Re: [PATCH v2 2/3] HID: logitech-hidpp: rework device validation

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

Hi Andrey,

On Wed, Oct 16, 2019 at 8:30 PM 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.
>
> 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@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: 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 # 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.

Other than that, I really like the series.

Cheers,
Benjamin

> +                       goto bad_device;
>
> -static bool hidpp_validate_device(struct hid_device *hdev)
> -{
> -       return hidpp_validate_report(hdev, REPORT_ID_HIDPP_SHORT,
> -                                    HIDPP_REPORT_SHORT_LENGTH, false) &&
> -              hidpp_validate_report(hdev, REPORT_ID_HIDPP_LONG,
> -                                    HIDPP_REPORT_LONG_LENGTH, true);
> +               supported_reports++;
> +               hidpp->very_long_report_length = report_length;
> +       }
> +
> +       return supported_reports;
> +
> +bad_device:
> +       hid_warn(hdev, "not enough values in hidpp report %d\n", id);
> +       return false;
>  }
>
>  static bool hidpp_application_equals(struct hid_device *hdev,
> @@ -3572,11 +3583,6 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
>                 return hid_hw_start(hdev, HID_CONNECT_DEFAULT);
>         }
>
> -       hidpp->very_long_report_length =
> -               hidpp_get_report_length(hdev, REPORT_ID_HIDPP_VERY_LONG);
> -       if (hidpp->very_long_report_length > HIDPP_REPORT_VERY_LONG_MAX_LENGTH)
> -               hidpp->very_long_report_length = HIDPP_REPORT_VERY_LONG_MAX_LENGTH;
> -
>         if (id->group == HID_GROUP_LOGITECH_DJ_DEVICE)
>                 hidpp->quirks |= HIDPP_QUIRK_UNIFYING;
>
> --
> 2.21.0
>