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tailscale/tailfs/remote.go

390 lines
10 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package tailfs
import (
"bufio"
"encoding/hex"
"fmt"
"log"
"math"
"net"
"net/http"
"net/netip"
"os"
"os/exec"
"strings"
"sync"
"time"
"github.com/tailscale/xnet/webdav"
"tailscale.com/safesocket"
"tailscale.com/tailfs/compositefs"
"tailscale.com/tailfs/shared"
"tailscale.com/tailfs/webdavfs"
"tailscale.com/types/logger"
)
var (
disallowShareAs = false
)
// AllowShareAs reports whether sharing files as a specific user is allowed.
func AllowShareAs() bool {
return !disallowShareAs && doAllowShareAs()
}
// Share represents a folder that's shared with remote Tailfs nodes.
type Share struct {
// Name is how this share appears on remote nodes.
Name string `json:"name"`
// Path is the path to the directory on this machine that's being shared.
Path string `json:"path"`
// As is the UNIX or Windows username of the local account used for this
// share. File read/write permissions are enforced based on this username.
As string `json:"who"`
}
func NewFileSystemForRemote(logf logger.Logf) *FileSystemForRemote {
if logf == nil {
logf = log.Printf
}
fs := &FileSystemForRemote{
logf: logf,
lockSystem: webdav.NewMemLS(),
fileSystems: make(map[string]webdav.FileSystem),
userServers: make(map[string]*userServer),
}
return fs
}
// FileSystemForRemote is the Tailfs filesystem exposed to remote nodes. It
// provides a unified WebDAV interface to local directories that have been
// shared.
type FileSystemForRemote struct {
logf logger.Logf
lockSystem webdav.LockSystem
// mu guards the below values. Acquire a write lock before updating any of
// them, acquire a read lock before reading any of them.
mu sync.RWMutex
fileServerAddr string
shares map[string]*Share
fileSystems map[string]webdav.FileSystem
userServers map[string]*userServer
}
// SetFileServerAddr sets the address of the file server to which we
// should proxy. This is used on platforms like Windows and MacOS
// sandboxed where we can't spawn user-specific sub-processes and instead
// rely on the UI application that's already running as an unprivileged
// user to access the filesystem for us.
func (s *FileSystemForRemote) SetFileServerAddr(addr string) {
s.mu.Lock()
s.fileServerAddr = addr
s.mu.Unlock()
}
// SetShares sets the complete set of shares exposed by this node. If
// AllowShareAs() reports true, we will use one subprocess per user to
// access the filesystem (see userServer). Otherwise, we will use the file
// server configured via SetFileServerAddr.
func (s *FileSystemForRemote) SetShares(shares map[string]*Share) {
userServers := make(map[string]*userServer)
if AllowShareAs() {
// set up per-user server
for _, share := range shares {
p, found := userServers[share.As]
if !found {
p = &userServer{
logf: s.logf,
}
userServers[share.As] = p
}
p.shares = append(p.shares, share)
}
for _, p := range userServers {
go p.runLoop()
}
}
fileSystems := make(map[string]webdav.FileSystem, len(shares))
for _, share := range shares {
fileSystems[share.Name] = s.buildWebDAVFS(share)
}
s.mu.Lock()
s.shares = shares
oldFileSystems := s.fileSystems
oldUserServers := s.userServers
s.fileSystems = fileSystems
s.userServers = userServers
s.mu.Unlock()
s.stopUserServers(oldUserServers)
s.closeFileSystems(oldFileSystems)
}
func (s *FileSystemForRemote) buildWebDAVFS(share *Share) webdav.FileSystem {
return webdavfs.New(webdavfs.Options{
Logf: s.logf,
URL: fmt.Sprintf("http://%v/%v", hex.EncodeToString([]byte(share.Name)), share.Name),
Transport: &http.Transport{
Dial: func(_, shareAddr string) (net.Conn, error) {
shareNameHex, _, err := net.SplitHostPort(shareAddr)
if err != nil {
return nil, fmt.Errorf("unable to parse share address %v: %w", shareAddr, err)
}
// We had to encode the share name in hex to make sure it's a valid hostname
shareNameBytes, err := hex.DecodeString(shareNameHex)
if err != nil {
return nil, fmt.Errorf("unable to decode share name from host %v: %v", shareNameHex, err)
}
shareName := string(shareNameBytes)
s.mu.RLock()
share, shareFound := s.shares[shareName]
userServers := s.userServers
fileServerAddr := s.fileServerAddr
s.mu.RUnlock()
if !shareFound {
return nil, fmt.Errorf("unknown share %v", shareName)
}
var addr string
if !AllowShareAs() {
addr = fileServerAddr
} else {
userServer, found := userServers[share.As]
if found {
userServer.mu.RLock()
addr = userServer.addr
userServer.mu.RUnlock()
}
}
if addr == "" {
return nil, fmt.Errorf("unable to determine address for share %v", shareName)
}
_, err = netip.ParseAddrPort(addr)
if err == nil {
// this is a regular network address, dial normally
return net.Dial("tcp", addr)
}
// assume this is a safesocket address
return safesocket.Connect(addr)
},
},
StatRoot: true,
})
}
// ServeHTTPWithPerms behaves like the similar method from http.Handler but
// also accepts a Permissions map that captures the permissions of the
// connecting node.
