linux-kernel - Re: [PATCH v2] z3fold: fix the potential encode bug in encod

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Date:   Mon, 17 Oct 2016 20:48:15 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Vitaly Wool <vitalywool@...il.com>
CC:     Dave Chinner <david@...morbit.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2] z3fold: fix the potential encode bug in encod_handle

On 2016/10/17 20:03, Vitaly Wool wrote:
> Hi Zhong Jiang,
>
> On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <zhongjiang@...wei.com> wrote:
>> Hi,  Vitaly
>>
>> About the following patch,  is it right?
>>
>> Thanks
>> zhongjiang
>> On 2016/10/13 12:02, zhongjiang wrote:
>>> From: zhong jiang <zhongjiang@...wei.com>
>>>
>>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>>> in encode_handle, it will lead to the the caller handle_to_buddy
>>> return the error value.
>>>
>>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>>> it will be consistent with handle_to_z3fold_header. At the same time,
>>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
> are you seeing problems with the existing code? first_num should wrap around
> BUDDY_MASK and this should be ok because it is way bigger than the number
> of buddies.
>
> ~vitaly
>
> .
>
 first_num plus buddies can exceed the BUDDY_MASK. is it right?
 (first_num + buddies) & BUDDY_MASK may be a smaller value than first_num.

  but (handle - zhdr->first_num) & BUDDY_MASK will return incorrect value
  in handle_to_buddy.

  Thanks
  zhongjiang