Merge pull request #128 from fosrl/dev

Pull system dns

dns/dns_proxy.go

@@ -741,6 +741,16 @@ func (p *DNSProxy) SetJITHandler(handler func(siteId int)) {
 	p.jitHandler = handler
 }
 
+// SetUpstreamDNS replaces the list of upstream DNS servers used to forward
+// queries that are not served by local records.  The servers must be in
+// "host:port" format (e.g. "8.8.8.8:53").
+func (p *DNSProxy) SetUpstreamDNS(servers []string) {
+	if len(servers) == 0 {
+		return
+	}
+	p.upstreamDNS = servers
+}
+
 // AddDNSRecord adds a DNS record to the local store
 // domain should be a domain name (e.g., "example.com" or "example.com.")
 // ip should be a valid IPv4 or IPv6 address

dns/platform/network_manager.go

@@ -4,6 +4,7 @@ package dns
 
 import (
 	"context"
+	"encoding/binary"
 	"errors"
 	"fmt"
 	"net/netip"
@@ -16,12 +17,25 @@ import (
 
 const (
 	// NetworkManager D-Bus constants
-	networkManagerDest                       = "org.freedesktop.NetworkManager"
-	networkManagerDbusObjectNode             = "/org/freedesktop/NetworkManager"
-	networkManagerDbusDNSManagerInterface    = "org.freedesktop.NetworkManager.DnsManager"
-	networkManagerDbusDNSManagerObjectNode   = networkManagerDbusObjectNode + "/DnsManager"
-	networkManagerDbusDNSManagerModeProperty = networkManagerDbusDNSManagerInterface + ".Mode"
-	networkManagerDbusVersionProperty        = "org.freedesktop.NetworkManager.Version"
+	networkManagerDest                        = "org.freedesktop.NetworkManager"
+	networkManagerDbusObjectNode              = "/org/freedesktop/NetworkManager"
+	networkManagerDbusDNSManagerInterface     = "org.freedesktop.NetworkManager.DnsManager"
+	networkManagerDbusDNSManagerObjectNode    = networkManagerDbusObjectNode + "/DnsManager"
+	networkManagerDbusDNSManagerModeProperty  = networkManagerDbusDNSManagerInterface + ".Mode"
+	networkManagerDbusVersionProperty         = "org.freedesktop.NetworkManager.Version"
+	networkManagerDbusActiveConnsProperty     = networkManagerDest + ".ActiveConnections"
+	networkManagerDbusActiveInterface         = "org.freedesktop.NetworkManager.Connection.Active"
+	networkManagerDbusActiveIP4ConfigProperty = networkManagerDbusActiveInterface + ".Ip4Config"
+	networkManagerDbusActiveIP6ConfigProperty = networkManagerDbusActiveInterface + ".Ip6Config"
+	networkManagerDbusActiveDevicesProperty   = networkManagerDbusActiveInterface + ".Devices"
+	networkManagerDbusIP4ConfigInterface      = "org.freedesktop.NetworkManager.IP4Config"
+	networkManagerDbusIP6ConfigInterface      = "org.freedesktop.NetworkManager.IP6Config"
+	networkManagerDbusDeviceInterface         = "org.freedesktop.NetworkManager.Device"
+	networkManagerDbusDeviceDhcp4ConfigProp   = networkManagerDbusDeviceInterface + ".Dhcp4Config"
+	networkManagerDbusDeviceDhcp6ConfigProp   = networkManagerDbusDeviceInterface + ".Dhcp6Config"
+	networkManagerDbusDhcp4ConfigInterface    = "org.freedesktop.NetworkManager.DHCP4Config"
+	networkManagerDbusDhcp6ConfigInterface    = "org.freedesktop.NetworkManager.DHCP6Config"
+	networkManagerDbusGetAppliedConnMethod    = networkManagerDbusDeviceInterface + ".GetAppliedConnection"
 
 	// NetworkManager dispatcher script path
 	networkManagerDispatcherDir  = "/etc/NetworkManager/dispatcher.d"
@@ -301,6 +315,220 @@ func GetNetworkManagerDNSMode() (string, error) {
 	return mode, nil
 }
 