func (s *FileSystemForRemote) ServeHTTPWithPerms(permissions Permissions, w http.ResponseWriter, r *http.Request) {
isWrite := writeMethods[r.Method]
if isWrite {
share := shared.CleanAndSplit(r.URL.Path)[0]
switch permissions.For(share) {
case PermissionNone:
// If we have no permissions to this share, treat it as not found
// to avoid leaking any information about the share's existence.
http.Error(w, "not found", http.StatusNotFound)
return
case PermissionReadOnly:
http.Error(w, "permission denied", http.StatusForbidden)
return
}
}
s.mu.RLock()
fileSystems := s.fileSystems
s.mu.RUnlock()
children := make([]*compositefs.Child, 0, len(fileSystems))
// filter out shares to which the connecting principal has no access
for name, fs := range fileSystems {
if permissions.For(name) == PermissionNone {
continue
}
children = append(children, &compositefs.Child{Name: name, FS: fs})
}
cfs := compositefs.New(
compositefs.Options{
Logf: s.logf,
StatChildren: true,
})
cfs.SetChildren(children...)
h := webdav.Handler{
FileSystem: cfs,
LockSystem: s.lockSystem,
}
h.ServeHTTP(w, r)
}
func (s *FileSystemForRemote) stopUserServers(userServers map[string]*userServer) {
for _, server := range userServers {
if err := server.Close(); err != nil {
s.logf("error closing tailfs user server: %v", err)
}
}
}
func (s *FileSystemForRemote) closeFileSystems(fileSystems map[string]webdav.FileSystem) {
for _, fs := range fileSystems {
closer, ok := fs.(interface{ Close() error })
if ok {
if err := closer.Close(); err != nil {
s.logf("error closing tailfs filesystem: %v", err)
}
}
}
}
// Close() stops serving the WebDAV content
func (s *FileSystemForRemote) Close() error {
s.mu.Lock()
userServers := s.userServers
fileSystems := s.fileSystems
s.mu.Unlock()
s.stopUserServers(userServers)
s.closeFileSystems(fileSystems)
return nil
}
// userServer runs tailscaled serve-tailfs to serve webdav content for the
// given Shares. All Shares are assumed to have the same Share.As, and the
// content is served as that Share.As user.
type userServer struct {
logf logger.Logf
shares []*Share
// mu guards the below values. Acquire a write lock before updating any of
// them, acquire a read lock before reading any of them.
mu sync.RWMutex
cmd *exec.Cmd
addr string
closed bool
}
func (s *userServer) Close() error {
s.mu.Lock()
cmd := s.cmd
s.closed = true
s.mu.Unlock()
if cmd != nil && cmd.Process != nil {
return cmd.Process.Kill()
}
// not running, that's okay
return nil
}
func (s *userServer) runLoop() {
executable, err := os.Executable()
if err != nil {
s.logf("can't find executable: %v", err)
return
}
maxSleepTime := 30 * time.Second
consecutiveFailures := float64(0)
var timeOfLastFailure time.Time
for {
s.mu.RLock()
closed := s.closed
s.mu.RUnlock()
if closed {
return
}
err := s.run(executable)
now := time.Now()
timeSinceLastFailure := now.Sub(timeOfLastFailure)
timeOfLastFailure = now
if timeSinceLastFailure < maxSleepTime {
consecutiveFailures++
} else {
consecutiveFailures = 1
}
sleepTime := time.Duration(math.Pow(2, consecutiveFailures)) * time.Millisecond
if sleepTime > maxSleepTime {
sleepTime = maxSleepTime
}
s.logf("user server % v stopped with error %v, will try again in %v", executable, err, sleepTime)
time.Sleep(sleepTime)
}
}
// Run runs the executable (tailscaled). This function only works on UNIX systems,
// but those are the only ones on which we use userServers anyway.
func (s *userServer) run(executable string) error {
// set up the command
args := []string{"serve-tailfs"}
for _, s := range s.shares {
args = append(args, s.Name, s.Path)
}
allArgs := []string{"-u", s.shares[0].As, executable}
allArgs = append(allArgs, args...)
cmd := exec.Command("sudo", allArgs...)
stdout, err := cmd.StdoutPipe()
if err != nil {
return fmt.Errorf("stdout pipe: %w", err)
}
defer stdout.Close()
stderr, err := cmd.StderrPipe()
if err != nil {
return fmt.Errorf("stderr pipe: %w", err)
}
defer stderr.Close()
err = cmd.Start()
if err != nil {
return fmt.Errorf("start: %w", err)
}
s.mu.Lock()
s.cmd = cmd
s.mu.Unlock()
// read address
stdoutScanner := bufio.NewScanner(stdout)
stdoutScanner.Scan()
if stdoutScanner.Err() != nil {
return fmt.Errorf("read addr: %w", stdoutScanner.Err())
}
addr := stdoutScanner.Text()
// send the rest of stdout and stderr to logger to avoid blocking
go func() {
for stdoutScanner.Scan() {
s.logf("tailscaled serve-tailfs stdout: %v", stdoutScanner.Text())
}
}()
stderrScanner := bufio.NewScanner(stderr)
go func() {
for stderrScanner.Scan() {
s.logf("tailscaled serve-tailfs stderr: %v", stderrScanner.Text())
}
}()
s.mu.Lock()
s.addr = strings.TrimSpace(addr)
s.mu.Unlock()
return cmd.Wait()
}
var writeMethods = map[string]bool{
"PUT": true,
"POST": true,
"COPY": true,
"LOCK": true,
"UNLOCK": true,
"MKCOL": true,
"MOVE": true,
"PROPPATCH": true,
}