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=-12.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, 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 EA8D9C433FE for ; Tue, 14 Sep 2021 09:08:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C378661155 for ; Tue, 14 Sep 2021 09:08:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229863AbhINJJU (ORCPT ); Tue, 14 Sep 2021 05:09:20 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:19972 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229656AbhINJJU (ORCPT ); Tue, 14 Sep 2021 05:09:20 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4H7y7v6cRzzbmSt; Tue, 14 Sep 2021 17:03:55 +0800 (CST) Received: from dggema762-chm.china.huawei.com (10.1.198.204) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.8; Tue, 14 Sep 2021 17:08:01 +0800 Received: from [10.174.176.73] (10.174.176.73) by dggema762-chm.china.huawei.com (10.1.198.204) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Tue, 14 Sep 2021 17:08:00 +0800 Subject: Re: [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req() To: Ming Lei CC: , , , , , , References: <20210909141256.2606682-1-yukuai3@huawei.com> <20210909141256.2606682-6-yukuai3@huawei.com> <374c6b37-b4b2-fe01-66be-ca2dbbc283e9@huawei.com> From: "yukuai (C)" Message-ID: <39e628cc-496c-ba20-b53a-fbeecc1d7e4e@huawei.com> Date: Tue, 14 Sep 2021 17:08:00 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.73] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggema762-chm.china.huawei.com (10.1.198.204) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2021/09/14 15:46, Ming Lei wrote: > On Tue, Sep 14, 2021 at 03:13:38PM +0800, yukuai (C) wrote: >> On 2021/09/14 14:44, Ming Lei wrote: >>> On Tue, Sep 14, 2021 at 11:11:06AM +0800, yukuai (C) wrote: >>>> On 2021/09/14 9:11, Ming Lei wrote: >>>>> On Thu, Sep 09, 2021 at 10:12:55PM +0800, Yu Kuai wrote: >>>>>> blk_mq_tag_to_rq() can only ensure to return valid request in >>>>>> following situation: >>>>>> >>>>>> 1) client send request message to server first >>>>>> submit_bio >>>>>> ... >>>>>> blk_mq_get_tag >>>>>> ... >>>>>> blk_mq_get_driver_tag >>>>>> ... >>>>>> nbd_queue_rq >>>>>> nbd_handle_cmd >>>>>> nbd_send_cmd >>>>>> >>>>>> 2) client receive respond message from server >>>>>> recv_work >>>>>> nbd_read_stat >>>>>> blk_mq_tag_to_rq >>>>>> >>>>>> If step 1) is missing, blk_mq_tag_to_rq() will return a stale >>>>>> request, which might be freed. Thus convert to use >>>>>> blk_mq_find_and_get_req() to make sure the returned request is not >>>>>> freed. >>>>> >>>>> But NBD_CMD_INFLIGHT has been added for checking if the reply is >>>>> expected, do we still need blk_mq_find_and_get_req() for covering >>>>> this issue? BTW, request and its payload is pre-allocated, so there >>>>> isn't real use-after-free. >>>> >>>> Hi, Ming >>>> >>>> Checking NBD_CMD_INFLIGHT relied on the request founded by tag is valid, >>>> not the other way round. >>>> >>>> nbd_read_stat >>>> req = blk_mq_tag_to_rq() >>>> cmd = blk_mq_rq_to_pdu(req) >>>> mutex_lock(cmd->lock) >>>> checking NBD_CMD_INFLIGHT >>> >>> Request and its payload is pre-allocated, and either req->ref or cmd->lock can >>> serve the same purpose here. Once cmd->lock is held, you can check if the cmd is >>> inflight or not. If it isn't inflight, just return -ENOENT. Is there any >>> problem to handle in this way? >> >> Hi, Ming >> >> in nbd_read_stat: >> >> 1) get a request by tag first >> 2) get nbd_cmd by the request >> 3) hold cmd->lock and check if cmd is inflight >> >> If we want to check if the cmd is inflight in step 3), we have to do >> setp 1) and 2) first. As I explained in patch 0, blk_mq_tag_to_rq() >> can't make sure the returned request is not freed: >> >> nbd_read_stat >> blk_mq_sched_free_requests >> blk_mq_free_rqs >> blk_mq_tag_to_rq >> -> get rq before clear mapping >> blk_mq_clear_rq_mapping >> __free_pages -> rq is freed >> blk_mq_request_started -> UAF > > If the above can happen, blk_mq_find_and_get_req() may not fix it too, just Hi, Ming Why can't blk_mq_find_and_get_req() fix it? I can't think of any scenario that might have problem currently. > wondering why not take the following simpler way for avoiding the UAF? > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index 5170a630778d..dfa5cce71f66 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -795,9 +795,13 @@ static void recv_work(struct work_struct *work) > work); > struct nbd_device *nbd = args->nbd; > struct nbd_config *config = nbd->config; > + struct request_queue *q = nbd->disk->queue; > struct nbd_cmd *cmd; > struct request *rq; > > + if (!percpu_ref_tryget(&q->q_usage_counter)) > + return; > + We can't make sure freeze_queue is called before this, thus this approch can't fix the problem, right? nbd_read_stat blk_mq_tag_to_rq elevator_switch blk_mq_freeze_queue(q); elevator_switch_mq elevator_exit blk_mq_sched_free_requests blk_mq_request_started -> UAF Thanks, Kuai > while (1) { > cmd = nbd_read_stat(nbd, args->index); > if (IS_ERR(cmd)) { > @@ -813,6 +817,7 @@ static void recv_work(struct work_struct *work) > if (likely(!blk_should_fake_timeout(rq->q))) > blk_mq_complete_request(rq); > } > + blk_queue_exit(q); > nbd_config_put(nbd); > atomic_dec(&config->recv_threads); > wake_up(&config->recv_wq); > > Thanks, > Ming > > . >