ipn/ipnserver, paths, logpolicy: move Window config files out of %LocalAppData%

C:\WINDOWS\system32\config\systemprofile\AppData\Local\
is frequently cleared for almost any reason: Windows updates,
System Restore, even various System Cleaner utilities.

The server-state.conf file in AppData\Local could be deleted
at any time, which would break login until the node is removed
from the Admin Panel allowing it to create a new key.

Carefully copy any AppData state to ProgramData at startup.
If copying the state fails, continue to use AppData so at
least there will be connectivity. If there is no state,
use ProgramData.

We also migrate the log.conf file. Very old versions of
Tailscale named the EXE tailscale-ipn, so the log conf was
tailscale-ipn.log.conf and more recent versions preserved
this filename and cmdName in logs. In this migration we
always update the filename to
c:\ProgramData\Tailscale\tailscaled.log.conf

Updates https://github.com/tailscale/tailscale/issues/2856

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

ipn/ipnserver/server.go

@@ -20,6 +20,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"os/user"
+	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
@@ -37,6 +38,7 @@ import (
 	"tailscale.com/log/filelogger"
 	"tailscale.com/logtail/backoff"
 	"tailscale.com/net/netstat"
+	"tailscale.com/paths"
 	"tailscale.com/safesocket"
 	"tailscale.com/smallzstd"
 	"tailscale.com/types/logger"
@@ -581,6 +583,28 @@ func (s *server) writeToClients(n ipn.Notify) {
 	}
 }
 
+// tryWindowsAppDataMigration attempts to copy the Windows state file
+// from its old location to the new location. (Issue 2856)
+//
+// Tailscale 1.14 and before stored state under %LocalAppData%
+// (usually "C:\WINDOWS\system32\config\systemprofile\AppData\Local"
+// when tailscaled.exe is running as a non-user system service).
+// However it is frequently cleared for almost any reason: Windows
+// updates, System Restore, even various System Cleaner utilities.
+//
+// Returns a string of the path to use for the state file.
+// This will be a fallback %LocalAppData% path if migration fails,
+// a %ProgramData% path otherwise.
+func tryWindowsAppDataMigration(path string) string {
+	if path != paths.DefaultTailscaledStateFile() {
+		// If they're specifying a non-default path, just trust that they know
+		// what they are doing.
+		return path
+	}
+	oldFile := filepath.Join(os.Getenv("LocalAppData"), "Tailscale", "server-state.conf")
+	return paths.TryConfigFileMigration(oldFile, path)
+}
+
 // Run runs a Tailscale backend service.
 // The getEngine func is called repeatedly, once per connection, until it returns an engine successfully.
 func Run(ctx context.Context, logf logger.Logf, logid string, getEngine func() (wgengine.Engine, error), opts Options) error {
@@ -614,23 +638,27 @@ func Run(ctx context.Context, logf logger.Logf, logid string, getEngine func() (
 	var store ipn.StateStore
 	if opts.StatePath != "" {
 		const kubePrefix = "kube:"
+		path := opts.StatePath
 		switch {
-		case strings.HasPrefix(opts.StatePath, kubePrefix):
-			secretName := strings.TrimPrefix(opts.StatePath, kubePrefix)
+		case strings.HasPrefix(path, kubePrefix):
+			secretName := strings.TrimPrefix(path, kubePrefix)
 			store, err = ipn.NewKubeStore(secretName)
 			if err != nil {
 				return fmt.Errorf("ipn.NewKubeStore(%q): %v", secretName, err)
 			}
 		default:
-			store, err = ipn.NewFileStore(opts.StatePath)
+			if runtime.GOOS == "windows" {
+				path = tryWindowsAppDataMigration(path)
+			}
+			store, err = ipn.NewFileStore(path)
 			if err != nil {
-				return fmt.Errorf("ipn.NewFileStore(%q): %v", opts.StatePath, err)
+				return fmt.Errorf("ipn.NewFileStore(%q): %v", path, err)
 			}
 		}
 		if opts.AutostartStateKey == "" {
 			autoStartKey, err := store.ReadState(ipn.ServerModeStartKey)
 			if err != nil && err != ipn.ErrStateNotExist {
-				return fmt.Errorf("calling ReadState on %s: %w", opts.StatePath, err)
+				return fmt.Errorf("calling ReadState on %s: %w", path, err)
 			}
 			key := string(autoStartKey)
 			if strings.HasPrefix(key, "user-") {

log/filelogger/log.go

@@ -36,7 +36,7 @@ func New(fileBasePrefix, logID string, logf logger.Logf) logger.Logf {
 	if logf == nil {
 		panic("nil logf")
 	}
-	dir := filepath.Join(os.Getenv("LocalAppData"), "Tailscale", "Logs")
+	dir := filepath.Join(os.Getenv("ProgramData"), "Tailscale", "Logs")
 
 	if err := os.MkdirAll(dir, 0700); err != nil {
 		log.Printf("failed to create local log directory; not writing logs to disk: %v", err)

logpolicy/logpolicy.go

@@ -372,15 +372,34 @@ func New(collection string) *Policy {
 
 	cfgPath := filepath.Join(dir, fmt.Sprintf("%s.log.conf", cmdName))
 
