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Mon, 17 Feb 2020 06:45:03 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 561FA11385C9; Mon, 17 Feb 2020 07:45:02 +0100 (CET) From: Markus Armbruster To: Maxim Levitsky Subject: Re: QAPI schema for desired state of LUKS keyslots References: <20200114193350.10830-1-mlevitsk@redhat.com> <20200114193350.10830-3-mlevitsk@redhat.com> <87lfp36gzh.fsf_-_@dusky.pond.sub.org> <59039903dba3c277ef9dbc2397a896c906f120d1.camel@redhat.com> Date: Mon, 17 Feb 2020 07:45:02 +0100 In-Reply-To: <59039903dba3c277ef9dbc2397a896c906f120d1.camel@redhat.com> (Maxim Levitsky's message of "Sun, 16 Feb 2020 10:05:15 +0200") Message-ID: <87lfp1ww41.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 10.5.11.15 X-MC-Unique: x58YhQGwPzONc56Mh8RTgA-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain 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: 207.211.31.81 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: Kevin Wolf , Daniel =?utf-8?Q?P=2EBerrang=C3=A9?= , qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Maxim Levitsky writes: > On Sat, 2020-02-15 at 15:51 +0100, Markus Armbruster wrote: >> 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. > 100% agree. >>=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 keyslots >> 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 >> Four cases: >>=20 >> * @state is "active" >>=20 >> Desired state is active holding the secret given by @secret. Optional >> @iter-time tweaks key stretching. >>=20 >> The keyslot is chosen either by the user or by the system, as follows: >>=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. > I didn't really understand this, since in state=3Dactive we shouldn't > delete anything. Looks OK otherwise. Let me try to clarify. Option: make the "already active holding @secret" case an error like the "already active holding another secret" case. In longhand: - @keyslot present The keyslot given by @keyslot. If it's already active, error. It feels inelegant to me, because it deviates from "specify desired state" paradigm: the specified desired state is fine, the way to get there from current state is obvious (do nothing), yet it's still an error. >> * @state is "inactive" >>=20 >> Desired state is inactive. >>=20 >> Error if the current state has active keyslots, but the desired state >> 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. > Yea, that would be very nice to have. >>=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 state >> has no active keyslots" unless the current state has none, either. >>=20 >> Option: error out unconditionally. > Yep, that the best IMHO. It's a matter of taste. If we interpret "both absent" as "all keyslots", then all cases flow out of the following simple spec: 0. Start with the set of all keyslots 1. If @old-secret is present, interset it with the set of slots holding that secret. 2. If @keyslots is present, intersect it with the set of slots with that slot number. The order of steps 1 and 2 doesn't matter. To error out unconditionally, we have to make "both absent" a special case. A good way to resolve such matters of taste is to try writing doc comments for all proposals. If you find you hate one of them much less, you have a winner :) [...]