mirror of
https://github.com/tailscale/tailscale.git
synced 2024-12-04 23:45:34 +00:00
acfe5bd33b
Fixes https://github.com/tailscale/corp/issues/5198 The upstream forwarder will block indefinitely on `udpconn.ReadFrom` if no reply is recieved, due to the lack of deadline on the connection object. There still isn't a deadline on the connection object, but the automatic closing of the context on deadline expiry will close the connection via `closeOnCtxDone`, unblocking the read and resulting in a normal teardown. Signed-off-by: Tom DNetto <tom@tailscale.com>
502 lines
14 KiB
Go
502 lines
14 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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package dns
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import (
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"bufio"
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"context"
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"encoding/binary"
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"errors"
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"io"
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"net"
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"runtime"
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"sync/atomic"
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"time"
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"inet.af/netaddr"
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"tailscale.com/health"
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"tailscale.com/net/dns/resolver"
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"tailscale.com/net/packet"
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"tailscale.com/net/tsaddr"
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"tailscale.com/net/tsdial"
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"tailscale.com/net/tstun"
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"tailscale.com/types/dnstype"
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"tailscale.com/types/ipproto"
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"tailscale.com/types/logger"
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"tailscale.com/util/clientmetric"
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"tailscale.com/util/dnsname"
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"tailscale.com/wgengine/monitor"
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)
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var (
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magicDNSIP = tsaddr.TailscaleServiceIP()
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magicDNSIPv6 = tsaddr.TailscaleServiceIPv6()
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)
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var (
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errFullQueue = errors.New("request queue full")
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)
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// maxActiveQueries returns the maximal number of DNS requests that be
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// can running.
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// If EnqueueRequest is called when this many requests are already pending,
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// the request will be dropped to avoid blocking the caller.
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func maxActiveQueries() int32 {
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if runtime.GOOS == "ios" {
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// For memory paranoia reasons on iOS, match the
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// historical Tailscale 1.x..1.8 behavior for now
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// (just before the 1.10 release).
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return 64
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}
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// But for other platforms, allow more burstiness:
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return 256
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}
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// We use file-ignore below instead of ignore because on some platforms,
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// the lint exception is necessary and on others it is not,
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// and plain ignore complains if the exception is unnecessary.
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// reconfigTimeout is the time interval within which Manager.{Up,Down} should complete.
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//
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// This is particularly useful because certain conditions can cause indefinite hangs
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// (such as improper dbus auth followed by contextless dbus.Object.Call).
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// Such operations should be wrapped in a timeout context.
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const reconfigTimeout = time.Second
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type response struct {
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pkt []byte
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to netaddr.IPPort // response destination (request source)
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}
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// Manager manages system DNS settings.
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type Manager struct {
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logf logger.Logf
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// When netstack is not used, Manager implements magic DNS.
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// In this case, responses tracks completed DNS requests
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// which need a response, and NextPacket() synthesizes a
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// fake IP+UDP header to finish assembling the response.
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//
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// TODO(tom): Rip out once all platforms use netstack.
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responses chan response
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activeQueriesAtomic int32
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ctx context.Context // good until Down
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ctxCancel context.CancelFunc // closes ctx
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resolver *resolver.Resolver
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os OSConfigurator
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}
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// NewManagers created a new manager from the given config.
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func NewManager(logf logger.Logf, oscfg OSConfigurator, linkMon *monitor.Mon, dialer *tsdial.Dialer, linkSel resolver.ForwardLinkSelector) *Manager {
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if dialer == nil {
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panic("nil Dialer")
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}
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logf = logger.WithPrefix(logf, "dns: ")
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m := &Manager{
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logf: logf,
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resolver: resolver.New(logf, linkMon, linkSel, dialer),
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os: oscfg,
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responses: make(chan response),
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}
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m.ctx, m.ctxCancel = context.WithCancel(context.Background())
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m.logf("using %T", m.os)
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return m
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}
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// Resolver returns the Manager's DNS Resolver.
