Between you and Ben Greear the linux kernel will have every possible
scheme for sending packets to your self.
I still think my work on this (Virtual routing and forwarding:
http://linux-vrf.sf.net/) is the less perverted(*) then the work that either
you or Ben have come up with. Plus it has other applications besides
just being able to send packets to your self.
* in terms of the concept, not necessarily the actual implementation.
On Thu, Jul 10, 2003 at 06:47:05PM +1000, Rusty Russell wrote:
> Lots of people keep asking to be able to plug a crossover cables
> between to NICs in a machine, and use it for testing.
>
> This is a simple module which does this, by creating phantom
> machine(s) on each network with IP address 1 greater than the
> interface. Testers welcome.
>
> Ignore the backwards compat crap, it'll be out of the final version.
>
> Example usage:
> # Bring interfaces up
> ifconfig eth0 192.168.1.1
> ifconfig eth1 192.168.2.1
>
> # Add module which creates "phantom" machines 192.168.1.2, and 192.168.2.2.
> modprobe ip_crossover dev1=eth0 dev2=eth1
>
> # Tell kernel that 192.168.1.2 packets go to eth1, and .2.1 to eth0.
> arp -s 192.168.1.2 <hardware address of eth1>
> arp -s 192.168.2.2 <hardware address of eth0>
>
> It'd be nice to have the module hardwire the arps itself, but this was
> quickest. Patch welcome.
>
> Rusty.
>
> Name: Hardware Loopback Module
> Author: Rusty Russell
> Status: Tested on 2.5.74-bk5
>
> D: For testing it is often nice to connect two NICs with a crossover
> D: cable and have the machine route packets between them.
> D:
> D: Since Linux steadfastly regards IP addresses as properties of the
> D: box, not the individual NICs, this requires some trickery. A simple
> D: netfilter module makes this possible, by producing "phantom" boxes.
>
> diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal
> linux-2.5.74-bk5/net/ipv4/netfilter/Kconfig
> working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/Kconfig
> --- linux-2.5.74-bk5/net/ipv4/netfilter/Kconfig 2003-07-03
> 09:44:02.000000000 +1000
> +++ working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/Kconfig
> 2003-07-08 18:03:29.000000000 +1000
> @@ -587,5 +587,18 @@ config IP_NF_COMPAT_IPFWADM
> If you want to compile it as a module, say M here and read
> <file:Documentation/modules.txt>. If unsure, say `N'.
>
> +config IP_NF_CROSSOVER
> + tristate "IP forced crossover support (EXPERIMENTAL)"
> + depends on EXPERIMENTAL
> + help
> + This option allows you to connect two local network cards
> + with a crossover cable, and then force packets to pass over
> + that cable (Linux will normally short-circuit such packets).
> +
> + If you want to compile it as a module, say M here and read
> + <file:Documentation/modules.txt>: the module will be called
> + ip_crossover.
> +
> + Say `N'.
> endmenu
>
> diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal
> linux-2.5.74-bk5/net/ipv4/netfilter/Makefile
> working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/Makefile
> --- linux-2.5.74-bk5/net/ipv4/netfilter/Makefile 2003-07-03
> 09:44:02.000000000 +1000
> +++ working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/Makefile
> 2003-07-08 18:03:29.000000000 +1000
> @@ -92,3 +92,5 @@ obj-$(CONFIG_IP_NF_COMPAT_IPCHAINS) += i
> obj-$(CONFIG_IP_NF_COMPAT_IPFWADM) += ipfwadm.o
>
> obj-$(CONFIG_IP_NF_QUEUE) += ip_queue.o
> +
> +obj-$(CONFIG_IP_NF_CROSSOVER) += ip_crossover.o
> diff -urNp --exclude TAGS -X /home/rusty/current-dontdiff --minimal
> linux-2.5.74-bk5/net/ipv4/netfilter/ip_crossover.c
> working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/ip_crossover.c
> --- linux-2.5.74-bk5/net/ipv4/netfilter/ip_crossover.c 1970-01-01
> 10:00:00.000000000 +1000
> +++ working-2.5.74-bk5-hardware_loopback/net/ipv4/netfilter/ip_crossover.c
> 2003-07-10 18:04:59.000000000 +1000
> @@ -0,0 +1,257 @@
> +/* Copyright 2003 Rusty Russell, IBM Corporation.
> + *
> + * Simple packet mangling. The idea is to use a crossover between two
> + * local NICs for testing, then this module creates "phantom" boxes on
> + * each network at the interface address + 1.
> + *
> + * Packets sent to one phantom will come in like they came from the other.
