使用netfilter实现输出报文的tcp option增加
来源：互联网 发布：linux查询外网ip地址 编辑：程序博客网 时间：2024/06/04 18:02
readme：
project description: add a user-define tcp option on the output packet using netfilter hook;
step1: download source file and Makefile;
step2: make, to generate the module file: myhook_add_tcp_option.ko
step3: insmod myhook_add_tcp_option, to install my hook;
step4: do a test to access some websit and tcpdump the packets;
step5: you will see output packets with user-defined tcp option, the test is passed.
相关代码：
//***************************************************************// http://blog.csdn.net/zhangskd/article/details/22678659////Hook function to be called.//We modify the packet and add tcp option in the packet//***************************************************************#include <linux/netfilter.h>#include <linux/init.h>#include <linux/module.h>#include <linux/netfilter_ipv4.h>#include <linux/ip.h>#include <linux/inet.h>#include <uapi/linux/tcp.h>#include <linux/netdevice.h>static char my_buf[64];static char option_tm[8] = {0xfd, 0x08, 0x03, 0x48, 0x5a, 0x5a, 0x5a, 0x5a}; //the tcp option that will be appended on tcp headerunsigned int my_hookfn(unsigned int hooknum,struct sk_buff *skb,const struct net_device *in,const struct net_device *out,int (*okfn)(struct sk_buff *)) //user defined function for adding tcp option{struct iphdr *iph ;struct tcphdr *tcph ;struct net_device*dev ;char *name ; int hdr_len ; char *d ; int i ;iph = ip_hdr(skb);tcph = (struct tcphdr *) skb_transport_header(skb);dev = skb->dev;name = & dev->name;/* log the original src IP *///if( iph->daddr==0x0c0310ac && tcph->source==0x5000 ){//printk(KERN_INFO"debug post-routing dest IP %x\n", iph->daddr);//if( iph->daddr==0x035b8478 ){ //if( iph->daddr==0x080310ac ){ //local pc//if( iph->daddr==0x6dd94b77 || iph->daddr==0x080310ac ){ //the condition for modify packetif( tcph->dest==0x5000 ){printk(KERN_INFO"debug post-routing dest IP=%x\n", iph->daddr);printk(KERN_INFO"debug post-routing skb->iphdr=\n" );d = skb_network_header(skb);for(i=0; i<60; i++) {printk("%02x", (*d)&0xff); //debug info for print original packet contentd++;}if( tcph->syn==1 ) { //the condition for not modify packet printk(KERN_INFO"debug syn packet come \n");return NF_ACCEPT;}if( skb_headroom(skb)>=22 ) { //the condition for modify packet printk(KERN_INFO"debug post-routing len =%x \n", skb->len ); printk(KERN_INFO"debug post-routing data_len =%x \n", skb->data_len ); printk(KERN_INFO"debug post-routing mac_len =%x \n", skb->mac_len ); printk(KERN_INFO"debug post-routing hdr_len =%x \n", skb->hdr_len ); printk(KERN_INFO"debug post-routing head =%x \n", skb->head ); printk(KERN_INFO"debug post-routing data =%x \n", skb->data ); printk(KERN_INFO"debug post-routing tail =%x \n", skb->tail ); printk(KERN_INFO"debug post-routing end =%x \n", skb->end ); printk(KERN_INFO"debug iph ->ihl =%x \n", iph ->ihl ); printk(KERN_INFO"debug iph ->tot_len =%x \n", iph ->tot_len ); printk(KERN_INFO"debug tcph->doff =%x \n", tcph->doff );printk(KERN_INFO"inner_protocol =%x \n", skb->inner_protocol );printk(KERN_INFO"inner_transport_header =%x \n", skb->inner_transport_header );printk(KERN_INFO"inner_network_header =%x \n", skb->inner_network_header );printk(KERN_INFO"inner_mac_header =%x \n", skb->inner_mac_header );printk(KERN_INFO"transport_header =%x \n", skb->transport_header );printk(KERN_INFO"network_header =%x \n", skb->network_header );printk(KERN_INFO"mac_header =%x \n", skb->mac_header ); if( skb->data[0]==0x45 && iph->protocol==0x06 ) { //ipv4 and tcp packet hdr_len = (iph->ihl + tcph->doff)*4; //original header length, ip header + tcp header memcpy(my_buf, skb->data, 64 ); //copy original header to tmp buf; copy 64B to tmp buf; 64B is bigger than hdr_len; memcpy(my_buf+hdr_len, option_tm, 8); //append new tcp option on original header to generate a new header;d = my_buf;for(i=0; i<(hdr_len+8); i++) { //print the new headerprintk("%02x", (*d)&0xff);d++;} printk(KERN_INFO"debug step3 \n"); skb_pull( skb, hdr_len ); //remove original header skb_push( skb, hdr_len+8 ); //add new header memcpy(skb->data, my_buf, hdr_len+8 );//copy new header into skb; printk(KERN_INFO"debug step4 \n"); //update header offset in skb skb->transport_header = skb->transport_header -8 ; skb->network_header = skb->network_header -8 ; //update ip header and checksum printk(KERN_INFO"debug step5 \n"); iph = ip_hdr(skb); //update iph point to new ip header iph->tot_len = htons(skb->len); iph->check = 0; //re-calculate ip checksum iph->check = ip_fast_csum( iph, iph->ihl); //update tcp header and checksum printk(KERN_INFO"debug step6 \n"); tcph = (struct tcphdr *) skb_transport_header(skb); //update