HEVC slice parameters are shared stateless V4L2 controls, but the common
validation path does not verify the active L0/L1 reference counts before
driver-specific code consumes them.

The original report came from Cedrus, but the active count bounds are
not Cedrus-specific. Validate them in the common HEVC slice control path
so stateless HEVC drivers get the same basic guarantees as soon as the
control is queued.

Do not reject ref_idx_l0/ref_idx_l1 entries here. Existing userspace may
use out-of-range sentinel values such as 0xff for missing references, and
some hardware can use that information for concealment. Keep this common
check limited to the active reference counts.

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
v3:
- add the missing `p_hevc_slice_params` declaration to fix the build break
  reported by lkp
- keep only the active L0/L1 reference count validation in common code
- drop the ref_idx_l0/ref_idx_l1 rejection per Nicolas Dufresne's review,
  since existing userspace may use out-of-range sentinel values such as
  0xff for missing references

 drivers/media/v4l2-core/v4l2-ctrls-core.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
index 6b375720e395..ba047d7d8601 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
@@ -971,6 +971,7 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
 	struct v4l2_ctrl_hevc_ext_sps_st_rps *p_hevc_st_rps;
 	struct v4l2_ctrl_hevc_sps *p_hevc_sps;
 	struct v4l2_ctrl_hevc_pps *p_hevc_pps;
+	struct v4l2_ctrl_hevc_slice_params *p_hevc_slice_params;
 	struct v4l2_ctrl_hdr10_mastering_display *p_hdr10_mastering;
 	struct v4l2_ctrl_hevc_decode_params *p_hevc_decode_params;
 	struct v4l2_area *area;
@@ -1260,6 +1261,18 @@ static int std_validate_compound(const struct v4l2_ctrl *ctrl, u32 idx,
 		break;
 
 	case V4L2_CTRL_TYPE_HEVC_SLICE_PARAMS:
+		p_hevc_slice_params = p;
+
+		if (p_hevc_slice_params->num_ref_idx_l0_active_minus1 >=
+		    V4L2_HEVC_DPB_ENTRIES_NUM_MAX)
+			return -EINVAL;
+
+		if (p_hevc_slice_params->slice_type != V4L2_HEVC_SLICE_TYPE_B)
+			break;
+
+		if (p_hevc_slice_params->num_ref_idx_l1_active_minus1 >=
+		    V4L2_HEVC_DPB_ENTRIES_NUM_MAX)
+			return -EINVAL;
 		break;
 
 	case V4L2_CTRL_TYPE_HEVC_EXT_SPS_ST_RPS:
-- 
2.50.1 (Apple Git-155)