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

[Andy Shevchenko <andy.shevchenko@gmail.com>]

On Wed, Jul 29, 2020 at 5:00 PM Cengiz Can <cengiz@kernel.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
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