DNS: Simplify dns logic and switch to using 'search' instead of 'domain' which is obsolete.

src/linux/init/GnsEngine.cpp

@@ -315,21 +315,17 @@ void GnsEngine::ProcessDNSChange(Interface& interface, const wsl::shared::hns::D
         content << L"nameserver " << server << L"\n";
     }
 
-    if (!payload.Domain.empty())
-    {
-        content << L"domain " << payload.Domain << L"\n";
-    }
-
+    // Use 'search' for DNS suffixes.
+    // Per resolv.conf(5): "The domain directive is an obsolete name for the search directive
+    // that handles one search list entry only."
+    // See: https://man7.org/linux/man-pages/man5/resolv.conf.5.html
     if (!payload.Search.empty())
     {
         content << L"search " << wsl::shared::string::Join(wsl::shared::string::Split(payload.Search, L','), L' ') << L"\n";
     }
 
     GNS_LOG_INFO(
-        "Setting DNS server domain to {}: {} on interfaceName {} ",
-        payload.Domain.c_str(),
-        content.str().c_str(),
-        interface.Name().c_str());
+        "Setting DNS search to {}: {} on interfaceName {} ", payload.Search.c_str(), content.str().c_str(), interface.Name().c_str());
 
     std::wofstream resolvConf;
     resolvConf.exceptions(std::ofstream::badbit | std::ofstream::failbit);

src/windows/common/NatNetworking.cpp

@@ -26,8 +26,13 @@ static wil::srwlock g_endpointsInUseLock;
 static std::vector<GUID> g_endpointsInUse;
 
 NatNetworking::NatNetworking(
-    HCS_SYSTEM system, wsl::windows::common::hcs::unique_hcn_network&& network, GnsChannel&& gnsChannel, Config& config, wil::unique_socket&& dnsHvsocket) :
-    m_system(system), m_config(config), m_network(std::move(network)), m_gnsChannel(std::move(gnsChannel))
+    HCS_SYSTEM system,
+    wsl::windows::common::hcs::unique_hcn_network&& network,
+    GnsChannel&& gnsChannel,
+    Config& config,
+    wil::unique_socket&& dnsHvsocket,
+    LPCWSTR dnsOptions) :
+    m_system(system), m_config(config), m_network(std::move(network)), m_dnsOptions(dnsOptions), m_gnsChannel(std::move(gnsChannel))
 {
     m_connectivityTelemetryEnabled = config.EnableTelemetry && !WslTraceLoggingShouldDisableTelemetry();
 
@@ -48,7 +53,7 @@ NatNetworking::NatNetworking(
         // prioritized means:
         // - can only set 3 DNS servers (Linux limitation)
         // - when there are multiple host connected interfaces, we need to use the DNS servers from the most-likely-to-be-used interface on the host
-        m_mirrorDnsInfo.emplace();
+        m_useMirrorDnsSettings = true;
     }
 }
 
@@ -337,7 +342,7 @@ void NatNetworking::Initialize()
     UpdateDns(endpointProperties.GatewayAddress.c_str());
 
     // if using the shared access DNS proxy, ensure that the shared access service is allowed inbound UDP access.
-    if (!m_mirrorDnsInfo && !m_dnsTunnelingResolver)
+    if (!m_useMirrorDnsSettings && !m_dnsTunnelingResolver)
     {
         // N.B. This rule works around a host OS issue that prevents the DNS proxy from working on older versions of Windows.
         ConfigureSharedAccessFirewallRule();
@@ -433,35 +438,22 @@ _Requires_lock_held_(m_lock)
 void NatNetworking::UpdateDns(std::optional<PCWSTR> gatewayAddress) noexcept
 try
 {
-    if (!m_dnsTunnelingResolver && !m_mirrorDnsInfo && !gatewayAddress)
+    if (!m_dnsTunnelingResolver && !m_useMirrorDnsSettings && !gatewayAddress)
     {
         return;
     }
 
     networking::DnsInfo latestDnsSettings{};
 
