Re: [PATCH] xfs: abort extended attribute list operation if btree is obviously weird

[Brian Foster <bfoster@redhat.com>]

On Mon, Oct 23, 2017 at 05:28:24PM -0700, Darrick J. Wong wrote:
> Abort an attribute list operation if the attr btree has obvious problems
> like loops back to the root or pointers don't point down the tree.
> Found by fuzzing btree[0].before to zero in xfs/402.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_attr_list.c |   54 ++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 43 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/xfs/xfs_attr_list.c b/fs/xfs/xfs_attr_list.c
> index 5816786..9f6fcc6 100644
> --- a/fs/xfs/xfs_attr_list.c
> +++ b/fs/xfs/xfs_attr_list.c
...
> @@ -302,6 +306,30 @@ xfs_attr_node_list(xfs_attr_list_context_t *context)
>  			}
>  
>  			dp->d_ops->node_hdr_from_disk(&nodehdr, node);
> +
> +			/* Tree taller than we can handle; bail out! */
> +			if (nodehdr.level >= XFS_DA_NODE_MAXDEPTH) {
> +				xfs_trans_brelse(context->tp, bp);
> +				return -EFSCORRUPTED;
> +			}
> +
> +			if (cursor->blkno == 0) {
> +				/*
> +				 * This is the root node, set up for the
> +				 * next level we want to see.
> +				 */
> +				expected_level = nodehdr.level - 1;
> +			} else if (expected_level != nodehdr.level) {
> +				/*
> +				 * Not the level we were expecting, which
> +				 * implies that the tree is bad.
> +				 */
> +				xfs_trans_brelse(context->tp, bp);
> +				return -EFSCORRUPTED;
> +			} else {
> +				expected_level--;
> +			}
> +

It looks like we wouldn't catch the case of a two level tree having a
bad level, since we'd break out on leaf magic check above. Perhaps we
should check or assert that expected_level reaches 0? Otherwise looks Ok
to me.

Brian

>  			btree = dp->d_ops->node_tree_p(node);
>  			for (i = 0; i < nodehdr.count; btree++, i++) {
>  				if (cursor->hashval
> @@ -317,6 +345,10 @@ xfs_attr_node_list(xfs_attr_list_context_t *context)
>  				return 0;
>  			}
>  			xfs_trans_brelse(context->tp, bp);
> +
> +			/* We can't point back to the root. */
> +			if (cursor->blkno == 0)
> +				return -EFSCORRUPTED;
>  		}
>  	}
>  	ASSERT(bp != NULL);
> --
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