kernel: privilege escalation

From the Red Hat bugzilla entry:

A flaw was found in the way Netlink messages without explicitly set SCM_CREDENTIALS were delivered. The kernel passes all-zero SCM_CREDENTIALS ancillary data to the receiver if the sender did not provide such data, instead of including the correct data from the peer (as it is the case with AF_UNIX). Programs that set SO_PASSCRED option on the Netlink socket and rely on SCM_CREDENTIALS for authentication might accept spoofed messages and perform privileged actions on behalf of the unprivileged attacker.