Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1290 insertions, 0 deletions

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
new file mode 100644
index 000000000000..884835522224
--- /dev/null
+++ b/net/ipv4/ip_gre.c
@@ -0,0 +1,1290 @@
+/*
+ *	Linux NET3:	GRE over IP protocol decoder. 
+ *
+ *	Authors: Alexey Kuznetsov (kuznet@ms2.inr.ac.ru)
+ *
+ *	This program is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU General Public License
+ *	as published by the Free Software Foundation; either version
+ *	2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <asm/uaccess.h>
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/in.h>
+#include <linux/tcp.h>
+#include <linux/udp.h>
+#include <linux/if_arp.h>
+#include <linux/mroute.h>
+#include <linux/init.h>
+#include <linux/in6.h>
+#include <linux/inetdevice.h>
+#include <linux/igmp.h>
+#include <linux/netfilter_ipv4.h>
+
+#include <net/sock.h>
+#include <net/ip.h>
+#include <net/icmp.h>
+#include <net/protocol.h>
+#include <net/ipip.h>
+#include <net/arp.h>
+#include <net/checksum.h>
+#include <net/dsfield.h>
+#include <net/inet_ecn.h>
+#include <net/xfrm.h>
+
+#ifdef CONFIG_IPV6
+#include <net/ipv6.h>
+#include <net/ip6_fib.h>
+#include <net/ip6_route.h>
+#endif
+
+/*
+   Problems & solutions
+   --------------------
+
+   1. The most important issue is detecting local dead loops.
+   They would cause complete host lockup in transmit, which
+   would be "resolved" by stack overflow or, if queueing is enabled,
+   with infinite looping in net_bh.
+
+   We cannot track such dead loops during route installation,
+   it is infeasible task. The most general solutions would be
+   to keep skb->encapsulation counter (sort of local ttl),
+   and silently drop packet when it expires. It is the best
+   solution, but it supposes maintaing new variable in ALL
+   skb, even if no tunneling is used.
+
+   Current solution: t->recursion lock breaks dead loops. It looks 
+   like dev->tbusy flag, but I preferred new variable, because
+   the semantics is different. One day, when hard_start_xmit
+   will be multithreaded we will have to use skb->encapsulation.
+
+
+
+   2. Networking dead loops would not kill routers, but would really
+   kill network. IP hop limit plays role of "t->recursion" in this case,
+   if we copy it from packet being encapsulated to upper header.
+   It is very good solution, but it introduces two problems:
+
+   - Routing protocols, using packets with ttl=1 (OSPF, RIP2),
+     do not work over tunnels.
+   - traceroute does not work. I planned to relay ICMP from tunnel,
+     so that this problem would be solved and traceroute output
+     would even more informative. This idea appeared to be wrong:
+     only Linux complies to rfc1812 now (yes, guys, Linux is the only
+     true router now :-)), all routers (at least, in neighbourhood of mine)
+     return only 8 bytes of payload. It is the end.
+
+   Hence, if we want that OSPF worked or traceroute said something reasonable,
+   we should search for another solution.
+
+   One of them is to parse packet trying to detect inner encapsulation
+   made by our node. It is difficult or even impossible, especially,
+   taking into account fragmentation. TO be short, tt is not solution at all.
+
+   Current solution: The solution was UNEXPECTEDLY SIMPLE.
+   We force DF flag on tunnels with preconfigured hop limit,
+   that is ALL. :-) Well, it does not remove the problem completely,
+   but exponential growth of network traffic is changed to linear
+   (branches, that exceed pmtu are pruned) and tunnel mtu
+   fastly degrades to value <68, where looping stops.
+   Yes, it is not good if there exists a router in the loop,
+   which does not force DF, even when encapsulating packets have DF set.
+   But it is not our problem! Nobody could accuse us, we made
+   all that we could make. Even if it is your gated who injected
+   fatal route to network, even if it were you who configured
+   fatal static route: you are innocent. :-)
+
+
+
+   3. Really, ipv4/ipip.c, ipv4/ip_gre.c and ipv6/sit.c contain
+   practically identical code. It would be good to glue them
+   together, but it is not very evident, how to make them modular.
+   sit is integral part of IPv6, ipip and gre are naturally modular.