-	// The Windows service previously ran as tailscale-ipn.exe, so
-	// let's keep using that log base name if it exists.
 	if runtime.GOOS == "windows" && cmdName == "tailscaled" {
-		const oldCmdName = "tailscale-ipn"
-		oldPath := filepath.Join(dir, oldCmdName+".log.conf")
-		if fi, err := os.Stat(oldPath); err == nil && fi.Mode().IsRegular() {
-			cfgPath = oldPath
-			cmdName = oldCmdName
+		// Tailscale 1.14 and before stored state under %LocalAppData%
+		// (usually "C:\WINDOWS\system32\config\systemprofile\AppData\Local"
+		// when tailscaled.exe is running as a non-user system service).
+		// However it is frequently cleared for almost any reason: Windows
+		// updates, System Restore, even various System Cleaner utilities.
+		//
+		// The Windows service previously ran as tailscale-ipn.exe, so
+		// machines which ran very old versions might still have their
+		// log conf named %LocalAppData%\tailscale-ipn.log.conf
+		//
+		// Machines which started using Tailscale more recently will have
+		// %LocalAppData%\tailscaled.log.conf
+		//
+		// Attempt to migrate the log conf to C:\ProgramData\Tailscale
+		oldDir := filepath.Join(os.Getenv("LocalAppData"), "Tailscale")
+
+		oldPath := filepath.Join(oldDir, "tailscaled.log.conf")
+		if fi, err := os.Stat(oldPath); err != nil || !fi.Mode().IsRegular() {
+			// *Only* if tailscaled.log.conf does not exist,
+			// check for tailscale-ipn.log.conf
+			oldPathOldCmd := filepath.Join(oldDir, "tailscale-ipn.log.conf")
+			if fi, err := os.Stat(oldPathOldCmd); err == nil && fi.Mode().IsRegular() {
+				oldPath = oldPathOldCmd
+			}
 		}
+
+		cfgPath = paths.TryConfigFileMigration(oldPath, cfgPath)
 	}
 
 	var oldc *Config

paths/migrate.go

@@ -0,0 +1,54 @@
+// 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 paths
+
+import (
+	"log"
+	"os"
+	"path/filepath"
+)
+
+// TryConfigFileMigration carefully copies the contents of oldFile to
+// newFile, returning the path which should be used to read the config.
+// - if newFile already exists, don't modify it just return its path
+// - if neither oldFile nor newFile exist, return newFile for a fresh
+//   default config to be written to.
+// - if oldFile exists but copying to newFile fails, return oldFile so
+//   there will at least be some config to work with.
+func TryConfigFileMigration(oldFile, newFile string) string {
+	_, err := os.Stat(newFile)
+	if err == nil {
+		// Common case for a system which has already been migrated.
+		return newFile
+	}
+	if !os.IsNotExist(err) {
+		log.Printf("TryConfigFileMigration failed; new file: %v", err)
+		return newFile
+	}
+
+	contents, err := os.ReadFile(oldFile)
+	if err != nil {
+		// Common case for a new user.
+		return newFile
+	}
+
+	os.MkdirAll(filepath.Dir(newFile), 0700)
+	err = os.WriteFile(newFile, contents, 0600)
+	if err != nil {
+		removeErr := os.Remove(newFile)
+		if removeErr != nil {
+			log.Printf("TryConfigFileMigration failed; write newFile no cleanup: %v, remove err: %v",
+				err, removeErr)
+			return oldFile
+		}
+		log.Printf("TryConfigFileMigration failed; write newFile: %v", err)
+		return oldFile
+	}
+
+	log.Printf("TryConfigFileMigration: successfully migrated: from %v to %v",
+		oldFile, newFile)
+
+	return newFile
+}

paths/paths.go

@@ -55,7 +55,7 @@ func DefaultTailscaledStateFile() string {
 		return f()
 	}
 	if runtime.GOOS == "windows" {
-		return filepath.Join(os.Getenv("LocalAppData"), "Tailscale", "server-state.conf")
+		return filepath.Join(os.Getenv("ProgramData"), "Tailscale", "server-state.conf")
 	}
 	return ""
 }