add use-after-free test for common linked list deallocation bug

demofiles/use-after-free-2.c

@@ -0,0 +1,40 @@
+// use-after-free
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+
+struct Link
+{
+    int          data;
+    struct Link *next;
+};
+
+struct Link *newLink(int data, struct Link *next)
+{
+    struct Link *link = (struct Link *)malloc(sizeof(struct Link));
+    link->data = data;
+    link->next = next;
+    return link;
+}
+
+int main()
+{
+    struct Link *list = 0;
+
+    // create linked list of 10 elements
+    for (int i = 0;  i < 10;  ++i)
+	list = newLink(i*i, list);
+
+    // print contents of list
+    for (struct Link *ptr = list;  ptr;  ptr = ptr->next) {
+	printf("%d\n", ptr->data);
+    }
+
+    // deallocate list
+    for (struct Link *ptr = list;  ptr;  ptr = ptr->next) {
+	free(ptr); // ptr is now dangling in the update expression
+    }
+
+    return 0;
+}