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=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 DC3DEC433EF for ; Wed, 15 Sep 2021 03:46:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDDD161211 for ; Wed, 15 Sep 2021 03:46:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236078AbhIODrk (ORCPT ); Tue, 14 Sep 2021 23:47:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:58867 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235956AbhIODrj (ORCPT ); Tue, 14 Sep 2021 23:47:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631677581; 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=laMJBZMfAA5GFR18gmCaz0BRGaBhHTinBYyhHApQWKQ=; b=h/tmFKgqr2JwNOUvSJXOZEtCY07s09ST+DYx8hx1sG/me9UGH7NBNHKQDuEMc5UqsAuMzi BQRpu2KYY4XCWfppQqmPRK3pTBffelcA7lYGmQejAFZxV0YYGD3L/f5EjKq9+YJs+eVaYG a6VHvULLBoPPW/PIZcclB2BiazHe1co= 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-560-ZiTgKBd1PpyNzJ0dXKzqDA-1; Tue, 14 Sep 2021 23:46:19 -0400 X-MC-Unique: ZiTgKBd1PpyNzJ0dXKzqDA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 898F8101796D; Wed, 15 Sep 2021 03:46:18 +0000 (UTC) Received: from T590 (ovpn-12-59.pek2.redhat.com [10.72.12.59]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E493E78433; Wed, 15 Sep 2021 03:46:10 +0000 (UTC) Date: Wed, 15 Sep 2021 11:46:21 +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: <374c6b37-b4b2-fe01-66be-ca2dbbc283e9@huawei.com> <8f1849a3-6bf2-6b14-7ef9-4969a9a5425b@huawei.com> <60f68f6b-5fff-6a39-b77b-4bbb86f1c87e@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <60f68f6b-5fff-6a39-b77b-4bbb86f1c87e@huawei.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Sep 15, 2021 at 11:36:47AM +0800, yukuai (C) wrote: > On 2021/09/15 11:16, Ming Lei wrote: > > On Wed, Sep 15, 2021 at 09:54:09AM +0800, yukuai (C) wrote: > > > 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? > > > > OK, looks I missed that nbd_read_stat() needs to wait for incoming reply > > first, so how about the following change by partitioning nbd_read_stat() > > into nbd_read_reply() and nbd_handle_reply()? > > Hi, Ming > > The change looks good to me. > > Do you want to send a patch to fix this? I guess you may add inflight check or sort of change in nbd_read_stat(), so feel free to fold it into your series. Thanks, Ming