From 44f55e2ee6df0b317df3029675afce86219cd9cd Mon Sep 17 00:00:00 2001
From: Ivan Hu <ivan.hu@canonical.com>
Date: Fri, 17 Jan 2020 15:50:28 +0800
Subject: [PATCH] Correctly delete UEFI variables

UEFI runtime service GetVariable with DataSize NULL, will fail and get
EFI_INVALID_PARAMETER returned. Set DataSize 0 and allocate the buffer for
getting attributes for the deleted variable.

Also, fix the real reason Boot#### was never found.
---
 plugins/uefi/efi/fwup-efi.c | 19 +++++++++++++++----
 plugins/uefi/efi/fwupdate.c |  4 +++-
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/plugins/uefi/efi/fwup-efi.c b/plugins/uefi/efi/fwup-efi.c
index 8da6b2021..db864e10e 100644
--- a/plugins/uefi/efi/fwup-efi.c
+++ b/plugins/uefi/efi/fwup-efi.c
@@ -17,16 +17,27 @@ fwup_delete_variable(CHAR16 *name, EFI_GUID *guid)
 {
 	EFI_STATUS rc;
 	UINT32 attrs = 0;
+	UINTN size = 0;
 
 	/* get the attrs so we can delete it */
-	rc = uefi_call_wrapper(RT->GetVariable, 5, name, guid, &attrs, NULL, NULL);
+	rc = uefi_call_wrapper(RT->GetVariable, 5, name, guid, &attrs, &size, NULL);
 	if (EFI_ERROR(rc)) {
-		if (rc == EFI_NOT_FOUND) {
+		if (rc == EFI_BUFFER_TOO_SMALL) {
+			_cleanup_free VOID *buf = fwup_malloc(size);
+			if (buf == NULL)
+				return EFI_OUT_OF_RESOURCES;
+			rc = uefi_call_wrapper(RT->GetVariable, 5, name, guid, &attrs, &size, buf);
+			if (EFI_ERROR(rc)) {
+				fwup_debug(L"Could not get attr: %r", rc);
+				return rc;
+			}
+		} else if (rc == EFI_NOT_FOUND) {
 			fwup_debug(L"Not deleting variable '%s' as not found", name);
 			return EFI_SUCCESS;
+		} else {
+			fwup_debug(L"Could not get variable '%s' for delete: %r", name, rc);
+			return rc;
 		}
-		fwup_debug(L"Could not get variable '%s' for delete: %r", name, rc);
-		return rc;
 	}
 	return uefi_call_wrapper(RT->SetVariable, 5, name, guid, attrs, 0, NULL);
 }
diff --git a/plugins/uefi/efi/fwupdate.c b/plugins/uefi/efi/fwupdate.c
index f4c740a3d..abacc10bb 100644
--- a/plugins/uefi/efi/fwupdate.c
+++ b/plugins/uefi/efi/fwupdate.c
@@ -408,7 +408,9 @@ fwup_delete_boot_entry(VOID)
 		/* check if the variable name is Boot#### */
 		if (CompareGuid(&vendor_guid, &global_variable_guid) != 0)
 			continue;
-		if (StrCmp(variable_name, L"Boot") != 0)
+		if (StrLen(variable_name) != 8)
+			continue;
+		if (StrnCmp(variable_name, L"Boot", 4) != 0)
 			continue;
 
 		UINTN info_size = 0;