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

[Andrew Morgan <morgan@kernel.org>]

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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 !.

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

Cheers

Andrew

> 
> In the initial state, any process have no inheritable capability set
> and full bounding set. Thus, we cannot do capset() always.
> 
> Thanks,

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