** Description changed: + [Impact] + + The default listening sockets for sshd are different depending on + whether socket activation is used or not, even when /etc/ssh/sshd_config + is the default. E.g.: + + # Socket-activated + + root@n2:~# systemctl status ssh.socket + ● ssh.socket - OpenBSD Secure Shell server socket + Loaded: loaded (/usr/lib/systemd/system/ssh.socket; enabled; preset: enabled) + Active: active (listening) since Tue 2024-10-01 20:36:15 UTC; 12min ago + Triggers: ● ssh.service + Listen: [::]:22 (Stream) + CGroup: /system.slice/ssh.socket + + Oct 01 20:36:15 n2 systemd[1]: Listening on ssh.socket - OpenBSD Secure Shell server socket. + root@n2:~# lsof -i :22 + COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME + systemd 1 root 47u IPv6 2781411 0t0 TCP *:ssh (LISTEN) + + # Non-socket-activated + + root@n2:~# systemctl disable --now ssh.socket + Removed "/etc/systemd/system/ssh.service.requires/ssh.socket". + Removed "/etc/systemd/system/sockets.target.wants/ssh.socket". + root@n2:~# ln -s /dev/null /etc/systemd/system-generators/sshd-socket-generator + root@n2:~# systemctl enable --now ssh.service + Synchronizing state of ssh.service with SysV service script with /usr/lib/systemd/systemd-sysv-install. + Executing: /usr/lib/systemd/systemd-sysv-install enable ssh + Created symlink /etc/systemd/system/sshd.service → /usr/lib/systemd/system/ssh.service. + Created symlink /etc/systemd/system/multi-user.target.wants/ssh.service → /usr/lib/systemd/system/ssh.service. + root@n2:~# lsof -i :22 + COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME + sshd 798 root 3u IPv4 2793622 0t0 TCP *:ssh (LISTEN) + sshd 798 root 4u IPv6 2793624 0t0 TCP *:ssh (LISTEN) + + By default, we have net.ipv6.bindv6only=0 sysctl, and BindIPv6Only=both + on ssh.socket, which means usually users can connect over IPv4 + regardless. However, the fact remains that the resulting listening + sockets are different in these two cases, and socket-activated ssh does + not accurately reflect the settings in /etc/ssh/sshd_config. + + [Test Plan] + + 1. Check that on a noble system, without custom sshd_config, sshd is + listening on both IPv4 and IPv6 on port 22: + + $ lsof -i :22 + + 2. Check that setting AddressFamily to e.g. inet results in only an IPv4 + socket: + + $ echo "AddressFamily inet" >> /etc/ssh/sshd_config.d/custom.conf + $ systemctl daemon-reload + $ systemctl restart ssh.socket + $ lsof -i :22 + + There should only be one listener now. + + 3. Check the same thing with inet6, and a custom port for good measure: + + $ echo "AddressFamily inet6" >> /etc/ssh/sshd_config.d/custom.conf + $ echo "Port 1234" >> /etc/ssh/sshd_config.d/custom.conf + $ systemctl daemon-reload + $ systemctl restart ssh.socket + $ lsof -i :1234 + + 4. The new tests in debian/tests/sshd-socket-generator should all pass + in autopkgtest. + + [Where problems could occur] + + The fix requires new default settings in the [Socket] section of + ssh.socket, and handling for new defaults in sshd-socket-generator. It + would be more likely to see problems with the generator as opposed to + the changes in ssh.socket. However, new subtests were added to + debian/tests/sshd-socket-generator to help avoid this. + + [Original Description] + After upgrading from 22.04 to 24.04 I noticed that my sshd only listening on IPv6 interface (::), while previously it was listening both IPv4 (0.0.0.0) and IPv6 (::). I tried to explicitly specify ListenAddress 0.0.0.0 (assuming it would bind to IPv4 only) but after restart sshd was still listening on IPv6 only. This problem affects other packages as well, for example, openvpn. Rebuilding applications from sources seems to fix the issue. Setting net.ipv6.bindv6only=0 also helps, but that's not a solution. ProblemType: Bug DistroRelease: Ubuntu 24.04 Package: openssh-server 1:9.6p1-3ubuntu13.5 ProcVersionSignature: Ubuntu 6.8.0-41.41-generic 6.8.12 Uname: Linux 6.8.0-41-generic x86_64 ApportVersion: 2.28.1-0ubuntu3.1 Architecture: amd64 CasperMD5CheckResult: unknown Date: Tue Sep 10 16:45:54 2024 ProcEnviron: - LANG=C.UTF-8 - PATH=(custom, no user) - SHELL=/bin/bash - TERM=screen.xterm-256color + LANG=C.UTF-8 + PATH=(custom, no user) + SHELL=/bin/bash + TERM=screen.xterm-256color SourcePackage: openssh UpgradeStatus: Upgraded to noble on 2024-09-10 (0 days ago)
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2080216 Title: sshd cannot bind to IPv4 interfaces To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/2080216/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
