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

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Date:	Thu, 06 Dec 2007 11:01:01 +0900
From:	KaiGai Kohei <kaigai@...jp.nec.com>
To:	serge@...lyn.com
CC:	Andrew Morgan <morgan@...nel.org>,
	"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)

>>> (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.
> 
> That would have been my first inclination, but Andrew actually
> wanted to be able to keep a pI with bits not in the capability
> bounding set.  And it's really not a big problem, since
> 
> 	1. you can never grow cap_bset
> 	2. the capbound.c program just makes sure to call capset
> 	   to take the bit being removed from cap_bset out of
> 	   pI'
> 	3. It could be advantageous for some daemon to keep a bit
> 	   in pI which can never be gained through fP but can be
> 	   gained by a child through (fI&pI).
> 
> Does that seem reasonable to you?

OK, I got understood the intention of the condition.
It seems to me reasonable policy.

Thanks,
-- 
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai@...jp.nec.com>


This patch fixes incorrect condition added by per-process capability
bounding set patch.
It intends to limit no new pI capabilities outside bounding set.

Signed-off-by: KaiGai Kohei <kaigai@...jp.nec.com>

  commoncap.c |    6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

--- linux-2.6.24-rc3/security/commoncap.c.old	2007-12-06 10:51:48.000000000 +0900
+++ linux-2.6.24-rc3/security/commoncap.c	2007-12-06 10:52:15.000000000 +0900
@@ -119,9 +119,9 @@ int cap_capset_check (struct task_struct
  		/* incapable of using this inheritable set */
  		return -EPERM;
  	}
-	if (!!cap_issubset(*inheritable,
-			   cap_combine(target->cap_inheritable,
-				       current->cap_bset))) {
+	if (!cap_issubset(*inheritable,
+			  cap_combine(target->cap_inheritable,
+				      current->cap_bset))) {
  		/* no new pI capabilities outside bounding set */
  		return -EPERM;
  	}

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