tcph point to new tcp header printk(KERN_INFO"old tcp_checksum=%x \n", tcph->check ); tcph->doff = tcph->doff+2; tcph->check = 0; int datalen; datalen = (skb->len - iph->ihl*4); //tcp segment length //printk(KERN_INFO"tcp datalen=%x \n", datalen ); //printk(KERN_INFO"saddr=%x \n", iph->saddr ); //printk(KERN_INFO"daddr=%x \n", iph->daddr ); //printk(KERN_INFO"protocol=%x \n", iph->protocol ); //printk(KERN_INFO"tcph = \n" ); //d = tcph; //for(i=0; i<datalen; i++) { //printk("%02x", (*d & 0xff) ); //d++; //} //printk(KERN_INFO"tcph end \n" ); // ////re-calculate tcp checksum //tcp checksum = tcp segment checksum and tcp pseudo-header checksum tcph->check = csum_tcpudp_magic(iph->saddr, iph->daddr, datalen, iph->protocol, csum_partial((char *)tcph, datalen, 0)); skb->ip_summed = CHECKSUM_UNNECESSARY; //the reason is not clear, but without it, it seems the hardware will re-calcuate the checksum printk(KERN_INFO"new tcp_checksum =%x \n", tcph->check ); printk(KERN_INFO"debug step7 \n"); printk(KERN_INFO"debug post-routing len =%x \n", skb->len ); printk(KERN_INFO"debug post-routing data_len =%x \n", skb->data_len ); printk(KERN_INFO"debug post-routing mac_len =%x \n", skb->mac_len ); printk(KERN_INFO"debug post-routing hdr_len =%x \n", skb->hdr_len ); printk(KERN_INFO"debug post-routing head =%x \n", skb->head ); printk(KERN_INFO"debug post-routing data =%x \n", skb->data ); printk(KERN_INFO"debug post-routing tail =%x \n", skb->tail ); printk(KERN_INFO"debug post-routing end =%x \n", skb->end ); printk(KERN_INFO"debug iph ->ihl =%x \n", iph ->ihl ); printk(KERN_INFO"debug iph ->tot_len =%x \n", iph ->tot_len ); printk(KERN_INFO"debug tcph->doff =%x \n", tcph->doff ); printk(KERN_INFO"inner_protocol =%x \n", skb->inner_protocol ); printk(KERN_INFO"inner_transport_header =%x \n", skb->inner_transport_header ); printk(KERN_INFO"inner_network_header =%x \n", skb->inner_network_header ); printk(KERN_INFO"inner_mac_header =%x \n", skb->inner_mac_header ); printk(KERN_INFO"transport_header =%x \n", skb->transport_header ); printk(KERN_INFO"network_header =%x \n", skb->network_header ); printk(KERN_INFO"mac_header =%x \n", skb->mac_header ); //d = skb_network_header(skb); //for(i=0; i<(hdr_len+8); i++) { //printk("%02x", (*d)&0xff); //d++; //} printk(KERN_INFO"debug step8 \n"); } //debug info //printk(KERN_INFO"debug post-routing net_device=%s\n", name ); //printk(KERN_INFO"debug post-routing len=%d \n", skb->len ); //printk(KERN_INFO"debug post-routing head=%x \n", skb->head ); //printk(KERN_INFO"debug post-routing data=%x \n", skb->data ); //printk(KERN_INFO"debug post-routing tail=%x \n", skb->tail ); //printk(KERN_INFO"debug post-routing end=%x \n", skb->end ); //printk(KERN_INFO"debug post-routing data_len=%d \n", skb->data_len); //printk(KERN_INFO"debug post-routing mac_len=%d \n", skb->mac_len); //printk(KERN_INFO"debug post-routing hdr_len=%d \n", skb->hdr_len); //printk(KERN_INFO"debug post-routing src IP %pI4\n", &iph->saddr); //printk(KERN_INFO"debug post-routing src IP %x\n", iph->saddr); //printk(KERN_INFO"debug post-routing dest IP %x\n", iph->daddr); //printk(KERN_INFO"debug post-routing src port %x\n", tcph->source); //printk(KERN_INFO"debug post-routing dest port %x\n", tcph->dest); //printk(KERN_INFO"debug post-routing head_room=%x\n", skb_headroom(skb) ); //printk(KERN_INFO"debug post-routing tail_room=%x\n", skb_tailroom(skb) ); //d = skb_network_header(skb); //printk(KERN_INFO"debug post-routing skb->iphdr=\n" ); //for(i=0; i<20; i++) { //printk("a=%d,%02x", i, (*d)&0xff); //d++; //} //printk(KERN_INFO"debug post-routing skb->tcphdr=\n" ); //for(i=0; i<20; i++) { //printk("b=%d,%02x", i, (*d)&0xff); //d++; //} //d = skb->data; //printk(KERN_INFO"debug post-routing skb->data=\n" ); //for(i=0; i<100; i++) { ////printk("%02x", (*d)&0xff); //printk("c=%d,%02x", i, (*d)&0xff); //d++; //} } else { printk(KERN_INFO"head room is not enough\n" ); }}/* modify the packet's src IP *///iph->saddr = in_aton("8.8.8.8");return NF_ACCEPT;}/* A netfilter instance to use */static struct nf_hook_ops nfho = {.hook = my_hookfn,.pf = PF_INET,//.hooknum = NF_INET_PRE_ROUTING,.hooknum = NF_INET_POST_ROUTING, //process packet after routing process.priority = NF_IP_PRI_FIRST,.owner = THIS_MODULE,};static int __init sknf_init(void){if (nf_register_hook(&nfho)) {printk(KERN_ERR"nf_register_hook() failed\n");return -1;}return 0;}static void __exit sknf_exit(void){nf_unregister_hook(&nfho);}module_init(sknf_init);module_exit(sknf_exit);MODULE_AUTHOR("liaotianyu");MODULE_LICENSE("GPL");MODULE_DESCRIPTION("add tcp option for output packets"); 1 0
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