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.
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