[Unit]
Description=restic-manager agent
Documentation=https://gitea.dcglab.co.uk/steve/restic-manager
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
ExecStart=/usr/local/bin/restic-manager-agent -config /etc/restic-manager/agent.yaml
Restart=always
RestartSec=5

# The agent runs as root. A fleet-backup tool needs to read every
# file on the system regardless of DAC permissions; running as a
# dedicated unprivileged user means either silent skips on /home,
# /root, /var/lib/<other-daemons>, or operators having to add the
# service user to every group whose files they want backed up. Both
# are worse than the threat model already implies (the agent holds
# repo credentials, executes arbitrary restic, and runs operator-
# defined hooks — its blast radius is already large).
#
# The mitigation is aggressive systemd sandboxing of the root
# process: drop all capabilities except the few we need, deny
# writes outside our state dirs, and forbid privilege escalation.
User=root
Group=root

# CAP_DAC_READ_SEARCH lets us read any file regardless of DAC perms
# (the "backup everything" capability). CAP_DAC_OVERRIDE is needed
# during restore for chown/chmod to recreate ownership. Drop the
# rest — root in this process means "can read", not "can do".
CapabilityBoundingSet=CAP_DAC_READ_SEARCH CAP_DAC_OVERRIDE CAP_FOWNER CAP_CHOWN
AmbientCapabilities=CAP_DAC_READ_SEARCH CAP_DAC_OVERRIDE CAP_FOWNER CAP_CHOWN

# Hardening — blocks privilege escalation even from root, and
# confines writes / network / kernel access to what restic actually
# needs. Filesystem reads stay open: that's the whole job.
NoNewPrivileges=true
ProtectSystem=strict
# /etc/restic-manager: agent.yaml + secrets.enc.
# /var/lib/restic-manager: agent state (currently unused but reserved).
# /root/rm-restore: default target for new-directory restores
#   ($HOME/rm-restore/<job-id>/ resolves here for User=root).
#   ReadWritePaths overrides ProtectHome=read-only on this subdir only.
ReadWritePaths=/etc/restic-manager /var/lib/restic-manager -/root/rm-restore
ProtectHome=read-only
ProtectHostname=true
ProtectKernelTunables=true
ProtectKernelModules=true
ProtectKernelLogs=true
ProtectControlGroups=true
ProtectClock=true
PrivateTmp=true
RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
RestrictRealtime=true
RestrictSUIDSGID=true
RestrictNamespaces=true
LockPersonality=true
MemoryDenyWriteExecute=true
SystemCallArchitectures=native
# (No SystemCallFilter — the cap drop above already constrains what
# root can do; an allow-list filter killed restic with SIGSYS during
# init because @system-service excludes some of the syscalls Go's
# runtime + restic's file scanner reach for. The Protect*/Restrict*
# toggles still cover network / kernel / mount / namespace.)

[Install]
WantedBy=multi-user.target
