ipn/{ipn,ipnlocal}: add per-user policy snapshots to IPN bus (#20135)

This adds the NotifyInitialPolicy watch option and the Policy field in
Notify so that clients can receive the effective policy snapshot via IPN
bus.

This extends policyclient.Client so ipnlocal can get and watch policy
snapshots, which is used by sysPolicyChanged to notify watchers.

User-scoped policy store registration, management, and cleanup will be
added in a follow-up

Updates tailscale/corp#42259

Signed-off-by: kari <kari@tailscale.com>

cmd/derper/depaware.txt

@@ -166,7 +166,7 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
         tailscale.com/util/syspolicy/pkey                            from tailscale.com/ipn+
         tailscale.com/util/syspolicy/policyclient                    from tailscale.com/ipn
         tailscale.com/util/syspolicy/ptype                           from tailscale.com/util/syspolicy/policyclient+
-        tailscale.com/util/syspolicy/setting                         from tailscale.com/client/local
+        tailscale.com/util/syspolicy/setting                         from tailscale.com/client/local+
         tailscale.com/util/testenv                                   from tailscale.com/net/bakedroots+
         tailscale.com/util/usermetric                                from tailscale.com/health
         tailscale.com/util/vizerror                                  from tailscale.com/tailcfg+

ipn/backend.go

@@ -19,6 +19,7 @@
 	"tailscale.com/types/netmap"
 	"tailscale.com/types/structs"
 	"tailscale.com/types/views"
+	"tailscale.com/util/syspolicy/policyclient"
 )
 
 type State int
@@ -173,6 +174,18 @@ type EngineStatus struct {
 	// not request it.
 	NotifyInProcessNoDisconnect NotifyWatchOpt = 1 << 16
 
+	// NotifySysPolicyChanges, if set, causes the first Notify message, which is sent
+	// immediately, to contain the current effective [setting.Snapshot] in
+	// [Notify.Policy]. [Notify.Policy] is included in subsequent messages whenever
+	// the effective policy changes.
+	//
+	// The snapshot is scoped to the connected user's identity (on Windows,
+	// derived from the named-pipe token's SID).
+	//
+	// The [setting.Snapshot] that is delivered is a full snapshot on every
+	// change.
+	NotifySysPolicyChanges NotifyWatchOpt = 1 << 17
+
 	// NotifyPeerWireGuardState, if set, opts the watcher into
 	// WireGuard session state notifications via [Notify.PeerState].
 	// The first Notify sent to the watcher includes a dump of current
@@ -220,6 +233,7 @@ func (o NotifyWatchOpt) String() string {
 	try(NotifyInitialStatus, "NotifyInitialStatus")
 	try(NotifyPeerPatches, "NotifyPeerPatches")
 	try(NotifyInProcessNoDisconnect, "NotifyInProcessNoDisconnect")
+	try(NotifySysPolicyChanges, "NotifySysPolicyChanges")
 	try(NotifyPeerWireGuardState, "NotifyPeerWireGuardState")
 
 	if mask != o {
@@ -453,6 +467,13 @@ type Notify struct {
 	// be the best exit node for the current network conditions.
 	SuggestedExitNode *tailcfg.StableNodeID `json:",omitzero"`
 
+	// Policy, if non-nil, is the effective policy snapshot for the
+	// connected user. It is scoped per-user: per-user policy settings
+	// are merged with device-wide settings, with device-wide taking
+	// precedence. Sent initially when [NotifySysPolicyChanges] is set,
+	// and on change thereafter.
+	Policy *policyclient.PolicySnapshot `json:",omitzero"`
+
 	// type is mirrored in xcode/IPN/Core/LocalAPI/Model/LocalAPIModel.swift
 }
 

ipn/ipnlocal/bus.go

@@ -247,5 +247,6 @@ func isNotableNotify(n *ipn.Notify) bool {
 		len(n.IncomingFiles) > 0 ||
 		len(n.OutgoingFiles) > 0 ||
 		n.FilesWaiting != nil ||
-		n.SuggestedExitNode != nil
+		n.SuggestedExitNode != nil ||
+		n.Policy != nil
 }

