Re: [PATCH 3/3] HID: logitech-hidpp: add G920 device validation quirk

[Andrey Smirnov <andrew.smirnov@gmail.com>]

On Fri, Oct 11, 2019 at 3:33 PM Benjamin Tissoires
<benjamin.tissoires@redhat.com> wrote:
>
> On Fri, Oct 11, 2019 at 9:39 PM Andrey Smirnov <andrew.smirnov@gmail.com> wrote:
> >
> > On Fri, Oct 11, 2019 at 7:56 AM Benjamin Tissoires
> > <benjamin.tissoires@redhat.com> wrote:
> > >
> > > On Mon, Oct 7, 2019 at 7:13 AM Andrey Smirnov <andrew.smirnov@gmail.com> wrote:
> > > >
> > > > G920 device only advertises REPORT_ID_HIDPP_LONG and
> > > > REPORT_ID_HIDPP_VERY_LONG in its HID report descriptor, so querying
> > > > for REPORT_ID_HIDPP_SHORT with optional=false will always fail and
> > > > prevent G920 to be recognized as a valid HID++ device.
> > > >
> > > > Modify hidpp_validate_device() to check only REPORT_ID_HIDPP_LONG with
> > > > optional=false on G920 to fix this.
> > > >
> > > > Fixes: fe3ee1ec007b ("HID: logitech-hidpp: allow non HID++ devices to be handled by this module")
> > > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204191
> > > > Reported-by: Sam Bazely <sambazley@fastmail.com>
> > > > Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> > > > Cc: Jiri Kosina <jikos@kernel.org>
> > > > Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
> > > > Cc: Henrik Rydberg <rydberg@bitmath.org>
> > > > Cc: Sam Bazely <sambazley@fastmail.com>
> > > > Cc: Pierre-Loup A. Griffais <pgriffais@valvesoftware.com>
> > > > Cc: Austin Palmer <austinp@valvesoftware.com>
> > > > Cc: linux-input@vger.kernel.org
> > > > Cc: linux-kernel@vger.kernel.org
> > > > Cc: stable@vger.kernel.org
> > > > ---
> > > >  drivers/hid/hid-logitech-hidpp.c | 6 ++++++
> > > >  1 file changed, 6 insertions(+)
> > > >
> > > > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> > > > index cadf36d6c6f3..f415bf398e17 100644
> > > > --- a/drivers/hid/hid-logitech-hidpp.c
> > > > +++ b/drivers/hid/hid-logitech-hidpp.c
> > > > @@ -3511,6 +3511,12 @@ static bool hidpp_validate_report(struct hid_device *hdev, int id,
> > > >
> > > >  static bool hidpp_validate_device(struct hid_device *hdev)
> > > >  {
> > > > +       struct hidpp_device *hidpp = hid_get_drvdata(hdev);
> > > > +
> > > > +       if (hidpp->quirks & HIDPP_QUIRK_CLASS_G920)
> > > > +               return hidpp_validate_report(hdev, REPORT_ID_HIDPP_LONG,
> > > > +                                            HIDPP_REPORT_SHORT_LENGTH, false);
> > > > +
> > >
> > > with https://patchwork.kernel.org/patch/11184749/ we also have a need
> > > for such a trick for BLE mice.
> > >
> > > I wonder if we should not have a more common way of validating the devices
> > >
> >
> > What about just checking for:
> >
> > hidpp_validate_report(REPORT_ID_HIDPP_SHORT,
> >                                     HIDPP_REPORT_SHORT_LENGTH, true) ||
> > hidpp_validate_report(hdev, REPORT_ID_HIDPP_LONG,
> >                                     HIDPP_REPORT_LONG_LENGTH, true);
> >
> > and probably dropping the "optional" argument for
> > hidpp_validate_report()? Original code allows there to be devices
> > supporting shorts reports only, but it seems that devices that support
> > only long reports are legitimate too, so maybe the only "invalid"
> > combination is if both are invalid length or missing?
>
> Well, the problem is we also want to detect 2 things:
> - devices that do not have any of the HID++ collections, and handle
> them as generic ones (the second mouse/keyboard collection in the
> gaming mice should still be exported by the driver, or this will kill
> the macros / rebinding capabilities
> - malicious devices that pretends to have a HID++ collection but want
> to trigger a buffer overflow by having a shorter than expected report
> length
>
> Point 2 above should still be fine, but point 1 is why we have the
> enforcement of the HID++ short report in the first place.
>

It sounds like the result of hidpp_validate_report() can't really be
contained in a bool. If we modify it to return -EINVAL for bogus
report length, -ENOTSUPP if report ID is not supported and 0 if
everything is valid we should be able to capture all valid permutation
by checking for with

int id_short = hidpp_validate_report(ID_SHORT);
int id_long  = hidpp_validate_report(ID_LONG);

return (!id_short && !id_long) || (id_short == -ENOTSUPP && !id_long)
|| (id_long == -ENOTSUPP && !id_short)

no?

Thanks,
Andrey Smirnov