Re: remounts (was: Re: adding "noschg" to ssh and friends)

From: Crist Clark (crist.clark@globalstar.com)
Date: 05/31/01 

Date: Thu, 31 May 2001 11:00:18 -0700
From: "Crist Clark" <crist.clark@globalstar.com>
To: Dan Pelleg <dpelleg+bsd@REMOVEcs.cmu.edu>

Dan Pelleg wrote:
>
> "Karsten W. Rohrbach" <karsten@rohrbach.de> wrote:
> > there are some real high-impact tweaks to be a little bit safer from
> > rootkits. one of them is mounting /tmp noexec. drawback: you got to
> > remount it exec for make installworld.
>
> I always wondered... Why are remounts permitted in all securelevels? I
> mean, in a locked-down system where it's acceptable to force a reboot in
> order to upgrade (or run a rootkit), I should be able to enforce read-only
> mounts. Currently anyone (well, root) can just mount -u -w them.
>
> Is this an implementation problem in mount(2)? (I haven't looked at the
> code). Or is this going to break things for people (amd? in high
> securelevels?). What am I missing?

I wrote a very simple patch that disallows mount(2) calls at elevated
securelevel some time ago. Check the -security archives for December
or so. Also look for a long thread on the whole question of turning off
mount(2) at high securelevel.

As for breaking things, yes, it will. You cannot mount stuff. But that's
the whole idea. ;)

OK, found it in the archive,

  http://docs.freebsd.org/mail/archive/2000/freebsd-security/20001224.freebsd-security.html

Look at the 'Read-Only Filesystems' thread. 

-- 
Crist J. Clark                                Network Security Engineer
crist.clark@globalstar.com                    Globalstar, L.P.
(408) 933-4387                                FAX: (408) 933-4926
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