Re: [RESEND][PATCH] Documentation: added order requirement for ima_hash=

["Guozihua (Scott)" <guozihua@huawei.com>]

On 2022/1/26 22:43, Roberto Sassu wrote:
>> From: Mimi Zohar [mailto:zohar@linux.ibm.com]
>> Sent: Wednesday, January 26, 2022 3:35 PM
>> On Wed, 2022-01-26 at 13:24 +0000, Roberto Sassu wrote:
>>>> From: Mimi Zohar [mailto:zohar@linux.ibm.com]
>>>> Sent: Wednesday, January 26, 2022 1:48 PM
>>>> On Wed, 2022-01-26 at 15:41 +0800, Guozihua (Scott) wrote:
>>>>>
>>>>>
>>>>> The main issue lies in ima_template_desc_current called by hash_setup,
>>>>> which does not just read ima_template global variable, but also tries to
>>>>> set it if that hasn't been done already. Causing ima_template_setup to quit.
>>>>
>>>> Right, which calls ima_init_template_list().  So part of the solution
>>>> could be to conditionally call ima_init_template_list()
>>>> in ima_template_setup().
>>>>
>>>> -       if (ima_template)
>>>> -               return 1;
>>>> -
>>>> -       ima_init_template_list();
>>>> +       if (!ima_template
>>>> +               ima_init_template_list();
>>>>
>>>> Roberto, what do you think?
>>>
>>> Hi Mimi
>>>
>>> I think we wanted to prevent to set a digest algorithm
>>> incompatible with the chosen template.
>>>
>>> If we have in the kernel command line:
>>>
>>> ima_template=ima ima_hash=sha256
>>>
>>> ima_hash_algo would be set to HASH_ALGO_SHA1 despite
>>> the user choice and the template would be set to 'ima'.
>>>
>>> In the opposite case:
>>>
>>> ima_hash=sha256 ima_template=ima
>>>
>>> if the default template is 'ima', then ima_hash_algo would be
>>> set to HASH_ALGO_SHA1. Otherwise, it would be
>>> HASH_ALGO_SHA256. If we allow the template to be set after
>>> the digest algorithm is evaluated, the template selection will
>>> be rejected if the algorithm is incompatible with the template.
>>
>> The only time that would occur is in the unlikely case that the
>> template is being set to "ima".   That sounds reasonable.  In fact we
>> should consider preventing the template format being set to "ima".
> 
> Ok.
> 
>>> I'm trying to remember why we still have the digest recalculation
>>> in ima_eventdigest_init(). Maybe the only possibility is if we
>>> set the template from the policy?
>>
>> The recalculation was relatively recently added in commit 6cc7c266e5b4
>> ("ima: Call ima_calc_boot_aggregate() in ima_eventdigest_init()").
> 
> There is also recalculation for the file digest:
> 
>          hash.hdr.algo = ima_template_hash_algo_allowed(ima_hash_algo) ?
>              ima_hash_algo : HASH_ALGO_SHA1;
>          result = ima_calc_file_hash(event_data->file, &hash.hdr);
> 
> I understood that Jonathan already applied the patch. If it is possible
> to make a new patch according to your suggestion, I would ask Zihua
> to do that.
Hi Mimi and Roberto,

I understand that the solution proposed here is to decommission template 
"ima" and potentially removing related algo checks altogether?

-- 
Best
GUO Zihua