Test policy firewall ownership across Docker modes

README.md

@@ -114,6 +114,13 @@ go build -trimpath -o bin/network-policy-manager ./cmd/network-policy-manager
 
 Run `sh scripts/validate.sh` on Unix-like systems or `pwsh -File scripts/validate.ps1` on Windows for formatting, tests, vetting, module verification, and reproducible-build checks.
 
+On a disposable root VM only, set `PASTURESTACK_POLICY_VM_MODE` to the actual
+Docker firewall mode (`nftables`, `iptables-nft`, or `iptables-legacy`) and run
+`go test ./internal/enforcement -run TestOwnedPolicyTableCoexistsWithDockerFirewallOnVM`.
+The test refuses an existing policy table, applies and removes only its own
+table, and compares Docker-owned rules before and after. This coexistence
+check does not claim a complete multi-host policy-traffic or upgrade gate.
+
 ## Licensing
 
 The inherited root `LICENSE` is preserved byte-for-byte and contains the Apache License 2.0 text. Go toolchain notices used for reproducible builds are included under `LICENSES/`. See `ORIGIN.md` for the preservation and release boundary.

internal/enforcement/firewall_vm_test.go

@@ -0,0 +1,89 @@
+package enforcement
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"net/netip"
+	"os"
+	"os/exec"
+	"strings"
+	"testing"
+)
+
+// Opt-in isolated-VM gate: policy owns only its table, regardless of which
+// firewall frontend Docker and Network Plugin Manager use on the host.
+func TestOwnedPolicyTableCoexistsWithDockerFirewallOnVM(t *testing.T) {
+	mode := os.Getenv("PASTURESTACK_POLICY_VM_MODE")
+	if mode == "" {
+		t.Skip("set PASTURESTACK_POLICY_VM_MODE on an isolated root VM")
+	}
+	if os.Geteuid() != 0 {
+		t.Fatal("firewall integration test requires root")
+	}
+	containers, err := exec.Command("docker", "ps", "-aq").CombinedOutput()
+	if err != nil || len(bytes.TrimSpace(containers)) != 0 {
+		t.Fatalf("refusing nonempty or uninspectable Docker host: %v: %s", err, containers)
+	}
+	if tableExists(context.Background(), "nft") {
+		t.Fatal("refusing to replace a pre-existing policy table")
+	}
+	driver, err := exec.Command("docker", "info", "--format", "{{.FirewallBackend.Driver}}").CombinedOutput()
+	if err != nil {
+		t.Fatalf("inspect Docker firewall driver: %v: %s", err, driver)
+	}
+	var snapshot []string
+	switch mode {
+	case "nftables":
+		if strings.TrimSpace(string(driver)) != "nftables" {
+			t.Fatalf("expected native Docker firewall, got %q", driver)
+		}
+		snapshot = []string{"nft", "list", "table", "ip", "docker-bridges"}
+	case "iptables-nft", "iptables-legacy":
+		if strings.TrimSpace(string(driver)) != "iptables" {
+			t.Fatalf("expected Docker iptables firewall, got %q", driver)
+		}
+		command := mode
+		if out, err := exec.Command(command, "-t", "nat", "-S", "DOCKER").CombinedOutput(); err != nil {
+			t.Fatalf("Docker does not own %s NAT: %v: %s", mode, err, out)
+		}
+		snapshot = []string{command + "-save"}
+	default:
+		t.Fatalf("unsupported VM test mode %q", mode)
+	}
+	readDocker := func() []byte {
+		out, err := exec.Command(snapshot[0], snapshot[1:]...).CombinedOutput()
+		if err != nil {
+			t.Fatalf("read Docker firewall snapshot: %v: %s", err, out)
+		}
+		return out
+	}
+	before := readDocker()
+	backend := NFTBackend{}
+	t.Cleanup(func() {
+		if err := backend.Cleanup(context.Background()); err != nil {
+			t.Errorf("cleanup test-owned policy table: %v", err)
+		}
+	})
+	plan := FirewallPlan{Subnet: netip.MustParsePrefix("198.18.250.0/24"), DefaultAction: "allow"}
+	for iteration := 0; iteration < 2; iteration++ {
+		if err := backend.Apply(context.Background(), plan); err != nil {
+			t.Fatalf("apply policy iteration %d: %v", iteration, err)
+		}
+		if !tableExists(context.Background(), "nft") {
+			t.Fatalf("policy table absent after apply %d", iteration)
+		}
+		if after := readDocker(); !bytes.Equal(before, after) {
+			t.Fatalf("Docker-owned rules changed after policy apply %d: %s", iteration, fmt.Sprint(snapshot))
+		}
+	}
+	if err := backend.Cleanup(context.Background()); err != nil {
+		t.Fatalf("cleanup policy table: %v", err)
+	}
+	if tableExists(context.Background(), "nft") {
+		t.Fatal("test-owned policy table remains after cleanup")
+	}
+	if after := readDocker(); !bytes.Equal(before, after) {
+		t.Fatalf("Docker-owned rules changed after policy cleanup: %s", fmt.Sprint(snapshot))
+	}
+}