sk_buff network_header access

[duten_max]

Hi,

I have to write a module to implement a simple Firewall taking the datas directly from the sk_buff. I donīt know how to make a test to determine the packet network header (to know if it is IP or sth else).
Here is what I do, but does not work:


if (&skb->network_header == ETH_P_IP){
name_NLP = "IP";
printk("Network Layer Header = %s\n",name_NLP);
}

I tried to use access function skb_network_header(skb) but does not work neither.

Any ideas?

[agent_0range]

I am just learning this stuff too but if I had to venture a guess, I beleive that skb->network_header is probably in network byte order so for a comparison you would need

skb->network_header == htons(ETH_P_IP)

[duten_max]

thks but I finally find it. Here is my module:

/******************************************************
 * file:     LengthSkbuff.c
 * Date:     05/07/2010
 * Author:   Maxime ZAGO
 * Simple packet capture && analysis programm
 * Uses SKbuff
 *****************************************************/

#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/init.h>
#include<linux/cdev.h>
#include<linux/skbuff.h>
#include<linux/netdevice.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <linux/ip.h>


/* Module Information */
#define AUTHOR "Maxime ZAGO <mzago@etu.enseeiht.fr>"
#define DESCRIPTION   " Simple packet capture programm"
MODULE_AUTHOR(AUTHOR);
MODULE_DESCRIPTION(DESCRIPTION);	
MODULE_LICENSE("GPL");

/* Is the module used */
#define	MOD_INC_USE_COUNT
#define MOD_DEC_USE_COUNT

/* Number of packets to capture */
#define NB_PACKETS 10

int pck_cptr;   /* Counter for number of packets */


/* This is the function that handles the packets. */
static __s32 packetprocessor_func(struct sk_buff *skb,
		struct net_device *dev, 
		struct packet_type *pt,
		struct net_device *orig_dev){

	struct iphdr *network_header;  // ip header struct
	struct tcphdr *tcp_header;     // tcp header struct
	struct udphdr *udp_header;     // udp header struct 
	int sport, dport;              // source & dest port


	if(pck_cptr<NB_PACKETS){
		printk("\n==> Packet number %d\n",pck_cptr+1);
		network_header = (struct iphdr *)skb_network_header(skb);
		if (network_header->protocol==IPPROTO_UDP){
			udp_header = (struct udphdr *)skb_transport_header(skb); 
			sport = ntohs((unsigned short int) udp_header->source);
			dport = ntohs((unsigned short int) udp_header->dest);
			printk(" IN: %s\n",skb->dev->name);
			printk(" Protocol: UDP\n");
			printk(" Length: %d\n",skb->len);
			printk(" TTL: %d\n",network_header->ttl);
			printk(" ID: %d\n",network_header->id);
			printk(" S_PORT: %d\n",sport);
			printk(" D_PORT: %d\n",dport);
			printk(" @_SRC: %d.%d.%d.%d\n",NIPQUAD(network_header->saddr));
			printk(" @_DST: %d.%d.%d.%d\n",NIPQUAD(network_header->daddr));
		}
		if (network_header->protocol==IPPROTO_TCP){
			tcp_header = (struct tcphdr *)skb_transport_header(skb); 
			sport = ntohs((unsigned short int) tcp_header->source);
			dport = ntohs((unsigned short int) tcp_header->dest);
			printk(" IN: %s\n",skb->dev->name);
			printk(" Protocol: TCP\n");
			printk(" Length: %d\n",skb->len);
			printk(" TTL: %d\n",network_header->ttl);
			printk(" ID: %d\n",network_header->id);
			printk(" S_PORT: %d\n",sport);
			printk(" D_PORT: %d\n",dport);
			printk(" @_SRC: %d.%d.%d.%d\n",NIPQUAD(network_header->saddr));
			printk(" @_DST: %d.%d.%d.%d\n",NIPQUAD(network_header->daddr));

		}
		pck_cptr ++;
		kfree_skb(skb);
	}
	return 0;
}

static struct packet_type pt = { 
	.type = __constant_htons(ETH_P_IP),
	.func = packetprocessor_func,
};

static __s32 __init packetprocessor_init(void){
	MOD_INC_USE_COUNT; // Module in use
	printk(KERN_ALERT "\n<==========================>\n");
	printk(KERN_ALERT "Loading Packet Processor.\n");
	printk(KERN_ALERT "Letīs catch %d packets\n",NB_PACKETS);
	printk(KERN_ALERT "<==========================>\n");
	dev_add_pack(&pt); // Register the packet handler.
	return 0;
}

static void __exit packetprocessor_exit(void){
	printk(KERN_ALERT "\n<==========================>\n");
	printk(KERN_ALERT "Unloading Packet Processor.\n");
	printk(KERN_ALERT "<==========================>\n");
	dev_remove_pack(&pt);
	MOD_DEC_USE_COUNT;
}

module_init(packetprocessor_init);
module_exit(packetprocessor_exit);