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Unrated severityNVD Advisory· Published Feb 18, 2025· Updated Apr 2, 2026

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

CVE-2025-21703

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.

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Affected products

204

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