drm/amd/display: Fix NULL pointer dereferences in dm_update_crtc_state() v2

Added checks for NULL values after retrieving drm_new_conn_state
to prevent dereferencing NULL pointers.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:10751 dm_update_crtc_state()
	warn: 'drm_new_conn_state' can also be NULL

drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c
    10672 static int dm_update_crtc_state(struct amdgpu_display_manager *dm,
    10673                          struct drm_atomic_state *state,
    10674                          struct drm_crtc *crtc,
    10675                          struct drm_crtc_state *old_crtc_state,
    10676                          struct drm_crtc_state *new_crtc_state,
    10677                          bool enable,
    10678                          bool *lock_and_validation_needed)
    10679 {
    10680         struct dm_atomic_state *dm_state = NULL;
    10681         struct dm_crtc_state *dm_old_crtc_state, *dm_new_crtc_state;
    10682         struct dc_stream_state *new_stream;
    10683         int ret = 0;
    10684
    ...
    10703
    10704         /* TODO This hack should go away */
    10705         if (connector && enable) {
    10706                 /* Make sure fake sink is created in plug-in scenario */
    10707                 drm_new_conn_state = drm_atomic_get_new_connector_state(state,
    10708                                                                         connector);

drm_atomic_get_new_connector_state() can't return error pointers, only NULL.

    10709                 drm_old_conn_state = drm_atomic_get_old_connector_state(state,
    10710                                                                         connector);
    10711
    10712                 if (IS_ERR(drm_new_conn_state)) {
                                     ^^^^^^^^^^^^^^^^^^

    10713                         ret = PTR_ERR_OR_ZERO(drm_new_conn_state);

Calling PTR_ERR_OR_ZERO() doesn't make sense.  It can't be success.

    10714                         goto fail;
    10715                 }
    10716
    ...
    10748
    10749                 dm_new_crtc_state->abm_level = dm_new_conn_state->abm_level;
    10750
--> 10751                 ret = fill_hdr_info_packet(drm_new_conn_state,
                                                     ^^^^^^^^^^^^^^^^^^ Unchecked dereference

    10752                                            &new_stream->hdr_static_metadata);
    10753                 if (ret)
    10754                         goto fail;
    10755

v2: Modified the NULL pointer check for drm_new_conn_state in the
    dm_update_crtc_state function to  include a warning via WARN_ON and
    return -EINVAL to indicate an invalid state when the pointer is NULL.

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Alex Hung <alex.hung@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: srishanm

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -10864,8 +10864,8 @@ static int dm_update_crtc_state(struct amdgpu_display_manager *dm,
 		drm_old_conn_state = drm_atomic_get_old_connector_state(state,
 									connector);
 
-		if (IS_ERR(drm_new_conn_state)) {
-			ret = PTR_ERR_OR_ZERO(drm_new_conn_state);
+		if (WARN_ON(!drm_new_conn_state)) {
+			ret = -EINVAL;
 			goto fail;
 		}