Re: Network Security hole (was -> Re: arp bug )

Russell King (rmk@arm.linux.org.uk)
Sun, 3 Mar 2002 00:33:51 +0000

On Sat, Mar 02, 2002 at 04:21:24PM -0800, erich@uruk.org wrote:
> The fact that the routing layer and application layers of Linux's
> TCP/IP stack are one and the same is a difficulty here which the
> IP firewalling code in Linux does not fix. I.e. if I wanted to
> have routing as well, but not accept any packets internally *not*
> destined for my interface, I'm not sure how to specify it without
> something like TCP wrappers, as sleazy as they can be, and they
> don't offer this kind of capability in general as is.

Linux 2.4 netfilter:

Incoming Outgoing
interface interface
----+------------------- FORWARD -----------------+------->
| ^
v |
INPUT -------------> Application -----------> OUTPUT

The names in capitals are the names of the tables. You can control
packets that the local machine sees completely independently of what
gets routed through the machine with a kernel supporting iptables
by adding the appropriate rules to the input and forward tables.

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html


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