Kernel memory disclosure and crash via undersized optlen

Out-of-bounds access in Linux kernel AF_XDP socket handling allows local users to read kernel memory and crash the system. The xsk_setsockopt function copies a four-byte ring value from a supplied socket pointer without first requiring optlen to contain four bytes, so an undersized buffer is read past its allocation. A local user must invoke setsockopt on an AF_XDP socket; successful triggering exposes adjacent kernel memory and can interrupt the host.