Bug 2367500 (CVE-2025-37914)

Summary: CVE-2025-37914 kernel: net_sched: ets: Fix double list add in class with netem as child qdisc
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedCC: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A use-after-free vulnerability was found in the Linux kernel’s `netem` qdisc. This issue occurs when it incorrectly manages duplicated packets in classful parent qdiscs. This leads to a corrupted internal state and eventual dereferencing of freed memory, resulting in unpredictable behavior, system instability, or a crash.
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Description OSIDB Bzimport 2025-05-20 16:01:14 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net_sched: ets: 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 ets, 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
doing the addition to cater for the reentrant case.

[1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/
Comment 1 Jon Moroney 2025-05-20 19:43:08 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025052000-CVE-2025-37914-1a4f@gregkh/T