linux-kernel - Re: [PATCH v2 2/2] drm/client: Prevent NULL dereference in drm_client_buffer

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Date:   Wed, 2 Nov 2022 10:15:56 +0100
From:   Christian König <christian.koenig@....com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, noralf@...nnes.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] drm/client: Prevent NULL dereference in
 drm_client_buffer_delete()

Am 30.10.22 um 16:44 schrieb Dmitry Osipenko:
> The drm_gem_vunmap() will crash with a NULL dereference if the passed
> object pointer is NULL. It wasn't a problem before we added the locking
> support to drm_gem_vunmap function because the mapping argument was always
> NULL together with the object. Make drm_client_buffer_delete() to check
> whether GEM is NULL before trying to unmap the GEM, it will happen on
> framebuffer creation error.
>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Link: https://lore.kernel.org/dri-devel/Y1kFEGxT8MVlf32V@kili/
> Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap operations")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
>   drivers/gpu/drm/drm_client.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
> index 38e1be991caa..fd67efe37c63 100644
> --- a/drivers/gpu/drm/drm_client.c
> +++ b/drivers/gpu/drm/drm_client.c
> @@ -235,10 +235,10 @@ static void drm_client_buffer_delete(struct drm_client_buffer *buffer)
>   {
>   	struct drm_device *dev = buffer->client->dev;
>   
> -	drm_gem_vunmap_unlocked(buffer->gem, &buffer->map);
> -
> -	if (buffer->gem)
> +	if (buffer->gem) {
> +		drm_gem_vunmap_unlocked(buffer->gem, &buffer->map);
>   		drm_gem_object_put(buffer->gem);
> +	}
>   
>   	if (buffer->handle)
>   		drm_mode_destroy_dumb(dev, buffer->handle, buffer->client->file);