all: fix OS resolver looping issue on Windows

By making dnsFromAdapter ignores DNS server which is the same IP address
of the adapter.

While at it, also changes OS resolver to use ctrld bootstrap DNS only if
there's no available nameservers.

cmd/cli/cli.go

@@ -507,7 +507,7 @@ func initCLI() {
 			iface = runningIface(s)
 			tasks := []task{
 				{s.Stop, false},
-				{func() error { p.resetDNS(); return nil }, false},
+				{func() error { resetDnsNoLog(p); return nil }, false},
 				{s.Start, true},
 			}
 			if doTasks(tasks) {
@@ -887,7 +887,10 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 			sc := &service.Config{}
 			*sc = *svcConfig
 			sc.Executable = bin
-			s, err := newService(&prog{}, sc)
+			readConfig(false)
+			v.Unmarshal(&cfg)
+			p := &prog{router: router.New(&cfg, runInCdMode())}
+			s, err := newService(p, sc)
 			if err != nil {
 				mainLog.Load().Error().Msg(err.Error())
 				return
@@ -931,6 +934,7 @@ NOTE: Uninstalling will set DNS to values provided by DHCP.`,
 				}
 				tasks := []task{
 					{s.Stop, false},
+					{func() error { resetDnsNoLog(p); return nil }, false},
 					{s.Start, false},
 				}
 				if doTasks(tasks) {
@@ -2541,3 +2545,11 @@ func runningIface(s service.Service) string {
 	}
 	return ""
 }
+
+// resetDnsNoLog performs resetting DNS with logging disable.
+func resetDnsNoLog(p *prog) {
+	lvl := zerolog.GlobalLevel()
+	zerolog.SetGlobalLevel(zerolog.Disabled)
+	p.resetDNS()
+	zerolog.SetGlobalLevel(lvl)
+}

nameservers_windows.go

@@ -1,10 +1,8 @@
 package ctrld
 
 import (
-	"net"
 	"syscall"
 
-	"golang.org/x/sys/windows"
 	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
 )
 
@@ -19,37 +17,23 @@ func dnsFromAdapter() []string {
 	}
 	ns := make([]string, 0, len(aas)*2)
 	seen := make(map[string]bool)
-	do := func(addr windows.SocketAddress) {
-		sa, err := addr.Sockaddr.Sockaddr()
-		if err != nil {
-			return
+	addressMap := make(map[string]struct{})
+	for _, aa := range aas {
+		for a := aa.FirstUnicastAddress; a != nil; a = a.Next {
+			addressMap[a.Address.IP().String()] = struct{}{}
 		}
-		var ip net.IP
-		switch sa := sa.(type) {
-		case *syscall.SockaddrInet4:
-			ip = net.IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])
-		case *syscall.SockaddrInet6:
-			ip = make(net.IP, net.IPv6len)
-			copy(ip, sa.Addr[:])
-			if ip[0] == 0xfe && ip[1] == 0xc0 {
-				// Ignore these fec0/10 ones. Windows seems to
-				// populate them as defaults on its misc rando
-				// interfaces.
-				return
-			}
-		default:
-			return
-
-		}
-		if ip.IsLoopback() || seen[ip.String()] {
-			return
-		}
-		seen[ip.String()] = true
-		ns = append(ns, ip.String())
 	}
 	for _, aa := range aas {
 		for dns := aa.FirstDNSServerAddress; dns != nil; dns = dns.Next {
-			do(dns.Address)
+			ip := dns.Address.IP()
+			if ip == nil || ip.IsLoopback() || seen[ip.String()] {
+				continue
+			}
+			if _, ok := addressMap[ip.String()]; ok {
+				continue
+			}
+			seen[ip.String()] = true
+			ns = append(ns, ip.String())
 		}
 	}
 	return ns

resolver.go

@@ -39,10 +39,13 @@ var OsNameservers = defaultNameservers()
 // or is the Resolver used for ResolverTypeOS.
 var or = &osResolver{nameservers: OsNameservers}
 
-// defaultNameservers returns OS nameservers plus ctrld bootstrap nameserver.
+// defaultNameservers returns nameservers used by the OS.
+// If no nameservers can be found, ctrld bootstrap nameserver will be used.
 func defaultNameservers() []string {
 	ns := nameservers()
-	ns = append(ns, net.JoinHostPort(bootstrapDNS, "53"))
+	if len(ns) == 0 {
+		ns = append(ns, net.JoinHostPort(bootstrapDNS, "53"))
+	}
 	return ns
 }