tailscale/ipn/ipnlocal/peerapi.go

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// Copyright (c) 2021 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 ipnlocal
import (
"context"
"encoding/base64"
"encoding/json"
"errors"
"fmt"
"hash/crc32"
"html"
"io"
"io/fs"
"net"
"net/http"
"net/url"
"os"
"path"
"path/filepath"
"runtime"
"sort"
"strconv"
"strings"
"sync"
"time"
"unicode"
"unicode/utf8"
"golang.org/x/net/dns/dnsmessage"
"inet.af/netaddr"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/health"
"tailscale.com/hostinfo"
"tailscale.com/ipn"
"tailscale.com/logtail/backoff"
"tailscale.com/net/dns/resolver"
"tailscale.com/net/interfaces"
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/util/clientmetric"
"tailscale.com/wgengine"
"tailscale.com/wgengine/filter"
)
var initListenConfig func(*net.ListenConfig, netaddr.IP, *interfaces.State, string) error
// addH2C is non-nil on platforms where we want to add H2C
// ("cleartext" HTTP/2) support to the peerAPI.
var addH2C func(*http.Server)
type peerAPIServer struct {
b *LocalBackend
rootDir string // empty means file receiving unavailable
selfNode *tailcfg.Node
knownEmpty syncs.AtomicBool
resolver *resolver.Resolver
// directFileMode is whether we're writing files directly to a
// download directory (as *.partial files), rather than making
// the frontend retrieve it over localapi HTTP and write it
// somewhere itself. This is used on the GUI macOS versions
// and on Synology.
// In directFileMode, the peerapi doesn't do the final rename
// from "foo.jpg.partial" to "foo.jpg" unless
// directFileDoFinalRename is set.
directFileMode bool
// directFileDoFinalRename is whether in directFileMode we
// additionally move the *.direct file to its final name after
// it's received.
directFileDoFinalRename bool
}
const (
// partialSuffix is the suffix appened to files while they're
// still in the process of being transferred.
partialSuffix = ".partial"
// deletedSuffix is the suffix for a deleted marker file
// that's placed next to a file (without the suffix) that we
// tried to delete, but Windows wouldn't let us. These are
// only written on Windows (and in tests), but they're not
// permitted to be uploaded directly on any platform, like
// partial files.
deletedSuffix = ".deleted"
)
func (s *peerAPIServer) canReceiveFiles() bool {
return s != nil && s.rootDir != ""
}
func validFilenameRune(r rune) bool {
switch r {
case '/':
return false
case '\\', ':', '*', '"', '<', '>', '|':
// Invalid stuff on Windows, but we reject them everywhere
// for now.
// TODO(bradfitz): figure out a better plan. We initially just
// wrote things to disk URL path-escaped, but that's gross
// when debugging, and just moves the problem to callers.
// So now we put the UTF-8 filenames on disk directly as
// sent.
return false
}
return unicode.IsPrint(r)
}
func (s *peerAPIServer) diskPath(baseName string) (fullPath string, ok bool) {
if !utf8.ValidString(baseName) {
return "", false
}
if strings.TrimSpace(baseName) != baseName {
return "", false
}
if len(baseName) > 255 {
return "", false
}
// TODO: validate unicode normalization form too? Varies by platform.
clean := path.Clean(baseName)
if clean != baseName ||
clean == "." || clean == ".." ||
strings.HasSuffix(clean, deletedSuffix) ||
strings.HasSuffix(clean, partialSuffix) {
return "", false
}
for _, r := range baseName {
if !validFilenameRune(r) {
return "", false
}
}
return filepath.Join(s.rootDir, baseName), true
}
// hasFilesWaiting reports whether any files are buffered in the
// tailscaled daemon storage.
func (s *peerAPIServer) hasFilesWaiting() bool {
if s == nil || s.rootDir == "" || s.directFileMode {
return false
}
if s.knownEmpty.Get() {
// Optimization: this is usually empty, so avoid opening
// the directory and checking. We can't cache the actual
// has-files-or-not values as the macOS/iOS client might
// in the future use+delete the files directly. So only
// keep this negative cache.
