The cursor can be freely moved around and used to erase characters on the TTY while at the login prompt

[Aaron Rainbolt]

Welp, this is a weird one. Known to affect Ubuntu Server and multiple flavors of Ubuntu.

Steps to reproduce:

1: If you are shown a graphical login prompt (e.g. GDM or SDDM), switch to a TTY.
2. At the login prompt, press the up arrow key twice.
3: Press Backspace twice.
4: Press Enter.

Expected result: Nothing should happen, or possibly key codes should appear when the arrow keys are pressed, and those key codes should be erased when backspace is pressed.

Actual result: The cursor moves up two lines when the up arrow key is pressed twice, and the "." and "4" of "22.04.1" are erased when Backspace is pressed twice. Upon pressing Enter, the TTY seems to freeze (no user input causes anything to happen), then the login prompt reverts back to its original state and the cursor assumes its proper location.

Notes:
This bug was first reported by a user named Liver_K on IRC as happening on Ubuntu Server 22.04 after upgrading from 20.04. alkisg then confirmed it on Ubuntu MATE 22.04, and I confirmed it on Kubuntu Focus Suite 22.04.

Yes, you can indeed use this to erase everything in the TTY screen and leave the cursor in the upper-left corner as if the system was stuck. Pressing Enter resolves it after a while.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: login 1:4.8.1-2ubuntu2
ProcVersionSignature: Ubuntu 5.17.0-1017.18-oem 5.17.15
Uname: Linux 5.17.0-1017-oem x86_64
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: KDE
Date: Thu Oct 13 00:44:03 2022
InstallationDate: Installed on 2022-10-04 (8 days ago)
InstallationMedia: Kubuntu 22.04.1 LTS "Jammy Jellyfish" (20220916)
SourcePackage: shadow
UpgradeStatus: No upgrade log present (probably fresh install)

[Alkis Georgopoulos (alkisg)]

Reproduced in Ubuntu 22.04 and 20.04.
Could NOT reproduce in Ubuntu 18.04.

I think the problem is in `agetty` though, not in `login`.
Added `util-linux` to affected packages.

[Nick Rosbrook (enr0n)]

I also confirmed this by testing a 22.04 VM with QEMU/KVM. I agree with Alkis that this is agetty, so util-linux would be the appropriate package.