agent: avoid possible leakage of storage device

When a storage device is used by more than one container, the second
and forth instances will cause storage device reference count leakage,
thus cause storage device leakage. The reason is:
add_storages() will increase reference count of existing storage device,
but forget to add the device to the `mount_list` array, thus leak the
reference count.

Fixes: #7820

Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>

src/agent/src/sandbox.rs

@@ -71,6 +71,10 @@ impl StorageState {
         }
     }
 
+    pub fn path(&self) -> &str {
+        self.device.path()
+    }
+
     pub async fn ref_count(&self) -> u32 {
         self.count.load(Ordering::Relaxed)
     }

src/agent/src/storage/mod.rs

@@ -103,6 +103,10 @@ pub async fn add_storages(
         let path = storage.mount_point.clone();
         let state = sandbox.lock().await.add_sandbox_storage(&path).await;
         if state.ref_count().await > 1 {
+            let path = state.path();
+            if !path.is_empty() {
+                mount_list.push(path.to_string());
+            }
             // The device already exists.
             continue;
         }