ovl: do not cleanup directory and whiteout index entries

Directory index entries are going to be used for looking up
redirected upper dirs by lower dir fh when decoding an overlay
file handle of a merge dir.

Whiteout index entries are going to be used as an indication that
an exported overlay file handle should be treated as stale (i.e.
after unlink of the overlay inode).

We don't know the verification rules for directory and whiteout
index entries, because they have not been implemented yet, so fail
to mount overlay rw if those entries are found to avoid corrupting
an index that was created by a newer kernel.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/namei.c

@@ -397,8 +397,19 @@ int ovl_verify_index(struct dentry *index, struct path *lowerstack,
 	if (!d_inode(index))
 		return 0;
 
-	err = -EISDIR;
-	if (d_is_dir(index))
+	/*
+	 * Directory index entries are going to be used for looking up
+	 * redirected upper dirs by lower dir fh when decoding an overlay
+	 * file handle of a merge dir. Whiteout index entries are going to be
+	 * used as an indication that an exported overlay file handle should
+	 * be treated as stale (i.e. after unlink of the overlay inode).
+	 * We don't know the verification rules for directory and whiteout
+	 * index entries, because they have not been implemented yet, so return
+	 * EROFS if those entries are found to avoid corrupting an index that
+	 * was created by a newer kernel.
+	 */
+	err = -EROFS;
+	if (d_is_dir(index) || ovl_is_whiteout(index))
 		goto fail;
 
 	err = -EINVAL;
@@ -436,8 +447,8 @@ out:
 	return err;
 
 fail:
-	pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, err=%i)\n",
-			    index, err);
+	pr_warn_ratelimited("overlayfs: failed to verify index (%pd2, ftype=%x, err=%i)\n",
+			    index, d_inode(index)->i_mode & S_IFMT, err);
 	goto out;
 }
 

fs/overlayfs/readdir.c

@@ -703,7 +703,10 @@ int ovl_indexdir_cleanup(struct dentry *dentry, struct vfsmount *mnt,
 			err = PTR_ERR(index);
 			break;
 		}
-		if (ovl_verify_index(index, lowerstack, numlower)) {
+		err = ovl_verify_index(index, lowerstack, numlower);
+		if (err) {
+			if (err == -EROFS)
+				break;
 			err = ovl_cleanup(dir, index);
 			if (err)
 				break;