media: v4l2-ctrls: validate HEVC active reference counts

In the Linux kernel, the following vulnerability has been resolved: media: v4l2-ctrls: validate HEVC active reference counts 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.

Where it's fixed