linux-kernel - [PATCH for v4.9 LTS 85/87] mm: don't dereference struct page fields of invalid pages

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Date:   Sat, 15 Jul 2017 01:26:27 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Robert Richter <rrichter@...ium.com>,
        James Morse <james.morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
Subject: [PATCH for v4.9 LTS 85/87] mm: don't dereference struct page fields
 of invalid pages

From: Ard Biesheuvel <ard.biesheuvel@...aro.org>

[ 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.

Link: http://lkml.kernel.org/r/1481706707-6211-2-git-send-email-ard.biesheuvel@linaro.org
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Acked-by: Will Deacon <will.deacon@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Hanjun Guo <hanjun.guo@...aro.org>
Cc: Yisheng Xie <xieyisheng1@...wei.com>
Cc: Robert Richter <rrichter@...ium.com>
Cc: James Morse <james.morse@....com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 mm/page_alloc.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 56df8c24689d..85881bf01776 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1875,14 +1875,14 @@ 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;
-- 
2.11.0