linux-kernel - Re: [PATCH 5/6] ima: do not include field length in template digest calc for ima template

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Date:	Mon, 18 Nov 2013 21:40:59 +0200
From:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	Roberto Sassu <roberto.sassu@...ito.it>,
	linux-security-module@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-ima-devel@...ts.sourceforge.net,
	Mimi Zohar <zohar@...ibm.com>,
	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	james.l.morris@...cle.com
Subject: Re: [PATCH 5/6] ima: do not include field length in template digest
 calc for ima template

On Mon, Nov 18, 2013 at 5:50 PM, Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> On Mon, 2013-11-18 at 17:30 +0200, Dmitry Kasatkin wrote:
>> On Fri, Nov 15, 2013 at 3:45 PM, Roberto Sassu <roberto.sassu@...ito.it> wrote:
>
>> > @@ -160,12 +161,13 @@ static int ima_calc_field_array_hash_tfm(struct ima_field_data *field_data,
>> >                 return rc;
>> >
>> >         for (i = 0; i < num_fields; i++) {
>> > -               rc = crypto_shash_update(&desc.shash,
>> > -                                        (const u8 *) &field_data[i].len,
>> > -                                        sizeof(field_data[i].len));
>> > -               if (rc)
>> > -                       break;
>> > -
>> > +               if (strcmp(td->name, IMA_TEMPLATE_IMA_NAME) != 0) {
>> > +                       rc = crypto_shash_update(&desc.shash,
>> > +                                               (const u8 *) &field_data[i].len,
>> > +                                               sizeof(field_data[i].len));
>> > +                       if (rc)
>> > +                               break;
>> > +               }
>>
>> What was actually the point in including field length in the hash calculation?
>> Does it really make it cryptographically stronger?
>> If not then remove it at all...
>
> We should be able to walk the measurement list without needing to
> understand template specific data.  All of the template data, including
> the field lengths, needs to be included in the template hash.
>

Sorry, how adding field length helps walking measurement list?
It makes it even more tricky...

Previously, I could calculate the hash over the whole template data
from binary_measurement_list
to get template hash.
Now every field must be processed separately to get template hash...


- Dmitry


> Mimi
>



-- 
Thanks,
Dmitry
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