net/sched: sch_qfq: Fix race condition on qfq_aggregate

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_qfq: Fix race condition on qfq_aggregate

A race condition can occur when 'agg' is modified in qfq_change_agg

(called during qfq_enqueue) while other threads access it

concurrently. For example, qfq_dump_class may trigger a NULL

dereference, and qfq_delete_class may cause a use-after-free.

This patch addresses the issue by:

1. Moved qfq_destroy_class into the critical section.

2. Added sch_tree_lock protection to qfq_dump_class and

qfq_dump_class_stats.