[PATCH] drm/amd/display: Add null check for top_pipe_to_program in commit_planes_for_stream

[Chung, ChiaHsuan (Tom)]

Reviewed-by: Tom Chung <chiahsuan.chung at amd.com>

On 7/25/2024 10:54 AM, Srinivasan Shanmugam wrote:
> This commit addresses a null pointer dereference issue in the
> `commit_planes_for_stream` function at line 4140. The issue could occur
> when `top_pipe_to_program` is null.
>
> The fix adds a check to ensure `top_pipe_to_program` is not null before
> accessing its stream_res. This prevents a null pointer dereference.
>
> Reported by smatch:
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:4140 commit_planes_for_stream() error: we previously assumed 'top_pipe_to_program' could be null (see line 3906)
>
> Cc: Tom Chung <chiahsuan.chung at amd.com>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira at amd.com>
> Cc: Roman Li <roman.li at amd.com>
> Cc: Alex Hung <alex.hung at amd.com>
> Cc: Aurabindo Pillai <aurabindo.pillai at amd.com>
> Cc: Harry Wentland <harry.wentland at amd.com>
> Cc: Hamza Mahfooz <hamza.mahfooz at amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
> ---
>   drivers/gpu/drm/amd/display/dc/core/dc.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc.c b/drivers/gpu/drm/amd/display/dc/core/dc.c
> index b8a6c062426d..95d6e29d5e47 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc.c
> @@ -4137,7 +4137,8 @@ static void commit_planes_for_stream(struct dc *dc,
>   	}
>   
>   	if ((update_type != UPDATE_TYPE_FAST) && stream->update_flags.bits.dsc_changed)
> -		if (top_pipe_to_program->stream_res.tg->funcs->lock_doublebuffer_enable) {
> +		if (top_pipe_to_program &&
> +		    top_pipe_to_program->stream_res.tg->funcs->lock_doublebuffer_enable) {
>   			top_pipe_to_program->stream_res.tg->funcs->wait_for_state(
>   				top_pipe_to_program->stream_res.tg,
>   				CRTC_STATE_VACTIVE);