Re: AppArmor FAQ

James Morris
2007-04-18T21:14:36Z

On Wed, 18 Apr 2007, Crispin Cowan wrote:

> James Morris wrote:
> > On Tue, 17 Apr 2007, Alan Cox wrote:
> >
> >> I'm not sure if AppArmor can be made good security for the general case,
> >> but it is a model that works in the limited http environment
> >> (eg .htaccess) and is something people can play with and hack on and may
> >> be possible to configure to be very secure.
> >>
> > Perhaps -- until your httpd is compromised via a buffer overflow or
> > simply misbehaves due to a software or configuration flaw, then the
> > assumptions being made about its use of pathnames and their security
> > properties are out the window.
> >
> How is it that you think a buffer overflow in httpd could allow an
> attacker to break out of an AppArmor profile?

Because you can change the behavior of the application and then bypass
policy entirely by utilizing any mechanism other than direct filesystem
access: IPC, shared memory, Unix domain sockets, local IP networking,
remote networking etc.

This not even considering object aliasing (which would allow you to
inappropriately access objects with full blessing of policy), as I'm
assuming that the limited environment Alan is referring to entirely
prevents them.

Also worth noting here is that you have to consider any limited
environment as enforcing security policy, and thus its configuration
becomes an additional component of security policy.

So, your real security policy is actually more complicated than it appears
to be, is not represented completely in the policy configuration file, and
must be managed disparately. And it's still only capable of controlling
access to filesystem objects.

- James
--
James Morris
<jmorris@namei.org>