How to print correctly a IP using NETFILTER in C

Question

I have the following code, it only catch the packets and prints the IP source and destination:

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/ip.h>

static struct nf_hook_ops nfho;

unsigned int hook_func(void *priv, struct sk_buff *skb, const struct nf_hook_state *state) {
    struct iphdr *ip_header = (struct iphdr *)skb_network_header(skb);
    unsigned int src_ip = (unsigned int)ip_header->saddr;
    unsigned int dest_ip = (unsigned int)ip_header->daddr;
    printk(KERN_INFO "IPs: %u \t to \t %u \n", src_ip, dest_ip);
    return NF_ACCEPT;   
}

int init_module() { /* Fill in our hook structure */
    nfho.hook = hook_func; /* Handler function */
    nfho.hooknum = NF_INET_PRE_ROUTING; /* First hook for IPv4 */
    nfho.pf = PF_INET;
    nfho.priority = NF_IP_PRI_FIRST; /* Make our function first */
    nf_register_hook(&nfho);
    return 0;
}

void cleanup_module() {
    nf_unregister_hook(&nfho);
}

But, I don't know how to print it correctly (like a IP X.X.X.X) because it shows the following information:

IPs: 16777343 to 16842879

IPs: 4198316624 to 67108884

IPs: 16842879 to 16777343

Can someone help me? Thanks!

Answer 1

Use %pI4 for the format specifier.

e.g. printk(KERN_DEBUG "IPs: %pI4 \t to \t %pI4 \n", &src_ip, &dest_ip);

This is documented in Documentation/printk-formats.txt.