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Date: Thu, 26 Feb 2015 13:32:00 -0600
From: "Serge E. Hallyn" <serge@hallyn.com>
To: Christoph Lameter <cl@linux.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
        Serge Hallyn <serge.hallyn@ubuntu.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Andy Lutomirski <luto@amacapital.net>,
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        "Andrew G. Morgan" <morgan@kernel.org>,
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        Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH] capabilities: Ambient capability set V1
Message-ID: <20150226193200.GA17709@mail.hallyn.com>
References: <20150223181553.GE25477@ubuntumail>
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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'