netfilter hook打印应用层内容

#include <asm/atomic.h>
#include <asm/byteorder.h>
#include <asm/checksum.h>
#include <asm/unaligned.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/net.h>
#include <linux/in.h>
#include <linux/types.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#include <linux/sysctl.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>
#include <linux/workqueue.h>
#include <linux/jiffies.h>
#include <linux/route.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/slab.h>
#include <linux/stddef.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/icmp.h>
#include <linux/jhash.h>
#include <linux/list.h>
#include <linux/inet.h>
#include <linux/ctype.h>
#include <linux/spinlock_types.h>
#include <net/net_namespace.h>
#include <net/sock.h>
#include <net/route.h>
#include <net/inet_connection_sock.h>
#include <net/request_sock.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>

#define err(msg) printk(KERN_ERR "%s failed.\n", msg)
#define SA struct sockaddr

static unsigned int nf_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 *iph;
    struct tcphdr *tcph;
    char *data_start;

    iph = ip_hdr(skb);
    tcph = (struct tcphdr *)(skb_network_header(skb) + ip_hdrlen(skb));
    if (tcph->dest == htons(8888)) {
        if (skb_is_nonlinear(skb)) {
            if (skb_linearize(skb) != 0)    /* TODO must do this */
                err("skb_linearize");
        }
        iph = ip_hdr(skb);
        tcph = (struct tcphdr *)(skb_network_header(skb) + ip_hdrlen(skb));

        data_start = ((char *)tcph) + (tcph->doff << 2);
        printk(KERN_INFO "%s", data_start);
    }
    return NF_ACCEPT;
}

static struct nf_hook_ops nf_ops = {
    .hook        = nf_in,    
    .owner        = THIS_MODULE,
    .pf        = PF_INET,
    .hooknum = NF_INET_LOCAL_IN,        
};

static int __init main_init(void)
{
    if (nf_register_hook(&nf_ops) != 0) {
        err("nf_register_hook");
        goto out;
    }

    return 0;
out:
    return -1;
}

static void __exit main_exit(void)
{    
    nf_unregister_hook(&nf_ops);
}

module_init(main_init);
module_exit(main_exit);
MODULE_LICENSE("GPL");