[PATCH] mm: fix a overflow in test_pages_in_a_zone()

[PATCH] mm: fix a overflow in test_pages_in_a_zone()

[zhongjiang]

From: zhong jiang <zhongjiang@huawei.com>

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

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

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
---
 mm/memory_hotplug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b8c11e0..f611584 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1521,7 +1521,7 @@ 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;
-- 
1.8.3.1

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Re: [PATCH] mm: fix a overflow in test_pages_in_a_zone()

[Kani, Toshimitsu]

On Tue, 2017-02-07 at 19:34 +0800, zhongjiang wrote:
> From: zhong jiang <zhongjiang@huawei.com>
> 
> when the mailline introduce the commit a96dfddbcc04
> ("base/memory, hotplug: fix a kernel oops in show_valid_zones()"),
> it obtains the valid start and end pfn from the given pfn range.
> The valid start pfn can fix the actual issue, but it introduce
> another issue. The valid end pfn will may exceed the given end_pfn.
> 
> Ahthough the incorrect overflow will not result in actual problem
> at present, but I think it need to be fixed.

Yes, test_pages_in_a_zone() assumes that end_pfn is aligned by
MAX_ORDER_NR_PAGES.  This is true for both callers, show_valid_zones()
and __offline_pages().  I did not introduce this assumption. :-)

As you pointed out, it is prudent to remove this assumption for future
usages.  In this case, I think we need the following change as well.

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index a40c0c2..09c8b99 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1513,7 +1513,7 @@ 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)


Thanks,
-Toshi

Re: [PATCH] mm: fix a overflow in test_pages_in_a_zone()

[zhong jiang]

On 2017/2/8 1:35, Kani, Toshimitsu wrote:
> On Tue, 2017-02-07 at 19:34 +0800, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> when the mailline introduce the commit a96dfddbcc04
>> ("base/memory, hotplug: fix a kernel oops in show_valid_zones()"),
>> it obtains the valid start and end pfn from the given pfn range.
>> The valid start pfn can fix the actual issue, but it introduce
>> another issue. The valid end pfn will may exceed the given end_pfn.
>>
>> Ahthough the incorrect overflow will not result in actual problem
>> at present, but I think it need to be fixed.
> Yes, test_pages_in_a_zone() assumes that end_pfn is aligned by
> MAX_ORDER_NR_PAGES.  This is true for both callers, show_valid_zones()
> and __offline_pages().  I did not introduce this assumption. :-)
>
> As you pointed out, it is prudent to remove this assumption for future
> usages.  In this case, I think we need the following change as well.
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index a40c0c2..09c8b99 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1513,7 +1513,7 @@ 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)
>
>
> Thanks,
> -Toshi
>
 Indeed, sorry, I forget the change.

 Thanks
 zhongjiang

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