Problem Description:
A file descriptor can be closed while a thread is blocked in a
poll(2) or select(2) call waiting for that descriptor. Because the
blocked thread does not hold a reference to the underlying object,
this closure may result in the object being freed while the thread
remains blocked. In this situation, the kernel must remove the
blocked thread from the per-object wait queue prior to freeing the
object.
In the case of some file descriptor types, the kernel failed to
unlink blocked threads from the object before freeing it. When the
blocked thread is subsequently woken, it accesses memory that has
already been freed resulting in a use-after-free vulnerability.
Impact:
The use-after-free vulnerability may be triggered by an
unprivileged local user and can be exploited to obtain superuser
privileges.