CVE-2020-10690

There is a use-after-free in kernel versions before 5.5 due to a race
condition between the release of ptp_clock 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 can cause an exploitable condition as the
process wakes up to terminate and clean all attached files. The system
crashes due to the cdev structure being invalid (as already freed) which is
pointed to by the inode.