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

LSN-0083-1: Linux kernel vulnerability

Linux kernel vulnerabilities

A security issue affects these releases of Ubuntu and its derivatives:
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 ESM

Summary

Several security issues were fixed in the 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-gke - Linux kernel for Google Container Engine (GKE) systems - linux-gkeop - Linux kernel for Google Container Engine (GKE) systems - linux-oem - Linux kernel for OEM systems

Details

The BPF subsystem in the Linux kernel before 4.17
mishandles situations with a long jump over an instruction sequence where inner instructions require substantial expansions into multiple BPF instructions, leading to an overflow. This affects kernel/bpf/core.c and net/core/filter.c. (CVE-2018-25020)

Maxim Levitsky discovered that the KVM hypervisor implementation for AMD processors in the Linux kernel did not properly prevent a guest VM from enabling AVIC in nested guest VMs. An attacker in a guest VM could use this to write to portions of the host’s physical memory. (CVE-2021-3653)
Nadav Amit discovered that the hugetlb implementation in the Linux kernel did not perform TLB flushes under certain conditions. A local attacker could use this to leak or alter data from other processes that use huge pages. (CVE-2021-4002)

Andy Nguyen discovered that the netfilter subsystem in the Linux kernel contained an out-of-bounds write in its setsockopt() implementation. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2021-22555)

It was discovered that the virtual file system implementation in the Linux kernel contained an unsigned to signed integer conversion error. A local attacker could use this to cause a denial of service (system crash) or execute arbitrary code. (CVE-2021-33909)

Update instructions

The problem can be corrected by updating your kernel livepatch to the following versions:

Ubuntu 20.04 LTS
aws - 83.1
azure - 83.1
gcp - 83.1
generic - 83.1
gke - 83.1
gkeop - 83.1
lowlatency - 83.1

Ubuntu 18.04 LTS
aws - 83.1
generic - 83.1
gke - 83.1
gke - 83.2
gkeop - 83.1
gkeop - 83.2
lowlatency - 83.1
oem - 83.1

Ubuntu 16.04 ESM
aws - 83.1
azure - 83.1
generic - 83.1
lowlatency - 83.1

Support Information

Kernels older than the levels listed below do not receive livepatch updates. If you are running a kernel version earlier than the one listed below, please upgrade your kernel as soon as possible.

Ubuntu 20.04 LTS
linux-aws - 5.4.0-1009
linux-azure - 5.4.0-1010
linux-gcp - 5.4.0-1009
linux-gke - 5.4.0-1033
linux-gkeop - 5.4.0-1009
linux-oem - 5.4.0-26
linux - 5.4.0-26

Ubuntu 18.04 LTS
linux-aws - 4.15.0-1054
linux-azure-4.15 - 4.15.0-1115
linux-gke-4.15 - 4.15.0-1076
linux-gke-5.4 - 5.4.0-1009
linux-gkeop-5.4 - 5.4.0-1007
linux-hwe-5.4 - 5.4.0-26
linux-oem - 4.15.0-1063
linux - 4.15.0-69

Ubuntu 16.04 ESM
linux-aws - 4.4.0-1098
linux-azure - 4.15.0-1063
linux-hwe - 4.15.0-143
linux - 4.4.0-168

Ubuntu 14.04 ESM
linux-lts-xenial - 4.4.0-168

References

- CVE-2018-25020
- CVE-2021-3653
- CVE-2021-4002
- CVE-2021-22555
- CVE-2021-33909