CVE-2025-38000

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

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

When enqueuing the first packet to an HFSC class, hfsc_enqueue() calls the

child qdisc's peek() operation before incrementing sch->q.qlen and

sch->qstats.backlog. If the child qdisc uses qdisc_peek_dequeued(), this may

trigger an immediate dequeue and potential packet drop. In such cases,

qdisc_tree_reduce_backlog() is called, but the HFSC qdisc's qlen and backlog

have not yet been updated, leading to inconsistent queue accounting. This

can leave an empty HFSC class in the active list, causing further

consequences like use-after-free.

This patch fixes the bug by moving the increment of sch->q.qlen and

sch->qstats.backlog before the call to the child qdisc's peek() operation.

This ensures that queue length and backlog are always accurate when packet

drops or dequeues are triggered during the peek.