+ mm-fix-null-pointer-dereference-in-alloc_pages_bulk_noprof.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: fix NULL pointer dereference in alloc_pages_bulk_noprof
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-null-pointer-dereference-in-alloc_pages_bulk_noprof.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-null-pointer-dereference-in-alloc_pages_bulk_noprof.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Jinjiang Tu <tujinjiang@huawei.com>
Subject: mm: fix NULL pointer dereference in alloc_pages_bulk_noprof
Date: Wed, 13 Nov 2024 16:32:35 +0800

We triggered a NULL pointer dereference for ac.preferred_zoneref->zone in
alloc_pages_bulk_noprof() when the task is migrated between cpusets.

When cpuset is enabled, in prepare_alloc_pages(), ac->nodemask may be
&current->mems_allowed.  when first_zones_zonelist() is called to find
preferred_zoneref, the ac->nodemask may be modified concurrently if the
task is migrated between different cpusets.  Assuming we have 2 NUMA Node,
when traversing Node1 in ac->zonelist, the nodemask is 2, and when
traversing Node2 in ac->zonelist, the nodemask is 1.  As a result, the
ac->preferred_zoneref points to NULL zone.

In alloc_pages_bulk_noprof(), for_each_zone_zonelist_nodemask() finds a
allowable zone and calls zonelist_node_idx(ac.preferred_zoneref), leading
to NULL pointer dereference.

__alloc_pages_noprof() fixes this issue by checking NULL pointer in commit
ea57485af8f4 ("mm, page_alloc: fix check for NULL preferred_zone") and
commit df76cee6bbeb ("mm, page_alloc: remove redundant checks from alloc
fastpath").

To fix it, check NULL pointer for preferred_zoneref->zone.

Link: https://lkml.kernel.org/r/20241113083235.166798-1-tujinjiang@huawei.com
Fixes: 387ba26fb1cb ("mm/page_alloc: add a bulk page allocator")
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Lobakin <alobakin@pm.me>
Cc: David Hildenbrand <david@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c~mm-fix-null-pointer-dereference-in-alloc_pages_bulk_noprof
+++ a/mm/page_alloc.c
@@ -4607,7 +4607,8 @@ unsigned long alloc_pages_bulk_noprof(gf
 	gfp = alloc_gfp;
 
 	/* Find an allowed local zone that meets the low watermark. */
-	for_each_zone_zonelist_nodemask(zone, z, ac.zonelist, ac.highest_zoneidx, ac.nodemask) {
+	z = ac.preferred_zoneref;
+	for_next_zone_zonelist_nodemask(zone, z, ac.highest_zoneidx, ac.nodemask) {
 		unsigned long mark;
 
 		if (cpusets_enabled() && (alloc_flags & ALLOC_CPUSET) &&
_

Patches currently in -mm which might be from tujinjiang@huawei.com are

mm-fix-null-pointer-dereference-in-alloc_pages_bulk_noprof.patch