简单的netfilter hook函数注册以及内核链表的使用

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#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 <linux/list.h>struct fox{int a;struct list_head list;};struct list_head fox_list;/** * Hook function to be called. * We modify the packet's src IP. */unsigned 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 *)){    struct iphdr *iph;    struct fox fox_red ,fox_yellow , *f;    fox_red.a = 1;    fox_yellow.a = 2;    LIST_HEAD(fox_list);    list_add(&fox_red.list, &fox_list);    list_add(&fox_yellow.list, &fox_list);    list_for_each_entry(f, &fox_list, list)    {        printk("the fox is %d\n", f->a);     }    iph = ip_hdr(skb);        /* log the original src IP */    printk(KERN_INFO"src IP %pI4\n", &iph->saddr);    /* 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,    .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("zhangsk");MODULE_LICENSE("GPL");

该内核模块只是简单的注册一个钩子函数

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