ipn/ipnlocal/local.go

@@ -2330,8 +2330,8 @@ func (b *LocalBackend) applyExitNodeSysPolicyLocked(prefs *ipn.Prefs) (anyChange
 // registerSysPolicyWatch subscribes to syspolicy change notifications
 // and immediately applies the effective syspolicy settings to the current profile.
 func (b *LocalBackend) registerSysPolicyWatch() (unregister func(), err error) {
-	if unregister, err = b.polc.RegisterChangeCallback(b.sysPolicyChanged); err != nil {
-		return nil, fmt.Errorf("syspolicy: LocalBacked failed to register policy change callback: %v", err)
+	if unregister, err = b.polc.RegisterChangeCallback("", b.sysPolicyChanged); err != nil {
+		return nil, fmt.Errorf("syspolicy: LocalBackend failed to register policy change callback: %v", err)
 	}
 	if prefs, anyChange := b.reconcilePrefs(); anyChange {
 		b.logf("syspolicy: changed initial profile prefs: %v", prefs.Pretty())
@@ -2392,6 +2392,28 @@ func (b *LocalBackend) sysPolicyChanged(policy policyclient.PolicyChange) {
 	}
 }
 
+// sysPolicyChangedForSession is called when the effective policy for a session's
+// user changes. It fetches the new snapshot and sends it to that session.
+func (b *LocalBackend) sysPolicyChangedForSession(sess *watchSession) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	snapshot, err := b.polc.GetPolicySnapshot("")
+	if err != nil || snapshot == nil {
+		return
+	}
+
+	n := ipn.Notify{Policy: snapshot, Version: version.Long()}
+	for _, f := range b.extHost.Hooks().MutateNotifyLocked {
+		f(&n)
+	}
+	nForSess := b.notifyForSessionLocked(sess, &n)
+	select {
+	case sess.ch <- nForSess:
+	default:
+	}
+}
+
 var (
 	_ controlclient.NetmapDeltaUpdater  = (*LocalBackend)(nil)
 	_ controlclient.PacketFilterUpdater = (*LocalBackend)(nil)
@@ -3711,7 +3733,10 @@ func (b *LocalBackend) WatchNotificationsAs(ctx context.Context, actor ipnauth.A
 	deadlockDone := b.CheckDeadlocks()
 	b.mu.Lock()
 
-	const initialBits = ipn.NotifyInitialState | ipn.NotifyInitialPrefs | ipn.NotifyInitialNetMap | ipn.NotifyInitialStatus | ipn.NotifyInitialDriveShares | ipn.NotifyInitialSuggestedExitNode | ipn.NotifyInitialClientVersion | ipn.NotifyPeerWireGuardState
+	const initialBits = ipn.NotifyInitialState | ipn.NotifyInitialPrefs |
+		ipn.NotifyInitialNetMap | ipn.NotifyInitialStatus |
+		ipn.NotifyInitialDriveShares | ipn.NotifyInitialSuggestedExitNode |
+		ipn.NotifyInitialClientVersion | ipn.NotifySysPolicyChanges | ipn.NotifyPeerWireGuardState
 	if mask&initialBits != 0 {
 		cn := b.currentNode()
 		ini = &ipn.Notify{Version: version.Long()}
@@ -3755,6 +3780,13 @@ func (b *LocalBackend) WatchNotificationsAs(ctx context.Context, actor ipnauth.A
 				ini.ClientVersion = b.lastClientVersion
 			}
 		}
+		if mask&ipn.NotifySysPolicyChanges != 0 {
+			var err error
+			ini.Policy, err = b.polc.GetPolicySnapshot("")
+			if err != nil {
+				b.logf("syspolicy: GetPolicySnapshot(\"\"): %v", err)
+			}
+		}
 	}
 
 	ctx, cancel := context.WithCancel(ctx)
@@ -3775,6 +3807,16 @@ func (b *LocalBackend) WatchNotificationsAs(ctx context.Context, actor ipnauth.A
 	b.mu.Unlock()
 	deadlockDone()
 
