[USN-2851-1] Linux kernel vulnerabilities

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==========================================================================
Ubuntu Security Notice USN-2851-1
December 19, 2015

linux vulnerabilities
==========================================================================

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

- Ubuntu 15.10

Summary:

Several security issues were fixed in the kernel.

Software Description:
- linux: Linux kernel

Details:

Felix Wilhelm discovered a race condition in the Xen paravirtualized
drivers which can cause double fetch vulnerabilities. An attacker in the
paravirtualized guest could exploit this flaw to cause a denial of service
(crash the host) or potentially execute arbitrary code on the host.
(CVE-2015-8550)

Konrad Rzeszutek Wilk discovered the Xen PCI backend driver does not
perform sanity checks on the device's state. An attacker could exploit this
flaw to cause a denial of service (NULL dereference) on the host.
(CVE-2015-8551)

Konrad Rzeszutek Wilk discovered the Xen PCI backend driver does not
perform sanity checks on the device's state. An attacker could exploit this
flaw to cause a denial of service by flooding the logging system with
WARN() messages causing the initial domain to exhaust disk space.
(CVE-2015-8552)

Jann Horn discovered a ptrace issue with user namespaces in the Linux
kernel. The namespace owner could potentially exploit this flaw by ptracing
a root owned process entering the user namespace to elevate its privileges
and potentially gain access outside of the namespace.
(http://bugs.launchpad.net/bugs/1527374)

Update instructions:

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

Ubuntu 15.10:
linux-image-4.2.0-22-generic 4.2.0-22.27
linux-image-4.2.0-22-generic-lpae 4.2.0-22.27
linux-image-4.2.0-22-lowlatency 4.2.0-22.27
linux-image-4.2.0-22-powerpc-e500mc 4.2.0-22.27
linux-image-4.2.0-22-powerpc-smp 4.2.0-22.27
linux-image-4.2.0-22-powerpc64-emb 4.2.0-22.27
linux-image-4.2.0-22-powerpc64-smp 4.2.0-22.27

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:
http://www.ubuntu.com/usn/usn-2851-1
CVE-2015-8550, CVE-2015-8551, CVE-2015-8552, http://bugs.launchpad.net/bugs/1527374

Package Information:
https://launchpad.net/ubuntu/+source/linux/4.2.0-22.27