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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 AB233C2BA83 for ; Thu, 13 Feb 2020 13:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F4ED2168B for ; Thu, 13 Feb 2020 13:58:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581602292; bh=XnmOcvXBs7+P4hR2gFffatGsVimLcQPm8t+FbZHlakw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=rQNEPNiak2Io0cXdLDhzwD3MNKXFJasVqmwWne6DxVs8QOOoIAn3KmqYcNGd6r4tf 46l5fmMfsY/RnOT6fpCzodbQhEJtVCI36KS20yuBPXmMZYHzG+82KZzrEHL/QUjHQ2 YGpbrl4sb58eO5Dl8zr04cyuLP5mKDxMLsMcEc+k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730030AbgBMN6M (ORCPT ); Thu, 13 Feb 2020 08:58:12 -0500 Received: from mail-qt1-f193.google.com ([209.85.160.193]:42694 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729991AbgBMN6L (ORCPT ); Thu, 13 Feb 2020 08:58:11 -0500 Received: by mail-qt1-f193.google.com with SMTP id r5so4385758qtt.9 for ; Thu, 13 Feb 2020 05:58:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=SC0nsyrjx2XKfrv1CGhfKOeix8vEYOlvybsPllHLtRU=; b=Z+uK78blswzFN+KYUHE1lpfYBBmzW7UpIxkQzwb3y3qOxA1zaBCOuHLaCvd84hUoyY 5iLqHOsEGrSFZZHZ7E5TY2lnDkRKtHHWAhLO/pGrHgZhEiGb65wu8Ol3voXyBRpQ/kHr 0vc/KtkaNo08CLzONc9lLT+FWaE0NHTbE/6Q2v29l+3SUyp+w0aVMKneihAw1pQtWbhe rowXLft6kJN+SHbU0dSEY7ASwdbmAtzkzJBOAobtX7qX4OPbdECvG8Sxg+vHIFYaWhmp INXVYnm8YZ+lwylhNOxbg9UArKw5+oGEN5bcv6CycohEJ12k+XzVImdSf5Dex11uAbKi 9cPw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=SC0nsyrjx2XKfrv1CGhfKOeix8vEYOlvybsPllHLtRU=; b=g4UlRndu32RtyL+BW9V5eOeM5llundN3xIla3xVGMQPGfka1rl4Y5dNzFJR+brK6pm orKPLeYkY/lNHe+E5FhELQWZeoljvELSOy3DjNGSqw2OMoow20zbeL9m5bGAGBEqy2h6 eWAwhRi+Uogcay1/r5M0xvq7nOigT8j7i+46tjpT4GF5/Ic4iuQppGDjGQ8gUcmrgSGV +/sYZowO5oUlsGptS29jiyKD+CGODNXQMlBN7jw1aq/tMOT2ioX4OuJZY/ycYDwpnZ88 ZCsyjyWlrO3xjwGJRC31jC4bJgY2O9v9zRaK7Xmf5waGtX9TYq8L0thUcsFo5YuYIWGD peCg== X-Gm-Message-State: APjAAAWLddlcCgLv3g6x3tTuLuhDLtzErhHGXUMC8b4TC8aQGsww0jXo afNMjSE0jY8AMFW981vgJcgHv7IMc8Q= X-Google-Smtp-Source: APXvYqznmb7+P0zyDPzqtbpLWQaNUR4/Hjga6bj44ojBWMV2NgrH4Ddm8H6bF493r00DdWUd3DdaHw== X-Received: by 2002:ac8:36f5:: with SMTP id b50mr24477701qtc.268.1581602290918; Thu, 13 Feb 2020 05:58:10 -0800 (PST) Received: from localhost ([2620:10d:c091:500::1:f3be]) by smtp.gmail.com with ESMTPSA id f32sm1542331qtk.89.2020.02.13.05.58.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Feb 2020 05:58:10 -0800 (PST) Date: Thu, 13 Feb 2020 08:58:09 -0500 From: Tejun Heo To: Yufen Yu Cc: axboe@kernel.dk, linux-block@vger.kernel.org, jack@suse.cz, bvanassche@acm.org Subject: Re: [PATCH] bdi: fix use-after-free for bdi device Message-ID: <20200213135809.GH88887@mtj.thefacebook.com> References: <20200211140038.146629-1-yuyufen@huawei.com> <20200212213344.GE80993@mtj.thefacebook.com> <20200213034818.GE88887@mtj.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hello, On Thu, Feb 13, 2020 at 03:51:40PM +0800, Yufen Yu wrote: > If we destroy the device asynchronously by call_rcu(), we may need to > add a new member 'rcu_head' into struct backing_dev_info. Right? Yes. > The code may be like: > > bdi_unregister() > { > ... > if (bdi->dev) { > ... > device_get(bdi->dev); > device_unregister(bdi->dev); > bdi->dev = NULL; //XXX > bdi_get(bdi); //avoiding bdi to be freed before calling bdi_release_device > call_rcu(&bdi->rcu_head, bdi_release_device); > } > ... > } > > bdi_release_device() > { > ... > put_device(bdi->dev);//XXX > bdi_put(bdi); > } > > But, the problem is how do we get 'bdi->dev' in bdi_release_device(). > If we do not set bdi->dev as 'NULL', re-registration bdi may cannot work well. So, unregistering can leave ->dev along and re-registering can test whether it's NULL and if not put the existing one and put a new one there. Wouldn't that work? Thanks. -- tejun