Question

作为我的任务的一部分，我必须在我的linux框中演示stackoverflow。

我的盒子配置：操作系统：Ubuntu 13.04

GCC版本：4.6.3

我尝试用标志-fno-stack-protector编译程序，程序成功符合但是当我触发堆栈溢出时出现Segmentation fault错误。我怎样才能显示实际的o / p。缓冲区溢出Pgm：

int main(int argc, char**argv)
 {
   int authentication=0;
   char cUsername[10], cPassword[10];
   strcpy(cUsername, argv[1]);
   strcpy(cPassword, argv[2]);
   if(strcmp(cUsername, "admin") == 0 && strcmp(cPassword, "adminpass") == 0)
{
       authentication = 1;}
if(authentication)
{
       printf("Access granted");} 
else
{
       printf("Wrong username and password");
    }return 0;}

如果我给出像AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA的IP 然后它应该显示授予Acess但现在它显示分段错误

Answer 1

如果您使用以下参数启动程序，我的c编译器会发生这种情况：AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA B：

int main(int argc, char**argv)
{
  int authentication=0;
  char cUsername[10], cPassword[10];

  strcpy(cUsername, argv[1]);
  // now cUsername contains "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
  // and authentication contains "0x41414141" because it has been overwritten because of the
  // buffer overflow of cUsername

  strcpy(cPassword, argv[2]);
  //now cPassword contains "B"

  if(strcmp(cUsername, "admin") == 0 && strcmp(cPassword, "adminpass") == 0)
  {
    // strings are different so we don't get here
    authentication = 1;
  }

  if (authentication)
  {
    // authentication still contains 0x41414141 therefore we get here
    printf("Access granted");
  } 
  else
  {
    printf("Wrong username and password");
  }

  // here we will get a segmentation fault, because the return adress which is on the
  // stack will have been overwritten with 0x41414141 which is most probably an
  // invalid address
  return 0;
}

顺便说一句，如果你正确格式化你的代码，它就会更容易阅读。

重要

根据您的系统，“允许访问”可能不会被打印出来，因为如果输出被缓冲，输出缓冲区通常会在>从主函数返回后清空并且因为程序段出错之前，输出缓冲区永远不会被清空，并且永远不会显示消息。尝试在“已授予访问权限”字符串的末尾添加\ n。

在Ubuntu 13.04中演示C中的缓冲区溢出

1 个答案: