Re: [PATCH try #2] security: Convert LSM into a static interface

From: Adrian Bunk <bunk@stusta.de>
To: "Serge E. Hallyn" <serue@us.ibm.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
	James Morris <jmorris@namei.org>,
	Andreas Gruenbacher <agruen@suse.de>,
	Chris Wright <chrisw@sous-sol.org>,
	linux-security-module@vger.kernel.org,
	Andrew Morgan <agm@google.com>, Andrew Morton <akpm@google.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	lkml <linux-kernel@vger.kernel.org>,
	Arjan van de Ven <arjan@infradead.org>, Greg KH <greg@kroah.com>,
	Eric Paris <eparis@redhat.com>
Subject: Re: [PATCH try #2] security: Convert LSM into a static interface
Date: Tue, 26 Jun 2007 20:52:28 +0200	[thread overview]
Message-ID: <20070626185228.GJ1094@stusta.de> (raw)
In-Reply-To: <20070626155329.GA24038@sergelap.ibm.com>

On Tue, Jun 26, 2007 at 10:53:29AM -0500, Serge E. Hallyn wrote:
> Quoting Adrian Bunk (bunk@stusta.de):
> > On Tue, Jun 26, 2007 at 09:06:44AM -0500, Serge E. Hallyn wrote:
> > > Quoting Adrian Bunk (bunk@stusta.de):
> > > > On Mon, Jun 25, 2007 at 10:57:31PM -0500, Serge E. Hallyn wrote:
> > > > > Quoting James Morris (jmorris@namei.org):
> > > > > > On Mon, 25 Jun 2007, Andreas Gruenbacher wrote:
> > > > > > 
> > > > > > > It's useful for some LSMs to be modular, and LSMs which are y/n options won't 
> > > > > > > have any security architecture issues with unloading at all. 
> > > > > > 
> > > > > > Which LSMs?  Upstream, there are SELinux and capabilty, and they're not 
> > > > > > safe as loadable modules.
> > > > > > 
> > > > > > > The mere fact 
> > > > > > > that SELinux cannot be built as a module is a rather weak argument for 
> > > > > > > disabling LSM modules as a whole, so  please don't.
> > > > > > 
> > > > > > That's not the argument.  Please review the thread.
> > > > > 
> > > > > The argument is 'abuse', right?
> > > > > 
> > > > > Abuse is defined as using the LSM hooks for non-security applications,
> > > > > right?
> > > > > 
> > > > > It seems to me that the community is doing a good job of discouraging
> > > > > such abuse - by redirecting the "wrong-doers" to implement proper
> > > > > upstream solutions, i.e. taskstats, the audit subsystem, etc.
> > > > > 
> > > > > Such encouragement seems a far better response than taking away freedoms
> > > > > and flexibility from everyone.
> > > > 
> > > > We are not living in a world where everyone had good intentions...
> > > 
> > > Oh no, i took a wrong turn somewhere  :)
> > > 
> > > > For _some_ "wrong-doers" your approach works.
> > > > 
> > > > But how do you convince the "wrong-doers" who do things like putting 
> > > > MODULE_LICENSE("GPL") into their binary-only modules and who ignore you 
> > > > and get away because noone sues them?
> > > 
> > > Do these really exist?  Maybe noone sues them because noone knows who
> > > they are...
> > 
> >    http://lwn.net/Articles/82306/
> 
> LinuxAnt?  Are they using LSM?
> 
> It looks to me like this patch will do nothing about them.

It was an example how creative "wrong-doers" sometimes are.

> > > But - note that you've changed completely the meaning of 'abuse'.
> > > So mine was wrong?
> > 
> > Technical and legal abuse are related.
> 
> True but going by your logic we could remove support for modules period
> to prevent legal abuse by non-gpl modules.

The problem is that this would result in distributions having to ship
50 MB kernel images.

> > For GPL'ed modules you might assume good faith and get the authors to do 
> > things in a proper way. Authors of legally questionable modules that 
> > cheat in many ways are quite a different issue.
> > 
> > > > The spirit of the GPLv2 is to defend the freedom of the software 
> > > > (different from the spirit of the BSD licence), and considering that 
> > > > there aren't many people defending the GPLv2 copyright of the Linux 
> > > > kernel at court against abusers, making it harder for people to do the 
> > > > abuse might not be the worst choice...
> > > 
> > > Well, but you seem to be saying that the license means squat, and
> > > resorting to making things inconvenient rather than illegal.
> > 
> > No, the point is that there's no reason for making illegal things 
> > convenient.
> 
> But no, the point is that that you are making legal things very
> inconvenient.
> 
> > I'm not talking about removing things that are used inside the kernel, 
> 
> Since capabilities can currently be compiled as a module, you are.
> (Though that sounds weird, so maybe I'm misreading what you are saying)

If the LSM maintainer says non-modular capabilities is the way to go
then there's no user left.

> > but what you call "freedom" can also be called "hooks for possible abuse".
> 
> Yup, that is true.
> 
> > Additionally, it both makes the kernel bigger for everyone and requires 
> > proper handling of loading/unloading in the security architecture.
> > 
> > > Now I guess if it really is accepted that that's the way it should be,
> > > then this patch will go in.
> 
> thanks,
> -serge

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed