linux-cve-announce - CVE-2022-49995: writeback: avoid use-after-free after removing device

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Message-ID: <2025061826-CVE-2022-49995-2d74@gregkh>
Date: Wed, 18 Jun 2025 13:01:00 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-49995: writeback: avoid use-after-free after removing device

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

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

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

writeback: avoid use-after-free after removing device

When a disk is removed, bdi_unregister gets called to stop further
writeback and wait for associated delayed work to complete.  However,
wb_inode_writeback_end() may schedule bandwidth estimation dwork after
this has completed, which can result in the timer attempting to access the
just freed bdi_writeback.

Fix this by checking if the bdi_writeback is alive, similar to when
scheduling writeback work.

Since this requires wb->work_lock, and wb_inode_writeback_end() may get
called from interrupt, switch wb->work_lock to an irqsafe lock.

The Linux kernel CVE team has assigned CVE-2022-49995 to this issue.


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

	Issue introduced in 5.15 with commit 45a2966fd64147518dc5bca25f447bd0fb5359ac and fixed in 5.15.64 with commit f96b9f7c1676923bce871e728bb49c0dfa5013cc
	Issue introduced in 5.15 with commit 45a2966fd64147518dc5bca25f447bd0fb5359ac and fixed in 5.19.6 with commit 9a6c710f3bc10bc9cc23e1c080b53245b7f9d5b7
	Issue introduced in 5.15 with commit 45a2966fd64147518dc5bca25f447bd0fb5359ac and fixed in 6.0 with commit f87904c075515f3e1d8f4a7115869d3b914674fd

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-2022-49995
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:
	fs/fs-writeback.c
	mm/backing-dev.c
	mm/page-writeback.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/f96b9f7c1676923bce871e728bb49c0dfa5013cc
	https://git.kernel.org/stable/c/9a6c710f3bc10bc9cc23e1c080b53245b7f9d5b7
	https://git.kernel.org/stable/c/f87904c075515f3e1d8f4a7115869d3b914674fd