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=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 6CFB6C433F5 for ; Tue, 14 Sep 2021 07:47:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5373F61355 for ; Tue, 14 Sep 2021 07:47:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235916AbhINHsq (ORCPT ); Tue, 14 Sep 2021 03:48:46 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:50950 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237039AbhINHru (ORCPT ); Tue, 14 Sep 2021 03:47:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631605593; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HViiRnu75I46+r5aoAeD0e3kDx7NMxZUbAuKksyTKDo=; b=AwC2ahWfEiqgh0WHluo7VygOcgwrlKmlgm2tRU4n6GnH8W09razsQU1Doobq+977qRK4C3 uCbMkhrGU+84xqMV50TTwBiAIcBsQm3QtIyeyeqtSk+GeXMLDo+GvIceuV0YfZtmmFt4Gu lbXAwPBJ8ZE6BxqBj0UrXbe3OU93mEI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-537-EytKr-llMZaAcjwQWjDUtg-1; Tue, 14 Sep 2021 03:46:29 -0400 X-MC-Unique: EytKr-llMZaAcjwQWjDUtg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 14FB71017965; Tue, 14 Sep 2021 07:46:28 +0000 (UTC) Received: from T590 (ovpn-13-174.pek2.redhat.com [10.72.13.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D650210016F5; Tue, 14 Sep 2021 07:46:19 +0000 (UTC) Date: Tue, 14 Sep 2021 15:46:28 +0800 From: Ming Lei To: "yukuai (C)" Cc: axboe@kernel.dk, josef@toxicpanda.com, hch@infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, nbd@other.debian.org, yi.zhang@huawei.com Subject: Re: [PATCH v5 5/6] nbd: convert to use blk_mq_find_and_get_req() Message-ID: References: <20210909141256.2606682-1-yukuai3@huawei.com> <20210909141256.2606682-6-yukuai3@huawei.com> <374c6b37-b4b2-fe01-66be-ca2dbbc283e9@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <374c6b37-b4b2-fe01-66be-ca2dbbc283e9@huawei.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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 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); Thanks, Ming