moby/hack/dind-systemd

#!/bin/bash
set -e

# Set the container env-var, so that AppArmor is enabled in the daemon and
# containerd when running docker-in-docker.
#
# see: https://github.com/containerd/containerd/blob/787943dc1027a67f3b52631e084db0d4a6be2ccc/pkg/apparmor/apparmor_linux.go#L29-L45
# see: https://github.com/moby/moby/commit/de191e86321f7d3136ff42ff75826b8107399497
container=docker
export container

if [ $# -eq 0 ]; then
	echo >&2 'ERROR: No command specified. You probably want to run `journalctl -f`, or maybe `bash`?'
	exit 1
fi

if [ ! -t 0 ]; then
	echo >&2 'ERROR: TTY needs to be enabled (`docker run -t ...`).'
	exit 1
fi

# Change mount propagation to shared, which SystemD PID 1 would normally do
# itself when started by the kernel. SystemD skips that when it detects it is
# running in a container.
mount --make-rshared /

# Allow AppArmor to work inside the container;
#
#     aa-status
#     apparmor filesystem is not mounted.
#     apparmor module is loaded.
#
#     mount -t securityfs none /sys/kernel/security
#
#     aa-status
#     apparmor module is loaded.
#     30 profiles are loaded.
#     30 profiles are in enforce mode.
#       /snap/snapd/18357/usr/lib/snapd/snap-confine
#       ...
#
# Note: https://0xn3va.gitbook.io/cheat-sheets/container/escaping/sensitive-mounts#sys-kernel-security
#
#     ## /sys/kernel/security
#
#     In /sys/kernel/security mounted the securityfs interface, which allows
#     configuration of Linux Security Modules. This allows configuration of
#     AppArmor policies, and so access to this may allow a container to disable
#     its MAC system.
#
# Given that we're running privileged already, this should not be an issue.
if [ -d /sys/kernel/security ] && ! mountpoint -q /sys/kernel/security; then
	mount -t securityfs none /sys/kernel/security || {
		echo >&2 'Could not mount /sys/kernel/security.'
		echo >&2 'AppArmor detection and --privileged mode might break.'
	}
fi

env > /etc/docker-entrypoint-env

cat > /etc/systemd/system/docker-entrypoint.target << EOF
[Unit]
Description=the target for docker-entrypoint.service
Requires=docker-entrypoint.service systemd-logind.service systemd-user-sessions.service
EOF

quoted_args="$(printf " %q" "${@}")"
echo "${quoted_args}" > /etc/docker-entrypoint-cmd

cat > /etc/systemd/system/docker-entrypoint.service << EOF
[Unit]
Description=docker-entrypoint.service

[Service]
ExecStart=/bin/bash -exc "source /etc/docker-entrypoint-cmd"
# EXIT_STATUS is either an exit code integer or a signal name string, see systemd.exec(5)
ExecStopPost=/bin/bash -ec "if echo \${EXIT_STATUS} | grep [A-Z] > /dev/null; then echo >&2 \"got signal \${EXIT_STATUS}\"; systemctl exit \$(( 128 + \$( kill -l \${EXIT_STATUS} ) )); else systemctl exit \${EXIT_STATUS}; fi"
StandardInput=tty-force
StandardOutput=inherit
StandardError=inherit
WorkingDirectory=$(pwd)
EnvironmentFile=/etc/docker-entrypoint-env

[Install]
WantedBy=multi-user.target
EOF

systemctl mask systemd-firstboot.service systemd-udevd.service
systemctl unmask systemd-logind
systemctl enable docker-entrypoint.service

systemd=
if [ -x /lib/systemd/systemd ]; then
	systemd=/lib/systemd/systemd
elif [ -x /usr/lib/systemd/systemd ]; then
	systemd=/usr/lib/systemd/systemd
elif [ -x /sbin/init ]; then
	systemd=/sbin/init
else
	echo >&2 'ERROR: systemd is not installed'
	exit 1
fi
systemd_args="--show-status=false --unit=docker-entrypoint.target"
echo "$0: starting $systemd $systemd_args"
exec $systemd $systemd_args