systemd.link MACAddress=<whatever> matches OpenVPN tun device

Name            : systemd (commit c38499d476026d999558a7eee9c95ca2fa41e115)
Version         : 239.2-1

It appears that the `50-usbmodem.link` file is being applied to the `tunvpn` device, even though the file has a MACAddress filter to match only the usbmodem.


I have the following file:

/etc/systemd/network/50-usbmodem.link

[Match]
MACAddress=aa:bb:cc:dd:ee:ff

[Link]
Name=usbmodem

And by running the following command, it can be seen that the problem really occurs.

$ udevadm test-builtin net_setup_link /sys/class/net/tunvpn/

calling: test-builtin
Load module index
Parsed configuration file /etc/systemd/network/50-usbmodem.link
Created link configuration context.
ID_NET_DRIVER=tun
Config file /etc/systemd/network/50-usbmodem.link applies to device tunvpn
link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
ID_NET_LINK_FILE=/etc/systemd/network/50-usbmodem.link
ID_NET_NAME=usbmodem
Unload module index
Unloaded link configuration context.

$ ip link show tunvpn
xx: tunvpn: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 100
    link/none

I fixed this temporarily by adding the following line to the [Match] section:

Driver=huawei_cdc_ncm

Maybe relevant section: https://github.com/systemd/systemd/blob/c38499d476026d999558a7eee9c95ca2fa41e115/src/udev/net/link-config.c#L218