Add fallback to mount syscall

tiann · Feb 5, 2024 · 9207101 · 9207101
1 parent 263b986
commit 9207101
Showing 1 changed file with 102 additions and 50 deletions.
diff --git a/userspace/ksud/src/mount.rs b/userspace/ksud/src/mount.rs
@@ -13,6 +13,12 @@ use procfs::process::Process;
 use std::path::Path;
 use std::path::PathBuf;
 
+macro_rules! null_arg {
+    () => {
+        unsafe { std::ffi::CStr::from_ptr(std::ptr::null()) }
+    };
+}
+
 pub struct AutoMountExt4 {
     target: String,
     auto_umount: bool,
@@ -59,18 +65,27 @@ pub fn mount_ext4(source: impl AsRef<Path>, target: impl AsRef<Path>) -> Result<
     let new_loopback = loopdev::LoopControl::open()?.next_free()?;
     new_loopback.with().attach(source)?;
     let lo = new_loopback.path().ok_or(anyhow!("no loop"))?;
-    let fs = fsopen("ext4", FsOpenFlags::FSOPEN_CLOEXEC)?;
-    let fs = fs.as_fd();
-    fsconfig_set_string(fs, "source", lo)?;
-    fsconfig_create(fs)?;
-    let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
-    move_mount(
-        mount.as_fd(),
-        "",
-        CWD,
-        target.as_ref(),
-        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
-    )?;
+    if let Result::Ok(fs) = fsopen("ext4", FsOpenFlags::FSOPEN_CLOEXEC) {
+        let fs = fs.as_fd();
+        fsconfig_set_string(fs, "source", lo)?;
+        fsconfig_create(fs)?;
+        let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
+        move_mount(
+            mount.as_fd(),
+            "",
+            CWD,
+            target.as_ref(),
+            MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
+        )?;
+    } else {
+        mount(
+            lo,
+            target.as_ref(),
+            "ext4",
+            MountFlags::empty(),
+            null_arg!(),
+        )?;
+    }
     Ok(())
 }
 
@@ -102,43 +117,71 @@ pub fn mount_overlayfs(
         upperdir,
         workdir
     );
-    let fs = fsopen("overlay", FsOpenFlags::FSOPEN_CLOEXEC)?;
-    let fs = fs.as_fd();
-    fsconfig_set_string(fs, "lowerdir", lowerdir_config)?;
-    if let (Some(upperdir), Some(workdir)) = (upperdir, workdir) {
-        if upperdir.exists() && workdir.exists() {
-            fsconfig_set_string(fs, "upperdir", upperdir.display().to_string())?;
-            fsconfig_set_string(fs, "workdir", workdir.display().to_string())?;
+    if let Result::Ok(fs) = fsopen("overlay", FsOpenFlags::FSOPEN_CLOEXEC) {
+        let fs = fs.as_fd();
+        fsconfig_set_string(fs, "lowerdir", lowerdir_config)?;
+        if let (Some(upperdir), Some(workdir)) = (upperdir, workdir) {
+            if upperdir.exists() && workdir.exists() {
+                fsconfig_set_string(fs, "upperdir", upperdir.display().to_string())?;
+                fsconfig_set_string(fs, "workdir", workdir.display().to_string())?;
+            }
+        }
+        fsconfig_set_string(fs, "source", KSU_OVERLAY_SOURCE)?;
+        fsconfig_create(fs)?;
+        let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
+        move_mount(
+            mount.as_fd(),
+            "",
+            CWD,
+            dest.as_ref(),
+            MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
+        )?;
+    } else {
+        let mut data = format!("lowerdir={lowerdir_config}");
+        if let (Some(upperdir), Some(workdir)) = (upperdir, workdir) {
+            if upperdir.exists() && workdir.exists() {
+                data = format!(
+                    "{data},upperdir={},workdir={}",
+                    upperdir.display(),
+                    workdir.display()
+                );
+            }
         }
+        mount(
+            KSU_OVERLAY_SOURCE,
+            dest.as_ref(),
+            "overlay",
+            MountFlags::empty(),
+            data,
+        )?;
     }
-    fsconfig_set_string(fs, "source", KSU_OVERLAY_SOURCE)?;
-    fsconfig_create(fs)?;
-    let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
-    move_mount(
-        mount.as_fd(),
-        "",
-        CWD,
-        dest.as_ref(),
-        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
-    )?;
     Ok(())
 }
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub fn mount_tmpfs(dest: impl AsRef<Path>) -> Result<()> {
     info!("mount tmpfs on {}", dest.as_ref().display());
-    let fs = fsopen("tmpfs", FsOpenFlags::FSOPEN_CLOEXEC)?;
-    let fs = fs.as_fd();
-    fsconfig_set_string(fs, "source", KSU_OVERLAY_SOURCE)?;
-    fsconfig_create(fs)?;
-    let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
-    move_mount(
-        mount.as_fd(),
-        "",
-        CWD,
-        dest.as_ref(),
-        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
-    )?;
+    if let Result::Ok(fs) = fsopen("tmpfs", FsOpenFlags::FSOPEN_CLOEXEC) {
+        let fs = fs.as_fd();
+        fsconfig_set_string(fs, "source", KSU_OVERLAY_SOURCE)?;
+        fsconfig_create(fs)?;
+        let mount = fsmount(fs, FsMountFlags::FSMOUNT_CLOEXEC, MountAttrFlags::empty())?;
+        move_mount(
+            mount.as_fd(),
+            "",
+            CWD,
+            dest.as_ref(),
+            MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
+        )?;
+    } else {
+        mount(
+            KSU_OVERLAY_SOURCE,
+            dest.as_ref(),
+            "tmpfs",
+            MountFlags::empty(),
+            null_arg!(),
+        )?;
+    }
     Ok(())
 }
 
@@ -149,20 +192,29 @@ fn bind_mount(from: impl AsRef<Path>, to: impl AsRef<Path>) -> Result<()> {
         from.as_ref().display(),
         to.as_ref().display()
     );
-    let tree = open_tree(
+    if let Result::Ok(tree) = open_tree(
         CWD,
         from.as_ref(),
         OpenTreeFlags::OPEN_TREE_CLOEXEC
             | OpenTreeFlags::OPEN_TREE_CLONE
             | OpenTreeFlags::AT_RECURSIVE,
-    )?;
-    move_mount(
-        tree.as_fd(),
-        "",
-        CWD,
-        to.as_ref(),
-        MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
-    )?;
+    ) {
+        move_mount(
+            tree.as_fd(),
+            "",
+            CWD,
+            to.as_ref(),
+            MoveMountFlags::MOVE_MOUNT_F_EMPTY_PATH,
+        )?;
+    } else {
+        mount(
+            from.as_ref(),
+            to.as_ref(),
+            null_arg!(),
+            MountFlags::BIND | MountFlags::REC,
+            null_arg!(),
+        )?;
+    }
     Ok(())
 }