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=-11.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 94909C43387 for ; Tue, 8 Jan 2019 08:22:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56F0B20665 for ; Tue, 8 Jan 2019 08:22:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="lQzfz6Zk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726333AbfAHIWU (ORCPT ); Tue, 8 Jan 2019 03:22:20 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:53234 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728018AbfAHIWU (ORCPT ); Tue, 8 Jan 2019 03:22:20 -0500 Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id x088Iq8v074290; Tue, 8 Jan 2019 08:22:10 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : from : to : cc : references : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=bukR5O++t4PtDOG8l2y85xS76OnoCjkQVLylX5e+pp4=; b=lQzfz6Zknp6XNwuE5WW3CWmmB/uegrqUjFEAeTqpIhw9g+0pU6zzkZWPTt+R+11pGyt7 ADzAVZXr8CGM/7GXF4ltsGmikoDcY+h5ycrp4I9KiEbHfBYebm3JEbjY4iaCkOZbamEV iSMdp/vDjY2blZrCWf7EcEVRpoRttG2ZMZHGKiqwijo6sy6RRjsYuKJZlvS53Hf+enEN YapYDlMtvX7/zKNdzZT4wv+JF/xaGrQ2ERt+6XzTbYs/wnlohXTMJlEujVV4ZfxBY+CV 2Agxrdxg0E8n0s0E5HnAiz2MSaFNQbDBTtaS83/BD21G8O7g6BvYQyEwo+k33tSxYk42 yQ== Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by aserp2130.oracle.com with ESMTP id 2ptj3dt6kg-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 08 Jan 2019 08:22:10 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x088MAIW003863 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 8 Jan 2019 08:22:10 GMT Received: from abhmp0018.oracle.com (abhmp0018.oracle.com [141.146.116.24]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x088M9v2001885; Tue, 8 Jan 2019 08:22:10 GMT Received: from [10.182.71.41] (/10.182.71.41) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 08 Jan 2019 00:22:09 -0800 Subject: Re: [Xen-devel] [PATCH v5 2/2] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront From: Dongli Zhang To: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: axboe@kernel.dk, roger.pau@citrix.com, paul.durrant@citrix.com, konrad.wilk@oracle.com References: <1546935350-20957-1-git-send-email-dongli.zhang@oracle.com> <1546935350-20957-2-git-send-email-dongli.zhang@oracle.com> Message-ID: <5c3760a1-4f45-a67b-3b70-80fa68ee4358@oracle.com> Date: Tue, 8 Jan 2019 16:24:32 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <1546935350-20957-2-git-send-email-dongli.zhang@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9129 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901080069 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org oops. Please ignore this v5 patch. I just realized Linus suggested in an old email not use BUG()/BUG_ON() in the code. I will switch to the WARN() solution and resend again. Sorry for the junk email. Dongli Zhang On 2019/1/8 下午4:15, 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 > * use xenbus_read_unsigned() in connect_ring() > > Changed since v2: > * simplify the condition check as "(err != 1 && nr_grefs > 1)" > * avoid setting err as -EINVAL to remove extra one line of code > > Changed since v3: > * exit at the beginning if !nr_grefs > * change the if statements to avoid test (err != 1) twice > * initialize a 'blkif' stack variable (refer to PATCH 1/2) > > Changed since v4: > * use BUG_ON() when (nr_grefs == 0) to reminder the developer > * set err = -EINVAL before xenbus_dev_fatal() > > drivers/block/xen-blkback/xenbus.c | 69 ++++++++++++++++++++++---------------- > 1 file changed, 40 insertions(+), 29 deletions(-) > > diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c > index a4aadac..f6146cd 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 +936,39 @@ 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]); > + nr_grefs = blkif->nr_ring_pages; > + > + BUG_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) { > + if (nr_grefs == 1) > + break; > + > err = -EINVAL; > - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > + xenbus_dev_fatal(dev, err, "reading %s/%s", > + dir, ring_ref_name); > return err; > } > - nr_grefs = 1; > - } else { > - unsigned int i; > + } > > - if (ring_page_order > xen_blkif_max_ring_order) { > + if (err != 1) { > + WARN_ON(nr_grefs != 1); > + > + err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", > + &ring_ref[0]); > + if (err != 1) { > err = -EINVAL; > - xenbus_dev_fatal(dev, err, "%s/request %d ring page order exceed max:%d", > - dir, ring_page_order, > - xen_blkif_max_ring_order); > + xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); > return err; > } > - > - nr_grefs = 1 << ring_page_order; > - 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) { > - err = -EINVAL; > - xenbus_dev_fatal(dev, err, "reading %s/%s", > - dir, ring_ref_name); > - return err; > - } > - } > } > - blkif->nr_ring_pages = nr_grefs; > > for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) { > req = kzalloc(sizeof(*req), GFP_KERNEL); > @@ -1031,6 +1027,7 @@ static int connect_ring(struct backend_info *be) > size_t xspathsize; > const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-NNN" */ > unsigned int requested_num_queues = 0; > + unsigned int ring_page_order; > > pr_debug("%s %s\n", __func__, dev->otherend); > > @@ -1076,6 +1073,20 @@ static int connect_ring(struct backend_info *be) > blkif->nr_rings, blkif->blk_protocol, protocol, > pers_grants ? "persistent grants" : ""); > > + ring_page_order = xenbus_read_unsigned(dev->otherend, > + "ring-page-order", 0); > + > + if (ring_page_order > xen_blkif_max_ring_order) { > + err = -EINVAL; > + xenbus_dev_fatal(dev, err, > + "requested ring page order %d exceed max:%d", > + ring_page_order, > + xen_blkif_max_ring_order); > + return err; > + } > + > + blkif->nr_ring_pages = 1 << ring_page_order; > + > if (blkif->nr_rings == 1) > return read_per_ring_refs(&blkif->rings[0], dev->otherend); > else { >