state: add regression test for NodeKey-rotation binding

hscontrol/state/auth_nodekey_binding_test.go

@@ -0,0 +1,74 @@
+package state
+
+import (
+	"testing"
+	"time"
+
+	"github.com/juanfont/headscale/hscontrol/db"
+	"github.com/juanfont/headscale/hscontrol/types"
+	"github.com/stretchr/testify/require"
+	"tailscale.com/tailcfg"
+)
+
+// TestPreAuthKeyReauthRejectsVictimNodeKey ensures the PAK re-registration
+// rotation path enforces the same 1:1 NodeKey<->MachineKey binding the other
+// registration paths do. NodeKeys are public (peers learn them from the
+// netmap), so an authenticated attacker must not be able to rotate their own
+// node's NodeKey onto a victim's NodeKey: doing so poisons the NodeStore
+// NodeKey index and denies the victim service.
+func TestPreAuthKeyReauthRejectsVictimNodeKey(t *testing.T) {
+	dbPath := t.TempDir() + "/headscale.db"
+	cfg := persistTestConfig(dbPath)
+
+	database, err := db.NewHeadscaleDatabase(cfg)
+	require.NoError(t, err)
+
+	// Attacker owns N_a under U_a with machine key M_a.
+	attacker := database.CreateUserForTest("attacker")
+	attackerNode := database.CreateRegisteredNodeForTest(attacker, "attacker-node")
+	attackerMachineKey := attackerNode.MachineKey
+
+	// Victim owns N_v under U_v with a distinct, public NodeKey K_v.
+	victim := database.CreateUserForTest("victim")
+	victimNode := database.CreateRegisteredNodeForTest(victim, "victim-node")
+	victimNodeKey := victimNode.NodeKey
+
+	require.NotEqual(t, attackerNode.NodeKey, victimNodeKey,
+		"precondition: attacker and victim must have distinct NodeKeys")
+	require.NotEqual(t, attackerNode.MachineKey, victimNode.MachineKey,
+		"precondition: attacker and victim must have distinct MachineKeys")
+
+	require.NoError(t, database.Close())
+
+	s, err := NewState(cfg)
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = s.Close() })
+
+	// Attacker mints their own valid pre-auth key for their own user.
+	attackerUserID := types.UserID(attacker.ID)
+	pak, err := s.CreatePreAuthKey(&attackerUserID, true, false, nil, nil)
+	require.NoError(t, err)
+
+	// Attacker re-registers over their own noise session (machine key M_a)
+	// with a valid PAK but carries the victim's NodeKey K_v and a non-past
+	// expiry (skipping the logout-first branch).
+	clientExpiry := time.Now().Add(180 * 24 * time.Hour)
+	regReq := tailcfg.RegisterRequest{
+		Auth:    &tailcfg.RegisterResponseAuth{AuthKey: pak.Key},
+		NodeKey: victimNodeKey,
+		Expiry:  clientExpiry,
+		Hostinfo: &tailcfg.Hostinfo{
+			Hostname: "attacker-node",
+		},
+	}
+
+	_, _, err = s.HandleNodeFromPreAuthKey(regReq, attackerMachineKey)
+	require.ErrorIs(t, err, ErrNodeKeyInUse,
+		"attacker must not be able to claim the victim's NodeKey via PAK re-registration")
+
+	// The victim's NodeKey index must still resolve to the victim's node.
+	resolved, ok := s.nodeStore.GetNodeByNodeKey(victimNodeKey)
+	require.True(t, ok, "victim NodeKey must still be present in the index")
+	require.Equal(t, victimNode.MachineKey, resolved.MachineKey(),
+		"victim NodeKey must remain bound to the victim's MachineKey")
+}