Re: [PATCH] capabilities: introduce per-process capability bounding set (v10)

[KaiGai Kohei <kaigai@ak.jp.nec.com>]

Andrew Morgan wrote:
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> KaiGai Kohei wrote:
>> Serge,
>>
>> Please tell me the meanings of the following condition.
>>
>>> diff --git a/security/commoncap.c b/security/commoncap.c
>>> index 3a95990..cb71bb0 100644
>>> --- a/security/commoncap.c
>>> +++ b/security/commoncap.c
>>> @@ -133,6 +119,12 @@ int cap_capset_check (struct task_struct *target,
>>> kernel_cap_t *effective,
>>>          /* incapable of using this inheritable set */
>>>          return -EPERM;
>>>      }
>>> +    if (!!cap_issubset(*inheritable,
>>> +               cap_combine(target->cap_inheritable,
>>> +                       current->cap_bset))) {
>>> +        /* no new pI capabilities outside bounding set */
>>> +        return -EPERM;
>>> +    }
>>>  
>>>      /* verify restrictions on target's new Permitted set */
>>>      if (!cap_issubset (*permitted,
>> It seems to me this condition requires the new inheritable capability
>> set must have a capability more than bounding set, at least.
>> What is the purpose of this checking?
> 
> Yes, the !! was a bug. The correct check is a single !.

I was in trouble with getting -EPERM at pam_cap.so :-)

> (Thus, the correct check says no 'new' pI bits can be outside cap_bset.)

If this condition intends to dominate 'new' pI bits by 'old' pI bits masked
with bounding set, we should not apply cap_combine() here.
I think applying cap_intersect() is correct for the purpose.

Thanks,
--
KaiGai Kohei