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38a83e937f
interfaces.Tailscale only returns an interface if it has at least one Tailscale
IP assigned to it. In the resolved DNS manager, when we're called upon to tear
down DNS config, the interface no longer has IPs.
Instead, look up the interface index on construction and reuse it throughout
the daemon lifecycle.
Fixes #1892.
Signed-off-by: David Anderson <dave@natulte.net>
(cherry picked from commit cfde997699
)
233 lines
6.9 KiB
Go
233 lines
6.9 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build linux
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//lint:file-ignore U1000 refactoring, temporarily unused code.
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package dns
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import (
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"context"
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"errors"
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"fmt"
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"net"
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"github.com/godbus/dbus/v5"
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"golang.org/x/sys/unix"
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"inet.af/netaddr"
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"tailscale.com/types/logger"
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"tailscale.com/util/dnsname"
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)
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// resolvedListenAddr is the listen address of the resolved stub resolver.
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//
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// We only consider resolved to be the system resolver if the stub resolver is;
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// that is, if this address is the sole nameserver in /etc/resolved.conf.
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// In other cases, resolved may be managing the system DNS configuration directly.
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// Then the nameserver list will be a concatenation of those for all
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// the interfaces that register their interest in being a default resolver with
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// SetLinkDomains([]{{"~.", true}, ...})
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// which includes at least the interface with the default route, i.e. not us.
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// This does not work for us: there is a possibility of getting NXDOMAIN
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// from the other nameservers before we are asked or get a chance to respond.
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// We consider this case as lacking resolved support and fall through to dnsDirect.
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//
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// While it may seem that we need to read a config option to get at this,
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// this address is, in fact, hard-coded into resolved.
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var resolvedListenAddr = netaddr.IPv4(127, 0, 0, 53)
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var errNotReady = errors.New("interface not ready")
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type resolvedLinkNameserver struct {
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Family int32
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Address []byte
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}
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type resolvedLinkDomain struct {
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Domain string
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RoutingOnly bool
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}
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// isResolvedActive determines if resolved is currently managing system DNS settings.
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func isResolvedActive() bool {
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ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
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defer cancel()
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conn, err := dbus.SystemBus()
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if err != nil {
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// Probably no DBus on the system, or we're not allowed to use
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// it. Cannot control resolved.
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return false
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}
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rd := conn.Object("org.freedesktop.resolve1", dbus.ObjectPath("/org/freedesktop/resolve1"))
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call := rd.CallWithContext(ctx, "org.freedesktop.DBus.Peer.Ping", 0)
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if call.Err != nil {
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// Can't talk to resolved.
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return false
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}
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config, err := readResolvConf()
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if err != nil {
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return false
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}
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// The sole nameserver must be the systemd-resolved stub.
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if len(config.Nameservers) == 1 && config.Nameservers[0] == resolvedListenAddr {
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return true
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}
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return false
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}
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// resolvedManager uses the systemd-resolved DBus API.
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type resolvedManager struct {
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logf logger.Logf
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ifidx int
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resolved dbus.BusObject
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}
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func newResolvedManager(logf logger.Logf, interfaceName string) (*resolvedManager, error) {
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conn, err := dbus.SystemBus()
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if err != nil {
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return nil, err
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}
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iface, err := net.InterfaceByName(interfaceName)
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if err != nil {
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return nil, err
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}
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return &resolvedManager{
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logf: logf,
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ifidx: iface.Index,
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resolved: conn.Object("org.freedesktop.resolve1", dbus.ObjectPath("/org/freedesktop/resolve1")),
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}, nil
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}
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// Up implements managerImpl.
