Configure GNOME3 DConf User Profile

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Description

By default, DConf provides a standard user profile. This profile contains a list of DConf configuration databases. The user profile and database always take the highest priority. As such the DConf User profile should always exist and be configured correctly.

To make sure that the gdm profile is configured correctly, the /etc/dconf/profile/gdm should be set as follows:

user-db:user
system-db:gdm

To make sure that the user profile is configured correctly, the /etc/dconf/profile/user should be set as follows:

user-db:user
system-db:local

Rationale

Failure to have a functional DConf profile prevents GNOME3 configuration settings from being enforced for all users and allows various security risks.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

#!/bin/bash

# Remediation is applicable only in certain platforms
if dpkg-query --show --showformat='${db:Status-Status}\n' 'gdm3' 2>/dev/null | grep -q installed && { [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; }; then

# configure two dconf profiles:
# - gdm: required for banner/user_list settings
# - user: required for screenlock,automount,ctrlaltdel,... settings
mkdir -p /etc/dconf/profile
dconf_profile_path=/etc/dconf/profile/user

[[ -s "${dconf_profile_path}" ]] || echo > "${dconf_profile_path}"

if ! grep -Pzq "(?s)^\s*user-db:user.*\n\s*system-db:local" "${dconf_profile_path}"; then
    sed -i --follow-symlinks "1s/^/user-db:user\nsystem-db:local\n/" "${dconf_profile_path}"
fi

# Make sure the corresponding directories exist
mkdir -p /etc/dconf/db/local.d

# Make sure permissions allow regular users to read dconf settings.
# Also define the umask to avoid `dconf update` changing permissions.
chmod -R u=rwX,go=rX /etc/dconf/profile
(umask 0022 && dconf update)
mkdir -p /etc/dconf/profile
dconf_profile_path=/etc/dconf/profile/gdm

[[ -s "${dconf_profile_path}" ]] || echo > "${dconf_profile_path}"

if ! grep -Pzq "(?s)^\s*user-db:user.*\n\s*system-db:gdm" "${dconf_profile_path}"; then
    sed -i --follow-symlinks "1s/^/user-db:user\nsystem-db:gdm\n/" "${dconf_profile_path}"
fi

# Make sure the corresponding directories exist
mkdir -p /etc/dconf/db/gdm.d

# Make sure permissions allow regular users to read dconf settings.
# Also define the umask to avoid `dconf update` changing permissions.
chmod -R u=rwX,go=rX /etc/dconf/profile
(umask 0022 && dconf update)

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi