On Sat, 18 Apr 2020, Dmitry Torokhov wrote: > 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()? No, it isn't. If it were, for example, why would evdev_disconnect() -> evdev_cleanup() need to call input_close_device()? And why would usbhid_disconnect() deallocate the usbhid structure which usbhid_stop() accesses? > > It could be that we again get confused by the "easiness" of devm APIs > > and completely screwing up unwind order. That's probably what happened. Alan Stern > Let's also add Ping and Jason to the conversation...
