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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by aws-us-west-2-korg-lkml-1.web.codeaurora.org (Postfix) with ESMTP id AE321C07D5C for ; Thu, 14 Jun 2018 08:29:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E4A1208D7 for ; Thu, 14 Jun 2018 08:29:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E4A1208D7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754858AbeFNI3t (ORCPT ); Thu, 14 Jun 2018 04:29:49 -0400 Received: from verein.lst.de ([213.95.11.211]:45136 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752882AbeFNI3r (ORCPT ); Thu, 14 Jun 2018 04:29:47 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id EB74668C4E; Thu, 14 Jun 2018 10:38:06 +0200 (CEST) Date: Thu, 14 Jun 2018 10:38:06 +0200 From: Christoph Hellwig To: Anatoliy Glagolev Cc: linux-block@vger.kernel.org, "James E.J. Bottomley" , FUJITA Tomonori , Jens Axboe , linux-scsi@vger.kernel.org, Christoph Hellwig , linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: fix bsg_unregister and bsg_open race Message-ID: <20180614083806.GA18966@lst.de> References: <20180613221417.GA22778@xldev-tmpl.dev.purestorage.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180613221417.GA22778@xldev-tmpl.dev.purestorage.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 13, 2018 at 04:14:18PM -0600, Anatoliy Glagolev wrote: > The existing implementation allows races between bsg_unregister and > bsg_open paths. bsg_ungegister and request_queue cleanup and > deletion may start and complete right after bsg_get_device (in bsg_open path) > retrieves bsg_class_device and releases the mutex. Then bsg_open path > touches freed memory of bsg_class_device and request_queue. > > One possible fix is to hold the mutex all the way through bsg_get_device > instead of releasing it after bsg_class_device retrieval. This looks generally fine to me. Nitpicks below: > @@ -746,16 +745,18 @@ static struct bsg_device *bsg_get_device(struct inode *inode, struct file *file) > */ > mutex_lock(&bsg_mutex); > bcd = idr_find(&bsg_minor_idr, iminor(inode)); > - mutex_unlock(&bsg_mutex); > > if (!bcd) > return ERR_PTR(-ENODEV); This needs to unlock the mutex. E.g. if (!bcd) { bd = ERR_PTR(-ENODEV); goto out_unlock; } > bd = __bsg_get_device(iminor(inode), bcd->queue); > + if (bd) { > + mutex_unlock(&bsg_mutex); > return bd; > + } > > bd = bsg_add_device(inode, bcd->queue, file); > + mutex_unlock(&bsg_mutex); > > return bd; I'd simply do: bd = __bsg_get_device(iminor(inode), bcd->queue); if (!bd) bd = bsg_add_device(inode, bcd->queue, file); out_unlock: mutex_unlock(&bsg_mutex); return bd;