Re: [PATCH 02/13] qcrypto-luks: implement encryption key management

[Maxim Levitsky]

On Tue, 2020-01-28 at 17:32 +0000, Daniel P. Berrangé wrote:
> On Tue, Jan 28, 2020 at 05:11:16PM +0000, Daniel P. Berrangé 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:
> > > 
> > > <trimmed>
> > > 
> > > > > +##
> > > > > +# @LUKSKeyslotUpdate:
> > > > > +#
> > > > > +# @keyslot:         If specified, will update only keyslot with this 
> > > > > index
> > > > > +#
> > > > > +# @old-secret:      If specified, will only update keyslots that
> > > > > +#                   can be opened with password which is contained in
> > > > > +#                   QCryptoSecret with @old-secret ID
> > > > > +#
> > > > > +#                   If neither @keyslot nor @old-secret is specified,
> > > > > +#                   first empty keyslot is selected for the update
> > > > > +#
> > > > > +# @new-secret:      The ID of a QCryptoSecret object providing a new 
> > > > > decryption
> > > > > +#                   key to place in all matching keyslots.
> > > > > +#                   null/empty string erases all matching keyslots
> > > > 
> > > > I hate making the empty string do something completely different than a
> > > > non-empty string.
> > > > 
> > > > What about making @new-secret optional, and have absent @new-secret
> > > > erase?
> > > 
> > > 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 pass null 
> > > on command line.
> > 
> > IIUC this a result of using  "StrOrNull" for this one field...
> > 
> > 
> > > > > +# Since: 5.0
> > > > > +##
> > > > > +{ 'struct': 'LUKSKeyslotUpdate',
> > > > > +  'data': {
> > > > > +           '*keyslot': 'int',
> > > > > +           '*old-secret': 'str',
> > > > > +           'new-secret' : 'StrOrNull',
> > > > > +           '*iter-time' : 'int' } }
> > 
> > It looks wierd here to be special casing "new-secret" to "StrOrNull"
> > instead of just marking it as an optional string field
> > 
> >    "*new-secret": "str"
> > 
> > which would be possible to use from the command line, as you simply
> > omit the field.
> > 
> > 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.
> 
> Thinking about this again, I really believe we ought to be moire
> explicit about disabling the keyslot by having the "active" field.
> eg
> 
> { 'struct': 'LUKSKeyslotUpdate',
>   'data': {
>           'active': 'bool',
>           '*keyslot': 'int',
>           '*old-secret': 'str',
>           '*new-secret' : 'str',
>           '*iter-time' : 'int' } }
> 
> "new-secret" is thus only needed when "active" == true.
> 
> This avoids the problem with being unable to specify a
> null for StrOrNull on the command line too.
I fully support this idea.
If no objections from anybody else, I'll do it this way.

Best regards,
        Maxim Levitsky

> 
> Regards,
> Daniel