net: fixes to dnsReadConfig in dnsconfig_windows.go

- Only search DNS servers for network interfaces with at least one gateway
- Clarify comment on deprecated site local anycast fec0/10 DNS IPv6 addresses
- Minor maintenance: skip not "up" interfaces earlier in outer loop

Change-Id: I98ca7b81d3d51e6aa6bfa4a10dcd651305a843df
GitHub-Last-Rev: 3b358c7e3f89971d069286f997dc19e092ec8f08
GitHub-Pull-Request: golang/go#64441
Reviewed-on: https://go-review.googlesource.com/c/go/+/545775
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index be7ade9e324294b249187fe05c1df61be1a8ee64..be629cc0f9772067678f005a2746d1486d7b5451 100644 (file)
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -42,7 +42,10 @@ const (
        ERROR_NO_UNICODE_TRANSLATION syscall.Errno = 1113
 )
 
-const GAA_FLAG_INCLUDE_PREFIX = 0x00000010
+const (
+       GAA_FLAG_INCLUDE_PREFIX   = 0x00000010
+       GAA_FLAG_INCLUDE_GATEWAYS = 0x0080
+)
 
 const (
        IF_TYPE_OTHER              = 1
@@ -104,27 +107,45 @@ type IpAdapterPrefix struct {
        PrefixLength uint32
 }
 
+type IpAdapterWinsServerAddress struct {
+       Length   uint32
+       Reserved uint32
+       Next     *IpAdapterWinsServerAddress
+       Address  SocketAddress
+}
+
+type IpAdapterGatewayAddress struct {
+       Length   uint32
+       Reserved uint32
+       Next     *IpAdapterGatewayAddress
+       Address  SocketAddress
+}
+
 type IpAdapterAddresses struct {
-       Length                uint32
-       IfIndex               uint32
-       Next                  *IpAdapterAddresses
-       AdapterName           *byte
-       FirstUnicastAddress   *IpAdapterUnicastAddress
-       FirstAnycastAddress   *IpAdapterAnycastAddress
-       FirstMulticastAddress *IpAdapterMulticastAddress
-       FirstDnsServerAddress *IpAdapterDnsServerAdapter
-       DnsSuffix             *uint16
-       Description           *uint16
-       FriendlyName          *uint16
-       PhysicalAddress       [syscall.MAX_ADAPTER_ADDRESS_LENGTH]byte
-       PhysicalAddressLength uint32
-       Flags                 uint32
-       Mtu                   uint32
-       IfType                uint32
-       OperStatus            uint32
-       Ipv6IfIndex           uint32
-       ZoneIndices           [16]uint32
-       FirstPrefix           *IpAdapterPrefix
+       Length                 uint32
+       IfIndex                uint32
+       Next                   *IpAdapterAddresses
+       AdapterName            *byte
+       FirstUnicastAddress    *IpAdapterUnicastAddress
+       FirstAnycastAddress    *IpAdapterAnycastAddress
+       FirstMulticastAddress  *IpAdapterMulticastAddress
+       FirstDnsServerAddress  *IpAdapterDnsServerAdapter
+       DnsSuffix              *uint16
+       Description            *uint16
+       FriendlyName           *uint16
+       PhysicalAddress        [syscall.MAX_ADAPTER_ADDRESS_LENGTH]byte
+       PhysicalAddressLength  uint32
+       Flags                  uint32
+       Mtu                    uint32
+       IfType                 uint32
+       OperStatus             uint32
+       Ipv6IfIndex            uint32
+       ZoneIndices            [16]uint32
+       FirstPrefix            *IpAdapterPrefix
+       TransmitLinkSpeed      uint64
+       ReceiveLinkSpeed       uint64
+       FirstWinsServerAddress *IpAdapterWinsServerAddress
+       FirstGatewayAddress    *IpAdapterGatewayAddress
        /* more fields might be present here. */
 }
 

diff --git a/src/net/dnsconfig_windows.go b/src/net/dnsconfig_windows.go
index f3d242366ae2cd59f50672286277298bff8afd66..34455309dbb297b513ed84b5eaa1540b4b0142a1 100644 (file)
--- a/src/net/dnsconfig_windows.go
+++ b/src/net/dnsconfig_windows.go
@@ -25,16 +25,19 @@ func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
        if err != nil {
                return
        }
-       // TODO(bradfitz): this just collects all the DNS servers on all
-       // the interfaces in some random order. It should order it by
-       // default route, or only use the default route(s) instead.
-       // In practice, however, it mostly works.
+
        for _, aa := range aas {
+               // Only take interfaces whose OperStatus is IfOperStatusUp(0x01) into DNS configs.
+               if aa.OperStatus != windows.IfOperStatusUp {
+                       continue
+               }
+
+               // Only take interfaces which have at least one gateway
+               if aa.FirstGatewayAddress == nil {
+                       continue
+               }
+
                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
@@ -47,9 +50,11 @@ func dnsReadConfig(ignoredFilename string) (conf *dnsConfig) {
                                ip = make(IP, 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.
+                                       // fec0/10 IPv6 addresses are site local anycast DNS
+                                       // addresses Microsoft sets by default if no other
+                                       // IPv6 DNS address is set. Site local anycast is
+                                       // deprecated since 2004, see
+                                       // https://datatracker.ietf.org/doc/html/rfc3879
                                        continue
                                }
                        default:

diff --git a/src/net/interface_windows.go b/src/net/interface_windows.go
index 22a13128499bcf31d8f37ac0741b3a1a3454987c..1b487dc474825fca990dfe66a556ff100cbb87c8 100644 (file)
--- a/src/net/interface_windows.go
+++ b/src/net/interface_windows.go
@@ -20,7 +20,8 @@ func adapterAddresses() ([]*windows.IpAdapterAddresses, error) {
        l := uint32(15000) // recommended initial size
        for {
                b = make([]byte, l)
-               err := windows.GetAdaptersAddresses(syscall.AF_UNSPEC, windows.GAA_FLAG_INCLUDE_PREFIX, 0, (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])), &l)
+               const flags = windows.GAA_FLAG_INCLUDE_PREFIX | windows.GAA_FLAG_INCLUDE_GATEWAYS
+               err := windows.GetAdaptersAddresses(syscall.AF_UNSPEC, flags, 0, (*windows.IpAdapterAddresses)(unsafe.Pointer(&b[0])), &l)
                if err == nil {
                        if l == 0 {
                                return nil, nil