linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: avoid overflow when large directory feathure is enabled

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Date:	Tue, 27 May 2014 15:23:07 +0900
From:	Changman Lee <cm224.lee@...sung.com>
To:	Chao Yu <chao2.yu@...sung.com>
Cc:	Jaegeuk Kim <jaegeuk.kim@...sung.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: avoid overflow when large directory
 feathure is enabled

Hi, Chao
Good catch. Please, modify Documentation/filesytems/f2fs.txt

On Tue, May 27, 2014 at 09:06:52AM +0800, Chao Yu wrote:
> When large directory feathure is enable, We have one case which could cause
> overflow in dir_buckets() as following:
> special case: level + dir_level >= 32 and level < MAX_DIR_HASH_DEPTH / 2.
> 
> Here we define MAX_DIR_BUCKETS to limit the return value when the condition
> could trigger potential overflow.
> 
> Signed-off-by: Chao Yu <chao2.yu@...sung.com>
> ---
>  fs/f2fs/dir.c           |    4 ++--
>  include/linux/f2fs_fs.h |    3 +++
>  2 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index c3f1485..966acb0 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -23,10 +23,10 @@ static unsigned long dir_blocks(struct inode *inode)
>  
>  static unsigned int dir_buckets(unsigned int level, int dir_level)
>  {
> -	if (level < MAX_DIR_HASH_DEPTH / 2)
> +	if (level + dir_level < MAX_DIR_HASH_DEPTH / 2)
>  		return 1 << (level + dir_level);
>  	else
> -		return 1 << ((MAX_DIR_HASH_DEPTH / 2 + dir_level) - 1);
> +		return MAX_DIR_BUCKETS;
>  }
>  
>  static unsigned int bucket_blocks(unsigned int level)
> diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
> index 8c03f71..ba6f312 100644
> --- a/include/linux/f2fs_fs.h
> +++ b/include/linux/f2fs_fs.h
> @@ -394,6 +394,9 @@ typedef __le32	f2fs_hash_t;
>  /* MAX level for dir lookup */
>  #define MAX_DIR_HASH_DEPTH	63
>  
> +/* MAX buckets in one level of dir */
> +#define MAX_DIR_BUCKETS		(1 << ((MAX_DIR_HASH_DEPTH / 2) - 1))
> +
>  #define SIZE_OF_DIR_ENTRY	11	/* by byte */
>  #define SIZE_OF_DENTRY_BITMAP	((NR_DENTRY_IN_BLOCK + BITS_PER_BYTE - 1) / \
>  					BITS_PER_BYTE)
> -- 
> 1.7.10.4
> 
> 
> 
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