Re: In-/Outbound firewall configuration for Tor relay

[Michael Tremer <michael.tremer@ipfire.org>]

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On Sun, 2018-07-01 at 08:00 +0200, Peter Müller wrote:
> Hello Michael,
> 
> > On Fri, 2018-06-29 at 23:26 +0200, Peter Müller wrote:
> > > Hello,
> > > while incoming firewall rules seem to work by now, there are still
> > > some issues with outgoing traffic:
> > > (a) Since tor runs as "nobody" (why?), allowing traffic from this
> > > user is out of questions because also untrusted services like Apache
> > > occupy this user.
> > 
> > Everything that is non-privileged runs as this. In IPFire 3 everything has
> > its
> > own user.
> 
> Is there a technical reason why we did not split this up into several
> users in 2.x as well? How much work would it be to change this for 2.x too?

Yes, useradd isn't very well configured and does (or did) not support system
users and all this stuff. You can give it a try.

> > 
> > > (b) Filtering by PID seems the only way, but creates error messages:
> > > iptables v1.4.21: unknown option "--pid-owner"
> > > Try `iptables -h' or 'iptables --help' for more information.
> > 
> > Did you try the updated iptables that you submitted this week?
> 
> Not yet. It might be possible that "--pid-owner" is implemented there,
> as it does not appear in the documentation for 1.4.x .
> 
> Either way, filtering by PID has some disadvantages:
> (a) Every time a process changes its PID, we need to reload firewall.local.
> (What do we do with forks anyway?) Since PIDs may not be unique on Linux
> systems, some other program could obtain these network privileges.
> 
> (b) The initscript of Tor needs to be patched in order to reload
> firewall.local .
> During boot sequence, things are loaded the other way round, so the PID
> cannot be determined. A dedicated user would help here a lot.

Agreed.

> At the moment, running a relay on an ARM board in the local DMZ seems to
> be a more elegant way. However, on systems with any outbound connection
> allowed
> (which I _strongly_ advise against), this is not a pity since inbound
> connections
> can be handled even by using the WebUI.
> 
> Best regards,
> Peter Müller
> > 
> > > In firewall.local, this rule is currently placed:
> > > iptables -A CUSTOMOUTPUT -o ppp0 -m owner --pid-owner $TORPID -p tcp -d
> > > 0.0.0.0/0 -j ACCEPT
> > > Besides from making things more easy in the future (development ;-) ),
> > > is "--pid-owner" even supported by iptables running here? Or does it
> > > require some special module?
> > 
> > Not that I am aware of.
> > 
> > -Michael
> > 
> > 
> > > Best regards,
> > > Peter Müller
> > > Am 28.06.2018 um 19:14 schrieb Peter Müller:
> > > > Hello Michael,
> > > > 
> > > > thanks for the clarification.
> > > > 
> > > > > Hello,
> > > > > 
> > > > > On Wed, 2018-06-27 at 22:53 +0200, Peter Müller wrote:
> > > > > > Hello,
> > > > > > for quite some time, IPFire includes Tor via Pakfire as an add-on.
> > > > > > Trying to set up a Tor relay there, I stumbled into several problems
> > > > > > regarding firewall rule configuration:
> > > > > > (a) Inbound
> > > > > > It turns out that Tor is not working correctly if GeoIP block is
> > > > > > active (this occurred after a reboot - strange). Of course, one
> > > > > > possibility is to disable GeoIP block at all, allow access to the
> > > > > > Tor relay ports, and deny any except those of legitimate countries
> > > > > > to other services on the firewall machine.
> > > > > 
> > > > > You can use the normal firewall rules for a more granular
> > > > > configuration.
> > > > > 
> > > > > The geoip filter comes first and then all the rest. Depending on how
> > > > > many
> > > > > countries you block here, Tor connectivity becomes a little bit
> > > > > useless.
> > > > 
> > > > Indeed. And I block many... :-)
> > > > > 
> > > > > > Since this enlarges the ruleset (already quite complex here :-| ),
> > > > > > I am wondering if there is a more simple way to achieve this.
> > > > > 
> > > > > We could move tor rules before the GeoIP filter, but I am not sure if
> > > > > that
> > > > > is
> > > > > very intuitive.
> > > > 
> > > > I do not think so since users may expect anything is blocked then and
> > > > wonder why Tor still works fine. We should keep firewall things
> > > > intentional
> > > > in order not to puzzle users.
> > > > 
> > > > OK, incoming way is solved then.
> > > > > 
> > > > > > (b) Outbound
> > > > > > For security reasons (surprise!), outgoing connections are heavily
> > > > > > limited here - only DNS, NTP and web traffic is allowed, and only
> > > > > > to a certain list of countries. Some call that "racist routing"...
> > > > > > This does not work with Tor since it needs to open connections to
> > > > > > almost any port on almost any IP address. Allowing outbound traffic
> > > > > > in general is out of question, so there seems to possibility left.
> > > > > > Besides from running a Tor relay in the local DMZ and apply the
> > > > > > firewall rules for this machine, is there another way?
> > > > > 
> > > > > Not that I am aware of.
> > > > > 
> > > > > You can build something custom here by using the -m owner module of
> > > > > iptables and
> > > > > make an exception in the OUTPUT chain for the tor process. You just
> > > > > need a
> > > > > little script that puts the pid into it if you cannot check by uid.
> > > > 
> > > > Hm, I never used the "owner" module before...
> > > > 
> > > > I guess these custom firewall will need to be placed in "firewall.local"
> > > > (https://wiki.ipfire.org/configuration/firewall/firewall.local)?
> > > > According
> > > > to the firewall processing scheme
> > > > (https://wiki.ipfire.org/_media/configuration/firewall/ipfire_fw_chains.
> > > > jpg)
> > > > ,
> > > > it is processed before anything else, so this would suit.
> > > > 
> > > > Will test this and get back if problems occur.
> > > > > 
> > > > 
> > > > Best regards,
> > > > Peter Müller
> > > > 
> > 
> > 
> > 
> 
> 
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