linux-cve-announce - CVE-2025-40083: net/sched: sch_qfq: Fix null-deref in agg

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Message-ID: <2025102908-CVE-2025-40083-1481@gregkh>
Date: Wed, 29 Oct 2025 14:37:09 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40083: net/sched: sch_qfq: Fix null-deref in agg_dequeue

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

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

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

net/sched: sch_qfq: Fix null-deref in agg_dequeue

To prevent a potential crash in agg_dequeue (net/sched/sch_qfq.c)
when cl->qdisc->ops->peek(cl->qdisc) returns NULL, we check the return
value before using it, similar to the existing approach in sch_hfsc.c.

To avoid code duplication, the following changes are made:

1. Changed qdisc_warn_nonwc(include/net/pkt_sched.h) into a static
inline function.

2. Moved qdisc_peek_len from net/sched/sch_hfsc.c to
include/net/pkt_sched.h so that sch_qfq can reuse it.

3. Applied qdisc_peek_len in agg_dequeue to avoid crashing.

The Linux kernel CVE team has assigned CVE-2025-40083 to this issue.

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

	Fixed in 6.16 with commit dd831ac8221e691e9e918585b1003c7071df0379

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-2025-40083
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:
	include/net/pkt_sched.h
	net/sched/sch_api.c
	net/sched/sch_hfsc.c
	net/sched/sch_qfq.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/dd831ac8221e691e9e918585b1003c7071df0379