xfs: flag inode corruption if parent ptr doesn't get us a real inode

If a directory's parent inode pointer doesn't point to an inode, the
directory should be flagged as corrupt.  Enable IGET_UNTRUSTED here so
that _iget will return -EINVAL if the inobt does not confirm that the
inode is present and allocated and we can flag the directory corruption.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/scrub/parent.c

@@ -167,8 +167,18 @@ xfs_scrub_parent_validate(
 	 * if the parent pointer erroneously points to a file, we
 	 * can't use DONTCACHE here because DONTCACHE inodes can trigger
 	 * immediate inactive cleanup of the inode.
+	 *
+	 * If _iget returns -EINVAL then the parent inode number is garbage
+	 * and the directory is corrupt.  If the _iget returns -EFSCORRUPTED
+	 * or -EFSBADCRC then the parent is corrupt which is a cross
+	 * referencing error.  Any other error is an operational error.
 	 */
-	error = xfs_iget(mp, sc->tp, dnum, 0, 0, &dp);
+	error = xfs_iget(mp, sc->tp, dnum, XFS_IGET_UNTRUSTED, 0, &dp);
+	if (error == -EINVAL) {
+		error = -EFSCORRUPTED;
+		xfs_scrub_fblock_process_error(sc, XFS_DATA_FORK, 0, &error);
+		goto out;
+	}
 	if (!xfs_scrub_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
 		goto out;
 	if (dp == sc->ip || !S_ISDIR(VFS_I(dp)->i_mode)) {