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=-8.9 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,USER_AGENT_NEOMUTT 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 A7442C43387 for ; Tue, 18 Dec 2018 09:33:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7CD642133F for ; Tue, 18 Dec 2018 09:33:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726364AbeLRJdI (ORCPT ); Tue, 18 Dec 2018 04:33:08 -0500 Received: from smtp.eu.citrix.com ([185.25.65.24]:41907 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726358AbeLRJdI (ORCPT ); Tue, 18 Dec 2018 04:33:08 -0500 X-IronPort-AV: E=Sophos;i="5.56,367,1539648000"; d="scan'208";a="83480015" Date: Tue, 18 Dec 2018 10:33:00 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Dongli Zhang CC: , , , , , Subject: Re: [PATCH v2 1/1] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront Message-ID: <20181218093300.qfslnloxooqnu2im@mac> References: <1545094538-31426-1-git-send-email-dongli.zhang@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1545094538-31426-1-git-send-email-dongli.zhang@oracle.com> User-Agent: NeoMutt/20180716 X-ClientProxiedBy: AMSPEX02CAS02.citrite.net (10.69.22.113) To AMSPEX02CL01.citrite.net (10.69.22.125) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Dec 18, 2018 at 08:55:38AM +0800, Dongli Zhang wrote: > The xenstore 'ring-page-order' is used globally for each blkback queue and > therefore should be read from xenstore only once. However, it is obtained > in read_per_ring_refs() which might be called multiple times during the > initialization of each blkback queue. > > If the blkfront is malicious and the 'ring-page-order' is set in different > value by blkfront every time before blkback reads it, this may end up at > the "WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));" in > xen_blkif_disconnect() when frontend is destroyed. > > This patch reworks connect_ring() to read xenstore 'ring-page-order' only > once. > > Signed-off-by: Dongli Zhang > --- > Changed since v1: > * change the order of xenstore read in read_per_ring_refs(suggested by Roger Pau Monne) > * use xenbus_read_unsigned() in connect_ring() (suggested by Roger Pau Monne) > > drivers/block/xen-blkback/xenbus.c | 70 ++++++++++++++++++++++---------------- > 1 file changed, 40 insertions(+), 30 deletions(-) > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > index a4bc74e..7178f0f 100644 > --- a/drivers/block/xen-blkback/xenbus.c > +++ b/drivers/block/xen-blkback/xenbus.c > @@ -926,7 +926,7 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) > int err, i, j; > struct xen_blkif *blkif = ring->blkif; > struct xenbus_device *dev = blkif->be->dev; > - unsigned int ring_page_order, nr_grefs, evtchn; > + unsigned int nr_grefs, evtchn; > > err = xenbus_scanf(XBT_NIL, dir, "event-channel", "%u", > &evtchn); > @@ -936,43 +936,38 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) > return err; > } > > - err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", > - &ring_page_order); > - if (err != 1) { > - err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", &ring_ref[0]); > - if (err != 1) { > + nr_grefs = blkif->nr_ring_pages; > + WARN_ON(!nr_grefs); > + > + for (i = 0; i < nr_grefs; i++) { > + char ring_ref_name[RINGREF_NAME_LEN]; > + > + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i); > + err = xenbus_scanf(XBT_NIL, dir, ring_ref_name, > + "%u", &ring_ref[i]); > + > + if (err != 1 && (i || (!i && nr_grefs > 1))) { AFAICT the above condition can be simplified as "err != 1 && nr_grefs". > err = -EINVAL; There's no point in setting err here... > - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > + xenbus_dev_fatal(dev, err, "reading %s/%s", > + dir, ring_ref_name); > return err; ...since you can just return -EINVAL (same applies to the other instance below). The rest LGTM, Thanks.