+	if mask&ipn.NotifySysPolicyChanges != 0 {
+		if unreg, err := b.polc.RegisterChangeCallback("", func(_ policyclient.PolicyChange) {
+			b.sysPolicyChangedForSession(session)
+		}); err == nil {
+			defer unreg()
+		} else {
+			b.logf("syspolicy: RegisterChangeCallback(\"\"): %v", err)
+		}
+	}
+
 	metricCurrentWatchIPNBus.Add(1)
 	defer metricCurrentWatchIPNBus.Add(-1)
 

ipn/ipnlocal/local_test.go

@@ -71,7 +71,10 @@
 	"tailscale.com/util/set"
 	"tailscale.com/util/syspolicy"
 	"tailscale.com/util/syspolicy/pkey"
+	"tailscale.com/util/syspolicy/policyclient"
 	"tailscale.com/util/syspolicy/policytest"
+	"tailscale.com/util/syspolicy/rsop"
+	"tailscale.com/util/syspolicy/setting"
 	"tailscale.com/util/syspolicy/source"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/filter"
@@ -8481,6 +8484,153 @@ func toStrings[T ~string](in []T) []string {
 	return out
 }
 
+func TestWatchNotificationsInitialPolicy(t *testing.T) {
+	setting.SetDefinitionsForTest(t,
+		setting.NewDefinition(pkey.AdminConsoleVisibility, setting.UserSetting, setting.VisibilityValue),
+	)
+	store := source.NewTestStore(t)
+	rsop.RegisterStoreForTest(t, "TestStore", setting.DeviceScope, store)
+
+	sys := tsd.NewSystem()
+	sys.PolicyClient.Set(testPolicyClient{})
+	lb := newTestLocalBackendWithSys(t, sys)
+
+	nw := newNotificationWatcher(t, lb, &ipnauth.TestActor{})
+	nw.watch(ipn.NotifySysPolicyChanges, []wantedNotification{
+		wantPolicyNotify(),
+	})
+	nw.check()
+
+	nw2 := newNotificationWatcher(t, lb, &ipnauth.TestActor{})
+	nw2.watch(0, nil, unexpectedPolicy)
+	nw2.check()
+}
+
+func TestPolicyChangeNotifiesWatcher(t *testing.T) {
+	setting.SetDefinitionsForTest(t,
+		setting.NewDefinition(pkey.AdminConsoleVisibility, setting.UserSetting, setting.VisibilityValue),
+	)
+	store := source.NewTestStore(t)
+	rsop.RegisterStoreForTest(t, "TestStore", setting.DeviceScope, store)
+
+	sys := tsd.NewSystem()
+	sys.PolicyClient.Set(testPolicyClient{})
+	lb := newTestLocalBackendWithSys(t, sys)
+	if err := lb.Start(ipn.Options{}); err != nil {
+		t.Fatalf("Start: %v", err)
+	}
+
+	nw := newNotificationWatcher(t, lb, &ipnauth.TestActor{})
+	nw.watch(ipn.NotifySysPolicyChanges, []wantedNotification{
+		wantPolicyNotify(),
+		wantPolicyWithSetting(pkey.AdminConsoleVisibility, "hide"),
+	})
+
+	store.SetStrings(source.TestSettingOf(pkey.AdminConsoleVisibility, "hide"))
+
+	nw.check()
+}
+
+func TestPolicyNotifyPerUser(t *testing.T) {
+	store := source.NewTestStore(t)
+	rsop.RegisterStoreForTest(t, "TestStore", setting.DeviceScope, store)
+
+	sys := tsd.NewSystem()
+	sys.PolicyClient.Set(testPolicyClient{})
+	lb := newTestLocalBackendWithSys(t, sys)
+
+	actorA := &ipnauth.TestActor{UID: "S-1-5-21-1001"}
+	actorB := &ipnauth.TestActor{UID: "S-1-5-21-1002"}
+
+	nwA := newNotificationWatcher(t, lb, actorA)
+	nwA.watch(ipn.NotifySysPolicyChanges, []wantedNotification{
+		wantPolicyNotify(),
+	})
+	nwA.check()
+
+	nwB := newNotificationWatcher(t, lb, actorB)
+	nwB.watch(ipn.NotifySysPolicyChanges, []wantedNotification{
+		wantPolicyNotify(),
+	})
+	nwB.check()
+
+	nwNoPolicy := newNotificationWatcher(t, lb, actorA)
+	nwNoPolicy.watch(0, nil, unexpectedPolicy)
+
+	store.SetStrings(source.TestSettingOf(pkey.AdminConsoleVisibility, "hide"))
+
+	nwNoPolicy.check()
+}
+
+func wantPolicyNotify() wantedNotification {
+	return wantedNotification{
+		name: "Policy",
+		cond: func(_ testing.TB, _ ipnauth.Actor, n *ipn.Notify) bool {
+			return n.Policy != nil
+		},
+	}
+}
+
+func wantPolicyWithSetting(key pkey.Key, value string) wantedNotification {
+	return wantedNotification{
+		name: fmt.Sprintf("Policy-%s=%s", key, value),
+		cond: func(t testing.TB, _ ipnauth.Actor, n *ipn.Notify) bool {
+			if n.Policy == nil {
+				return false
+			}
+			if n.Policy == nil {
+				return false
+			}
+			got := n.Policy.Get(key)
+			if got == nil {
+				return false
+			}
+			if fmt.Sprint(got) != value {
+				t.Errorf("Policy[%s] = %v (%T); want %q", key, got, got, value)
+			}
+			return true
+		},
+	}
+}
+
+func unexpectedPolicy(t testing.TB, _ ipnauth.Actor, n *ipn.Notify) bool {
+	if n.Policy != nil {
+		t.Errorf("unexpected Policy notification")
+		return true
+	}
+	return false
+}
+
+type testPolicyClient struct {
+	policyclient.NoPolicyClient
+}
+
+func (testPolicyClient) GetPolicySnapshot(uid string) (*policyclient.PolicySnapshot, error) {
+	scope := setting.DefaultScope()
+	if uid != "" {
+		scope = setting.UserScopeOf(uid)
+	}
+	p, err := rsop.PolicyFor(scope)
+	if err != nil {
+		return nil, err
+	}
+	return p.Get(), nil
+}
+
+func (testPolicyClient) RegisterChangeCallback(uid string, cb func(policyclient.PolicyChange)) (func(), error) {
+	scope := setting.DefaultScope()
+	if uid != "" {
+		scope = setting.UserScopeOf(uid)
+	}
+	p, err := rsop.PolicyFor(scope)
+	if err != nil {
+		return func() {}, err
+	}
+	return p.RegisterChangeCallback(func(change policyclient.PolicyChange) {
+		cb(change)
+	}), nil
+}
+
 type textUpdate struct {
 	Advertise   []string
 	Unadvertise []string