return false
}
f, err := os.Open(s.rootDir)
if err != nil {
return false
}
defer f.Close()
for {
des, err := f.ReadDir(10)
for _, de := range des {
name := de.Name()
if strings.HasSuffix(name, partialSuffix) {
continue
}
if strings.HasSuffix(name, deletedSuffix) { // for Windows + tests
// After we're done looping over files, then try
// to delete this file. Don't do it proactively,
// as the OS may return "foo.jpg.deleted" before "foo.jpg"
// and we don't want to delete the ".deleted" file before
// enumerating to the "foo.jpg" file.
defer tryDeleteAgain(filepath.Join(s.rootDir, strings.TrimSuffix(name, deletedSuffix)))
continue
}
if de.Type().IsRegular() {
_, err := os.Stat(filepath.Join(s.rootDir, name+deletedSuffix))
if os.IsNotExist(err) {
return true
}
if err == nil {
tryDeleteAgain(filepath.Join(s.rootDir, name))
continue
}
}
}
if err == io.EOF {
s.knownEmpty.Set(true)
}
if err != nil {
break
}
}
return false
}
// WaitingFiles returns the list of files that have been sent by a
// peer that are waiting in the buffered "pick up" directory owned by
// the Tailscale daemon.
//
// As a side effect, it also does any lazy deletion of files as
// required by Windows.
func (s *peerAPIServer) WaitingFiles() (ret []apitype.WaitingFile, err error) {
if s == nil {
return nil, errNilPeerAPIServer
}
if s.rootDir == "" {
return nil, errNoTaildrop
}
if s.directFileMode {
return nil, nil
}
f, err := os.Open(s.rootDir)
if err != nil {
return nil, err
}
defer f.Close()
var deleted map[string]bool // "foo.jpg" => true (if "foo.jpg.deleted" exists)
for {
des, err := f.ReadDir(10)
for _, de := range des {
name := de.Name()
if strings.HasSuffix(name, partialSuffix) {
continue
}
if strings.HasSuffix(name, deletedSuffix) { // for Windows + tests
if deleted == nil {
deleted = map[string]bool{}
}
deleted[strings.TrimSuffix(name, deletedSuffix)] = true
continue
}
if de.Type().IsRegular() {
fi, err := de.Info()
if err != nil {
continue
}
ret = append(ret, apitype.WaitingFile{
Name: filepath.Base(name),
Size: fi.Size(),
})
}
}
if err == io.EOF {
break
}
if err != nil {
return nil, err
}
}
if len(deleted) > 0 {
// Filter out any return values "foo.jpg" where a
// "foo.jpg.deleted" marker file exists on disk.
all := ret
ret = ret[:0]
for _, wf := range all {
if !deleted[wf.Name] {
ret = append(ret, wf)
}
}
// And do some opportunistic deleting while we're here.
// Maybe Windows is done virus scanning the file we tried
// to delete a long time ago and will let us delete it now.
for name := range deleted {
tryDeleteAgain(filepath.Join(s.rootDir, name))
}
}
sort.Slice(ret, func(i, j int) bool { return ret[i].Name < ret[j].Name })
return ret, nil
}
var (
errNilPeerAPIServer = errors.New("peerapi unavailable; not listening")
errNoTaildrop = errors.New("Taildrop disabled; no storage directory")
)
// tryDeleteAgain tries to delete path (and path+deletedSuffix) after
// it failed earlier. This happens on Windows when various anti-virus
// tools hook into filesystem operations and have the file open still
// while we're trying to delete it. In that case we instead mark it as
// deleted (writing a "foo.jpg.deleted" marker file), but then we
// later try to clean them up.
