CVE-2024-50019

In the Linux kernel, the following vulnerability has been resolved:

kthread: unpark only parked kthread

Calling into kthread unparking unconditionally is mostly harmless when the kthread is already unparked. The wake up is then simply ignored because the target is not in TASK_PARKED state.

However if the kthread is per CPU, the wake up is preceded by a call to kthreadbind() which expects the task to be inactive and in TASKPARKED state, which obviously isn't the case if it is unparked.

As a result, calling kthread_stop() on an unparked per-cpu kthread triggers such a warning:

WARNING: CPU: 0 PID: 11 at kernel/kthread.c:525 __kthread_bind_mask kernel/kthread.c:525
 <TASK>
 kthread_stop+0x17a/0x630 kernel/kthread.c:707
 destroy_workqueue+0x136/0xc40 kernel/workqueue.c:5810
 wg_destruct+0x1e2/0x2e0 drivers/net/wireguard/device.c:257
 netdev_run_todo+0xe1a/0x1000 net/core/dev.c:10693
 default_device_exit_batch+0xa14/0xa90 net/core/dev.c:11769
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x89d/0xcc0 net/core/net_namespace.c:640
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
 worker_thread+0x86d/0xd70 kernel/workqueue.c:3393
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Fix this with skipping unecessary unparking while stopping a kthread.