[PATCH AUTOSEL 4.9 02/98] mm/memory_hotplug.c: fix overflow in test_pages_in_a_zone()

[Sasha Levin]

From: zhong jiang <zhongjiang@xxxxxxxxxx>

[ Upstream commit d6d8c8a48291b929b2e039f220f0b62958cccfea ]

When mainline introduced commit a96dfddbcc04 ("base/memory, hotplug: fix
a kernel oops in show_valid_zones()"), it obtained the valid start and
end pfn from the given pfn range.  The valid start pfn can fix the
actual issue, but it introduced another issue.  The valid end pfn will
may exceed the given end_pfn.

Although the incorrect overflow will not result in actual problem at
present, but I think it need to be fixed.

[toshi.kani@xxxxxxx: remove assumption that end_pfn is aligned by MAX_ORDER_NR_PAGES]
Fixes: a96dfddbcc04 ("base/memory, hotplug: fix a kernel oops in show_valid_zones()")
Link: http://lkml.kernel.org/r/1486467299-22648-1-git-send-email-zhongjiang@xxxxxxxxxx
Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx>
Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 mm/memory_hotplug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c9f715b2917f..0f962cc3f1bf 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1508,7 +1508,7 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
 			while ((i < MAX_ORDER_NR_PAGES) &&
 				!pfn_valid_within(pfn + i))
 				i++;
-			if (i == MAX_ORDER_NR_PAGES)
+			if (i == MAX_ORDER_NR_PAGES || pfn + i >= end_pfn)
 				continue;
 			page = pfn_to_page(pfn + i);
 			if (zone && page_zone(page) != zone)
@@ -1522,7 +1522,7 @@ int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
 
 	if (zone) {
 		*valid_start = start;
-		*valid_end = end;
+		*valid_end = min(end, end_pfn);
 		return 1;
 	} else {
 		return 0;
-- 
2.17.1