+// GetNetworkManagerNameservers returns the DNS servers NetworkManager knows
+// about for every active connection, read live via D-Bus.
+//
+// olm's own NetworkManager DNS override (see NetworkManagerDNSConfigurator)
+// works by writing a [global-dns-domain-*] section to
+// /etc/NetworkManager/conf.d/olm-dns.conf and reloading NetworkManager. That
+// is NetworkManager's global DNS override mechanism: it replaces the DNS
+// servers NetworkManager's DnsManager computes as "effective" system-wide,
+// for every connection - not just what gets written to /etc/resolv.conf. So
+// once olm's override is active, even each connection's merged
+// IP4Config/IP6Config.NameserverData (the previous, sole source used here)
+// can end up reporting olm's own proxy address instead of the real network
+// DNS.
+//
+// To recover the real DNS regardless, this also reads two further sources
+// that NetworkManager's DNS merging - and therefore olm's global-dns override
+// - never touches, since both are populated independently of it:
+//   - Dhcp4Config/Dhcp6Config.Options["*name_servers"]: the raw nameserver
+//     list straight from the DHCP lease.
+//   - Device.GetAppliedConnection()'s ipv4.dns/ipv6.dns: the DNS servers
+//     explicitly configured on the connection profile itself, e.g. a static
+//     DNS override set by the user directly in NetworkManager (the
+//     NetworkManager equivalent of a manually-set Windows adapter DNS).
+//
+// IP4Config/IP6Config.NameserverData is still queried too, as a fallback for
+// setups the other two don't cover. Any of olm's own address that leaks
+// through any of these sources is expected to be dropped by the caller via
+// SystemDNSMonitor.SetExcludeIP.
+func GetNetworkManagerNameservers() ([]netip.Addr, error) {
+	conn, err := dbus.SystemBus()
+	if err != nil {
+		return nil, fmt.Errorf("connect to system bus: %w", err)
+	}
+	defer conn.Close()
+
+	nm := conn.Object(networkManagerDest, networkManagerDbusObjectNode)
+
+	activeVariant, err := nm.GetProperty(networkManagerDbusActiveConnsProperty)
+	if err != nil {
+		return nil, fmt.Errorf("get active connections: %w", err)
+	}
+	activePaths, ok := activeVariant.Value().([]dbus.ObjectPath)
+	if !ok {
+		return nil, errors.New("ActiveConnections is not a list of object paths")
+	}
+
+	ipConfigSources := []struct {
+		activeProperty string
+		configIface    string
+	}{
+		{networkManagerDbusActiveIP4ConfigProperty, networkManagerDbusIP4ConfigInterface},
+		{networkManagerDbusActiveIP6ConfigProperty, networkManagerDbusIP6ConfigInterface},
+	}
+
+	seen := make(map[netip.Addr]bool)
+	var servers []netip.Addr
+	add := func(addr netip.Addr) {
+		addr = addr.Unmap()
+		if !addr.IsValid() || addr.IsLoopback() || addr.IsLinkLocalUnicast() {
+			return
+		}
+		if !seen[addr] {
+			seen[addr] = true
+			servers = append(servers, addr)
+		}
+	}
+
+	for _, activePath := range activePaths {
+		active := conn.Object(networkManagerDest, activePath)
+
+		for _, src := range ipConfigSources {
+			cfgVariant, err := active.GetProperty(src.activeProperty)
+			if err != nil {
+				continue
+			}
+			cfgPath, ok := cfgVariant.Value().(dbus.ObjectPath)
+			if !ok || cfgPath == "" || cfgPath == "/" {
+				continue
+			}
+
+			nsVariant, err := conn.Object(networkManagerDest, cfgPath).GetProperty(src.configIface + ".NameserverData")
+			if err != nil {
+				continue
+			}
+			entries, ok := nsVariant.Value().([]map[string]dbus.Variant)
+			if !ok {
+				continue
+			}
+			for _, entry := range entries {
+				addrVariant, ok := entry["address"]
+				if !ok {
+					continue
+				}
+				addrStr, ok := addrVariant.Value().(string)
+				if !ok {
+					continue
+				}
+				if addr, err := netip.ParseAddr(addrStr); err == nil {
+					add(addr)
+				}
+			}
+		}
+
+		devicesVariant, err := active.GetProperty(networkManagerDbusActiveDevicesProperty)
+		if err != nil {
+			continue
+		}
+		devicePaths, ok := devicesVariant.Value().([]dbus.ObjectPath)
+		if !ok {
+			continue
+		}
+
+		for _, devicePath := range devicePaths {
+			device := conn.Object(networkManagerDest, devicePath)
+
+			for _, addr := range dhcpLeaseNameservers(conn, device, networkManagerDbusDeviceDhcp4ConfigProp, networkManagerDbusDhcp4ConfigInterface, "domain_name_servers") {
+				add(addr)
+			}
+			for _, addr := range dhcpLeaseNameservers(conn, device, networkManagerDbusDeviceDhcp6ConfigProp, networkManagerDbusDhcp6ConfigInterface, "dhcp6_name_servers") {
+				add(addr)
+			}
+			for _, addr := range appliedConnectionNameservers(device) {
+				add(addr)
+			}
+		}
+	}
+
+	return servers, nil
+}
+
+// dhcpLeaseNameservers reads a space-separated nameserver list out of a
+// device's Dhcp4Config/Dhcp6Config Options, straight from the DHCP lease -
+// data NetworkManager's DNS merging (and therefore olm's own global-dns
+// override) never touches.
+func dhcpLeaseNameservers(conn *dbus.Conn, device dbus.BusObject, configProperty, configIface, optionsKey string) []netip.Addr {
+	cfgVariant, err := device.GetProperty(configProperty)
+	if err != nil {
+		return nil
+	}
+	cfgPath, ok := cfgVariant.Value().(dbus.ObjectPath)
+	if !ok || cfgPath == "" || cfgPath == "/" {
+		return nil
+	}
+
+	optsVariant, err := conn.Object(networkManagerDest, cfgPath).GetProperty(configIface + ".Options")
+	if err != nil {
+		return nil
+	}
+	opts, ok := optsVariant.Value().(map[string]dbus.Variant)
+	if !ok {
+		return nil
+	}
+	raw, ok := opts[optionsKey]
+	if !ok {
+		return nil
+	}
+	str, ok := raw.Value().(string)
+	if !ok {
+		return nil
+	}
+
+	var addrs []netip.Addr
+	for _, field := range strings.Fields(str) {
+		if addr, err := netip.ParseAddr(field); err == nil {
+			addrs = append(addrs, addr)
+		}
+	}
+	return addrs
+}
+
+// appliedConnectionNameservers reads the ipv4.dns/ipv6.dns servers configured
+// on the device's currently-applied connection profile - e.g. a static DNS
+// override set by the user directly in NetworkManager - independent of DHCP
+// and of olm's own global-dns override.
+func appliedConnectionNameservers(device dbus.BusObject) []netip.Addr {
+	var settings map[string]map[string]dbus.Variant
+	var versionID uint64
+	if err := device.Call(networkManagerDbusGetAppliedConnMethod, 0, uint32(0)).Store(&settings, &versionID); err != nil {
+		return nil
+	}
+
+	var addrs []netip.Addr
+
+	if ipv4, ok := settings["ipv4"]; ok {
+		if dnsVariant, ok := ipv4["dns"]; ok {
+			if raw, ok := dnsVariant.Value().([]uint32); ok {
+				for _, v := range raw {
+					var b [4]byte
+					// NetworkManager encodes IPv4 addresses in this setting as
+					// network-byte-order bytes reinterpreted as a native uint32.
+					binary.LittleEndian.PutUint32(b[:], v)
+					addrs = append(addrs, netip.AddrFrom4(b))
+				}
+			}
+		}
+	}
+
+	if ipv6, ok := settings["ipv6"]; ok {
+		if dnsVariant, ok := ipv6["dns"]; ok {
+			if raw, ok := dnsVariant.Value().([][]byte); ok {
+				for _, b := range raw {
+					if len(b) == 16 {
+						var arr [16]byte
+						copy(arr[:], b)
+						addrs = append(addrs, netip.AddrFrom16(arr))
+					}
+				}
+			}
+		}
+	}
+
+	return addrs
+}
+
 // GetNetworkManagerVersion returns the version of NetworkManager
 func GetNetworkManagerVersion() (string, error) {
 	conn, err := dbus.SystemBus()

