Date: Sat, 26 May 2007 15:58:50 -0700 (PDT)
From: Casey Schaufler <casey@schaufler-ca.com>
Reply-To: casey@schaufler-ca.com
Subject: Re: [AppArmor 01/41] Pass struct vfsmount to the inode_create LSM hook
To: Andreas Gruenbacher <agruen@suse.de>
Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org,
       linux-fsdevel@vger.kernel.org
In-Reply-To: <200705261410.19541.agruen@suse.de>
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--- Andreas Gruenbacher <agruen@suse.de> wrote:

> On Friday 25 May 2007 21:06, Casey Schaufler wrote:
> > --- Jeremy Maitin-Shepard <jbms@cmu.edu> wrote:
> > > ...
> > > Well, my point was exactly that App Armor doesn't (as far as I know) do
> > > anything to enforce the argv[0] convention,
> >
> > Sounds like an opportunity for improvement then.
> 
> Jeez, what argv[0] convention are you both talking about?

>From the exec(3) man page:

   "The first argument, by convention, should point to the
    file name associated with the file being executed."

since the man page calls it a convention, so do I.

> argv[0] is not guaranteed to have any association with the
> name of the executable. Feel free to have any discussion
> about argv[0] you want, but *please* keep it away from
> AppArmor, which really has nothing to do with it.

As I pointed out, if you wanted to trust the argv[0] value
(which I understand AppArmor makes no claims about) and you
wanted to use the argv[0] value to determine application
behavior (which several people claim is a Bad Idea) you could
use Name Based Access Control to provide different access
to the common binary. As I pointed out before, that's a lot
of "if's".

> It would be nice if you could stop calling argv[0] checks ``name-based access
> 
> control'': from the point of view of the kernel no access control is 
> involved, and even application-level argv[0] based access control makes no 
> sense whatsoever.
 
Fair enough, I don't believe that an argv[0] check ought to
be used as a security mechanism. I am not convinced that everyone
would agree with us.


Casey Schaufler
casey@schaufler-ca.com
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