linux-kernel - Re: [PATCH] drm/sun4i: backend: Fix error pointers in sun4i_backend_atomic

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Message-ID: <aJSBSLvIeSpvaYpK@stanley.mountain>
Date: Thu, 7 Aug 2025 13:34:48 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Chenyuan Yang <chenyuan0y@...il.com>
Cc: Maxime Ripard <mripard@...nel.org>, wens@...e.org,
	maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de,
	airlied@...il.com, simona@...ll.ch, jernej.skrabec@...il.com,
	samuel@...lland.org, neil.armstrong@...aro.org,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sun4i: backend: Fix error pointers in
 sun4i_backend_atomic_check

On Fri, Mar 14, 2025 at 11:00:26AM -0500, Chenyuan Yang wrote:
> HI Maxime.
> 
> Thanks so much for pointing that out!
> 
> How about such a patch?
> 

This patch is corrupted so we can't review it.

> diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c
> b/drivers/gpu/drm/sun4i/sun4i_backend.c
> index 2dded3b828df..5ad0e90d3e6b 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> @@ -490,9 +490,14 @@ static int sun4i_backend_atomic_check(struct
> sunxi_engine *engine,
>   drm_for_each_plane_mask(plane, drm, crtc_state->plane_mask) {
>   struct drm_plane_state *plane_state =
>   drm_atomic_get_plane_state(state, plane);
> - struct sun4i_layer_state *layer_state =
> - state_to_sun4i_layer_state(plane_state);
> - struct drm_framebuffer *fb = plane_state->fb;
> + struct sun4i_layer_state *layer_state = NULL;
> + struct drm_framebuffer *fb = NULL;

No need to initialize things like this.  NULL isn't a valid pointer.
This just disables static checker tools from finding uninitialized
variable warnings so all the expense of writing the checker tools is
now wasted.

regards,
dan carpenter

> +
> + if (IS_ERR(plane_state))
> + return PTR_ERR(plane_state);
> +
> + layer_state = state_to_sun4i_layer_state(plane_state);
> + fb = plane_state->fb;
> 
>   if (!sun4i_backend_plane_is_supported(plane_state,
>         &layer_state->uses_frontend))
> -- 
> 
> -Chenyuan
> 
> On Fri, Mar 14, 2025 at 2:17 AM Maxime Ripard <mripard@...nel.org> wrote:
> >
> > Hi,
> >
> > On Thu, Mar 13, 2025 at 08:20:29PM -0500, Chenyuan Yang wrote:
> > > The function sun4i_backend_atomic_check was dereferencing pointers
> > > returned by drm_atomic_get_plane_state without checking for errors. This
> > > could lead to undefined behavior if the function returns an error pointer.
> > >
> > > This commit adds checks using IS_ERR to ensure that plane_state is
> > > valid before dereferencing them.
> > >
> > > Similar to commit da29abe71e16
> > > ("drm/amd/display: Fix error pointers in amdgpu_dm_crtc_mem_type_changed").
> > >
> > > Fixes: 96180dde23b7 ("drm/sun4i: backend: Add a custom atomic_check for the frontend")
> > > Signed-off-by: Chenyuan Yang <chenyuan0y@...il.com>
> > > ---
> > >  drivers/gpu/drm/sun4i/sun4i_backend.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > index 2dded3b828df..a8e0e2123764 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> > > @@ -490,6 +490,10 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
> > >       drm_for_each_plane_mask(plane, drm, crtc_state->plane_mask) {
> > >               struct drm_plane_state *plane_state =
> > >                       drm_atomic_get_plane_state(state, plane);
> > > +
> > > +             if (IS_ERR(plane_state))
> > > +                     return PTR_ERR(plane_state);
> > > +
> >
> > This introduces a build warning. You shouldn't mix declarations and code.
> >
> > Maxime