CVE-2025-21703 Information

Description

In the Linux kernel the following vulnerability has been resolved:

netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()

qdisc_tree_reduce_backlog() notifies parent qdisc only if child qdisc becomes empty therefore we need to reduce the backlog of the child qdisc before calling it. Otherwise it would miss the opportunity to call cops->qlen_notify() in the case of DRR it resulted in UAF since DRR uses ->qlen_notify() to maintain its active list.

Reference

https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5 https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83 https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71 https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32