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

net_sched: prio: fix a race in prio_tune()

Gerrard Tai reported a race condition in PRIO, whenever SFQ perturb timer
fires at the wrong time.

The race is as follows:

CPU 0                                 CPU 1
[1]: lock root
[2]: qdisc_tree_flush_backlog()
[3]: unlock root
 |
 |                                    [5]: lock root
 |                                    [6]: rehash
 |                                    [7]: qdisc_tree_reduce_backlog()
 |
[4]: qdisc_put()

This can be abused to underflow a parent's qlen.

Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog()
should fix the race, because all packets will be purged from the qdisc
before releasing the lock.

https://git.kernel.org/stable/c/46c15c9d0f65c9ba857d63f53264f4b17e8a715f

https://git.kernel.org/stable/c/93f9eeb678d4c9c1abf720b3615fa8299a490845

https://git.kernel.org/stable/c/d35acc1be3480505b5931f17e4ea9b7617fea4d3

https://git.kernel.org/stable/c/e3f6745006dc9423d2b065b90f191cfa11b1b584