Merge pull request #60448 from Random-Liu/image-cache-return-copy

Automatic merge from submit-queue (batch tested with PRs 59365, 60446, 60448, 55019, 60431). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Let image manager return a copy of image list.

Fixes https://github.com/kubernetes/kubernetes/issues/60443.
/cc @kubernetes/sig-node-pr-reviews 

**Release note**:

```release-note
none
```

pkg/kubelet/images/image_gc_manager.go

@@ -124,7 +124,7 @@ func (i *imageCache) set(images []container.Image) {
 func (i *imageCache) get() []container.Image {
 	i.RLock()
 	defer i.RUnlock()
-	return i.images
+	return append([]container.Image{}, i.images...)
 }
 
 // Information about the images we track.

pkg/kubelet/images/image_gc_manager_test.go

@@ -548,6 +548,16 @@ func TestValidateImageGCPolicy(t *testing.T) {
 	}
 }
 
+func TestImageCacheReturnCopiedList(t *testing.T) {
+	cache := &imageCache{}
+	testList := []container.Image{{ID: "1"}, {ID: "2"}}
+	cache.set(testList)
+	list := cache.get()
+	assert.Len(t, list, 2)
+	list[0].ID = "3"
+	assert.Equal(t, cache.get(), testList)
+}
+
 func uint64Ptr(i uint64) *uint64 {
 	return &i
 }