tailscale/wf/firewall.go

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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build windows
package wf
import (
"fmt"
"net/netip"
"os"
"golang.org/x/sys/windows"
"inet.af/wf"
"tailscale.com/net/netaddr"
)
// Known addresses.
var (
linkLocalRange = netip.MustParsePrefix("ff80::/10")
linkLocalDHCPMulticast = netip.MustParseAddr("ff02::1:2")
siteLocalDHCPMulticast = netip.MustParseAddr("ff05::1:3")
linkLocalRouterMulticast = netip.MustParseAddr("ff02::2")
)
type direction int
const (
directionInbound direction = iota
directionOutbound
directionBoth
)
type protocol int
const (
protocolV4 protocol = iota
protocolV6
protocolAll
)
// getLayers returns the wf.LayerIDs where the rules should be added based
// on the protocol and direction.
func (p protocol) getLayers(d direction) []wf.LayerID {
var layers []wf.LayerID
if p == protocolAll || p == protocolV4 {
if d == directionBoth || d == directionInbound {
layers = append(layers, wf.LayerALEAuthRecvAcceptV4)
}
if d == directionBoth || d == directionOutbound {
layers = append(layers, wf.LayerALEAuthConnectV4)
}
}
if p == protocolAll || p == protocolV6 {
if d == directionBoth || d == directionInbound {
layers = append(layers, wf.LayerALEAuthRecvAcceptV6)
}
if d == directionBoth || d == directionOutbound {
layers = append(layers, wf.LayerALEAuthConnectV6)
}
}
return layers
}
func ruleName(action wf.Action, l wf.LayerID, name string) string {
switch l {
case wf.LayerALEAuthConnectV4:
return fmt.Sprintf("%s outbound %s (IPv4)", action, name)
case wf.LayerALEAuthConnectV6:
return fmt.Sprintf("%s outbound %s (IPv6)", action, name)
case wf.LayerALEAuthRecvAcceptV4:
return fmt.Sprintf("%s inbound %s (IPv4)", action, name)
case wf.LayerALEAuthRecvAcceptV6:
return fmt.Sprintf("%s inbound %s (IPv6)", action, name)
}
return ""
}
// Firewall uses the Windows Filtering Platform to implement a network firewall.
type Firewall struct {
luid uint64
providerID wf.ProviderID
sublayerID wf.SublayerID
session *wf.Session
permittedRoutes map[netip.Prefix][]*wf.Rule
}
// New returns a new Firewall for the provided interface ID.
func New(luid uint64) (*Firewall, error) {
session, err := wf.New(&wf.Options{
Name: "Tailscale firewall",
Dynamic: true,
})
if err != nil {
return nil, err
}
wguid, err := windows.GenerateGUID()
if err != nil {
return nil, err
}
providerID := wf.ProviderID(wguid)
if err := session.AddProvider(&wf.Provider{
ID: providerID,
Name: "Tailscale provider",
}); err != nil {
return nil, err
}
wguid, err = windows.GenerateGUID()
if err != nil {
return nil, err
}
sublayerID := wf.SublayerID(wguid)
if err := session.AddSublayer(&wf.Sublayer{
ID: sublayerID,
Name: "Tailscale permissive and blocking filters",
Weight: 0,
}); err != nil {
return nil, err
}
f := &Firewall{
luid: luid,
session: session,
providerID: providerID,
sublayerID: sublayerID,
permittedRoutes: make(map[netip.Prefix][]*wf.Rule),
}
if err := f.enable(); err != nil {
return nil, err
}
return f, nil
}
type weight uint64
const (
weightTailscaleTraffic weight = 15
weightKnownTraffic weight = 12
weightCatchAll weight = 0
)
func (f *Firewall) enable() error {
if err := f.permitTailscaleService(weightTailscaleTraffic); err != nil {
return fmt.Errorf("permitTailscaleService failed: %w", err)
}
if err := f.permitTunInterface(weightTailscaleTraffic); err != nil {
return fmt.Errorf("permitTunInterface failed: %w", err)
}
if err := f.permitDNS(weightTailscaleTraffic); err != nil {
return fmt.Errorf("permitDNS failed: %w", err)
}
if err := f.permitLoopback(weightTailscaleTraffic); err != nil {
return fmt.Errorf("permitLoopback failed: %w", err)
}
if err := f.permitDHCPv4(weightKnownTraffic); err != nil {
return fmt.Errorf("permitDHCPv4 failed: %w", err)
}
if err := f.permitDHCPv6(weightKnownTraffic); err != nil {
return fmt.Errorf("permitDHCPv6 failed: %w", err)
}
if err := f.permitNDP(weightKnownTraffic); err != nil {
return fmt.Errorf("permitNDP failed: %w", 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.
