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=-7.2 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 DF296C43387 for ; Tue, 18 Dec 2018 11:32:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4B6320578 for ; Tue, 18 Dec 2018 11:32:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="omhYynkm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726430AbeLRLcX (ORCPT ); Tue, 18 Dec 2018 06:32:23 -0500 Received: from userp2120.oracle.com ([156.151.31.85]:57266 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726341AbeLRLcX (ORCPT ); Tue, 18 Dec 2018 06:32:23 -0500 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id wBIBSfAP021950; Tue, 18 Dec 2018 11:32:14 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : references : cc : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=rc2n2PdIOD99CHH+mQgZLbXHr29zF2EPT2WexxFdsOQ=; b=omhYynkmo+qCmkZn69GZT1sHtHlKP77PTyA4IwVwWhS0BLfbfLkinZgplnB/lLN0oL38 mjMd+Rz/bQNz4M/X19jbqBMeC35fZgTpcNv0OSo/eV0Y39jXwAAZKvgmaeW5qRfQNhCG Y/DZoOIGHsQT5z+RpaVflKwx23kImUPqso1TdSgNdjjTtxJqicqWO1F6l4zDyjGTcQ+y VbmmvrSnH89kJGz8p4gWe+MfW9qG1HITzpC+MDzfjNliSSz6ikRXSMJSgZkVXmpDaDyp ABGxVj2BCE2O9b9gwDyKSqzRaUNrpzuAIt3J6SUFRwbPlw3DFYB1j2HDm1WuYI4XLTyQ 8Q== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by userp2120.oracle.com with ESMTP id 2pct8qtnae-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 18 Dec 2018 11:32:13 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id wBIBWCXH002302 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 18 Dec 2018 11:32:13 GMT Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id wBIBWBT4021035; Tue, 18 Dec 2018 11:32:12 GMT Received: from [192.168.2.8] (/1.202.67.146) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 18 Dec 2018 03:32:11 -0800 Subject: Re: [Xen-devel] [PATCH v2 1/1] xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= References: <1545094538-31426-1-git-send-email-dongli.zhang@oracle.com> <20181218093300.qfslnloxooqnu2im@mac> Cc: axboe@kernel.dk, konrad.wilk@oracle.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, paul.durrant@citrix.com, xen-devel@lists.xenproject.org From: Dongli Zhang Message-ID: <51ea8086-e5fd-b1db-f935-101160ca9359@oracle.com> Date: Tue, 18 Dec 2018 19:31:59 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20181218093300.qfslnloxooqnu2im@mac> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9110 signatures=668679 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-1812180102 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi Roger, On 12/18/2018 05:33 PM, Roger Pau Monné wrote: > 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). I would like to confirm if I would keep the err = -EINVAL in below because most of the below code is copied from original implementation without modification. There is no err set by xenbus_read_unsigned(). + 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; + } + + be->blkif->nr_ring_pages = 1 << ring_page_order; For the rest, I would do something like: + err = xenbus_scanf(XBT_NIL, dir, ring_ref_name, + "%u", &ring_ref[i]); + + if (err != 1 && nr_grefs > 1) { + xenbus_dev_fatal(dev, err, "reading %s/%s", + dir, ring_ref_name); + return -EINVAL; + } Thank you very much! Dongi Zhang