linux-cve-announce - CVE-2025-22126: md: fix mddev uaf while iterating all

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Message-ID: <2025041629-CVE-2025-22126-50e3@gregkh>
Date: Wed, 16 Apr 2025 16:13:37 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-22126: md: fix mddev uaf while iterating all_mddevs list

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

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

md: fix mddev uaf while iterating all_mddevs list

While iterating all_mddevs list from md_notify_reboot() and md_exit(),
list_for_each_entry_safe is used, and this can race with deletint the
next mddev, causing UAF:

t1:
spin_lock
//list_for_each_entry_safe(mddev, n, ...)
 mddev_get(mddev1)
 // assume mddev2 is the next entry
 spin_unlock
            t2:
            //remove mddev2
            ...
            mddev_free
            spin_lock
            list_del
            spin_unlock
            kfree(mddev2)
 mddev_put(mddev1)
 spin_lock
 //continue dereference mddev2->all_mddevs

The old helper for_each_mddev() actually grab the reference of mddev2
while holding the lock, to prevent from being freed. This problem can be
fixed the same way, however, the code will be complex.

Hence switch to use list_for_each_entry, in this case mddev_put() can free
the mddev1 and it's not safe as well. Refer to md_seq_show(), also factor
out a helper mddev_put_locked() to fix this problem.

The Linux kernel CVE team has assigned CVE-2025-22126 to this issue.


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

	Issue introduced in 6.0 with commit f26514342255855f4ca3c0a92cb1cdea01c33004 and fixed in 6.14.2 with commit 5462544ccbad3fc938a71b01fa5bd3a0dc2b750a
	Issue introduced in 6.0 with commit f26514342255855f4ca3c0a92cb1cdea01c33004 and fixed in 6.15-rc1 with commit 8542870237c3a48ff049b6c5df5f50c8728284fa

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-2025-22126
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:
	drivers/md/md.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/5462544ccbad3fc938a71b01fa5bd3a0dc2b750a
	https://git.kernel.org/stable/c/8542870237c3a48ff049b6c5df5f50c8728284fa