Guard only packets addressed to this machine, and load the guard before the network and stop it only at shutdown (hq ADR 0103)

internal/bootstrap/adopted.go

@@ -36,7 +36,8 @@ const (
 // by default; it refuses the ports except from the machine itself — its loopback and the container
 // runtime's own networks — and from the private network, known by the interface a packet arrives
 // on and never by its source address; at prerouting, ahead of the runtime's destination
-// translation, in the inet family so both address families.
+// translation, in the inet family so both address families. It matches only packets addressed to
+// this machine: what the machine routes for others is never its business (novox/hq ADR 0103).
 //
 // Character for character the controller's (mesh-controller internal/catalogue AsGuard); a test
 // on each side holds its copy to the same golden text.
@@ -53,7 +54,7 @@ func AsGuard(ports []int) string {
 	b.WriteString("table inet mesh_guard {\n")
 	b.WriteString("\tchain prerouting {\n")
 	b.WriteString("\t\ttype filter hook prerouting priority raw; policy accept;\n")
-	fmt.Fprintf(&b, "\t\tiifname != \"lo\" iifname != \"docker0\" iifname != \"br-*\" "+
+	fmt.Fprintf(&b, "\t\tfib daddr type local iifname != \"lo\" iifname != \"docker0\" iifname != \"br-*\" "+
 		"iifname != \"mesh0\" tcp dport { %s } drop\n", strings.Join(listed, ", "))
 	b.WriteString("\t}\n")
 	b.WriteString("}\n")
@@ -65,8 +66,10 @@ func AsGuard(ports []int) string {
 func guardUnitText() string {
 	return "[Unit]\n" +
 		"Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)\n" +
-		"Before=network-pre.target\n" +
+		"DefaultDependencies=no\n" +
 		"Wants=network-pre.target\n" +
+		"Before=network-pre.target shutdown.target\n" +
+		"Conflicts=shutdown.target\n" +
 		"\n" +
 		"[Service]\n" +
 		"Type=oneshot\n" +

internal/bootstrap/adopted_test.go

@@ -21,7 +21,7 @@ delete table inet mesh_guard
 table inet mesh_guard {
 	chain prerouting {
 		type filter hook prerouting priority raw; policy accept;
-		iifname != "lo" iifname != "docker0" iifname != "br-*" iifname != "mesh0" tcp dport { 5432, 15672 } drop
+		fib daddr type local iifname != "lo" iifname != "docker0" iifname != "br-*" iifname != "mesh0" tcp dport { 5432, 15672 } drop
 	}
 }
 `
@@ -32,6 +32,42 @@ func TestTheGuardIsExactlyThisTable(t *testing.T) {
 	}
 }
 
+// The same golden unit the controller's test holds its guard unit to. It is loaded before the
+// network is up, so it carries no default dependencies, and it is stopped only at shutdown.
+const goldenGuardUnit = `[Unit]
+Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)
+DefaultDependencies=no
+Wants=network-pre.target
+Before=network-pre.target shutdown.target
+Conflicts=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=nft -f /etc/mesh/guard.nft
+ExecReload=nft -f /etc/mesh/guard.nft
+ExecStop=nft delete table inet mesh_guard
+
+[Install]
+WantedBy=multi-user.target
+`
+
+func TestTheGuardUnitIsExactlyThisUnit(t *testing.T) {
+	if got := guardUnitText(); got != goldenGuardUnit {
+		t.Fatalf("the guard's unit changed:\n%s", got)
+	}
+}
+
+func TestTheGuardRefusesOnlyWhatIsAddressedToThisMachine(t *testing.T) {
+	// A machine that routes for others — a predecessor's private-network hub — must not have a
+	// packet for another machine's database port refused (novox/hq ADR 0103).
+	for _, line := range strings.Split(AsGuard([]int{5432}), "\n") {
+		if strings.Contains(line, " drop") && !strings.HasPrefix(strings.TrimSpace(line), "fib daddr type local ") {
+			t.Errorf("a refusal matches packets not addressed to this machine: %q", line)
+		}
+	}
+}
+
 func TestAnAdoptedBundleLoadsNoDroppingTableAndExactlyTheGuard(t *testing.T) {
 	r := producedBundle(t)
 	p := FoundationPorts{Store: 5433, Management: 15673}