linux-kernel - Re: [PATCH 5/5] drm/mediatek: Fix dereference before null check

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Message-ID: <4ea5f2579f802e886eab057cc2635e91766ac45a.camel@mediatek.com>
Date:   Mon, 12 Jun 2023 09:10:40 +0000
From:   CK Hu (胡俊光) <ck.hu@...iatek.com>
To:     Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Jason-ch Chen (陳建豪) 
        <Jason-ch.Chen@...iatek.com>,
        Shawn Sung (宋孝謙) 
        <Shawn.Sung@...iatek.com>,
        Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        Rex-BC Chen (陳柏辰) 
        <Rex-BC.Chen@...iatek.com>
Subject: Re: [PATCH 5/5] drm/mediatek: Fix dereference before null check

Hi, Jason:

On Fri, 2023-04-07 at 14:46 +0800, Jason-JH.Lin wrote:
> Null-checking state suggests that it may be null, but it has already
> been dereferenced on drm_atomic_get_new_plane_state(state, plane).
> 
> The parameter state will never be NULL currently, so just remove the
> state is NULL flow in this function.
> 
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> Fixes: 5ddb0bd4ddc3 ("drm/atomic: Pass the full state to planes async
> atomic check and update")
> ---
>  drivers/gpu/drm/mediatek/mtk_drm_plane.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> index a1337f386bbf..e14b2920d242 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> @@ -103,8 +103,7 @@ static void mtk_drm_plane_destroy_state(struct
> drm_plane *plane,
>  static int mtk_plane_atomic_async_check(struct drm_plane *plane,
>  					struct drm_atomic_state *state)
>  {
> -	struct drm_plane_state *new_plane_state =
> drm_atomic_get_new_plane_state(state,
> -									
> 	 plane);
> +	struct drm_plane_state *new_plane_state =
> drm_atomic_get_new_plane_state(state, plane);

This is not related to this patch, so move to another patch.

Regards,
CK

>  	struct drm_crtc_state *crtc_state;
>  	int ret;
>  
> @@ -122,11 +121,7 @@ static int mtk_plane_atomic_async_check(struct
> drm_plane *plane,
>  	if (ret)
>  		return ret;
>  
> -	if (state)
> -		crtc_state = drm_atomic_get_existing_crtc_state(state,
> -								new_pla
> ne_state->crtc);
> -	else /* Special case for asynchronous cursor updates. */
> -		crtc_state = new_plane_state->crtc->state;
> +	crtc_state = drm_atomic_get_existing_crtc_state(state,
> new_plane_state->crtc);
>  
>  	return drm_atomic_helper_check_plane_state(plane->state,
> crtc_state,
>  						   DRM_PLANE_NO_SCALING
> ,