Enable systemd service hardening features for default system services

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

Improve security by enabling some of the high level systemd security hardening settings that isolate and sandbox default system services.

Owner

Name: Rahul Sundaram
Email: metherid@gmail.com

Targeted release: Fedora 40
Last updated: 2023-11-18
[<will be assigned by the Wrangler> devel thread]
FESCo issue: <will be assigned by the Wrangler>
Tracker bug: <will be assigned by the Wrangler>
Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

systemd provides a number of settings that can harden security for services. We are selecting a few high level ones to enable by default on a service by service basis as suitable for that particular service.

PrivateTmp=yes
ProtectSystem=yes/full/strict
ProtectHome=yes/read-only
ProtectClock=yes
ProtectHostname=yes
ProtectControlGroups=yes
ProtectHostname=yes
ProtectKernelLogs=yes
ProtectKernelModules=yes
ProtectKernelTunables=yes
ProtectProc=invisible
PrivateDevices=yes
PrivateNetwork=yes
NoNewPrivileges=yes
User= or DynamicUser=yes'

If we want to go further, we could also consider:

CapabilityBoundingSet=

DevicePolicy=closed

KeyringMode=private

LockPersonality=yes

MemoryDenyWriteExecute=yes

PrivateUsers=yes

RemoveIPC=yes

RestrictAddressFamilies=

RestrictNamespaces=yes

RestrictRealtime=yes

RestrictSUIDSGID=yes

SystemCallFilter=

SystemCallArchitectures=native

We will aim to cover all the default system services as well as some of the high profile services such as Nginx or PostgreSQL. All of these settings need to be configured on a per service basis instead of using a global override to facilitate fine tuning the settings based on service requirements and limit the impact for users on upgrades. Certain services have a very targeted scope. For instance, a service that only needs to read or write from only one directory could leverage more fine grained settings to restrict access even further. We will enable as many of these as feasible for the services but not every knob is going to be applicable to every service. For example,PrivateNetwork=yescan only be used for services that does not need network connectivity by default. As a base starting point, from Fedora 39 workstation, we have the following system services installed by default which should considered within the scope of the change (excluding systemd associated ones which already have a number of these security settings enabled). We may also consider doing this for some of the high profile services including say Nginx and PostgreSQL permitting time considerations and other contributors if any joining this effort. We will prioritize critical or long running services.

abrtd.service

abrt-journal-core.service

abrt-oops.service

abrt-pstoreoops.service

abrt-vmcore.service

abrt-xorg.service

accounts-daemon.service

alsa-restore.service

alsa-state.service

anaconda-direct.service

anaconda-fips.service

anaconda-nm-config.service

anaconda-nm-disable-autocons.service

anaconda-noshell.service

anaconda-pre.service

anaconda.service

anaconda-sshd.service

arp-ethers.service

auditd.service

auth-rpcgss-module.service

avahi-daemon.service

blivet.service

blk-availability.service

bluetooth.service

bolt.service

brltty.service

canberra-system-bootup.service

canberra-system-shutdown-reboot.service

canberra-system-shutdown.service

chronyd-restricted.service

chronyd.service

chrony-wait.service

colord.service

console-getty.service

cups-browsed.service

cups.service

dbus-broker.service

dbus-daemon.service

dbus-org.freedesktop.hostname1.service

dbus-org.freedesktop.import1.service

dbus-org.freedesktop.locale1.service

dbus-org.freedesktop.login1.service

dbus-org.freedesktop.machine1.service

dbus-org.freedesktop.portable1.service

dbus-org.freedesktop.timedate1.service

~~debug-shell.service~~ (opens a user shell that must be able to do arbitrary stuff)

dm-event.service

dnf-makecache.service

dnf-system-upgrade-cleanup.service

dnf-system-upgrade.service

dnsmasq.service

dracut-cmdline.service

dracut-initqueue.service

dracut-mount.service

dracut-pre-mount.service

dracut-pre-pivot.service

dracut-pre-trigger.service

dracut-pre-udev.service

dracut-shutdown-onfailure.service

dracut-shutdown.service

~~emergency.service~~ (opens a user shell that must be able to do arbitrary stuff)

