linux-cve-announce - CVE-2025-38686: userfaultfd: fix a crash in UFFDIO

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Message-ID: <2025090447-CVE-2025-38686-281b@gregkh>
Date: Thu,  4 Sep 2025 17:32:51 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38686: userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry

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

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

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

userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry

When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with
obtaining a folio and accessing it even though the entry is swp_entry_t. 
Add the missing check and let split_huge_pmd() handle migration entries. 
While at it also remove unnecessary folio check.

[surenb@...gle.com: remove extra folio check, per David]

The Linux kernel CVE team has assigned CVE-2025-38686 to this issue.


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

	Issue introduced in 6.8 with commit adef440691bab824e39c1b17382322d195e1fab0 and fixed in 6.12.43 with commit bb81c18dbd42650c844e160cafa7cbb20243a96a
	Issue introduced in 6.8 with commit adef440691bab824e39c1b17382322d195e1fab0 and fixed in 6.15.11 with commit 1202abad7a7ccd28c426d2844771a387b07629a4
	Issue introduced in 6.8 with commit adef440691bab824e39c1b17382322d195e1fab0 and fixed in 6.16.2 with commit 7f1101a0a181243ad587ececdffc4845f035549f
	Issue introduced in 6.8 with commit adef440691bab824e39c1b17382322d195e1fab0 and fixed in 6.17-rc2 with commit aba6faec0103ed8f169be8dce2ead41fcb689446

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-2025-38686
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/userfaultfd.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/bb81c18dbd42650c844e160cafa7cbb20243a96a
	https://git.kernel.org/stable/c/1202abad7a7ccd28c426d2844771a387b07629a4
	https://git.kernel.org/stable/c/7f1101a0a181243ad587ececdffc4845f035549f
	https://git.kernel.org/stable/c/aba6faec0103ed8f169be8dce2ead41fcb689446