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SubjectRe: [PATCH 5/6] ima: do not include field length in template digest calc for ima template
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On Mon, Nov 18, 2013 at 5:50 PM, Mimi Zohar <zohar@linux.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@polito.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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