+   We could extract common parts (hash table, ioctl etc)
+   to a separate module (ip_tunnel.c).
+
+   Alexey Kuznetsov.
+ */
+
+static int ipgre_tunnel_init(struct net_device *dev);
+static void ipgre_tunnel_setup(struct net_device *dev);
+
+/* Fallback tunnel: no source, no destination, no key, no options */
+
+static int ipgre_fb_tunnel_init(struct net_device *dev);
+
+static struct net_device *ipgre_fb_tunnel_dev;
+
+/* Tunnel hash table */
+
+/*
+   4 hash tables:
+
+   3: (remote,local)
+   2: (remote,*)
+   1: (*,local)
+   0: (*,*)
+
+   We require exact key match i.e. if a key is present in packet
+   it will match only tunnel with the same key; if it is not present,
+   it will match only keyless tunnel.
+
+   All keysless packets, if not matched configured keyless tunnels
+   will match fallback tunnel.
+ */
+
+#define HASH_SIZE  16
+#define HASH(addr) ((addr^(addr>>4))&0xF)
+
+static struct ip_tunnel *tunnels[4][HASH_SIZE];
+
+#define tunnels_r_l	(tunnels[3])
+#define tunnels_r	(tunnels[2])
+#define tunnels_l	(tunnels[1])
+#define tunnels_wc	(tunnels[0])
+
+static DEFINE_RWLOCK(ipgre_lock);
+
+/* Given src, dst and key, find appropriate for input tunnel. */
+
+static struct ip_tunnel * ipgre_tunnel_lookup(u32 remote, u32 local, u32 key)
+{
+	unsigned h0 = HASH(remote);
+	unsigned h1 = HASH(key);
+	struct ip_tunnel *t;
+
+	for (t = tunnels_r_l[h0^h1]; t; t = t->next) {
+		if (local == t->parms.iph.saddr && remote == t->parms.iph.daddr) {
+			if (t->parms.i_key == key && (t->dev->flags&IFF_UP))
+				return t;
+		}
+	}
+	for (t = tunnels_r[h0^h1]; t; t = t->next) {
+		if (remote == t->parms.iph.daddr) {
+			if (t->parms.i_key == key && (t->dev->flags&IFF_UP))
+				return t;
+		}
+	}
+	for (t = tunnels_l[h1]; t; t = t->next) {
+		if (local == t->parms.iph.saddr ||
+		     (local == t->parms.iph.daddr && MULTICAST(local))) {
+			if (t->parms.i_key == key && (t->dev->flags&IFF_UP))
+				return t;
+		}
+	}
+	for (t = tunnels_wc[h1]; t; t = t->next) {
+		if (t->parms.i_key == key && (t->dev->flags&IFF_UP))
+			return t;
+	}
+
+	if (ipgre_fb_tunnel_dev->flags&IFF_UP)
+		return ipgre_fb_tunnel_dev->priv;
+	return NULL;
+}
+
+static struct ip_tunnel **ipgre_bucket(struct ip_tunnel *t)
+{
+	u32 remote = t->parms.iph.daddr;
+	u32 local = t->parms.iph.saddr;
+	u32 key = t->parms.i_key;
+	unsigned h = HASH(key);
+	int prio = 0;
+
+	if (local)
+		prio |= 1;
+	if (remote && !MULTICAST(remote)) {
+		prio |= 2;
+		h ^= HASH(remote);
+	}
+
+	return &tunnels[prio][h];
+}
+
+static void ipgre_tunnel_link(struct ip_tunnel *t)
+{
+	struct ip_tunnel **tp = ipgre_bucket(t);
+
+	t->next = *tp;
+	write_lock_bh(&ipgre_lock);
+	*tp = t;
+	write_unlock_bh(&ipgre_lock);
+}
+
+static void ipgre_tunnel_unlink(struct ip_tunnel *t)
+{
+	struct ip_tunnel **tp;
+
+	for (tp = ipgre_bucket(t); *tp; tp = &(*tp)->next) {
+		if (t == *tp) {
+			write_lock_bh(&ipgre_lock);
+			*tp = t->next;
+			write_unlock_bh(&ipgre_lock);
+			break;
+		}
+	}
+}
+
+static struct ip_tunnel * ipgre_tunnel_locate(struct ip_tunnel_parm *parms, int create)