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func (m *resolvedManager) SetDNS(config OSConfig) error {
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ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
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defer cancel()
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var linkNameservers = make([]resolvedLinkNameserver, len(config.Nameservers))
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for i, server := range config.Nameservers {
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ip := server.As16()
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if server.Is4() {
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linkNameservers[i] = resolvedLinkNameserver{
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Family: unix.AF_INET,
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Address: ip[12:],
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}
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} else {
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linkNameservers[i] = resolvedLinkNameserver{
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Family: unix.AF_INET6,
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Address: ip[:],
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}
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}
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}
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err := m.resolved.CallWithContext(
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ctx, "org.freedesktop.resolve1.Manager.SetLinkDNS", 0,
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m.ifidx, linkNameservers,
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).Store()
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if err != nil {
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return fmt.Errorf("setLinkDNS: %w", err)
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}
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linkDomains := make([]resolvedLinkDomain, 0, len(config.SearchDomains)+len(config.MatchDomains))
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seenDomains := map[dnsname.FQDN]bool{}
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for _, domain := range config.SearchDomains {
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if seenDomains[domain] {
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continue
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}
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seenDomains[domain] = true
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linkDomains = append(linkDomains, resolvedLinkDomain{
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Domain: domain.WithTrailingDot(),
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RoutingOnly: false,
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})
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}
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for _, domain := range config.MatchDomains {
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if seenDomains[domain] {
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// Search domains act as both search and match in
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// resolved, so it's correct to skip.
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continue
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}
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seenDomains[domain] = true
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linkDomains = append(linkDomains, resolvedLinkDomain{
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Domain: domain.WithTrailingDot(),
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RoutingOnly: true,
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})
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}
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if len(config.MatchDomains) == 0 && len(config.Nameservers) > 0 {
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// Caller requested full DNS interception, install a
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// routing-only root domain.
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linkDomains = append(linkDomains, resolvedLinkDomain{
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Domain: ".",
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RoutingOnly: true,
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})
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}
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err = m.resolved.CallWithContext(
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ctx, "org.freedesktop.resolve1.Manager.SetLinkDomains", 0,
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m.ifidx, linkDomains,
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).Store()
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if err != nil {
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return fmt.Errorf("setLinkDomains: %w", err)
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}
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.SetLinkDefaultRoute", 0, m.ifidx, len(config.MatchDomains) == 0); call.Err != nil {
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return fmt.Errorf("setLinkDefaultRoute: %w", err)
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}
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// Some best-effort setting of things, but resolved should do the
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// right thing if these fail (e.g. a really old resolved version
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// or something).
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// Disable LLMNR, we don't do multicast.
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.SetLinkLLMNR", 0, m.ifidx, "no"); call.Err != nil {
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m.logf("[v1] failed to disable LLMNR: %v", call.Err)
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}
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// Disable mdns.
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.SetLinkMulticastDNS", 0, m.ifidx, "no"); call.Err != nil {
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m.logf("[v1] failed to disable mdns: %v", call.Err)
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}
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// We don't support dnssec consistently right now, force it off to
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// avoid partial failures when we split DNS internally.
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.SetLinkDNSSEC", 0, m.ifidx, "no"); call.Err != nil {
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m.logf("[v1] failed to disable DNSSEC: %v", call.Err)
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}
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.SetLinkDNSOverTLS", 0, m.ifidx, "no"); call.Err != nil {
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m.logf("[v1] failed to disable DoT: %v", call.Err)
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}
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.FlushCaches", 0); call.Err != nil {
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m.logf("failed to flush resolved DNS cache: %v", call.Err)
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}
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return nil
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}
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func (m *resolvedManager) SupportsSplitDNS() bool {
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return true
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}
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func (m *resolvedManager) GetBaseConfig() (OSConfig, error) {
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return OSConfig{}, ErrGetBaseConfigNotSupported
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}
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func (m *resolvedManager) Close() error {
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ctx, cancel := context.WithTimeout(context.Background(), reconfigTimeout)
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defer cancel()
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if call := m.resolved.CallWithContext(ctx, "org.freedesktop.resolve1.Manager.RevertLink", 0, m.ifidx); call.Err != nil {
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return fmt.Errorf("RevertLink: %w", call.Err)
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}
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return nil
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}
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