Linux 4.14-rc6 bisected regression tun devices not working anymore in openvpn

[Sander Eikelenboom]

L.S.,

While testing a linux 4.14-rc6 kernel i noticed OpenVPN didn't function anymore. 
My openvpn config uses tun devices and is pretty standard.
The openvpn version is current Debian stable: openvpn 2.4.0-6+deb9u2

>From the openvpn logging:
    Sat Oct 28 16:03:34 2017 us=175829 TUN/TAP device  opened
    Sat Oct 28 16:03:34 2017 us=183027 Note: Cannot set tx queue length on : No such device (errno=19)
    Sat Oct 28 16:03:34 2017 us=183055 do_ifconfig, tt->did_ifconfig_ipv6_setup=0
    Sat Oct 28 16:03:34 2017 us=183071 /sbin/ip link set dev  up mtu 1500
    Cannot find device ""
    Sat Oct 28 16:03:34 2017 us=200445 Linux ip link set failed: external program exited with error status: 1
    Sat Oct 28 16:03:34 2017 us=200482 Exiting due to fatal error
    Sat Oct 28 16:38:17 2017 us=923381 TCP/UDP: Closing socket
    Sat Oct 28 16:38:17 2017 us=925986 Closing TUN/TAP interface


The offending commit is: 
    0ad646c81b2182f7fa67ec0c8c825e0ee165696d
    "tun: call dev_get_valid_name() before register_netdevice()" 

Reverting this commit fixes the issue for me, it's unfortunate that the commit it self seems to fix an other issue.

--
Sander