Question

使用我的netfilter我使用以下代码更改传入数据包的数据：

unsigned int hook_func_in(unsigned int hooknum, struct sk_buff *skb, const struct net_device *in, const struct net_device *out, int (*okfn)(struct sk_buff *)) 
{
    struct iphdr *ip = 0;
    struct tcphdr *tcp = 0;
    unsigned char *user_data = 0; 
    unsigned char *tail = 0;
    int datasize =0;

    if ( skb )
    {
        ip = (struct iphdr *)skb_network_header(skb);
        if (ip && ip->protocol == IPPROTO_TCP)
        {
            skb_set_transport_header(skb, ip->ihl * 4);
            tcp = (struct tcphdr *)skb_transport_header(skb);

            if ( tcp && tcp->dest == htons(63947))
            {               
                if (tcp->syn)
                {
                    printk ( "Connect %d\r\n", ip->saddr);
                }
                else if (tcp->fin || tcp->rst)
                {
                    printk ("Disconnect %d\r\n", ip->saddr);
                }
                else
                {
                    user_data = (unsigned char *)((unsigned char *)tcp + (tcp->doff * 4));
                    tail = skb_tail_pointer(skb);
                    if( user_data && tail )
                    {
                        datasize = (int)((long)tail-(long)user_data);
                        if( datasize > 0 )
                        {
                            ModifyData((unsigned char*)user_data, (unsigned char*)user_data, datasize);
                            // function above changes all data, but not resizes
                        }
                    }
                }
            }
        }
    }

    return NF_ACCEPT;
}

函数ModifyData更改数据中的所有字节，但不会更改数据大小。现在我应该如何重新计算tcp校验和？我知道函数tcp_check_send，但我不确定它是否适合传入的数据包。也许在改变数据后我也应该改变一些东西？

我需要这个，因为如果我更改数据而不重新计算相同的数据包将再次收到几次，然后连接将被终止

如何在skbuff中重新计算TCP数据校验和

0 个答案: