linux-kernel - Re: [PATCH] capabilities: Ambient capability set V1

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Message-ID: <20150224051928.GA14755@mail.hallyn.com>
Date:	Mon, 23 Feb 2015 23:19:29 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Serge Hallyn <serge.hallyn@...ntu.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
	linux-security-module@...r.kernel.org, akpm@...uxfoundation.org,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Markku Savela <msa@...h.iki.fi>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] capabilities: Ambient capability set V1

On Mon, Feb 23, 2015 at 06:15:53PM +0000, Serge Hallyn wrote:
> Quoting Christoph Lameter (cl@...ux.com):
> > On Mon, 23 Feb 2015, Serge E. Hallyn wrote:
> > 
> > > > I do not see a problem with dropping privilege since the ambient set
> > > > is supposed to be preserved across a drop of priviledge.
> > >
> > > Because you're tricking the program into thinking it has dropped
> > > the privilege, when in fact it has not.
> > 
> > So the cap was dropped from the cap perm set but it is still active
> > in the ambient set?
> 
> Right, and the legacy program doesn't know to check the new set.

we've been assuming the ambient set must be like fP.  is there any
reason why it doesn't suffice for them to be or'ed with fI instead at
exec?  then the bits would need to ne in pI. this might sufice for
Christoph's use case, as pI will generally not change.  and for programs
that really care, they can check pI.
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