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func (m *Manager) Resolver() *resolver.Resolver { return m.resolver }
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func (m *Manager) Set(cfg Config) error {
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m.logf("Set: %v", logger.ArgWriter(func(w *bufio.Writer) {
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cfg.WriteToBufioWriter(w)
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}))
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rcfg, ocfg, err := m.compileConfig(cfg)
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if err != nil {
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return err
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}
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m.logf("Resolvercfg: %v", logger.ArgWriter(func(w *bufio.Writer) {
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rcfg.WriteToBufioWriter(w)
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}))
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m.logf("OScfg: %+v", ocfg)
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if err := m.resolver.SetConfig(rcfg); err != nil {
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return err
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}
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if err := m.os.SetDNS(ocfg); err != nil {
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health.SetDNSOSHealth(err)
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return err
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}
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health.SetDNSOSHealth(nil)
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return nil
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}
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// compileConfig converts cfg into a quad-100 resolver configuration
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// and an OS-level configuration.
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func (m *Manager) compileConfig(cfg Config) (rcfg resolver.Config, ocfg OSConfig, err error) {
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// The internal resolver always gets MagicDNS hosts and
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// authoritative suffixes, even if we don't propagate MagicDNS to
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// the OS.
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rcfg.Hosts = cfg.Hosts
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routes := map[dnsname.FQDN][]*dnstype.Resolver{} // assigned conditionally to rcfg.Routes below.
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for suffix, resolvers := range cfg.Routes {
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if len(resolvers) == 0 {
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rcfg.LocalDomains = append(rcfg.LocalDomains, suffix)
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} else {
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routes[suffix] = resolvers
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}
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}
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// Similarly, the OS always gets search paths.
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ocfg.SearchDomains = cfg.SearchDomains
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// Deal with trivial configs first.
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switch {
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case !cfg.needsOSResolver():
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// Set search domains, but nothing else. This also covers the
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// case where cfg is entirely zero, in which case these
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// configs clear all Tailscale DNS settings.
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return rcfg, ocfg, nil
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case cfg.hasDefaultIPResolversOnly():
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// Trivial CorpDNS configuration, just override the OS
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// resolver.
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// TODO: for OSes that support it, pass IP:port and DoH
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// addresses directly to OS.
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// https://github.com/tailscale/tailscale/issues/1666
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ocfg.Nameservers = toIPsOnly(cfg.DefaultResolvers)
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return rcfg, ocfg, nil
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case cfg.hasDefaultResolvers():
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// Default resolvers plus other stuff always ends up proxying
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// through quad-100.
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rcfg.Routes = routes
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rcfg.Routes["."] = cfg.DefaultResolvers
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ocfg.Nameservers = []netaddr.IP{cfg.serviceIP()}
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return rcfg, ocfg, nil
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}
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// From this point on, we're figuring out split DNS
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// configurations. The possible cases don't return directly any
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// more, because as a final step we have to handle the case where
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// the OS can't do split DNS.
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// Workaround for
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// https://github.com/tailscale/corp/issues/1662. Even though
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// Windows natively supports split DNS, it only configures linux
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// containers using whatever the primary is, and doesn't apply
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// NRPT rules to DNS traffic coming from WSL.
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//
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// In order to make WSL work okay when the host Windows is using
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// Tailscale, we need to set up quad-100 as a "full proxy"
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// resolver, regardless of whether Windows itself can do split
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// DNS. We still make Windows do split DNS itself when it can, but
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// quad-100 will still have the full split configuration as well,
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// and so can service WSL requests correctly.
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//
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// This bool is used in a couple of places below to implement this
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// workaround.
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isWindows := runtime.GOOS == "windows"
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if cfg.singleResolverSet() != nil && m.os.SupportsSplitDNS() && !isWindows {
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// Split DNS configuration requested, where all split domains
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// go to the same resolvers. We can let the OS do it.
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ocfg.Nameservers = toIPsOnly(cfg.singleResolverSet())
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ocfg.MatchDomains = cfg.matchDomains()
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return rcfg, ocfg, nil
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}
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// Split DNS configuration with either multiple upstream routes,
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// or routes + MagicDNS, or just MagicDNS, or on an OS that cannot
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// split-DNS. Install a split config pointing at quad-100.
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rcfg.Routes = routes
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ocfg.Nameservers = []netaddr.IP{cfg.serviceIP()}
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// If the OS can't do native split-dns, read out the underlying
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// resolver config and blend it into our config.
