linux - Use Netfilter to write kernel module to modify source IP error, computer crash -


i want write kernel module uses netfilter modify source ip "100.100.100.100" whiche packet destination ip "192.68.4.103" , protocol tcp. write .c file when install module ,it cause computer crash. how should rewrite it? system ubuntu16.04 . here code wrote:

#include <linux/init.h> #include <linux/module.h> #include <linux/netfilter.h> #include <linux/netfilter_ipv4.h> #include<linux/inet.h> #include<net/ip.h> #include<net/tcp.h> #include <linux/netdevice.h> #include <linux/inet.h> #include <linux/socket.h> #include <linux/skbuff.h>   module_license("gpl");   module_author("linhos");   #define if_name "eno1"  //network name got command "ifconfig" struct nf_hook_ops nfho;  static unsigned int checkip(         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 *skb;      struct net_device *dev;      struct iphdr *iph;       struct tcphdr *tcph;       int tot_len;       unsigned int iph_len;       int tcph_len;       int ret;     skb = __skb;     if (skb == null)         return nf_accept;     iph = ip_hdr(skb);      if (iph == null)         return nf_accept;     tot_len = ntohs(iph->tot_len);     if (iph->daddr =="192.68.4.103") {  //locla ip         iph_len = ip_hdrlen(skb);         skb_pull(skb, iph_len);         skb_reset_transport_header(skb);         if (iph->protocol == ipproto_tcp) {             tcph = tcp_hdr(skb);             tcph_len = tcp_hdrlen(skb);             iph->saddr = in_aton("100.100.100.100");              dev = dev_get_by_name(&init_net, if_name);               tcph->check = 0;               skb->csum = csum_partial((unsigned char *) tcph,                                      tot_len - iph_len,                                      0);              tcph->check = csum_tcpudp_magic(iph->saddr,                                             iph->daddr,                                              ntohs(iph->tot_len) - iph_len,                                             iph->protocol,                                             skb->csum);              iph->check = 0;             iph->check = ip_fast_csum(iph, iph->ihl);               skb->ip_summed = checksum_none;               skb->pkt_type = packet_host;               skb->dev = dev;             skb_push(skb, iph_len);               skb_push(skb, eth_alen);               ret = dev_queue_xmit(skb);               if (ret < 0) {                    printk(kern_err "dev_queue_xmit() error!\n");                 return nf_drop;               }             return nf_stolen;           }         skb_push(skb, iph_len);         skb_reset_transport_header(skb);     }     return nf_accept; }   static int __initfilter_init(void){     printk("----------------checkip  ok!--------------");     nfho.hook = checkip;     nfho.pf = af_inet;       nfho.hooknum = nf_inet_pre_routing;     nfho.priority = nf_ip_pri_first;      int ret = nf_register_hook(&nfho);        if (ret < 0) {         printk(kern_err "can't modify skb hook!");         return ret;     }     return 0; }  static void filter_exit(void) {     nf_unregister_hook(&nfho); }  module_init(filter_init); module_exit(filter_exit);

could explain me doing wrong?


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