-    // true if the "domain" entry of /etc/resolv.conf should be configured
-    // Note: the "domain" entry allows a single DNS suffix to be configured
-    bool configureLinuxDomain = false;
-
     // NAT mode with DNS tunneling
     if (m_dnsTunnelingResolver)
     {
         latestDnsSettings = HostDnsInfo::GetDnsTunnelingSettings(m_dnsTunnelingIpAddress);
     }
     // NAT mode without Shared Access DNS proxy
-    else if (m_mirrorDnsInfo)
+    else if (m_useMirrorDnsSettings)
     {
-        m_mirrorDnsInfo->UpdateNetworkInformation();
-        const auto settings = m_mirrorDnsInfo->GetDnsSettings(DnsSettingsFlags::IncludeVpn);
-
-        latestDnsSettings.Servers = std::move(settings.Servers);
-
-        if (!settings.Domains.empty())
-        {
-            latestDnsSettings.Domains.emplace_back(std::move(settings.Domains.front()));
-            configureLinuxDomain = true;
-        }
+        latestDnsSettings = HostDnsInfo::GetDnsSettings(DnsSettingsFlags::IncludeVpn);
     }
     // NAT mode with Shared Access DNS proxy
     else if (gatewayAddress)
@@ -472,11 +464,10 @@ try
 
     if (latestDnsSettings != m_trackedDnsSettings)
     {
-        auto dnsNotification = BuildDnsNotification(latestDnsSettings, configureLinuxDomain);
+        auto dnsNotification = BuildDnsNotification(latestDnsSettings, m_dnsOptions);
 
         WSL_LOG(
             "NatNetworking::UpdateDns",
-            TraceLoggingValue(dnsNotification.Domain.c_str(), "domain"),
             TraceLoggingValue(dnsNotification.Options.c_str(), "options"),
             TraceLoggingValue(dnsNotification.Search.c_str(), "search"),
             TraceLoggingValue(dnsNotification.ServerList.c_str(), "serverList"));

src/windows/common/NatNetworking.h

@@ -18,7 +18,13 @@ namespace wsl::core {
 class NatNetworking final : public INetworkingEngine
 {
 public:
-    NatNetworking(HCS_SYSTEM system, wsl::windows::common::hcs::unique_hcn_network&& network, GnsChannel&& gnsChannel, Config& config, wil::unique_socket&& dnsHvsocket);
+    NatNetworking(
+        HCS_SYSTEM system,
+        wsl::windows::common::hcs::unique_hcn_network&& network,
+        GnsChannel&& gnsChannel,
+        Config& config,
+        wil::unique_socket&& dnsHvsocket,
+        LPCWSTR dnsOptions = LX_INIT_RESOLVCONF_FULL_HEADER);
     ~NatNetworking() override;
 
     // Note: This class cannot be moved because m_networkNotifyHandle captures a 'this' pointer.
@@ -69,12 +75,18 @@ class NatNetworking final : public INetworkingEngine
     // The latest DNS settings configured in Linux
     _Guarded_by_(m_lock) networking::DnsInfo m_trackedDnsSettings {};
 
+    // If true, DNS settings are retrieved from host adapters (mirrored mode)
+    // rather than using the shared access DNS proxy
+    bool m_useMirrorDnsSettings = false;
+
+    // Options/header for /etc/resolv.conf
+    LPCWSTR m_dnsOptions = nullptr;
+
     GnsChannel m_gnsChannel;
     std::shared_ptr<networking::NetworkSettings> m_networkSettings;
     networking::EphemeralHcnEndpoint m_endpoint;
     ULONG m_networkMtu = 0;
 
-    std::optional<networking::HostDnsInfo> m_mirrorDnsInfo;
     networking::unique_notify_handle m_networkNotifyHandle{};
 };
 

src/windows/common/VirtioNetworking.cpp

@@ -14,11 +14,12 @@ using wsl::core::VirtioNetworking;
 static constexpr auto c_loopbackDeviceName = TEXT(LX_INIT_LOOPBACK_DEVICE_NAME);
 
