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Mon, 24 Feb 2020 14:46:24 +0000 (UTC) Received: from redhat.com (unknown [10.42.16.105]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 234EF91833; Mon, 24 Feb 2020 14:46:23 +0000 (UTC) Date: Mon, 24 Feb 2020 14:46:21 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Maxim Levitsky Subject: Re: QAPI schema for desired state of LUKS keyslots (was: [PATCH 02/13] qcrypto-luks: implement encryption key management) Message-ID: <20200224144621.GT635661@redhat.com> References: <20200114193350.10830-1-mlevitsk@redhat.com> <20200114193350.10830-3-mlevitsk@redhat.com> <87lfp36gzh.fsf_-_@dusky.pond.sub.org> <20200217103700.GC6309@linux.fritz.box> MIME-Version: 1.0 In-Reply-To: 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] X-Received-From: 205.139.110.120 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: Kevin Wolf , qemu-block@nongnu.org, qemu-devel@nongnu.org, Markus Armbruster , Max Reitz , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Feb 17, 2020 at 01:07:23PM +0200, Maxim Levitsky wrote: > On Mon, 2020-02-17 at 11:37 +0100, Kevin Wolf wrote: > > Am 15.02.2020 um 15:51 hat Markus Armbruster geschrieben: > > > Review of this patch led to a lengthy QAPI schema design discussion. > > > Let me try to condense it into a concrete proposal. > > >=20 > > > This is about the QAPI schema, and therefore about QMP. The > > > human-friendly interface is out of scope. Not because it's not > > > important (it clearly is!), only because we need to *focus* to have a > > > chance at success. > > >=20 > > > I'm going to include a few design options. I'll mark them "Option:". > > >=20 > > > The proposed "amend" interface takes a specification of desired state= , > > > and figures out how to get from here to there by itself. LUKS keyslo= ts > > > are one part of desired state. > > >=20 > > > We commonly have eight LUKS keyslots. Each keyslot is either active = or > > > inactive. An active keyslot holds a secret. > > >=20 > > > Goal: a QAPI type for specifying desired state of LUKS keyslots. > > >=20 > > > Proposal: > > >=20 > > > { 'enum': 'LUKSKeyslotState', > > > 'data': [ 'active', 'inactive' ] } > > >=20 > > > { 'struct': 'LUKSKeyslotActive', > > > 'data': { 'secret': 'str', > > > '*iter-time': 'int } } > > >=20 > > > { 'struct': 'LUKSKeyslotInactive', > > > 'data': { '*old-secret': 'str' } } > > >=20 > > > { 'union': 'LUKSKeyslotAmend', > > > 'base': { '*keyslot': 'int', > > > 'state': 'LUKSKeyslotState' } > > > 'discriminator': 'state', > > > 'data': { 'active': 'LUKSKeyslotActive', > > > 'inactive': 'LUKSKeyslotInactive' } } > > >=20 > > > LUKSKeyslotAmend specifies desired state for a set of keyslots. > >=20 > > Though not arbitrary sets of keyslots, it's only a single keyslot or > > multiple keyslots containing the same secret. Might be good enough in > > practice, though it means that you may have to issue multiple amend > > commands to get to the final state that you really want (even if doing > > everything at once would be safe). > >=20 > > > Four cases: > > >=20 > > > * @state is "active" > > >=20 > > > Desired state is active holding the secret given by @secret. Optio= nal > > > @iter-time tweaks key stretching. > > >=20 > > > The keyslot is chosen either by the user or by the system, as follo= ws: > > >=20 > > > - @keyslot absent > > >=20 > > > One inactive keyslot chosen by the system. If none exists, error= . > > >=20 > > > - @keyslot present > > >=20 > > > The keyslot given by @keyslot. > > >=20 > > > If it's already active holding @secret, no-op. Rationale: the > > > current state is the desired state. > > >=20 > > > If it's already active holding another secret, error. Rationale: > > > update in place is unsafe. > > >=20 > > > Option: delete the "already active holding @secret" case. Feels > > > inelegant to me. Okay if it makes things substantially simpler. > > >=20 > > > * @state is "inactive" > > >=20 > > > Desired state is inactive. > > >=20 > > > Error if the current state has active keyslots, but the desired sta= te > > > has none. > > >=20 > > > The user choses the keyslot by number and/or by the secret it holds= , > > > as follows: > > >=20 > > > - @keyslot absent, @old-secret present > > >=20 > > > All active keyslots holding @old-secret. If none exists, error. > > >=20 > > > - @keyslot present, @old-secret absent > > >=20 > > > The keyslot given by @keyslot. > > >=20 > > > If it's already inactive, no-op. Rationale: the current state is > > > the desired state. > > >=20 > > > - both @keyslot and @old-secret present > > >=20 > > > The keyslot given by keyslot. > > >=20 > > > If it's inactive or holds a secret other than @old-secret, error. > > >=20 > > > Option: error regardless of @old-secret, if that makes things > > > simpler. > > >=20 > > > - neither @keyslot not @old-secret present > > >=20 > > > All keyslots. Note that this will error out due to "desired stat= e > > > has no active keyslots" unless the current state has none, either= . > > >=20 > > > Option: error out unconditionally. > > >=20 > > > Note that LUKSKeyslotAmend can specify only one desired state for > > > commonly just one keyslot. Rationale: this satisfies practical needs= . > > > An array of LUKSKeyslotAmend could specify desired state for all > > > keyslots. However, multiple array elements could then apply to the s= ame > > > slot. We'd have to specify how to resolve such conflicts, and we'd h= ave > > > to code up conflict detection. Not worth it. > > >=20 > > > Examples: > > >=20 > > > * Add a secret to some free keyslot: > > >=20 > > > { "state": "active", "secret": "CIA/GRU/MI6" } > > >=20 > > > * Deactivate all keyslots holding a secret: > > >=20 > > > { "state": "inactive", "old-secret": "CIA/GRU/MI6" } > > >=20 > > > * Add a secret to a specific keyslot: > > >=20 > > > { "state": "active", "secret": "CIA/GRU/MI6", "keyslot": 0 } > > >=20 > > > * Deactivate a specific keyslot: > > >=20 > > > { "state": "inactive", "keyslot": 0 } > > >=20 > > > Possibly less dangerous: > > >=20 > > > { "state": "inactive", "keyslot": 0, "old-secret": "CIA/GRU/MI6" } > > >=20 > > > Option: Make use of Max's patches to support optional union tag with > > > default value to let us default @state to "active". I doubt this mak= es > > > much of a difference in QMP. A human-friendly interface should proba= bly > > > be higher level anyway (Daniel pointed to cryptsetup). > > >=20 > > > Option: LUKSKeyslotInactive member @old-secret could also be named > > > @secret. I don't care. > > >=20 > > > Option: delete @keyslot. It provides low-level slot access. > > > Complicates the interface. Fine if we need lov-level slot access. D= o > > > we? > > >=20 > > > I apologize for the time it has taken me to write this. > > >=20 > > > Comments? > >=20 > > Works for me (without taking any of the options). > >=20 > > The unclear part is what the human-friendly interface should look like > > and where it should live. I'm afraid doing only the QMP part and callin= g > > the feature completed like we do so often won't work in this case. >=20 > IMHO, I think that the best way to create human friendly part is to imple= ment > luks specific commands for qemu-img and use interface very similar > to what cryptsetup does. I think we can have a generic 'qemu-img amend' for machine type, with the complex dotted syntax. And then have two human friendly commands 'qemu-img crypt-add-key' and 'qemu-img crypt-del-key' similarish to cryptsetup. 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= :|