dns/sysresolver.go

@@ -0,0 +1,274 @@
+package dns
+
+import (
+	"context"
+	"net"
+	"net/netip"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/fosrl/newt/logger"
+	"github.com/miekg/dns"
+)
+
+const defaultPollInterval = 30 * time.Second
+
+// dnsHealthCheckTimeout bounds how long we wait for a candidate DNS server to
+// answer a health-check query before considering it unusable.
+const dnsHealthCheckTimeout = 2 * time.Second
+
+// SystemDNSMonitor monitors the host system's DNS configuration and notifies
+// callers when it changes. The reported servers are in "host:port" format
+// (e.g. "8.8.8.8:53") and can be used directly as UpstreamDNS and PublicDNS.
+//
+// Platform behaviour:
+//   - Linux: reads /run/systemd/resolve/resolv.conf when present (updated by
+//     systemd-resolved on every DHCP change), then falls back to
+//     /etc/resolv.conf.olm.backup (written before olm overrides DNS), and
+//     finally /etc/resolv.conf.
+//   - macOS: reads the unscoped resolvers from `scutil --dns`, falling back
+//     to /etc/resolv.conf if scutil is unavailable. This includes olm's own
+//     supplemental scutil DNS override entry, which is expected to be
+//     filtered out via SetExcludeIP.
+//   - Windows: enumerates every network adapter's effective DNS servers
+//     (static if set, else DHCP-assigned) from the registry.
+//   - Other platforms: returns an empty list (no-op monitor).
+type SystemDNSMonitor struct {
+	mu         sync.RWMutex
+	current    []string // last health-checked, applied server list
+	lastRaw    []string // last raw (exclude-filtered but unvalidated) candidate list seen
+	onChange   func(servers []string)
+	interval   time.Duration
+	stopCh     chan struct{}
+	excludeMu  sync.RWMutex
+	excludeIPs map[netip.Addr]bool
+}
+
+// NewSystemDNSMonitor creates a new monitor. onChange is called with the new
+// server list whenever a change is detected; it is also called once from Start
+// with the initial values. A zero interval uses the 30-second default.
+func NewSystemDNSMonitor(interval time.Duration, onChange func(servers []string)) *SystemDNSMonitor {
+	if interval <= 0 {
+		interval = defaultPollInterval
+	}
+	return &SystemDNSMonitor{
+		interval:   interval,
+		onChange:   onChange,
+		stopCh:     make(chan struct{}),
+		excludeIPs: make(map[netip.Addr]bool),
+	}
+}
+
+// SetExcludeIP registers an IP address that must never appear in the reported
+// DNS server list. Call this after olm's DNS proxy is created to prevent the
+// proxy's own IP from being returned as an upstream server when the OS DNS has
+// been overridden to point at the proxy.
+func (m *SystemDNSMonitor) SetExcludeIP(ip netip.Addr) {
+	m.excludeMu.Lock()
+	m.excludeIPs[ip.Unmap()] = true
+	m.excludeMu.Unlock()
+}
+
+// Start reads the current system DNS immediately, fires onChange, then polls
+// in the background until Stop is called or ctx is cancelled.
+func (m *SystemDNSMonitor) Start(ctx context.Context) {
+	m.applyCandidates(m.readFiltered())
+	go m.run(ctx)
+}
+
+// Stop halts the background polling goroutine.
+func (m *SystemDNSMonitor) Stop() {
+	select {
+	case <-m.stopCh:
+	default:
+		close(m.stopCh)
+	}
+}
+
+// Current returns the most recently observed system DNS servers.
+func (m *SystemDNSMonitor) Current() []string {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	out := make([]string, len(m.current))
+	copy(out, m.current)
+	return out
+}
+
+// readFiltered calls the platform-specific readSystemDNS and removes any
+// addresses that have been excluded via SetExcludeIP. If all addresses are
+// excluded the function returns nil so the caller can retain the last
+// known-good value.
+func (m *SystemDNSMonitor) readFiltered() []string {
+	return m.filterExcluded(readSystemDNS())
+}
+
+// filterExcluded removes any addresses that have been excluded via
+// SetExcludeIP from servers. Used both for the internally-polled server list
+// (readFiltered) and for server lists reported externally (ReportExternal) by
+// platforms - Android, iOS - where olm cannot read the OS's DNS configuration
+// itself.
+func (m *SystemDNSMonitor) filterExcluded(servers []string) []string {
+	m.excludeMu.RLock()
+	excludeIPs := m.excludeIPs
+	m.excludeMu.RUnlock()
+
+	if len(excludeIPs) == 0 {
+		return servers
+	}
+
+	var filtered []string
+	for _, s := range servers {
+		host, _, err := net.SplitHostPort(s)
+		if err != nil {
+			filtered = append(filtered, s)
+			continue
+		}
+		addr, err := netip.ParseAddr(host)
+		if err != nil || excludeIPs[addr.Unmap()] {
+			continue
+		}
+		filtered = append(filtered, s)
+	}
+	return filtered
+}
+
+// ReportExternal applies an externally-observed DNS server list (e.g. from
+// Android's ConnectivityManager or iOS's SCDynamicStore, where the platform
+// itself - not olm - must detect the OS's real DNS configuration) through the
+// same exclude-IP filtering, health-check validation, and change-detection as
+// the internal poll loop, firing onChange if the result differs from the last
+// known value.
+func (m *SystemDNSMonitor) ReportExternal(servers []string) {
+	m.applyCandidates(m.filterExcluded(servers))
+}
+
+func (m *SystemDNSMonitor) run(ctx context.Context) {
+	ticker := time.NewTicker(m.interval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-m.stopCh:
+			return
+		case <-ticker.C:
+			m.applyCandidates(m.readFiltered())
+		}
+	}
+}
+
+// applyCandidates takes an exclude-filtered (but not yet health-checked) list
+// of candidate DNS servers - from either the internal poll loop or
+// ReportExternal - and, only if it differs from the last raw list seen (to
+// avoid re-running network health checks on every 30-second poll tick when
+// nothing has actually changed), health-checks it via filterUnreachable and
+// applies whatever passes, firing onChange if the result changed.
+//
+// If none of the candidates pass the health check, the previous known-good
+// value is retained rather than clobbered - this is what protects against
+// e.g. a carrier reporting a DNS server (such as T-Mobile's internal ULA
+// DNS64 resolvers) that is technically "the system DNS" but not actually
+// reachable/usable from wherever queries are sent.
+func (m *SystemDNSMonitor) applyCandidates(raw []string) {
+	if len(raw) == 0 {
+		return
+	}
+
+	m.mu.Lock()
+	if dnsSlicesEqual(m.lastRaw, raw) {
+		m.mu.Unlock()
+		logger.Debug("System DNS candidates unchanged, skipping health check: %v", raw)
+		return
+	}
+	m.lastRaw = raw
+	m.mu.Unlock()
+
+	logger.Debug("System DNS candidates changed, health-checking: %v", raw)
+	validated := filterUnreachable(raw)
+	if len(validated) == 0 {
+		logger.Warn("None of the detected DNS servers answered a health-check query, keeping previous value: %v", raw)
+		return
+	}
+
+	m.mu.Lock()
+	changed := !dnsSlicesEqual(m.current, validated)
+	if changed {
+		m.current = validated
+	}
+	m.mu.Unlock()
+
+	if changed && m.onChange != nil {
+		logger.Info("System DNS changed: %v", validated)
+		m.onChange(validated)
+	}
+}
+
+// dnsServerReachable is a seam for tests; production code always uses probeDNSServerErr.
+var dnsServerReachable = probeDNSServerErr
+
+// filterUnreachable validates that each candidate server actually answers a
+// DNS query before it's trusted, rather than statically guessing from the
+// address (e.g. rejecting all private/ULA addresses, which would also reject
+// a perfectly valid home router forwarding to a real resolver). Checks run
+// concurrently so multiple candidates don't serialize the timeout.
+func filterUnreachable(servers []string) []string {
+	if len(servers) == 0 {
+		return servers
+	}
+
+	reachable := make([]bool, len(servers))
+	errs := make([]error, len(servers))
+	var wg sync.WaitGroup
+	for i, server := range servers {
+		wg.Add(1)
+		go func(i int, server string) {
+			defer wg.Done()
+			reachable[i], errs[i] = dnsServerReachable(server)
+		}(i, server)
+	}
+	wg.Wait()
+
+	var result []string
+	for i, server := range servers {
+		if reachable[i] {
+			result = append(result, server)
+		} else {
+			logger.Debug("Discarding DNS server %s: failed health check: %v", server, errs[i])
+		}
+	}
+	return result
+}
+
+// probeDNSServerErr sends a minimal root NS query to confirm a candidate server
+// actually answers, without depending on any specific external hostname being
+// reachable (which could itself be blocked/filtered independently of whether
+// the resolver works). The returned error is kept (rather than just a bool) so
+// callers can log why a candidate was rejected (unreachable route, timeout, etc.).
+func probeDNSServerErr(server string) (bool, error) {
+	client := &dns.Client{Timeout: dnsHealthCheckTimeout}
+	msg := new(dns.Msg)
+	msg.SetQuestion(".", dns.TypeNS)
+	_, _, err := client.Exchange(msg, server)
+	return err == nil, err
+}
+
+// dnsSlicesEqual reports whether two server lists are equal regardless of order.
+func dnsSlicesEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	ac := make([]string, len(a))
+	bc := make([]string, len(b))
+	copy(ac, a)
+	copy(bc, b)
+	sort.Strings(ac)
+	sort.Strings(bc)
+	for i := range ac {
+		if ac[i] != bc[i] {
+			return false
+		}
+	}
+	return true
+}

dns/sysresolver_android.go

@@ -0,0 +1,18 @@
+//go:build android
+
+package dns
+
+// readSystemDNS returns nil on Android: olm cannot read the OS's DNS
+// configuration itself here, so the app detects it (via ConnectivityManager)
+// and pushes it in through Olm.SetSystemDNS instead (see SystemDnsMonitor.java).
+//
+// This is a dedicated file (rather than falling through the general
+// sysresolver_stub.go catch-all) because wireguard-android's build passes
+// "-tags linux" to share Linux netlink code with Android, and that custom tag
+// makes "!linux" evaluate to false even on a real GOOS=android build, which
+// would otherwise make sysresolver_stub.go stop applying and leave
+// readSystemDNS undefined. An explicit "android" constraint isn't affected by
+// that, since nothing passes a conflicting "-tags android".
+func readSystemDNS() []string {
+	return nil
+}

