Upgrade nameserver to take over the DNS port when in use by another process

nameserver/nameserver.go

@@ -5,7 +5,7 @@ package nameserver
 import (
 	"context"
 	"net"
-	"time"
+	"runtime"
 
 	"github.com/miekg/dns"
 
@@ -23,8 +23,17 @@ var (
 	localhostIPs []dns.RR
 )
 
+var (
+	listenAddress = "127.0.0.1:53"
+	localhostIP   = net.IPv4(127, 0, 0, 1)
+)
+
 func init() {
 	modules.Register("nameserver", prep, start, nil, "intel")
+
+	if runtime.GOOS == "windows" {
+		listenAddress = "0.0.0.0:53"
+	}
 }
 
 func prep() error {
@@ -44,7 +53,7 @@ func prep() error {
 }
 
 func start() error {
-	server := &dns.Server{Addr: "0.0.0.0:53", Net: "udp"}
+	server := &dns.Server{Addr: listenAddress, Net: "udp"}
 	dns.HandleFunc(".", handleRequest)
 	go run(server)
 	return nil
@@ -55,8 +64,7 @@ func run(server *dns.Server) {
 		err := server.ListenAndServe()
 		if err != nil {
 			log.Errorf("nameserver: server failed: %s", err)
-			log.Info("nameserver: restarting server in 10 seconds")
-			time.Sleep(10 * time.Second)
+			checkForConflictingService(err)
 		}
 	}
 }
@@ -95,6 +103,9 @@ func handleRequest(w dns.ResponseWriter, query *dns.Msg) {
 		log.Warningf("nameserver: could not get remote address of request for %s%s, ignoring", fqdn, qtype)
 		return
 	}
+	if !remoteAddr.IP.Equal(localhostIP) {
+		// if request is not coming from 127.0.0.1, check if it's really local
+
 		localAddr, ok := w.RemoteAddr().(*net.UDPAddr)
 		if !ok {
 			log.Warningf("nameserver: could not get local address of request for %s%s, ignoring", fqdn, qtype)
@@ -106,6 +117,7 @@ func handleRequest(w dns.ResponseWriter, query *dns.Msg) {
 			log.Warningf("nameserver: external request for %s%s, ignoring", fqdn, qtype)
 			return
 		}
+	}
 
 	// check if valid domain name
 	if !netutils.IsValidFqdn(fqdn) {
@@ -121,9 +133,7 @@ func handleRequest(w dns.ResponseWriter, query *dns.Msg) {
 	// TODO: if there are 3 request for the same domain/type in a row, delete all caches of that domain
 
 	// get connection
-	// start = time.Now()
 	comm, err := network.GetCommunicationByDNSRequest(ctx, remoteAddr.IP, uint16(remoteAddr.Port), fqdn)
-	// log.Tracef("nameserver: took %s to get comms (and maybe process)", time.Since(start))
 	if err != nil {
 		log.ErrorTracef(ctx, "nameserver: could not identify process of %s:%d, returning nxdomain: %s", remoteAddr.IP, remoteAddr.Port, err)
 		nxDomain(w, query)
@@ -141,9 +151,7 @@ func handleRequest(w dns.ResponseWriter, query *dns.Msg) {
 	}
 
 	// check profile before we even get intel and rr
-	// start = time.Now()
 	firewall.DecideOnCommunicationBeforeIntel(comm, fqdn)
-	// log.Tracef("nameserver: took %s to make decision", time.Since(start))
 
 	if comm.GetVerdict() == network.VerdictBlock || comm.GetVerdict() == network.VerdictDrop {
 		log.InfoTracef(ctx, "nameserver: %s denied before intel, returning nxdomain", comm)
@@ -152,9 +160,7 @@ func handleRequest(w dns.ResponseWriter, query *dns.Msg) {
 	}
 
 	// get intel and RRs
-	// start = time.Now()
 	domainIntel, rrCache := intel.GetIntelAndRRs(ctx, fqdn, qtype, comm.Process().ProfileSet().SecurityLevel())
-	// log.Tracef("nameserver: took %s to get intel and RRs", time.Since(start))
 	if rrCache == nil {
 		// TODO: analyze nxdomain requests, malware could be trying DGA-domains
 		log.WarningTracef(ctx, "nameserver: %s requested %s%s, is nxdomain", comm.Process(), fqdn, qtype)

nameserver/takeover.go

@@ -0,0 +1,59 @@
+package nameserver
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"time"
+
+	"github.com/Safing/portbase/log"
+	"github.com/Safing/portbase/notifications"
+	"github.com/Safing/portmaster/network/packet"
+	"github.com/Safing/portmaster/process"
+)
+
+func checkForConflictingService(err error) {
+	pid, err := takeover()
+	if err != nil || pid == 0 {
+		log.Info("nameserver: restarting server in 10 seconds")
+		time.Sleep(10 * time.Second)
+		return
+	}
+
+	log.Infof("nameserver: stopped conflicting name service with pid %d", pid)
+
+	// notify user
+	(&notifications.Notification{
+		ID:      "nameserver-stopped-conflicting-service",
+		Message: fmt.Sprintf("Portmaster stopped a conflicting name service (pid %d) to gain required system integration.", pid),
+	}).Init().Save()
+
+	// wait for a short duration for the other service to shut down
+	time.Sleep(100 * time.Millisecond)
+}
+
+func takeover() (int, error) {
+	pid, _, err := process.GetPidByEndpoints(net.IPv4(127, 0, 0, 1), 53, net.IPv4(127, 0, 0, 1), 65535, packet.UDP)
+	if err != nil {
+		// there may be nothing listening on :53
+		log.Tracef("nameserver: expected conflicting name service, but could not find anything listenting on :53")
+		return 0, nil
+	}
+
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		// huh. gone already? I guess we'll wait then...
+		return 0, err
+	}
+
+	err = proc.Signal(os.Interrupt)
+	if err != nil {
+		err = proc.Kill()
+		if err != nil {
+			log.Errorf("nameserver: failed to stop conflicting service (pid %d): %s", pid, err)
+			return 0, err
+		}
+	}
+
+	return pid, nil
+}