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

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Message-ID: <20150226193200.GA17709@mail.hallyn.com>
Date:	Thu, 26 Feb 2015 13:32:00 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	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 Thu, Feb 26, 2015 at 12:28:30PM -0600, Christoph Lameter wrote:
> On Thu, 26 Feb 2015, Serge E. Hallyn wrote:
> 
> > > Well doing that breaks su.
> >
> > Don't what exactly?  You're saying that doing
> >
> > pI' = pI
> > pA' = pA  (pA is ambient)
> > pP' = (X & fP) | (pI & (fI | pA))
> > pE' = pP' & (fE | pA)
> >
> > stopped su from having CAP_SETGID while
> >
> > pI' = pI
> > pA' = pA  (pA is ambient)
> > pP' = (X & fP) | (pI & (fI | pA))
> > pE' = pP' & fE
> >
> > worked?  I'll hope you're saying both "fail", in which case
> 
> fE does not exist in cpu_vfs_cap_data. We only get fI and fP. Why in the
> world does setcap allow setting fE?

It sets a bit in the magic_etc.  So fE is either all on or all off.

> V1 does not use fE. In my newer attempt, I seemed to have worked
> with zeroed field that I assumed was filled in.
> 
> I will just do
> 
> pE' = pP'
> 
> Ok?

Andrew Morgan was against that.  What if we changed

pE' = pP' & (fE | pA)

to

	if (pA)
		pE' = pP' & fE
	else
		pE' = pP'

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