kernel: drm/dp_mst: Ensure mst_primary pointer is valid in drm_dp_mst_handle_up_req()

In the Linux kernel, the following vulnerability has been resolved: drm/dpmst: Ensure mstprimary pointer is valid in drmdpmsthandleupreq While receiving an MST up request message from one thread in drmdpmsthandleupreq, the MST topology could be removed from another thread via...