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Subject: Re: [PATCH 2/2] ima: Support appraise_type=imasig_optional
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: "Kasatkin, Dmitry" <dmitry.kasatkin@intel.com>
Cc: Vivek Goyal <vgoyal@redhat.com>, linux-security-module@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date: Wed, 13 Feb 2013 07:56:35 -0500
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On Wed, 2013-02-13 at 14:31 +0200, Kasatkin, Dmitry wrote:
> On Mon, Feb 11, 2013 at 10:11 PM, Vivek Goyal <vgoyal@redhat.com> wrote:

> > @@ -158,7 +165,8 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
> >         }
> >         switch (xattr_value->type) {
> >         case IMA_XATTR_DIGEST:
> > -               if (iint->flags & IMA_DIGSIG_REQUIRED) {
> > +               if (iint->flags & IMA_DIGSIG_REQUIRED ||
> > +                   iint->flags & IMA_DIGSIG_OPTIONAL) {
> >                         cause = "IMA signature required";
> >                         status = INTEGRITY_FAIL;
> >                         break;
> 
> This looks a bit odd... If "optional" signature is missing  - we fail..
> It is optional... Why we should fail?

'imasig_optional' does not only mean that the signature is optional, but
also implies that it has to be a digital signature, not a hash.  This
latter part is what IMA_DIGSIG_REQUIRED means.

If 'imasig_optional' set both 'IMA_DIGSIG_OPTIONAL' and
'IMA_DIGSIG_REQUIRED', then this change wouldn't be necessary.

IMA_DIGSIG_REQUIRED would enforce that it is a signature.
IMA_DIGSIG_OPTIONAL would fail only for files with invalid signatures.

thanks,

Mimi