linux-cve-announce - CVE-2021-47646: Revert "Revert "block, bfq: honor already-setup queue merges""

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Message-ID: <2025022648-CVE-2021-47646-d726@gregkh>
Date: Wed, 26 Feb 2025 02:53:57 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2021-47646: Revert "Revert "block, bfq: honor already-setup queue merges""

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

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

Revert "Revert "block, bfq: honor already-setup queue merges""

A crash [1] happened to be triggered in conjunction with commit
2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The
latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq:
honor already-setup queue merges""). Yet, the reverted commit was not
the one introducing the bug. In fact, it actually triggered a UAF
introduced by a different commit, and now fixed by commit d29bd41428cf
("block, bfq: reset last_bfqq_created on group change").

So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq:
honor already-setup queue merges") out. This commit restores it.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

The Linux kernel CVE team has assigned CVE-2021-47646 to this issue.


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

	Fixed in 4.19.238 with commit f990f0985eda59d4f29fc83fcf300c92b1225d39
	Fixed in 5.4.189 with commit 931aff627469a75c77b9fd3823146d0575afffd6
	Fixed in 5.10.110 with commit cc051f497eac9d8a0d816cd4bffa3415f2724871
	Fixed in 5.15.33 with commit 65d8a737452e88f251fe5d925371de6d606df613
	Fixed in 5.16.19 with commit abc2129e646af7b43025d90a071f83043f1ae76c
	Fixed in 5.17.2 with commit 4083925bd6dc89216d156474a8076feec904e607
	Fixed in 5.18 with commit 15729ff8143f8135b03988a100a19e66d7cb7ecd

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-2021-47646
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:
	block/bfq-iosched.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/f990f0985eda59d4f29fc83fcf300c92b1225d39
	https://git.kernel.org/stable/c/931aff627469a75c77b9fd3823146d0575afffd6
	https://git.kernel.org/stable/c/cc051f497eac9d8a0d816cd4bffa3415f2724871
	https://git.kernel.org/stable/c/65d8a737452e88f251fe5d925371de6d606df613
	https://git.kernel.org/stable/c/abc2129e646af7b43025d90a071f83043f1ae76c
	https://git.kernel.org/stable/c/4083925bd6dc89216d156474a8076feec904e607
	https://git.kernel.org/stable/c/15729ff8143f8135b03988a100a19e66d7cb7ecd