dns/sysresolver_darwin.go

@@ -0,0 +1,116 @@
+//go:build darwin && !ios && !nosysresolver
+
+package dns
+
+import (
+	"bufio"
+	"net"
+	"net/netip"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+// scutilPath is the well-known location of scutil on macOS.
+const scutilPath = "/usr/sbin/scutil"
+
+// readSystemDNS returns the current system DNS servers in "host:53" format.
+//
+// olm's own DNS override is itself a scutil supplemental resolver (see
+// dns/platform/darwin.go), and macOS gives supplemental resolvers priority
+// over the primary network service's resolver when generating the merged
+// configuration - which is also what gets mirrored into /etc/resolv.conf.  So
+// once olm's override is active, /etc/resolv.conf (and a naive read of just
+// the top of "scutil --dns") reflects olm's own proxy address, not the
+// physical network's real DNS.
+//
+// Instead this reads every resolver in the unscoped "DNS configuration"
+// section of `scutil --dns` (the "(for scoped queries)" section that follows
+// only duplicates per-interface resolvers and is skipped), which includes
+// both the real physical-network resolver and olm's own supplemental one.
+// olm's own address is expected to be filtered out by the caller via
+// SystemDNSMonitor.SetExcludeIP, the same mechanism used on Windows to drop
+// olm's own adapter DNS entry.
+//
+// /etc/resolv.conf is kept as a fallback for when scutil is unavailable.
+func readSystemDNS() []string {
+	if out, err := exec.Command(scutilPath, "--dns").Output(); err == nil {
+		if servers := parseScutilDNS(string(out)); len(servers) > 0 {
+			return servers
+		}
+	}
+	return parseMacResolvConf("/etc/resolv.conf")
+}
+
+// parseScutilDNS extracts nameserver addresses from the unscoped "DNS
+// configuration" section at the top of `scutil --dns` output, stopping at
+// the "DNS configuration (for scoped queries)" section that follows it.
+func parseScutilDNS(output string) []string {
+	var result []string
+	seen := make(map[string]bool)
+
+	scanner := bufio.NewScanner(strings.NewReader(output))
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if strings.HasPrefix(line, "DNS configuration (for scoped queries)") {
+			break
+		}
+		if !strings.HasPrefix(line, "nameserver[") {
+			continue
+		}
+
+		parts := strings.SplitN(line, ":", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		addr, err := netip.ParseAddr(strings.TrimSpace(parts[1]))
+		if err != nil {
+			continue
+		}
+		if addr.IsLoopback() || addr.IsLinkLocalUnicast() {
+			continue
+		}
+		hp := net.JoinHostPort(addr.String(), "53")
+		if !seen[hp] {
+			seen[hp] = true
+			result = append(result, hp)
+		}
+	}
+	return result
+}
+
+func parseMacResolvConf(path string) []string {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil
+	}
+	defer f.Close()
+
+	var result []string
+	seen := make(map[string]bool)
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if !strings.HasPrefix(line, "nameserver") {
+			continue
+		}
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		addr, err := netip.ParseAddr(fields[1])
+		if err != nil {
+			continue
+		}
+		if addr.IsLoopback() || addr.IsLinkLocalUnicast() {
+			continue
+		}
+		s := net.JoinHostPort(addr.String(), "53")
+		if !seen[s] {
+			seen[s] = true
+			result = append(result, s)
+		}
+	}
+	return result
+}

dns/sysresolver_darwin_nosysresolver.go

@@ -0,0 +1,17 @@
+//go:build darwin && !ios && nosysresolver
+
+package dns
+
+// readSystemDNS is disabled by the nosysresolver build tag. This is used for
+// the macOS app build: unlike the CLI, the app's PacketTunnel system
+// extension additionally applies NEDNSSettings (see apple/PacketTunnel),
+// which can become the system's primary resolver and make /etc/resolv.conf
+// reflect olm's own proxy IP instead of the real upstream DNS. Rather than
+// have olm poll a value that may be self-referential, the app pushes the
+// real DNS servers in via SetSystemDNS (detected in Swift via
+// SCDynamicStore) exactly like Android and iOS. The CLI keeps the real
+// implementation in sysresolver_darwin.go, since it has no such override
+// mechanism and /etc/resolv.conf always reflects the physical network there.
+func readSystemDNS() []string {
+	return nil
+}

dns/sysresolver_ios.go

@@ -0,0 +1,18 @@
+//go:build ios
+
+package dns
+
+// readSystemDNS returns nil on iOS: olm cannot read the OS's DNS
+// configuration itself here, so the app must detect it and push it in
+// through the equivalent of Olm.SetSystemDNS instead.
+//
+// This is a dedicated file (rather than falling through the general
+// sysresolver_stub.go catch-all) because Go's build constraint evaluator
+// treats GOOS=ios as implicitly satisfying the "darwin" tag as well as
+// "ios". sysresolver_stub.go excludes with "!darwin", which is false for an
+// iOS build, so the stub silently stops applying and would leave
+// readSystemDNS undefined. An explicit "ios" constraint isn't affected by
+// that ambiguity.
+func readSystemDNS() []string {
+	return nil
+}

dns/sysresolver_linux.go

@@ -0,0 +1,129 @@
+//go:build linux && !android
+
+package dns
+
+import (
+	"bufio"
+	"net"
+	"net/netip"
+	"os"
+	"strings"
+
+	platform "github.com/fosrl/olm/dns/platform"
+)
+
+// readSystemDNS returns the current system DNS servers in "host:53" format.
+//
+// Resolution order:
+//  1. /run/systemd/resolve/resolv.conf, but only when systemd-resolved is
+//     actually running (checked live via D-Bus) — the file lives in /run and
+//     can linger there, frozen at whatever it last contained, long after the
+//     service that maintained it has stopped (e.g. it ran earlier in the
+//     boot and was since disabled). Trusting its mere existence would report
+//     that stale snapshot forever instead of falling through to a live
+//     source. When the service is actually up the file is maintained with
+//     the real per-link DNS servers, updated on every DHCP change and never
+//     touched by olm's D-Bus DNS override.
+//  2. NetworkManager, queried live over D-Bus — NetworkManager's own view of
+//     each active connection's DNS servers, independent of what is currently
+//     written to /etc/resolv.conf. This covers NetworkManager's "dnsmasq" and
+//     "unbound" DNS modes, where /etc/resolv.conf only contains a loopback
+//     stub address, and stays accurate even if olm's own override has
+//     directly overwritten /etc/resolv.conf, without going stale the way a
+//     one-time backup snapshot would if the real DNS changes mid-override
+//     (e.g. the user switches WiFi networks). olm's own NetworkManager
+//     override is itself a NetworkManager-level global DNS override (see
+//     platform.GetNetworkManagerNameservers), so this also reads each
+//     device's raw DHCP lease and applied-connection settings, which that
+//     override does not touch, to recover the real servers.
+//  3. /etc/resolv.conf.olm.backup — written by olm before it overrides
+//     /etc/resolv.conf on non-systemd systems, for when NetworkManager isn't
+//     in use at all.
+//  4. /etc/resolv.conf — plain fallback.
+//
+// Loopback and link-local addresses (e.g. 127.0.0.53, ::1) are excluded
+// because they are stub resolver addresses, not real upstream servers.
+func readSystemDNS() []string {
+	// Prefer systemd-resolved's resolved (non-stub) resolv.conf, but only if
+	// systemd-resolved is actually alive right now - see resolution order
+	// note above on why the file's existence alone isn't enough.
+	if platform.IsSystemdResolvedAvailable() {
+		if servers := parseResolvConf("/run/systemd/resolve/resolv.conf"); len(servers) > 0 {
+			return servers
+		}
+	}
+
+	if servers := readNetworkManagerDNS(); len(servers) > 0 {
+		return servers
+	}
+
+	// If olm has already overridden /etc/resolv.conf the backup holds the
+	// original pre-override DNS servers.
+	if _, err := os.Stat("/etc/resolv.conf.olm.backup"); err == nil {
+		if servers := parseResolvConf("/etc/resolv.conf.olm.backup"); len(servers) > 0 {
+			return servers
+		}
+	}
+
+	return parseResolvConf("/etc/resolv.conf")
+}
+
+// readNetworkManagerDNS returns the DNS servers NetworkManager reports over
+// D-Bus for its active connections, in "host:53" format. Returns nil if
+// NetworkManager isn't running or reports nothing usable.
+func readNetworkManagerDNS() []string {
+	addrs, err := platform.GetNetworkManagerNameservers()
+	if err != nil || len(addrs) == 0 {
+		return nil
+	}
+
+	result := make([]string, 0, len(addrs))
+	for _, addr := range addrs {
+		result = append(result, addrToHostPort(addr))
+	}
+	return result
+}
+
+// parseResolvConf reads nameserver lines from a resolv.conf-style file,
+// skipping loopback and link-local addresses.
+func parseResolvConf(path string) []string {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil
+	}
+	defer f.Close()
+
+	var result []string
+	seen := make(map[string]bool)
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if !strings.HasPrefix(line, "nameserver") {
+			continue
+		}
+		fields := strings.Fields(line)
+		if len(fields) < 2 {
+			continue
+		}
+		addr, err := netip.ParseAddr(fields[1])
+		if err != nil {
+			continue
+		}
+		if addr.IsLoopback() || addr.IsLinkLocalUnicast() {
+			continue
+		}
+		s := addrToHostPort(addr)
+		if !seen[s] {
+			seen[s] = true
+			result = append(result, s)
+		}
+	}
+	return result
+}
+
+// addrToHostPort converts a netip.Addr to "addr:53" format, wrapping IPv6
+// addresses in brackets as required by net.JoinHostPort.
+func addrToHostPort(addr netip.Addr) string {
+	return net.JoinHostPort(addr.String(), "53")
+}

