USN-3835-1: Linux kernel vulnerabilities

3 December 2018

linux, linux-gcp, linux-kvm, linux-raspi2 vulnerabilities

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

  • Ubuntu 18.10

Summary

Several security issues were fixed in the Linux kernel.

Software Description

  • linux - Linux kernel
  • linux-gcp - Linux kernel for Google Cloud Platform (GCP) systems
  • linux-kvm - Linux kernel for cloud environments
  • linux-raspi2 - Linux kernel for Raspberry Pi 2

Details

Jann Horn discovered that the procfs file system implementation in the Linux kernel did not properly restrict the ability to inspect the kernel stack of an arbitrary task. A local attacker could use this to expose sensitive information. (CVE-2018-17972)

Jann Horn discovered that the mremap() system call in the Linux kernel did not properly flush the TLB when completing, potentially leaving access to a physical page after it has been released to the page allocator. A local attacker could use this to cause a denial of service (system crash), expose sensitive information, or possibly execute arbitrary code. (CVE-2018-18281)

It was discovered that the BPF verifier in the Linux kernel did not correctly compute numeric bounds in some situations. A local attacker could use this to cause a denial of service (system crash) or possibly execute arbitrary code. (CVE-2018-18445)

Daniel Dadap discovered that the module loading implementation in the Linux kernel did not properly enforce signed module loading when booted with UEFI Secure Boot in some situations. A local privileged attacker could use this to execute untrusted code in the kernel. (CVE-2018-18653)

Jann Horn discovered that the Linux kernel mishandles mapping UID or GID ranges inside nested user namespaces in some situations. A local attacker could use this to bypass access controls on resources outside the namespace. (CVE-2018-18955)

Philipp Wendler discovered that the overlayfs implementation in the Linux kernel did not properly verify the directory contents permissions from within a unprivileged user namespace. A local attacker could use this to expose sensitive information (protected file names). (CVE-2018-6559)

Update instructions

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

Ubuntu 18.10
linux-image-4.18.0-1004-gcp - 4.18.0-1004.5
linux-image-4.18.0-1005-kvm - 4.18.0-1005.5
linux-image-4.18.0-1007-raspi2 - 4.18.0-1007.9
linux-image-4.18.0-12-generic - 4.18.0-12.13
linux-image-4.18.0-12-generic-lpae - 4.18.0-12.13
linux-image-4.18.0-12-lowlatency - 4.18.0-12.13
linux-image-4.18.0-12-snapdragon - 4.18.0-12.13
linux-image-gcp - 4.18.0.1004.4
linux-image-generic - 4.18.0.12.13
linux-image-generic-lpae - 4.18.0.12.13
linux-image-gke - 4.18.0.1004.4
linux-image-kvm - 4.18.0.1005.5
linux-image-lowlatency - 4.18.0.12.13
linux-image-raspi2 - 4.18.0.1007.4
linux-image-snapdragon - 4.18.0.12.13

To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.

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