From 17c0e73b1d60c4544fad4667c8d45d588fe664cf Mon Sep 17 00:00:00 2001
From: Jessica Clarke <jrtc27@FreeBSD.org>
Date: Fri, 23 Feb 2024 02:36:21 +0000
Subject: [PATCH] efibootmgr: Simplify make_next_boot_var_name and fix cnt == 0
 case

If cnt == 0 we access element 0 unconditionally, which is out of bounds,
and then if that doesn't crash and happens to be 0 we will access
element - 1, also out of bounds, and then if that doesn't crash will add
1 to whatever junk is there and use that for the variable. On CHERI,
though, this does crash. This code is also overly complicated, with
unnecessary special cases and tracking more state than needed.

Rewrite it in a more general manner that doesn't need those special
cases and naturally works for cnt == 0.

Found by:	CHERI
Reviewed by:	imp
Fixes:		1285bcc833a3 ("Import Netflix's efibootmgr to help manage UEFI boot variables")
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D44029

(cherry picked from commit 09cb8031b43c8e98abb5ff9b43ff649031d1e808)
---
 usr.sbin/efibootmgr/efibootmgr.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/usr.sbin/efibootmgr/efibootmgr.c b/usr.sbin/efibootmgr/efibootmgr.c
index dfe8bfb1c14..74b59863d6c 100644
--- a/usr.sbin/efibootmgr/efibootmgr.c
+++ b/usr.sbin/efibootmgr/efibootmgr.c
@@ -555,7 +555,7 @@ static char *
 make_next_boot_var_name(void)
 {
 	struct entry *v;
-	uint16_t *vals, next_free = 0;
+	uint16_t *vals;
 	char *name;
 	int cnt = 0;
 	int i;
@@ -573,21 +573,14 @@ make_next_boot_var_name(void)
 		vals[i++] = v->idx;
 	}
 	qsort(vals, cnt, sizeof(uint16_t), compare);
-	/* if the hole is at the beginning, just return zero */
-	if (vals[0] > 0) {
-		next_free = 0;
-	} else {
-		/* now just run the list looking for the first hole */
-		for (i = 0; i < cnt - 1 && next_free == 0; i++)
-			if (vals[i] + 1 != vals[i + 1])
-				next_free = vals[i] + 1;
-		if (next_free == 0)
-			next_free = vals[cnt - 1] + 1;
-		/* In theory we could have used all 65k slots -- what to do? */
-	}
+	/* Find the first hole (could be at start or end) */
+	for (i = 0; i < cnt; ++i)
+		if (vals[i] != i)
+			break;
 	free(vals);
+	/* In theory we could have used all 65k slots -- what to do? */
 
-	asprintf(&name, "%s%04X", "Boot", next_free);
+	asprintf(&name, "%s%04X", "Boot", i);
 	if (name == NULL)
 		err(1, "asprintf");
 	return name;