libpam-google-authenticator, kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010

[James Kelley]

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu

lsb_release -rd
Description: Ubuntu 18.04.4 LTS
Release: 18.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in

apt-cache policy libpam-google-authenticator
libpam-google-authenticator:
  Installed: 20170702-1
  Candidate: 20170702-1
  Version table:
 *** 20170702-1 500
        500 http://us.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

3) What you expected to happen
Didn't expect a Kernel reboot, just an error message

4) What happened instead
server crashed

https://errors.ubuntu.com/user/58ef3f64f201a5f60a086141e3751b91a710dbf811d9f5824ebe26eab6c42e229a24677e6c0b1ea5361c25158042dbfa77fd3a3c0bedd28377dfe9f43d91eca8

There is a bug that will cause a ubuntu to crash from bad configuration of libpam-google-authenticator on
4.15.0-109-generic #110-Ubuntu SMP Tue Jun 23 02:39:32 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux.

kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
-- Reboot --

Steps to reproduce :

 • sudo apt-get update

 • sudo apt-get install libpam-google-authenticator

 • vi /etc/pam.d/sshd
add below line without nullok
auth required pam_google_authenticator.so
Then restart ssh,
 • sudo systemctl restart sshd.service
without initializing / running google-authenticator for ssh user.
 • ssh -l user yourUbuntuServer.com
Work around is to add nullok to end of pam.d/sshd line

[James Kelley (knowever)]

journalctl
Jul 03 21:33:26 yourUbuntuServer.com systemd[1]: Stopping OpenBSD Secure Shell server...
Jul 03 21:33:26 yourUbuntuServer.com sshd[1719]: Received signal 15; terminating.
Jul 03 21:33:26 yourUbuntuServer.com systemd[1]: Stopped OpenBSD Secure Shell server.
Jul 03 21:33:26 yourUbuntuServer.com systemd[1]: Starting OpenBSD Secure Shell server...
Jul 03 21:33:26 yourUbuntuServer.com sshd[20393]: Server listening on 0.0.0.0 port 22.
Jul 03 21:33:26 yourUbuntuServer.com sshd[20393]: Server listening on :: port 22.
Jul 03 21:33:26 yourUbuntuServer.com systemd[1]: Started OpenBSD Secure Shell server.
Jul 03 21:34:05 yourUbuntuServer.com kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
-- Reboot --
Jul 03 21:42:01 yourUbuntuServer.com kernel: microcode: microcode updated early to revision 0x5002f01, date = 2020-04-23