 VirtioNetworking::VirtioNetworking(
-    GnsChannel&& gnsChannel, bool enableLocalhostRelay, std::shared_ptr<GuestDeviceManager> guestDeviceManager, wil::shared_handle userToken) :
+    GnsChannel&& gnsChannel, bool enableLocalhostRelay, LPCWSTR dnsOptions, std::shared_ptr<GuestDeviceManager> guestDeviceManager, wil::shared_handle userToken) :
     m_guestDeviceManager(std::move(guestDeviceManager)),
     m_userToken(std::move(userToken)),
     m_gnsChannel(std::move(gnsChannel)),
-    m_enableLocalhostRelay(enableLocalhostRelay)
+    m_enableLocalhostRelay(enableLocalhostRelay),
+    m_dnsOptions(dnsOptions)
 {
 }
 
@@ -66,7 +67,7 @@ void VirtioNetworking::Initialize()
     }
 
     // Get initial DNS settings for device options.
-    auto initialDns = m_dnsUpdateHelper.GetCurrentDnsSettings(networking::DnsSettingsFlags::IncludeVpn);
+    auto initialDns = networking::HostDnsInfo::GetDnsSettings(networking::DnsSettingsFlags::IncludeVpn);
     if (!initialDns.Servers.empty())
     {
         if (device_options.tellp() > 0)
@@ -260,7 +261,7 @@ try
     UpdateMtu();
 
     // Check for DNS changes and send update if needed.
-    auto currentDns = m_dnsUpdateHelper.GetCurrentDnsSettings(networking::DnsSettingsFlags::IncludeVpn);
+    auto currentDns = networking::HostDnsInfo::GetDnsSettings(networking::DnsSettingsFlags::IncludeVpn);
     if (currentDns != m_trackedDnsSettings)
     {
         m_trackedDnsSettings = currentDns;
@@ -274,7 +275,7 @@ void VirtioNetworking::SendDnsUpdate(const networking::DnsInfo& dnsSettings)
     hns::ModifyGuestEndpointSettingRequest<hns::DNS> notification{};
     notification.RequestType = hns::ModifyRequestType::Update;
     notification.ResourceType = hns::GuestEndpointResourceType::DNS;
-    notification.Settings = networking::BuildDnsNotification(dnsSettings);
+    notification.Settings = networking::BuildDnsNotification(dnsSettings, m_dnsOptions);
     m_gnsChannel.SendHnsNotification(ToJsonW(notification).c_str(), m_adapterId);
 }
 

src/windows/common/VirtioNetworking.h

@@ -13,7 +13,7 @@ namespace wsl::core {
 class VirtioNetworking : public INetworkingEngine
 {
 public:
-    VirtioNetworking(GnsChannel&& gnsChannel, bool enableLocalhostRelay, std::shared_ptr<GuestDeviceManager> guestDeviceManager, wil::shared_handle userToken);
+    VirtioNetworking(GnsChannel&& gnsChannel, bool enableLocalhostRelay, LPCWSTR dnsOptions, std::shared_ptr<GuestDeviceManager> guestDeviceManager, wil::shared_handle userToken);
     ~VirtioNetworking();
 
     // Note: This class cannot be moved because m_networkNotifyHandle captures a 'this' pointer.
@@ -49,12 +49,12 @@ class VirtioNetworking : public INetworkingEngine
     std::optional<GnsPortTrackerChannel> m_gnsPortTrackerChannel;
     std::shared_ptr<networking::NetworkSettings> m_networkSettings;
     bool m_enableLocalhostRelay;
+    LPCWSTR m_dnsOptions = nullptr;
     GUID m_localhostAdapterId;
     GUID m_adapterId;
 
     std::optional<ULONGLONG> m_interfaceLuid;
     ULONG m_networkMtu = 0;
-    networking::DnsUpdateHelper m_dnsUpdateHelper;
     networking::DnsInfo m_trackedDnsSettings;
 
     // Note: this field must be destroyed first to stop the callbacks before any other field is destroyed.

src/windows/common/WslCoreHostDnsInfo.cpp

@@ -105,12 +105,6 @@ wsl::core::networking::DnsInfo wsl::core::networking::HostDnsInfo::GetDnsTunneli
     return dnsInfo;
 }
 
