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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 AC489C43387 for ; Fri, 4 Jan 2019 03:26:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 86A222087F for ; Fri, 4 Jan 2019 03:26:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727148AbfADD05 (ORCPT ); Thu, 3 Jan 2019 22:26:57 -0500 Received: from gate.crashing.org ([63.228.1.57]:35610 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727112AbfADD04 (ORCPT ); Thu, 3 Jan 2019 22:26:56 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id x043Q4ms011435; Thu, 3 Jan 2019 21:26:05 -0600 Message-ID: <7bbf788adeac78da48a83b100f820b962b16ba19.camel@kernel.crashing.org> Subject: Re: [PATCH] fsi:fsi-sbefifo: Fix possible concurrency use-after-free bugs in sbefifo_user_release From: Benjamin Herrenschmidt To: Jia-Ju Bai , dhowells@redhat.com, joel@jms.id.au, eajames@linux.vnet.ibm.com, andrew@aj.id.au Cc: linux-kernel@vger.kernel.org Date: Fri, 04 Jan 2019 14:26:03 +1100 In-Reply-To: <798fbb98-0cba-07f8-2165-180c63012e95@gmail.com> References: <20181226135618.12784-1-baijiaju1990@gmail.com> <0adee96b58a533bc8c5927039e96b5ed77c9bbad.camel@kernel.crashing.org> <798fbb98-0cba-07f8-2165-180c63012e95@gmail.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.3 (3.30.3-1.fc29) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2019-01-04 at 10:26 +0800, Jia-Ju Bai wrote: > > On 2019/1/4 8:47, Benjamin Herrenschmidt wrote: > > On Wed, 2018-12-26 at 21:56 +0800, Jia-Ju Bai wrote: > > > In drivers/fsi/fsi-sbefifo.c, the functions sbefifo_user_release(), > > > sbefifo_user_read() and sbefifo_user_write() may be concurrently executed. > > So after refreshing my mind, looking at the code and talking with Al, I > > really dont' see what race you are trying to fix here. > > > > read/write should never be concurrent with release for a given file and > > the stuff we are protecting here is local to the file instance. > > > > Do you have an actual problem you observed ? > > > > Thanks for the reply. > > In fact, this report is found by a static tool written by myself, > instead of real execution. > My tool found that in some drivers, for the structure "struct > file_operations", the code in intetrfaces ".read" , "write" and > ".release" are protected by the same lock. > The functions kcs_bmc_read(), kcs_bmc_write() and kcs_bmc_release() are > examples. > Thus, my tool inferred that the intetrfaces ".read" , "write" and > ".release" of "struct file_operations" can be concurrently executed, and > generated this report. > I manually checked this report, but I was not very sure of it, so I > marked it as a "possible bug" and reported it. So what happens is that they cannot be executed concurrently for a given struct file. But they can be for separate files. In the fsi-sbefifo case, all of the data and the lock are part of a private structure which is allocated in open() and thus is per-file instance, so there should be no race. In the example you gave, kcs_bmc.c, the data and lock are part of a per-device (struct kcs_bmc) and thus shared by all file instances. So in that case, the race does exist. > From your message, now I know my report is false, and ".read" , "write" > cannot be concurrently executed with ".release" for a given file. > Sorry for my false report, and thanks for your message. Right, your tool is valuable as pre-screening but you need in addition to check (probably manually) whether the data accessed (and lock) are shared by multiple open file instances or are entirely local to a given file instance. Cheers, Ben.