[no subject]

[=?gb2312?q?=D0=C2=20=D4=C2?= <xinyuepeng@yahoo.com>]

hi!
   I just start to read the network of source code.
I get a test module program.But I can understand how
and where it handles the packet. The code is put in
accessory.
THX.



/* 
 * Obscure Transport Protocol
 *
 * Goal: Change TCP behavior to evade IDS and firewall policies.
 *
 * lifeline (c) 1999 
 * <arai@hackers-pt.org>
 *
 * gcc -O6 -c otp.c -I/usr/src/linux/include
 * insmod otp.o dev=eth0 ip=123.123.123.123
 *
 * In ip= use only numerical dotted ip's!!
 * Btw, this is the ip of the other machine that also has the module.
 *
 * Load this module in both machines putting in the ip= argument each other's
 * machine numerical dotted ip.
 *
 * Oh, and don't even think about flaming me if this fucks up your machine,
 * it works fine on mine with kernel 2.2.5.
 * This tool stands on its own. I'm not responsible for any damage caused by it.
 *
 * You will probably want to make some arrangements with the #define's below.
 *
 */

#define MODULE
#define __KERNEL__

#include <linux/config.h>
#include <linux/module.h>
#include <linux/version.h>

#include <linux/byteorder/generic.h>
#include <linux/netdevice.h>
#include <net/protocol.h>
#include <net/pkt_sched.h>
#include <net/tcp.h>
#include <net/ip.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/skbuff.h>
#include <linux/icmp.h>

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <asm/uaccess.h>


/* Define here if you want to swap ports also */
#define	REALPORT	23 		/* port you which to communicate */
#define FAKEPORT	80		/* port that appears on the wire */


char *dev, *ip;
MODULE_PARM(dev, "s"); 
MODULE_PARM(ip, "s");
struct device *d;

struct packet_type otp_proto;

__u32 in_aton(const char *);

/* Packet Handler Function */
int otp_func(struct sk_buff *skb, struct device *dv, struct packet_type *pt) {

	unsigned long int magic_ip;
    unsigned int fin = skb->h.th->fin; 
	unsigned int syn = skb->h.th->syn;

	magic_ip = in_aton(ip);

	if ((skb->pkt_type == PACKET_HOST || skb->pkt_type == PACKET_OUTGOING)
	&& (skb->nh.iph->saddr == magic_ip || skb->nh.iph->daddr == magic_ip)
	&& (skb->h.th->source == FAKEPORT) || (skb->h.th->dest == FAKEPORT)) {

		if (skb->h.th->source == FAKEPORT) skb->h.th->source = htons(REALPORT);
		if (skb->h.th->dest == FAKEPORT) skb->h.th->dest = htons(REALPORT);

		if (skb->h.th->fin == 1) {
			skb->h.th->fin = 0;
			skb->h.th->syn = 1;
			goto bye;
		}
		if (skb->h.th->syn == 1) {
			skb->h.th->fin = 1;
			skb->h.th->syn = 0;			
		}
	}

	bye:
	kfree_skb(skb);
    return 0;
}

/*
 *      Convert an ASCII string to binary IP.
 */

__u32 in_aton(const char *str) {
        unsigned long l;
        unsigned int val;
        int i;

        l = 0;
        for (i = 0; i < 4; i++) {
                l <<= 8;
                if (*str != '\0') {
                        val = 0;
                        while (*str != '\0' && *str != '.') {
                                val *= 10;
                                val += *str - '0';
                                str++;
                        }
                        l |= val;
                        if (*str != '\0')
                                str++;
                }
        }
        return(htonl(l));
}

int init_module() {

	if(!ip) {
		printk("Error: missing end-host ip.\n");
		printk("Usage: insmod otp.o ip=x.x.x.x [dev=devname]\n\n");
		return -ENXIO;
	}		

	if (dev) {
		d = dev_get(dev);
		if (!d) {
			printk("Did not find device %s!\n", dev);
			printk("Using all known devices...");
		} 
		else {
			printk("Using device %s, ifindex: %i\n", 
				dev, d->ifindex);
			otp_proto.dev = d;
		}
	}
	else
		printk("Using all known devices(wildcarded)...\n");

	otp_proto.type = htons(ETH_P_ALL); 

    otp_proto.func = otp_func;
    dev_add_pack(&otp_proto);

	return(0);
}

void cleanup_module() {
	dev_remove_pack(&otp_proto);
    printk("OTP unloaded\n");
}