ACPI: video: check for error while searching for backlit device parent

If acpi_get_parent called in acpi_video_dev_register_backlight fails
(for example, acpi_ut_acquire_mutex fails inside acpi_get_parent),
this can lead to incorrect (uninitialized) acpi_parent handler being
passed to acpi_get_pci_dev for detecting parent pci device.

Check acpi_get_parent result and set parent device only in case of success.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 9661e92c10a9 ("acpi: tie ACPI backlight devices to PCI devices if 
possible")
Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
---
  drivers/acpi/acpi_video.c | 12 ++++++------
  1 file changed, 6 insertions(+), 6 deletions(-)

2.34.1

On Thu, Nov 9, 2023 at 2:49 PM Nikita Kiryushin <kiryushin@ancud.ru> wrote:
>
> If acpi_get_parent called in acpi_video_dev_register_backlight fails
> (for example, acpi_ut_acquire_mutex fails inside acpi_get_parent),
> this can lead to incorrect (uninitialized) acpi_parent handler being
> passed to acpi_get_pci_dev for detecting parent pci device.
>
> Check acpi_get_parent result and set parent device only in case of success.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Fixes: 9661e92c10a9 ("acpi: tie ACPI backlight devices to PCI devices if
> possible")
> Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
> ---
>   drivers/acpi/acpi_video.c | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
> index 0b7a01f38b65..1d550887349a 100644
> --- a/drivers/acpi/acpi_video.c
> +++ b/drivers/acpi/acpi_video.c
> @@ -1717,12 +1717,12 @@ static void
> acpi_video_dev_register_backlight(struct acpi_video_device *device)
>                 return;
>         count++;
>   -     acpi_get_parent(device->dev->handle, &acpi_parent);
> -
> -       pdev = acpi_get_pci_dev(acpi_parent);
> -       if (pdev) {
> -               parent = &pdev->dev;
> -               pci_dev_put(pdev);
> +       if (ACPI_SUCCESS(acpi_get_parent(device->dev->handle, &acpi_parent))) {
> +               pdev = acpi_get_pci_dev(acpi_parent);
> +               if (pdev) {
> +                       parent = &pdev->dev;
> +                       pci_dev_put(pdev);
> +               }
>         }
>         memset(&props, 0, sizeof(struct backlight_properties));
> --

Applied as 6.8 material with some minor adjustments in the subject and
changeolog, but please note that your mailer garbles the patch context
lines.

Thanks!