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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 6DA3CC43461 for ; Wed, 12 May 2021 15:12:25 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 188FB61C1E for ; Wed, 12 May 2021 15:12:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 188FB61C1E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:49070 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lgqX7-0004B3-N4 for qemu-devel@archiver.kernel.org; Wed, 12 May 2021 11:12:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43944) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lgqVQ-0002tG-PQ for qemu-devel@nongnu.org; Wed, 12 May 2021 11:10:36 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:20970) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lgqVO-0004Gv-3e for qemu-devel@nongnu.org; Wed, 12 May 2021 11:10:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620832232; 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=8zxBCpfgTN4i4/eL/ZTNPM0YT/TDrIunAP9mxeoKgIk=; b=boxu/HAya/OJgiKXGRf47oz0pFDm2Gl4LQboL2wLfmqemHf3ZVWRgxHJRI26ZNSCNC+HAx p/ZJ7pwNqWjUrHADUfBqIc8Ov28OnzkcJCOcvWUNJbfPi42vtnZOWr28i5dpuRl0MNgayg 5FT9tGlFqQbv3lOgOe3ka5CtbGacSRY= 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-515-nG0lj0drPlaor75IMtmyKg-1; Wed, 12 May 2021 11:10:30 -0400 X-MC-Unique: nG0lj0drPlaor75IMtmyKg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6CC7C801817; Wed, 12 May 2021 15:10:26 +0000 (UTC) Received: from merkur.fritz.box (ovpn-114-75.ams2.redhat.com [10.36.114.75]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2643A1001B2C; Wed, 12 May 2021 15:10:25 +0000 (UTC) Date: Wed, 12 May 2021 17:10:23 +0200 From: Kevin Wolf To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH v2] block: Improve backing file validation Message-ID: References: <20210511055518.31876-1-lizhijian@cn.fujitsu.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.7, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Li Zhijian , mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 11.05.2021 um 10:35 hat Daniel P. Berrangé geschrieben: > On Tue, May 11, 2021 at 01:55:18PM +0800, Li Zhijian wrote: > > Image below user cases: > > case 1: > > ``` > > $ qemu-img create -f raw source.raw 1G > > $ qemu-img create -f qcow2 -F raw -b source.raw ./source.raw > > qemu-img info source.raw > > image: source.raw > > file format: qcow2 > > virtual size: 193K (197120 bytes) > > disk size: 196K > > cluster_size: 65536 > > backing file: source.raw <<<<<< > > backing file format: raw > > Format specific information: > > compat: 1.1 > > lazy refcounts: false > > refcount bits: 16 > > corrupt: false > > ``` > > > > case 2: > > ``` > > $ qemu-img create -f raw source.raw 1G > > $ ln -sf source.raw destination.qcow2 > > $ qemu-img create -f qcow2 -F raw -b source.raw ./destination.qcow2 > > qemu-img info source.raw > > image: source.raw > > file format: qcow2 <<<<<< > > virtual size: 2.0G (2147483648 bytes) > > disk size: 196K > > cluster_size: 65536 > > backing file: source.raw > > backing file format: raw > > Format specific information: > > compat: 1.1 > > lazy refcounts: false > > refcount bits: 16 > > corrupt: false > > ``` > > Generally, we don't expect to corrupte the source.raw anyway, while > > actually it does. > > > > Here we check their inode number instead of file name. > > > > Suggested-by: Daniel P. Berrangé > > Signed-off-by: Li Zhijian > > > > --- > > v2: utilize stat() instead of realpath() (Daniel) > > > > Signed-off-by: Li Zhijian > > --- > > block.c | 39 ++++++++++++++++++++++++++++++++------- > > 1 file changed, 32 insertions(+), 7 deletions(-) > > > > diff --git a/block.c b/block.c > > index 9ad725d205..db4ae57959 100644 > > --- a/block.c > > +++ b/block.c > > @@ -6431,6 +6431,37 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs) > > return true; > > } > > > > +static bool validate_backing_file(const char *filename, > > + const char *backing_file, Error **errp) > > +{ > > + struct stat filename_stat, backing_stat; > > + > > + if (backing_file[0] == '\0') { > > + error_setg(errp, "Expected backing file name, got empty string"); > > + goto out; > > + } > > + > > + /* check whether filename and backing_file are refering to the same file */ > > + if (stat(backing_file, &backing_stat) == -1) { > > + error_setg(errp, "Cannot stat backing file %s", backing_file); > > + goto out; > > + } > > + if (stat(filename, &filename_stat) == -1) { > > + /* Simply consider filename doesn't exist, no need to further check */ > > + return true; > > + } > > + if ((filename_stat.st_dev == backing_stat.st_dev) && > > + (filename_stat.st_ino == backing_stat.st_ino)) { > > + error_setg(errp, "Error: Trying to create an image with the " > > + "same filename as the backing file"); > > + goto out; > > + } > > + > > + return true; > > +out: > > + return false; > > +} > > + > > void bdrv_img_create(const char *filename, const char *fmt, > > const char *base_filename, const char *base_fmt, > > char *options, uint64_t img_size, int flags, bool quiet, > > @@ -6507,13 +6538,7 @@ void bdrv_img_create(const char *filename, const char *fmt, > > > > backing_file = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE); > > if (backing_file) { > > - if (!strcmp(filename, backing_file)) { > > - error_setg(errp, "Error: Trying to create an image with the " > > - "same filename as the backing file"); > > - goto out; > > - } > > - if (backing_file[0] == '\0') { > > - error_setg(errp, "Expected backing file name, got empty string"); > > + if (!validate_backing_file(filename, backing_file, errp)) { > > goto out; > > } > > } > > Thinking about this again, this seems to be quite high in the generic block > layer code. As such I don't think we can assume that the backing file here > is actually a plain file on disk. IIUC the backing file could still be any > of the block drivers. Only once we get down into the protocol specific > drivers can be validate the type of backend. Yes, you definitely can't assume that filename is really a local file name here. It could be any other protocol supported by QEMU, or even use the json: pseudo-protocol. > I'm not sure what the right way to deal with that is, so perhaps Kevin or > Max can make a suggestion. Can we just keep the backing file open with write permissions unshared so that locking will fail for the new image? Or would that error condition be detected too late so that the image would already be truncated? Kevin