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

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Message-ID: <137bc2a57c0eaeac7228fd3d1e1bb1fb126fe234.camel@mediatek.com>
Date:   Tue, 13 Jun 2023 09:05:03 +0000
From:   Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>
To:     CK Hu (胡俊光) <ck.hu@...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>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        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 CK,

Thanks for the reviews.

On Mon, 2023-06-12 at 09:10 +0000, CK Hu (胡俊光) wrote:
> 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

OK, I'll drop the modification here.

Regards,
Jason-JH.Lin
> 
> >  	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
> > ,