tempfork/wireguard-windows/firewall: add.

This is a fork of wireguard-windows's firewall package, with
the firewall rules adjusted to better line up with tailscale's
needs.

The package was taken from commit 3cc76ed5f222ec82748ef3bd8c41d4b059e28cdb
in our fork of wireguard-go.

Signed-off-by: David Anderson <danderson@tailscale.com>

tempfork/wireguard-windows/firewall/blocker.go

@@ -0,0 +1,190 @@
+// +build windows
+
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019-2021 WireGuard LLC. All Rights Reserved.
+ */
+
+package firewall
+
+import (
+	"errors"
+	"net"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+type wfpObjectInstaller func(uintptr) error
+
+//
+// Fundamental WireGuard specific WFP objects.
+//
+type baseObjects struct {
+	provider windows.GUID
+	filters  windows.GUID
+}
+
+var wfpSession uintptr
+
+func createWfpSession() (uintptr, error) {
+	sessionDisplayData, err := createWtFwpmDisplayData0("WireGuard", "WireGuard dynamic session")
+	if err != nil {
+		return 0, wrapErr(err)
+	}
+
+	session := wtFwpmSession0{
+		displayData:          *sessionDisplayData,
+		flags:                cFWPM_SESSION_FLAG_DYNAMIC,
+		txnWaitTimeoutInMSec: windows.INFINITE,
+	}
+
+	sessionHandle := uintptr(0)
+
+	err = fwpmEngineOpen0(nil, cRPC_C_AUTHN_WINNT, nil, &session, unsafe.Pointer(&sessionHandle))
+	if err != nil {
+		return 0, wrapErr(err)
+	}
+
+	return sessionHandle, nil
+}
+
+func registerBaseObjects(session uintptr) (*baseObjects, error) {
+	bo := &baseObjects{}
+	var err error
+	bo.provider, err = windows.GenerateGUID()
+	if err != nil {
+		return nil, wrapErr(err)
+	}
+	bo.filters, err = windows.GenerateGUID()
+	if err != nil {
+		return nil, wrapErr(err)
+	}
+
+	//
+	// Register provider.
+	//
+	{
+		displayData, err := createWtFwpmDisplayData0("WireGuard", "WireGuard provider")
+		if err != nil {
+			return nil, wrapErr(err)
+		}
+		provider := wtFwpmProvider0{
+			providerKey: bo.provider,
+			displayData: *displayData,
+		}
+		err = fwpmProviderAdd0(session, &provider, 0)
+		if err != nil {
+			// TODO: cleanup entire call chain of these if failure?
+			return nil, wrapErr(err)
+		}
+	}
+
+	//
+	// Register filters sublayer.
+	//
+	{
+		displayData, err := createWtFwpmDisplayData0("WireGuard filters", "Permissive and blocking filters")
+		if err != nil {
+			return nil, wrapErr(err)
+		}
+		sublayer := wtFwpmSublayer0{
+			subLayerKey: bo.filters,
+			displayData: *displayData,
+			providerKey: &bo.provider,
+			weight:      ^uint16(0),
+		}
+		err = fwpmSubLayerAdd0(session, &sublayer, 0)
+		if err != nil {
+			return nil, wrapErr(err)
+		}
+	}
+
+	return bo, nil
+}
+
+func EnableFirewall(luid uint64, doNotRestrict bool, restrictToDNSServers []net.IP) error {
+	if wfpSession != 0 {
+		return errors.New("The firewall has already been enabled")
+	}
+
+	session, err := createWfpSession()
+	if err != nil {
+		return wrapErr(err)
+	}
+
+	objectInstaller := func(session uintptr) error {
+		baseObjects, err := registerBaseObjects(session)
+		if err != nil {
+			return wrapErr(err)
+		}
+
+		err = permitWireGuardService(session, baseObjects, 15)
+		if err != nil {
+			return wrapErr(err)
+		}
+
+		if !doNotRestrict {
+			err = allowDNS(session, baseObjects)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			err = permitLoopback(session, baseObjects, 13)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			err = permitTunInterface(session, baseObjects, 12, luid)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			err = permitDHCPIPv4(session, baseObjects, 12)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			err = permitDHCPIPv6(session, baseObjects, 12)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			err = permitNdp(session, baseObjects, 12)
+			if err != nil {
+				return wrapErr(err)
+			}
+
+			/* TODO: actually evaluate if this does anything and if we need this. It's layer 2; our other rules are layer 3.
+			 *  In other words, if somebody complains, try enabling it. For now, keep it off.
+			err = permitHyperV(session, baseObjects, 12)
+			if err != nil {
+				return wrapErr(err)
+			}
+			*/
+
+			err = blockAll(session, baseObjects, 0)
+			if err != nil {
+				return wrapErr(err)
+			}
+		}
+
+		return nil
+	}
+
+	err = runTransaction(session, objectInstaller)
+	if err != nil {
+		fwpmEngineClose0(session)
+		return wrapErr(err)
+	}
+
+	wfpSession = session
+	return nil
+}
+
+func DisableFirewall() {
+	if wfpSession != 0 {
+		fwpmEngineClose0(wfpSession)
+		wfpSession = 0
+	}
+}