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

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Date:	Mon, 23 Feb 2015 10:46:23 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Serge Hallyn <serge.hallyn@...ntu.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 10:44:32AM -0600, Christoph Lameter wrote:
> On Mon, 23 Feb 2015, Serge Hallyn wrote:
> 
> > The core concern for amorgan is that an unprivileged user not be
> > able to cause a privileged program to run in a way that it fails to
> > drop privilege before running unprivileged-user-provided code.
> 
> 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.

> > Since your desire is precisely for a mode where dropping privilege
> > works as usual, but exec then re-gains some or all of that privilege,
> 
> I would say that the ambient set stays active even if the setuid binary
> drops to regular perms.
> 
> > we need to either agree on a way to enter that mode that ordinary
> > use caes can't be tricked into using, or find a way for legacy
> > users to be tpiped off as to what's going on (without having to be
> > re-written)
> 
> Well if the ambient set is completely separate then the existing
> semantics are preserved while the ambient set stays active as intended.
> 
> --
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