CVE-2026-93227: mm/mm_init: deferred_grow_zone(): fix out-of-range first_deferred_pfn

CVE-2026-93227: mm/mm_init: deferred_grow_zone(): fix out-of-range first_deferred_pfn

[Greg Kroah-Hartman]

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

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

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

mm/mm_init: deferred_grow_zone(): fix out-of-range first_deferred_pfn

With CONFIG_DEFERRED_STRUCT_PAGE_INIT enabled, deferred_grow_zone()
initializes struct pages early in boot to satisfy an allocation.

With a large CMA reservation in place, the ranges deferred_init_memmap()
finds may not add up to the allocation it was asked for, and the function
ends up initializing the memory map of the entire zone and still falls
short.

That is fine in itself: the function accounts for it and leaves the
caller to decide whether it now has enough memory.

However, the update of pgdat->first_deferred_pfn that tracks where
uninitialized memory map starts could overflow.

If the node's RAM end is not aligned on PAGES_PER_SECTION boundaries and
some deferred struct pages were initialized, pgdat->first_deferred_pfn
would point past the end of the node's memory.

deferred_init_memmap() later picks up from pgdat->first_deferred_pfn and
hits a BUG_ON(), because it expects a pfn within its node.

For example, when running a kernel with CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
and CONFIG_CMA=y using the following qemu command line

  qemu-system-x86_64 -enable-kvm -m 8032M -kernel bzImage \
      -append "nokaslr cma=4768M@0x100000000"

the kernel panics:

  kernel BUG at mm/mm_init.c:2131!
  CPU: 3 UID: 0 PID: 36 Comm: pgdatinit0 Not tainted 7.2.0-rc6 #1
  RIP: 0010:deferred_init_memmap+0x1b8/0x1c0
  RAX: 0000000000236000 R13: 0000000000238000
  Call Trace:
   kthread+0xdf/0x120
   ret_from_fork+0x187/0x250

Make sure that the update of pgdta->first_deferred_pfn does not overflow
when the entire zone's (and therefore node's) memory map is initialized.

[rppt: massaged the changelog]

The Linux kernel CVE team has assigned CVE-2026-93227 to this issue.


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

	Issue introduced in 6.18 with commit 3acb913c9d5bd8dcf61677ccba96d349e7681cf8 and fixed in 6.18.50 with commit 45489d4f95802903ab35799b400b346fa4e13151
	Issue introduced in 6.18 with commit 3acb913c9d5bd8dcf61677ccba96d349e7681cf8 and fixed in 7.2.4 with commit 84339578c2d6936ac3a93cd1f0bbaa3468a988f2
	Issue introduced in 6.18 with commit 3acb913c9d5bd8dcf61677ccba96d349e7681cf8 and fixed in 7.3-rc1 with commit 97090500d776c3f6d08e857e3a0a7cf092999094

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-2026-93227
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/45489d4f95802903ab35799b400b346fa4e13151
	https://git.kernel.org/stable/c/84339578c2d6936ac3a93cd1f0bbaa3468a988f2
	https://git.kernel.org/stable/c/97090500d776c3f6d08e857e3a0a7cf092999094