linux-cve-announce - CVE-2023-53421: blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset

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Message-ID: <2025091855-CVE-2023-53421-0dd9@gregkh>
Date: Thu, 18 Sep 2025 18:04:12 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-53421: blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

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

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

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

blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

When blkg_alloc() is called to allocate a blkcg_gq structure
with the associated blkg_iostat_set's, there are 2 fields within
blkg_iostat_set that requires proper initialization - blkg & sync.
The former field was introduced by commit 3b8cc6298724 ("blk-cgroup:
Optimize blkcg_rstat_flush()") while the later one was introduced by
commit f73316482977 ("blk-cgroup: reimplement basic IO stats using
cgroup rstat").

Unfortunately those fields in the blkg_iostat_set's are not properly
re-initialized when they are cleared in v1's blkcg_reset_stats(). This
can lead to a kernel panic due to NULL pointer access of the blkg
pointer. The missing initialization of sync is less problematic and
can be a problem in a debug kernel due to missing lockdep initialization.

Fix these problems by re-initializing them after memory clearing.

The Linux kernel CVE team has assigned CVE-2023-53421 to this issue.

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

	Issue introduced in 5.5 with commit f73316482977ac401ac37245c9df48079d4e11f3 and fixed in 6.3.13 with commit b0d26283af612b9e0cc3188b0b88ad7fdea447e8
	Issue introduced in 5.5 with commit f73316482977ac401ac37245c9df48079d4e11f3 and fixed in 6.4.4 with commit abbce7f82613ea5eeefd0fc3c1c8e449b9cef2a2
	Issue introduced in 5.5 with commit f73316482977ac401ac37245c9df48079d4e11f3 and fixed in 6.5 with commit 3d2af77e31ade05ff7ccc3658c3635ec1bea0979

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-2023-53421
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/blk-cgroup.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/b0d26283af612b9e0cc3188b0b88ad7fdea447e8
	https://git.kernel.org/stable/c/abbce7f82613ea5eeefd0fc3c1c8e449b9cef2a2
	https://git.kernel.org/stable/c/3d2af77e31ade05ff7ccc3658c3635ec1bea0979