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Wed, 5 Feb 2020 11:02:52 +0000 (UTC) Date: Wed, 5 Feb 2020 12:02:50 +0100 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH 02/13] qcrypto-luks: implement encryption key management Message-ID: <20200205110250.GB5768@dhcp-200-226.str.redhat.com> References: <20200128171116.GU1446339@redhat.com> <20200128173251.GZ1446339@redhat.com> <20200130123847.GE6438@linux.fritz.box> <20200130125319.GD1891831@redhat.com> <87zhe5ovbv.fsf@dusky.pond.sub.org> <20200130150108.GM1891831@redhat.com> <877e18oq76.fsf@dusky.pond.sub.org> <87mu9xxwzv.fsf@dusky.pond.sub.org> <20200205093011.GA5768@dhcp-200-226.str.redhat.com> <87tv45wdui.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87tv45wdui.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: _oKoZvf6OUiKKrradIwmWg-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii 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: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , Maxim Levitsky , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 05.02.2020 um 11:03 hat Markus Armbruster geschrieben: > Kevin Wolf writes: >=20 > > Am 05.02.2020 um 09:24 hat Markus Armbruster geschrieben: > >> Daniel, Kevin, any comments or objections to the QAPI schema design > >> sketch developed below? > >>=20 > >> For your convenience, here's the result again: > >>=20 > >> { 'enum': 'LUKSKeyslotState', > >> 'data': [ 'active', 'inactive' ] } > >> { 'struct': 'LUKSKeyslotActive', > >> 'data': { 'secret': 'str', > >> '*iter-time': 'int } } > >> { 'union': 'LUKSKeyslotAmend', > >> 'base': { '*keyslot': 'int', > >> 'state': 'LUKSKeyslotState' } > >> 'discriminator': 'state', > >> 'data': { 'active': 'LUKSKeyslotActive' } } > > > > I think one of the requirements was that you can specify the keyslot no= t > > only by using its number, but also by specifying the old secret. >=20 > Quoting myself: >=20 > When we don't specify the slot#, then "new state active" selects an > inactive slot (chosen by the system, and "new state inactive selects > slots by secret (commonly just one slot). >=20 > This takes care of selecting (active) slots by old secret with "new > state inactive". "new secret inactive" can't select a slot by secret because 'secret' doesn't even exist for inactive. > I intentionally did not provide for selecting (active) slots by old > secret with "new state active", because that's unsafe update in place. >=20 > We want to update secrets, of course. But the safe way to do that is to > put the new secret into a free slot, and if that succeeds, deactivate > the old secret. If deactivation fails, you're left with both old and > new secret, which beats being left with no secret when update in place > fails. Right. I wonder if qemu-img wants support for that specifically (possibly with allowing to enter the key interactively) rather than requiring the user to call qemu-img amend twice. > > Trivia= l > > extension, you just get another optional field that can be specified > > instead of 'keyslot'. > > > > Resulting commands: > > > > Adding a key: > > qemu-img amend -o encrypt.keys.0.state=3Dactive,encrypt.keys.0.secr= et=3Dsec0 test.qcow2 >=20 > This activates an inactive slot chosen by the sysem. >=20 > You can activate a specific keyslot N by throwing in > encrypt.keys.0.keyslot=3DN. Yes. The usual case is that you just want to add a new key somwhere. > > Deleting a key: > > qemu-img amend -o encrypt.keys.0.state=3Dinactive,encrypt.keys.0.ke= yslot=3D2 test.qcow2 >=20 > This deactivates keyslot#2. >=20 > You can deactivate slots holding a specific secret S by replacing > encrypt.keys.0.keyslot=3D2 by encrypt.keys.0.secret=3DS. Not with your definition above, but with the appropriate changes, this makes sense. > > Previous version (if this series is applied unchanged): > > > > Adding a key: > > qemu-img amend -o encrypt.keys.0.new-secret=3Dsec0 test.qcow2 > > > > Deleting a key: > > qemu-img amend -o encrypt.keys.0.new-secret=3D,encrypt.keys.0.keysl= ot=3D2 test.qcow2 > > > > Adding a key gets more complicated with your proposed interface because > > state must be set explicitly now whereas before it was derived > > automatically from the fact that if you give a key, only active makes > > sense. >=20 > The explicitness could be viewed as an improvement :) Not really. I mean, I really know to appreciate the advantages of -blockdev where needed, but usually I don't want to type all that stuff for the most common tasks. qemu-img amend is similar. For deleting, I might actually agree that explicitness is an improvement, but for creating it's just unnecessary verbosity. > If you'd prefer implicit here: Max has patches for making union tags > optional with a default. They'd let you default active to true. I guess this would improve the usability in this case. Kevin