linux-kernel - Re: [PATCH v2] ext3, ext4: do_split() fix loop, with obvious unsigned wrap

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Message-Id: <20081202220510.ddef1115.akpm@linux-foundation.org>
Date:	Tue, 2 Dec 2008 22:05:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	roel kluin <roel.kluin@...il.com>
Cc:	davidsen@....com, tytso@....edu, adilger@....com,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ext3, ext4: do_split() fix loop, with obvious
 unsigned wrap

On Mon, 01 Dec 2008 14:28:25 -0500 roel kluin <roel.kluin@...il.com> wrote:

> Fix loop, with obvious unsigned wrap
> 

Please raise separate patches for ext3 and ext4 - their paths into the
tree are different.

> --- a/fs/ext3/namei.c
> +++ b/fs/ext3/namei.c
> @@ -1188,7 +1188,7 @@ static struct ext3_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
>  	/* Split the existing block in the middle, size-wise */
>  	size = 0;
>  	move = 0;
> -	for (i = count-1; i >= 0; i--) {
> +	for (i = count; i--; ) {

So we're replacing an accidental for(;;) with something which can
really terminate.  This is potentially a functional change, and it's
perhaps telling us that we should replace it with a real for (;;) loop
anyway.

Plus we still have a local unsigned variable called "i".

Ted, could you please take a look at this sometime, work out the best
course of action?

Thanks.

>  		/* is more than half of this entry in 2nd half of the block? */
>  		if (size + map[i].size/2 > blocksize/2)
>  			break;
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 63adcb7..34232c6 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -1198,7 +1198,7 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir,
>  	/* Split the existing block in the middle, size-wise */
>  	size = 0;
>  	move = 0;
> -	for (i = count-1; i >= 0; i--) {
> +	for (i = count; i--; ) {
>  		/* is more than half of this entry in 2nd half of the block? */
>  		if (size + map[i].size/2 > blocksize/2)
>  			break;

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