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

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Message-ID: <20150226203308.GA18926@mail.hallyn.com>
Date:	Thu, 26 Feb 2015 14:33:08 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Christoph Lameter <cl@...ux.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
	LSM List <linux-security-module@...r.kernel.org>,
	Andrew Morton <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-kernel@...r.kernel.org>,
	Linux API <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 11:38:01AM -0800, Andy Lutomirski wrote:
> On Thu, Feb 26, 2015 at 11:32 AM, Serge E. Hallyn <serge@...lyn.com> wrote:
> > 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'
> >
> 
> Is this backwards?

D'oh, yes.

> Also, on further bikeshedding consideration, I think I like the name
> "persistent" much better than "ambient".  Alas, "persistent" starts
> with a P.
> 
> --Andy
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