dns/sysresolver_stub.go

@@ -0,0 +1,23 @@
+//go:build !linux && !darwin && !windows && !android
+
+package dns
+
+// readSystemDNS returns nil on platforms where automatic DNS discovery is not
+// implemented (freebsd, etc.).  Callers should fall back to a statically
+// configured DNS server.
+//
+// android and ios are excluded from this constraint (and have their own
+// sysresolver_android.go / sysresolver_ios.go with an explicit "android" /
+// "ios" tag) rather than falling through the "!linux" / "!darwin" catch-all
+// here:
+//   - wireguard-android's build passes "-tags linux" to share Linux netlink code
+//     (a deliberate, long-standing convention, since Android's kernel is Linux), and Go's
+//     build constraint evaluator can't distinguish a custom "-tags linux" from the real
+//     GOOS=linux - so with that tag set, "!linux" is false even though GOOS is actually
+//     android, and this file would silently stop applying, leaving readSystemDNS undefined.
+//   - Go's build constraint evaluator treats GOOS=ios as implicitly satisfying the
+//     "darwin" tag as well as "ios", so "!darwin" is false on an iOS build too, which
+//     would otherwise leave readSystemDNS undefined there as well.
+func readSystemDNS() []string {
+	return nil
+}

dns/sysresolver_test.go

@@ -0,0 +1,149 @@
+package dns
+
+import (
+	"net/netip"
+	"reflect"
+	"testing"
+)
+
+// stubReachable overrides dnsServerReachable for the duration of the test so
+// tests don't depend on real network access, restoring the original on
+// cleanup.
+func stubReachable(t *testing.T, fn func(server string) bool) {
+	t.Helper()
+	orig := dnsServerReachable
+	dnsServerReachable = func(server string) (bool, error) { return fn(server), nil }
+	t.Cleanup(func() { dnsServerReachable = orig })
+}
+
+func allReachable(t *testing.T) {
+	stubReachable(t, func(string) bool { return true })
+}
+
+func TestReportExternalFiltersExcludedIP(t *testing.T) {
+	allReachable(t)
+
+	var got []string
+	m := &SystemDNSMonitor{
+		excludeIPs: make(map[netip.Addr]bool),
+		onChange: func(servers []string) {
+			got = servers
+		},
+	}
+	m.SetExcludeIP(netip.MustParseAddr("10.0.0.1"))
+
+	m.ReportExternal([]string{"10.0.0.1:53", "8.8.8.8:53"})
+
+	want := []string{"8.8.8.8:53"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("onChange servers = %v, want %v", got, want)
+	}
+	if !reflect.DeepEqual(m.Current(), want) {
+		t.Fatalf("Current() = %v, want %v", m.Current(), want)
+	}
+}
+
+func TestReportExternalAllExcludedIsNoop(t *testing.T) {
+	allReachable(t)
+
+	called := false
+	m := &SystemDNSMonitor{
+		excludeIPs: make(map[netip.Addr]bool),
+		current:    []string{"1.1.1.1:53"},
+		onChange: func(servers []string) {
+			called = true
+		},
+	}
+	m.SetExcludeIP(netip.MustParseAddr("10.0.0.1"))
+
+	m.ReportExternal([]string{"10.0.0.1:53"})
+
+	if called {
+		t.Fatal("onChange should not fire when all reported servers are excluded")
+	}
+	want := []string{"1.1.1.1:53"}
+	if !reflect.DeepEqual(m.Current(), want) {
+		t.Fatalf("Current() = %v, want unchanged %v", m.Current(), want)
+	}
+}
+
+func TestReportExternalOnlyFiresOnChange(t *testing.T) {
+	allReachable(t)
+
+	calls := 0
+	m := &SystemDNSMonitor{
+		excludeIPs: make(map[netip.Addr]bool),
+		onChange: func(servers []string) {
+			calls++
+		},
+	}
+
+	m.ReportExternal([]string{"8.8.8.8:53"})
+	m.ReportExternal([]string{"8.8.8.8:53"})
+
+	if calls != 1 {
+		t.Fatalf("onChange fired %d times, want 1", calls)
+	}
+}
+
+func TestReportExternalDropsUnreachableServer(t *testing.T) {
+	// Simulates e.g. T-Mobile's private ULA DNS64 resolver: technically "the
+	// system DNS" per the OS, but doesn't actually answer queries.
+	stubReachable(t, func(server string) bool {
+		return server != "[fd00:976a::9]:53"
+	})
+
+	var got []string
+	m := &SystemDNSMonitor{
+		excludeIPs: make(map[netip.Addr]bool),
+		onChange: func(servers []string) {
+			got = servers
+		},
+	}
+
+	m.ReportExternal([]string{"[fd00:976a::9]:53", "8.8.8.8:53"})
+
+	want := []string{"8.8.8.8:53"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("onChange servers = %v, want %v", got, want)
+	}
+}
+
+func TestReportExternalKeepsPreviousValueWhenAllUnreachable(t *testing.T) {
+	stubReachable(t, func(string) bool { return true })
+
+	called := false
+	m := &SystemDNSMonitor{
+		excludeIPs: make(map[netip.Addr]bool),
+		current:    []string{"1.1.1.1:53"},
+		onChange: func(servers []string) {
+			called = true
+		},
+	}
+
+	// Now simulate every candidate failing the health check (e.g. moved to a
+	// network where none of the reported servers actually respond).
+	stubReachable(t, func(string) bool { return false })
+
+	m.ReportExternal([]string{"[fd00:976a::9]:53", "[fd00:976a::10]:53"})
+
+	if called {
+		t.Fatal("onChange should not fire when no candidate passes the health check")
+	}
+	want := []string{"1.1.1.1:53"}
+	if !reflect.DeepEqual(m.Current(), want) {
+		t.Fatalf("Current() = %v, want unchanged %v", m.Current(), want)
+	}
+}
+
+func TestFilterUnreachable(t *testing.T) {
+	stubReachable(t, func(server string) bool {
+		return server == "8.8.8.8:53"
+	})
+
+	got := filterUnreachable([]string{"10.0.0.1:53", "8.8.8.8:53", "9.9.9.9:53"})
+	want := []string{"8.8.8.8:53"}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("filterUnreachable() = %v, want %v", got, want)
+	}
+}

