cmd/tailscaled, ipn: add tailscaled --statedir flag for var directory

Fixes #2932

Change-Id: I1aa2b323ad542386d140f8336bcc4dcbb8310bd0
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -20,6 +20,7 @@
 	"net/http/pprof"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"runtime"
 	"runtime/debug"
 	"strconv"
@@ -78,6 +79,7 @@ func defaultTunName() string {
 	debug          string
 	port           uint16
 	statepath      string
+	statedir       string
 	socketpath     string
 	birdSocketPath string
 	verbose        int
@@ -114,7 +116,8 @@ func main() {
 	flag.StringVar(&args.httpProxyAddr, "outbound-http-proxy-listen", "", `optional [ip]:port to run an outbound HTTP proxy (e.g. "localhost:8080")`)
 	flag.StringVar(&args.tunname, "tun", defaultTunName(), `tunnel interface name; use "userspace-networking" (beta) to not use TUN`)
 	flag.Var(flagtype.PortValue(&args.port, 0), "port", "UDP port to listen on for WireGuard and peer-to-peer traffic; 0 means automatically select")
-	flag.StringVar(&args.statepath, "state", paths.DefaultTailscaledStateFile(), "path of state file; use 'kube:<secret-name>' to use Kubernetes secrets or 'arn:aws:ssm:...' to store in AWS SSM")
+	flag.StringVar(&args.statepath, "state", paths.DefaultTailscaledStateFile(), "absolute path of state file; use 'kube:<secret-name>' to use Kubernetes secrets or 'arn:aws:ssm:...' to store in AWS SSM. If empty and --statedir is provided, the default is <statedir>/tailscaled.state")
+	flag.StringVar(&args.statedir, "statedir", "", "path to directory for storage of config state, TLS certs, temporary incoming Taildrop files, etc. If empty, it's derived from --state when possible.")
 	flag.StringVar(&args.socketpath, "socket", paths.DefaultTailscaledSocket(), "path of the service unix socket")
 	flag.StringVar(&args.birdSocketPath, "bird-socket", "", "path of the bird unix socket")
 	flag.BoolVar(&printVersion, "version", false, "print version information and exit")
@@ -202,6 +205,16 @@ func trySynologyMigration(p string) error {
 	return nil
 }
 
+func statePathOrDefault() string {
+	if args.statepath != "" {
+		return args.statepath
+	}
+	if args.statedir != "" {
+		return filepath.Join(args.statedir, "tailscaled.state")
+	}
+	return ""
+}
+
 func ipnServerOpts() (o ipnserver.Options) {
 	// Allow changing the OS-specific IPN behavior for tests
 	// so we can e.g. test Windows-specific behaviors on Linux.
@@ -211,8 +224,17 @@ func ipnServerOpts() (o ipnserver.Options) {
 	}
 
 	o.Port = 41112
-	o.StatePath = args.statepath
+	o.StatePath = statePathOrDefault()
 	o.SocketPath = args.socketpath // even for goos=="windows", for tests
+	o.VarRoot = args.statedir
+
+	// If an absolute --state is provided but not --statedir, try to derive
+	// a state directory.
+	if o.VarRoot == "" && filepath.IsAbs(args.statepath) {
+		if dir := filepath.Dir(args.statepath); strings.EqualFold(filepath.Base(dir), "tailscale") {
+			o.VarRoot = dir
+		}
+	}
 
 	switch goos {
 	default:
@@ -261,10 +283,10 @@ func run() error {
 		return nil
 	}
 
-	if args.statepath == "" {
-		log.Fatalf("--state is required")
+	if args.statepath == "" && args.statedir == "" {
+		log.Fatalf("--statedir (or at least --state) is required")
 	}
-	if err := trySynologyMigration(args.statepath); err != nil {
+	if err := trySynologyMigration(statePathOrDefault()); err != nil {
 		log.Printf("error in synology migration: %v", err)
 	}
 

ipn/ipnlocal/local.go

@@ -96,6 +96,7 @@ type LocalBackend struct {
 	gotPortPollRes        chan struct{}    // closed upon first readPoller result
 	serverURL             string           // tailcontrol URL
 	newDecompressor       func() (controlclient.Decompressor, error)
+	varRoot               string // or empty if SetVarRoot never called
 
 	filterHash deephash.Sum
 
@@ -1998,34 +1999,29 @@ func normalizeResolver(cfg dnstype.Resolver) dnstype.Resolver {
 	return cfg
 }
 
+// SetVarRoot sets the root directory of Tailscale's writable
+// storage area . (e.g. "/var/lib/tailscale")
+//
+// It should only be called before the LocalBackend is used.
+func (b *LocalBackend) SetVarRoot(dir string) {
+	b.varRoot = dir
+}
+
 // TailscaleVarRoot returns the root directory of Tailscale's writable
 // storage area. (e.g. "/var/lib/tailscale")
 //
 // It returns an empty string if there's no configured or discovered
 // location.
 func (b *LocalBackend) TailscaleVarRoot() string {
+	if b.varRoot != "" {
+		return b.varRoot
+	}
 	switch runtime.GOOS {
 	case "ios", "android":
 		dir, _ := paths.AppSharedDir.Load().(string)
 		return dir
 	}
-	// Temporary (2021-09-27) transitional fix for #2927 (Synology
-	// cert dir) on the way towards a more complete fix
-	// (#2932). It fixes any case where the state file is provided
-	// to tailscaled explicitly when it's not in the default
-	// location.
-	if fs, ok := b.store.(*ipn.FileStore); ok {
-		if fp := fs.Path(); fp != "" {
-			if dir := filepath.Dir(fp); strings.EqualFold(filepath.Base(dir), "tailscale") {
-				return dir
-			}
-		}
-	}
-	stateFile := paths.DefaultTailscaledStateFile()
-	if stateFile == "" {
-		return ""
-	}
-	return filepath.Dir(stateFile)
+	return ""
 }
 
 func (b *LocalBackend) fileRootLocked(uid tailcfg.UserID) string {

ipn/ipnserver/server.go

@@ -61,8 +61,25 @@ type Options struct {
 	Port int
 
 	// StatePath is the path to the stored agent state.
+	// It should be an absolute path to a file.
+	//
+	// Special cases:
+	//
+	//   * empty string means to use an in-memory store
+	//   * if the string begins with "kube:", the suffix
+	//     is a Kubernetes secret name
+	//   * if the string begins with "arn:", the value is
+	//     an AWS ARN for an SSM.
 	StatePath string
 
+	// VarRoot is the the Tailscale daemon's private writable
+	// directory (usually "/var/lib/tailscale" on Linux) that
+	// contains the "tailscaled.state" file, the "certs" directory
+	// for TLS certs, and the "files" directory for incoming
+	// Taildrop files before they're moved to a user directory.
+	// If empty, Taildrop and TLS certs don't function.
+	VarRoot string
+
 	// AutostartStateKey, if non-empty, immediately starts the agent
 	// using the given StateKey. If empty, the agent stays idle and
 	// waits for a frontend to start it.
@@ -744,6 +761,7 @@ func New(logf logger.Logf, logid string, store ipn.StateStore, eng wgengine.Engi
 	if err != nil {
 		return nil, fmt.Errorf("NewLocalBackend: %v", err)
 	}
+	b.SetVarRoot(opts.VarRoot)
 	b.SetDecompressor(func() (controlclient.Decompressor, error) {
 		return smallzstd.NewDecoder(nil)
 	})