In the Linux kernel, the following vulnerability has been resolved:
net/sched: sch_taprio: Replace direct dequeue call with peek and qdisc_dequeue_peeked
When taprios software path peeks a non-work-conserving child qdisc, the child stashes the peeked skb in its gso_skb; taprio_dequeue_from_txq() then takes the packet with a direct child ->dequeue() call, which ignores that stash, orphans the peeked skb and desyncs the childs qlen/backlog. With a qfq child this re-enters the child on an emptied list and dereferences NULL, panicking the kernel from softirq on ordinary egress.
Take the packet through qdisc_dequeue_peeked(), as sch_red and sch_sfb now do. The helper returns the childs stashed skb first and is a no-op when there is none, so a work-conserving child is unaffected and the gated path now consumes the skb whose length was charged to the budget.
References
- https://git.kernel.org/stable/c/18d580cb00c55805633bae45e90cf22ed6b8e424
- https://git.kernel.org/stable/c/2dcebbd1ad2e180fe7b98bf346ced69a872e11e6
- https://git.kernel.org/stable/c/6ee5a7665a9080bcb05d703bf981a579436fd05e
- https://git.kernel.org/stable/c/e056e1dfcddca877dd46d704e8ec9860cfc9ec44
- https://git.kernel.org/stable/c/e2b7ee61989f2d39df6c2cc06f9db1aea69bdb09