* TODO(maisem): implement this.
err = permitHyperV(session, baseObjects, weightKnownTraffic)
if err != nil {
return wrapErr(err)
}
*/
if err := f.blockAll(weightCatchAll); err != nil {
return fmt.Errorf("blockAll failed: %w", err)
}
return nil
}
// UpdatedPermittedRoutes adds rules to allow incoming and outgoing connections
// from the provided prefixes. It will also remove rules for routes that were
// previously added but have been removed.
func (f *Firewall) UpdatePermittedRoutes(newRoutes []netip.Prefix) error {
var routesToAdd []netip.Prefix
routeMap := make(map[netip.Prefix]bool)
for _, r := range newRoutes {
routeMap[r] = true
if _, ok := f.permittedRoutes[r]; !ok {
routesToAdd = append(routesToAdd, r)
}
}
var routesToRemove []netip.Prefix
for r := range f.permittedRoutes {
if !routeMap[r] {
routesToRemove = append(routesToRemove, r)
}
}
for _, r := range routesToRemove {
for _, rule := range f.permittedRoutes[r] {
if err := f.session.DeleteRule(rule.ID); err != nil {
return err
}
}
delete(f.permittedRoutes, r)
}
for _, r := range routesToAdd {
conditions := []*wf.Match{
{
Field: wf.FieldIPRemoteAddress,
Op: wf.MatchTypeEqual,
Value: r,
},
}
var p protocol
if r.Addr().Is4() {
p = protocolV4
} else {
p = protocolV6
}
rules, err := f.addRules("local route", weightKnownTraffic, conditions, wf.ActionPermit, p, directionBoth)
if err != nil {
return err
}
f.permittedRoutes[r] = rules
}
return nil
}
func (f *Firewall) newRule(name string, w weight, layer wf.LayerID, conditions []*wf.Match, action wf.Action) (*wf.Rule, error) {
id, err := windows.GenerateGUID()
if err != nil {
return nil, err
}
return &wf.Rule{
Name: ruleName(action, layer, name),
ID: wf.RuleID(id),
Provider: f.providerID,
Sublayer: f.sublayerID,
Layer: layer,
Weight: uint64(w),
Conditions: conditions,
Action: action,
}, nil
}
func (f *Firewall) addRules(name string, w weight, conditions []*wf.Match, action wf.Action, p protocol, d direction) ([]*wf.Rule, error) {
var rules []*wf.Rule
for _, l := range p.getLayers(d) {
r, err := f.newRule(name, w, l, conditions, action)
if err != nil {
return nil, err
}
if err := f.session.AddRule(r); err != nil {
return nil, err
}
rules = append(rules, r)
}
return rules, nil
}
func (f *Firewall) blockAll(w weight) error {
_, err := f.addRules("all", w, nil, wf.ActionBlock, protocolAll, directionBoth)
return err
}
func (f *Firewall) permitNDP(w weight) error {
// These are aliased according to:
// https://social.msdn.microsoft.com/Forums/azure/en-US/eb2aa3cd-5f1c-4461-af86-61e7d43ccc23/filtering-icmp-by-type-code?forum=wfp
fieldICMPType := wf.FieldIPLocalPort
fieldICMPCode := wf.FieldIPRemotePort
var icmpConditions = func(t, c uint16, remoteAddress any) []*wf.Match {
conditions := []*wf.Match{
{
Field: wf.FieldIPProtocol,
Op: wf.MatchTypeEqual,
Value: wf.IPProtoICMPV6,
},
{
Field: fieldICMPType,
Op: wf.MatchTypeEqual,
Value: t,
},
{
Field: fieldICMPCode,
Op: wf.MatchTypeEqual,
Value: c,
},
}
if remoteAddress != nil {
conditions = append(conditions, &wf.Match{
Field: wf.FieldIPRemoteAddress,
Op: wf.MatchTypeEqual,
Value: linkLocalRouterMulticast,
})
}
return conditions
}
/* TODO: actually handle the hop limit somehow! The rules should vaguely be:
* - icmpv6 133: must be outgoing, dst must be FF02::2/128, hop limit must be 255
* - icmpv6 134: must be incoming, src must be FE80::/10, hop limit must be 255
* - icmpv6 135: either incoming or outgoing, hop limit must be 255
* - icmpv6 136: either incoming or outgoing, hop limit must be 255
* - icmpv6 137: must be incoming, src must be FE80::/10, hop limit must be 255
*/
//
// Router Solicitation Message
// ICMP type 133, code 0. Outgoing.
//
conditions := icmpConditions(133, 0, linkLocalRouterMulticast)
if _, err := f.addRules("NDP type 133", w, conditions, wf.ActionPermit, protocolV6, directionOutbound); err != nil {
return err
}
//
// Router Advertisement Message
// ICMP type 134, code 0. Incoming.
//
conditions = icmpConditions(134, 0, linkLocalRange)
if _, err := f.addRules("NDP type 134", w, conditions, wf.ActionPermit, protocolV6, directionInbound); err != nil {
return err
}
//
// Neighbor Solicitation Message
// ICMP type 135, code 0. Bi-directional.
//
conditions = icmpConditions(135, 0, nil)
if _, err := f.addRules("NDP type 135", w, conditions, wf.ActionPermit, protocolV6, directionBoth); err != nil {
return err
}
//
// Neighbor Advertisement Message
// ICMP type 136, code 0. Bi-directional.
