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Unrated severityNVD Advisory· Published May 20, 2025· Updated Nov 3, 2025

net_sched: drr: Fix double list add in class with netem as child qdisc

CVE-2025-37915

Description

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

net_sched: drr: Fix double list add in class with netem as child qdisc

As described in Gerrard's report [1], there are use cases where a netem child qdisc will make the parent qdisc's enqueue callback reentrant. In the case of drr, there won't be a UAF, but the code will add the same classifier to the list twice, which will cause memory corruption.

In addition to checking for qlen being zero, this patch checks whether the class was already added to the active_list (cl_is_active) before adding to the list to cover for the reentrant case.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/

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