Re: [PATCH v8 10/10] integrity: support EC-RDSA signatures for asymmetric_verify

[Vitaly Chikunov]

On Wed, Mar 27, 2019 at 02:10:20PM -0400, Mimi Zohar wrote:
> On Tue, 2019-03-26 at 15:58 +0300, Vitaly Chikunov wrote:
> > Allow to use EC-RDSA signatures for IMA by determining signature type by
> > the hash algorithm name. This works good for EC-RDSA since Streebog and
> > EC-RDSA should always be used together.
> > 
> > Cc: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> > Cc: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxx>
> > Cc: linux-integrity@xxxxxxxxxxxxxxx
> > Signed-off-by: Vitaly Chikunov <vt@xxxxxxxxxxxx>
> > ---
> >  security/integrity/digsig_asymmetric.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/security/integrity/digsig_asymmetric.c b/security/integrity/digsig_asymmetric.c
> > index d775e03fbbcc..99080871eb9f 100644
> > --- a/security/integrity/digsig_asymmetric.c
> > +++ b/security/integrity/digsig_asymmetric.c
> > @@ -104,9 +104,16 @@ int asymmetric_verify(struct key *keyring, const char *sig,
> >  
> >  	memset(&pks, 0, sizeof(pks));
> >  
> > -	pks.pkey_algo = "rsa";
> >  	pks.hash_algo = hash_algo_name[hdr->hash_algo];
> > -	pks.encoding = "pkcs1";
> > +	if (hdr->hash_algo == HASH_ALGO_STREEBOG_256 ||
> > +	    hdr->hash_algo == HASH_ALGO_STREEBOG_512) {
> > +		/* EC-RDSA and Streebog should go together. */
> > +		pks.pkey_algo = "ecrdsa";
> > +		pks.encoding = "raw";
> 
> IMA signatures are stored as xattrs, making them persistent.  Support
> for streebog was upstreamed in linux-5.0.  This change would break
> existing systems using streebog.  As long as this is not yet a concern

In what sense it would break systems?

Unless kernel crashes or signature is recognized as valid, I think, it should
not be called a break.

> Reviewed-by:  Mimi Zohar <zohar@xxxxxxxxxxxxx>

Thanks!

> 
> > +	} else {
> > +		pks.pkey_algo = "rsa";
> > +		pks.encoding = "pkcs1";
> > +	}
> >  	pks.digest = (u8 *)data;
> >  	pks.digest_size = datalen;
> >  	pks.s = hdr->sig;