linux-kernel - Re: [PATCH] drivers/hid: avoid invalid denominator

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Date:   Sat, 24 Apr 2021 14:11:44 -0700
From:   Roderick Colenbrander <thunderbird2k@...il.com>
To:     Henry Castro <hcvcastro@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/hid: avoid invalid denominator

Hi Henry,

Thanks for your patch. In what case has this been an issue? Or was it
more theoretical.

During normal operation this condition should never be triggered for a
DualShock 4 when calibration succeeds. If it doesn't succeed the
device is not registered. We had an issue recently with the DS4 dongle
where the calibration data was 0, which was due to a race condition
with Steam, but that was resolved recently.

Thanks,
Roderick

On Sun, Apr 11, 2021 at 10:19 AM Henry Castro <hcvcastro@...il.com> wrote:
>
> Avoid a potential panic in case wrong denominator
> is given.
>
> Signed-off-by: Henry Castro <hcvcastro@...il.com>
> ---
>  drivers/hid/hid-sony.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hid/hid-sony.c b/drivers/hid/hid-sony.c
> index 8319b0ce385a..67b45d82cc3b 100644
> --- a/drivers/hid/hid-sony.c
> +++ b/drivers/hid/hid-sony.c
> @@ -1134,11 +1134,16 @@ static void dualshock4_parse_report(struct sony_sc *sc, u8 *rd, int size)
>                  * Note: we swap numerator 'x' and 'numer' in mult_frac for
>                  *       precision reasons so we don't need 64-bit.
>                  */
> -               int calib_data = mult_frac(calib->sens_numer,
> -                                          raw_data - calib->bias,
> -                                          calib->sens_denom);
> +               if (calib->sens_denom != 0) {
> +                       int calib_data = mult_frac(calib->sens_numer,
> +                                                  raw_data - calib->bias,
> +                                                  calib->sens_denom);
> +
> +                       input_report_abs(sc->sensor_dev, calib->abs_code, calib_data);
> +               } else {
> +                       hid_warn(sc->hdev, "DualShock 4 parse report, avoid invalid denominator");
> +               }
>
> -               input_report_abs(sc->sensor_dev, calib->abs_code, calib_data);
>                 offset += 2;
>         }
>         input_sync(sc->sensor_dev);
> --
> 2.20.1
>