[PATCH] xfs: don't perform lookups on zero-height btrees

[Brian Foster]

On Fri, Aug 19, 2016 at 01:30:22PM -0700, Darrick J. Wong wrote:
> If the caller passes in a cursor to a zero-height btree (which is
> impossible), we never set block to anything but NULL, which causes the
> later dereference of it to crash.  Instead, just return -EFSCORRUPTED.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
> ---

Did something actually cause this to happen?

Brian

>  fs/xfs/libxfs/xfs_btree.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index 64fd847..4bffea4 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
> @@ -1814,6 +1814,10 @@ xfs_btree_lookup(
>  
>  	XFS_BTREE_STATS_INC(cur, lookup);
>  
> +	/* No such thing as a zero-level tree. */
> +	if (cur->bc_nlevels == 0)
> +		return -EFSCORRUPTED;
> +
>  	block = NULL;
>  	keyno = 0;
>  
> 
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