steve
83d97a27cc
Smoke caught this: ProtectSystem=full mounts /usr read-only so the agent couldn't write its own .new staging file or atomic-rename over the running binary. Adding /usr/local/bin to ReadWritePaths is the minimum diff that lets self-update work; the whole-dir grant is required because os.Rename needs write on the parent directory.
83 lines
3.6 KiB
Desktop File
83 lines
3.6 KiB
Desktop File
[Unit]
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Description=restic-manager agent
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Documentation=https://gitea.dcglab.co.uk/steve/restic-manager
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After=network-online.target
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Wants=network-online.target
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[Service]
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Type=simple
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ExecStart=/usr/local/bin/restic-manager-agent -config /etc/restic-manager/agent.yaml
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Restart=always
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RestartSec=5
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# The agent runs as root. A fleet-backup tool needs to read every
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# file on the system regardless of DAC permissions; running as a
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# dedicated unprivileged user means either silent skips on /home,
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# /root, /var/lib/<other-daemons>, or operators having to add the
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# service user to every group whose files they want backed up. Both
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# are worse than the threat model already implies (the agent holds
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# repo credentials, executes arbitrary restic, and runs operator-
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# defined hooks — its blast radius is already large).
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#
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# The mitigation is aggressive systemd sandboxing of the root
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# process: drop all capabilities except the few we need, deny
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# writes outside our state dirs, and forbid privilege escalation.
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User=root
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Group=root
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# CAP_DAC_READ_SEARCH lets us read any file regardless of DAC perms
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# (the "backup everything" capability). CAP_DAC_OVERRIDE is needed
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# during restore for chown/chmod to recreate ownership. Drop the
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# rest — root in this process means "can read", not "can do".
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CapabilityBoundingSet=CAP_DAC_READ_SEARCH CAP_DAC_OVERRIDE CAP_FOWNER CAP_CHOWN
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AmbientCapabilities=CAP_DAC_READ_SEARCH CAP_DAC_OVERRIDE CAP_FOWNER CAP_CHOWN
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# Hardening — blocks privilege escalation even from root, and
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# confines kernel / namespace / privilege surface. Filesystem reads
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# stay open (that's the whole job) and restore writes are
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# unrestricted: a backup tool whose entire purpose is "put files
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# back where they belong" can't have ProtectHome=read-only or
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# ProtectSystem=strict without breaking on the first cross-user
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# restore. ProtectSystem=full keeps /usr, /boot, /efi read-only so a
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# compromised agent can't swap out /usr/bin/restic or drop a kernel
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# module, while leaving /home, /root, /var, /opt, /srv, /tmp etc.
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# writable for arbitrary restore targets. The agent is treated as a
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# high-trust component (it runs operator hooks as root and holds
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# repo credentials); the residual hardening is about kernel + privesc
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# protection, not write confinement.
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NoNewPrivileges=true
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ProtectSystem=full
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# ProtectSystem=full mounts /usr, /boot, /efi *and* /etc read-only.
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# The agent rewrites /etc/restic-manager/agent.yaml on enrolment and
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# whenever a new SecretsKey is minted, so we need a targeted
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# write-exemption for that dir. No exemption for the rest of /etc:
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# the agent has no business editing /etc/passwd, /etc/sudoers, etc.
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#
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# /usr/local/bin is writable so the self-update flow (P6-01) can
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# atomic-rename a fresh binary over the running one. Permitting the
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# whole directory (rather than just the binary path) is required
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# because os.Rename takes a write lock on the parent dir.
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ReadWritePaths=/etc/restic-manager /usr/local/bin
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ProtectHostname=true
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ProtectKernelTunables=true
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ProtectKernelModules=true
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ProtectKernelLogs=true
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ProtectControlGroups=true
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ProtectClock=true
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PrivateTmp=true
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RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
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RestrictRealtime=true
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RestrictSUIDSGID=true
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RestrictNamespaces=true
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LockPersonality=true
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MemoryDenyWriteExecute=true
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SystemCallArchitectures=native
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# (No SystemCallFilter — the cap drop above already constrains what
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# root can do; an allow-list filter killed restic with SIGSYS during
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# init because @system-service excludes some of the syscalls Go's
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# runtime + restic's file scanner reach for. The Protect*/Restrict*
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# toggles still cover network / kernel / mount / namespace.)
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[Install]
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WantedBy=multi-user.target
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