//
// fullPath is the full path to the file without the deleted suffix.
func tryDeleteAgain(fullPath string) {
if err := os.Remove(fullPath); err == nil || os.IsNotExist(err) {
os.Remove(fullPath + deletedSuffix)
}
}
func (s *peerAPIServer) DeleteFile(baseName string) error {
if s == nil {
return errNilPeerAPIServer
}
if s.rootDir == "" {
return errNoTaildrop
}
if s.directFileMode {
return errors.New("deletes not allowed in direct mode")
}
path, ok := s.diskPath(baseName)
if !ok {
return errors.New("bad filename")
}
var bo *backoff.Backoff
logf := s.b.logf
t0 := time.Now()
for {
err := os.Remove(path)
if err != nil && !os.IsNotExist(err) {
err = redactErr(err)
// Put a retry loop around deletes on Windows. Windows
// file descriptor closes are effectively asynchronous,
// as a bunch of hooks run on/after close, and we can't
// necessarily delete the file for a while after close,
// as we need to wait for everybody to be done with
// it. (on Windows, unlike Unix, a file can't be deleted
// if it's open anywhere)
// So try a few times but ultimately just leave a
// "foo.jpg.deleted" marker file to note that it's
// deleted and we clean it up later.
if runtime.GOOS == "windows" {
if bo == nil {
bo = backoff.NewBackoff("delete-retry", logf, 1*time.Second)
}
if time.Since(t0) < 5*time.Second {
bo.BackOff(context.Background(), err)
continue
}
if err := touchFile(path + deletedSuffix); err != nil {
logf("peerapi: failed to leave deleted marker: %v", err)
}
}
logf("peerapi: failed to DeleteFile: %v", err)
return err
}
return nil
}
}
// redacted is a fake path name we use in errors, to avoid
// accidentally logging actual filenames anywhere.
const redacted = "redacted"
func redactErr(err error) error {
if pe, ok := err.(*os.PathError); ok {
pe.Path = redacted
}
return err
}
func touchFile(path string) error {
f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
if err != nil {
return redactErr(err)
}
return f.Close()
}
func (s *peerAPIServer) OpenFile(baseName string) (rc io.ReadCloser, size int64, err error) {
if s == nil {
return nil, 0, errNilPeerAPIServer
}
if s.rootDir == "" {
return nil, 0, errNoTaildrop
}
if s.directFileMode {
return nil, 0, errors.New("opens not allowed in direct mode")
}
path, ok := s.diskPath(baseName)
if !ok {
return nil, 0, errors.New("bad filename")
}
if fi, err := os.Stat(path + deletedSuffix); err == nil && fi.Mode().IsRegular() {
tryDeleteAgain(path)
return nil, 0, &fs.PathError{Op: "open", Path: redacted, Err: fs.ErrNotExist}
}
f, err := os.Open(path)
if err != nil {
return nil, 0, redactErr(err)
}
fi, err := f.Stat()
if err != nil {
f.Close()
return nil, 0, redactErr(err)
}
return f, fi.Size(), nil
}
func (s *peerAPIServer) listen(ip netaddr.IP, ifState *interfaces.State) (ln net.Listener, err error) {
ipStr := ip.String()
var lc net.ListenConfig
if initListenConfig != nil {
// On iOS/macOS, this sets the lc.Control hook to
// setsockopt the interface index to bind to, to get
// out of the network sandbox.
if err := initListenConfig(&lc, ip, ifState, s.b.dialer.TUNName()); err != nil {
return nil, err
}
if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
ipStr = ""
}
}
if wgengine.IsNetstack(s.b.e) {
ipStr = ""
}
tcp4or6 := "tcp4"
if ip.Is6() {
tcp4or6 = "tcp6"
}
// Make a best effort to pick a deterministic port number for
// the ip The lower three bytes are the same for IPv4 and IPv6
// Tailscale addresses (at least currently), so we'll usually
// get the same port number on both address families for
// dev/debugging purposes, which is nice. But it's not so
// deterministic that people will bake this into clients.
