kernel: sch_hfsc: Fix qlen accounting bug when using peek in hfsc_enqueue()

A flaw was found in the HFSC queueing discipline implementation in the Linux kernel. When a packet is enqueued and the child qdisc's peek function is called before properly updating the HFSC queue's length and backlog counters, a race condition can occur. In some cases, the peek operation may...

CVE-2025-21971

CVE-2025-21971 in the Linux kernel net_sched subsystem: creation of a Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) could terminate traversal early during qdisc tree walk, causing incorrect root backlog statistics and potential CRASH in DRR. The fix prevents creating any Qdisc class with TC_H_R...

CVE-2025-21971 net_sched: Prevent creation of classes with TC_H_ROOT

In the Linux kernel, the following vulnerability has been resolved: netsched: Prevent creation of classes with TCHROOT The function qdisctreereducebacklog uses TCHROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created wi...