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if m.os.SupportsSplitDNS() {
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ocfg.MatchDomains = cfg.matchDomains()
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}
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if !m.os.SupportsSplitDNS() || isWindows {
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bcfg, err := m.os.GetBaseConfig()
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if err != nil {
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health.SetDNSOSHealth(err)
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return resolver.Config{}, OSConfig{}, err
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}
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var defaultRoutes []*dnstype.Resolver
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for _, ip := range bcfg.Nameservers {
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defaultRoutes = append(defaultRoutes, &dnstype.Resolver{Addr: ip.String()})
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}
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rcfg.Routes["."] = defaultRoutes
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ocfg.SearchDomains = append(ocfg.SearchDomains, bcfg.SearchDomains...)
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}
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return rcfg, ocfg, nil
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}
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// toIPsOnly returns only the IP portion of dnstype.Resolver.
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// Only safe to use if the resolvers slice has been cleared of
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// DoH or custom-port entries with something like hasDefaultIPResolversOnly.
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func toIPsOnly(resolvers []*dnstype.Resolver) (ret []netaddr.IP) {
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for _, r := range resolvers {
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if ipp, ok := r.IPPort(); ok && ipp.Port() == 53 {
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ret = append(ret, ipp.IP())
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}
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}
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return ret
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}
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// EnqueuePacket is the legacy path for handling magic DNS traffic, and is
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// called with a DNS request payload.
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//
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// TODO(tom): Rip out once all platforms use netstack.
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func (m *Manager) EnqueuePacket(bs []byte, proto ipproto.Proto, from, to netaddr.IPPort) error {
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if to.Port() != 53 || proto != ipproto.UDP {
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return nil
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}
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if n := atomic.AddInt32(&m.activeQueriesAtomic, 1); n > maxActiveQueries() {
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atomic.AddInt32(&m.activeQueriesAtomic, -1)
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metricDNSQueryErrorQueue.Add(1)
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return errFullQueue
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}
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go func() {
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resp, err := m.resolver.Query(m.ctx, bs, from)
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if err != nil {
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atomic.AddInt32(&m.activeQueriesAtomic, -1)
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m.logf("dns query: %v", err)
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return
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}
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select {
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case <-m.ctx.Done():
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return
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case m.responses <- response{resp, from}:
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}
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}()
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return nil
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}
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// NextPacket is the legacy path for obtaining DNS results in response to
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// magic DNS queries. It blocks until a response is available.
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//
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// TODO(tom): Rip out once all platforms use netstack.
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func (m *Manager) NextPacket() ([]byte, error) {
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var resp response
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select {
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case <-m.ctx.Done():
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return nil, net.ErrClosed
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case resp = <-m.responses:
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// continue
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}
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// Unused space is needed further down the stack. To avoid extra
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// allocations/copying later on, we allocate such space here.
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const offset = tstun.PacketStartOffset
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var buf []byte
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switch {
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case resp.to.IP().Is4():
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h := packet.UDP4Header{
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IP4Header: packet.IP4Header{
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Src: magicDNSIP,
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Dst: resp.to.IP(),
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},
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SrcPort: 53,
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DstPort: resp.to.Port(),
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}
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hlen := h.Len()
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buf = make([]byte, offset+hlen+len(resp.pkt))
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copy(buf[offset+hlen:], resp.pkt)
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h.Marshal(buf[offset:])
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case resp.to.IP().Is6():
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h := packet.UDP6Header{
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IP6Header: packet.IP6Header{
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Src: magicDNSIPv6,
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Dst: resp.to.IP(),
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},
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SrcPort: 53,
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DstPort: resp.to.Port(),
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}
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hlen := h.Len()
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buf = make([]byte, offset+hlen+len(resp.pkt))
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copy(buf[offset+hlen:], resp.pkt)
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h.Marshal(buf[offset:])
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}
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atomic.AddInt32(&m.activeQueriesAtomic, -1)
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return buf, nil
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}
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// Query executes a DNS query recieved from the given address. The query is
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// provided in bs as a wire-encoded DNS query without any transport header.
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// This method is called for requests arriving over UDP and TCP.
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func (m *Manager) Query(ctx context.Context, bs []byte, from netaddr.IPPort) ([]byte, error) {
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select {
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case <-m.ctx.Done():
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return nil, net.ErrClosed
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default:
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// continue
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}
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if n := atomic.AddInt32(&m.activeQueriesAtomic, 1); n > maxActiveQueries() {
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atomic.AddInt32(&m.activeQueriesAtomic, -1)
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metricDNSQueryErrorQueue.Add(1)
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return nil, errFullQueue
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}
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defer atomic.AddInt32(&m.activeQueriesAtomic, -1)
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return m.resolver.Query(ctx, bs, from)
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}
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const (
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// RFC 7766 6.2 recommends connection reuse & request pipelining
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// be undertaken, and the connection be closed by the server
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// using an idle timeout on the order of seconds.
