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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 9F1F7C2D0DB for ; Thu, 30 Jan 2020 14:24:00 +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 6991420674 for ; Thu, 30 Jan 2020 14:24:00 +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="TqMnrf8+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6991420674 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]:33294 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ixAjf-0007Re-Hy for qemu-devel@archiver.kernel.org; Thu, 30 Jan 2020 09:23:59 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34184) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ixAj3-0006v4-Nd for qemu-devel@nongnu.org; Thu, 30 Jan 2020 09:23:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ixAj1-0003D4-Ih for qemu-devel@nongnu.org; Thu, 30 Jan 2020 09:23:20 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:51758 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 1ixAj1-0003CL-E7 for qemu-devel@nongnu.org; Thu, 30 Jan 2020 09:23:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580394199; 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=7uX3k//2paewfysSrBA4sRPwnjZkxjSLwwKHvZIvQXM=; b=TqMnrf8+2LYqOykdhQdAZbjHP6T/qQPM6+/RSve7FVsJJ++PtspYt97j/rLo8kL/noghGb 9AMaciEp6HkoL+jSH6X1ExBoFw3Z1ZFU2FsryAxtHV5tQsKNQ4So1MhVlfXlWMFQnqszA3 3zDONJTo9VwEXPwaEbQrvuBl/gjQi7U= 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-177-XoDnw-KyO0OvLa9xEluW6w-1; Thu, 30 Jan 2020 09:23:16 -0500 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 60F21800D4E; Thu, 30 Jan 2020 14:23:15 +0000 (UTC) Received: from linux.fritz.box (ovpn-117-25.ams2.redhat.com [10.36.117.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6754284D8F; Thu, 30 Jan 2020 14:23:11 +0000 (UTC) Date: Thu, 30 Jan 2020 15:23:10 +0100 From: Kevin Wolf To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH 02/13] qcrypto-luks: implement encryption key management Message-ID: <20200130142310.GF6438@linux.fritz.box> References: <20200114193350.10830-1-mlevitsk@redhat.com> <20200114193350.10830-3-mlevitsk@redhat.com> <87r1zti6r8.fsf@dusky.pond.sub.org> <20200128171116.GU1446339@redhat.com> <20200128173251.GZ1446339@redhat.com> <20200130123847.GE6438@linux.fritz.box> <20200130125319.GD1891831@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200130125319.GD1891831@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: XoDnw-KyO0OvLa9xEluW6w-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 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: , Cc: qemu-block@nongnu.org, Markus Armbruster , qemu-devel@nongnu.org, Maxim Levitsky , Max Reitz , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 30.01.2020 um 13:53 hat Daniel P. Berrang=E9 geschrieben: > On Thu, Jan 30, 2020 at 01:38:47PM +0100, Kevin Wolf wrote: > > Am 28.01.2020 um 18:32 hat Daniel P. Berrang=E9 geschrieben: > > > On Tue, Jan 28, 2020 at 05:11:16PM +0000, Daniel P. Berrang=E9 wrote: > > > > On Tue, Jan 21, 2020 at 03:13:01PM +0200, Maxim Levitsky wrote: > > > > > On Tue, 2020-01-21 at 08:54 +0100, Markus Armbruster wrote: > > > > >=20 > > > > > > > > > >=20 > > > > > > > +## > > > > > > > +# @LUKSKeyslotUpdate: > > > > > > > +# > > > > > > > +# @keyslot: If specified, will update only keyslot w= ith this index > > > > > > > +# > > > > > > > +# @old-secret: If specified, will only update keyslots = that > > > > > > > +# can be opened with password which is con= tained in > > > > > > > +# QCryptoSecret with @old-secret ID > > > > > > > +# > > > > > > > +# If neither @keyslot nor @old-secret is s= pecified, > > > > > > > +# first empty keyslot is selected for the = update > > > > > > > +# > > > > > > > +# @new-secret: The ID of a QCryptoSecret object providi= ng a new decryption > > > > > > > +# key to place in all matching keyslots. > > > > > > > +# null/empty string erases all matching ke= yslots > > > > > >=20 > > > > > > I hate making the empty string do something completely differen= t than a > > > > > > non-empty string. > > > > > >=20 > > > > > > What about making @new-secret optional, and have absent @new-se= cret > > > > > > erase? > > > > >=20 > > > > > I don't remember already why I and Keven Wolf decided to do this = this way, but I think that you are right