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 8FE8AC433F5 for ; Wed, 15 Sep 2021 01:54:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6654961216 for ; Wed, 15 Sep 2021 01:54:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231629AbhIOBzb (ORCPT ); Tue, 14 Sep 2021 21:55:31 -0400 Received: from szxga03-in.huawei.com ([45.249.212.189]:16255 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229489AbhIOBza (ORCPT ); Tue, 14 Sep 2021 21:55:30 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4H8NXt1jF2z8t84; Wed, 15 Sep 2021 09:53:34 +0800 (CST) Received: from dggema762-chm.china.huawei.com (10.1.198.204) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.8; Wed, 15 Sep 2021 09:54:11 +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; Wed, 15 Sep 2021 09:54:10 +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: <8f1849a3-6bf2-6b14-7ef9-4969a9a5425b@huawei.com> Date: Wed, 15 Sep 2021 09:54:09 +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="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.176.73] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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 22:37, Ming Lei wrote: > On Tue, Sep 14, 2021 at 05:19:31PM +0800, yukuai (C) wrote: >> On 在 2021/09/14 15:46, Ming Lei wrote: >> >>> If the above can happen, blk_mq_find_and_get_req() may not fix it too, just >>> 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; >>> + >>> 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); >>> >> >> Hi, Ming >> >> This apporch is wrong. >> >> If blk_mq_freeze_queue() is called, and nbd is waiting for all >> request to complete. percpu_ref_tryget() will fail here, and deadlock >> will occur because request can't complete in recv_work(). > > No, percpu_ref_tryget() won't fail until ->q_usage_counter is zero, when > it is perfectly fine to do nothing in recv_work(). > Hi Ming This apporch is a good idea, however we should not get q_usage_counter in reccv_work(), because It will block freeze queue. How about get q_usage_counter in nbd_read_stat(), and put in error path or after request completion? Thanks Kuai