// We try a few times just in case something's already
// listening on that port (on all interfaces, probably).
for try := uint8(0); try < 5; try++ {
a16 := ip.As16()
hashData := a16[len(a16)-3:]
hashData[0] += try
tryPort := (32 << 10) | uint16(crc32.ChecksumIEEE(hashData))
ln, err = lc.Listen(context.Background(), tcp4or6, net.JoinHostPort(ipStr, strconv.Itoa(int(tryPort))))
if err == nil {
return ln, nil
}
}
// Fall back to random ephemeral port.
return lc.Listen(context.Background(), tcp4or6, net.JoinHostPort(ipStr, "0"))
}
type peerAPIListener struct {
ps *peerAPIServer
ip netaddr.IP
lb *LocalBackend
// ln is the Listener. It can be nil in netstack mode if there are more than
// 1 local addresses (e.g. both an IPv4 and IPv6). When it's nil, port
// and urlStr are still populated.
ln net.Listener
// urlStr is the base URL to access the peer API (http://ip:port/).
urlStr string
// port is just the port of urlStr.
port int
}
func (pln *peerAPIListener) Close() error {
if pln.ln != nil {
return pln.ln.Close()
}
return nil
}
func (pln *peerAPIListener) serve() {
if pln.ln == nil {
return
}
defer pln.ln.Close()
logf := pln.lb.logf
for {
c, err := pln.ln.Accept()
if errors.Is(err, net.ErrClosed) {
return
}
if err != nil {
logf("peerapi.Accept: %v", err)
return
}
ta, ok := c.RemoteAddr().(*net.TCPAddr)
if !ok {
c.Close()
logf("peerapi: unexpected RemoteAddr %#v", c.RemoteAddr())
continue
}
ipp, ok := netaddr.FromStdAddr(ta.IP, ta.Port, "")
if !ok {
logf("peerapi: bogus TCPAddr %#v", ta)
c.Close()
continue
}
peerNode, peerUser, ok := pln.lb.WhoIs(ipp)
if !ok {
logf("peerapi: unknown peer %v", ipp)
c.Close()
continue
}
h := &peerAPIHandler{
ps: pln.ps,
isSelf: pln.ps.selfNode.User == peerNode.User,
remoteAddr: ipp,
peerNode: peerNode,
peerUser: peerUser,
}
httpServer := &http.Server{
Handler: h,
}
if addH2C != nil {
addH2C(httpServer)
}
go httpServer.Serve(&oneConnListener{Listener: pln.ln, conn: c})
}
}
type oneConnListener struct {
net.Listener
conn net.Conn
}
func (l *oneConnListener) Accept() (c net.Conn, err error) {
c = l.conn
if c == nil {
err = io.EOF
return
}
err = nil
l.conn = nil
return
}
func (l *oneConnListener) Close() error { return nil }
// peerAPIHandler serves the Peer API for a source specific client.
type peerAPIHandler struct {
ps *peerAPIServer
remoteAddr netaddr.IPPort
isSelf bool // whether peerNode is owned by same user as this node
peerNode *tailcfg.Node // peerNode is who's making the request
peerUser tailcfg.UserProfile // profile of peerNode
}
func (h *peerAPIHandler) logf(format string, a ...interface{}) {
h.ps.b.logf("peerapi: "+format, a...)
}
func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
if strings.HasPrefix(r.URL.Path, "/v0/put/") {
h.handlePeerPut(w, r)
return
}
if strings.HasPrefix(r.URL.Path, "/dns-query") {
h.handleDNSQuery(w, r)
return
}
switch r.URL.Path {
case "/v0/goroutines":
h.handleServeGoroutines(w, r)
return
case "/v0/env":
h.handleServeEnv(w, r)
return
case "/v0/metrics":
h.handleServeMetrics(w, r)
return
case "/v0/magicsock":
h.handleServeMagicsock(w, r)
return
case "/v0/dnsfwd":
h.handleServeDNSFwd(w, r)
return
}
who := h.peerUser.DisplayName
fmt.Fprintf(w, `<html>
<meta name="viewport" content="width=device-width, initial-scale=1">
<body>
<h1>Hello, %s (%v)</h1>
This is my Tailscale device. Your device is %v.
