Patch "mm: don't dereference struct page fields of invalid pages" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

mm: don't dereference struct page fields of invalid pages

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-don-t-dereference-struct-page-fields-of-invalid-pages.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ard Biesheuvel <[email protected]>
Date: Tue, 10 Jan 2017 16:58:00 -0800
Subject: mm: don't dereference struct page fields of invalid pages

From: Ard Biesheuvel <[email protected]>

[ Upstream commit f073bdc51771f5a5c7a8d1191bfc3ae371d44de7 ]

The VM_BUG_ON() check in move_freepages() checks whether the node id of a page matches the node id of its zone. However, it does this before having checked whether the struct page pointer refers to a valid struct page to begin with. This is guaranteed in most cases, but may not be the case if CONFIG_HOLES_IN_ZONE=y.

So reorder the VM_BUG_ON() with the pfn_valid_within() check.

---
 mm/page_alloc.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

@@ -1527,14 +1527,14 @@ int move_freepages(struct zone *zone,
 #endif
 
 	for (page = start_page; page <= end_page;) {
-		/* Make sure we are not inadvertently changing nodes */
-		VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
-
 		if (!pfn_valid_within(page_to_pfn(page))) {
 			page++;
 			continue;
 		}
 
+		/* Make sure we are not inadvertently changing nodes */
+		VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page);
+
 		if (!PageBuddy(page)) {
 			page++;
 			continue;

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mm-don-t-dereference-struct-page-fields-of-invalid-pages.patch