linux-cve-announce - CVE-2025-22015: mm/migrate: fix shmem xarray update during migration

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Message-ID: <2025040843-CVE-2025-22015-3408@gregkh>
Date: Tue,  8 Apr 2025 10:16:49 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-22015: mm/migrate: fix shmem xarray update during migration

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

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

mm/migrate: fix shmem xarray update during migration

A shmem folio can be either in page cache or in swap cache, but not at the
same time.  Namely, once it is in swap cache, folio->mapping should be
NULL, and the folio is no longer in a shmem mapping.

In __folio_migrate_mapping(), to determine the number of xarray entries to
update, folio_test_swapbacked() is used, but that conflates shmem in page
cache case and shmem in swap cache case.  It leads to xarray multi-index
entry corruption, since it turns a sibling entry to a normal entry during
xas_store() (see [1] for a userspace reproduction).  Fix it by only using
folio_test_swapcache() to determine whether xarray is storing swap cache
entries or not to choose the right number of xarray entries to update.

[1] https://lore.kernel.org/linux-mm/Z8idPCkaJW1IChjT@casper.infradead.org/

Note:
In __split_huge_page(), folio_test_anon() && folio_test_swapcache() is
used to get swap_cache address space, but that ignores the shmem folio in
swap cache case.  It could lead to NULL pointer dereferencing when a
in-swap-cache shmem folio is split at __xa_store(), since
!folio_test_anon() is true and folio->mapping is NULL.  But fortunately,
its caller split_huge_page_to_list_to_order() bails out early with EBUSY
when folio->mapping is NULL.  So no need to take care of it here.

The Linux kernel CVE team has assigned CVE-2025-22015 to this issue.

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

	Issue introduced in 6.1.71 with commit be72d197b2281e2ee3f28017fc9be1ab17e26d16 and fixed in 6.1.132 with commit 49100c0b070e900f87c8fac3be9b9ef8a30fa673
	Issue introduced in 6.6.10 with commit 07550b1461d4d0499165e7d6f7718cfd0e440427 and fixed in 6.6.85 with commit 29124ae980e2860f0eec7355949d3d3292ee81da
	Issue introduced in 6.7 with commit fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c and fixed in 6.12.21 with commit c057ee03f751d6cecf7ee64f52f6545d94082aaa
	Issue introduced in 6.7 with commit fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c and fixed in 6.13.9 with commit 75cfb92eb63298d717b6b0118f91ba12c4fcfeb5
	Issue introduced in 6.7 with commit fc346d0a70a13d52fe1c4bc49516d83a42cd7c4c and fixed in 6.14 with commit 60cf233b585cdf1f3c5e52d1225606b86acd08b0

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-2025-22015
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/migrate.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/49100c0b070e900f87c8fac3be9b9ef8a30fa673
	https://git.kernel.org/stable/c/29124ae980e2860f0eec7355949d3d3292ee81da
	https://git.kernel.org/stable/c/c057ee03f751d6cecf7ee64f52f6545d94082aaa
	https://git.kernel.org/stable/c/75cfb92eb63298d717b6b0118f91ba12c4fcfeb5
	https://git.kernel.org/stable/c/60cf233b585cdf1f3c5e52d1225606b86acd08b0