Fix temp dir on Android 10 or below (#1250)

Co-authored-by: Ylarod <me@ylarod.cn>

userspace/ksud/src/utils.rs

@@ -5,6 +5,8 @@ use std::{
     path::Path,
 };
 
+use crate::defs;
+use std::fs::metadata;
 #[allow(unused_imports)]
 use std::fs::{set_permissions, Permissions};
 #[cfg(unix)]
@@ -163,3 +165,13 @@ pub fn umask(_mask: u32) {
 pub fn has_magisk() -> bool {
     which::which("magisk").is_ok()
 }
+
+pub fn get_tmp_path() -> &'static str {
+    if metadata(defs::TEMP_DIR_LEGACY).is_ok() {
+        return defs::TEMP_DIR_LEGACY;
+    }
+    if metadata(defs::TEMP_DIR).is_ok() {
+        return defs::TEMP_DIR;
+    }
+    ""
+}