linux-kernel - Re: [PATCH] staging: atomisp: move null check to earlier point

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Message-ID: <CAHp75VfM3OapAkYJ-sN-MG2yuGDqaqDjc6p0gXT9cHYgnH+5LQ@mail.gmail.com>
Date:   Wed, 29 Jul 2020 18:13:44 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Cengiz Can <cengiz@...nel.wtf>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: atomisp: move null check to earlier point

On Wed, Jul 29, 2020 at 5:00 PM Cengiz Can <cengiz@...nel.wtf> wrote:
>
> `find_gmin_subdev` function that returns a pointer to `struct
> gmin_subdev` can return NULL.
>
> In `gmin_v2p8_ctrl` there's a call to this function but the possibility
> of a NULL was not checked before its being dereferenced. ie:
>
> ```
> /* Acquired here --------v */
> struct gmin_subdev *gs = find_gmin_subdev(subdev);
> int ret;
> int value;
>
> /*  v------Dereferenced here */
> if (gs->v2p8_gpio >= 0) {
>         pr_info("atomisp_gmin_platform: 2.8v power on GPIO %d\n",
>                 gs->v2p8_gpio);
>         ret = gpio_request(gs->v2p8_gpio, "camera_v2p8");
>         if (!ret)
>                 ret = gpio_direction_output(gs->v2p8_gpio, 0);
>         if (ret)
>                 pr_err("V2P8 GPIO initialization failed\n");
> }
> ```
>
> I have moved the NULL check before deref point.

"Move the NULL check..."
See Submitting Patches documentation how to avoid "This patch", "I", "we", etc.

> diff --git a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
> index 0df46a1af5f0..8e9c5016f299 100644
> --- a/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
> +++ b/drivers/staging/media/atomisp/pci/atomisp_gmin_platform.c
> @@ -871,6 +871,11 @@ static int gmin_v2p8_ctrl(struct v4l2_subdev *subdev, int on)
>         int ret;
>         int value;
>
> +       if (!gs) {
> +               pr_err("Unable to find gmin subdevice\n");

> +               return -EINVAL;

And here is a change of semantics...

> +       }

...

> -       if (!gs || gs->v2p8_on == on)
> +       if (gs->v2p8_on == on)
>                 return 0;

...compared to above.

-- 
With Best Regards,
Andy Shevchenko