efi_loader: LoadImage() check parent image

If the parent image handle does not refer to a loaded image return
EFI_INVALID_PARAMETER.
(UEFI SCT II 2017: 3.4.1 LoadImage() - 5.1.4.1.1)

Mark our root node as a loaded image to avoid an error when using it as
parent image.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index 6d86daf..ef9e378 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -1760,7 +1760,7 @@
 	EFI_ENTRY("%d, %p, %pD, %p, %zd, %p", boot_policy, parent_image,
 		  file_path, source_buffer, source_size, image_handle);
 
-	if (!image_handle || !parent_image) {
+	if (!image_handle || !efi_search_obj(parent_image)) {
 		ret = EFI_INVALID_PARAMETER;
 		goto error;
 	}
@@ -1769,6 +1769,11 @@
 		ret = EFI_NOT_FOUND;
 		goto error;
 	}
+	/* The parent image handle must refer to a loaded image */
+	if (!parent_image->type) {
+		ret = EFI_INVALID_PARAMETER;
+		goto error;
+	}
 
 	if (!source_buffer) {
 		ret = efi_load_image_from_path(file_path, &dest_buffer,