A flaw was found in the linux kernel related to the user namespace
lazily unmounting filesystems. The fs_pin struct had two members
(m_list and s_list) which are usually initialized on use in the pin_insert_group function.
It is possible that these lists go unmodified and are then attempted to be
destroyed/freed panicing the system.
This issue does not affect the Linux kernels as shipped with Red Hat Enterprise Linux 5, 6, 7, MRG-2, realtime and arm-kernels.