Bluetooth: hci_core: cancel all works upon hci_unregister_dev()

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

Bluetooth: hci_core: cancel all works upon hci_unregister_dev()

syzbot is reporting that calling hci_release_dev() from hci_error_reset()

due to hci_dev_put() from hci_error_reset() can cause deadlock at

destroy_workqueue(), for hci_error_reset() is called from

hdev->req_workqueue which destroy_workqueue() needs to flush.

We need to make sure that hdev->{rx_work,cmd_work,tx_work} which are

queued into hdev->workqueue and hdev->{power_on,error_reset} which are

queued into hdev->req_workqueue are no longer running by the moment

destroy_workqueue(hdev->workqueue);

destroy_workqueue(hdev->req_workqueue);

are called from hci_release_dev().

Call cancel_work_sync() on these work items from hci_unregister_dev()

as soon as hdev->list is removed from hci_dev_list.