From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1020C433E6 for ; Sun, 30 Aug 2020 08:30:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 813D6206C0 for ; Sun, 30 Aug 2020 08:30:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727859AbgH3Iam (ORCPT ); Sun, 30 Aug 2020 04:30:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726078AbgH3Ial (ORCPT ); Sun, 30 Aug 2020 04:30:41 -0400 Received: from gofer.mess.org (gofer.mess.org [IPv6:2a02:8011:d000:212::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BCA6C061573; Sun, 30 Aug 2020 01:30:41 -0700 (PDT) Received: by gofer.mess.org (Postfix, from userid 1000) id DFD70C63F6; Sun, 30 Aug 2020 09:30:36 +0100 (BST) Date: Sun, 30 Aug 2020 09:30:36 +0100 From: Sean Young To: Jia-Ju Bai Cc: mchehab@kernel.org, pavel@ucw.cz, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] media: pci: ttpci: av7110: avoid compiler optimization of reading data[0] in debiirq() Message-ID: <20200830083036.GA17715@gofer.mess.org> References: <20200830082042.17462-1-baijiaju@tsinghua.edu.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200830082042.17462-1-baijiaju@tsinghua.edu.cn> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 30, 2020 at 04:20:42PM +0800, Jia-Ju Bai wrote: > In debiirq(), data_0 stores the value of data[0], but it can be dropped > by compiler optimization. Thus, data[0] is read through READ_ONCE(). > > Fixes: 6499a0db9b0f ("media: pci: ttpci: av7110: fix possible buffer overflow caused by bad DMA value in debiirq()") > Reported-by: Pavel Machek Pavel reported that your patch was garbage, if you are trying to defend against a malicious pci device. READ_ONCE() will not help here. Sean > Signed-off-by: Jia-Ju Bai > --- > drivers/media/pci/ttpci/av7110.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/media/pci/ttpci/av7110.c b/drivers/media/pci/ttpci/av7110.c > index bf36b1e22b63..f7d098d5b198 100644 > --- a/drivers/media/pci/ttpci/av7110.c > +++ b/drivers/media/pci/ttpci/av7110.c > @@ -406,7 +406,7 @@ static void debiirq(unsigned long cookie) > case DATA_CI_GET: > { > u8 *data = av7110->debi_virt; > - u8 data_0 = data[0]; > + u8 data_0 = READ_ONCE(data[0]); > > if (data_0 < 2 && data[2] == 0xff) { > int flags = 0; > -- > 2.17.1