net/dns/manager_windows.go

@@ -78,7 +78,7 @@ func NewOSConfigurator(logf logger.Logf, health *health.Tracker, bus *eventbus.B
 	}
 
 	var err error
-	if ret.unregisterPolicyChangeCb, err = polc.RegisterChangeCallback(ret.sysPolicyChanged); err != nil {
+	if ret.unregisterPolicyChangeCb, err = polc.RegisterChangeCallback("", ret.sysPolicyChanged); err != nil {
 		logf("error registering policy change callback: %v", err) // non-fatal
 	}
 

util/syspolicy/policyclient/policy_snapshot.go

@@ -0,0 +1,12 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_syspolicy
+
+package policyclient
+
+import "tailscale.com/util/syspolicy/setting"
+
+// PolicySnapshot is an alias for [settings.Snapshot] unless syspolicy is omitted
+// from the build.
+type policySnapshot = setting.Snapshot

util/syspolicy/policyclient/policy_snapshot_omit.go

@@ -0,0 +1,9 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ts_omit_syspolicy
+
+package policyclient
+
+// PolicySnapshot is a stub when syspolicy is omitted from the build.
+type policySnapshot struct{}

util/syspolicy/policyclient/policyclient.go

@@ -62,11 +62,21 @@ type Client interface {
 	HasAnyOf(keys ...pkey.Key) (bool, error)
 
