CVE-2021-47280 drm: Fix use-after-free read in drm_getunique()

In the Linux kernel, the following vulnerability has been resolved: drm: Fix use-after-free read in drmgetunique There is a time-of-check-to-time-of-use error in drmgetunique due to retrieving filepriv-master prior to locking the device's master mutex. An example can be seen in the crash report o...