[PATCH v2] drm/amd/display: Add null check for dm_state in create_validate_stream_for_sink

[SRINIVASAN SHANMUGAM]

I think we can ignore this change, as it already exists in the below 
commit of asdn.

commit b90c2f233397f40c757995b9c00f8c6e380c6913
Author: Alex Hung <alex.hung at amd.com>
Date:   Thu Jun 27 17:38:16 2024 -0600

      drm/amd/display: Check null pointers before using them

On 7/17/2024 8:10 AM, Srinivasan Shanmugam wrote:
> This commit adds a null check for the dm_state variable in the
> create_validate_stream_for_sink function. Previously, dm_state was being
> checked for nullity at line 7194, but then it was being dereferenced
> without any nullity check at line 7200. This could potentially lead to a
> null pointer dereference error if dm_state is indeed null.
>
> we now ensure that dm_state is not null before  dereferencing it. We do
> this by adding a nullity check for dm_state  before the call to
> create_stream_for_sink at line 7200. If dm_state  is null, we log an
> error message and return NULL immediately.
>
> This fix prevents a null pointer dereference error.
>
> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:7201 create_validate_stream_for_sink()
> error: we previously assumed 'dm_state' could be null (see line 7194)
>
> drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c
>      7185 struct dc_stream_state *
>      7186 create_validate_stream_for_sink(struct amdgpu_dm_connector *aconnector,
>      7187                                 const struct drm_display_mode *drm_mode,
>      7188                                 const struct dm_connector_state *dm_state,
>      7189                                 const struct dc_stream_state *old_stream)
>      7190 {
>      7191         struct drm_connector *connector = &aconnector->base;
>      7192         struct amdgpu_device *adev = drm_to_adev(connector->dev);
>      7193         struct dc_stream_state *stream;
>      7194         const struct drm_connector_state *drm_state = dm_state ? &dm_state->base : NULL;
>                                                                 ^^^^^^^^
>                                       ^^^^^^^^^ This used check connector->state but then we changed it to dm_state instead
>
>      7195         int requested_bpc = drm_state ? drm_state->max_requested_bpc : 8;
>      7196         enum dc_status dc_result = DC_OK;
>      7197
>      7198         do {
>      7199                 stream = create_stream_for_sink(connector, drm_mode,
>      7200                                                 dm_state, old_stream,
>                                                           ^^^^^^^^
>
> But dm_state is dereferenced on the next line without checking.  (Presumably the NULL check can be removed).
>
> --> 7201                                                 requested_bpc);
>      7202                 if (stream == NULL) {
>      7203                         DRM_ERROR("Failed to create stream for sink!\n");
>      7204                         break;
>      7205                 }
>      7206
>      7207                 if (aconnector->base.connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
>
> Fixes: fa7041d9d2fc ("drm/amd/display: Fix ineffective setting of max bpc property")
> Reported-by: Dan Carpenter<dan.carpenter at linaro.org>
> 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: Hersen Wu<hersenxs.wu 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>
> ---
> v2: s/DRM_ERROR/drm_err() (Hamza)
>     
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index d1527c2e46a1..e7516a2dcb10 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -7195,6 +7195,11 @@ create_validate_stream_for_sink(struct amdgpu_dm_connector *aconnector,
>   	int requested_bpc = drm_state ? drm_state->max_requested_bpc : 8;
>   	enum dc_status dc_result = DC_OK;
>   
> +	if (!dm_state) {
> +		drm_err(&adev->ddev, "dm_state is NULL!\n");
> +		return NULL;
> +	}
> +
>   	do {
>   		stream = create_stream_for_sink(connector, drm_mode,
>   						dm_state, old_stream,
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