NIS/NFS question

[Ed Wilts]

On Thu, Jun 30, 2005 at 05:25:03PM -0400, Ryan Golhar wrote:
> But what if someone just enters in an ip address on their laptop to be
> the same as the machine they unplugged...then limiting dhcp to known mac
> addresses doesn't work.
> 
> I use this to control who my dhcp server gives ip addresses out to, but
> that doesn't stop anyone from setting the ip address on their own
> laptops...

About 15 years ago I had a lengthy discussion with one of the leading
security experts at the time.  He said that NFS simply stands for "Not
F*ing Secure".  The protocol depends on the server trusting the client
not to lie to it.  In a hostile environment, you're out of luck unless
things have drastically changed over time.

It's cases like this where Microsoft actually has a more secure solution
by forcing a workstation to enter a domain administrator's credentials
before joining a domain...  Of course, you shouldn't do this with an
untrusted laptop since some bad student could give you his laptop with a
keystroke capture utility nicely installed.

In a hostile environment, you can't trust the IP address nor the Mac
address.  That means that you have to physically control the ports that
somebody can plug into and verify them that way, or force the user to
enter some other set of credentials to authenticate.

        .../Ed

> -----Original Message-----
> From: redhat-list-bounces at redhat.com
> [mailto:redhat-list-bounces at redhat.com] On Behalf Of Chiu, PCM (Peter)
> Sent: Thursday, June 30, 2005 3:11 AM
> To: General Red Hat Linux discussion list
> Cc: Chiu, PCM (Peter)
> Subject: RE: NIS/NFS question
> 
> 
> I suppose a similar approach with iptables, is to
> enforce DHCP to known MAC addresses.
> 
> Peter
> 
> -----Original Message-----
> From: redhat-list-bounces at redhat.com
> [mailto:redhat-list-bounces at redhat.com] On Behalf Of Wayne Pinette
> Sent: 29 June 2005 22:37
> To: redhat-list at redhat.com
> Subject: NIS/NFS question
> 
> 
> I have a question regarding NIS and was wondering if anyone had any
> ideas.
> 
> We are creating a Linux workstation lab for students.  We have a central
> linux box which teh students can ssh into from home. The lab is a place
> where they can log in and work on their work.  We are using NIS to
> authenticate the workstations and we are nfs mounting the /home
> directory.  This is all pretty standard and make sense.  Here is the
> problem : 
> 
> If a student walks into the lab with their laptop running their
> favourite linux to which they have root access, unplugs a workstation,
> plugs in their laptop, hardcodes the worksation's ip, sets ups his
> laptop to nis authenticate and nfs share just like the workstation, logs
> in as root, he can now su to any student id on the system. 
> Although I quash root on the nfs share, it does not stop this student
> from getting access to any other students (or instructors) material on
> the server.  Although my nis server only trusts a small list of 
> ip addresses, it's trust is still only based on ip.  Is there a way to
> add some sort of certificate trust to nis or some other mechanism to
> check against before nis will trust a machine on it network other than
> just ip?
> 
> Wayner

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts at ewilts.org
Member #1, Red Hat Community Ambassador Program