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_NONE 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 82FC8C433EF for ; Tue, 14 Sep 2021 14:37:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6856960698 for ; Tue, 14 Sep 2021 14:37:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233923AbhINOjA (ORCPT ); Tue, 14 Sep 2021 10:39:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:43939 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234029AbhINOiz (ORCPT ); Tue, 14 Sep 2021 10:38:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631630257; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OttAcz4NMYxVushPx3IV+Bq6AS7PXnqsl2qz+4gqrCQ=; b=jVmgF+GAjEP1eiOYyEtYfX10OyuiJrHOI1vBr2dmJST9dfjnu7uhDWrXHl84s0wJSrtzGM AbAQula9RCpRo99vruWhibTzHvSirvOcXkxsOz8BRR2goPYlNzJPex+HUDaQwZ/stDS3Gg jA3ueRyL1hoG5JaMffJDLVfIt2AuvA8= 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-497-GwTGfonYOOqIdWIiu4MWrw-1; Tue, 14 Sep 2021 10:37:35 -0400 X-MC-Unique: GwTGfonYOOqIdWIiu4MWrw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6FB7710053FB; Tue, 14 Sep 2021 14:37:34 +0000 (UTC) Received: from T590 (ovpn-12-32.pek2.redhat.com [10.72.12.32]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9588369FC8; Tue, 14 Sep 2021 14:37:25 +0000 (UTC) Date: Tue, 14 Sep 2021 22:37:35 +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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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(). Thanks, Ming