** Description changed: - [Description] + [Impact] + + * If a fully numeric username is created, it will cause + problems with systemd. One example is that the user with + this type of name can log in, but loginctl will not create + a session for them. + * This can also cause users to be unable to log in to a gdm + environment + + [Test Case] + + * `useradd 123` (this command should succeed) + * `userdel 123` to clean up the user that was just added + * Install `shadow` from -proposed + * `useradd 123` should now fail + + [Regression Potential] + * If there were a logic error in the fix, it is possible + that valid usernames would now be disallowed. + * Many test cases have been added to ensure this is not + the case, and --badnames would still provide a work-around + + [Original Description] Fully numeric names support in Ubuntu is inconsistent in Focal onwards because systemd does not like them[1] but are still allowed by default by useradd, leaving the session behavior in hands of the running applications. Two examples: 1. After creating a user named "0", the user can log in via ssh or console but loginctl won't create a session for it: root@focal:/home/ubuntu# useradd -m 0 root@focal:/home/ubuntu# id 0 uid=1005(0) gid=1005(0) groups=1005(0) .. 0@192.168.122.6's password: Welcome to Ubuntu 20.04.2 LTS (GNU/Linux 5.8.0-48-generic x86_64) Last login: Thu Apr 8 16:17:06 2021 from 192.168.122.1 $ loginctl No sessions. $ w - 16:20:09 up 4 min, 1 user, load average: 0.03, 0.14, 0.08 + 16:20:09 up 4 min, 1 user, load average: 0.03, 0.14, 0.08 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT - 0 pts/0 192.168.122.1 16:17 0.00s 0.00s 0.00s w + 0 pts/0 192.168.122.1 16:17 0.00s 0.00s 0.00s w And pam-systemd shows the following message: Apr 08 16:17:06 focal sshd[1584]: pam_unix(sshd:session): session opened for user 0 by (uid=0) Apr 08 16:17:06 focal sshd[1584]: pam_systemd(sshd:session): pam-systemd initializing Apr 08 16:17:06 focal sshd[1584]: pam_systemd(sshd:session): Failed to get user record: Invalid argument + 2. With that same username, every successful authentication in gdm will + loop back to gdm again instead of starting gnome, making the user unable + to login. - 2. With that same username, every successful authentication in gdm will loop back to gdm again instead of starting gnome, making the user unable to login. - - - Making useradd fail (unless --badnames is set) when a fully numeric name is used will make the default OS behavior consistent. - + Making useradd fail (unless --badnames is set) when a fully numeric name + is used will make the default OS behavior consistent. [Other info] - Upstream does not support fully numeric usernames - useradd has a --badnames parameter that would still allow the use of these type of names
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1927078 Title: Don't allow useradd to use fully numeric names To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/shadow/+bug/1927078/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
