mirror of
https://github.com/jmcorgan/fips.git
synced 2026-07-30 19:46:15 +00:00
Johnathan Corgan
507086e39d
Pre-cut documentation pass for the 0.4.0 release, verified against current source. Corrections: - fipsctl: stale 'show identities'/'show node' -> 'show status' (host-a-service, run-as-unprivileged-user) - mesh address derivation: first 16 bytes of SHA-256(pubkey) with the leading byte set to 0xfd, not a fixed fd97: prefix (reach-mesh-services, ipv6-adapter-walkthrough) - gateway control socket mode 0660 -> 0770 (troubleshoot-gateway) - Tor example: add advertised_port: 8443 so the published port matches the prose (enable-nostr-discovery) - bloom mesh-size estimate rewritten to the OR-union-of-peer-filters algorithm; plus mtu deep-link, gateway pool wording, and a NAT failure-mode line - examples: delete orphaned nostr-rs-relay config, accept inbound to the local 8443 TCP listener, fix fd::/8 -> fd00::/8 typos, dotless wireguard alias Additions: - new Nym mixnet transport section (fips-transport-layer) and the architecture transport list - new LAN/mDNS discovery section (fips-nostr-discovery) - reference docs: Nym transport, LAN discovery, and new control/stats surfaces; drop ble from the connect transport list
196 lines
5.8 KiB
Markdown
196 lines
5.8 KiB
Markdown
# Run the FIPS Daemon as an Unprivileged User
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By default, the FIPS daemon runs as `root` — the shipped Debian
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systemd unit configures this, and no further setup is required.
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The trade-off is that the daemon has full root authority,
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including outside its actual network needs. Acceptable for
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single-purpose hosts; less desirable for shared hosts.
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This guide covers the alternative: drop privileges and run the
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daemon under a dedicated unprivileged user account. The TUN
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device that the FIPS IPv6 adapter creates requires
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`CAP_NET_ADMIN` on Linux; the recipe below grants that privilege
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via a file capability on the binary, plus everything else the
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daemon needs to keep working without root: a service user
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account, file permissions on the config directory, and a systemd
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unit override to drop privileges.
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For the design context (why the adapter needs a TUN, how the
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adapter integrates with the kernel routing table), see
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[../design/fips-ipv6-adapter.md](../design/fips-ipv6-adapter.md).
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## Prerequisites
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- FIPS package installed (the postinst already creates the `fips`
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system group used for control-socket access).
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- `setcap` available (`apt install libcap2-bin` on Debian/Ubuntu;
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it is a standard utility on most distributions).
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- Operator access to systemd unit overrides (`systemctl edit`).
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## Step 1: Create a `fips` system user
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The package creates a `fips` system *group* but no matching user.
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Add a system user that belongs to the `fips` group:
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```sh
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sudo useradd --system --gid fips --no-create-home --shell /usr/sbin/nologin fips
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```
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The user has no home directory and no login shell — this account
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exists only to run the daemon.
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## Step 2: Grant `CAP_NET_ADMIN` to the binary
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Apply the file capability so the daemon can create the TUN device
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without root authority:
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```sh
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sudo setcap cap_net_admin+ep /usr/bin/fips
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```
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Verify:
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```sh
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getcap /usr/bin/fips
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# /usr/bin/fips cap_net_admin=ep
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```
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The binary can now create TUN devices when run by any user.
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**File-capability caveats:**
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- The capability is attached to the binary file. **Re-applying
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the capability after every package upgrade is required**,
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because package upgrades replace the binary file and lose the
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cap. The systemd override in Step 4 includes an `ExecStartPre`
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line that automates this.
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- File capabilities are stripped when the binary is copied across
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most filesystems and when it is downloaded via web tooling. If
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you build from source and install manually, remember to
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re-`setcap` after each rebuild.
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- `LD_LIBRARY_PATH` and similar environment-driven loader
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controls are stripped at exec time when file capabilities are
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present; this is normally what you want, but development
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workflows that rely on custom library paths may be surprised.
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## Step 3: Adjust config-file permissions
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The shipped `/etc/fips/fips.yaml` is mode `0600` and owned by
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`root:root`. The daemon needs to read it and, if persistent
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identity is enabled, write `/etc/fips/fips.key` into the same
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directory.
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```sh
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sudo chown -R fips:fips /etc/fips
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sudo chmod 0640 /etc/fips/fips.yaml
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```
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If `node.identity.persistent: true` is set and `fips.key` does
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not exist yet, leave `/etc/fips` itself writable by the `fips`
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user so the daemon can create it on first start. After the key
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file exists, you can tighten further:
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```sh
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sudo chmod 0600 /etc/fips/fips.key
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```
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## Step 4: Drop privileges in the systemd unit
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Create an override:
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```sh
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sudo systemctl edit fips.service
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```
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Add:
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```ini
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[Service]
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User=fips
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Group=fips
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AmbientCapabilities=CAP_NET_ADMIN
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NoNewPrivileges=no
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ExecStartPre=/sbin/setcap cap_net_admin+ep /usr/bin/fips
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```
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`User=` / `Group=` set the service identity.
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`AmbientCapabilities=` ensures the file capability granted in
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Step 2 actually carries into the daemon's process tree.
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`NoNewPrivileges=no` is required for file-capability execution
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to work — systemd defaults this to `yes` for hardened units,
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which would block the `setcap` from taking effect.
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`ExecStartPre=` re-applies the capability before each start,
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which makes the package-upgrade path self-heal.
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The unit's `RuntimeDirectory=fips` directive already arranges
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for `/run/fips/` to be created with the right ownership at
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service start, now as `fips:fips 0750` instead of
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`root:fips 0750`.
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Reload and restart:
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```sh
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sudo systemctl daemon-reload
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sudo systemctl restart fips
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```
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## Step 5: Verify
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Confirm the daemon is running as `fips`:
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```sh
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ps -eo user,cmd | grep '[/]usr/bin/fips'
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# fips /usr/bin/fips --config /etc/fips/fips.yaml
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```
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Confirm the TUN device came up (the `setcap` worked):
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```sh
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ip link show fips0
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# fips0: <POINTOPOINT,UP,...> mtu 1280 ...
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```
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Confirm the control socket is bound and accessible to the `fips`
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group:
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```sh
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ls -la /run/fips/control.sock
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# srwxrwx--- 1 fips fips ... /run/fips/control.sock
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```
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Add yourself to the `fips` group so you can use `fipsctl` /
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`fipstop` without `sudo`:
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```sh
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sudo usermod -aG fips $USER
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# log out and back in for the group change to take effect
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```
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Then:
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```sh
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fipsctl show status
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```
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## Caveats
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- **`fips-firewall.service` still runs as root.** Loading nftables
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rules into the kernel requires root regardless. The firewall
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unit is intentionally separate from the daemon unit.
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- **Bluetooth peers (`transports.ble.*`)** require additional
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privileges the `CAP_NET_ADMIN` setcap doesn't cover. If you use
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the BLE transport, you'll likely need to keep running as root
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or layer additional capability/D-Bus configuration; that path
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is not covered here.
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## See also
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- [persistent-identity.md](persistent-identity.md) — how the
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daemon manages `/etc/fips/fips.key`
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- [../design/fips-ipv6-adapter.md](../design/fips-ipv6-adapter.md)
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— IPv6 adapter design, TUN interface architecture
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- [../reference/security.md](../reference/security.md) —
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consolidated security surface
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- [../reference/configuration.md](../reference/configuration.md)
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— `tun.*` configuration block
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