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

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Message-ID: <4754F053.8060303@kernel.org>
Date:	Mon, 03 Dec 2007 22:14:43 -0800
From:	Andrew Morgan <morgan@...nel.org>
To:	KaiGai Kohei <kaigai@...jp.nec.com>
CC:	"Serge E. Hallyn" <serue@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Chris Wright <chrisw@...s-sol.org>,
	Stephen Smalley <sds@...ch.ncsc.mil>,
	jmorris@...gelap.austin.ibm.com, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] capabilities: introduce per-process capability bounding
 set (v10)

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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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