Re: [PATCH 1/7] dm: measure data on table load

[Mike Snitzer <snitzer@redhat.com>]

On Tue, Jul 20 2021 at 10:12P -0400,
Mimi Zohar <zohar@linux.ibm.com> wrote:

> Hi Tushar, Mike, 
> 
> On Mon, 2021-07-12 at 17:48 -0700, Tushar Sugandhi wrote:
> > +struct dm_ima_device_table_metadata {
> > +       /*
> > +        * Contains data specific to the device which is common across
> > +        * all the targets in the table.e.g. name, uuid, major, minor etc.
> > +        * The values are stored in comma separated list of key1=val1,key2=val2; pairs
> > +        * delimited by a semicolon at the end of the list.
> > +        */
> > +       char *device_metadata;
> > +       unsigned int device_metadata_len;
> > +       unsigned int num_targets;
> > +
> > +       /*
> > +        * Contains the sha256 hashs of the IMA measurements of the
> > +        * target attributes key-value pairs from the active/inactive tables.
> > +        */
> 
> From past experience hard coding the hash algorithm is really not a
> good idea.
> 
> Mimi
> 
> > +       char *hash;
> > +       unsigned int hash_len;
> > +
> > +};

Hi Mimi,

The dm-ima.c code is using SHASH_DESC_ON_STACK and then storing the
more opaque result via 'hash' and 'hash_len'.

So if/when the dm-ima.c hash algorithm were to change this detail
won't change the dm_ima_device_table_metadata structure at all right?
But even if changes were needed this is purely an implementation
detail correct?  Why might users care which algorithm is used by
dm-ima to generate the hashes?

Assuming there is a valid reason for users to care about this, we can
improve this aspect as follow-on work.. so I don't consider this a
blocker for this patchset at this point.  Please clarify if you feel
it should be a blocker.

Thanks,
Mike