Bug 2376059 (CVE-2025-38107)

Summary: CVE-2025-38107 kernel: net_sched: ets: fix a race in ets_qdisc_change()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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Description OSIDB Bzimport 2025-07-03 09:02:52 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net_sched: ets: fix a race in ets_qdisc_change()

Gerrard Tai reported a race condition in ETS, 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.
Comment 1 Avinash Hanwate 2025-07-03 18:00:55 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025070323-CVE-2025-38107-9344@gregkh/T