-std::vector<wsl::core::networking::IpAdapterAddress> wsl::core::networking::HostDnsInfo::GetAdapterAddresses()
-{
-    std::lock_guard<std::mutex> lock(m_lock);
-    return m_addresses;
-}
-
 std::vector<std::string> wsl::core::networking::HostDnsInfo::GetDnsServerStrings(
     _In_ const PIP_ADAPTER_DNS_SERVER_ADDRESS& FirstDnsServer, _In_ USHORT IpFamilyFilter, _In_ USHORT MaxValues)
 {
@@ -233,7 +227,7 @@ std::vector<std::string> wsl::core::networking::HostDnsInfo::GetInterfaceDnsSuff
 
 wsl::core::networking::DnsInfo wsl::core::networking::HostDnsInfo::GetDnsSettings(_In_ DnsSettingsFlags Flags)
 {
-    std::vector<IpAdapterAddress> Addresses = GetAdapterAddresses();
+    std::vector<IpAdapterAddress> Addresses = AdapterAddresses::GetCurrent();
 
     auto RemoveFilter = [&](const IpAdapterAddress& Address) {
         // Ignore interfaces that are not currently "up".
@@ -326,12 +320,6 @@ wsl::core::networking::DnsInfo wsl::core::networking::HostDnsInfo::GetDnsSetting
     return DnsSettings;
 }
 
-void wsl::core::networking::HostDnsInfo::UpdateNetworkInformation()
-{
-    std::lock_guard<std::mutex> lock(m_lock);
-    m_addresses = AdapterAddresses::GetCurrent();
-}
-
 std::string wsl::core::networking::GenerateResolvConf(_In_ const DnsInfo& Info)
 {
     std::string contents{};
@@ -345,7 +333,10 @@ std::string wsl::core::networking::GenerateResolvConf(_In_ const DnsInfo& Info)
             contents += c_asciiNewLine;
         }
 
-        // Add domain information if it is available.
+        // Add DNS suffix information using 'search' directive.
+        // Per resolv.conf(5): "The domain directive is an obsolete name for the search directive
+        // that handles one search list entry only."
+        // See: https://man7.org/linux/man-pages/man5/resolv.conf.5.html
         if (!Info.Domains.empty())
         {
             contents += "search ";
@@ -497,28 +488,21 @@ wsl::core::networking::DnsSuffixRegistryWatcher::DnsSuffixRegistryWatcher(Regist
     m_registryWatchers.swap(localRegistryWatchers);
 }
 
-wsl::shared::hns::DNS wsl::core::networking::BuildDnsNotification(const DnsInfo& settings, bool useLinuxDomainEntry)
+wsl::shared::hns::DNS wsl::core::networking::BuildDnsNotification(const DnsInfo& settings, PCWSTR options)
 {
     wsl::shared::hns::DNS dnsNotification{};
-    dnsNotification.Options = LX_INIT_RESOLVCONF_FULL_HEADER;
-    dnsNotification.ServerList = wsl::shared::string::MultiByteToWide(wsl::shared::string::Join(settings.Servers, ','));
-
-    if (useLinuxDomainEntry && !settings.Domains.empty())
+    if (options)
     {
-        // Use 'domain' entry for single DNS suffix (typically used when mirroring host DNS without tunneling)
-        dnsNotification.Domain = wsl::shared::string::MultiByteToWide(settings.Domains.front());
-    }
-    else
-    {
-        // Use 'search' entry for DNS suffix list
-        dnsNotification.Search = wsl::shared::string::MultiByteToWide(wsl::shared::string::Join(settings.Domains, ','));
+        dnsNotification.Options = options;
     }
 
-    return dnsNotification;
-}
+    dnsNotification.ServerList = wsl::shared::string::MultiByteToWide(wsl::shared::string::Join(settings.Servers, ','));
 
-wsl::core::networking::DnsInfo wsl::core::networking::DnsUpdateHelper::GetCurrentDnsSettings(DnsSettingsFlags flags)
-{
-    m_hostDnsInfo.UpdateNetworkInformation();
-    return m_hostDnsInfo.GetDnsSettings(flags);
+    // Use 'search' entry for DNS suffix list.
+    // Per resolv.conf(5): "The domain directive is an obsolete name for the search directive
+    // that handles one search list entry only."
+    // See: https://man7.org/linux/man-pages/man5/resolv.conf.5.html
+    dnsNotification.Search = wsl::shared::string::MultiByteToWide(wsl::shared::string::Join(settings.Domains, ','));
+
+    return dnsNotification;
 }

src/windows/common/WslCoreHostDnsInfo.h

@@ -1,7 +1,6 @@
 // Copyright (C) Microsoft Corporation. All rights reserved.
 
