mesh-controller/internal/overlay/declaration_test.go

package overlay

import (
	"encoding/json"
	"fmt"
	"strings"
	"testing"
)

func declarationFor(t *testing.T, node Node, peers []Peer) (string, []map[string]any) {
	t.Helper()
	raw, err := Declaration(node, peers, "")
	if err != nil {
		t.Fatal(err)
	}
	var d struct {
		Declaration int              `json:"declaration"`
		Resources   []map[string]any `json:"resources"`
	}
	if err := json.Unmarshal(raw, &d); err != nil {
		t.Fatal(err)
	}
	if d.Declaration != 1 {
		t.Fatalf("declaration version %d", d.Declaration)
	}
	for _, r := range d.Resources {
		if r["type"] == "file" {
			return r["content"].(string), d.Resources
		}
	}
	t.Fatal("the declaration has no configuration file in it")
	return "", nil
}

func TestNoPrivateKeyEverTravels(t *testing.T) {
	// The property the whole design rests on: the node generated its keypair and kept the private
	// half, so the mesh composes a configuration for a node it cannot impersonate. A private key
	// appearing here would mean the control plane had one — and a copy of its database would then
	// be every node's network identity.
	config, _ := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"},
		[]Peer{{Name: "anchor", Key: "HUB", Allowed: "10.42.0.0/16", Endpoint: "198.51.100.1:51820"}})

	if strings.Contains(config, "PrivateKey") {
		t.Error("the configuration carries a PrivateKey line; the mesh must never hold one")
	}
	if !strings.Contains(config, "private-key "+DefaultKeyPath) {
		t.Error("the configuration does not point at the key file the node wrote, so the " +
			"interface would come up with no key at all")
	}
}

func TestTheDeclarationUsesOnlyShapesTheHostAlreadyHas(t *testing.T) {
	// Connectivity needs nothing new from tier 0, and that is worth holding: the host does not
	// know what a private network is, and should not learn.
	_, resources := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)

	allowed := map[string]bool{"package": true, "file": true, "service": true,
		"directory": true, "container": true, "action": true}
	for _, r := range resources {
		if !allowed[r["type"].(string)] {
			t.Errorf("the overlay declaration uses %q, which the host does not have", r["type"])
		}
	}
}

func TestTheInterfaceComesBackAfterAReboot(t *testing.T) {
	// A node whose overlay only exists while something is watching is not a node that survives
	// being switched off and on — and it would come back unreachable, which is the worst way to
	// come back.
	_, resources := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	for _, r := range resources {
		if r["type"] == "service" {
			if r["boot"] != "enabled" {
				t.Error("the overlay interface is not enabled at boot")
			}
			if r["state"] != "running" {
				t.Error("the overlay interface is not asked to be running")
			}
			return
		}
	}
	t.Error("nothing in the declaration brings the interface up")
}

func TestTheConfigurationIsNotWorldReadable(t *testing.T) {
	// It lists every peer's key and endpoint, which is a map of the mesh. Not secret the way a
	// private key is, and not something to leave readable on a machine somebody else also uses.
	// The peer list specifically, not every file. `/etc/hosts` is in here too and must be
	// world-readable, or nothing on the machine resolves anything — a check that swept all files
	// would force it to 0600 and break the machine to protect a file that is not secret.
	_, resources := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	for _, r := range resources {
		if r["id"] == "overlay-config" && r["mode"] != "0600" {
			t.Errorf("the peer list is mode %v", r["mode"])
		}
		if r["id"] == "mesh-names" && r["mode"] != "0644" {
			t.Errorf("the name file is mode %v; nothing on the machine could read it", r["mode"])
		}
	}
}

func TestAPeerThatCannotBeDialledSaysSo(t *testing.T) {
	// A [Peer] with no Endpoint is correct and looks like a mistake. Saying why stops somebody
	// helpfully adding one that cannot work.
	config, _ := declarationFor(t, Node{Name: "anchor", Key: "HUB", Address: "10.42.0.1",
		Endpoint: "198.51.100.1:51820", Hub: true},
		[]Peer{{Name: "laptop", Key: "PUB", Allowed: "10.42.0.2/32", Why: "routes through this hub"}})

	if strings.Contains(config, "Endpoint =") {
		t.Error("an endpoint was written for a peer that has none")
	}
	if !strings.Contains(config, "cannot be dialled") {
		t.Error("the file does not say why that peer has no endpoint")
	}
}

func TestTheFileSaysNotToEditIt(t *testing.T) {
	// It is replaced whenever the graph changes. An edit survives until then and vanishes, which
	// is worse than never being applied — the machine works, then stops, and nothing changed
	// that anybody remembers.
	config, _ := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	if !strings.Contains(config, "Do not edit") {
		t.Error("a generated file does not say it is generated")
	}
}

