[PATCH 1/2] drm/amd/display: Add null check for head_pipe in dcn201_acquire_free_pipe_for_layer

[Chung, ChiaHsuan (Tom)]

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

On 7/22/2024 9:46 AM, Srinivasan Shanmugam wrote:
> This commit addresses a potential null pointer dereference issue in the
> `dcn201_acquire_free_pipe_for_layer` function. The issue could occur
> when `head_pipe` is null.
>
> The fix adds a check to ensure `head_pipe` is not null before asserting
> it. If `head_pipe` is null, the function returns NULL to prevent a
> potential null pointer dereference.
>
> Reported by smatch:
> drivers/gpu/drm/amd/amdgpu/../display/dc/resource/dcn201/dcn201_resource.c:1016 dcn201_acquire_free_pipe_for_layer() error: we previously assumed 'head_pipe' could be null (see line 1010)
>
> 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>
> ---
>   .../gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c  | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c b/drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c
> index 131d98025bd4..fc54483b9104 100644
> --- a/drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c
> +++ b/drivers/gpu/drm/amd/display/dc/resource/dcn201/dcn201_resource.c
> @@ -1007,8 +1007,10 @@ static struct pipe_ctx *dcn201_acquire_free_pipe_for_layer(
>   	struct pipe_ctx *head_pipe = resource_get_otg_master_for_stream(res_ctx, opp_head_pipe->stream);
>   	struct pipe_ctx *idle_pipe = resource_find_free_secondary_pipe_legacy(res_ctx, pool, head_pipe);
>   
> -	if (!head_pipe)
> +	if (!head_pipe) {
>   		ASSERT(0);
> +		return NULL;
> +	}
>   
>   	if (!idle_pipe)
>   		return NULL;