From 23983afe82e61d7aa1b4cdfd192a88b5317e20bb Mon Sep 17 00:00:00 2001
From: "Roger A. Light" <roger@atchoo.org>
Date: Mon, 13 Feb 2023 22:08:44 +0000
Subject: [PATCH] Fix invalid handling of long hex in config file.

Closes oss-fuzz #55948.
---
 lib/util_mosq.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/util_mosq.c b/lib/util_mosq.c
index 8402c515..18ba330d 100644
--- a/lib/util_mosq.c
+++ b/lib/util_mosq.c
@@ -174,15 +174,17 @@ int mosquitto__hex2bin(const char *hex, unsigned char *bin, int bin_max_len)
 	BIGNUM *bn = NULL;
 	int len;
 	int leading_zero = 0;
-	int start = 0;
 	size_t i = 0;
 
 	/* Count the number of leading zero */
 	for(i=0; i<strlen(hex); i=i+2) {
 		if(strncmp(hex + i, "00", 2) == 0) {
-			leading_zero++;
+			if(leading_zero >= bin_max_len){
+				return 0;
+			}
 			/* output leading zero to bin */
-			bin[start++] = 0;
+			bin[leading_zero] = 0;
+			leading_zero++;
 		}else{
 			break;
 		}