USN-3816-3: systemd regression

USN-3816-1 fixed vulnerabilities in systemd. The fix for CVE-2018-6954
caused a regression in systemd-tmpfiles when running Ubuntu inside a
container on some older kernels. This issue only affected Ubuntu 16.04
LTS. In order to continue to support this configuration, the fixes for
CVE-2018-6954 have been reverted.

We apologize for the inconvenience.

Original advisory details:

Jann Horn discovered that unit_deserialize incorrectly handled status messages
above a certain length. A local attacker could potentially exploit this via
NotifyAccess to inject arbitrary state across re-execution and obtain root
privileges. (CVE-2018-15686)

Jann Horn discovered a race condition in chown_one(). A local attacker
could potentially exploit this by setting arbitrary permissions on certain
files to obtain root privileges. This issue only affected Ubuntu 18.04 LTS
and Ubuntu 18.10. (CVE-2018-15687)

It was discovered that systemd-tmpfiles mishandled symlinks in
non-terminal path components. A local attacker could potentially exploit
this by gaining ownership of certain files to obtain root privileges. This
issue only affected Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. (CVE-2018-6954)