CVE-2026-72172: mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE

CVE-2026-72172: mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE

[Greg Kroah-Hartman]

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

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

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

mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE

If DAX memory is hotplugged into an unoccupied subsection of an early
section, section_activate() reuses the unoptimized boot memmap.  However,
compound_nr_pages() still assumes that vmemmap optimization is in effect
and initializes only the reduced number of struct pages.  As a result, the
remaining tail struct pages are left uninitialized, which can later lead
to unexpected behavior or crashes.

Fix this by treating early sections as unoptimized when calculating how
many struct pages to initialize.

The Linux kernel CVE team has assigned CVE-2026-72172 to this issue.


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

	Issue introduced in 5.19 with commit 6fd3620b342861de9547ea01d28f664892ef51a1 and fixed in 6.6.145 with commit 511a60e71aec308b24722cffc1912bf6befb87bf
	Issue introduced in 5.19 with commit 6fd3620b342861de9547ea01d28f664892ef51a1 and fixed in 6.12.97 with commit 11f2826e9ee6f24aaa774e3dcd75abbe4b3091b6
	Issue introduced in 5.19 with commit 6fd3620b342861de9547ea01d28f664892ef51a1 and fixed in 6.18.40 with commit da5234df0941665f3a3f5b80f3dab94046537be0
	Issue introduced in 5.19 with commit 6fd3620b342861de9547ea01d28f664892ef51a1 and fixed in 7.1.5 with commit b91e27bce37cab9f35de0059278ebe457ca9878b
	Issue introduced in 5.19 with commit 6fd3620b342861de9547ea01d28f664892ef51a1 and fixed in 7.2-rc1 with commit cd681403a87085562499d60325b7b45d3be11217

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-2026-72172
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/mm_init.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/511a60e71aec308b24722cffc1912bf6befb87bf
	https://git.kernel.org/stable/c/11f2826e9ee6f24aaa774e3dcd75abbe4b3091b6
	https://git.kernel.org/stable/c/da5234df0941665f3a3f5b80f3dab94046537be0
	https://git.kernel.org/stable/c/b91e27bce37cab9f35de0059278ebe457ca9878b
	https://git.kernel.org/stable/c/cd681403a87085562499d60325b7b45d3be11217