[v17] Fix CTMU re-execution downgraded version

lib/autoupdate/tools/helper.go

@@ -187,7 +187,7 @@ func updateAndReExec(ctx context.Context, updater *Updater, toolsVersion string,
 	}
 
 	// Re-execute client tools with the correct version of client tools.
-	code, err := updater.Exec(toolsVersion, args)
+	code, err := updater.Exec(ctx, toolsVersion, args)
 	if err != nil && !errors.Is(err, os.ErrNotExist) {
 		slog.DebugContext(ctx, "Failed to re-exec client tool", "error", err, "code", code)
 		os.Exit(code)

lib/autoupdate/tools/updater.go

@@ -34,6 +34,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"strings"
 	"syscall"
 	"time"
 
@@ -207,11 +208,7 @@ func (u *Updater) CheckLocal(ctx context.Context, profileName string) (resp *Upd
 // operate with this cluster. It returns the semantic version that needs updating and whether
 // re-execution is necessary, by re-execution flag we understand that update and re-execute is required.
 func (u *Updater) CheckRemote(ctx context.Context, proxyAddr string, insecure bool) (response *UpdateResponse, err error) {
-	proxyHost, err := utils.Host(proxyAddr)
-	if err != nil {
-		return nil, trace.Wrap(err)
-	}
-
+	proxyHost := utils.TryHost(proxyAddr)
 	// Check if the user has requested a specific version of client tools.
 	requestedVersion := os.Getenv(teleportToolsVersionEnv)
 	switch requestedVersion {
@@ -402,7 +399,7 @@ func (u *Updater) ToolPath(toolName, toolVersion string) (path string, err error
 }
 
 // Exec re-executes tool command with same arguments and environ variables.
-func (u *Updater) Exec(toolsVersion string, args []string) (int, error) {
+func (u *Updater) Exec(ctx context.Context, toolsVersion string, args []string) (int, error) {
 	executablePath, err := os.Executable()
 	if err != nil {
 		return 0, trace.Wrap(err)
@@ -423,14 +420,19 @@ func (u *Updater) Exec(toolsVersion string, args []string) (int, error) {
 	env := append(os.Environ(), fmt.Sprintf("%s=%s", teleportToolsDirsEnv, u.toolsDir))
 	// To prevent re-execution loop we have to disable update logic for re-execution,
 	// by unsetting current tools version env variable and setting it to "off".
-	if path == executablePath {
+	// The re-execution path and tools directory are absolute. Since the v2 logic
+	// no longer uses a static path, any re-execution from the tools directory
+	// must disable further re-execution.
+	if path == executablePath || strings.HasPrefix(path, u.toolsDir) {
 		if err := os.Unsetenv(teleportToolsVersionEnv); err != nil {
 			return 0, trace.Wrap(err)
 		}
 		env = append(env, teleportToolsVersionEnv+"=off")
+		slog.DebugContext(ctx, "Disable next re-execution")
 	}
 	env = append(env, fmt.Sprintf("%s=%s", teleportToolsVersionReExecEnv, u.localVersion))
 
+	slog.DebugContext(ctx, "Re-execute updated version", "execute", path, "from", executablePath)
 	if runtime.GOOS == constants.WindowsOS {
 		cmd := exec.Command(path, args...)
 		cmd.Env = env