linux-kernel - Re: [PATCH v3 1/2] capabilities: Ambient capabilities

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Message-ID: <CAGXu5jKLa1JtoSvoUTRPb02=NFh62Ge4oNSv=z=Z9q9SG62D6A@mail.gmail.com>
Date:	Wed, 10 Jun 2015 12:24:58 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Andrew Morton <akpm@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	"Ted Ts'o" <tytso@....edu>, "Andrew G. Morgan" <morgan@...nel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Aaron Jones <aaronmdjones@...il.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Markku Savela <msa@...h.iki.fi>,
	Jonathan Corbet <corbet@....net>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v3 1/2] capabilities: Ambient capabilities

On Tue, Jun 9, 2015 at 5:00 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Tue, Jun 9, 2015 at 4:09 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Wed, May 27, 2015 at 4:47 PM, Andy Lutomirski <luto@...nel.org> wrote:
>>> [1] Files that are missing the "security.capability" xattr or that
>>> have unrecognized values for that xattr end up with has_cap set to
>>> false.  The code that does that appears to be complicated for no
>>> good reason.
>>
>> Would it make more sense to have has_cap true, but have it lack any actual caps?
>
> I assume you're referring to the case where we fail to parse the
> xattr.  If so, I don't really know if or when this happens.  Should
> that be addressed separately from this patch set?

No, no. All of these footnotes seem to be separate from the series. I
just wanted to chime in on them, since none of them really sounded
like they should get dropped.

>>> [2] The libcap capability mask parsers and formatters are
>>> dangerously misleading and the documentation is flat-out wrong.  fE
>>> is *not* a mask; it's a single bit.  This has probably confused
>>> every single person who has tried to use file capabilities.
>>
>> Sounds like it would be a valuable documentation patch.
>
> I'll try.  Let's get the current thing done first.

Yup! No worries. I'm happy to help with the docs, too.

>>> [3] Linux very confusingly processes both the script and the
>>> interpreter if applicable, for reasons that elude me.  The results
>>> from thinking about a script's file capabilities and/or setuid bits
>>> are mostly discarded.
>>
>> I wonder if this is important enough to fix?
>
> Not sure.
>
> However, the fact that AFAICT LSM due to a script (as opposed to an
> interpreter) is preserved sounds rather dangerous to me.  I'm not sure
> whether we can safely fix that at this point.

Agreed.

I missed adding:

Acked-by: Kees Cook <keescook@...omium.org>

I would love to use this already. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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