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

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Message-ID: <57FF061D.2030708@huawei.com>
Date:   Thu, 13 Oct 2016 11:57:17 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     <vitalywool@...il.com>, <david@...morbit.com>,
        <sjenning@...hat.com>, <ddstreet@...e.org>,
        <akpm@...ux-foundation.org>, <mhocko@...nel.org>, <vbabka@...e.cz>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH] z3fold: fix the potential encode bug in encod_handle

On 2016/10/13 11:33, 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,
> The code will much comprehensible to change the BUDDY_MASK to
> BUDDIES_MAX in handle_to_buddy.
>
> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
> ---
>  mm/z3fold.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/z3fold.c b/mm/z3fold.c
> index 8f9e89c..5884b9e 100644
> --- a/mm/z3fold.c
> +++ b/mm/z3fold.c
> @@ -169,7 +169,7 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
>  
>  	handle = (unsigned long)zhdr;
>  	if (bud != HEADLESS)
> -		handle += (bud + zhdr->first_num) & BUDDY_MASK;
> +		handle += (bud + zhdr->first_num) & PAGE_MASK;
>  	return handle;
>  }
>  
> @@ -183,7 +183,7 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
>  static enum buddy handle_to_buddy(unsigned long handle)
>  {
>  	struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
> -	return (handle - zhdr->first_num) & BUDDY_MASK;
> +	return (handle - zhdr->first_num) & BUDDIES_MAX;
>  }
>  
>  /*
  oh,  a  obvious problem, please ignore it. I will resent the patch in v2.  Thanks