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=-6.6 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 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 45032C43331 for ; Thu, 2 Apr 2020 13:10:55 +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 13FDA20784 for ; Thu, 2 Apr 2020 13:10:55 +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="C0eNRhV7" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 13FDA20784 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]:38410 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJzcU-0005Ht-7f for qemu-devel@archiver.kernel.org; Thu, 02 Apr 2020 09:10:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38573) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jJzbp-0004lj-3m for qemu-devel@nongnu.org; Thu, 02 Apr 2020 09:10:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jJzbm-0005U9-MO for qemu-devel@nongnu.org; Thu, 02 Apr 2020 09:10:12 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:31750 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 1jJzbm-0005Tv-3n for qemu-devel@nongnu.org; Thu, 02 Apr 2020 09:10:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585833009; 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=K4lJHnbN/1slg+JDMkmAvpYJ6x1YI1TYOmYL0AVqZAk=; b=C0eNRhV7ZkfOrrqMSzSBW6ilR4RDNfxSLM5FgcTTYjfS7H/h6Sgei2UlUrt4g0Mu6e/p8b 3zOumlKCmsojshQPRq2Hxtw6p/M5qOY1Lak43GTCYAeGiFL/knrzTawXci8F0yhBKh6Rey 3CSk0I8Y1mrpzdDMfXbeH9bLWCkzadY= 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-269-tr_hpxvBOsy167fg0q0U0Q-1; Thu, 02 Apr 2020 09:10:01 -0400 X-MC-Unique: tr_hpxvBOsy167fg0q0U0Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0C83A801E5C; Thu, 2 Apr 2020 13:10:00 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-112-69.ams2.redhat.com [10.36.112.69]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BD7AA18A85; Thu, 2 Apr 2020 13:09:56 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 419FF11385E2; Thu, 2 Apr 2020 15:09:55 +0200 (CEST) From: Markus Armbruster To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH-for-5.0 v2 4/4] qga: Restrict guest-file-read count to 10 MB to avoid crashes References: <20200331140638.16464-1-philmd@redhat.com> <20200331140638.16464-5-philmd@redhat.com> Date: Thu, 02 Apr 2020 15:09:55 +0200 In-Reply-To: <20200331140638.16464-5-philmd@redhat.com> ("Philippe =?utf-8?Q?Mathieu-Daud=C3=A9=22's?= message of "Tue, 31 Mar 2020 16:06:38 +0200") Message-ID: <87v9mi3ufw.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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: , Cc: "Daniel P . =?utf-8?Q?Berrang=C3=A9?=" , Michael Roth , "Dr . David Alan Gilbert" , Fakhri Zulkifli , qemu-devel@nongnu.org, Sameeh Jubran , Basil Salman , Dietmar Maurer Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Philippe Mathieu-Daud=C3=A9 writes: > 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 10= MB) > # > # 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, bo= ol 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 co= unt", > count); > return NULL; What about qmp-guest-file-write? 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. 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. We additionally limit the number of tokens within a top-level expression, and its nesting depth. The stated reason for these limits is /* * Security consideration, we limit total memory allocated per object * and the maximum recursion depth that a message can force. */ "Security" is misleading; we use this parser only for parsing QMP input, QGA input, and string literals. All trusted. It's actually a robustness consideration. We fail to put similar limits on JSON output. While we protect you from the rather far-fetched mistake of driving QEMU into OOM state by sending ridiculously huge QMP/QGA input, we do nothing to protect you from the more realistic mistake of sending a QMP/QGA command that produces ridiculously huge output. Could use a rethink, I guess :)