btrfs: qgroup: return EINVAL if level of parent is not higher than child's.

When we create a subvol inheriting a qgroup, we need to check the level
of them. Otherwise, there is a chance a qgroup can inherit another qgroup
at the same level.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/qgroup.c

@@ -2230,6 +2230,11 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans,
 				ret = -EINVAL;
 				goto out;
 			}
+
+			if ((srcgroup->qgroupid >> 48) <= (objectid >> 48)) {
+				ret = -EINVAL;
+				goto out;
+			}
 			++i_qgroups;
 		}
 	}