Message-ID: <2025090455-CVE-2025-38708-6792@gregkh>
Date: Thu,  4 Sep 2025 17:33:13 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38708: drbd: add missing kref_get in handle_write_conflicts

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

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

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

drbd: add missing kref_get in handle_write_conflicts

With `two-primaries` enabled, DRBD tries to detect "concurrent" writes
and handle write conflicts, so that even if you write to the same sector
simultaneously on both nodes, they end up with the identical data once
the writes are completed.

In handling "superseeded" writes, we forgot a kref_get,
resulting in a premature drbd_destroy_device and use after free,
and further to kernel crashes with symptoms.

Relevance: No one should use DRBD as a random data generator, and apparently
all users of "two-primaries" handle concurrent writes correctly on layer up.
That is cluster file systems use some distributed lock manager,
and live migration in virtualization environments stops writes on one node
before starting writes on the other node.

Which means that other than for "test cases",
this code path is never taken in real life.

FYI, in DRBD 9, things are handled differently nowadays.  We still detect
"write conflicts", but no longer try to be smart about them.
We decided to disconnect hard instead: upper layers must not submit concurrent
writes. If they do, that's their fault.

The Linux kernel CVE team has assigned CVE-2025-38708 to this issue.


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

	Fixed in 5.4.297 with commit 0336bfe9c237476bd7c45605a36ca79c2bca62e5
	Fixed in 5.10.241 with commit 810cd546a29bfac90ed1328ea01d693d4bd11cb1
	Fixed in 5.15.190 with commit 84ef8dd3238330d1795745ece83b19f0295751bf
	Fixed in 6.1.149 with commit 57418de35420cedab035aa1da8a26c0499b7f575
	Fixed in 6.6.103 with commit 9f53b2433ad248cd3342cc345f56f5c7904bd8c4
	Fixed in 6.12.43 with commit 7d483ad300fc0a06f69b019dda8f74970714baf8
	Fixed in 6.15.11 with commit 46e3763dcae0ffcf8fcfaff4fc10a90a92ffdd89
	Fixed in 6.16.2 with commit 3a896498f6f577e57bf26aaa93b48c22b6d20c20
	Fixed in 6.17-rc1 with commit 00c9c9628b49e368d140cfa61d7df9b8922ec2a8

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-2025-38708
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/block/drbd/drbd_receiver.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/0336bfe9c237476bd7c45605a36ca79c2bca62e5
	https://git.kernel.org/stable/c/810cd546a29bfac90ed1328ea01d693d4bd11cb1
	https://git.kernel.org/stable/c/84ef8dd3238330d1795745ece83b19f0295751bf
	https://git.kernel.org/stable/c/57418de35420cedab035aa1da8a26c0499b7f575
	https://git.kernel.org/stable/c/9f53b2433ad248cd3342cc345f56f5c7904bd8c4
	https://git.kernel.org/stable/c/7d483ad300fc0a06f69b019dda8f74970714baf8
	https://git.kernel.org/stable/c/46e3763dcae0ffcf8fcfaff4fc10a90a92ffdd89
	https://git.kernel.org/stable/c/3a896498f6f577e57bf26aaa93b48c22b6d20c20
	https://git.kernel.org/stable/c/00c9c9628b49e368d140cfa61d7df9b8922ec2a8

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