tunnel: help people fix their DNS Cache service

Too many people follow silly Internet guides and disable this, making it
impossible for us to then set activestore-style DNS servers for the
interface.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/tunnel/addressconfig.go b/tunnel/addressconfig.go
index 350dd645..c887f7b7 100644
--- a/tunnel/addressconfig.go
+++ b/tunnel/addressconfig.go
@@ -13,6 +13,7 @@ import (
 	"sort"
 
 	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/svc/mgr"
 	"golang.zx2c4.com/wireguard/windows/conf"
 	"golang.zx2c4.com/wireguard/windows/tunnel/firewall"
 	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
@@ -56,6 +57,25 @@ func cleanupAddressesOnDisconnectedInterfaces(family winipcfg.AddressFamily, add
 	}
 }
 
+func isDnsCacheDisabled() (bool, string) {
+	scm, err := mgr.Connect()
+	if err != nil {
+		return false, ""
+	}
+	defer scm.Disconnect()
+	svc := mgr.Service{Name: "dnscache"}
+	svc.Handle, err = windows.OpenService(scm.Handle, windows.StringToUTF16Ptr(svc.Name), windows.SERVICE_QUERY_CONFIG)
+	if err != nil {
+		return false, ""
+	}
+	defer svc.Close()
+	cfg, err := svc.Config()
+	if err != nil {
+		return false, ""
+	}
+	return cfg.StartType == mgr.StartDisabled, cfg.DisplayName
+}
+
 func configureInterface(family winipcfg.AddressFamily, conf *conf.Config, luid winipcfg.LUID, clamper mtuClamper) error {
 	estimatedRouteCount := 0
 	for _, peer := range conf.Peers {
@@ -167,6 +187,11 @@ func configureInterface(family winipcfg.AddressFamily, conf *conf.Config, luid w
 
 	err = luid.SetDNS(family, conf.Interface.DNS, conf.Interface.DNSSearch)
 	if err != nil {
+		if err == windows.RPC_S_INVALID_BINDING || err == windows.ERROR_SERVICE_NOT_ACTIVE {
+			if disabled, name := isDnsCacheDisabled(); disabled {
+				err = fmt.Errorf("the %q service (dnscache) is disabled; please re-enable it", name)
+			}
+		}
 		return fmt.Errorf("unable to set DNS %v %v: %w", conf.Interface.DNS, conf.Interface.DNSSearch, err)
 	}
 	return nil