USN-8496-3: cifs-utils vulnerability

USN-8496-1 fixed vulnerabilities in cifs-utils. The update caused a
regression and was backed out in USN-8496-2. This update reintroduces the
security fix, along with a fix for the regression.

Original advisory details:

It was discovered that cifs-utils incorrectly dropped root privileges
before looking up user information. A local attacker could possibly use
this issue to execute arbitrary code as the root user.