CVE request Linux kernel: forbid uaddr == uaddr2 in futex_wait_requeue_pi() to avoid null dereference

[P J P <ppandit () redhat com>]

   Hello,

Linux kernel built with the fast userspace mutexes(CONFIG_FUTEX) support is 
vulnerable to a NULL pointer dereference flaw. It could occur when a waiting 
task requests wait to be re-queued from non-PI futex to a PI-aware futex via 
FUTEX_WAIT_REQUEUE_PI operation.

An unprivileged user/program could use this flaw to crash the system kernel 
resulting in DoS.

Upstream fix:
-------------
  -> https://git.kernel.org/linus/6f7b0a2a5c0fb03be7c25bd1745baa50582348ef

Introduced in:
--------------
  -> https://git.kernel.org/linus/52400ba946759af28442dee6265c5c0180ac7122


Thank you.
--
Prasad J Pandit / Red Hat Security Response Team