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

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Message-ID: <4755701C.7070407@ak.jp.nec.com>
Date:	Wed, 05 Dec 2007 00:19:56 +0900
From:	KaiGai Kohei <kaigai@...jp.nec.com>
To:	Andrew Morgan <morgan@...nel.org>
CC:	KaiGai Kohei <kaigai@...jp.nec.com>,
	"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>,
	James Morris <jmorris@...ei.org>, Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] capabilities: introduce per-process capability bounding
 set (v10)

Andrew Morgan wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> 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
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