system-proxy/init/system-proxy.conf

# Copyright 2020 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

description     "System-proxy daemon"
author          "chromium-os-dev@chromium.org"

# The service is started by Chrome on demand.
stop on stopping ui
respawn
respawn limit 3 5

# Do not respawn if the service is terminated on purpose.
normal exit 0

# Sacrifice before OOM panic.
oom score 0
# TODO (acostinas, crbug.com/1045862) Add virtual memory size limit after
# run-time analysis.

# Minijail actually forks off the desired process.
expect fork

pre-start script
  # Check if ui is still running before starting the system proxy daemon.
  # This is to prevent new dbus-activated instances from getting started once
  # the system is beginning to shut down.
  if ! initctl status ui | grep -q running; then
    stop
    exit 0
  fi
end script

script
  # Start constructing minijail0 args...
  args=""

  # Make sure minijail0 exits right away and won't block upstart.
  args="${args} -i"

  # Create a UTS namespace to isolate changes to the host / domain name.
  args="${args} --uts"

  # Create an IPC namespace (isolate System V IPC objects/POSIX message queues).
  args="${args} -l"

  # Remount /proc read-only (prevents any messing with it).
  args="${args} -r"

  # Creates new, empty tmp directory (technically, mounts tmpfs).
  args="${args} -t"

  # Prevent that execve gains privileges, required for seccomp filters.
  args="${args} -n"

  # Apply seccomp policy.
  args="${args} -S /usr/share/policy/system-proxy-seccomp.policy"

  # Use a minimalistic mount namespace.
  args="${args} --profile minimalistic-mountns"

  # Mount /run as tmpfs read-only.
  args="${args} -k tmpfs,/run,tmpfs,MS_NOSUID|MS_NODEV|MS_NOEXEC"

  # Bind-mount /run/dbus read-only for D-Bus to work.
  args="${args} -b /run/dbus"

  # Bind-mount /sbin read-only to start sandboxed processes using minijail0.
  args="${args} -b /sbin"

  # Bind-mount /run/shill for DNS resolution.
  args="${args} -b /run/shill"

  # Run as system-proxy user and group.
  args="${args} -u system-proxy -g system-proxy"

  # Inherit system-proxy's supplementary groups, in particular
  # 'password-viewers' to read the login password.
  args="${args} -G"

  # Run with root permissions so that the daemon can start sandboxed processes.
  args="${args} -c cap_sys_admin=e"

  # Execute system-proxy.
  args="${args} /usr/sbin/system_proxy"

  # -e is not specified because the service needs to connect to servers.

  exec minijail0 ${args}
end script

# Wait for daemon to claim its D-Bus name before transitioning to started.
post-start exec minijail0 -u system-proxy -g system-proxy /usr/bin/gdbus \
    wait --system --timeout 15 org.chromium.SystemProxy