kernel: use-after-free in cdev_put() when a PTP device is removed while it's chardev is open

There is a use-after-free problem seen due to a race condition between the release of ptpclock and cdev while resource deallocation. When a high privileged process allocates a ptp device file like /dev/ptpX and voluntarily goes to sleep. During this time if the underlying device is removed, it ca...