dns/sysresolver_windows.go

@@ -0,0 +1,110 @@
+//go:build windows
+
+package dns
+
+import (
+	"fmt"
+	"net"
+	"net/netip"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+const (
+	tcpipInterfacesPath = `SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces`
+	dhcpNameServerKey   = "DhcpNameServer"
+	staticNameServerKey = "NameServer"
+)
+
+// readSystemDNS returns the current system DNS servers in "host:53" format by
+// enumerating every network adapter in the Windows registry.
+//
+// For each adapter olm reads the effective DNS servers: static (NameServer)
+// if set, since a static entry overrides DHCP for that adapter and is what
+// the OS resolver actually uses, otherwise falling back to the DHCP-assigned
+// servers (DhcpNameServer). This also picks up olm's own WireGuard adapter,
+// which olm points at its local DNS proxy via a static NameServer entry; that
+// address is expected to be filtered out by the caller via
+// SystemDNSMonitor.SetExcludeIP. Loopback and link-local addresses are
+// excluded.
+func readSystemDNS() []string {
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE, tcpipInterfacesPath, registry.ENUMERATE_SUB_KEYS)
+	if err != nil {
+		return nil
+	}
+	defer key.Close()
+
+	subkeys, err := key.ReadSubKeyNames(-1)
+	if err != nil {
+		return nil
+	}
+
+	seen := make(map[string]bool)
+	var result []string
+
+	for _, guid := range subkeys {
+		path := fmt.Sprintf(`%s\%s`, tcpipInterfacesPath, guid)
+		iKey, err := registry.OpenKey(registry.LOCAL_MACHINE, path, registry.QUERY_VALUE)
+		if err != nil {
+			continue
+		}
+
+		servers, _, err := iKey.GetStringValue(staticNameServerKey)
+		if err != nil || servers == "" {
+			servers, _, err = iKey.GetStringValue(dhcpNameServerKey)
+		}
+		iKey.Close()
+		if err != nil || servers == "" {
+			continue
+		}
+
+		for _, s := range splitWinDNSList(servers) {
+			addr, err := netip.ParseAddr(s)
+			if err != nil {
+				continue
+			}
+			if addr.IsLoopback() || addr.IsLinkLocalUnicast() {
+				continue
+			}
+			hp := net.JoinHostPort(addr.String(), "53")
+			if !seen[hp] {
+				seen[hp] = true
+				result = append(result, hp)
+			}
+		}
+	}
+
+	return result
+}
+
+// splitWinDNSList splits a Windows DNS server list that may be comma- or
+// space-separated.
+func splitWinDNSList(s string) []string {
+	var out []string
+	for _, part := range splitByRunes(s, []rune{',', ' '}) {
+		if part != "" {
+			out = append(out, part)
+		}
+	}
+	return out
+}
+
+func splitByRunes(s string, delims []rune) []string {
+	var result []string
+	start := 0
+	for i, r := range s {
+		for _, d := range delims {
+			if r == d {
+				if i > start {
+					result = append(result, s[start:i])
+				}
+				start = i + len(string(r))
+				break
+			}
+		}
+	}
+	if start < len(s) {
+		result = append(result, s[start:])
+	}
+	return result
+}

go.mod

@@ -4,15 +4,15 @@ go 1.25.0
 
 require (
 	github.com/Microsoft/go-winio v0.6.2
-	github.com/fosrl/newt v1.12.0
+	github.com/fosrl/newt v1.14.0
 	github.com/godbus/dbus/v5 v5.2.2
 	github.com/gorilla/websocket v1.5.3
 	github.com/miekg/dns v1.1.70
-	golang.org/x/sys v0.42.0
+	golang.org/x/sys v0.46.0
 	golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb
 	golang.zx2c4.com/wireguard/wgctrl v0.0.0-20241231184526-a9ab2273dd10
 	gvisor.dev/gvisor v0.0.0-20250503011706-39ed1f5ac29c
-	software.sslmate.com/src/go-pkcs12 v0.7.0
+	software.sslmate.com/src/go-pkcs12 v0.7.3
 )
 
 require (
@@ -20,15 +20,15 @@ require (
 	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/vishvananda/netlink v1.3.1 // indirect
 	github.com/vishvananda/netns v0.0.5 // indirect
-	golang.org/x/crypto v0.49.0 // indirect
+	golang.org/x/crypto v0.53.0 // indirect
 	golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 // indirect
-	golang.org/x/mod v0.33.0 // indirect
-	golang.org/x/net v0.52.0 // indirect
+	golang.org/x/mod v0.34.0 // indirect
+	golang.org/x/net v0.56.0 // indirect
 	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/time v0.12.0 // indirect
-	golang.org/x/tools v0.42.0 // indirect
+	golang.org/x/tools v0.43.0 // indirect
 	golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 // indirect
-	golang.zx2c4.com/wireguard/windows v0.5.3 // indirect
+	golang.zx2c4.com/wireguard/windows v1.0.1 // indirect
 )
 
