Add unit test to show that we handle tars safely

post-processor/vagrant/virtualbox.go

@@ -133,7 +133,15 @@ func DecompressOva(dir, src string) error {
 		if hdr == nil || err == io.EOF {
 			break
 		}
+		if err != nil {
+			return err
+		}
 
+		// We use the fileinfo to get the file name because we are not
+		// expecting path information as from the tar header. It's important
+		// that we not use the path name from the tar header without checking
+		// for the presence of `..`. If we accidentally allow for that, we can
+		// open ourselves up to a path traversal vulnerability.
 		info := hdr.FileInfo()
 
 		// Shouldn't be any directories, skip them

post-processor/vagrant/virtualbox_test.go

@@ -1,9 +1,27 @@
 package vagrant
 
 import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestVBoxProvider_impl(t *testing.T) {
 	var _ Provider = new(VBoxProvider)
 }
+
+func TestDecomressOVA(t *testing.T) {
+	td, err := ioutil.TempDir("", "pp-vagrant-virtualbox")
+	assert.NoError(t, err)
+	fixture := "../../common/test-fixtures/decompress-tar/outside_parent.tar"
+	err = DecompressOva(td, fixture)
+	assert.NoError(t, err)
+	_, err = os.Stat(filepath.Join(filepath.Base(td), "demo.poc"))
+	assert.Error(t, err)
+	_, err = os.Stat(filepath.Join(td, "demo.poc"))
+	assert.NoError(t, err)
+	os.RemoveAll(td)
+}