CVE-2026-43333 bpf: reject direct access to nullable PTR_TO_BUF pointers

In the Linux kernel, the following vulnerability has been resolved: bpf: reject direct access to nullable PTRTOBUF pointers checkmemaccess matches PTRTOBUF via basetype which strips PTRMAYBENULL, allowing direct dereference without a null check. Map iterator ctx-key and ctx-value are PTRTOBUF |...