[PATCH 6.6.y] drm/i915/hdcp: Add encoder check in intel_hdcp_get_capability

[Artem Dinaburg <artem@trailofbits.com>]

From: Suraj Kandpal <suraj.kandpal@intel.com>

[ Upstream commit 31b42af516afa1e184d1a9f9dd4096c54044269a ]

Sometimes during hotplug scenario or suspend/resume scenario encoder is
not always initialized when intel_hdcp_get_capability add
a check to avoid kernel null pointer dereference.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240722064451.3610512-2-suraj.kandpal@intel.com
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and drm i915 maintainers,

I am working through the small CVE backports still missing from 6.6.y.
This one addresses CVE-2024-53051. It rejects the HDCP capability query
when hotplug or resume left the encoder unset.

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 code change is identical to upstream.

Could you please queue it for 6.6.y?

CVE: CVE-2024-53051
Upstream: 31b42af516afa1e184d1a9f9dd4096c54044269a

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/i915/display/intel_hdcp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdcp.c b/drivers/gpu/drm/i915/display/intel_hdcp.c
index f377c4484e1857..f7987fb90bb1ac 100644
--- a/drivers/gpu/drm/i915/display/intel_hdcp.c
+++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
@@ -142,11 +142,16 @@ int intel_hdcp_read_valid_bksv(struct intel_digital_port *dig_port,
 /* Is HDCP1.4 capable on Platform and Sink */
 bool intel_hdcp_capable(struct intel_connector *connector)
 {
-	struct intel_digital_port *dig_port = intel_attached_dig_port(connector);
+	struct intel_digital_port *dig_port;
 	const struct intel_hdcp_shim *shim = connector->hdcp.shim;
 	bool capable = false;
 	u8 bksv[5];
 
+	if (!intel_attached_encoder(connector))
+		return capable;
+
+	dig_port = intel_attached_dig_port(connector);
+
 	if (!shim)
 		return capable;
 
-- 
2.39.5