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

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Message-ID: <CALCETrWpKiurZEEOT25i_xrtQyk5dht+wjUO4+tGs+N_7JCdYA@mail.gmail.com>
Date:	Thu, 26 Feb 2015 11:38:01 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	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 11:32 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?

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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