net: filter disabled interfaces in Windows DNS client

The Go DNS resolver on Windows should filter disabled
interfaces. Otherwise disabled TUN devices, VPNs will be also
considered as valid nameservers and finally timedout.

Fixes #56160

(Originally from Zhiyuan Zheng <zhzy0077@hotmail.com>
 in https://go.dev/cl/442375)

Co-authored-by: Zhiyuan Zheng <zhzy0077@hotmail.com>
GitHub-Last-Rev: db158625bb46692cbbc09e3fe4dfa023c733f4e6
GitHub-Pull-Request: golang/go#56161
Change-Id: I7becebc55c8ac612c670c533855f7e6ca397a496
Reviewed-on: https://go-review.googlesource.com/c/go/+/500375
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Auto-Submit: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

diff --git a/src/net/dnsconfig_windows.go b/src/net/dnsconfig_windows.go
index 5d640da1d740c9c8f5e01e24ff613d2d505f3e01..f3d242366ae2cd59f50672286277298bff8afd66 100644 (file)
--- a/src/net/dnsconfig_windows.go
+++ b/src/net/dnsconfig_windows.go
@@ -5,6 +5,7 @@
 package net
 
 import (
+       "internal/syscall/windows"
        "syscall"
        "time"
 )
@@ -30,6 +31,10 @@ func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
        // In practice, however, it mostly works.
        for _, aa := range aas {
                for dns := aa.FirstDnsServerAddress; dns != nil; dns = dns.Next {
+                       // Only take interfaces whose OperStatus is IfOperStatusUp(0x01) into DNS configs.
+                       if aa.OperStatus != windows.IfOperStatusUp {
+                               continue
+                       }
                        sa, err := dns.Address.Sockaddr.Sockaddr()
                        if err != nil {
                                continue