CVE-2026-89755: mm/migrate_device: clear stale mapping after freeing swapcache

CVE-2026-89755: mm/migrate_device: clear stale mapping after freeing swapcache

[Greg Kroah-Hartman]

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

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

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

mm/migrate_device: clear stale mapping after freeing swapcache

__migrate_device_pages() reads the folio mapping before calling
folio_free_swap().  When folio_free_swap() succeeds, the folio is removed
from the swap cache, but the saved mapping still points to swap_space.

Passing the stale mapping to folio_migrate_mapping() makes it use the
mapped-folio path for a folio that is no longer in swapcache.  It can then
operate on swap_space.i_pages with invalid reference accounting,
eventually triggering a folio reference count BUG.

After a successful split, nr still contains the number of pages in the
original large folio, although each resulting page is now a separate
order-0 folio.  Reset nr to 1 so each split folio is processed separately,
including its own swapcache removal and mapping lookup.

Refresh the saved mapping after folio_free_swap() so the current folio
state is used during migration.

The Linux kernel CVE team has assigned CVE-2026-89755 to this issue.


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

	Issue introduced in 6.6 with commit df263d9a7dffee94ca5391120ee3b0587efa07f1 and fixed in 7.2.4 with commit 8ffedc6573a665cdc31ebe47eae7b32b78d0df83
	Issue introduced in 6.6 with commit df263d9a7dffee94ca5391120ee3b0587efa07f1 and fixed in 7.3-rc1 with commit 34a00895d032a414830d41106a09329ae6c251b6

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-2026-89755
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_device.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/8ffedc6573a665cdc31ebe47eae7b32b78d0df83
	https://git.kernel.org/stable/c/34a00895d032a414830d41106a09329ae6c251b6