util/syspolicy: add policy counters (#10471)

Fixes tailscale/corp#16138

Signed-off-by: Claire Wang <claire@tailscale.com>

util/syspolicy/handler_windows.go

@@ -5,21 +5,72 @@
 
 import (
 	"errors"
+	"fmt"
 
+	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/winutil"
 )
 
+var (
+	windowsErrors = clientmetric.NewCounter("windows_mdm_setting_errors")
+	windowsAny    = clientmetric.NewGauge("windows_mdm_setting_any")
+)
+
 type windowsHandler struct{}
 
 func init() {
 	RegisterHandler(NewCachingHandler(windowsHandler{}))
+
+	keyList := []struct {
+		isSet func(Key) bool
+		keys  []Key
+	}{
+		{
+			isSet: func(k Key) bool {
+				_, err := handler.ReadString(string(k))
+				return err == nil
+			},
+			keys: stringKeys,
+		},
+		{
+			isSet: func(k Key) bool {
+				_, err := handler.ReadBoolean(string(k))
+				return err == nil
+			},
+			keys: boolKeys,
+		},
+		{
+			isSet: func(k Key) bool {
+				_, err := handler.ReadUInt64(string(k))
+				return err == nil
+			},
+			keys: uint64Keys,
+		},
+	}
+
+	var anySet bool
+	for _, l := range keyList {
+		for _, k := range l.keys {
+			if !l.isSet(k) {
+				continue
+			}
+			clientmetric.NewGauge(fmt.Sprintf("windows_mdm_setting_%s", k)).Set(1)
+			anySet = true
+		}
+	}
+	if anySet {
+		windowsAny.Set(1)
+	}
 }
 
 func (windowsHandler) ReadString(key string) (string, error) {
 	s, err := winutil.GetPolicyString(key)
 	if errors.Is(err, winutil.ErrNoValue) {
 		err = ErrNoSuchKey
+	} else if err != nil {
+		windowsErrors.Add(1)
 	}
+
 	return s, err
 }
 
@@ -27,6 +78,8 @@ func (windowsHandler) ReadUInt64(key string) (uint64, error) {
 	value, err := winutil.GetPolicyInteger(key)
 	if errors.Is(err, winutil.ErrNoValue) {
 		err = ErrNoSuchKey
+	} else if err != nil {
+		windowsErrors.Add(1)
 	}
 	return value, err
 }
@@ -35,6 +88,8 @@ func (windowsHandler) ReadBoolean(key string) (bool, error) {
 	value, err := winutil.GetPolicyInteger(key)
 	if errors.Is(err, winutil.ErrNoValue) {
 		err = ErrNoSuchKey
+	} else if err != nil {
+		windowsErrors.Add(1)
 	}
 	return value != 0, err
 }

util/syspolicy/policy_keys.go

@@ -50,3 +50,33 @@
 	// The default is "user-decides" unless otherwise stated.
 	PostureChecking Key = "PostureChecking"
 )
+
+var stringKeys = []Key{
+	ControlURL,
+	LogTarget,
+	Tailnet,
+	ExitNodeID,
+	ExitNodeIP,
+	EnableIncomingConnections,
+	EnableServerMode,
+	ExitNodeAllowLANAccess,
+	EnableTailscaleDNS,
+	EnableTailscaleSubnets,
+	AdminConsoleVisibility,
+	NetworkDevicesVisibility,
+	TestMenuVisibility,
+	UpdateMenuVisibility,
+	RunExitNodeVisibility,
+	PreferencesMenuVisibility,
+	ExitNodeMenuVisibility,
+	AutoUpdateVisibility,
+	KeyExpirationNoticeTime,
+	PostureChecking,
+}
+
+var boolKeys = []Key{
+	LogSCMInteractions,
+	FlushDNSOnSessionUnlock,
+}
+
+var uint64Keys = []Key{}