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

[Daniel P . Berrangé]

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.


Regards,
Daniel
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