[CVE-2014-1874] SELinux local DoS

[Andy Whitcroft]

CVE-2014-1874:
    Setting an empty security context (length=0) on a file will lead to
    incorrectly dereferencing the type and other fields of the security
    context structure, yielding a kernel BUG.  As a zero-length security
    context is never valid, just reject all such security contexts whether
    coming from userspace via setxattr or coming from the filesystem upon
    a getxattr request by SELinux.

Following this email is a patch for lucid, precise,
precise/lts-backport-raring, quantal, and saucy. Proposing for SRU to
those releases.

-apw