Hi Alan, On Sat, Apr 18, 2020 at 10:16:32PM -0400, Alan Stern wrote: > linux-input people: > > syzbot has found a bug related to USB/HID/input, and I have narrowed it > down to the wacom driver. As far as I can tell, the problem is caused > the fact that drivers/hid/wacom_sys.c calls input_register_device() > in several places, but it never calls input_unregister_device(). > > I know very little about the input subsystem, but this certainly seems > like a bug. Wacom driver uses devm_input_allocate_device(), so unregister should happen automatically on device removal once we exit wacom_probe(). > > When the device is unplugged, the disconnect pathway doesn't call > hid_hw_close(). That routine doesn't get called until the user closes > the device file (which can be long after the device is gone and > hid_hw_stop() has run). Then usbhid_close() gets a use-after-free > error when it tries to access data structures that were deallocated by > usbhid_stop(). No doubt there are other problems too, but this is > the one that syzbot found. Unregistering the input device should result in calling wacom_close() (if device was previously opened), which, as far as I can tell, calls hid_hw_close(). I wonder if it is valid to call hid_hw_stop() before hid_hw_close()? It could be that we again get confused by the "easiness" of devm APIs and completely screwing up unwind order. Thanks. -- Dmitry