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idleTimeoutTCP = 45 * time.Second
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// The RFCs don't specify the max size of a TCP-based DNS query,
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// but we want to keep this reasonable. Given payloads are typically
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// much larger and all known client send a single query, I've arbitrarily
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// chosen 2k.
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maxReqSizeTCP = 2048
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)
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// dnsTCPSession services DNS requests sent over TCP.
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type dnsTCPSession struct {
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m *Manager
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conn net.Conn
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srcAddr netaddr.IPPort
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readClosing chan struct{}
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responses chan []byte // DNS replies pending writing
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ctx context.Context
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closeCtx context.CancelFunc
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}
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func (s *dnsTCPSession) handleWrites() {
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defer s.conn.Close()
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defer close(s.responses)
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defer s.closeCtx()
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for {
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select {
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case <-s.readClosing:
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return // connection closed or timeout, teardown time
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case resp := <-s.responses:
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s.conn.SetWriteDeadline(time.Now().Add(idleTimeoutTCP))
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if err := binary.Write(s.conn, binary.BigEndian, uint16(len(resp))); err != nil {
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s.m.logf("tcp write (len): %v", err)
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return
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}
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if _, err := s.conn.Write(resp); err != nil {
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s.m.logf("tcp write (response): %v", err)
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return
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}
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}
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}
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}
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func (s *dnsTCPSession) handleQuery(q []byte) {
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resp, err := s.m.Query(s.ctx, q, s.srcAddr)
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if err != nil {
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s.m.logf("tcp query: %v", err)
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return
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}
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select {
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case <-s.ctx.Done():
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case s.responses <- resp:
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}
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}
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func (s *dnsTCPSession) handleReads() {
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defer close(s.readClosing)
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for {
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select {
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case <-s.ctx.Done():
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return
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default:
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s.conn.SetReadDeadline(time.Now().Add(idleTimeoutTCP))
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var reqLen uint16
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if err := binary.Read(s.conn, binary.BigEndian, &reqLen); err != nil {
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if err == io.EOF || err == io.ErrClosedPipe {
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return // connection closed nominally, we gucci
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}
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s.m.logf("tcp read (len): %v", err)
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return
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}
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if int(reqLen) > maxReqSizeTCP {
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s.m.logf("tcp request too large (%d > %d)", reqLen, maxReqSizeTCP)
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return
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}
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buf := make([]byte, int(reqLen))
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if _, err := io.ReadFull(s.conn, buf); err != nil {
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s.m.logf("tcp read (payload): %v", err)
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return
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}
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select {
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case <-s.ctx.Done():
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return
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default:
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go s.handleQuery(buf)
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}
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}
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}
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}
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// HandleTCPConn implements magicDNS over TCP, taking a connection and
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// servicing DNS requests sent down it.
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func (m *Manager) HandleTCPConn(conn net.Conn, srcAddr netaddr.IPPort) {
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s := dnsTCPSession{
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m: m,
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conn: conn,
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srcAddr: srcAddr,
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responses: make(chan []byte),
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readClosing: make(chan struct{}),
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}
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s.ctx, s.closeCtx = context.WithCancel(m.ctx)
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go s.handleReads()
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s.handleWrites()
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}
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func (m *Manager) Down() error {
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m.ctxCancel()
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if err := m.os.Close(); err != nil {
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return err
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}
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m.resolver.Close()
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return nil
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}
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func (m *Manager) FlushCaches() error {
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return flushCaches()
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}
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// Cleanup restores the system DNS configuration to its original state
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// in case the Tailscale daemon terminated without closing the router.
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// No other state needs to be instantiated before this runs.
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func Cleanup(logf logger.Logf, interfaceName string) {
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oscfg, err := NewOSConfigurator(logf, interfaceName)
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if err != nil {
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logf("creating dns cleanup: %v", err)
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return
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}
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dns := NewManager(logf, oscfg, nil, new(tsdial.Dialer), nil)
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if err := dns.Down(); err != nil {
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logf("dns down: %v", err)
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}
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}
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var (
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metricDNSQueryErrorQueue = clientmetric.NewCounter("dns_query_local_error_queue")
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)
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