linux-kernel - Re: [PATCH] HID: nintendo: check analog user calibration for plausibility

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Date:   Tue, 20 Sep 2022 12:21:43 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Johnothan King <johnothanking@...tonmail.com>
Cc:     "Daniel J. Ogorchock" <djogorchock@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: nintendo: check analog user calibration for plausibility

On Wed, Sep 14, 2022 at 9:51 AM Johnothan King
<johnothanking@...tonmail.com> wrote:
>
> Arne Wendt writes:
>   Cheap clone controllers may (falsely) report as having a user
>   calibration for the analog sticks in place, but return
>   wrong/impossible values for the actual calibration data.
>   In the present case at mine, the controller reports having a
>   user calibration in place and successfully executes the read
>   commands. The reported user calibration however is
>   min = center = max = 0.
>
>   This pull request addresses problems of this kind by checking the
>   provided user calibration-data for plausibility (min < center < max)
>   and falling back to the default values if implausible.
>
> I'll note that I was experiencing a crash because of this bug when using
> the GuliKit KingKong 2 controller. The crash manifests as a divide by
> zero error in the kernel logs:
> kernel: divide error: 0000 [#1] PREEMPT SMP NOPTI
>
> Link: https://github.com/nicman23/dkms-hid-nintendo/pull/25
> Link: https://github.com/DanielOgorchock/linux/issues/36
> Co-authored-by: Arne Wendt <arne.wendt@...h.de>
> Signed-off-by: Johnothan King <johnothanking@...tonmail.com>
> ---
>  drivers/hid/hid-nintendo.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
> index 6028af3c3aae..7f287f6a75f5 100644
> --- a/drivers/hid/hid-nintendo.c
> +++ b/drivers/hid/hid-nintendo.c
> @@ -793,7 +793,17 @@ static int joycon_request_calibration(struct joycon_ctlr *ctlr)
>                                             &ctlr->left_stick_cal_x,
>                                             &ctlr->left_stick_cal_y,
>                                             true);
> -       if (ret) {
> +
> +       /*
> +        * Check whether read succeeded and perform plausibility check
> +        * for retrieved values.
> +        */
> +       if (ret ||
> +               ctlr->left_stick_cal_x.min >= ctlr->left_stick_cal_x.center ||
> +               ctlr->left_stick_cal_x.center >= ctlr->left_stick_cal_x.max ||
> +               ctlr->left_stick_cal_y.min >= ctlr->left_stick_cal_y.center ||
> +               ctlr->left_stick_cal_y.center >= ctlr->left_stick_cal_y.max
> +       ) {
>                 hid_warn(ctlr->hdev,
>                          "Failed to read left stick cal, using dflts; e=%d\n",
>                          ret);
> @@ -812,7 +822,17 @@ static int joycon_request_calibration(struct joycon_ctlr *ctlr)
>                                             &ctlr->right_stick_cal_x,
>                                             &ctlr->right_stick_cal_y,
>                                             false);
> -       if (ret) {
> +
> +       /*
> +        * Check whether read succeeded and perform plausibility check
> +        * for retrieved values.
> +        */
> +       if (ret ||
> +               ctlr->right_stick_cal_x.min >= ctlr->right_stick_cal_x.center ||
> +               ctlr->right_stick_cal_x.center >= ctlr->right_stick_cal_x.max ||
> +               ctlr->right_stick_cal_y.min >= ctlr->right_stick_cal_y.center ||
> +               ctlr->right_stick_cal_y.center >= ctlr->right_stick_cal_y.max

Wouldn't it make sense to have a function that takes a single struct
joycon_stick_cal pointer and does the check?
This would make things more readable IMO.

Cheers,
Benjamin

> +       ) {
>                 hid_warn(ctlr->hdev,
>                          "Failed to read right stick cal, using dflts; e=%d\n",
>                          ret);
> --
> 2.37.3
>
>