linux-cve-announce - CVE-2025-68248: vmw_balloon: indicate success when effectively deflating during migration

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Message-ID: <2025121623-CVE-2025-68248-2695@gregkh>
Date: Tue, 16 Dec 2025 15:32:24 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68248: vmw_balloon: indicate success when effectively deflating during migration

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

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

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

vmw_balloon: indicate success when effectively deflating during migration

When migrating a balloon page, we first deflate the old page to then
inflate the new page.

However, if inflating the new page succeeded, we effectively deflated the
old page, reducing the balloon size.

In that case, the migration actually worked: similar to migrating+
immediately deflating the new page.  The old page will be freed back to
the buddy.

Right now, the core will leave the page be marked as isolated (as we
returned an error).  When later trying to putback that page, we will run
into the WARN_ON_ONCE() in balloon_page_putback().

That handling was changed in commit 3544c4faccb8 ("mm/balloon_compaction:
stop using __ClearPageMovable()"); before that change, we would have
tolerated that way of handling it.

To fix it, let's just return 0 in that case, making the core effectively
just clear the "isolated" flag + freeing it back to the buddy as if the
migration succeeded.  Note that the new page will also get freed when the
core puts the last reference.

Note that this also makes it all be more consistent: we will no longer
unisolate the page in the balloon driver while keeping it marked as being
isolated in migration core.

This was found by code inspection.

The Linux kernel CVE team has assigned CVE-2025-68248 to this issue.

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

	Issue introduced in 6.17 with commit 3544c4faccb8f0867bc65f8007ee70bfb5054305 and fixed in 6.17.6 with commit aa05a044c5c2e147d726ac2fae1a97e0775eac11
	Issue introduced in 6.17 with commit 3544c4faccb8f0867bc65f8007ee70bfb5054305 and fixed in 6.18 with commit 4ba5a8a7faa647ada8eae61a36517cf369f5bbe4

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-2025-68248
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/misc/vmw_balloon.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/aa05a044c5c2e147d726ac2fae1a97e0775eac11
	https://git.kernel.org/stable/c/4ba5a8a7faa647ada8eae61a36517cf369f5bbe4