thermal/debugfs: Prevent use-after-free from occurring after cdev removal

In the Linux kernel, the following vulnerability has been resolved: thermal/debugfs: Prevent use-after-free from occurring after cdev removal Since thermal_debug_cdev_remove() does not run under cdev->lock, it can run in parallel with thermal_debug_cdev_state_update() and it may free the struct thermal_debugfs object used by the latter after it has been checked against NULL. If that happens, thermal_debug_cdev_state_update() will access memory that has been freed already causing the kernel to crash. Address this by using cdev->lock in thermal_debug_cdev_remove() around the cdev->debugfs value check (in case the same cdev is removed at the same time in two different threads) and its reset to NULL. Cc :6.8+ <stable@vger.kernel.org> # 6.8+