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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 3701DC3B185 for ; Mon, 10 Feb 2020 09:15:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 19CD221739 for ; Mon, 10 Feb 2020 09:15:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727477AbgBJJPU (ORCPT ); Mon, 10 Feb 2020 04:15:20 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:42686 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726061AbgBJJPU (ORCPT ); Mon, 10 Feb 2020 04:15:20 -0500 Received: from DGGEMS408-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id AEEC67CCB37944FB8949; Mon, 10 Feb 2020 17:15:17 +0800 (CST) Received: from [127.0.0.1] (10.173.222.66) by DGGEMS408-HUB.china.huawei.com (10.3.19.208) with Microsoft SMTP Server id 14.3.439.0; Mon, 10 Feb 2020 17:15:12 +0800 Subject: Re: [PATCH] nbd: fix potential NULL pointer fault in connect and disconnect process To: Mike Christie , , CC: , , , Xiubo Li References: <20200117115005.37006-1-sunke32@huawei.com> <5E21EF96.1010204@redhat.com> <5E40CB1F.7070301@redhat.com> From: "sunke (E)" Message-ID: Date: Mon, 10 Feb 2020 17:15:11 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <5E40CB1F.7070301@redhat.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.173.222.66] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Mike Your idea looks good. Thanks, Sun Ke 在 2020/2/10 11:16, Mike Christie 写道: > On 01/19/2020 01:10 AM, sunke (E) wrote: >> >> Thanks for your detailed suggestions. >> >> 在 2020/1/18 1:32, Mike Christie 写道: >>> On 01/17/2020 05:50 AM, Sun Ke wrote: >>>> Connect and disconnect a nbd device repeatedly, will cause >>>> NULL pointer fault. >>>> >>>> It will appear by the steps: >>>> 1. Connect the nbd device and disconnect it, but now nbd device >>>> is not disconnected totally. >>>> 2. Connect the same nbd device again immediately, it will fail >>>> in nbd_start_device with a EBUSY return value. >>>> 3. Wait a second to make sure the last config_refs is reduced >>>> and run nbd_config_put to disconnect the nbd device totally. >>>> 4. Start another process to open the nbd_device, config_refs >>>> will increase and at the same time disconnect it. >>> >>> Just to make sure I understood this, for step 4 the process is doing: >>> >>> open(/dev/nbdX); >>> ioctl(NBD_DISCONNECT, /dev/nbdX) or nbd_genl_disconnect(for /dev/nbdX) >>> >>> ? >>> >> do nbd_genl_disconnect(for /dev/nbdX)； >> I tested it. Connect /dev/nbdX >> through ioctl interface by nbd-client -L -N export localhost /dev/nbdX and >> through netlink interface by nbd-client localhost XXXX /dev/nbdX, >> disconnect /dev/nbdX by nbd-client -d /dev/nbdX. >> Both call nbd_genl_disconnect(for /dev/nbdX) and both contain the same >> null pointer dereference. >>> There is no successful NBD_DO_IT / nbd_genl_connect between the open and >>> disconnect calls at step #4, because it would normally be done at #2 and >>> that failed. nbd_disconnect_and_put could then reference a null >>> recv_workq. If we are also racing with a close() then that could free >>> the device/config from under nbd_disconnect_and_put. >>> >> Yes, nbd_disconnect_and_put could then reference a null recv_workq. > > Hey Sunke > > How about the attached patch. I am still testing it. The basic idea is > that we need to do a flush whenever we have done a sock_shutdown and are > in the disconnect/connect/clear sock path, so it just adds the flush in > that function. We then do not need to keep adding these flushes everywhere. >