Subject: CVE-2021-47088: mm/damon/dbgfs: protect targets destructions with kdamond_lock

From: Greg Kroah-Hartman <[email-masked]>

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

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

mm/damon/dbgfs: protect targets destructions with kdamond_lock

DAMON debugfs interface iterates current monitoring targets in
'dbgfs_target_ids_read()' while holding the corresponding
'kdamond_lock'.  However, it also destructs the monitoring targets in
'dbgfs_before_terminate()' without holding the lock.  This can result in
a use_after_free bug.  This commit avoids the race by protecting the
destruction with the corresponding 'kdamond_lock'.

The Linux kernel CVE team has assigned CVE-2021-47088 to this issue.

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

	Issue introduced in 5.15 with commit 4bc05954d007 and fixed in 5.15.12 with commit 330c6117a82c
	Issue introduced in 5.15 with commit 4bc05954d007 and fixed in 5.16 with commit 34796417964b

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-2021-47088
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:
	mm/damon/dbgfs.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/330c6117a82c16a9a365a51cec5c9ab30b13245c
	https://git.kernel.org/stable/c/34796417964b8d0aef45a99cf6c2d20cebe33733