hwe-18.04 5.4.0.51.56~18.04.45

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/4576-1
CVE-2020-14314, CVE-2020-14385, CVE-2020-16119, CVE-2020-16120,
CVE-2020-25285, CVE-2020-25641

Package Information:
  https://launchpad.net/ubuntu/+source/linux/5.4.0-51.56
  https://launchpad.net/ubuntu/+source/linux-aws/5.4.0-1028.29
  https://launchpad.net/ubuntu/+source/linux-azure/5.4.0-1031.32
  https://launchpad.net/ubuntu/+source/linux-gcp/5.4.0-1028.29
  https://launchpad.net/ubuntu/+source/linux-kvm/5.4.0-1026.27
  https://launchpad.net/ubuntu/+source/linux-oracle/5.4.0-1028.29
  https://launchpad.net/ubuntu/+source/linux-raspi/5.4.0-1021.24
  https://launchpad.net/ubuntu/+source/linux-aws-5.4/5.4.0-1028.29~18.04.1
  https://launchpad.net/ubuntu/+source/linux-azure-5.4/5.4.0-1031.32~18.04.1
  https://launchpad.net/ubuntu/+source/linux-gcp-5.4/5.4.0-1028.29~18.04.1
  https://launchpad.net/ubuntu/+source/linux-hwe-5.4/5.4.0-51.56~18.04.1
  https://launchpad.net/ubuntu/+source/linux-oracle-5.4/5.4.0-1028.29~18.04.1
  https://launchpad.net/ubuntu/+source/linux-raspi-5.4/5.4.0-1021.24~18.04.1