From e11de8481c4c349456125e5ad6782d82d423a5b9 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Fri, 29 Jan 2021 22:29:22 +0100
Subject: winipcfg: move to undocumented DNS function

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 tunnel/winipcfg/netsh.go | 65 +++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 61 insertions(+), 4 deletions(-)

(limited to 'tunnel/winipcfg/netsh.go')

diff --git a/tunnel/winipcfg/netsh.go b/tunnel/winipcfg/netsh.go
index 803a9a35..1f3d12d0 100644
--- a/tunnel/winipcfg/netsh.go
+++ b/tunnel/winipcfg/netsh.go
@@ -7,25 +7,25 @@ package winipcfg
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
+	"net"
 	"os/exec"
 	"path/filepath"
 	"strings"
 	"syscall"
 
 	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/registry"
 )
 
-// I wish we didn't have to do this. netiohlp.dll (what's used by netsh.exe) has some nice tricks with writing directly
-// to the registry and the nsi kernel object, but it's not clear copying those makes for a stable interface. WMI doesn't
-// work with v6. CMI isn't in Windows 7.
 func runNetsh(cmds []string) error {
 	system32, err := windows.GetSystemDirectory()
 	if err != nil {
 		return err
 	}
-	cmd := exec.Command(filepath.Join(system32, "netsh.exe")) // I wish we could append (, "-f", "CONIN$") but Go sets up the process context wrong.
+	cmd := exec.Command(filepath.Join(system32, "netsh.exe"))
 	cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
 
 	stdin, err := cmd.StdinPipe()
@@ -49,3 +49,60 @@ func runNetsh(cmds []string) error {
 	}
 	return nil
 }
+
+const (
+	netshCmdTemplateFlush4 = "interface ipv4 set dnsservers name=%d source=static address=none validate=no register=both"
+	netshCmdTemplateFlush6 = "interface ipv6 set dnsservers name=%d source=static address=none validate=no register=both"
+	netshCmdTemplateAdd4   = "interface ipv4 add dnsservers name=%d address=%s validate=no"
+	netshCmdTemplateAdd6   = "interface ipv6 add dnsservers name=%d address=%s validate=no"
+)
+
+func (luid LUID) fallbackSetDNSForFamily(family AddressFamily, dnses []net.IP) error {
+	var templateFlush string
+	if family == windows.AF_INET {
+		templateFlush = netshCmdTemplateFlush4
+	} else if family == windows.AF_INET6 {
+		templateFlush = netshCmdTemplateFlush6
+	}
+
+	cmds := make([]string, 0, 1+len(dnses))
+	ipif, err := luid.IPInterface(family)
+	if err != nil {
+		return err
+	}
+	cmds = append(cmds, fmt.Sprintf(templateFlush, ipif.InterfaceIndex))
+	for i := 0; i < len(dnses); i++ {
+		if v4 := dnses[i].To4(); v4 != nil && family == windows.AF_INET {
+			cmds = append(cmds, fmt.Sprintf(netshCmdTemplateAdd4, ipif.InterfaceIndex, v4.String()))
+		} else if v6 := dnses[i].To16(); v4 == nil && v6 != nil && family == windows.AF_INET6 {
+			cmds = append(cmds, fmt.Sprintf(netshCmdTemplateAdd6, ipif.InterfaceIndex, v6.String()))
+		}
+	}
+	return runNetsh(cmds)
+}
+
+func (luid LUID) fallbackSetDNSDomain(domain string) error {
+	guid, err := luid.GUID()
+	if err != nil {
+		return fmt.Errorf("Error converting luid to guid: %w", err)
+	}
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE, fmt.Sprintf("SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Adapters\\%v", guid), registry.QUERY_VALUE)
+	if err != nil {
+		return fmt.Errorf("Error opening adapter-specific TCP/IP network registry key: %w", err)
+	}
+	paths, _, err := key.GetStringsValue("IpConfig")
+	key.Close()
+	if err != nil {
+		return fmt.Errorf("Error reading IpConfig registry key: %w", err)
+	}
+	if len(paths) == 0 {
+		return errors.New("No TCP/IP interfaces found on adapter")
+	}
+	key, err = registry.OpenKey(registry.LOCAL_MACHINE, fmt.Sprintf("SYSTEM\\CurrentControlSet\\Services\\%s", paths[0]), registry.SET_VALUE)
+	if err != nil {
+		return fmt.Errorf("Unable to open TCP/IP network registry key: %w", err)
+	}
+	err = key.SetStringValue("Domain", domain)
+	key.Close()
+	return err
+}
-- 
cgit v1.2.3-59-g8ed1b