From 50732ee914f23df541c77ffd83c3c1921249130d Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Mon, 26 Jul 2021 09:38:28 +0200
Subject: [PATCH] Fallback to default loader if parsed one does not exist

If the specified second stage loader does not exist (invalid
parameter), fall back to the DEFAULT_LOADER. This avoids failing
the boot on any garbage that made it through the load option parser
as a second stage loader name.

Bug-Ubuntu: https://bugs.launchpad.net/bugs/1937115
---
 shim.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/shim.c b/shim.c
index 65f51abc7..1e95e6df1 100644
--- a/shim.c
+++ b/shim.c
@@ -1116,6 +1116,19 @@ EFI_STATUS init_grub(EFI_HANDLE image_handle)
 					 use_fb ? FALLBACK : second_stage);
 	}
 
+	// If the filename is invalid, or the file does not exist,
+	// just fallback to the default loader.
+	if (!use_fb && (efi_status == EFI_INVALID_PARAMETER ||
+	                efi_status == EFI_NOT_FOUND)) {
+		console_print(
+			L"start_image() returned %r, falling back to default loader\n",
+			efi_status);
+		msleep(2000000);
+		load_options = NULL;
+		load_options_size = 0;
+		efi_status = start_image(image_handle, DEFAULT_LOADER);
+	}
+
 	if (EFI_ERROR(efi_status)) {
 		console_print(L"start_image() returned %r\n", efi_status);
 		msleep(2000000);