Don't write whiteout files if parent path got replaced with link

If a non-empty directory gets replaced with a link, the files in that
directory also get deleted. However, there should not be any whiteout
files for them in the layer. If there were, the resulting tar file would
not be extractable.

Fixes GoogleContainerTools#2308

pkg/snapshot/snapshot.go

@@ -224,6 +224,14 @@ func writeToTar(t util.Tar, files, whiteouts []string) error {
 	addedPaths := make(map[string]bool)
 
 	for _, path := range whiteouts {
+		skipWhiteout, err := parentPathIsLink(path)
+		if err != nil {
+			return err
+		}
+		if skipWhiteout {
+			continue
+		}
+
 		if err := addParentDirectories(t, addedPaths, path); err != nil {
 			return err
 		}
@@ -247,6 +255,21 @@ func writeToTar(t util.Tar, files, whiteouts []string) error {
 	return nil
 }
 
+func parentPathIsLink(path string) (bool, error) {
+	for _, parentPath := range util.ParentDirectories(path) {
+		lstat, err := os.Lstat(parentPath)
+		if err != nil {
+			return false, err
+		}
+
+		isLink := lstat.Mode()&os.ModeSymlink != 0
+		if isLink {
+			return true, err
+		}
+	}
+	return false, nil
+}
+
 func addParentDirectories(t util.Tar, addedPaths map[string]bool, path string) error {
 	for _, parentPath := range util.ParentDirectories(path) {
 		if _, pathAdded := addedPaths[parentPath]; pathAdded {

pkg/snapshot/snapshot_test.go

@@ -189,6 +189,51 @@ func TestSnapshotFSChangePermissions(t *testing.T) {
 	}
 }
 
+func TestSnapshotFSReplaceDirWithLink(t *testing.T) {
+	testDir, snapshotter, cleanup, err := setUpTest(t)
+	defer cleanup()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// replace non-empty directory "bar" with link to file "foo"
+	bar := filepath.Join(testDir, "bar")
+	err = os.RemoveAll(bar)
+	if err != nil {
+		t.Fatal(err)
+	}
+	foo := filepath.Join(testDir, "foo")
+	err = os.Symlink(foo, bar)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tarPath, err := snapshotter.TakeSnapshotFS()
+	if err != nil {
+		t.Fatalf("Error taking snapshot of fs: %s", err)
+	}
+
+	actualFiles, err := listFilesInTar(tarPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Expect "bar", which used to be a non-directory but now is a symlink. We don't want whiteout files for
+	// the deleted files in bar, because without a parent directory for them the tar cannot be extracted.
+	testDirWithoutLeadingSlash := strings.TrimLeft(testDir, "/")
+	expectedFiles := []string{
+		filepath.Join(testDirWithoutLeadingSlash, "bar"),
+		filepath.Join(testDirWithoutLeadingSlash, "foo"),
+	}
+	for _, path := range util.ParentDirectoriesWithoutLeadingSlash(filepath.Join(testDir, "foo")) {
+		expectedFiles = append(expectedFiles, strings.TrimRight(path, "/")+"/")
+	}
+
+	sort.Strings(expectedFiles)
+	sort.Strings(actualFiles)
+	testutil.CheckErrorAndDeepEqual(t, false, nil, expectedFiles, actualFiles)
+}
+
 func TestSnapshotFiles(t *testing.T) {
 	testDir, snapshotter, cleanup, err := setUpTest(t)
 	testDirWithoutLeadingSlash := strings.TrimLeft(testDir, "/")