CVE-2026-31422 net/sched: cls_flow: fix NULL pointer dereference on shared blocks

In the Linux kernel, the following vulnerability has been resolved: net/sched: clsflow: fix NULL pointer dereference on shared blocks flowchange calls tcfblockq and dereferences q-handle to derive a default baseclass. Shared blocks leave block-q NULL, causing a NULL deref when a flow filter witho...