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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C76F7C43331 for ; Fri, 3 Apr 2020 09:25:36 +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 8D8C820721 for ; Fri, 3 Apr 2020 09:25:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Xc8+ma+K" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8D8C820721 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]:52652 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jKIZz-00045M-L7 for qemu-devel@archiver.kernel.org; Fri, 03 Apr 2020 05:25:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56802) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jKIYU-0003Xc-BW for qemu-devel@nongnu.org; Fri, 03 Apr 2020 05:24:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jKIYR-0008FI-4v for qemu-devel@nongnu.org; Fri, 03 Apr 2020 05:24:01 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:59377 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jKIYQ-00089T-Py for qemu-devel@nongnu.org; Fri, 03 Apr 2020 05:23:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585905837; h=from:from:reply-to: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=eJJy1WT3kPY1U6bs3QG16OQMi/Oxvs51Sf5VUHXmTR0=; b=Xc8+ma+KKqohDwUyq0zR+EaATkaqUzF/h0CyNtpe1/vb8dMhI6boN+4qGqFWOMP4AWeD4X A6rqgmNM91aq1ZZXtUWptPvDTFlOMglvrnoKpYBsudvRaQSP/1ecbQ93Y+jnXSO+q5rL8S 9EznWPbBm0U3S7T7tSyKCzM/30fLS58= 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-425-kkOMkQ55On-ry-b4ELn7wQ-1; Fri, 03 Apr 2020 05:23:45 -0400 X-MC-Unique: kkOMkQ55On-ry-b4ELn7wQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C857519067E6; Fri, 3 Apr 2020 09:23:43 +0000 (UTC) Received: from redhat.com (unknown [10.36.110.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D38CC6EF97; Fri, 3 Apr 2020 09:23:37 +0000 (UTC) Date: Fri, 3 Apr 2020 10:23:34 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: [PATCH-for-5.0 v2 4/4] qga: Restrict guest-file-read count to 10 MB to avoid crashes Message-ID: <20200403092334.GC559148@redhat.com> References: <20200331140638.16464-1-philmd@redhat.com> <20200331140638.16464-5-philmd@redhat.com> <87v9mi3ufw.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87v9mi3ufw.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Michael Roth , "Dr . David Alan Gilbert" , Fakhri Zulkifli , qemu-devel@nongnu.org, Sameeh Jubran , Basil Salman , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Dietmar Maurer Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Apr 02, 2020 at 03:09:55PM +0200, Markus Armbruster wrote: > Philippe Mathieu-Daud=C3=A9 writes: >=20 > > On https://www.mail-archive.com/qemu-devel@nongnu.org/msg693176.html > > Daniel Berrang=C3=A9 commented: > > > > The QEMU guest agent protocol is not sensible way to access huge > > files inside the guest. It requires the inefficient process of > > reading the entire data into memory than duplicating it again in > > base64 format, and then copying it again in the JSON serializer / > > monitor code. > > > > For arbitrary general purpose file access, especially for large > > files, use a real file transfer program or use a network block > > device, not the QEMU guest agent. > > > > To avoid bug reports as BZ#1594054, follow his suggestion to put a > > low, hard limit on "count" in the guest agent QAPI schema, and don't > > allow count to be larger than 10 MB. > > > > Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=3D1594054 > > Reported-by: Fakhri Zulkifli > > Suggested-by: Daniel P. Berrang=C3=A9 > > Signed-off-by: Philippe Mathieu-Daud=C3=A9 > > --- > > qga/qapi-schema.json | 6 ++++-- > > qga/commands.c | 6 +++++- > > 2 files changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json > > index f6fcb59f34..7758d9daf8 100644 > > --- a/qga/qapi-schema.json > > +++ b/qga/qapi-schema.json > > @@ -266,11 +266,13 @@ > > ## > > # @guest-file-read: > > # > > -# Read from an open file in the guest. Data will be base64-encoded > > +# Read from an open file in the guest. Data will be base64-encoded. > > +# As this command is just for limited, ad-hoc debugging, such as log > > +# file access, the number of bytes to read is limited to 10 MB. > > # > > # @handle: filehandle returned by guest-file-open > > # > > -# @count: maximum number of bytes to read (default is 4KB) > > +# @count: maximum number of bytes to read (default is 4KB, maximum is = 10MB) > > # > > # Returns: @GuestFileRead on success. > > # > > diff --git a/qga/commands.c b/qga/commands.c > > index 8ee1244ebb..c130d1b0f5 100644 > > --- a/qga/commands.c > > +++ b/qga/commands.c > > @@ -11,6 +11,7 @@ > > */ > > =20 > > #include "qemu/osdep.h" > > +#include "qemu/units.h" > > #include "guest-agent-core.h" > > #include "qga-qapi-commands.h" > > #include "qapi/error.h" > > @@ -18,11 +19,14 @@ > > #include "qemu/base64.h" > > #include "qemu/cutils.h" > > #include "qemu/atomic.h" > > +#include "commands-common.h" > > =20 > > /* Maximum captured guest-exec out_data/err_data - 16MB */ > > #define GUEST_EXEC_MAX_OUTPUT (16*1024*1024) > > /* Allocation and I/O buffer for reading guest-exec out_data/err_data = - 4KB */ > > #define GUEST_EXEC_IO_SIZE (4*1024) > > +/* Maximum file size to read - 10MB */ > > +#define GUEST_FILE_READ_COUNT_MAX (10 * MiB) > > =20 > > /* Note: in some situations, like with the fsfreeze, logging may be > > * temporarilly disabled. if it is necessary that a command be able > > @@ -559,7 +563,7 @@ GuestFileRead *qmp_guest_file_read(int64_t handle, = bool has_count, > > } > > if (!has_count) { > > count =3D QGA_READ_COUNT_DEFAULT; > > - } else if (count < 0 || count >=3D UINT32_MAX) { > > + } else if (count < 0 || count > GUEST_FILE_READ_COUNT_MAX) { > > error_setg(errp, "value '%" PRId64 "' is invalid for argument = count", > > count); > > return NULL; >=20 > What about qmp-guest-file-write? >=20 > Hmm, the JSON parser already puts a limit on the base-64 encoded data, > namely MAX_TOKEN_SIZE, which is 64MiB. Yes, MAX_TOKEN_SIZE is > ridiculously generous. >=20 > In case you look at the code: there are *two* MAX_TOKEN_SIZE, both > 64MiB. One actually applies to tokens, the other to all the tokens in a > top-level expression. Yes, this is criminally confusing. Oh fun :-( Anyway, if the JSON parser has 64 MB limits in various places, then I'd be inclined to set the QGA guest-file-read limit such that the encoded JSON is at approx the 64 MB limit too so we're somewhat consistent in limits. Base64 has a 3:4 overhead, so that would suggest setting guest-file-read to be 48 MB limit. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberrange= :| |: https://libvirt.org -o- https://fstop138.berrange.com= :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange= :|