1.8.5 Ensure GDM screen locks cannot be overridden

[scfast]

Profile Applicability:  Level 1 - Server  Level 1 - Workstation

Description: GNOME Desktop Manager can make the screen lock automatically whenever the user is idle for some amount of time. By using the lockdown mode in dconf, you can prevent users from changing specific settings. To lock down a dconf key or subpath, create a locks subdirectory in the keyfile directory. The files inside this directory contain a list of keys or subpaths to lock. Just as with the keyfiles, you may add any number of files to this directory. Example Lock File:

# Lock desktop screensaver settings
/org/gnome/desktop/session/idle-delay
/org/gnome/desktop/screensaver/lock-delay

Rationale: Setting a lock-out value reduces the window of opportunity for unauthorized user access to another user's session that has been left unattended. Without locking down the system settings, user settings take precedence over the system settings.

Audit: Run the following script to verify that the screen lock can not be overridden:

#!/usr/bin/env bash
{
# Check if GNOME Desktop Manager is installed. If package isn't
installed, recommendation is Not Applicable\n
# determine system's package manager
l_pkgoutput=""
if command -v dpkg-query > /dev/null 2>&1; then
l_pq="dpkg-query -W"
elif command -v rpm > /dev/null 2>&1; then
l_pq="rpm -q"
fi
# Check if GDM is installed
l_pcl="gdm gdm3" # Space seporated list of packages to check
for l_pn in $l_pcl; do
$l_pq "$l_pn" > /dev/null 2>&1 && l_pkgoutput="$l_pkgoutput\n -
Package: \"$l_pn\" exists on the system\n - checking configuration"
done
# Check configuration (If applicable)
if [ -n "$l_pkgoutput" ]; then
l_output="" l_output2=""
# Look for idle-delay to determine profile in use, needed for remaining
tests

l_kfd="/etc/dconf/db/$(grep -Psril '^\h*idle-
delay\h*=\h*uint32\h+\d+\b' /etc/dconf/db/*/ | awk -F'/' '{split($(NF-
1),a,".");print a[1]}').d" #set directory of key file to be locked

l_kfd2="/etc/dconf/db/$(grep -Psril '^\h*lock-
delay\h*=\h*uint32\h+\d+\b' /etc/dconf/db/*/ | awk -F'/' '{split($(NF-
1),a,".");print a[1]}').d" #set directory of key file to be locked

if [ -d "$l_kfd" ]; then # If key file directory doesn't exist, options
can't be locked
if grep -Prilq '\/org\/gnome\/desktop\/session\/idle-delay\b'
"$l_kfd"; then
l_output="$l_output\n - \"idle-delay\" is locked in \"$(grep -
Pril '\/org\/gnome\/desktop\/session\/idle-delay\b' "$l_kfd")\""
else
l_output2="$l_output2\n - \"idle-delay\" is not locked"
fi
else
l_output2="$l_output2\n - \"idle-delay\" is not set so it can not be
locked"
fi
if [ -d "$l_kfd2" ]; then # If key file directory doesn't exist,
options can't be locked
if grep -Prilq '\/org\/gnome\/desktop\/screensaver\/lock-delay\b'
"$l_kfd2"; then
l_output="$l_output\n - \"lock-delay\" is locked in \"$(grep -
Pril '\/org\/gnome\/desktop\/screensaver\/lock-delay\b' "$l_kfd2")\""
else
l_output2="$l_output2\n - \"lock-delay\" is not locked"
fi
else
l_output2="$l_output2\n - \"lock-delay\" is not set so it can not be
locked"
fi
else
l_output="$l_output\n - GNOME Desktop Manager package is not installed
on the system\n - Recommendation is not applicable"
fi
# Report results. If no failures output in l_output2, we pass
[ -n "$l_pkgoutput" ] && echo -e "\n$l_pkgoutput"
if [ -z "$l_output2" ]; then
echo -e "\n- Audit Result:\n ** PASS **\n$l_output\n"
else
echo -e "\n- Audit Result:\n ** FAIL **\n - Reason(s) for audit
failure:\n$l_output2\n"
[ -n "$l_output" ] && echo -e "\n- Correctly set:\n$l_output\n"
fi
}

References:

1. https://help.gnome.org/admin/system-admin-guide/stable/desktop- lockscreen.html.en

2. https://help.gnome.org/admin/system-admin-guide/stable/dconf-lockdown.html.en