cve/published/2025/CVE-2025-37890.mbox

From bippy-1.2.0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@kernel.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2025-37890: net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

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

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

net_sched: hfsc: Fix a UAF vulnerability in class with netem as child qdisc

As described in Gerrard's report [1], we have a UAF case when an hfsc class
has a netem child qdisc. The crux of the issue is that hfsc is assuming
that checking for cl->qdisc->q.qlen == 0 guarantees that it hasn't inserted
the class in the vttree or eltree (which is not true for the netem
duplicate case).

This patch checks the n_active class variable to make sure that the code
won't insert the class in the vttree or eltree twice, catering for the
reentrant case.

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

The Linux kernel CVE team has assigned CVE-2025-37890 to this issue.


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

	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 5.4.294 with commit 273bbcfa53541cde38b2003ad88a59b770306421
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 5.10.238 with commit e0cf8ee23e1915431f262a7b2dee0c7a7d699af0
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 5.15.182 with commit e3e949a39a91d1f829a4890e7dfe9417ac72e4d0
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 6.1.138 with commit 8df7d37d626430035b413b97cee18396b3450bef
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 6.6.90 with commit 6082a87af4c52f58150d40dec1716011d871ac21
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 6.12.28 with commit 2e7093c7a8aba5d4f8809f271488e5babe75e202
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 6.14.6 with commit ac39fd4a757584d78ed062d4f6fd913f83bd98b5
	Issue introduced in 5.0 with commit 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea and fixed in 6.15 with commit 141d34391abbb315d68556b7c67ad97885407547

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-2025-37890
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_hfsc.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/273bbcfa53541cde38b2003ad88a59b770306421
	https://git.kernel.org/stable/c/e0cf8ee23e1915431f262a7b2dee0c7a7d699af0
	https://git.kernel.org/stable/c/e3e949a39a91d1f829a4890e7dfe9417ac72e4d0
	https://git.kernel.org/stable/c/8df7d37d626430035b413b97cee18396b3450bef
	https://git.kernel.org/stable/c/6082a87af4c52f58150d40dec1716011d871ac21
	https://git.kernel.org/stable/c/2e7093c7a8aba5d4f8809f271488e5babe75e202
	https://git.kernel.org/stable/c/ac39fd4a757584d78ed062d4f6fd913f83bd98b5
	https://git.kernel.org/stable/c/141d34391abbb315d68556b7c67ad97885407547