kernel: net/sched: Return NULL when htb_lookup_leaf encounters an empty rbtree

In the Linux kernel, the following vulnerability has been resolved: net/sched: Return NULL when htblookupleaf encounters an empty rbtree htblookupleaf has a BUGON that can trigger with the following: tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo...