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tailscale/net/dns/manager.go

220 lines
6.8 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package dns
import (
"bufio"
"runtime"
"time"
"inet.af/netaddr"
"tailscale.com/net/dns/resolver"
"tailscale.com/net/tsaddr"
"tailscale.com/types/logger"
"tailscale.com/util/dnsname"
"tailscale.com/wgengine/monitor"
)
// We use file-ignore below instead of ignore because on some platforms,
// the lint exception is necessary and on others it is not,
// and plain ignore complains if the exception is unnecessary.
// reconfigTimeout is the time interval within which Manager.{Up,Down} should complete.
//
// This is particularly useful because certain conditions can cause indefinite hangs
// (such as improper dbus auth followed by contextless dbus.Object.Call).
// Such operations should be wrapped in a timeout context.
const reconfigTimeout = time.Second
// Manager manages system DNS settings.
type Manager struct {
logf logger.Logf
resolver *resolver.Resolver
os OSConfigurator
config Config
}
// NewManagers created a new manager from the given config.
func NewManager(logf logger.Logf, oscfg OSConfigurator, linkMon *monitor.Mon, linkSel resolver.ForwardLinkSelector) *Manager {
logf = logger.WithPrefix(logf, "dns: ")
m := &Manager{
logf: logf,
resolver: resolver.New(logf, linkMon, linkSel),
os: oscfg,
}
m.logf("using %T", m.os)
return m
}
func (m *Manager) Set(cfg Config) error {
m.logf("Set: %v", logger.ArgWriter(func(w *bufio.Writer) {
cfg.WriteToBufioWriter(w)
}))
rcfg, ocfg, err := m.compileConfig(cfg)
if err != nil {
return err
}
m.logf("Resolvercfg: %v", logger.ArgWriter(func(w *bufio.Writer) {
rcfg.WriteToBufioWriter(w)
}))
m.logf("OScfg: %+v", ocfg)
if err := m.resolver.SetConfig(rcfg); err != nil {
return err
}
if err := m.os.SetDNS(ocfg); err != nil {
return err
}
return nil
}
// compileConfig converts cfg into a quad-100 resolver configuration
// and an OS-level configuration.
func (m *Manager) compileConfig(cfg Config) (rcfg resolver.Config, ocfg OSConfig, err error) {
// The internal resolver always gets MagicDNS hosts and
// authoritative suffixes, even if we don't propagate MagicDNS to
// the OS.
rcfg.Hosts = cfg.Hosts
routes := map[dnsname.FQDN][]netaddr.IPPort{} // assigned conditionally to rcfg.Routes below.
for suffix, resolvers := range cfg.Routes {
if len(resolvers) == 0 {
rcfg.LocalDomains = append(rcfg.LocalDomains, suffix)
} else {
routes[suffix] = resolvers
}
}
// Similarly, the OS always gets search paths.
ocfg.SearchDomains = cfg.SearchDomains
// Deal with trivial configs first.
switch {
case !cfg.needsOSResolver():
// Set search domains, but nothing else. This also covers the
// case where cfg is entirely zero, in which case these
// configs clear all Tailscale DNS settings.
return rcfg, ocfg, nil
case cfg.hasDefaultResolversOnly():
// Trivial CorpDNS configuration, just override the OS
// resolver.
ocfg.Nameservers = toIPsOnly(cfg.DefaultResolvers)
return rcfg, ocfg, nil
case cfg.hasDefaultResolvers():
// Default resolvers plus other stuff always ends up proxying
// through quad-100.
rcfg.Routes = routes
rcfg.Routes["."] = cfg.DefaultResolvers
ocfg.Nameservers = []netaddr.IP{tsaddr.TailscaleServiceIP()}
return rcfg, ocfg, nil
}
// From this point on, we're figuring out split DNS
// configurations. The possible cases don't return directly any
// more, because as a final step we have to handle the case where
// the OS can't do split DNS.
// Workaround for
// https://github.com/tailscale/corp/issues/1662. Even though
// Windows natively supports split DNS, it only configures linux
// containers using whatever the primary is, and doesn't apply
// NRPT rules to DNS traffic coming from WSL.
//
// In order to make WSL work okay when the host Windows is using
// Tailscale, we need to set up quad-100 as a "full proxy"
// resolver, regardless of whether Windows itself can do split
// DNS. We still make Windows do split DNS itself when it can, but
// quad-100 will still have the full split configuration as well,
// and so can service WSL requests correctly.
//
// This bool is used in a couple of places below to implement this
// workaround.
isWindows := runtime.GOOS == "windows"
if cfg.singleResolverSet() != nil && m.os.SupportsSplitDNS() && !isWindows {
// Split DNS configuration requested, where all split domains
// go to the same resolvers. We can let the OS do it.
ocfg.Nameservers = toIPsOnly(cfg.singleResolverSet())
ocfg.MatchDomains = cfg.matchDomains()
return rcfg, ocfg, nil
}
// Split DNS configuration with either multiple upstream routes,
// or routes + MagicDNS, or just MagicDNS, or on an OS that cannot
// split-DNS. Install a split config pointing at quad-100.
rcfg.Routes = routes
ocfg.Nameservers = []netaddr.IP{tsaddr.TailscaleServiceIP()}
// If the OS can't do native split-dns, read out the underlying
// resolver config and blend it into our config.
if m.os.SupportsSplitDNS() {
ocfg.MatchDomains = cfg.matchDomains()
}
if !m.os.SupportsSplitDNS() || isWindows {
bcfg, err := m.os.GetBaseConfig()
if err != nil {
return resolver.Config{}, OSConfig{}, err
}
rcfg.Routes["."] = toIPPorts(bcfg.Nameservers)
ocfg.SearchDomains = append(ocfg.SearchDomains, bcfg.SearchDomains...)
}
return rcfg, ocfg, nil
}
// toIPsOnly returns only the IP portion of ipps.
// TODO: this discards port information on the assumption that we're
// always pointing at port 53.
// https://github.com/tailscale/tailscale/issues/1666 tracks making
// that not true, if we ever want to.
func toIPsOnly(ipps []netaddr.IPPort) (ret []netaddr.IP) {
ret = make([]netaddr.IP, 0, len(ipps))
for _, ipp := range ipps {
ret = append(ret, ipp.IP())
}
return ret
}
func toIPPorts(ips []netaddr.IP) (ret []netaddr.IPPort) {
ret = make([]netaddr.IPPort, 0, len(ips))
for _, ip := range ips {
ret = append(ret, netaddr.IPPortFrom(ip, 53))
}
return ret
}
func (m *Manager) EnqueueRequest(bs []byte, from netaddr.IPPort) error {
return m.resolver.EnqueueRequest(bs, from)
}
func (m *Manager) NextResponse() ([]byte, netaddr.IPPort, error) {
return m.resolver.NextResponse()
}
func (m *Manager) Down() error {
if err := m.os.Close(); err != nil {
return err
}
m.resolver.Close()
return nil
}
// Cleanup restores the system DNS configuration to its original state
// in case the Tailscale daemon terminated without closing the router.
// No other state needs to be instantiated before this runs.
func Cleanup(logf logger.Logf, interfaceName string) {
oscfg, err := NewOSConfigurator(logf, interfaceName)
if err != nil {
logf("creating dns cleanup: %v", err)
return
}
dns := NewManager(logf, oscfg, nil, nil)
if err := dns.Down(); err != nil {
logf("dns down: %v", err)
}
}