ksud: refine mount

- `magic_mount` now takes the tmp_path from its argument
- `.notmpfs` and `.nomount` now behave the same

skip:
ksud: cache tmp path (74ce44de21963fddc83897846eed28eca89d78aa)

Co-authored-by: shatyuka <shatyuka@qq.com>
Signed-off-by: Faris <rsuntk@yukiprjkt.my.id>

userspace/ksud/src/init_event.rs

@@ -7,6 +7,7 @@ use crate::{
     module::{handle_updated_modules, prune_modules},
     restorecon, uid_scanner, utils,
 };
+use crate::utils::find_tmp_path;
 use anyhow::{Context, Result};
 use log::{info, warn};
 use rustix::fs::{MountFlags, mount};
@@ -86,11 +87,15 @@ pub fn on_post_data_fs() -> Result<()> {
         warn!("KPM: Failed to load KPM modules: {}", e);
     }
 
+    let tmpfs_path = find_tmp_path();
+    // for compatibility
+    let no_mount = Path::new(NO_TMPFS_PATH).exists() || Path::new(NO_MOUNT_PATH).exists();
+
     // mount temp dir
-    if !Path::new(NO_TMPFS_PATH).exists() {
+    if !no_mount {
         if let Err(e) = mount(
             KSU_MOUNT_SOURCE,
-            utils::get_tmp_path(),
+            &tmpfs_path,
             "tmpfs",
             MountFlags::empty(),
             "",
@@ -113,9 +118,10 @@ pub fn on_post_data_fs() -> Result<()> {
     }
 
     // mount module systemlessly by magic mount
-    if !Path::new(NO_MOUNT_PATH).exists() {
-        if let Err(e) = mount_modules_systemlessly() {
-            warn!("do systemless mount failed: {}", e);
+    #[cfg(target_os = "android")]
+    if !no_mount {
+        if let Err(e) = crate::magic_mount::magic_mount(&tmpfs_path) {
+            warn!("do systemless mount failed: {e}");
         }
     } else {
         info!("no mount requested");
@@ -148,7 +154,7 @@ pub fn on_post_data_fs() -> Result<()> {
 
 #[cfg(target_os = "android")]
 pub fn mount_modules_systemlessly() -> Result<()> {
-    crate::magic_mount::magic_mount()
+    crate::magic_mount::magic_mount(&find_tmp_path())
 }
 
 #[cfg(not(target_os = "android"))]

userspace/ksud/src/magic_mount.rs

@@ -21,7 +21,7 @@ use crate::{
     defs::{DISABLE_FILE_NAME, KSU_MOUNT_SOURCE, MODULE_DIR, SKIP_MOUNT_FILE_NAME},
     magic_mount::NodeFileType::{Directory, RegularFile, Symlink, Whiteout},
     restorecon::{lgetfilecon, lsetfilecon},
-    utils::{ensure_dir_exists, get_work_dir},
+    utils::get_work_dir,
 };
 
 const REPLACE_DIR_XATTR: &str = "trusted.overlay.opaque";
@@ -435,10 +435,10 @@ fn do_magic_mount<P: AsRef<Path>, WP: AsRef<Path>>(
     Ok(())
 }
 
-pub fn magic_mount() -> Result<()> {
+pub fn magic_mount(tmp_path: &String) -> Result<()> {
     if let Some(root) = collect_module_files()? {
         log::debug!("collected: {:#?}", root);
-        let tmp_dir = PathBuf::from(get_work_dir());
+        let tmp_dir = Path::new(tmp_path).join("workdir");
         ensure_dir_exists(&tmp_dir)?;
         mount(KSU_MOUNT_SOURCE, &tmp_dir, "tmpfs", MountFlags::empty(), "").context("mount tmp")?;
         mount_change(&tmp_dir, MountPropagationFlags::PRIVATE).context("make tmp private")?;

userspace/ksud/src/utils.rs

@@ -183,7 +183,7 @@ fn is_ok_empty(dir: &str) -> bool {
     }
 }
 
-pub fn get_tmp_path() -> String {
+pub fn find_tmp_path() -> String {
     let dirs = ["/debug_ramdisk", "/patch_hw", "/oem", "/root", "/sbin"];
 
     // find empty directory
@@ -195,11 +195,6 @@ pub fn get_tmp_path() -> String {
     "".to_string()
 }
 
-pub fn get_work_dir() -> String {
-    let tmp_path = get_tmp_path();
-    format!("{}/workdir/", tmp_path)
-}
-
 #[cfg(target_os = "android")]
 fn link_ksud_to_bin() -> Result<()> {
     let ksu_bin = PathBuf::from(defs::DAEMON_PATH);