From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date: Wed, 11 Jan 2017 00:58:00 +0000 (-0800)
Subject: mm: don't dereference struct page fields of invalid pages
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=f073bdc51771f5a5c7a8d1191bfc3ae371d44de7;p=linux-beck.git

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

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.

Link: http://lkml.kernel.org/r/1481706707-6211-2-git-send-email-ard.biesheuvel@linaro.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Hanjun Guo <hanjun.guo@linaro.org>
Cc: Yisheng Xie <xieyisheng1@huawei.com>
Cc: Robert Richter <rrichter@cavium.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 872caae544ef..74afdb4177cb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1864,14 +1864,14 @@ 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;