`, html.EscapeString(who), h.remoteAddr.IP(), html.EscapeString(h.peerNode.ComputedName))
if h.isSelf {
fmt.Fprintf(w, "<p>You are the owner of this node.\n")
}
}
type incomingFile struct {
name string // "foo.jpg"
started time.Time
size int64 // or -1 if unknown; never 0
w io.Writer // underlying writer
ph *peerAPIHandler
partialPath string // non-empty in direct mode
mu sync.Mutex
copied int64
done bool
lastNotify time.Time
}
func (f *incomingFile) markAndNotifyDone() {
f.mu.Lock()
f.done = true
f.mu.Unlock()
b := f.ph.ps.b
b.sendFileNotify()
}
func (f *incomingFile) Write(p []byte) (n int, err error) {
n, err = f.w.Write(p)
b := f.ph.ps.b
var needNotify bool
defer func() {
if needNotify {
b.sendFileNotify()
}
}()
if n > 0 {
f.mu.Lock()
defer f.mu.Unlock()
f.copied += int64(n)
now := time.Now()
if f.lastNotify.IsZero() || now.Sub(f.lastNotify) > time.Second {
f.lastNotify = now
needNotify = true
}
}
return n, err
}
func (f *incomingFile) PartialFile() ipn.PartialFile {
f.mu.Lock()
defer f.mu.Unlock()
return ipn.PartialFile{
Name: f.name,
Started: f.started,
DeclaredSize: f.size,
Received: f.copied,
PartialPath: f.partialPath,
Done: f.done,
}
}
func (h *peerAPIHandler) handlePeerPut(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
if !h.ps.b.hasCapFileSharing() {
http.Error(w, "file sharing not enabled by Tailscale admin", http.StatusForbidden)
return
}
if r.Method != "PUT" {
http.Error(w, "expected method PUT", http.StatusMethodNotAllowed)
return
}
if h.ps.rootDir == "" {
http.Error(w, errNoTaildrop.Error(), http.StatusInternalServerError)
return
}
rawPath := r.URL.EscapedPath()
suffix := strings.TrimPrefix(rawPath, "/v0/put/")
if suffix == rawPath {
http.Error(w, "misconfigured internals", 500)
return
}
if suffix == "" {
http.Error(w, "empty filename", 400)
return
}
if strings.Contains(suffix, "/") {
http.Error(w, "directories not supported", 400)
return
}
baseName, err := url.PathUnescape(suffix)
if err != nil {
http.Error(w, "bad path encoding", 400)
return
}
dstFile, ok := h.ps.diskPath(baseName)
if !ok {
http.Error(w, "bad filename", 400)
return
}
t0 := time.Now()
// TODO(bradfitz): prevent same filename being sent by two peers at once
partialFile := dstFile + partialSuffix
f, err := os.Create(partialFile)
if err != nil {
h.logf("put Create error: %v", redactErr(err))
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
var success bool
defer func() {
if !success {
os.Remove(partialFile)
}
}()
var finalSize int64
var inFile *incomingFile
if r.ContentLength != 0 {
inFile = &incomingFile{
name: baseName,
started: time.Now(),
size: r.ContentLength,
w: f,
ph: h,
}
if h.ps.directFileMode {
inFile.partialPath = partialFile
}
h.ps.b.registerIncomingFile(inFile, true)
defer h.ps.b.registerIncomingFile(inFile, false)
n, err := io.Copy(inFile, r.Body)
if err != nil {
err = redactErr(err)
f.Close()
h.logf("put Copy error: %v", err)
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
finalSize = n
}
if err := redactErr(f.Close()); err != nil {
h.logf("put Close error: %v", err)
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
if h.ps.directFileMode && !h.ps.directFileDoFinalRename {
if inFile != nil { // non-zero length; TODO: notify even for zero length
inFile.markAndNotifyDone()
}
} else {
if err := os.Rename(partialFile, dstFile); err != nil {
err = redactErr(err)
h.logf("put final rename: %v", err)
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
}
d := time.Since(t0).Round(time.Second / 10)
h.logf("got put of %s in %v from %v/%v", approxSize(finalSize), d, h.remoteAddr.IP, h.peerNode.ComputedName)
// TODO: set modtime
// TODO: some real response
success = true
io.WriteString(w, "{}\n")
h.ps.knownEmpty.Set(false)
h.ps.b.sendFileNotify()
}
