Add free hook example on glibc 2.31

Author: r888800009

heap/free-hook-player

@@ -0,0 +1,19 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <malloc.h>
+
+int main() {
+  printf("%p\n", &system);
+  printf("%p\n", &__free_hook);
+
+  char *free_hook_arg = malloc(0x30);
+  printf("set free_hook_arg to");
+  scanf("%s", free_hook_arg);
+
+  puts("breakpoint here and set free_hook to system");
+  free(free_hook_arg);
+
+  return 0;
+}
+
+// gcc -g -o free-hook-player free-hook-player.c