Re: Unprivilegued settings for FreeBSD kernel variables
* Eygene A. Ryabinkin wrote on Thursday, 2004-06-17:
> On Tue, Jun 15, 2004 at 09:01:13PM +0200, Dag-Erling Smørgrav wrote:
> > I've already told you that there is no such threat, since the attack
> > you describe can only be initiated by someone who already has
> > unrestricted access. Please stop wasting everybody's time.
> You are wrong. Unrestricted access means _really unrestricted_ and
> kernel securelevel restricts access to certain places even to root.
Quite correct.
> IMHO, it's dagerous bug, because some administrators can think "...hmm,
> I've enabled the hardest securelevel and even if a hacker would break
> into my host with r00t privileges he will be restricted in certain ways.
Correct as well.
> But this bug changes things. One can lower securelevel, do some nasty
> things and raise it again _without reboots_. So, as I've already
> noted, you are wrong.
No. You CAN'T load or unload kernel modules if securelevel is > 0.
To make your attack work, the attacker would have to have access to
the system before it ever went to securelevel 1, 2 or 3, in order to
load the very kernel module your attack requires. Since that almost
certainly means that he had to be in the same room with the system,
I think "can only be initiated by someone who already has unrestricted
access" is completely correct.
--
Christian Ullrich
"There's nothing we can't face -- except for Bun-bun..."