Use multiple interfaces

[Lem]

Hi,

I would like to use knockd on multiple interfaces within one instance. For example interface=eth0,wlan0 would be nice.

[airwoflgh]

Will take a look at this. Am trying to get the codebase to have the issues fixed so I can add some cool functionality.

[airwoflgh]

Will need some more time playing with this - am working on the 0.8.0 release which will support dynamic port knocking using cryptographically strong mechanisms. Once complete, will take a look at this unless someone else has time?

[debuti]

This would be awesome

[o-jasper]

Maybe interface_cmd so this solution can be done in the configuration file instead of a systemd service.(Also i see a .service file in the knockd arch repo, maybe add a @.service so multiple configs can be provided.)

[TDFKAOlli]

I guess it can be done by a fork() before opening the pcap interface. So read-in multiple interfaces, let parent process handle the first and fork childs to handle subsequent interfaces. As such we would have multiple threads/process, for each interface one.
As a plus this would be relatively easy to implement, allow multiple interfaces and interate, fork at the right place, restructure the code a bit + check for other impacts.
As a drawback, each individual process would read-in the config file and build up the memory and pcap filters and as such for n interfaces it would require n-time memory, compared to one.

[zenonp]

This was quite easy to solve with the existing 0.8-1 version (instructions for redhattish systems):

mkdir /etc/sysconfig/knockd.d
echo 'OPTIONS=" -i eth0"' > /etc/sysconfig/knockd.d/eth0
echo 'OPTIONS=" -i wlan0"' > /etc/sysconfig/knockd.d/wlan0

cat <<EOF > /usr/lib/systemd/system/[email protected]
[Unit]
Description=A port-knocking server
After=network.target

[Service]
Type=forking
EnvironmentFile=-/etc/sysconfig/knockd.d/%i
ExecStart=/usr/sbin/knockd -d $OPTIONS

[Install]
WantedBy=multi-user.target
EOF

systemctl --now enable knockd@eth0
systemctl --now enable knockd@wlan0

This way you can have as many knock daemons as you have interfaces. The rpm-owned files /etc/sysconfig/knockd and /usr/lib/systemd/system/knockd.service are left alone, while /usr/lib/systemd/system/[email protected] and the files in /etc/sysconfig/knockd.d will be left alone by rpm updates. With less than 10 minutes of work, this could be integrated in the knock-server .spec and .deb, and be pushed out to most major distributions.

[porridge]

An even simpler (though less flexible) solution if you don't need to customize the options per interface would be to have just the following line in the unit template's Service section:

ExecStart=/usr/sbin/knockd -i %i

This removes the need for the environment files.

Kudos to @zenonp for the inspiration!