From 8d936b5756cb93741a4162edb778b86ac1f78e72 Mon Sep 17 00:00:00 2001
From: Simon Zolin <s.zolin@adguard.com>
Date: Tue, 2 Apr 2019 19:16:00 +0300
Subject: [PATCH] + control: /install/check_config: Check and deactivate
 DNSStubListener

---
 control.go | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 helpers.go | 26 ++++++++++++++++++++
 2 files changed, 95 insertions(+), 1 deletion(-)

diff --git a/control.go b/control.go
index a62b3b6d..08747e7c 100644
--- a/control.go
+++ b/control.go
@@ -9,6 +9,7 @@ import (
 	"net"
 	"net/http"
 	"os"
+	"os/exec"
 	"sort"
 	"strconv"
 	"strings"
@@ -1039,8 +1040,25 @@ func handleInstallCheckConfig(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	if reqData.DNS.Port != 0 && reqData.DNS.Port != config.DNS.Port {
+	if reqData.DNS.Port != 0 {
 		err = checkPacketPortAvailable(reqData.DNS.IP, reqData.DNS.Port)
+
+		if errorIsAddrInUse(err) {
+			canAutofix := checkDNSStubListener()
+			if canAutofix && reqData.DNS.Autofix {
+
+				err = disableDNSStubListener()
+				if err != nil {
+					log.Error("Couldn't disable DNSStubListener: %s", err)
+				}
+
+				err = checkPacketPortAvailable(reqData.DNS.IP, reqData.DNS.Port)
+				canAutofix = false
+			}
+
+			respData.DNS.CanAutofix = canAutofix
+		}
+
 		if err != nil {
 			respData.DNS.Status = fmt.Sprintf("%v", err)
 		}
@@ -1054,6 +1072,56 @@ func handleInstallCheckConfig(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// Check if DNSStubListener is active
+func checkDNSStubListener() bool {
+	cmd := exec.Command("systemctl", "is-enabled", "systemd-resolved")
+	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
+	_, err := cmd.Output()
+	if err != nil || cmd.ProcessState.ExitCode() != 0 {
+		log.Error("command %s has failed: %v code:%d",
+			cmd.Path, err, cmd.ProcessState.ExitCode())
+		return false
+	}
+
+	cmd = exec.Command("grep", "-E", "#?DNSStubListener=yes", "/etc/systemd/resolved.conf")
+	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
+	_, err = cmd.Output()
+	if err != nil || cmd.ProcessState.ExitCode() != 0 {
+		log.Error("command %s has failed: %v code:%d",
+			cmd.Path, err, cmd.ProcessState.ExitCode())
+		return false
+	}
+
+	return true
+}
+
+// Deactivate DNSStubListener
+func disableDNSStubListener() error {
+	cmd := exec.Command("sed", "-r", "-i.orig", "s/#?DNSStubListener=yes/DNSStubListener=no/g", "/etc/systemd/resolved.conf")
+	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
+	_, err := cmd.Output()
+	if err != nil {
+		return err
+	}
+	if cmd.ProcessState.ExitCode() != 0 {
+		return fmt.Errorf("process %s exited with an error: %d",
+			cmd.Path, cmd.ProcessState.ExitCode())
+	}
+
+	cmd = exec.Command("systemctl", "reload-or-restart", "systemd-resolved")
+	log.Tracef("executing %s %v", cmd.Path, cmd.Args)
+	_, err = cmd.Output()
+	if err != nil {
+		return err
+	}
+	if cmd.ProcessState.ExitCode() != 0 {
+		return fmt.Errorf("process %s exited with an error: %d",
+			cmd.Path, cmd.ProcessState.ExitCode())
+	}
+
+	return nil
+}
+
 type applyConfigReqEnt struct {
 	IP   string `json:"ip"`
 	Port int    `json:"port"`
diff --git a/helpers.go b/helpers.go
index 184789d4..e4bb0d10 100644
--- a/helpers.go
+++ b/helpers.go
@@ -15,6 +15,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/AdguardTeam/dnsproxy/upstream"
@@ -346,6 +347,31 @@ func customDialContext(ctx context.Context, network, addr string) (net.Conn, err
 	return nil, firstErr
 }
 
+// check if error is "address already in use"
+func errorIsAddrInUse(err error) bool {
+	errOpError, ok := err.(*net.OpError)
+	if !ok {
+		return false
+	}
+
+	errSyscallError, ok := errOpError.Err.(*os.SyscallError)
+	if !ok {
+		return false
+	}
+
+	errErrno, ok := errSyscallError.Err.(syscall.Errno)
+	if !ok {
+		return false
+	}
+
+	if runtime.GOOS == "windows" {
+		const WSAEADDRINUSE = 10048
+		return errErrno == WSAEADDRINUSE
+	}
+
+	return errErrno == syscall.EADDRINUSE
+}
+
 // ---------------------
 // debug logging helpers
 // ---------------------