Public bug reported:
[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
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
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.
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
** Affects: shadow (Ubuntu)
Importance: Undecided
Status: New
** Affects: shadow (Ubuntu Focal)
Importance: Undecided
Status: New
** Affects: shadow (Ubuntu Groovy)
Importance: Undecided
Status: New
** Affects: shadow (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Affects: shadow (Ubuntu Impish)
Importance: Undecided
Status: New
** Also affects: shadow (Ubuntu Groovy)
Importance: Undecided
Status: New
** Also affects: shadow (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Also affects: shadow (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: shadow (Ubuntu Impish)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1927078
Title:
Don't allow useradd to use fully numeric names
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