> + *
> + * Usage:
> + * ifconfig eth0 192.168.1.1
> + * ifconfig eth1 192.168.2.1
> + * arp -s 192.168.1.2 <hardware address of eth1>
> + * arp -s 192.168.2.2 <hardware address of eth2>
> + * modprobe ip_crossover dev1=eth0 dev2=eth1
> + *
> + * Then doing ping 192.168.1.2, ICMP ping goes out eth0 and comes
> + * back in eth1. Reply goes out eth1 and comes back in eth0. */
> +#include <linux/config.h>
> +#include <linux/netfilter_ipv4.h>
> +#include <linux/ip.h>
> +#include <linux/skbuff.h>
> +#include <linux/moduleparam.h>
> +#include <linux/inetdevice.h>
> +#include <linux/tcp.h>
> +#include <linux/udp.h>
> +#include <linux/icmp.h>
> +#include <linux/version.h>
> +#include <net/ip.h>
> +#include <asm/checksum.h>
> +
> +struct ifinfo
> +{
> + /* Keep track of name so we can drop reference. */
> + char name[IFNAMSIZ];
> +
> + /* Cached interface addr. */
> + u32 ifaddr;
> +
> + /* "Phantom" box which gets mapped. */
> + u32 phantom;
> +};
> +
> +static struct ifinfo devinfo1, devinfo2;
> +
> +/* Stolen from Alexey's ip_nat_dumb. */
> +static int nat_header(struct sk_buff *skb, u32 saddr, u32 daddr)
> +{
> + struct iphdr *iph = skb->nh.iph;
> +
> + u32 odaddr = iph->daddr;
> + u32 osaddr = iph->saddr;
> + u16 check;
> +
> + /* Rewrite IP header */
> + iph->saddr = saddr;
> + iph->daddr = daddr;
> + iph->check = 0;
> + iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);
> +
> + /* If it is the first fragment, rewrite protocol headers */
> + if (!(iph->frag_off & htons(IP_OFFSET))) {
> + u16 *cksum;
> +
> + switch(iph->protocol) {
> + case IPPROTO_TCP:
> + cksum = (u16*)&((struct tcphdr*)
> + (((char*)iph)+(iph->ihl<<2)))->check;
> + if ((u8*)(cksum+1) > skb->tail)
> + return 0;
> + check = *cksum;
> + if (skb->ip_summed != CHECKSUM_HW)
> + check = ~check;
> + check = csum_tcpudp_magic(iph->saddr, iph->daddr,
> + 0, 0, check);
> + check = csum_tcpudp_magic(~osaddr, ~odaddr, 0, 0,
> + ~check);
> + if (skb->ip_summed == CHECKSUM_HW)
> + check = ~check;
> + *cksum = check;
> + break;
> + case IPPROTO_UDP:
> + cksum = (u16*)&((struct udphdr*)
> + (((char*)iph)+(iph->ihl<<2)))->check;
> + if ((u8*)(cksum+1) > skb->tail)
> + return 0;
> + if ((check = *cksum) != 0) {
> + check = csum_tcpudp_magic(iph->saddr,
> + iph->daddr, 0, 0,
> + ~check);
> + check = csum_tcpudp_magic(~osaddr, ~odaddr,
> + 0, 0, ~check);
> + *cksum = check ? : 0xFFFF;
> + }
> + break;
> + case IPPROTO_ICMP:
> + {
> + struct icmphdr *icmph
> + = (struct icmphdr*)((char*)iph+(iph->ihl<<2));
> + struct iphdr *ciph;
> + u32 idaddr, isaddr;
> +
> + if ((icmph->type != ICMP_DEST_UNREACH) &&
> + (icmph->type != ICMP_TIME_EXCEEDED) &&
> + (icmph->type != ICMP_PARAMETERPROB))
> + break;
> +
> + ciph = (struct iphdr *) (icmph + 1);
> +
> + if ((u8*)(ciph+1) > skb->tail)
> + return 0;
> +
> + isaddr = ciph->saddr;
> + idaddr = ciph->daddr;
> +
> + /* Change addresses inside ICMP packet. */
> + ciph->daddr = iph->saddr;
> + ciph->saddr = iph->daddr;
> + cksum = &icmph->checksum;
> + /* Using tcpudp primitive. Why not? */
> + check = csum_tcpudp_magic(ciph->saddr, ciph->daddr,
> + 0, 0, ~(*cksum));
> + *cksum = csum_tcpudp_magic(~isaddr, ~idaddr, 0, 0,
> + ~check);
> + break;
> + }
> + default:
> + break;
> + }
> + }
> + return 1;
> +}
> +
> +static unsigned int xover_hook(unsigned int hook,
> + struct sk_buff **pskb,
> + const struct net_device *in,
> + const struct net_device *out,
