CVE-2026-74284

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

net/sched: sch_hfsc: Don't make class passive twice

update_vf() is called from two places for the same class during a single

dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last

packets while dequeuing:

1. The child calls qdisc_tree_reduce_backlog(), which, now that the child

is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns

the class passive (cl_nactive is decremented up the hierarchy).

2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time)

to charge the dequeued bytes.

On the second call the class is already passive, but its child qdisc is

still empty, so update_vf() arms go_passive again:

if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC)

go_passive = 1;

The leaf is then skipped by the cl_nactive == 0 check inside the loop,

which does not clear go_passive, so the stale go_passive propagates to the

parent and decrements its cl_nactive a second time. A parent that still

has other active children is driven to cl_nactive == 0 and removed from

the vttree, even though those siblings are still backlogged. They are

never dequeued again and the qdisc stalls.

Fix this by only arming go_passive when the class is actually active, so an

already-passive class no longer triggers a second passive transition. The

byte accounting (cl->cl_total += len) still runs for every ancestor, so

dequeued bytes continue to be counted exactly once.