I'm filing this bug as way to document this change in the behavior and how to restore trusty's behavior, but also to get feedback from Foundations if this is something that could be fixed in the distro when a openssh-server is being upgraded from older versions.
-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to openssh in Ubuntu. https://bugs.launchpad.net/bugs/1588457 Title: authorized_keys using from="hostnamee" no longer work when upgrading to Xenial Status in openssh package in Ubuntu: New Bug description: [Impact] When a user has configured their authorized_keys file with the directive "from=" to restrict the usage of those keys, if that server is upgraded to Xenial (or Wily) the user may get locked out. [Test Case] * Create 3 containers (client, trusty, xenial) $ lxc launch ubuntu:14.04 client $ lxc launch ubuntu:14.04 ssh-trusty $ lxc launch ubuntu:16.04 ssh-trusty * To make sure their hostnames are properly registered in dnsmasq and dns resolution works, ssh into each container and run "sudo reboot" (restart the network should do the trick too) * In the 'client' container generate a ssh key $ lxc exec client /bin/bash (client)# ssh-keygen * Add the ssh key in the other two containers for the user ubuntu * Verify a connection can be established from client to ssh-xenial and ssh-trusty (client)# ssh ssh-xenial (client)# ssh ssh-trusty * Edit in add the prefix from="client.lxd" in both containers authorized_keys file (ssh-xenial and ssh-trusty) * Check if you can connect (client)# ssh ssh-trusty (client)# ssh ssh-xenial Expected: you can connect to both containers Actual results: You can connect to the trusty server, but you can't to the xenial one, because since Wily (openssh 1:6.9p1-1[0] ) the configuration key UseDNS default changed from "yes" to "no", so sshd is not doing a reverse dns request to know if the incoming connection matched "client.lxd" [Workaround] Edit /etc/ssh/sshd_config and set "UseDNS yes" $ echo "UseDNS yes" | sudo tee -a /etc/ssh/sshd_config [More Info] Relevant portion from the manpage[1]: UseDNS Specifies whether sshd(8) should look up the remote host name, and to check that the resolved host name for the remote IP address maps back to the very same IP address. If this option is set to “no” (the default) then only addresses and not host names may be used in ~/.ssh/known_hosts from and sshd_config Match Host directives. [0] http://changelogs.ubuntu.com/changelogs/pool/main/o/openssh/openssh_6.9p1-1/changelog [1] http://manpages.ubuntu.com/manpages/xenial/en/man5/sshd_config.5.html To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1588457/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
