USN-3509-4: Linux kernel (Xenial HWE) regression

USN-3509-2 fixed vulnerabilities in the Linux Hardware Enablement
kernel for Ubuntu 14.04 LTS. Unfortunately, it also introduced a
regression that prevented the Ceph network filesystem from being
used. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Mohamed Ghannam discovered that a use-after-free vulnerability existed in
the Netlink subsystem (XFRM) in the Linux kernel. A local attacker could
use this to cause a denial of service (system crash) or possibly execute
arbitrary code. (CVE-2017-16939)

It was discovered that the Linux kernel did not properly handle copy-on-
write of transparent huge pages. A local attacker could use this to cause a
denial of service (application crashes) or possibly gain administrative
privileges. (CVE-2017-1000405)

Fan Wu, Haoran Qiu, and Shixiong Zhao discovered that the associative array
implementation in the Linux kernel sometimes did not properly handle adding
a new entry. A local attacker could use this to cause a denial of service
(system crash). (CVE-2017-12193)

Andrey Konovalov discovered an out-of-bounds read in the GTCO digitizer USB
driver for the Linux kernel. A physically proximate attacker could use this
to cause a denial of service (system crash) or possibly execute arbitrary
code. (CVE-2017-16643)