 // To be used ONLY for local development

go.sum

@@ -1,7 +1,7 @@
 github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
 github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
-github.com/fosrl/newt v1.12.0 h1:IodzVlsprOYkHvKrXwDfDTh2ZMtXV6IG1rhUj6Jhd44=
-github.com/fosrl/newt v1.12.0/go.mod h1:IJW2sZ4WKKLRuxMz6oBm8PMyAEVkOxZk6d1OUV5/LPM=
+github.com/fosrl/newt v1.14.0 h1:9jpyfCNAtsH7rPojyIGJwqOqnLZdxm8b+njY5ZuY/6c=
+github.com/fosrl/newt v1.14.0/go.mod h1:l6kWoZPSaXT+ZRUjiyPgwflRqZWYaXpUj9oQ0sOPh4o=
 github.com/godbus/dbus/v5 v5.2.2 h1:TUR3TgtSVDmjiXOgAAyaZbYmIeP3DPkld3jgKGV8mXQ=
 github.com/godbus/dbus/v5 v5.2.2/go.mod h1:3AAv2+hPq5rdnr5txxxRwiGjPXamgoIHgz9FPBfOp3c=
 github.com/google/btree v1.1.3 h1:CVpQJjYgC4VbzxeGVHfvZrv1ctoYCAI8vbl07Fcxlyg=
@@ -16,33 +16,33 @@ github.com/vishvananda/netlink v1.3.1 h1:3AEMt62VKqz90r0tmNhog0r/PpWKmrEShJU0wJW
 github.com/vishvananda/netlink v1.3.1/go.mod h1:ARtKouGSTGchR8aMwmkzC0qiNPrrWO5JS/XMVl45+b4=
 github.com/vishvananda/netns v0.0.5 h1:DfiHV+j8bA32MFM7bfEunvT8IAqQ/NzSJHtcmW5zdEY=
 github.com/vishvananda/netns v0.0.5/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
-golang.org/x/crypto v0.49.0 h1:+Ng2ULVvLHnJ/ZFEq4KdcDd/cfjrrjjNSXNzxg0Y4U4=
-golang.org/x/crypto v0.49.0/go.mod h1:ErX4dUh2UM+CFYiXZRTcMpEcN8b/1gxEuv3nODoYtCA=
+golang.org/x/crypto v0.53.0 h1:QZ4Muo8THX6CizN2vPPd5fBGHyogrdK9fG4wLPFUsto=
+golang.org/x/crypto v0.53.0/go.mod h1:DNLU434OwVakk9PzuwV8w62mAJpRJL3vsgcfp4Qnsio=
 golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 h1:zfMcR1Cs4KNuomFFgGefv5N0czO2XZpUbxGUy8i8ug0=
 golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6/go.mod h1:46edojNIoXTNOhySWIWdix628clX9ODXwPsQuG6hsK0=
-golang.org/x/mod v0.33.0 h1:tHFzIWbBifEmbwtGz65eaWyGiGZatSrT9prnU8DbVL8=
-golang.org/x/mod v0.33.0/go.mod h1:swjeQEj+6r7fODbD2cqrnje9PnziFuw4bmLbBZFrQ5w=
-golang.org/x/net v0.52.0 h1:He/TN1l0e4mmR3QqHMT2Xab3Aj3L9qjbhRm78/6jrW0=
-golang.org/x/net v0.52.0/go.mod h1:R1MAz7uMZxVMualyPXb+VaqGSa3LIaUqk0eEt3w36Sw=
+golang.org/x/mod v0.34.0 h1:xIHgNUUnW6sYkcM5Jleh05DvLOtwc6RitGHbDk4akRI=
+golang.org/x/mod v0.34.0/go.mod h1:ykgH52iCZe79kzLLMhyCUzhMci+nQj+0XkbXpNYtVjY=
+golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
+golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
 golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
 golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
-golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/sys v0.46.0 h1:noSf2Fq6F8DBgS+LysIkx7rIExoNHJsxOAtPp4rthXw=
+golang.org/x/sys v0.46.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/time v0.12.0 h1:ScB/8o8olJvc+CQPWrK3fPZNfh7qgwCrY0zJmoEQLSE=
 golang.org/x/time v0.12.0/go.mod h1:CDIdPxbZBQxdj6cxyCIdrNogrJKMJ7pr37NYpMcMDSg=
-golang.org/x/tools v0.42.0 h1:uNgphsn75Tdz5Ji2q36v/nsFSfR/9BRFvqhGBaJGd5k=
-golang.org/x/tools v0.42.0/go.mod h1:Ma6lCIwGZvHK6XtgbswSoWroEkhugApmsXyrUmBhfr0=
+golang.org/x/tools v0.43.0 h1:12BdW9CeB3Z+J/I/wj34VMl8X+fEXBxVR90JeMX5E7s=
+golang.org/x/tools v0.43.0/go.mod h1:uHkMso649BX2cZK6+RpuIPXS3ho2hZo4FVwfoy1vIk0=
 golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2 h1:B82qJJgjvYKsXS9jeunTOisW56dUokqW/FOteYJJ/yg=
 golang.zx2c4.com/wintun v0.0.0-20230126152724-0fa3db229ce2/go.mod h1:deeaetjYA+DHMHg+sMSMI58GrEteJUUzzw7en6TJQcI=
 golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb h1:whnFRlWMcXI9d+ZbWg+4sHnLp52d5yiIPUxMBSt4X9A=
 golang.zx2c4.com/wireguard v0.0.0-20250521234502-f333402bd9cb/go.mod h1:rpwXGsirqLqN2L0JDJQlwOboGHmptD5ZD6T2VmcqhTw=
 golang.zx2c4.com/wireguard/wgctrl v0.0.0-20241231184526-a9ab2273dd10 h1:3GDAcqdIg1ozBNLgPy4SLT84nfcBjr6rhGtXYtrkWLU=
 golang.zx2c4.com/wireguard/wgctrl v0.0.0-20241231184526-a9ab2273dd10/go.mod h1:T97yPqesLiNrOYxkwmhMI0ZIlJDm+p0PMR8eRVeR5tQ=
-golang.zx2c4.com/wireguard/windows v0.5.3 h1:On6j2Rpn3OEMXqBq00QEDC7bWSZrPIHKIus8eIuExIE=
-golang.zx2c4.com/wireguard/windows v0.5.3/go.mod h1:9TEe8TJmtwyQebdFwAkEWOPr3prrtqm+REGFifP60hI=
+golang.zx2c4.com/wireguard/windows v1.0.1 h1:eOxiDVbywPC+ZQqvdCK7x+ZwWXKbYv50TtH8ysFIbw8=
+golang.zx2c4.com/wireguard/windows v1.0.1/go.mod h1:+fbT3FFdX4zzYDLwJh5+HPEcNN/3HyNdzhNSVsQM+zs=
 gvisor.dev/gvisor v0.0.0-20250503011706-39ed1f5ac29c h1:m/r7OM+Y2Ty1sgBQ7Qb27VgIMBW8ZZhT4gLnUyDIhzI=
 gvisor.dev/gvisor v0.0.0-20250503011706-39ed1f5ac29c/go.mod h1:3r5CMtNQMKIvBlrmM9xWUNamjKBYPOWyXOjmg5Kts3g=
-software.sslmate.com/src/go-pkcs12 v0.7.0 h1:Db8W44cB54TWD7stUFFSWxdfpdn6fZVcDl0w3R4RVM0=
-software.sslmate.com/src/go-pkcs12 v0.7.0/go.mod h1:Qiz0EyvDRJjjxGyUQa2cCNZn/wMyzrRJ/qcDXOQazLI=
+software.sslmate.com/src/go-pkcs12 v0.7.3 h1:JBQD3FDqYjTeyDAeZQklj2ar88ykBLtALloPJHyAauU=
+software.sslmate.com/src/go-pkcs12 v0.7.3/go.mod h1:Qiz0EyvDRJjjxGyUQa2cCNZn/wMyzrRJ/qcDXOQazLI=

olm/connect.go

@@ -150,6 +150,14 @@ func (o *Olm) handleConnect(msg websocket.WSMessage) {
 		logger.Error("Failed to create DNS proxy: %v", err)
 	}
 
+	// Tell the system DNS monitor to exclude the proxy IP so that subsequent
+	// polls never mistake the proxy for a real upstream server (on Linux the OS
+	// DNS is overridden to point at this IP, which would otherwise feed back
+	// into UpstreamDNS or PublicDNS on the next poll).
+	if o.dnsMonitor != nil && o.dnsProxy != nil {
+		o.dnsMonitor.SetExcludeIP(o.dnsProxy.GetProxyIP())
+	}
+
 	if err = network.ConfigureInterface(o.tunnelConfig.InterfaceName, wgData.TunnelIP, o.tunnelConfig.MTU); err != nil {
 		logger.Error("Failed to o.tunnelConfigure interface: %v", err)
 	}

olm/olm.go

@@ -43,12 +43,18 @@ type Olm struct {
 	middleDev    *olmDevice.MiddleDevice
 	sharedBind   *bind.SharedBind
 
-	dnsProxy         *dns.DNSProxy
-	apiServer        *api.API
-	websocket        *websocket.Client
-	holePunchManager *holepunch.Manager
-	peerManager      *peers.PeerManager
-	peerManagerMu    sync.RWMutex
+	dnsProxy   *dns.DNSProxy
+	dnsMonitor *dns.SystemDNSMonitor
+	// pendingSystemDNS holds a SetSystemDNS report received before dnsMonitor exists
+	// (e.g. Android/iOS push a value while the tunnel is still starting up), so it
+	// isn't silently dropped. Drained into dnsMonitor as soon as StartTunnel creates it.
+	pendingSystemDNSMu sync.Mutex
+	pendingSystemDNS   []string
+	apiServer          *api.API
+	websocket          *websocket.Client
+	holePunchManager   *holepunch.Manager
+	peerManager        *peers.PeerManager
+	peerManagerMu      sync.RWMutex
 	// Power mode management
 	currentPowerMode string
 	powerModeMu      sync.Mutex
@@ -392,11 +398,66 @@ func (o *Olm) StartTunnel(config TunnelConfig) {
 	o.tunnelRunning = true // Also set it here in case it is called externally
 	o.tunnelConfig = config
 