 #pragma once
-#include <mutex>
 #include <string>
 #include <vector>
 
@@ -42,9 +41,9 @@ std::string GenerateResolvConf(_In_ const DnsInfo& Info);
 /// Builds an hns::DNS notification from DnsInfo settings.
 /// </summary>
 /// <param name="settings">The DNS settings to convert</param>
-/// <param name="useLinuxDomainEntry">If true, uses 'domain' entry for single suffix; otherwise uses 'search' for all
-/// suffixes</param> <returns>The hns::DNS notification ready to send via GNS channel</returns>
-wsl::shared::hns::DNS BuildDnsNotification(const DnsInfo& settings, bool useLinuxDomainEntry = false);
+/// <param name="options">The resolv.conf header options (defaults to LX_INIT_RESOLVCONF_FULL_HEADER)</param>
+/// <returns>The hns::DNS notification ready to send via GNS channel</returns>
+wsl::shared::hns::DNS BuildDnsNotification(const DnsInfo& settings, PCWSTR options = LX_INIT_RESOLVCONF_FULL_HEADER);
 
 std::vector<std::string> GetAllDnsSuffixes(const std::vector<IpAdapterAddress>& AdapterAddresses);
 
@@ -53,27 +52,15 @@ DWORD GetBestInterface();
 class HostDnsInfo
 {
 public:
-    DnsInfo GetDnsSettings(_In_ DnsSettingsFlags Flags);
-
-    void UpdateNetworkInformation();
+    static DnsInfo GetDnsSettings(_In_ DnsSettingsFlags Flags);
 
     static DnsInfo GetDnsTunnelingSettings(const std::wstring& dnsTunnelingNameserver);
 
-    const std::vector<IpAdapterAddress>& CurrentAddresses() const
-    {
-        return m_addresses;
-    }
-
 private:
-    /// <summary>
-    /// Internal function to retrieve the latest copy of interface information.
-    /// </summary>
-    std::vector<IpAdapterAddress> GetAdapterAddresses();
-
     /// <summary>
     /// Internal function to retrieve interface DNS servers.
     /// </summary>
-    std::vector<std::string> GetInterfaceDnsServers(const std::vector<IpAdapterAddress>& AdapterAddresses, _In_ DnsSettingsFlags Flags);
+    static std::vector<std::string> GetInterfaceDnsServers(const std::vector<IpAdapterAddress>& AdapterAddresses, _In_ DnsSettingsFlags Flags);
 
     /// <summary>
     /// Internal function to retrieve all Windows DNS suffixes.
@@ -84,30 +71,6 @@ class HostDnsInfo
     /// Internal function to convert DNS server addresses into strings.
     /// </summary>
     static std::vector<std::string> GetDnsServerStrings(_In_ const PIP_ADAPTER_DNS_SERVER_ADDRESS& DnsServer, _In_ USHORT IpFamilyFilter, _In_ USHORT MaxValues);
-
-    /// <summary>
-    /// Stores latest copy of interface information.
-    /// </summary>
-    std::mutex m_lock;
-    _Guarded_by_(m_lock) std::vector<IpAdapterAddress> m_addresses;
-};
-
-/// <summary>
-/// Helper class that fetches current DNS settings from the host.
-/// Callers are responsible for tracking changes if needed.
-/// </summary>
-class DnsUpdateHelper
-{
-public:
-    /// <summary>
-    /// Fetches current DNS settings from the host.
-    /// </summary>
-    /// <param name="flags">Flags controlling which DNS settings to include</param>
-    /// <returns>Current DNS settings</returns>
-    DnsInfo GetCurrentDnsSettings(DnsSettingsFlags flags);
-
-private:
-    HostDnsInfo m_hostDnsInfo;
 };
 
 using RegistryChangeCallback = std::function<void()>;