From a4930e196933f602e975028cfd8373d20381e60c Mon Sep 17 00:00:00 2001
From: Tony Finch <fanf@isc.org>
Date: Mon, 13 Jun 2022 12:00:01 +0100
Subject: [PATCH] Improve DBC in isc_mem_free

Unlike standard free(), isc_mem_free() is not a no-op when passed a
NULL pointer. For size accounting purposes it calls sallocx(), which
crashes when passed a NULL pointer. To get more helpful diagnostics,
REQUIRE() that the pointer is not NULL so that when the programmer
makes a mistake they get a backtrace that shows what went wrong.
---
 lib/isc/mem.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index 767f910c13..a68d7d6766 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -981,6 +981,7 @@ isc__mem_free(isc_mem_t *ctx, void *ptr FLARG) {
 	size_t size = 0;
 
 	REQUIRE(VALID_CONTEXT(ctx));
+	REQUIRE(ptr != NULL);
 
 	size = sallocx(ptr, 0);