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

[zhong jiang <zhongjiang@huawei.com>]

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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