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From 21aef3fa9b9d0a4ab3c683afc28565924c424a85 Mon Sep 17 00:00:00 2001
From: Jan Setje-Eilers <jan.setjeeilers@oracle.com>
Date: Mon, 26 Jul 2021 20:24:13 -0700
Subject: [PATCH] fallback: find_boot_option() needs to return the index for
 the boot entry in optnum

The CopyMem() calls in add_to_boot_list() expect that
find_boot_option() returned an index to the matching entry in the
BootOrder array. The previous code returned the numerical portion of
the boot entry label, which in some cases resulted in -1 *
sizeof(CHAR16) being passed to CopyMem() which would in turn corrupt
the running firmware resulting in an exception and a failure to boot
or reset.
---
 fallback.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/fallback.c b/fallback.c
index 8d89917a5..87fc3c80e 100644
--- a/fallback.c
+++ b/fallback.c
@@ -462,10 +462,15 @@ find_boot_option(EFI_DEVICE_PATH *dp, EFI_DEVICE_PATH *fulldp,
 			first_new_option_size = StrLen(arguments) * sizeof (CHAR16);
 		}
 
-		*optnum = xtoi(varname + 4);
-		FreePool(candidate);
-		FreePool(data);
-		return EFI_SUCCESS;
+		/* find the index for the matching entry in BootOrder */
+		UINT16 bootnum = xtoi(varname + 4);
+		for (*optnum = 0; *optnum < nbootorder; (*optnum)++) {
+			if (bootorder[*optnum] == bootnum) {
+				FreePool(candidate);
+				FreePool(data);
+				return EFI_SUCCESS;
+			}
+		}
 	}
 	FreePool(candidate);
 	FreePool(data);