[PATCH 6.1.y 1/2] 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.

[ Backport to 6.1.y: this tree uses the older intel_hdcp_capable()
  helper name. Apply the same guard there; the code change is otherwise
  unchanged. ]

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 6.1.y.
This one addresses CVE-2024-53051. It rejects the HDCP capability query
when hotplug or resume left the encoder unset.

The 6.6.y backport went out as the same 2-patch series and has been
picked up for 6.6.y. The fix is already present in 6.12.y, 6.18.y, and
7.2.y, but not in 6.1.y.
The target-specific adjustment is recorded in the bracketed note above.

Could you please queue it for 6.1.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 cb7f86de967a88..507721c94f2fdd 100644
--- a/drivers/gpu/drm/i915/display/intel_hdcp.c
+++ b/drivers/gpu/drm/i915/display/intel_hdcp.c
@@ -182,11 +182,16 @@ 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