fedora-third-party-refresh.service

firewalld.service

flatpak-add-fedora-repos.service

flatpak-system-helper.service

fprintd.service

fsidd.service

fstrim.service

fwupd-offline-update.service

fwupd-refresh.service

fwupd.service

gdm.service

geoclue.service

grub-boot-indeterminate.service

gssproxy.service

htcacheclean.service

httpd.service

hypervfcopyd.service

hypervkvpd.service

hypervvssd.service

iio-sensor-proxy.service

import-state.service

initrd-cleanup.service

initrd-parse-etc.service

initrd-switch-root.service

initrd-udevadm-cleanup-db.service

instperf.service

ipp-usb.service

iscsid.service

iscsi-init.service

iscsi-onboot.service

iscsi.service

iscsi-shutdown.service

iscsi-starter.service

iscsiuio.service

kdump.service

kmod-static-nodes.service

ldconfig.service

libvirtd.service

libvirt-guests.service

livesys-late.service

livesys.service

loadmodules.service

logrotate.service

low-memory-monitor.service

lvm2-lvmdbusd.service

lvm2-lvmpolld.service

lvm2-monitor.service

man-db-cache-update.service

man-db-restart-cache-update.service

mcelog.service

mdcheck_continue.service

mdcheck_start.service

mdmonitor-oneshot.service

mdmonitor.service

ModemManager.service

ndctl-monitor.service

netavark-dhcp-proxy.service

NetworkManager-dispatcher.service

NetworkManager.service

NetworkManager-wait-online.service

nfs-blkmap.service

nfsdcld.service

nfs-idmapd.service

nfs-mountd.service

nfs-server.service

nfs-utils.service

nftables.service

nis-domainname.service

nm-priv-helper.service

numad.service

nvmefc-boot-connections.service

nvmf-autoconnect.service

ostree-boot-complete.service

ostree-finalize-staged-hold.service

ostree-finalize-staged.service

ostree-prepare-root.service

ostree-remount.service

packagekit-offline-update.service

packagekit.service

pam_namespace.service

pcscd.service

plocate-updatedb.service

plymouth-halt.service

plymouth-kexec.service

plymouth-poweroff.service

plymouth-quit.service

plymouth-quit-wait.service

plymouth-read-write.service

plymouth-reboot.service

plymouth-start.service

plymouth-switch-root-initramfs.service

plymouth-switch-root.service

podman-auto-update.service

podman-clean-transient.service

podman-restart.service

podman.service

polkit.service

power-profiles-daemon.service

psacct.service

qemu-guest-agent.service

qemu-pr-helper.service

quotaon.service

raid-check.service

~~rc-local.service~~ (this can do arbitrary stuff)

realmd.service

rescue.service

rpcbind.service

rpc-gssd.service

rpc-statd-notify.service

rpc-statd.service

rpmdb-migrate.service

rpmdb-rebuild.service

rtkit-daemon.service

saslauthd.service

selinux-autorelabel-mark.service

selinux-autorelabel.service

selinux-check-proper-disable.service

speech-dispatcherd.service

spice-vdagentd.service

spice-webdavd.service

sshd.service

ssh-host-keys-migration.service

sssd-autofs.service

sssd-kcm.service

sssd-nss.service

sssd-pac.service

sssd-pam.service

sssd.service

sssd-ssh.service

sssd-sudo.service

switcheroo-control.service

system-update-cleanup.service

tcsd.service

thermald.service

udisks2.service

unbound-anchor.service

upower.service

uresourced.service

usbmuxd.service

vboxclient.service

vboxservice.service

vgauthd.service

virtinterfaced.service

virtlockd.service

virtlogd.service

virtnetworkd.service

virtnodedevd.service

virtnwfilterd.service

virtproxyd.service

virtqemud.service

virtsecretd.service

virtstoraged.service

vmtoolsd.service

wpa_supplicant.service

zfs-fuse-scrub.service

zfs-fuse.service

zvbid.service`

We will also coordinate with upstream following https://docs.fedoraproject.org/en-US/packaging-guidelines/PatchUpstreamStatus/ and encourage package maintainers to upstream these changes. Systemd will ignore any of these settings it does not understand on older versions. Hence this should be safe for upstream to merge on any services.

