kernel: expose umount list to ioctl interface (#2950)

This idea is borrowed from simonpunk's susfs4ksu.
What we see here is that, yeah well, lets just have userspace send us
what it
wants unmounted, this is better than hardcoding everything.

This also solves that issue where MNT_DETACH fails, as long as we send
unmountables in proper order.

A small anti-duplicate mechanism is also added.

While in-kernel umount is a bit worse than zygisk-provider-based ones,
this can still
serve as a healthy alternative.

---------

- Remove duplicate checks

Signed-off-by: backslashxx <118538522+backslashxx@users.noreply.github.com>
Co-authored-by: weishu <twsxtd@gmail.com>
Co-authored-by: ShirkNeko <109797057+ShirkNeko@users.noreply.github.com>

userspace/ksud/src/cli.rs

@@ -390,6 +390,32 @@ enum Kernel {
         /// mount point
         mnt: String,
     },
+    /// Manage umount list
+    Umount {
+        #[command(subcommand)]
+        command: UmountOp,
+    },
+    /// Notify that module is mounted
+    NotifyModuleMounted,
+}
+
+#[derive(clap::Subcommand, Debug)]
+enum UmountOp {
+    /// Add mount point to umount list
+    Add {
+        /// mount point path
+        mnt: String,
+        /// umount flags (default: 0, MNT_DETACH: 2)
+        #[arg(short, long, default_value = "0")]
+        flags: u32,
+    },
+    /// Delete mount point from umount list
+    Del {
+        /// mount point path
+        mnt: String,
+    },
+    /// Wipe all entries from umount list
+    Wipe,
 }
 
 #[cfg(target_arch = "aarch64")]
@@ -425,7 +451,6 @@ enum Umount {
 
         /// Check mount type (overlay)
         #[arg(long, default_value = "false")]
-        check_mnt: bool,
 
         /// Umount flags (0 or 8 for MNT_DETACH)
         #[arg(long, default_value = "-1")]
@@ -606,6 +631,15 @@ pub fn run() -> Result<()> {
         } => crate::boot_patch::restore(boot, magiskboot, flash),
         Commands::Kernel { command } => match command {
             Kernel::NukeExt4Sysfs { mnt } => ksucalls::nuke_ext4_sysfs(&mnt),
+            Kernel::Umount { command } => match command {
+                UmountOp::Add { mnt, flags } => ksucalls::umount_list_add(&mnt, flags),
+                UmountOp::Del { mnt } => ksucalls::umount_list_del(&mnt),
+                UmountOp::Wipe => ksucalls::umount_list_wipe().map_err(Into::into),
+            },
+            Kernel::NotifyModuleMounted => {
+                ksucalls::report_module_mounted();
+                Ok(())
+            }
         },
         #[cfg(target_arch = "aarch64")]
         Commands::Kpm { command } => {
@@ -629,9 +663,8 @@ pub fn run() -> Result<()> {
         Commands::Umount { command } => match command {
             Umount::Add {
                 path,
-                check_mnt,
                 flags,
-            } => crate::umount_manager::add_umount_path(&path, check_mnt, flags),
+            } => crate::umount_manager::add_umount_path(&path, flags),
             Umount::Remove { path } => crate::umount_manager::remove_umount_path(&path),
             Umount::List => crate::umount_manager::list_umount_paths(),
             Umount::ClearCustom => crate::umount_manager::clear_custom_paths(),