From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1755362AbdDNTML (ORCPT <rfc822;w@1wt.eu>);
        Fri, 14 Apr 2017 15:12:11 -0400
Received: from aserp1040.oracle.com ([141.146.126.69]:36053 "EHLO
        aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1755106AbdDNTMC (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 14 Apr 2017 15:12:02 -0400
Date: Fri, 14 Apr 2017 22:11:53 +0300
From: Dan Carpenter <dan.carpenter@oracle.com>
To: Mike Marshall <hubcap@omnibond.com>
Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
Subject: [PATCH] orangefs: handle zero size write in debugfs
Message-ID: <20170414191153.GB30875@mwanda>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
X-Mailer: git-send-email haha only kidding
User-Agent: Mutt/1.6.0 (2016-04-01)
X-Source-IP: aserv0021.oracle.com [141.146.126.233]
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

If we write zero bytes to this debugfs file, then it will cause an
underflow when we do copy_from_user(buf, ubuf, count - 1).  Debugfs can
normally only be written to by root so the impact of this is low.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/fs/orangefs/orangefs-debugfs.c b/fs/orangefs/orangefs-debugfs.c
index 791912da97d7..716ed337f166 100644
--- a/fs/orangefs/orangefs-debugfs.c
+++ b/fs/orangefs/orangefs-debugfs.c
@@ -440,6 +440,9 @@ static ssize_t orangefs_debug_write(struct file *file,
 		"orangefs_debug_write: %pD\n",
 		file);
 
+	if (count == 0)
+		return 0;
+
 	/*
 	 * Thwart users who try to jamb a ridiculous number
 	 * of bytes into the debug file...