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=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,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 2D3FFC433EF for ; Thu, 16 Sep 2021 08:04:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B8FF61209 for ; Thu, 16 Sep 2021 08:04:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234943AbhIPIFg (ORCPT ); Thu, 16 Sep 2021 04:05:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:41314 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234968AbhIPIFe (ORCPT ); Thu, 16 Sep 2021 04:05:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631779453; 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=pwNZJ4rNg2Bbq40eOmQLhg4v/7JOjLDWypf+dMjwfo4=; b=FEGF8teIInliDi2Jh+VJoFc+2D+1R04vQpgtA23p/D0hE9lp5nI6GJQ5hTXuNyHPiw2pE4 TFVTCN8Mffc4ISCIAxFx9DoSegObmHYkhg/zuZ1ePfIV0EoGQuv7fhS2RXFlq52F0YnHRg 42bLEy3s9auoQs7OkALjW04y9TfcHzw= 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-271-RAYFqjLUNw6spN_5yVw8cw-1; Thu, 16 Sep 2021 04:04:12 -0400 X-MC-Unique: RAYFqjLUNw6spN_5yVw8cw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 38726802928; Thu, 16 Sep 2021 08:04:11 +0000 (UTC) Received: from T590 (ovpn-12-89.pek2.redhat.com [10.72.12.89]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A41CE60C82; Thu, 16 Sep 2021 08:04:04 +0000 (UTC) Date: Thu, 16 Sep 2021 16:04:16 +0800 From: Ming Lei To: Yu Kuai Cc: josef@toxicpanda.com, axboe@kernel.dk, hch@infradead.org, linux-block@vger.kernel.org, nbd@other.debian.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com Subject: Re: [PATCH v7 6/6] nbd: fix uaf in nbd_handle_reply() Message-ID: References: <20210915092010.2087371-1-yukuai3@huawei.com> <20210915092010.2087371-7-yukuai3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210915092010.2087371-7-yukuai3@huawei.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Sep 15, 2021 at 05:20:10PM +0800, Yu Kuai wrote: > There is a problem that nbd_handle_reply() might access freed request: > > 1) At first, a normal io is submitted and completed with scheduler: > > internel_tag = blk_mq_get_tag -> get tag from sched_tags > blk_mq_rq_ctx_init > sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag] > ... > blk_mq_get_driver_tag > __blk_mq_get_driver_tag -> get tag from tags > tags->rq[tag] = sched_tag->static_rq[internel_tag] > > So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing > to the request: sched_tags->static_rq[internal_tag]. Even if the > io is finished. > > 2) nbd server send a reply with random tag directly: > > recv_work > nbd_handle_reply > blk_mq_tag_to_rq(tags, tag) > rq = tags->rq[tag] > > 3) if the sched_tags->static_rq is freed: > > blk_mq_sched_free_requests > blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i) > -> step 2) access rq before clearing rq mapping > blk_mq_clear_rq_mapping(set, tags, hctx_idx); > __free_pages() -> rq is freed here > > 4) Then, nbd continue to use the freed request in nbd_handle_reply > > Fix the problem by get 'q_usage_counter' before blk_mq_tag_to_rq(), > thus request is ensured not to be freed because 'q_usage_counter' is > not zero. > > Signed-off-by: Yu Kuai > --- > drivers/block/nbd.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index 9a7bbf8ebe74..3e8b70b5d4f9 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -824,6 +824,7 @@ 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_sock *nsock; > struct nbd_cmd *cmd; > struct request *rq; > @@ -834,7 +835,24 @@ static void recv_work(struct work_struct *work) > if (nbd_read_reply(nbd, args->index, &reply)) > break; > > + /* > + * Grab ref of q_usage_counter can prevent request being freed > + * during nbd_handle_reply(). If q_usage_counter is zero, then > + * no request is inflight, which means something is wrong since > + * we expect to find a request to complete here. > + */ The above comment is wrong, the purpose is simply for avoiding request pool freed, such as elevator switching won't happen once ->q_usage_counter is grabbed. So no any request UAF can be triggered when calling into nbd_handle_reply(). > + if (!percpu_ref_tryget(&q->q_usage_counter)) { > + dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n", > + __func__); > + break; > + } > + > cmd = nbd_handle_reply(nbd, args->index, &reply); > + /* > + * It's safe to drop ref before request completion, inflight > + * request will ensure q_usage_counter won't be zero. > + */ The above comment is useless actually. -- Ming