[linux-cifs-client] Handling Kerberos principals that don't match hostnames

[Doug Kelly]

On Thu, Jan 07, 2010 at 04:30:17PM -0500, Jeff Layton wrote:
> The CIFS client doesn't currently do mutual krb5 authentication but
> eventually it would be nice if it did.
> 
> The problem with any scheme that relies on getting the SPN in this way
> is that it leaves you open to DNS spoofing attacks even if you can
> support mutual authentication.

That's true... I actually stumbled upon the debate on the mailing list
about a year ago about using Server 2003's SPN provided with the SPNEGO
setup, and it makes sense.  In fact, even from Windows hosts, it appears
the Kerberos authentication fails, and it falls back to NTLMSSP.

Correct me if I'm wrong, but doesn't the current method of operation
that cifs.upcall rely on this?  I guess the difference in expecting a
server's response to contain the real hostname leaves you open for a
man-in-the-middle attack, though, since another host could potentially
spoof the user to connect to a malicious host.

Anyway, not to bring up that whole debate again, but this would be
something that I'd find beneficial, simply because it'd allow me to
Kerberize the entire process of mounting the users' home directories.
I can't see how it'd weaken the security any more than what already
happens with DFS referrals, either.

Thanks!

Doug Kelly