3 files changed, 39 insertions, 0 deletions
diff --git a/malloc/beware_overflow/beware_overflow.c b/malloc/beware_overflow/beware_overflow.c
new file mode 100644
index 0000000..4b2555c
--- /dev/null
+++ b/malloc/beware_overflow/beware_overflow.c
@@ -0,0 +1,10 @@
+#include "beware_overflow.h"
+
+void *beware_overflow(void *ptr, size_t nmemb, size_t size)
+{
+    size_t res;
+    if (__builtin_umull_overflow(nmemb, size, &res))
+        return NULL;
+    char *r = ptr;
+    return r + res;
+}
diff --git a/malloc/beware_overflow/beware_overflow.h b/malloc/beware_overflow/beware_overflow.h
new file mode 100644
index 0000000..821e81e
--- /dev/null
+++ b/malloc/beware_overflow/beware_overflow.h
@@ -0,0 +1,8 @@
+#ifndef BEWARE_OVERFLOW_H
+#define BEWARE_OVERFLOW_H
+
+#include <stddef.h>
+
+void *beware_overflow(void *ptr, size_t nmemb, size_t size);
+
+#endif /* BEWARE_OVERFLOW_H */
diff --git a/malloc/beware_overflow/main.c b/malloc/beware_overflow/main.c
new file mode 100644
index 0000000..42fd689
--- /dev/null
+++ b/malloc/beware_overflow/main.c
@@ -0,0 +1,21 @@
+#include <stddef.h>
+#include <stdio.h>
+
+#include "beware_overflow.h"
+
+void print_overflow(void *ptr, size_t nmemb, size_t size)
+{
+    void *begin = ptr;
+    void *res = beware_overflow(ptr, nmemb, size);
+    if (res)
+        printf("Pointer was incremented from %p to %p.\n", begin, res);
+    else
+        printf("Overflow detected between %ld and %ld.\n", nmemb, size);
+}
+
+int main(void)
+{
+    print_overflow((void *)0x1000, 25, 6);
+    print_overflow((void *)0x40000, 12345678904, 12345678904);
+    return 0;
+}