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

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Message-ID: <50C6345C.8040804@schaufler-ca.com>
Date:	Mon, 10 Dec 2012 11:13:32 -0800
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Serge Hallyn <serge.hallyn@...onical.com>,
	"Andrew G. Morgan" <morgan@...nel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, 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>,
	Markku Savela <msa@...h.iki.fi>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC] Capabilities still can't be inherited by normal programs

On 12/10/2012 10:12 AM, Andy Lutomirski wrote:
> On Mon, Dec 10, 2012 at 7:47 AM, Casey Schaufler <casey@...aufler-ca.com> wrote:
>> Put an ACL on the program file.
>> If you want different users to run with different privilege
>> make two copies of the program and give them different
>> ACLs and cap sets.
>> If your program is so big that making a copy is a disk space issue
>> it is too big to have privilege.
>> If you can't deal with having the have different paths for different
>> users write a shell script that redirects to the correct version
>> based on user id.
>>
>> This is not rocket science. The kernel shouldn't be crammed
>> with mechanism and complexity just because disto/"OS"/site
>> developers can't be bothered with learning how the existing
>> facilities work.
> I agree.  But I think that the existing capability support is already
> overcomplicated, and I'd rather make it simpler.  Sticking the
> complexity in userspace is too difficult right now because it requires
> fiddling with the file inheritable mask.
>
> I think that the Windows approach is worth looking at.  See here:
>
> http://msdn.microsoft.com/en-us/library/windows/desktop/aa375202%28v=vs.85%29.aspx
>
> In the Windows model, each capability ("privilege") can be in one of
> three states: enabled (i.e working right now),

Effective

>  permitted (i.e.
> available upon request but not currently enabled),

Permitted

> or removed
> (disallowed to this process and all of its children).

~Inherited

> Permitted
> privileges are always inherited when a child process is created.
>
> This is *way* simpler than Linux's model, and it works just fine*.

I see a different set of complications, and Windows never had
a setuid bit to contend with. God created the universe in seven
days, but then, He didn't have an installed base.

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