Date:   Thu, 17 Oct 2019 10:48:09 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>
Cc:     "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        Sam Bazely <sambazley@...tmail.com>,
        Jiri Kosina <jikos@...nel.org>,
        Henrik Rydberg <rydberg@...math.org>,
        "Pierre-Loup A . Griffais" <pgriffais@...vesoftware.com>,
        Austin Palmer <austinp@...vesoftware.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "3.8+" <stable@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] HID: logitech-hidpp: rework device validation

On Wed, Oct 16, 2019 at 9:38 PM Andrey Smirnov <andrew.smirnov@...il.com> wrote:
>
> On Wed, Oct 16, 2019 at 12:24 PM Benjamin Tissoires
> <benjamin.tissoires@...hat.com> wrote:
> >
> > Hi Andrey,
> >
> > On Wed, Oct 16, 2019 at 8:30 PM Andrey Smirnov <andrew.smirnov@...il.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.
> > >
> > > To fix this and improve some other aspects, modify
> > > hidpp_validate_device() as follows:
> > >
> > >   - Inline the code of hidpp_validate_report() to simplify
> > >     distingushing between non-present and invalid report descriptors
> > >
> > >   - Drop the check for id >= HID_MAX_IDS || id < 0 since all of our
> > >     IDs are static and known to satisfy that at compile time
> > >
> > >   - Change the algorithms to check all possible report
> > >     types (including very long report) and deem the device as a valid
> > >     HID++ device if it supports at least one
> > >
> > >   - Treat invalid report length as a hard stop for the validation
> > >     algorithm, meaning that if any of the supported reports has
> > >     invalid length we assume the worst and treat the device as a
> > >     generic HID device.
> > >
> > >   - Fold initialization of hidpp->very_long_report_length into
> > >     hidpp_validate_device() since it already fetches very long report
> > >     length and validates its value
> > >
> > > 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@...tmail.com>
> > > Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> > > Cc: Jiri Kosina <jikos@...nel.org>
> > > Cc: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > > Cc: Henrik Rydberg <rydberg@...math.org>
> > > Cc: Pierre-Loup A. Griffais <pgriffais@...vesoftware.com>
> > > Cc: Austin Palmer <austinp@...vesoftware.com>
> > > Cc: linux-input@...r.kernel.org
> > > Cc: linux-kernel@...r.kernel.org
> > > Cc: stable@...r.kernel.org # 5.2+
> > > ---
> > >  drivers/hid/hid-logitech-hidpp.c | 54 ++++++++++++++++++--------------
> > >  1 file changed, 30 insertions(+), 24 deletions(-)
> > >
> > > diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
> > > index 85911586b3b6..8c4be991f387 100644
> > > --- a/drivers/hid/hid-logitech-hidpp.c
> > > +++ b/drivers/hid/hid-logitech-hidpp.c
> > > @@ -3498,34 +3498,45 @@ static int hidpp_get_report_length(struct hid_device *hdev, int id)
> > >         return report->field[0]->report_count + 1;
> > >  }
> > >
> > > -static bool hidpp_validate_report(struct hid_device *hdev, int id,
> > > -                                 int expected_length, bool optional)
> > > +static bool hidpp_validate_device(struct hid_device *hdev)
> > >  {
> > > -       int report_length;
> > > +       struct hidpp_device *hidpp = hid_get_drvdata(hdev);
> > > +       int id, report_length, supported_reports = 0;
> > > +
> > > +       id = REPORT_ID_HIDPP_SHORT;
> > > +       report_length = hidpp_get_report_length(hdev, id);
> > > +       if (report_length) {
> > > +               if (report_length < HIDPP_REPORT_SHORT_LENGTH)
> > > +                       goto bad_device;
> > >
> > > -       if (id >= HID_MAX_IDS || id < 0) {
> > > -               hid_err(hdev, "invalid HID report id %u\n", id);
> > > -               return false;
> > > +               supported_reports++;
> > >         }
> > >
> > > +       id = REPORT_ID_HIDPP_LONG;
> > >         report_length = hidpp_get_report_length(hdev, id);
> > > -       if (!report_length)
> > > -               return optional;
> > > +       if (report_length) {
> > > +               if (report_length < HIDPP_REPORT_LONG_LENGTH)
> > > +                       goto bad_device;
> > >
> > > -       if (report_length < expected_length) {
> > > -               hid_warn(hdev, "not enough values in hidpp report %d\n", id);
> > > -               return false;
> > > +               supported_reports++;
> > >         }
> > >
> > > -       return true;
> > > -}
> > > +       id = REPORT_ID_HIDPP_VERY_LONG;
> > > +       report_length = hidpp_get_report_length(hdev, id);
> > > +       if (report_length) {
> > > +               if (report_length > HIDPP_REPORT_LONG_LENGTH &&
> > > +                   report_length < HIDPP_REPORT_VERY_LONG_MAX_LENGTH)
> >
> > Can you double check the conditions here?
> > It's late, but I think you inverted the tests as we expect the report
> > length to be between HIDPP_REPORT_LONG_LENGTH and
> > HIDPP_REPORT_VERY_LONG_MAX_LENGTH inclusive, while here this creates a
> > bad_device.
>
> Hmm, I think you are right. Not sure why I didn't catch it on G920
> since it support very long reports AFAIR. Will re-spin and double
> check in v3. Sorry about that.
>

Oh, the issue is that the very long HID++ reports on the G920 are
HIDPP_REPORT_VERY_LONG_MAX_LENGTH long, which means the test will fail
for those.

Cheers,
Benjamin

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