linux-kernel - Re: ANN: libseccomp

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Date:	Mon, 09 Apr 2012 18:46:02 -0400
From:	Paul Moore <paul@...l-moore.com>
To:	Will Drewry <wad@...omium.org>
Cc:	Kees Cook <keescook@...omium.org>,
	libseccomp-discuss@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: ANN: libseccomp

On Monday, April 09, 2012 04:51:30 PM Will Drewry wrote:
> On Mon, Apr 9, 2012 at 4:32 PM, Paul Moore <paul@...l-moore.com> wrote:
> > On Monday, April 09, 2012 12:16:30 PM Kees Cook wrote:
> >> On Mon, Apr 9, 2012 at 11:58 AM, Paul Moore <paul@...l-moore.com> wrote:
> >> > With the seccomp patches finally stabilizing a bit, it seems like now
> >> > is a
> >> > good time to announce libseccomp: a library designed to make it easier
> >> > to
> >> > create complex, architecture independent seccomp filters.
> >> > 
> >> >  * http://sourceforge.net/projects/libseccomp/
> >> >  * git clone git://git.code.sf.net/p/libseccomp/libseccomp
> >> 
> >> This looks really great; nice work!
> 
> Agreed -- this is great to see!

Not as much as the actual kernel support :)

> >> I see that the arch check happens during _gen_bpf_build_bpf(), which
> >> is excellent. Do you have any thoughts about including a call to
> >> prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) by default as well?
> > 
> > That is a good question, and I guess it comes down to another question of
> > if anyone would want to use seccomp without NO_NEW_PRIVS.  If the answer
> > is no then I'm comfortable adding it into the seccomp_load() function;
> > however, if the answer is yes we might want to do something different.
> > 
> > I haven't given much thought to this yet, so if you or anyone else feels
> > strongly about the issue - either pro or con - I'd appreciate hearing the
> > argument.
> 
> I guess the question is if there is an expectation that this library
> be used with something like lxc, where a whole, functional system with
> suid/fcaps binaries is contained.  In that world, it may not be
> desirable to set the nnp bit.   The same is true if, for some reason,
> the init task was to set a system-wide filter.
> 
> Most likely, default use of nnp is probably "the right thing", but
> it'd be nice to be able to annotate when you really want to allow
> privileged contexts to set filters without nnp.

Okay, that seems reasonable: default to NO_NEW_PRIVS, but provide an override 
mechanism.

I've been wanting a mechanism/API for tweaking some of the default library 
parameters for the past few weeks, this is likely the last bit of motivation I 
need to start working on this.  I'll look into it once the license issue is 
sorted.

-- 
paul moore
www.paul-moore.com

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