[PATCH v2] xfs: fix possible overflow in xfs_ioc_trim()

[Christoph Hellwig]

On Tue, Sep 06, 2011 at 05:29:37PM +0200, Lukas Czerner wrote:
> In xfs_ioc_trim it is possible that start+len might overflow. Fix it by
> decrementing the len so that start+len equals to the file system size in
> the worst case.
> 
> Signed-off-by: Lukas Czerner <lczerner at redhat.com>

> @@ -146,6 +146,7 @@ xfs_ioc_trim(
>  	unsigned int		granularity = q->limits.discard_granularity;
>  	struct fstrim_range	range;
>  	xfs_fsblock_t		start, len, minlen;
> +	xfs_fsblock_t		max_blks = mp->m_sb.sb_dblocks;
>  	xfs_agnumber_t		start_agno, end_agno, agno;
>  	__uint64_t		blocks_trimmed = 0;
>  	int			error, last_error = 0;
> @@ -171,7 +172,8 @@ xfs_ioc_trim(
>  	start_agno = XFS_FSB_TO_AGNO(mp, start);
>  	if (start_agno >= mp->m_sb.sb_agcount)
>  		return -XFS_ERROR(EINVAL);
> -
> +	if (len > max_blks)
> +		len = max_blks - start;

Is this really the correct check?

Shouldn't it be

	if (start + len > max_blks)
		len = max_blks - start;

I'd also just use the mp->m_sb.sb_dblocks value directly instead
of assigning it to a local variable.