ovl: Fix dereferencing possible ERR_PTR()

if ovl_encode_real_fh() fails, no memory was allocated
and the error in the error-valued pointer should be returned.

Fixes: 9b6faee0 ("ovl: check ERR_PTR() return value from ovl_encode_fh()")
Signed-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Cc: <stable@vger.kernel.org> # v4.16+
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/export.c

@@ -227,9 +227,8 @@ static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen)
 	/* Encode an upper or lower file handle */
 	fh = ovl_encode_real_fh(enc_lower ? ovl_dentry_lower(dentry) :
 				ovl_dentry_upper(dentry), !enc_lower);
-	err = PTR_ERR(fh);
 	if (IS_ERR(fh))
-		goto fail;
+		return PTR_ERR(fh);
 
 	err = -EOVERFLOW;
 	if (fh->len > buflen)