Re: [PATCH] drm/sun4i: backend: Fix error pointers in sun4i_backend_atomic_check

[Chenyuan Yang <chenyuan0y@xxxxxxxxx>]

HI Maxime.

Thanks so much for pointing that out!

How about such a patch?

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;
+
+ 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@xxxxxxxxxx> 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@xxxxxxxxx>
> > ---
> >  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