Question about securelevel

[roberto at redix.it]

I want to discuss securelevel and whether it's a good or bad thing.

Now, I do not need help to get it working (but never say never ...).

I'll try to explain my idea.

Suppose I'm trying to setup a packet-filtering firewall based on FreeBSD,
and I want to harden it (I heard about TrustedBSD, but here I want to
speach about securelevel).

I made the assumption that the console (of my BSD) is in a safe place, so
I can exclude any hack from it. It should be the only place where the
administrator can access the O.S. with securelevel disabled (i.e.=0, by
means of a single user mode).

In normal condition, O.S. is running on securelevel=3 so nobody can:
 - kernel module connot be loaded or unloaded;
 - packet filtering rules connot be altered;
 - /dev/mem and kmem cannot be write;
 - immutable and sys flags cannot be turned off;

In addition (this is my idea), suppose to configured the root filesystem
read-only and there is no way to change this (remount it rw) when
securelevel is == 3.

Could this configuration be considered secure, according to you?
There are any weakness of securelevel still present?

Any comments are welcome...

Regards,
Roberto