linux-kernel - Re: [PATCH] drm/amd/display: Fix pointer dereferenced before checking

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Date:   Thu, 7 Apr 2022 10:17:55 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Haowen Bai <baihaowen@...zu.com>, Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: Fix pointer dereferenced before checking



On 2022-04-07 01:52, Haowen Bai wrote:
> The pointer dc is dereferencing pointer plane_state before plane_state
> is being null checked. Fix this by assigning plane_state->ctx->dc to
> dc only if plane_state is not NULL, otherwise just NULL.
> 
> Signed-off-by: Haowen Bai <baihaowen@...zu.com>
> ---
>  drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
> index 50820e79d3c4..ee22f4422d26 100644
> --- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
> +++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
> @@ -3211,7 +3211,7 @@ void dcn10_update_pending_status(struct pipe_ctx *pipe_ctx)
>  	struct dc_plane_state *plane_state = pipe_ctx->plane_state;
>  	struct timing_generator *tg = pipe_ctx->stream_res.tg;
>  	bool flip_pending;
> -	struct dc *dc = plane_state->ctx->dc;

This has worked for years now, meaning plane_state is never
NULL here. It might be better to drop the NULL check below.

Harry

> +	struct dc *dc = plane_state ? plane_state->ctx->dc : NULL;
>  
>  	if (plane_state == NULL)
>  		return;