linux-kernel - Re: [RFC] Capabilities still can't be inherited by normal programs

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Message-ID: <CALQRfL5EeqRFykLGVLJx3pfKdP4iF8r-8Ys7pVadOaCc3j1=iQ@mail.gmail.com>
Date:	Sun, 2 Dec 2012 14:26:54 -0800
From:	"Andrew G. Morgan" <morgan@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	James Morris <james.l.morris@...cle.com>,
	Eric Paris <eparis@...hat.com>,
	"Serge E. Hallyn" <serge@...onical.com>
Subject: Re: [RFC] Capabilities still can't be inherited by normal programs

On Sun, Dec 2, 2012 at 10:35 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Sun, Dec 2, 2012 at 9:21 AM, Andrew G. Morgan <morgan@...nel.org> wrote:
>> There is a fairly well written paper ;-) explaining how things are
>> supposed to work:
>>
>>   http://ols.fedoraproject.org/OLS/Reprints-2008/hallyn-reprint.pdf
>>
>> The inheritable set is not intended to work the way you seem to want.
>> Naive inheritance like that is quite explicitly the opposite of what
>> was designed.
>
> I'm aware that the system was designed, or perhaps evolved, to prevent
> users with uid != 0 from inheriting capabilities unless vfs
> inheritable caps are granted on a per-file basis.  I want a way around
> that -- I want to mix non-root, capabilities, and exec.  This is damn
> near impossible right now if I don't have CAP_SETFCAP or root's
> explicit, per-program cooperation.  CAP_SETFCAP is essentially
> equivalent to "let me do anything".
>
> As it stands, using something like pam_cap to grant a user cap_net_raw
> is useless -- that user can't use the privilege because (unless uid ==
> 0) the privilege will never end up in the permitted set.

Have you tried adding fI of cap_net_raw to the file to be executed?

Cheers

Andrew

>
> I want to come up with a way to change this that will, convincingly,
> not open up any new security holes.  The current concept of process
> inheritable capabilities seems so vague and so oddly defined that I'm
> not sure I want to touch it.  In an ideal world, I'd want pI <= pP and
> fP <= fI to be invariants, and I'd like programs without vfs caps set
> to have fI = <everything>.  Making this change will surely break
> something, though.
>
> I'm looking for ideas.
>
> --Andy
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