fix: add check to mmap to ensure file isn't mapped over stack segment (ed1223)

src/userprog/syscall.c

@@ -426,6 +426,10 @@ syscall_mmap (int fd, void *addr)
   if (file_size == 0)
     return MMAP_FAILURE;
 
+  /* Ensure that the mmap page doesn't overlap with the stack. */
+  if (addr >= (thread_current ()->curr_esp) - PGSIZE)
+    return MMAP_FAILURE;
+
   /* Check and ensure that there is enough space in the user virtual memory to
      hold the entire file. */
   for (off_t ofs = 0; ofs < file_size; ofs += PGSIZE)