here. > > > > > I don't mind personally to do this this way. > > > > > empty string though is my addition, since its not possible to pas= s null on command line. > > > >=20 > > > > IIUC this a result of using "StrOrNull" for this one field... > > > >=20 > > > >=20 > > > > > > > +# Since: 5.0 > > > > > > > +## > > > > > > > +{ 'struct': 'LUKSKeyslotUpdate', > > > > > > > + 'data': { > > > > > > > + '*keyslot': 'int', > > > > > > > + '*old-secret': 'str', > > > > > > > + 'new-secret' : 'StrOrNull', > > > > > > > + '*iter-time' : 'int' } } > > > >=20 > > > > It looks wierd here to be special casing "new-secret" to "StrOrNull= " > > > > instead of just marking it as an optional string field > > > >=20 > > > > "*new-secret": "str" > > > >=20 > > > > which would be possible to use from the command line, as you simply > > > > omit the field. > > > >=20 > > > > I guess the main danger here is that we're using this as a trigger > > > > to erase keyslots. So simply omitting "new-secret" can result > > > > in damage to the volume by accident which is not an attractive > > > > mode. > >=20 > > Right. It's been a while since I discussed this with Maxim, but I think > > this was the motivation for me to suggest an explicit null value. > >=20 > > As long as we don't support passing null from the command line, I see > > the problem with it, though. Empty string (which I think we didn't > > discuss before) looks like a reasonable enough workaround to me, but if > > you think this is too much magic, then maybe not. > >=20 > > > Thinking about this again, I really believe we ought to be moire > > > explicit about disabling the keyslot by having the "active" field. > > > eg > > >=20 > > > { 'struct': 'LUKSKeyslotUpdate', > > > 'data': { > > > 'active': 'bool', > > > '*keyslot': 'int', > > > '*old-secret': 'str', > > > '*new-secret' : 'str', > > > '*iter-time' : 'int' } } > > >=20 > > > "new-secret" is thus only needed when "active" =3D=3D true. > >=20 > > Hm. At the very least, I would make 'active' optional and default to > > true, so that for adding or updating you must only specify 'new-secret' > > and for deleting only 'active'. >=20 > Is that asymmetry really worth while ? It merely saves a few > characters of typing by omitting "active: true", so I'm not > really convinced. >=20 > >=20 > > > This avoids the problem with being unable to specify a null for > > > StrOrNull on the command line too. > >=20 > > If we ever get a way to pass null on the command line, how would we > > think about a struct like this? Will it still feel right, or will it > > feel like we feel about simple unions today (they exist, we would like > > to get rid of them, but we can't because compatibility)? >=20 > Personally I really don't like the idea of using "new-secret:null" > as a way to request deletion of a keyslot. That's too magical > for an action that is so dangerous to data IMhO. >=20 > I think of these operations as activating & deactivating keyslots, > hence my suggestion to use an explicit "active: true|false" to > associate the core action being performed, instead of inferring > the action indirectly from the secret. The general idea of the amend interface is more that you describe a desired state rather than operations to achieve it. > I think this could lend itself better to future extensions too. > eg currently we're just activating or deactivating a keyslot. > it is conceivable in future (LUKS2) we might want to modify an > existing keyslot in some way. In that scenario, "active" can > be updated to be allowed to be optional such that: >=20 > - active: true -> activate a currently inactive keyslot > - active: false -> deactivate a currently active keyslot > - active omitted -> modify a currently active keyslot This distinction feels artificial to me. All three operations just change the content of a keyslot. Whether it contained a key or not in the old state shouldn't make a difference for how to get a new value (which could be a new key or just an empty keyslot) written to it. Making an omitted key mean something different from the other options so that it's not just defaulting to one of them is problematic, too. We have at least one place where it works like this (backing files) and it tends to give us headaches. Kevin