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https://github.com/systemd/systemd/commit/0bd292567a543d124cd303f7dd61169a209cae64
From 0bd292567a543d124cd303f7dd61169a209cae64 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Thu, 31 Mar 2022 10:27:45 +0200
Subject: [PATCH] Support -D_FORTIFY_SOURCE=3 by using
__builtin_dynamic_object_size.
As explained in the issue, -D_FORTIFY_SOURCE=3 requires usage
of __builtin_dynamic_object_size in MALLOC_SIZEOF_SAFE macro.
Fixes: #22801
--- a/src/basic/alloc-util.h
+++ b/src/basic/alloc-util.h
@@ -174,13 +174,23 @@ void* greedy_realloc0(void **p, size_t need, size_t size);
* is compatible with _FORTIFY_SOURCES. If _FORTIFY_SOURCES is used many memory operations will take the
* object size as returned by __builtin_object_size() into account. Hence, let's return the smaller size of
* malloc_usable_size() and __builtin_object_size() here, so that we definitely operate in safe territory by
- * both the compiler's and libc's standards. Note that __builtin_object_size() evaluates to SIZE_MAX if the
- * size cannot be determined, hence the MIN() expression should be safe with dynamically sized memory,
- * too. Moreover, when NULL is passed malloc_usable_size() is documented to return zero, and
+ * both the compiler's and libc's standards. Note that _FORTIFY_SOURCES=3 handles also dynamically allocated
+ * objects and thus it's safer using __builtin_dynamic_object_size if _FORTIFY_SOURCES=3 is used (#22801).
+ * Moreover, when NULL is passed malloc_usable_size() is documented to return zero, and
* __builtin_object_size() returns SIZE_MAX too, hence we also return a sensible value of 0 in this corner
* case. */
+
+#if defined __has_builtin
+# if __has_builtin(__builtin_dynamic_object_size)
+# define MALLOC_SIZEOF_SAFE(x) \
+ MIN(malloc_usable_size(x), __builtin_dynamic_object_size(x, 0))
+# endif
+#endif
+
+#ifndef MALLOC_SIZEOF_SAFE
#define MALLOC_SIZEOF_SAFE(x) \
MIN(malloc_usable_size(x), __builtin_object_size(x, 0))
+#endif
/* Inspired by ELEMENTSOF() but operates on malloc()'ed memory areas: typesafely returns the number of items
* that fit into the specified memory block */
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