func approxSize(n int64) string {
if n <= 1<<10 {
return "<=1KB"
}
if n <= 1<<20 {
return "<=1MB"
}
return fmt.Sprintf("~%dMB", n>>20)
}
func (h *peerAPIHandler) handleServeGoroutines(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
var buf []byte
for size := 4 << 10; size <= 2<<20; size *= 2 {
buf = make([]byte, size)
buf = buf[:runtime.Stack(buf, true)]
if len(buf) < size {
break
}
}
w.Write(buf)
}
func (h *peerAPIHandler) handleServeEnv(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
var data struct {
Hostinfo *tailcfg.Hostinfo
Uid int
Args []string
Env []string
}
data.Hostinfo = hostinfo.New()
data.Uid = os.Getuid()
data.Args = os.Args
data.Env = os.Environ()
w.Header().Set("Content-Type", "application/json")
json.NewEncoder(w).Encode(data)
}
func (h *peerAPIHandler) handleServeMagicsock(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
eng := h.ps.b.e
if ig, ok := eng.(wgengine.InternalsGetter); ok {
if _, mc, ok := ig.GetInternals(); ok {
mc.ServeHTTPDebug(w, r)
return
}
}
http.Error(w, "miswired", 500)
}
func (h *peerAPIHandler) handleServeMetrics(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
w.Header().Set("Content-Type", "text/plain")
clientmetric.WritePrometheusExpositionFormat(w)
}
func (h *peerAPIHandler) handleServeDNSFwd(w http.ResponseWriter, r *http.Request) {
if !h.isSelf {
http.Error(w, "not owner", http.StatusForbidden)
return
}
dh := health.DebugHandler("dnsfwd")
if dh == nil {
http.Error(w, "not wired up", 500)
return
}
dh.ServeHTTP(w, r)
}
func (h *peerAPIHandler) replyToDNSQueries() bool {
if h.isSelf {
// If the peer is owned by the same user, just allow it
// without further checks.
return true
}
b := h.ps.b
if !b.OfferingExitNode() {
// If we're not an exit node, there's no point to
// being a DNS server for somebody.
return false
}
if !h.remoteAddr.IsValid() {
// This should never be the case if the peerAPIHandler
// was wired up correctly, but just in case.
return false
}
// Otherwise, we're an exit node but the peer is not us, so
// we need to check if they're allowed access to the internet.
// As peerapi bypasses wgengine/filter checks, we need to check
// ourselves. As a proxy for autogroup:internet access, we see
// if we would've accepted a packet to 0.0.0.0:53. We treat
// the IP 0.0.0.0 as being "the internet".
f, ok := b.filterAtomic.Load().(*filter.Filter)
if !ok {
return false
}
// Note: we check TCP here because the Filter type already had
// a CheckTCP method (for unit tests), but it's pretty
// arbitrary. DNS runs over TCP and UDP, so sure... we check
// TCP.
dstIP := netaddr.IPv4(0, 0, 0, 0)
remoteIP := h.remoteAddr.IP()
if remoteIP.Is6() {
// autogroup:internet for IPv6 is defined to start with 2000::/3,
// so use 2000::0 as the probe "the internet" address.
dstIP = netaddr.MustParseIP("2000::")
}
verdict := f.CheckTCP(remoteIP, dstIP, 53)
return verdict == filter.Accept
}
// handleDNSQuery implements a DoH server (RFC 8484) over the peerapi.
// It's not over HTTPS as the spec dictates, but rather HTTP-over-WireGuard.
func (h *peerAPIHandler) handleDNSQuery(w http.ResponseWriter, r *http.Request) {
if h.ps.resolver == nil {
http.Error(w, "DNS not wired up", http.StatusNotImplemented)
return
}
if !h.replyToDNSQueries() {
http.Error(w, "DNS access denied", http.StatusForbidden)
return
}
pretty := false // non-DoH debug mode for humans
q, publicError := dohQuery(r)
if publicError != "" && r.Method == "GET" {
if name := r.FormValue("q"); name != "" {
pretty = true
publicError = ""
q = dnsQueryForName(name, r.FormValue("t"))
}
}
if publicError != "" {
http.Error(w, publicError, http.StatusBadRequest)
return
}
// Some timeout that's short enough to be noticed by humans
// but long enough that it's longer than real DNS timeouts.
