From: Ondřej Surý <ondrej@isc.org>
Date: Thu, 5 Jun 2025 10:19:43 +0000 (+0200)
Subject: Don't use ssize_t for storing difference between sizes
X-Git-Tag: v9.21.10~9^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f689dc22973f528d375d8e197c9259c2d508c261;p=thirdparty%2Fbind9.git

Don't use ssize_t for storing difference between sizes

As POSIX guarantees only that the type ssize_t shall be capable of
storing values at least in the range [-1, {SSIZE_MAX}], it can't be used
to calculate the difference between two memory sizes.  Change the logic
for junk filling to test whether the new size is larger than old size
and then use size_t as the result will be always positive.
---

diff --git a/lib/isc/mem.c b/lib/isc/mem.c
index bb2805c1b41..e7421e012e3 100644
--- a/lib/isc/mem.c
+++ b/lib/isc/mem.c
@@ -339,9 +339,9 @@ mem_realloc(isc_mem_t *ctx, void *old_ptr, size_t old_size, size_t new_size,
 	if ((flags & ISC__MEM_ZERO) == 0 &&
 	    (ctx->flags & ISC_MEMFLAG_FILL) != 0)
 	{
-		ssize_t diff_size = new_size - old_size;
-		void *diff_ptr = (uint8_t *)new_ptr + old_size;
-		if (diff_size > 0) {
+		if (new_size > old_size) {
+			size_t diff_size = new_size - old_size;
+			void *diff_ptr = (uint8_t *)new_ptr + old_size;
 			/* Mnemonic for "beef". */
 			memset(diff_ptr, 0xbe, diff_size);
 		}