Moving the pf rc.d scripts to run before netif

[Doug Barton]

Howdy,

As you can see below, I've made a change to the order of execution of
the rc.d scripts in 8-current (soon to be 8-release) to run all of the
firewalls, including pf, before the network is up. However the
following PR gives an example of why this might be bad:

http://www.freebsd.org/cgi/query-pr.cgi?pr=130381

This leaves me with a few questions.

1. When the _kernel_ first starts, what is the condition of the pf
firewall? In other words, you have pf in the kernel, and let's pretend
that there is no rc.d/pf initialization script. What's going to happen
to the packets when the network comes up?

2. The previous rcorder for the pf script was right after netif (the
network coming up) and before routing .... why? Is this related to how
pf does its work? The reason I ask this question is that in order to
fix the IPv6 rcorder problem in the pr the way that Gert is suggesting
the "BEFORE: routing" would have to be removed because our IPv6
startup depends on RA which depends on routing being up. (Side note,
in the long term I'd like to revise this so that an IPv6-only host
and/or a host with statically assigned IPv6 addresses can easily be
configured within rc.d, but that's another thing altogether.)

3. Is the need to be able to use $ext_if after the network is up so
overwhelmingly important that it justifies running pf after netif? Or
is using ($ext_if) a reasonable solution?

Anything else y'all would like to add is welcome at this point.


Thanks,

Doug


-------- Original Message --------
Subject: Re: svn commit: r193198 - head/etc/rc.d
Date: Mon, 01 Jun 2009 10:38:41 -0700
From: Doug Barton <dougb at FreeBSD.org>

Bjoern A. Zeeb wrote:
> On Mon, 1 Jun 2009, Doug Barton wrote:
> 
>> Author: dougb Date: Mon Jun  1 05:35:03 2009 New Revision: 193198
>>  URL: http://svn.freebsd.org/changeset/base/193198
>> 
>> Log: Make the pf and ipfw firewalls start before netif, just like
>>  ipfilter already does. This eliminates a logical inconsistency, 
>> and a small window where the system is open after the network 
>> comes up.
> 
> Unfortunetaly this is contrary to a lot of PRs and requests on 
> mailing lists out there that actually want the netif/network_ipv6 
> to be run _before_ things come up.

Can you provide links to some of those PRs? I'd love to learn more
about this issue.

> Espescially pf really needs this to avoid rules that needs to do 
> per paket lookups of the interface address.

Not sure what you mean here.

> Further ipfw has a default option being setaable at compile time 
> and as TUNABLE to handle this window.

And what happens if someone sets the default to accept? You could
argue that they are knowingly opening a window of vulnerability but I
would argue that the right thing to do is to have the firewall rules
loaded before the network comes up regardless of the default. That way
you avoid both the potential window of vulnerability AND the window of
time between the network being loaded and the firewall allowing access
to the box.

To give a little more history, this patch was discussed and reviewed a
while back and someone told me that they would incorporate it into
some overall work they were doing to improve the way that rc.d handles
networking, so I stopped paying attention to it. Last night a user
pointed out to me that another patch that this same person said they
would handle never got in, so I reviewed other outstanding work and
found that this one had not been done either.

Obviously if this change breaks something it will have to be reverted.
However from the security standpoint (primary concern) it would seem
to be the right thing to do, and the previous rcorder was not
logically consistent in any case.

Max Laier wrote:
> Can you please add a note about this in UPDATING?

Yes. I was on the fence about this anyways, so now you've pushed me
over. :)

> It might be a slight POLA violation for people who rely on the
> interfaces being configured to setup the firewall.  For instance
> when one doesn't use dynamic address rules in pf i.e. "from/to ifX"
> instead of "from/to (ifX)".

I don't understand what you've written here. It seems to me that if
the interfaces are always the same then the firewall rules will be
fine, but if they are using dynamic rules it doesn't matter if it
starts before or after the network is up.

Doug


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