Re: [PATCH 2/2] debugfs: only allow root access to debugging interfaces

Kees Cook
2011-02-22T19:23:22Z

Hi Greg,

On Tue, Feb 22, 2011 at 11:13:33AM -0800, Greg KH wrote:
> On Tue, Feb 22, 2011 at 10:16:13AM -0800, Kees Cook wrote:
> > Har har, I forgot --compose to "git send-email".
> >
> > Anyway, with the continuing deluge of bugs in the "debug" filesystem, I
> > would like to make that filesystem's root directory mode 0700 by default
> > since it's filled with crazy stuff that regular users do not need to see.
>
> But that will break existing users of this interface, right?
>
> > Better to try to just close the door completely on all the stuff in there.
> > It is, after all, supposed to only be used for debugging, right?
>
> No, not really, people use it for all sorts of crazy things.
>
> Remember, the only rule in debugfs is:
> There are no rules in debugfs.

Right, which seems extremely dangerous to me. I think debugfs should either
be:
a) used only by the root user (would prefer this was actually CAP_DEBUG or
something)
or
b) used by userspace tools

But not both. Creating interfaces with no rules for userspace consumption
is going to lead to disaster. You can't disallow "break[ing] existing
users of this interface" and say there are no rules at the same time. :)

-Kees

--
Kees Cook
Ubuntu Security Team