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

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Message-ID: <20250314-prophetic-attentive-platypus-3ab214@houat>
Date: Fri, 14 Mar 2025 08:17:04 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Chenyuan Yang <chenyuan0y@...il.com>
Cc: 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

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

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