const arbitraryTimeout = 5 * time.Second
ctx, cancel := context.WithTimeout(r.Context(), arbitraryTimeout)
defer cancel()
res, err := h.ps.resolver.HandleExitNodeDNSQuery(ctx, q, h.remoteAddr, h.ps.b.allowExitNodeDNSProxyToServeName)
if err != nil {
h.logf("handleDNS fwd error: %v", err)
if err := ctx.Err(); err != nil {
http.Error(w, err.Error(), 500)
} else {
http.Error(w, "DNS forwarding error", 500)
}
return
}
if pretty {
// Non-standard response for interactive debugging.
w.Header().Set("Content-Type", "application/json")
writePrettyDNSReply(w, res)
return
}
w.Header().Set("Content-Type", "application/dns-message")
w.Header().Set("Content-Length", strconv.Itoa(len(res)))
w.Write(res)
}
func dohQuery(r *http.Request) (dnsQuery []byte, publicErr string) {
const maxQueryLen = 256 << 10
switch r.Method {
default:
return nil, "bad HTTP method"
case "GET":
q64 := r.FormValue("dns")
if q64 == "" {
return nil, "missing 'dns' parameter"
}
if base64.RawURLEncoding.DecodedLen(len(q64)) > maxQueryLen {
return nil, "query too large"
}
q, err := base64.RawURLEncoding.DecodeString(q64)
if err != nil {
return nil, "invalid 'dns' base64 encoding"
}
return q, ""
case "POST":
if r.Header.Get("Content-Type") != "application/dns-message" {
return nil, "unexpected Content-Type"
}
q, err := io.ReadAll(io.LimitReader(r.Body, maxQueryLen+1))
if err != nil {
return nil, "error reading post body with DNS query"
}
if len(q) > maxQueryLen {
return nil, "query too large"
}
return q, ""
}
}
func dnsQueryForName(name, typStr string) []byte {
typ := dnsmessage.TypeA
switch strings.ToLower(typStr) {
case "aaaa":
typ = dnsmessage.TypeAAAA
case "txt":
typ = dnsmessage.TypeTXT
}
b := dnsmessage.NewBuilder(nil, dnsmessage.Header{
OpCode: 0, // query
RecursionDesired: true,
ID: 0,
})
if !strings.HasSuffix(name, ".") {
name += "."
}
b.StartQuestions()
b.Question(dnsmessage.Question{
Name: dnsmessage.MustNewName(name),
Type: typ,
Class: dnsmessage.ClassINET,
})
msg, _ := b.Finish()
return msg
}
func writePrettyDNSReply(w io.Writer, res []byte) (err error) {
defer func() {
if err != nil {
j, _ := json.Marshal(struct {
Error string
}{err.Error()})
j = append(j, '\n')
w.Write(j)
return
}
}()
var p dnsmessage.Parser
hdr, err := p.Start(res)
if err != nil {
return err
}
if hdr.RCode != dnsmessage.RCodeSuccess {
return fmt.Errorf("DNS RCode = %v", hdr.RCode)
}
if err := p.SkipAllQuestions(); err != nil {
return err
}
var gotIPs []string
for {
h, err := p.AnswerHeader()
if err == dnsmessage.ErrSectionDone {
break
}
if err != nil {
return err
}
if h.Class != dnsmessage.ClassINET {
continue
}
switch h.Type {
case dnsmessage.TypeA:
r, err := p.AResource()
if err != nil {
return err
}
gotIPs = append(gotIPs, net.IP(r.A[:]).String())
case dnsmessage.TypeAAAA:
r, err := p.AAAAResource()
if err != nil {
return err
}
gotIPs = append(gotIPs, net.IP(r.AAAA[:]).String())
case dnsmessage.TypeTXT:
r, err := p.TXTResource()
if err != nil {
return err
}
gotIPs = append(gotIPs, r.TXT...)
}
}
j, _ := json.Marshal(gotIPs)
j = append(j, '\n')
w.Write(j)
return nil
}