CVE-2026-68330: In the Linux kernel, the following vulnerability has been resolved: net: airoha: Fix DMA direction for NPU mailbox buff

A bug in the Linux kernel's airoha network driver causes data corruption on systems without hardware cache coherency (like EN7581 processors). The driver maps a mailbox buffer (a shared memory area for communication between the CPU and NPU, which is a network processing unit) with DMA_TO_DEVICE (a setting that only allows CPU-to-device data transfer), but the NPU needs to write response data back into the same buffer. When the NPU writes data, the CPU cache isn't properly refreshed, so the calling code reads stale cached data instead of the NPU's response.