ovl: handle ENOENT on index lookup

Treat ENOENT from index entry lookup the same way as treating a returned
negative dentry. Apparently, either could be returned if file is not
found, depending on the underlying file system.

Fixes: 359f392c ("ovl: lookup index entry for copy up origin")
Cc: <stable@vger.kernel.org> # v4.13
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

fs/overlayfs/namei.c

@@ -507,6 +507,10 @@ static struct dentry *ovl_lookup_index(struct dentry *dentry,
 	index = lookup_one_len_unlocked(name.name, ofs->indexdir, name.len);
 	if (IS_ERR(index)) {
 		err = PTR_ERR(index);
+		if (err == -ENOENT) {
+			index = NULL;
+			goto out;
+		}
 		pr_warn_ratelimited("overlayfs: failed inode index lookup (ino=%lu, key=%*s, err=%i);\n"
 				    "overlayfs: mount with '-o index=off' to disable inodes index.\n",
 				    d_inode(origin)->i_ino, name.len, name.name,