-	// TODO: we are hardcoding this for now but we should really pull it from the current config of the system
-	if o.tunnelConfig.DNS != "" {
-		o.tunnelConfig.PublicDNS = []string{o.tunnelConfig.DNS + ":53"}
-	} else {
-		o.tunnelConfig.PublicDNS = []string{"8.8.8.8:53"}
+	// Determine whether the system DNS monitor should also manage UpstreamDNS.
+	// If the caller did not provide an explicit UpstreamDNS (it was defaulted to
+	// 8.8.8.8:53 by the API handler), we want the monitor to keep it updated
+	// with whatever DNS the host network is currently using.
+	upstreamFromConfig := len(config.UpstreamDNS) > 0 &&
+		!(len(config.UpstreamDNS) == 1 && config.UpstreamDNS[0] == "8.8.8.8:53")
+	if upstreamFromConfig {
+		logger.Info("UpstreamDNS is statically configured (%v); automatic system DNS detection will only update PublicDNS, DNS forwarding will keep using the configured value even if it becomes unreachable on a new network", config.UpstreamDNS)
+	}
+
+	// Start the system DNS monitor. The callback fires synchronously once with
+	// the initial values so that PublicDNS (and optionally UpstreamDNS) are
+	// populated before the tunnel goroutine proceeds.
+	o.dnsMonitor = dns.NewSystemDNSMonitor(0, func(servers []string) {
+		if len(servers) == 0 {
+			return
+		}
+		logger.Info("Applying system DNS: %v", servers)
+
+		// PublicDNS must always reflect the physical-network DNS so that
+		// WireGuard endpoint hostnames and hole-punch targets can be resolved
+		// even after the system resolver has been overridden by olm.
+		o.tunnelConfig.PublicDNS = servers
+		if o.holePunchManager != nil {
+			o.holePunchManager.SetPublicDNS(servers)
+		}
+		if pm := o.getPeerManager(); pm != nil {
+			pm.SetPublicDNS(servers)
+		}
+
+		// UpstreamDNS is updated only when the caller did not supply an
+		// explicit value; dynamic updates keep the proxy forwarding to the
+		// network's real resolver as the host moves between networks.
+		if !upstreamFromConfig {
+			o.tunnelConfig.UpstreamDNS = servers
+			if o.dnsProxy != nil {
+				o.dnsProxy.SetUpstreamDNS(servers)
+			}
+		} else {
+			logger.Debug("Not updating UpstreamDNS: statically configured to %v", config.UpstreamDNS)
+		}
+	})
+	o.dnsMonitor.Start(o.olmCtx)
+
+	// Apply any SetSystemDNS report that arrived before dnsMonitor existed (e.g. an
+	// Android/iOS push that raced ahead of this goroutine).
+	if pending := o.takePendingSystemDNS(); len(pending) > 0 {
+		o.dnsMonitor.ReportExternal(pending)
+	}
+
+	// Fall back to hardcoded DNS if the system monitor could not detect any.
+	if len(o.tunnelConfig.PublicDNS) == 0 {
+		if o.tunnelConfig.DNS != "" {
+			o.tunnelConfig.PublicDNS = []string{o.tunnelConfig.DNS + ":53"}
+		} else {
+			o.tunnelConfig.PublicDNS = []string{"8.8.8.8:53"}
+		}
+	}
+	if len(o.tunnelConfig.UpstreamDNS) == 0 {
+		o.tunnelConfig.UpstreamDNS = []string{"8.8.8.8:53"}
 	}
 
 	// Reset terminated status when tunnel starts
@@ -659,6 +720,13 @@ func (o *Olm) Close() {
 		o.holePunchManager = nil
 	}
 
+	// Stop the system DNS monitor after hole punch is stopped (it feeds
+	// publicDNS into the hole punch manager).
+	if o.dnsMonitor != nil {
+		o.dnsMonitor.Stop()
+		o.dnsMonitor = nil
+	}
+
 	// Close() also calls Stop() internally
 	o.peerManagerMu.Lock()
 	if o.peerManager != nil {
@@ -827,6 +895,38 @@ func (o *Olm) SetPostures(data map[string]any) {
 	o.postures = data
 }
 
+// SetSystemDNS reports DNS servers observed by platform-native code. On
+// Android and iOS olm cannot read the OS's DNS configuration itself (unlike
+// Linux/macOS/Windows, see dns.readSystemDNS), so the app/extension detects
+// the real pre-override DNS servers and pushes them here as the network
+// changes. The list is applied through the same exclude-IP filtering and
+// change detection as the internally-polled SystemDNSMonitor.
+func (o *Olm) SetSystemDNS(servers []string) {
+	logger.Info("SetSystemDNS called with: %v", servers)
+	if o.dnsMonitor == nil {
+		// StartTunnel hasn't created the monitor yet (mobile platforms may push a
+		// value the moment they start observing, before the tunnel goroutine has
+		// gotten far enough to construct it). Stash it so StartTunnel can apply it
+		// instead of falling back to a hardcoded default DNS server.
+		o.pendingSystemDNSMu.Lock()
+		o.pendingSystemDNS = servers
+		o.pendingSystemDNSMu.Unlock()
+		logger.Debug("dnsMonitor not yet started, queued SetSystemDNS value")
+		return
+	}
+	o.dnsMonitor.ReportExternal(servers)
+}
+
+// takePendingSystemDNS returns and clears any SetSystemDNS value reported before
+// dnsMonitor existed.
+func (o *Olm) takePendingSystemDNS() []string {
+	o.pendingSystemDNSMu.Lock()
+	defer o.pendingSystemDNSMu.Unlock()
+	pending := o.pendingSystemDNS
+	o.pendingSystemDNS = nil
+	return pending
+}
+
 // SetPowerMode switches between normal and low power modes
 // In low power mode: websocket is closed (stopping pings) and monitoring intervals are set to 10 minutes
 // In normal power mode: websocket is reconnected (restarting pings) and monitoring intervals are restored

peers/manager.go

@@ -103,6 +103,21 @@ func (pm *PeerManager) GetPeerMonitor() *monitor.PeerMonitor {
 	return pm.peerMonitor
 }
 
+// SetPublicDNS replaces the DNS servers used to resolve WireGuard peer
+// endpoints and hole-punch targets.  The servers must be in "host:port" format
+// (e.g. "8.8.8.8:53").  The change takes effect for all future peer
+// configuration calls; existing WireGuard peers are not re-resolved.
+func (pm *PeerManager) SetPublicDNS(servers []string) {
+	pm.mu.Lock()
+	pm.publicDNS = servers
+	mon := pm.peerMonitor
+	pm.mu.Unlock()
+
+	if mon != nil {
+		mon.SetPublicDNS(servers)
+	}
+}
+
 func (pm *PeerManager) GetAllPeers() []SiteConfig {
 	pm.mu.RLock()
 	defer pm.mu.RUnlock()

peers/monitor/monitor.go

@@ -36,7 +36,7 @@ type PeerMonitor struct {
 	timeout     time.Duration
 	maxAttempts int
 	wsClient    *websocket.Client
-	publicDNS []string
+	publicDNS   []string
 
 	// Relay sender tracking
 	relaySends  map[string]func()
@@ -85,8 +85,8 @@ type PeerMonitor struct {
 	apiServer *api.API
 
 	// WG connection status tracking
-	wgConnectionStatus  map[int]bool          // siteID -> WG connected status
-	wgConnectionRTT     map[int]time.Duration // siteID -> last known RTT
+	wgConnectionStatus   map[int]bool          // siteID -> WG connected status
+	wgConnectionRTT      map[int]time.Duration // siteID -> last known RTT
 	statusChangeCallback func(siteId int)      // called when any peer's connection status changes
 }
 
@@ -106,7 +106,7 @@ func NewPeerMonitor(wsClient *websocket.Client, middleDev *middleDevice.MiddleDe
 		wsClient:             wsClient,
 		middleDev:            middleDev,
 		localIP:              localIP,
-		publicDNS:          publicDNS,
+		publicDNS:            publicDNS,
 		activePorts:          make(map[uint16]bool),
 		nsCtx:                ctx,
 		nsCancel:             cancel,
@@ -148,6 +148,19 @@ func NewPeerMonitor(wsClient *websocket.Client, middleDev *middleDevice.MiddleDe
 	return pm
 }
 
+// SetPublicDNS replaces the DNS servers used to resolve peer endpoints and
+// hole-punch exit nodes.  The servers must be in "host:port" format.
+func (pm *PeerMonitor) SetPublicDNS(servers []string) {
+	pm.mutex.Lock()
+	pm.publicDNS = servers
+	tester := pm.holepunchTester
+	pm.mutex.Unlock()
+
+	if tester != nil {
+		tester.SetPublicDNS(servers)
+	}
+}
+
 // SetInterval changes how frequently peers are checked
 func (pm *PeerMonitor) SetPeerInterval(minInterval, maxInterval time.Duration) {
 	pm.mutex.Lock()