Question

我正在尝试向我的浏览器发送dns响应消息，现在我创建了一些结构并填写了一个用于drupal.org的网站。

当我发送响应wiresharks sais时，它是畸形的，有人可以看看吗？

dnsresponse response;
    unsigned char buf[sizeof response];


    response.id = (unsigned short) htons(GetCurrentProcessId());
    response.response = 1;
    response.opCode = 0;
    response.authoritative = 0;
    response.truncated = 0;
    response.recursion = 1;
    response.recursionAvField = 1;
    response.z = 0;

    response.replyCode = 0;

    response.questions = 1;
    response.answer = 1;
    response.authorityRRS = 0;
    response.additionalRRS = 0;

    response.qName = (unsigned char *)malloc(sizeof("www.drupal.org"));
    response.qType = 1;
    response.qClass = 1;

    response.aName = (unsigned char *)malloc(sizeof("www.drupal.org"));
    response.aType = 1;
    response.aClass = 1;
    response.ttl = 0;
    response.dataLength = 9;
    response.addr = 2362640912;

    memcpy(buf, &response, sizeof response);

我的结构如下：

typedef struct
{
unsigned short id; // ID nummer
unsigned short response :1; // 1 is reply 0 is query
unsigned short opCode :4;
unsigned short authoritative :1; // DNS server is authoritative server
unsigned short truncated :1;
unsigned short recursion :1; // Recursie of niet
unsigned short recursionAvField :1; // Recursie in reply
unsigned short z :3;
//unsigned short aa;
//unsigned short nAD;
unsigned short replyCode :4;

unsigned short questions;
unsigned short answer;
unsigned short authorityRRS;
unsigned short additionalRRS;

unsigned char * qName;
unsigned short qType;
unsigned short qClass;

unsigned char * aName;
unsigned short aType;
unsigned short aClass;
int ttl :32;
unsigned short dataLength;
unsigned int addr :32;
}dnsresponse;

亲切的问候，

Answer 1

我不知道协议级别的dns，但问题是

malloc(sizeof("string"))

不重复一个字符串，它只为所需的字节保留空间 - 提示：strdup

编辑：d＆＃39;哦，我只阅读＆＃34;获取dns规范＆＃34;诺斯的评论的一部分。对不起，重复。

Answer 2

您的方法存在根本缺陷。您不能用结构表示DNS数据包，因为DNS数据包中的字符串是可变长度的，即字符串后面的字段将在数据包中处于不同的偏移量，具体取决于前面字符串的长度。

你的struct有char指针代替每个字符串，每个指针通常是一个32位值，指向内存中的其他位置。因此，当您尝试发送内存中表示的结构时，您将发送或多或少的随机32位值来代替字符串。

以下是DNS数据包应该是什么样子的说明性指南： http://www.tcpipguide.com/free/t_DNSMessageProcessingandGeneralMessageFormat.htm

格式错误的dns响应

2 个答案: