[USN-3835-1] Linux kernel vulnerabilities

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==========================================================================
Ubuntu Security Notice USN-3835-1
December 03, 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

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/usn/usn-3835-1
CVE-2018-17972, CVE-2018-18281, CVE-2018-18445, CVE-2018-18653,
CVE-2018-18955, CVE-2018-6559

Package Information:
https://launchpad.net/ubuntu/+source/linux/4.18.0-12.13
https://launchpad.net/ubuntu/+source/linux-gcp/4.18.0-1004.5
https://launchpad.net/ubuntu/+source/linux-kvm/4.18.0-1005.5
https://launchpad.net/ubuntu/+source/linux-raspi2/4.18.0-1007.9

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