Re: [PATCH] HID: quirks: Add Apple Magic Trackpad 2 to hid_have_special_driver list

["Felix Hädicke" <felixhaedicke@web.de>]

Hello Benjamin,

On Wed, 2020-12-02 at 11:21 +0100, Benjamin Tissoires wrote:
> Hi Felix,
>
> On Wed, Dec 2, 2020 at 5:31 AM Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> >
> > On Thu, Nov 19, 2020 at 12:31 AM Felix Hädicke <
> > felixhaedicke@web.de> wrote:
> > >
> > > The Apple Magic Trackpad 2 is handled by the magicmouse driver.
> > > And
> > > there were severe stability issues when both drivers (hid-generic
> > > and
> > > hid-magicmouse) were loaded for this device.
> > >
> > > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=210241
>
> As mentioned in the bug, this hardly looks like the correct solution.
>
> The magicmouse is one of the 2 only drivers that calls
> `hid_register_report` and then overwrites the size of the report
> manually. I can not figure out immediately if this is wrong, and how
> that would impact a free in usbhid, but this is highly suspicious to
> me.

Sorry for my late reply.

Now I have now found time to investigate this further, and tried to
understand what effect overwriting the size of the report could have.
Without success, I found nothing about this, which could explain a
memory corruption.

But as I commented in bug 210241 (see comment #13), usbhid_stop() is
called twice for the same hid_device instance pointer. The first call
seems to happen when the HID default driver tries to initialise this
device, which failes (probably because the hid-magicmouse driver is
already active for this device).

Adding the Magic Trackpad 2 to the hid_have_special_driver list makes
hid_generic_match() return false (in the hid-generic driver), and the
device is ignored by this driver.

Is it not the right thing to have the Magic Trackpad 2 in the
hid_have_special_driver list anyway?

Regards,
Felix


>
> Cheers,
> Benjamin
>
> >
> > +Jiri Kosina +Benjamin Tissoires for visibility.
> >
> > >
> > > Signed-off-by: Felix Hädicke <felixhaedicke@web.de>
> > > ---
> > >  drivers/hid/hid-quirks.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
> > > index 7a2be0205dfd..0a589d956e5c 100644
> > > --- a/drivers/hid/hid-quirks.c
> > > +++ b/drivers/hid/hid-quirks.c
> > > @@ -473,6 +473,8 @@ static const struct hid_device_id
> > > hid_have_special_driver[] = {
> > >  #if IS_ENABLED(CONFIG_HID_MAGICMOUSE)
> > >         { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_APPLE,
> > > USB_DEVICE_ID_APPLE_MAGICMOUSE) },
> > >         { HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_APPLE,
> > > USB_DEVICE_ID_APPLE_MAGICTRACKPAD) },
> > > +       { HID_BLUETOOTH_DEVICE(BT_VENDOR_ID_APPLE,
> > > USB_DEVICE_ID_APPLE_MAGICTRACKPAD2) },
> > > +       { HID_USB_DEVICE(USB_VENDOR_ID_APPLE,
> > > USB_DEVICE_ID_APPLE_MAGICTRACKPAD2) },
> > >  #endif
> > >  #if IS_ENABLED(CONFIG_HID_MAYFLASH)
> > >         { HID_USB_DEVICE(USB_VENDOR_ID_DRAGONRISE,
> > > USB_DEVICE_ID_DRAGONRISE_PS3) },
> > > --
> > > 2.29.2
> > >
> >
> > Thanks.
> >
> > --
> > Dmitry
> >
>