linux-kernel - Re: [PATCH 2/4] vfs: explicitly cast s_maxbytes in fiemap_check

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Date:	Sat, 8 Aug 2009 00:12:52 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, hch@...radead.org, rlove@...gle.com,
	msb@...gle.com, viro@...iv.linux.org.uk
Subject: Re: [PATCH 2/4] vfs: explicitly cast s_maxbytes in fiemap_check_ranges

On Fri, Aug 07, 2009 at 02:57:39PM -0400, Jeff Layton wrote:
> If fiemap_check_ranges is passed a large enough value, then it's
> possible that the value would be cast to a signed value for comparison
> against s_maxbytes when we change it to loff_t. Make sure that doesn't
> happen by explicitly casting s_maxbytes to an unsigned value for the
> purposes of comparison.

I think this is unneeded, C garuantees that in this case the signed
value will get promoted to an unsigned value, not the other way round.

	Hannes

> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> ---
>  fs/ioctl.c |    9 +++++----
>  1 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 5612880..7b17a14 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -162,20 +162,21 @@ EXPORT_SYMBOL(fiemap_check_flags);
>  static int fiemap_check_ranges(struct super_block *sb,
>  			       u64 start, u64 len, u64 *new_len)
>  {
> +	u64 maxbytes = (u64) sb->s_maxbytes;
> +
>  	*new_len = len;
>  
>  	if (len == 0)
>  		return -EINVAL;
>  
> -	if (start > sb->s_maxbytes)
> +	if (start > maxbytes)
>  		return -EFBIG;
>  
>  	/*
>  	 * Shrink request scope to what the fs can actually handle.
>  	 */
> -	if ((len > sb->s_maxbytes) ||
> -	    (sb->s_maxbytes - len) < start)
> -		*new_len = sb->s_maxbytes - start;
> +	if (len > maxbytes || (maxbytes - len) < start)
> +		*new_len = maxbytes - start;
>  
>  	return 0;
>  }
> -- 
> 1.6.0.6
> 
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