On Sat, Apr 18, 2020 at 09:09:44PM -0700, Dmitry Torokhov wrote: > 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. Let's also add Ping and Jason to the conversation... -- Dmitry
