gpm prevents loging to the console: spurious “Enter” events seems inserted

[EOLE team]

Hello,

When our servers boot, We can't login because of spurious “enter”.

We have this problem on virtual and physical machines since:

* kernel linux-image-4.15.0-44-generic on bionic
* kernel linux-image-4.4.0-142-generic on xenial

To reproduce:

1. start an ubuntu server with the specific kernel
2. install GPM
3. on a console
   1. type the user name “root”
   2. hit “enter”
   3. wait few seconds => spurious “Enter” are send to the console
4. Stop gpm.service
5. retry to login on a console => no problem

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic

[Alexis Wilke (alexis-m2osw)]

I have the exact same problem on Ubuntu 16.04 (vmlinuz-4.4.0-142-generic).

I will try to turn off GPM and see how my console functions without it.

What a surprise though! Not being able to log in the simplest console. Not something I've seen in ages...

[Alexis Wilke (alexis-m2osw)]

I rebooted on Ubuntu 16.04 (4.4.0-142-generic) and it worked as expected once gpm was turned off.

I used the following command to prevent gpm from starting on a reboot and messing up the login screen:

sudo systemctl mask gpm

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Mike Wescott (wescott)]

Seen on linux-image-4.15.0-44-generic and linux-image-4.15.0-45-generic.

When /bin/login is exec'd by agetty it tries to read stdin and gets EAGAIN:

    5640 write(2, "Password: ", 10) = 10
    5640 read(0, 0x7ffcca86a7f0, 511) = -1 EAGAIN (Resource temporarily unavailable)
    ...
    55640 write(2, "\n", 1) = 1

taking that as a failed login attempt it tries again:

    55640 write(2, "hilbert login: ", 15) = 15
    55640 read(0, 0x7ffcca86a160, 511) = -1 EAGAIN (Resource temporarily unavailable)

eventually logging a failed login attempt

reverting to linux-image-4.15.0-43-generic also fixes the problem

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Norbert (nrbrtx)]

Yesterday I went to this bug on Ubuntu 16.04.5 LTS with all updates and without PPAs on physical hardware.
The problem was with 4.4.0-142-generic kernel. Rebooting with previous kernel (138 in may case) helped.