Feedback

Benefit to Fedora

Fedora services will get a significant security boost by default by avoiding or mitigating any unknown security vulnerabilities in default system services.

Scope

Proposal owners: Individual per service pull requests to enable various security features as applicable.
Other developers: Review PRs as needed
Release engineering: https://pagure.io/releng/issue/11785
Policies and guidelines:

Packaging guidelines will have to be modified to add recommendations to use more of the systemd security features by default. In particular, we should add a security settings section in https://fedoraproject.org/wiki/Packaging:Systemd. Current the guidance only recommends a couple of settings for long running services. Sample text:

Systemd services included in Fedora are recommended to use as many of the following security settings as applicable while maintaining the default functionality of the service.

PrivateTmp=yes
ProtectSystem=yes/full/strict
ProtectHome=yes
PrivateDevices=yes
ProtectKernelTunables=yes
ProtectKernelModules=yes
ProtectKernelLogs=yes
ProtectControlGroups=yes
NoNewPrivileges=yes
PrivateNetwork=yes

The full list of sandboxing features are available in https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#Sandboxing. Note that if you are submitting changes to upstream as recommended, systemd will warn and ignore any of these features it doesn't support. So it should be safe for upstream to enable as many of these features as applicable and not worry about distribution support for ones using older versions of systemd.

Trademark approval: N/A

Upgrade/compatibility impact

Packages will automatically get additional security features enabled by default transparently. In limited circumstances, they may need to override the defaults. Refer to user experience section for details.

How To Test

You can use tools like systemd-analyze security and systemctl cat to verify that specific security features are enabled by default. Default services with the default features should have no adverse impact and users shouldn't have to do anything beyond using the software as intended and report any regressions. High profile services not installed by default that gain these security features would benefit from more targeting testing to spot any unintended consequences especially for niche or advanced functionality. If advanced non-default functionality requires overrides default settings, we can document those in the release notes to provide guidance.

User Experience

This should be largely transparent change for users. The goal is to have the services work as expected with the default functionality but to potentially require tweaking the settings if the configuration is changed by users after installation. For instance, if we add ProtectHome=yes to Apache httpd.service and the user wishes to serve files out of their home directory, they will need to override the systemd setting to ProtectHome=read-only to allow for the service to read from the user home directory in addition to changing the service specific configuration files to enable this feature.

Dependencies

None. We are merely enabling some of systemd security features by default for default system services and potentially some high profile services.

Contingency Plan

Contingency mechanism: These settings can be enabled/disabled at a per service level. No wholesale reverts is necessary. If we don't finish the work for all the services, we can follow up in future releases.
Contingency deadline: N/A
Blocks release? No

Documentation

Release Notes

systemd security hardening features are enabled for default system services and following high profile services.

PostgreSQL
Apache Httpd
Nginx
MariaDB

....

If you wish to turn off any particular settings, you can follow the standard systemd method of overriding the config. For example,

$ cat /etc/systemd/system/httpd.service.d/override.conf

[Service]

ProtectHome=no

$ sudo systemctl daemon-reload

$ sudo systemctl restart httpd.service

$ systemctl status httpd.service

● httpd.service - The Apache HTTP Server

    Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
   Drop-In: /etc/systemd/system/httpd.service.d
            └─override.conf
    Active: active (running) since Mon 2023-11-15 18:29:25 EST; 3min 30s ago

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