linux-cve-announce - CVE-2025-38107: net_sched: ets: fix a race in ets_qdisc

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Message-ID: <2025070323-CVE-2025-38107-9344@gregkh>
Date: Thu,  3 Jul 2025 10:35:24 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38107: net_sched: ets: fix a race in ets_qdisc_change()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2025-38107 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.10.142 with commit 699d82e9a6db29d509a71f1f2f4316231e6232e6 and fixed in 5.10.239 with commit eb7b74e9754e1ba2088f914ad1f57a778b11894b
	Issue introduced in 5.15.66 with commit ce881ddbdc028fb1988b66e40e45ca0529c23b46 and fixed in 5.15.186 with commit 0b479d0aa488cb478eb2e1d8868be946ac8afb4f
	Issue introduced in 6.0 with commit b05972f01e7d30419987a1f221b5593668fd6448 and fixed in 6.1.142 with commit 347867cb424edae5fec1622712c8dd0a2c42918f
	Issue introduced in 6.0 with commit b05972f01e7d30419987a1f221b5593668fd6448 and fixed in 6.6.94 with commit 0383b25488a545be168744336847549d4a2d3d6c
	Issue introduced in 6.0 with commit b05972f01e7d30419987a1f221b5593668fd6448 and fixed in 6.12.34 with commit 073f64c03516bcfaf790f8edc772e0cfb8a84ec3
	Issue introduced in 6.0 with commit b05972f01e7d30419987a1f221b5593668fd6448 and fixed in 6.15.3 with commit fed94bd51d62d2e0e006aa61480e94e5cd0582b0
	Issue introduced in 6.0 with commit b05972f01e7d30419987a1f221b5593668fd6448 and fixed in 6.16-rc2 with commit d92adacdd8c2960be856e0b82acc5b7c5395fddb
	Issue introduced in 5.4.213 with commit fffa19b5e58c34004a0d6f642d9c24b11d213994
	Issue introduced in 5.19.8 with commit fb155f6597cd7bc3aeed668c3bb15fc3b7cb257d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-38107
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	net/sched/sch_ets.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/eb7b74e9754e1ba2088f914ad1f57a778b11894b
	https://git.kernel.org/stable/c/0b479d0aa488cb478eb2e1d8868be946ac8afb4f
	https://git.kernel.org/stable/c/347867cb424edae5fec1622712c8dd0a2c42918f
	https://git.kernel.org/stable/c/0383b25488a545be168744336847549d4a2d3d6c
	https://git.kernel.org/stable/c/073f64c03516bcfaf790f8edc772e0cfb8a84ec3
	https://git.kernel.org/stable/c/fed94bd51d62d2e0e006aa61480e94e5cd0582b0
	https://git.kernel.org/stable/c/d92adacdd8c2960be856e0b82acc5b7c5395fddb