func TestANodeWithNoAddressIsRefused(t *testing.T) {
	// Rather than a configuration with a blank address, which wg-quick would reject on the
	// machine, at boot, where the failure is much harder to see.
	if _, err := Declaration(Node{Name: "laptop", Key: "PUB"}, nil, ""); err == nil {
		t.Fatal("a node with no overlay address was given a configuration")
	}
}

func TestOnlyAReachableNodeListens(t *testing.T) {
	// A ListenPort on a node nothing can dial is a port open for no reason.
	config, _ := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	if strings.Contains(config, "ListenPort") {
		t.Error("a node that cannot be dialled was told to listen")
	}
	config, _ = declarationFor(t, Node{Name: "anchor", Key: "HUB", Address: "10.42.0.1",
		Endpoint: "198.51.100.1:51820"}, nil)
	if !strings.Contains(config, "ListenPort = 51820") {
		t.Error("a reachable node does not listen on the port its endpoint names")
	}
}

func TestTheServiceIsRestartedWhenThePeerListChanges(t *testing.T) {
	// The fault this exists to catch, found in the lab the moment a third node arrived: a running
	// WireGuard interface does not re-read its configuration. The file was replaced, the service
	// was already running so nothing reloaded it, and every existing node kept a network that no
	// longer matched the mesh — while looking entirely successful.
	//
	// So the declaration has to verify what the interface is *carrying*, not what the file says.
	//
	// And it must be declared state rather than a command: the host refuses an action arriving
	// over the link (novox/hq ADR 0005), correctly, which is how this shape was arrived at. There
	// is a test below that no action is ever in here.
	_, resources := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"},
		[]Peer{{Name: "anchor", Key: "HUBKEY", Allowed: "10.42.0.0/16"}})

	for _, r := range resources {
		if r["type"] != "service" {
			continue
		}
		reflects := fmt.Sprint(r["restart-on"])
		if !strings.Contains(reflects, "overlay-config") {
			t.Errorf("the interface does not restart when its configuration changes: %v", reflects)
		}
		return
	}
	t.Error("nothing in the declaration brings the interface up")
}

func TestTheOverlayDeclarationCarriesNoAction(t *testing.T) {
	// The link may not carry an action, and the host refuses a declaration containing one — whole,
	// not in part. An overlay declaration with an action in it does not half-apply: it leaves the
	// node with no network at all.
	_, resources := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	for _, r := range resources {
		if r["type"] == "action" {
			t.Errorf("the declaration contains an action (%v); the host will refuse the whole "+
				"thing and the node will have no network", r["id"])
		}
	}
}

func TestTheHubForwardsAndNobodyElseDoes(t *testing.T) {
	// A hub carries traffic between its spokes, and Linux does not forward packets unless told
	// to. Without it every spoke reaches the hub perfectly and no spoke reaches any other — which
	// is how it failed in the lab, and it presents as a peering problem rather than a kernel
	// setting, so it is worth being sure of.
	hub, _ := declarationFor(t, Node{Name: "anchor", Key: "HUB", Address: "10.42.0.1",
		Endpoint: "198.51.100.1:51820", Hub: true}, nil)
	if !strings.Contains(hub, "ip_forward=1") {
		t.Error("the hub does not enable forwarding, so its spokes cannot reach each other")
	}
	if !strings.Contains(hub, "ip_forward=0") {
		t.Error("the hub never stops forwarding; a machine that stops being the hub would keep " +
			"passing traffic it is no longer part of")
	}

	// And past the machine's own firewall. Any node with a container runtime has FORWARD set to
	// DROP by Docker, so enabling ip_forward alone changes nothing — which is exactly how it
	// failed, with every spoke reaching the hub and no spoke reaching any other.
	// Checked as PostUp specifically. "contains FORWARD" passes on the PostDown line alone,
	// which would leave a hub that tears down rules it never put up.
	if !strings.Contains(hub, "PostUp = command -v iptables") {
		t.Error("the hub does not open its own firewall, so a container runtime's DROP policy " +
			"silently eats everything it was supposed to carry")
	}
	if !strings.Contains(hub, "PostDown = command -v iptables") {
		t.Error("the hub never removes those rules, so a machine that stops being the hub keeps " +
			"passing traffic it is no longer part of")
	}

	spoke, _ := declarationFor(t, Node{Name: "laptop", Key: "PUB", Address: "10.42.0.2"}, nil)
	if strings.Contains(spoke, "FORWARD") {
		t.Error("a spoke was given forwarding rules it has no use for")
	}
	if strings.Contains(spoke, "ip_forward") {
		t.Error("a spoke was told to forward packets, which is not its job and widens what a " +
			"compromised one could do")
	}
}