Check for existing mounts when installing to disk

Signed-off-by: djach7 <[email protected]>

Author: djach7

lib/src/blockdev.rs

@@ -50,6 +50,23 @@ impl Device {
         self.children.as_ref().map_or(false, |v| !v.is_empty())
     }
 
+    // I know I can pretty this up, very much a wip
+    pub(crate) fn is_mounted_in_pid_mounts(&self, pid: rustix::process::Pid) -> Result<bool> {
+        let output = Command::new("findmnt")
+            .arg("-N")
+            .arg((pid.as_raw_nonzero()).to_string())
+            .arg("-S")
+            .arg(self.path())
+            .output()
+            .expect("Failed to execute findmnt");
+
+        let mounts = String::from_utf8(output.stdout).unwrap();
+
+        let mounts_present = mounts.is_empty();
+
+        Ok(!mounts_present)
+    }
+
     // The "start" parameter was only added in a version of util-linux that's only
     // in Fedora 40 as of this writing.
     fn backfill_start(&mut self) -> Result<()> {

lib/src/install/baseline.rs

@@ -179,6 +179,11 @@ pub(crate) fn install_create_rootfs(
         );
     }
 
+    // Always disallow writing to mounted device
+    if device.is_mounted_in_pid_mounts(rustix::process::getpid()).expect("Failed to check mountpoints") {
+        anyhow::bail!("Device {} is mounted", device.path())
+    }
+
     let run_bootc = Utf8Path::new(RUN_BOOTC);
     let mntdir = run_bootc.join("mounts");
     if mntdir.exists() {