Arch Linux

Description:

After upgrading to openssh 7.7p1-1, tun/tap forwarding stopped working, in both client and server mode.

Additional info:
core/openssh 7.7p1-1

Steps to reproduce:

# ssh -V
OpenSSH_7.7p1, OpenSSL 1.1.0h 27 Mar 2018
# ssh -o "Tunnel ethernet" -w 3:4 remote_host (used to work with openssh < 7.7)
Tunnel device open failed.
Could not request tunnel forwarding.

log:
May 26 18:50:12 systemd-networkd[345]: tap3: Failed
May 26 18:50:12 systemd-networkd[345]: Could not add new link, ignoring: No such device
May 26 18:50:12 systemd-udevd[11685]: link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
May 26 18:50:12 systemd-udevd[11685]: link_config: could not get ethtool features for tap3
May 26 18:50:12 systemd-udevd[11685]: Could not set offload features of tap3: No such device

# ssh -o "Tunnel yes" -w 3:4 remote_host (used to work with openssh < 7.7)
Tunnel device open failed.
Could not request tunnel forwarding.

log:
May 26 18:51:41 systemd-networkd[345]: tun3: Failed
May 26 18:51:41 charon[613]: 11[KNL] interface tun3 deleted
May 26 18:51:41 systemd-networkd[345]: Could not add new link, ignoring: No such device
May 26 18:51:41 systemd-udevd[11704]: link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
May 26 18:51:41 systemd-udevd[11704]: link_config: could not get ethtool features for tun3
May 26 18:51:41 systemd-udevd[11704]: Could not set offload features of tun3: No such device

(connection from a remote system)
# ssh -V
OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
# ssh -o "Tunnel ethernet" -w 3:4 remote_host
channel 0: open failed: connect failed: open failed

log:
May 26 18:55:41 systemd-networkd[345]: tap4: Could not find udev device: No such device
May 26 18:55:41 systemd-networkd[345]: tap4: Failed
May 26 18:55:41 systemd-networkd[345]: Could not add new link, ignoring: No such device
May 26 18:55:41 systemd-udevd[11785]: link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
May 26 18:55:41 systemd-udevd[11785]: link_config: could not get ethtool features for tap4
May 26 18:55:41 systemd-udevd[11785]: Could not set offload features of tap4: No such device

Downgrading to openssh 7.6p1-2 fixes this issue.

openssh 7.7 changelog (https://www.openssh.com/txt/release-7.7) related to tun/tap forwarding:
* ssh(1): Expose device allocated for tun/tap forwarding via a new
%T expansion for LocalCommand. This allows LocalCommand to be used
to prepare the interface.

* sshd(8): Expose the device allocated for tun/tap forwarding via a
new SSH_TUNNEL environment variable. This allows automatic setup of
the interface and surrounding network configuration automatically on
the server.