Re: [Xen-devel] [PATCH] xsm/flask: Handle policy load failures properly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/02/15 18:00, Wei Liu wrote:
> On Mon, Feb 23, 2015 at 12:53:52PM -0500, Daniel De Graaf wrote:
>> On 02/23/2015 11:48 AM, Wei Liu wrote:
>>> On Mon, Feb 23, 2015 at 11:11:39AM -0500, Daniel De Graaf wrote:
>>> [...]
>>>> -    if ( flask_enforcing )
>>>> +    if ( ret && policy_size )
>>>> +        panic("Flask: Unable to load XSM policy");
>>>> +
>>>> +    if ( ret )
>>>> +        printk("Flask:  Starting with no policy loaded.\n");
>>>> +    else if ( flask_enforcing )
>>>>          printk("Flask:  Starting in enforcing mode.\n");
>>> I have a question with regard to XSM in general.
>>>
>>> This branching gives me the impression that if no policy is provided
>>> flask is not enforced even if you have flask_enforned=1. What mode is it
>>> in? Enforcing or permissive? Is it in permissive mode until a policy is
>>> loaded? Is it enforcing dummy policy (though it appears to pass every
>>> check)?
>>>
>>> Wei.
>> When no policy is loaded, the FLASK policy is equivalent to an allow-all
>> policy; see xen/xsm/flask/ss/services.c:security_compute_av where it
>> bails out if !ss_initialized.  It could be considered as either enforcing
>> or being permissive with an allow-all policy, but the actual access is
>> the same.
>>
>> When a policy is loaded later, the value of flask_enforcing will be used
>> to decide if the policy is applied in enforcing or permissive mode; by
>> that time, the value could also have been changed using xl setenforce.
>>
> Thanks for the explanation.
>
>> I decided to make the messages exclusive so that you could more easily
>> tell by looking at a single line if the policy was loaded and enforced
>> correctly.  Combining both pieces of information in a single line like
>> the following would also work, if you think this would be better:
>>
>> printk("Flask: Starting with%s policy loaded in %s mode.\n",
>>        ret ? " no" : "", flask_enforcing ? "enforcing" : "permissive");
>>
> Yes, I think this is clearer. Thanks.

One possible string out of that printk is "Starting with no policy
loaded in permissive mode" which is ambiguous.

Perhaps: "Flask: Starting in %s mode.  Policy is %s loaded"

with s/no/not/ ?

~Andrew

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