gitRepo volume: directory must be max 1 level deep

More details on Hackerone #2266560

pkg/volume/git_repo/git_repo.go

@@ -261,6 +261,12 @@ func validateVolume(src *v1.GitRepoVolumeSource) error {
 	if err := validateNonFlagArgument(src.Directory, "directory"); err != nil {
 		return err
 	}
+	if (src.Revision != "") && (src.Directory != "") {
+		cleanedDir := filepath.Clean(src.Directory)
+		if strings.Contains(cleanedDir, "/") || (strings.Contains(cleanedDir, "\\")) {
+			return fmt.Errorf("%q is not a valid directory, it must not contain a directory separator", src.Directory)
+		}
+	}
 	return nil
 }