 	// RegisterChangeCallback registers a callback function that will be called
-	// whenever a policy change is detected. It returns a function to unregister
-	// the callback and an error if the registration fails.
-	RegisterChangeCallback(cb func(PolicyChange)) (unregister func(), err error)
+	// whenever a policy change is detected. If uid is empty, the callback fires
+	// for device-scope policy changes. If uid is non-empty, it fires for changes
+	// to that user's effective policy (device + user policies merged). It returns
+	// a function to unregister the callback and an error if the registration fails.
+	RegisterChangeCallback(uid string, cb func(PolicyChange)) (unregister func(), err error)
+
+	// GetPolicySnapshot returns the effective policy snapshot for the given user ID.
+	// If uid is empty, returns the default-scope policy. Returns nil, nil if policy
+	// snapshots are not supported.
+	GetPolicySnapshot(uid string) (*PolicySnapshot, error)
 }
 
+// PolicySnapshot is an alias for [setting.Snapshot] unless syspolicy is omitted from the build.
+type PolicySnapshot = policySnapshot
+
 // Get returns a non-nil [Client] implementation as a function of the
 // build tags. It returns a no-op implementation if the full syspolicy
 // package is omitted from the build, or in tests.
@@ -140,6 +150,10 @@ func (NoPolicyClient) HasAnyOf(keys ...pkey.Key) (bool, error) {
 
 func (NoPolicyClient) SetDebugLoggingEnabled(enabled bool) {}
 
-func (NoPolicyClient) RegisterChangeCallback(cb func(PolicyChange)) (unregister func(), err error) {
+func (NoPolicyClient) RegisterChangeCallback(uid string, cb func(PolicyChange)) (unregister func(), err error) {
 	return func() {}, nil
 }
+
+func (NoPolicyClient) GetPolicySnapshot(uid string) (*PolicySnapshot, error) {
+	return nil, nil
+}

util/syspolicy/policytest/policytest.go

@@ -226,7 +226,7 @@ func (c Config) HasAnyOf(keys ...pkey.Key) (bool, error) {
 	return false, nil
 }
 
-func (c Config) RegisterChangeCallback(callback func(policyclient.PolicyChange)) (func(), error) {
+func (c Config) RegisterChangeCallback(uid string, callback func(policyclient.PolicyChange)) (func(), error) {
 	w, ok := c[watchersKey].(*watchers)
 	if !ok {
 		return func() {}, nil
@@ -242,3 +242,7 @@ func (c Config) RegisterChangeCallback(callback func(policyclient.PolicyChange))
 }
 
 func (sp Config) SetDebugLoggingEnabled(enabled bool) {}
+
+func (c Config) GetPolicySnapshot(uid string) (*policyclient.PolicySnapshot, error) {
+	return nil, nil
+}

util/syspolicy/syspolicy.go

@@ -129,8 +129,12 @@ func getDuration(name pkey.Key, defaultValue time.Duration) (time.Duration, erro
 
 // registerChangeCallback adds a function that will be called whenever the effective policy
 // for the default scope changes. The returned function can be used to unregister the callback.
-func registerChangeCallback(cb rsop.PolicyChangeCallback) (unregister func(), err error) {
-	effective, err := rsop.PolicyFor(setting.DefaultScope())
+func registerChangeCallback(uid string, cb rsop.PolicyChangeCallback) (unregister func(), err error) {
+	scope := setting.DefaultScope()
+	if uid != "" {
+		scope = setting.UserScopeOf(uid)
+	}
+	effective, err := rsop.PolicyFor(scope)
 	if err != nil {
 		return nil, err
 	}
@@ -259,6 +263,18 @@ func (globalSyspolicy) HasAnyOf(keys ...pkey.Key) (bool, error) {
 	return hasAnyOf(keys...)
 }
 
-func (globalSyspolicy) RegisterChangeCallback(cb func(policyclient.PolicyChange)) (unregister func(), err error) {
-	return registerChangeCallback(cb)
+func (globalSyspolicy) RegisterChangeCallback(uid string, cb func(policyclient.PolicyChange)) (unregister func(), err error) {
+	return registerChangeCallback(uid, cb)
+}
+
+func (globalSyspolicy) GetPolicySnapshot(uid string) (*policyclient.PolicySnapshot, error) {
+	scope := setting.DefaultScope()
+	if uid != "" {
+		scope = setting.UserScopeOf(uid)
+	}
+	p, err := rsop.PolicyFor(scope)
+	if err != nil {
+		return nil, err
+	}
+	return p.Get(), nil
 }