Fix syscall path execution

Fix archive cleanup if hash is not valid
Limit the archive write bytes

lib/autoupdate/client_update.go

@@ -239,7 +239,7 @@ func (u *ClientUpdater) Update(ctx context.Context, toolsVersion string) error {
 	if err != nil {
 		return trace.Wrap(err)
 	}
-	archivePath, err := u.downloadArchive(signalCtx, u.toolsDir, archiveURL, hash)
+	archivePath, archiveHash, err := u.downloadArchive(signalCtx, u.toolsDir, archiveURL)
 	if err != nil {
 		return trace.Wrap(err)
 	}
@@ -248,6 +248,9 @@ func (u *ClientUpdater) Update(ctx context.Context, toolsVersion string) error {
 			slog.WarnContext(ctx, "failed to remove archive", "error", err)
 		}
 	}()
+	if archiveHash != hash {
+		return trace.BadParameter("hash of archive does not match downloaded archive")
+	}
 
 	pkgName := fmt.Sprint(uuid.New().String(), updatePackageSuffix)
 	extractDir := filepath.Join(u.toolsDir, pkgName)
@@ -291,7 +294,7 @@ func (u *ClientUpdater) Exec() (int, error) {
 		return cmd.ProcessState.ExitCode(), nil
 	}
 
-	if err := syscall.Exec(path, os.Args, env); err != nil {
+	if err := syscall.Exec(path, append([]string{path}, os.Args[1:]...), env); err != nil {
 		return 0, trace.Wrap(err)
 	}
 
@@ -324,47 +327,44 @@ func (u *ClientUpdater) downloadHash(ctx context.Context, url string) (string, e
 	return raw, nil
 }
 
-func (u *ClientUpdater) downloadArchive(ctx context.Context, downloadDir string, url string, hash string) (string, error) {
+func (u *ClientUpdater) downloadArchive(ctx context.Context, downloadDir string, url string) (string, string, error) {
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
-		return "", trace.Wrap(err)
+		return "", "", trace.Wrap(err)
 	}
 	resp, err := u.client.Do(req)
 	if err != nil {
-		return "", trace.Wrap(err)
+		return "", "", trace.Wrap(err)
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode != http.StatusOK {
-		return "", trace.BadParameter("bad status when downloading archive: %v", resp.StatusCode)
+		return "", "", trace.BadParameter("bad status when downloading archive: %v", resp.StatusCode)
 	}
 
 	if resp.ContentLength != -1 {
 		if err := checkFreeSpace(u.toolsDir, uint64(resp.ContentLength)); err != nil {
-			return "", trace.Wrap(err)
+			return "", "", trace.Wrap(err)
 		}
 	}
 
 	// Caller of this function will remove this file after the atomic swap has
 	// occurred.
 	f, err := os.CreateTemp(downloadDir, "tmp-")
 	if err != nil {
-		return "", trace.Wrap(err)
+		return "", "", trace.Wrap(err)
 	}
 
 	h := sha256.New()
 	pw := &progressWriter{n: 0, limit: resp.ContentLength}
 	body := io.TeeReader(io.TeeReader(resp.Body, h), pw)
 
 	// It is a little inefficient to download the file to disk and then re-load
-	// it into memory to unarchive later, but this is safer as it allows {tsh,
-	// tctl} to validate the hash before trying to operate on the archive.
-	_, err = io.Copy(f, body)
+	// it into memory to unarchive later, but this is safer as it allows client
+	// tools to validate the hash before trying to operate on the archive.
+	_, err = io.CopyN(f, body, resp.ContentLength)
 	if err != nil {
-		return "", trace.Wrap(err)
-	}
-	if fmt.Sprintf("%x", h.Sum(nil)) != hash {
-		return "", trace.BadParameter("hash of archive does not match downloaded archive")
+		return "", "", trace.Wrap(err)
 	}
 
-	return f.Name(), nil
+	return f.Name(), fmt.Sprintf("%x", h.Sum(nil)), nil
 }