The firewall that remembers the different networks you connect to.
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README.md

ServiceWall

What to expect

ServiceWall is a firewall intended for laptops and all devices that connect to several different networks. It will drop incoming requests, excepted for those that you allow. Each service you allow in will be remembered either :

  • for the network realm you're connected to (the realm's ruleset), or
  • for unregistered network realms (the ServiceWall:default ruleset)

WARNING : ServiceWall only supports IPv4 networks ; as of today, it will drop any packet on the IPv6 stack without logging it.

At the moment the default ruleset is : accept ssh and DHCP incoming connections. ssh connections are accepted from anywhere, whereas DHCP ones are only accepted from the local network (connected to the same gateway as you).

It won't remember the realm you're connected to until you change the default ruleset. Once you do, it writes down an identifier for the network realm, together with the default ruleset plus the rule you added. Now when you connect to another network, it will put this identified ruleset aside, and try to find a ruleset for the new network. If it can't find any, it'll fallback to the default ruleset. When you connect to the identified network back, it will automagically bring back the rules you chose (magic here involves a network dispatcher telling it network changes).

The default ruleset also has a few basic stateful rules : accept icmp requests, accept all from the localhost loop, accept already established connections, drop invalid packets, and log anything dropped.

Installation

Dependencies

Required dependencies are python 3, iptables, ulogd, systemd, and either NetworkManager or systemd-networkd, with its dispatcher enabled. If you run a linux on a laptop, you should be all set.

There are python packages needed as well, but if you use a decent install method like pip, they should be managed all right. Those are :

  • python-iptables
  • python-netifaces
  • python-argparse
  • optional : python-argcomplete
  • build-time : python-setuptools

You might really wish to have python-argcomplete for the command-line completion to work. This can really prove handy when you're looking for a service to allow.

Install

Once you have the required dependencies, install the package with :

# pip install servicewall

For those using Arch linux, there is a PKGBUILD for this into AUR, called servicewall-git. Give it a try !

ServiceWall uses ulogd to dispatch the logs. It has its own dependent servicewall-ulogd.service that gets pulled in automatically, don't try to run ulogd.service as it could cause race problems between them.

Usage

The firewall is disabled by default. To enable it, as root do sw enable, or :

# systemctl enable --now servicewall

You can suspend it with systemctl stop servicewall or

# sw stop

(you indeed get the corresponding disable and start and stop options). Note that at bootup ServiceWall starts before the nework target. At that point the interfaces are not connected at all. It's actually reloaded when the connection is established to a realm. To have details on the status, use :

# sw status

Once started, the default behaviour is to drop all that come in, excepted for ssh from anywhere and DHCP from the local network. All that go out is allowed. You can check the table of rules applied for the realm we're connected to :

# sw show table

Services

ServiceWall works with service definitions provided by jhansonxi. They link a service to ports it needs. To allow a specific service, do :

# sw allow service "Service Name"

which will add this service in this realm's ruleset. If you connect to internet in another place, the ruleset for this place will be put aside, and brought back when you connect to it again. You can move back with sw disallow service ... when you are connected to this realm only. Otherwise you would have to manually edit /etc/servicewall/realms.json.

The service will be limited to machines on the same realm as you (connected to the same ESSID). If you want to make it available from anywhere, do a

# sw allow service "Service Name" --globally

Don't know what's the exact name of the service you want to allow ? You'll need to :

# sw show services

And if you wonder which services use to use port 80, do

# sw show port 80

Sometimes the service you want to use doesn't exist in the service definitions. In this case you can drop a service def inside /etc/servicewall/services. The syntax is the same as the one you get with

# sw show service "Service Name"

Realms

When you allow a service the relevant rules are associated with the realm you're connected to, in a dictionary inside /etc/servicewall/realms.json. To interrogate it, do :

# sw show realms

When allowing a service you might want to modify the default ruleset. There's the --in-default-profile option to allow just for this. It will modify the ruleset named ServiceWall:default inside realms.json.

Logs

WARNING : ServiceWall will not log igmp traffic. All igmp packets are silently dropped. You may allow those, in which case they will be silently accepted.

Particular attention was taken to logs. Logs are stored in systemd's servicewall-logs.service. Journald takes care it can't fill the hard drive, and that it's readable only to staff. Firewall logs are critical information, and with this setup you can choose who has access. In Arch it's controlled with an access list, you can view it with :

# getfacl /var/log/journal

The firewall logs all that it drops, excepted for igmp packets, as they bloat logs. There's a log processor tool included ; try it with

# sw show logs -w
# sw show logs since NUMBER_OF_SECONDS
# sw show logs -w last NUMBER_OF_LATEST_HITS

The -w|--with-hostnames option lets it show hostnames. This will let you see what service queries were dropped. Now if the service name begins with a < it means that it is the source that is operating the service, not the destination. It might be a packet that iptables failed to recognize as belonging to an established connection.

This software is copyrighted under the GNU Version 3 license.