//
conditions = icmpConditions(136, 0, nil)
if _, err := f.addRules("NDP type 136", w, conditions, wf.ActionPermit, protocolV6, directionBoth); err != nil {
return err
}
//
// Redirect Message
// ICMP type 137, code 0. Incoming.
//
conditions = icmpConditions(137, 0, linkLocalRange)
if _, err := f.addRules("NDP type 137", w, conditions, wf.ActionPermit, protocolV6, directionInbound); err != nil {
return err
}
return nil
}
func (f *Firewall) permitDHCPv6(w weight) error {
var dhcpConditions = func(remoteAddrs ...any) []*wf.Match {
conditions := []*wf.Match{
{
Field: wf.FieldIPProtocol,
Op: wf.MatchTypeEqual,
Value: wf.IPProtoUDP,
},
{
Field: wf.FieldIPLocalAddress,
Op: wf.MatchTypeEqual,
Value: linkLocalRange,
},
{
Field: wf.FieldIPLocalPort,
Op: wf.MatchTypeEqual,
Value: uint16(546),
},
{
Field: wf.FieldIPRemotePort,
Op: wf.MatchTypeEqual,
Value: uint16(547),
},
}
for _, a := range remoteAddrs {
conditions = append(conditions, &wf.Match{
Field: wf.FieldIPRemoteAddress,
Op: wf.MatchTypeEqual,
Value: a,
})
}
return conditions
}
conditions := dhcpConditions(linkLocalDHCPMulticast, siteLocalDHCPMulticast)
if _, err := f.addRules("DHCP request", w, conditions, wf.ActionPermit, protocolV6, directionOutbound); err != nil {
return err
}
conditions = dhcpConditions(linkLocalRange)
if _, err := f.addRules("DHCP response", w, conditions, wf.ActionPermit, protocolV6, directionInbound); err != nil {
return err
}
return nil
}
func (f *Firewall) permitDHCPv4(w weight) error {
var dhcpConditions = func(remoteAddrs ...any) []*wf.Match {
conditions := []*wf.Match{
{
Field: wf.FieldIPProtocol,
Op: wf.MatchTypeEqual,
Value: wf.IPProtoUDP,
},
{
Field: wf.FieldIPLocalPort,
Op: wf.MatchTypeEqual,
Value: uint16(68),
},
{
Field: wf.FieldIPRemotePort,
Op: wf.MatchTypeEqual,
Value: uint16(67),
},
}
for _, a := range remoteAddrs {
conditions = append(conditions, &wf.Match{
Field: wf.FieldIPRemoteAddress,
Op: wf.MatchTypeEqual,
Value: a,
})
}
return conditions
}
conditions := dhcpConditions(netaddr.IPv4(255, 255, 255, 255))
if _, err := f.addRules("DHCP request", w, conditions, wf.ActionPermit, protocolV4, directionOutbound); err != nil {
return err
}
conditions = dhcpConditions()
if _, err := f.addRules("DHCP response", w, conditions, wf.ActionPermit, protocolV4, directionInbound); err != nil {
return err
}
return nil
}
func (f *Firewall) permitTunInterface(w weight) error {
condition := []*wf.Match{
{
Field: wf.FieldIPLocalInterface,
Op: wf.MatchTypeEqual,
Value: f.luid,
},
}
_, err := f.addRules("on TUN", w, condition, wf.ActionPermit, protocolAll, directionBoth)
return err
}
func (f *Firewall) permitLoopback(w weight) error {
condition := []*wf.Match{
{
Field: wf.FieldFlags,
Op: wf.MatchTypeFlagsAllSet,
Value: wf.ConditionFlagIsLoopback,
},
}
_, err := f.addRules("on loopback", w, condition, wf.ActionPermit, protocolAll, directionBoth)
return err
}
func (f *Firewall) permitDNS(w weight) error {
conditions := []*wf.Match{
{
Field: wf.FieldIPRemotePort,
Op: wf.MatchTypeEqual,
Value: uint16(53),
},
// Repeat the condition type for logical OR.
{
Field: wf.FieldIPProtocol,
Op: wf.MatchTypeEqual,
Value: wf.IPProtoUDP,
},
{
Field: wf.FieldIPProtocol,
Op: wf.MatchTypeEqual,
Value: wf.IPProtoTCP,
},
}
_, err := f.addRules("DNS", w, conditions, wf.ActionPermit, protocolAll, directionBoth)
return err
}
func (f *Firewall) permitTailscaleService(w weight) error {
currentFile, err := os.Executable()
if err != nil {
return err
}
appID, err := wf.AppID(currentFile)
if err != nil {
return fmt.Errorf("could not get app id for %q: %w", currentFile, err)
}
conditions := []*wf.Match{
{
Field: wf.FieldALEAppID,
Op: wf.MatchTypeEqual,
Value: appID,
},
}
_, err = f.addRules("unrestricted traffic for Tailscale service", w, conditions, wf.ActionPermit, protocolAll, directionBoth)
return err
}