> + int (*okfn)(struct sk_buff *))
> +{
> + /* Going out to phantom box 1: change it to coming from
> + phantom box 2, and vice versa. */
> + if ((*pskb)->nh.iph->daddr == devinfo1.phantom) {
> + printk(KERN_DEBUG "dev1: %u.%u.%u.%u->%u.%u.%u.%u"
> + " becomes %u.%u.%u.%u->%u.%u.%u.%u\n",
> + NIPQUAD((*pskb)->nh.iph->saddr),
> + NIPQUAD((*pskb)->nh.iph->daddr),
> + NIPQUAD(devinfo2.phantom),
> + NIPQUAD(devinfo2.ifaddr));
> + if (!nat_header(*pskb, devinfo2.phantom, devinfo2.ifaddr))
> + return NF_DROP;
> + } else if ((*pskb)->nh.iph->daddr == devinfo2.phantom) {
> + printk(KERN_DEBUG "dev1: %u.%u.%u.%u->%u.%u.%u.%u"
> + " becomes %u.%u.%u.%u->%u.%u.%u.%u\n",
> + NIPQUAD((*pskb)->nh.iph->saddr),
> + NIPQUAD((*pskb)->nh.iph->daddr),
> + NIPQUAD(devinfo1.phantom),
> + NIPQUAD(devinfo1.ifaddr));
> + if (!nat_header(*pskb, devinfo1.phantom, devinfo1.ifaddr))
> + return NF_DROP;
> + }
> +
> + return NF_ACCEPT;
> +}
> +
> +static struct nf_hook_ops xover_ops
> += { .hook = xover_hook,
> + .owner = THIS_MODULE,
> + .pf = PF_INET,
> + .hooknum = NF_IP_POST_ROUTING,
> + .priority = NF_IP_PRI_MANGLE,
> +};
> +
> +static int __set_dev(const char *name, struct ifinfo *ifi)
> +{
> + struct net_device *dev;
> + struct in_device *indev;
> +
> + dev = dev_get_by_name(name);
> + if (!dev)
> + goto fail;
> + indev = __in_dev_get(dev);
> + if (!indev || !indev->ifa_list)
> + goto put_fail;
> +
> + ifi->ifaddr = indev->ifa_list->ifa_address;
> + ifi->phantom = htonl(ntohl(indev->ifa_list->ifa_address) + 1);
> + if (ifi->phantom == indev->ifa_list->ifa_broadcast)
> + goto put_fail;
> +
> + strlcpy(ifi->name, name, sizeof(ifi->name));
> + printk(KERN_INFO "ip_crossover: phantom for %s: %u.%u.%u.%u\n",
> + ifi->name, NIPQUAD(ifi->phantom));
> + return 0;
> +
> +put_fail:
> + dev_put(dev);
> +fail:
> + printk(KERN_WARNING "ip_crossover: device %s is not usable.\n", name);
> + return -ENOENT;
> +}
> +
> +#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,5,50)
> +static int set_dev(const char *val, struct kernel_param *kp)
> +{
> + return __set_dev(val, kp->arg);
> +}
> +module_param_call(dev1, set_dev, NULL, &devinfo1, 0);
> +module_param_call(dev2, set_dev, NULL, &devinfo2, 0);
> +
> +#define compat_parse_params()
> +#else
> +static char *dev1, *dev2;
> +
> +MODULE_PARM(dev1, "s");
> +MODULE_PARM(dev2, "s");
> +
> +static void compat_parse_params(void)
> +{
> + if (dev1)
> + __set_dev(dev1, &devinfo1);
> + if (dev2)
> + __set_dev(dev2, &devinfo2);
> +}
> +#endif /* KERNEL_VERSION */
> +
> +static int __init init(void)
> +{
> + compat_parse_params();
> +
> + if (!devinfo1.name[0] || !devinfo2.name[0]) {
> + printk(KERN_ERR "ip_crossover: need dev1 and dev2 args\n");
> + return -EINVAL;
> + }
> +
> + return nf_register_hook(&xover_ops);
> +}
> +
> +static void __exit fini(void)
> +{
> + struct net_device *dev;
> +
> + nf_unregister_hook(&xover_ops);
> +
> + /* Release devices. */
> + dev = dev_get_by_name(devinfo1.name);
> + dev_put(dev);
> + dev_put(dev);
> +
> + dev = dev_get_by_name(devinfo2.name);
> + dev_put(dev);
> + dev_put(dev);
> +}
> +
> +module_init(init);
> +module_exit(fini);
> +MODULE_LICENSE("GPL");
> +MODULE_PARM_DESC(dev1, "First device for crossover (required)");
> +MODULE_PARM_DESC(dev2, "Second device for crossover (required)");
>
> --
> Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
--
James R. Leu
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