linux-kernel - Re: [PATCH] drm/vc4: Fix NULL pointer access in vc4_platform_drm

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Message-ID: <CAPY8ntB-LdH-oy86x-4Ox-JzgLLpmBNKu7j=bQo+Danj-r3+Dw@mail.gmail.com>
Date:   Mon, 21 Nov 2022 11:14:04 +0000
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
Cc:     airlied@...il.com, daniel@...ll.ch, eric@...olt.net,
        emma@...olt.net, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, stable@...r.kernel.org,
        l.sanfilippo@...bus.com, p.rosenberger@...bus.com
Subject: Re: [PATCH] drm/vc4: Fix NULL pointer access in vc4_platform_drm_probe()

Hi Lino

On Sun, 20 Nov 2022 at 15:26, Lino Sanfilippo <LinoSanfilippo@....de> wrote:
>
> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>
> In vc4_platform_drm_probe() function vc4_match_add_drivers() is called to
> find component matches for the component drivers. If no such match is found
> the passed variable "match" is still NULL after the function returns.

This would imply a very strange device tree that has bothered to add
the drm device but none of the devices that are required to run the
DRM pipeline, but avoiding a NULL deref is certainly preferable.

> Do not pass "match" to component_master_add_with_match() in this case since
> this results in a NULL pointer access as soon as match->num is used to
> allocate a component_match array. Instead return with -ENODEV from the
> drivers probe function.
>
> Fixes: c8b75bca92cb ("drm/vc4: Add KMS support for Raspberry Pi.")
> Cc: stable@...r.kernel.org
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>

Acked-by: Dave Stevenson <dave.stevenson@...pberrypi.com>

> ---
>  drivers/gpu/drm/vc4/vc4_drv.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_drv.c b/drivers/gpu/drm/vc4/vc4_drv.c
> index 2027063fdc30..2e53d7f8ad44 100644
> --- a/drivers/gpu/drm/vc4/vc4_drv.c
> +++ b/drivers/gpu/drm/vc4/vc4_drv.c
> @@ -437,6 +437,9 @@ static int vc4_platform_drm_probe(struct platform_device *pdev)
>         vc4_match_add_drivers(dev, &match,
>                               component_drivers, ARRAY_SIZE(component_drivers));
>
> +       if (!match)
> +               return -ENODEV;
> +
>         return component_master_add_with_match(dev, &vc4_drm_ops, match);
>  }
>
>
> base-commit: 30a0b95b1335e12efef89dd78518ed3e4a71a763
> --
> 2.36.1
>