It is possible for the guest to set an invalid block
size which is larger then the fifo_buffer[] array. This
could cause a buffer overflow.

To avoid this limit the maximum size of the blksize variable.
Signed-off-by: NAlistair Francis <alistair.francis@xilinx.com>
Reported-by: NIntel Security ATR <secure@intel.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NPeter Crosthwaite <crosthwaite.peter@gmail.com>
Message-id: abe4c51f513290bbb85d1ee271cb1a3d463d7561.1444067470.git.alistair.francis@xilinx.com
Suggested-by: NIgor Mitsyanko <i.mitsyanko@gmail.com>
Reported-by: NIntel Security ATR <secure@intel.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>