[PATCH 6.6.y] drm/amd/display: Check null pointers before using them

[Artem Dinaburg <artem@trailofbits.com>]

From: Alex Hung <alex.hung@amd.com>

[ Upstream commit 1ff12bcd7deaeed25efb5120433c6a45dd5504a8 ]

[WHAT & HOW]
These pointers are null checked previously in the same function,
indicating they might be null as reported by Coverity. As a result,
they need to be checked when used again.

This fixes 3 FORWARD_NULL issue reported by Coverity.

[ Backport to 6.6.y: kept the applicable dm_state and dc_link guards; the
  vulnerable acrtc loop shape is absent. ]

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and drm amd maintainers,

I am working through the small CVE backports still missing from 6.6.y.
This one addresses CVE-2024-49922. It prevents the applicable HDCP path
from dereferencing a NULL dc_link.

The fix is already present in 6.12.y, 6.18.y, and 7.2.y, but not in 6.6.y.
This fix also affects 6.1.y, which will need a separate backport; this
submission contains only the 6.6.y patch.
The target-specific adjustment is recorded in the bracketed note above.

Could you please queue it for 6.6.y?

CVE: CVE-2024-49922
Upstream: 1ff12bcd7deaeed25efb5120433c6a45dd5504a8

AI assistance: An LLM helped identify, adapt, and validate this backport; I
reviewed the resulting code and validation evidence.

Thanks,
Artem Dinaburg

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

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 7c72caac7b4d71..702c9f5c3d006e 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -6630,6 +6630,9 @@ 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)
+		return NULL;
+
 	do {
 		stream = create_stream_for_sink(aconnector, drm_mode,
 						dm_state, old_stream,
@@ -8859,9 +8862,13 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
 
 			DRM_INFO("[HDCP_DM] hdcp_update_display enable_encryption = %x\n", enable_encryption);
 
-			hdcp_update_display(
-				adev->dm.hdcp_workqueue, aconnector->dc_link->link_index, aconnector,
-				new_con_state->hdcp_content_type, enable_encryption);
+			if (aconnector->dc_link)
+				hdcp_update_display(
+					adev->dm.hdcp_workqueue,
+					aconnector->dc_link->link_index,
+					aconnector,
+					new_con_state->hdcp_content_type,
+					enable_encryption);
 		}
 	}
 
-- 
2.39.5