builder/amazon/chroot: validate that chroot_mounts are 3 elements

builder/amazon/chroot/builder.go

@@ -83,6 +83,14 @@ func (b *Builder) Prepare(raws ...interface{}) error {
 	errs := common.CheckUnusedConfig(md)
 	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare()...)
 
+	for _, mounts := range b.config.ChrootMounts {
+		if len(mounts) != 3 {
+			errs = packer.MultiErrorAppend(
+				errs, errors.New("Each chroot_mounts entry should be three elements."))
+			break
+		}
+	}
+
 	if b.config.SourceAmi == "" {
 		errs = packer.MultiErrorAppend(errs, errors.New("source_ami is required."))
 	}

builder/amazon/chroot/builder_test.go

@@ -19,6 +19,24 @@ func TestBuilder_ImplementsBuilder(t *testing.T) {
 	}
 }
 
+func TestBuilderPrepare_ChrootMounts(t *testing.T) {
+	b := &Builder{}
+	config := testConfig()
+
+	config["chroot_mounts"] = nil
+	err := b.Prepare(config)
+	if err != nil {
+		t.Errorf("err: %s", err)
+	}
+
+	config["chroot_mounts"] = [][]string{
+		[]string{"bad"},
+	}
+	err = b.Prepare(config)
+	if err == nil {
+		t.Fatal("should have error")
+	}
+}
 func TestBuilderPrepare_SourceAmi(t *testing.T) {
 	b := &Builder{}
 	config := testConfig()