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软件工程.NET开发
基于Netfilter的网络数据包分析

作者：未知 来源：月光软件站 加入时间：2005-6-5　月光软件站

前面的几篇文章我已经对Netfilter的大概的机制作了比较详细的介绍，这篇文章我就说一下如何分析网络数据包。我刚刚写了一个程序，程序的功能很简单，就是提取出网络数据包的源地址和改包所使用的网络协议，大家可以看看源代码：

 

#define __KERNEL__
#define MODULE

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netfilter.h>
#include <linux/skbuff.h>
#include <linux/ip.h>
#include <linux/netdevice.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <net/tcp.h>
#include <linux/netfilter_ipv4.h>


static struct nf_hook_ops nfho;


unsigned int hook_func(unsigned int hooknum,
                       struct sk_buff **skb,
                       const struct net_device *in,
                       const struct net_device *out,
                       int (*okfn)(struct sk_buff *))
{
    struct sk_buff *sb = *skb;
    unsigned char src_ip[4];
    *(unsigned int *)src_ip = sb->nh.iph->saddr;
    printk("A packet from:%d.%d.%d.%d Detected!",
                 src_ip[0],src_ip[1],src_ip[2],src_ip[3]);
    switch(sb->nh.iph->protocol)
    {
       case IPPROTO_TCP:
           printk("It's a TCP PACKET\n");break;
       case IPPROTO_ICMP:
          printk("It's a ICMP PACKET\n");break;
      case IPPROTO_UDP:
         printk("It's a UDP PACKET\n");break;
    }
    return NF_ACCEPT;         
}


int init_module()
{
 
    nfho.hook = hook_func;        
    nfho.hooknum  = NF_IP_PRE_ROUTING;
    nfho.pf       = PF_INET;
    nfho.priority = NF_IP_PRI_FIRST; 

    nf_register_hook(&nfho);

    return 0;
}

void cleanup_module()
{
    nf_unregister_hook(&nfho);
}

这实际上是对前面几篇文章的几个小程序的组合，实际上就是对sk_buff 结构体的的两个元素进行了检测，就得到了源地址和协议的信息。上面的这条语句对于那些C不是很熟悉的人可能吃力了一点：

*(unsigned int *)src_ip = sb->nh.iph->saddr;

我稍微的解释一下，网络的源地址是4个子节的int，因此我定义了一个4个子节的数组src_ip，从而每一个子节里面就存储的点分十进制的一个数，为了一次完成赋值，我把src_ip 转成unsigned int指针，就可以一次4个字节一起访问了。

下面是这个程序的测试结果：

A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.8 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.246 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.107.8 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.246 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.246 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.254 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.107.230 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:192.168.1.1 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a ICMP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.214 Detected!It's a UDP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a ICMP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a ICMP PACKET
A packet from:210.43.106.96 Detected!It's a UDP PACKET
A packet from:210.43.106.210 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.106.112 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET
A packet from:210.43.107.136 Detected!It's a UDP PACKET
A packet from:210.43.107.130 Detected!It's a TCP PACKET

如果需要对包的端口进行分析的话，就要对IP报文的数据段(sb->data)进行分析了（TCP和UDP等包都是作为IP的数据而存在的），大家可以参考一下相应的资料。

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