+{
+	u32 remote = parms->iph.daddr;
+	u32 local = parms->iph.saddr;
+	u32 key = parms->i_key;
+	struct ip_tunnel *t, **tp, *nt;
+	struct net_device *dev;
+	unsigned h = HASH(key);
+	int prio = 0;
+	char name[IFNAMSIZ];
+
+	if (local)
+		prio |= 1;
+	if (remote && !MULTICAST(remote)) {
+		prio |= 2;
+		h ^= HASH(remote);
+	}
+	for (tp = &tunnels[prio][h]; (t = *tp) != NULL; tp = &t->next) {
+		if (local == t->parms.iph.saddr && remote == t->parms.iph.daddr) {
+			if (key == t->parms.i_key)
+				return t;
+		}
+	}
+	if (!create)
+		return NULL;
+
+	if (parms->name[0])
+		strlcpy(name, parms->name, IFNAMSIZ);
+	else {
+		int i;
+		for (i=1; i<100; i++) {
+			sprintf(name, "gre%d", i);
+			if (__dev_get_by_name(name) == NULL)
+				break;
+		}
+		if (i==100)
+			goto failed;
+	}
+
+	dev = alloc_netdev(sizeof(*t), name, ipgre_tunnel_setup);
+	if (!dev)
+	  return NULL;
+
+	dev->init = ipgre_tunnel_init;
+	nt = dev->priv;
+	nt->parms = *parms;
+
+	if (register_netdevice(dev) < 0) {
+		free_netdev(dev);
+		goto failed;
+	}
+
+	nt = dev->priv;
+	nt->parms = *parms;
+
+	dev_hold(dev);
+	ipgre_tunnel_link(nt);
+	/* Do not decrement MOD_USE_COUNT here. */
+	return nt;
+
+failed:
+	return NULL;
+}
+
+static void ipgre_tunnel_uninit(struct net_device *dev)
+{
+	ipgre_tunnel_unlink((struct ip_tunnel*)dev->priv);
+	dev_put(dev);
+}
+
+
+static void ipgre_err(struct sk_buff *skb, u32 info)
+{
+#ifndef I_WISH_WORLD_WERE_PERFECT
+
+/* It is not :-( All the routers (except for Linux) return only
+   8 bytes of packet payload. It means, that precise relaying of
+   ICMP in the real Internet is absolutely infeasible.
+
+   Moreover, Cisco "wise men" put GRE key to the third word
+   in GRE header. It makes impossible maintaining even soft state for keyed
+   GRE tunnels with enabled checksum. Tell them "thank you".
+
+   Well, I wonder, rfc1812 was written by Cisco employee,
+   what the hell these idiots break standrads established
+   by themself???
+ */
+
+	struct iphdr *iph = (struct iphdr*)skb->data;
+	u16	     *p = (u16*)(skb->data+(iph->ihl<<2));
+	int grehlen = (iph->ihl<<2) + 4;
+	int type = skb->h.icmph->type;
+	int code = skb->h.icmph->code;
+	struct ip_tunnel *t;
+	u16 flags;
+
+	flags = p[0];
+	if (flags&(GRE_CSUM|GRE_KEY|GRE_SEQ|GRE_ROUTING|GRE_VERSION)) {
+		if (flags&(GRE_VERSION|GRE_ROUTING))
+			return;
+		if (flags&GRE_KEY) {
+			grehlen += 4;
+			if (flags&GRE_CSUM)
+				grehlen += 4;
+		}
+	}
+
+	/* If only 8 bytes returned, keyed message will be dropped here */
+	if (skb_headlen(skb) < grehlen)
+		return;
+
+	switch (type) {
+	default:
+	case ICMP_PARAMETERPROB:
+		return;
+
+	case ICMP_DEST_UNREACH:
+		switch (code) {
+		case ICMP_SR_FAILED:
+		case ICMP_PORT_UNREACH:
+			/* Impossible event. */
+			return;
+		case ICMP_FRAG_NEEDED:
+			/* Soft state for pmtu is maintained by IP core. */
+			return;
+		default:
+			/* All others are translated to HOST_UNREACH.
+			   rfc2003 contains "deep thoughts" about NET_UNREACH,
+			   I believe they are just ether pollution. --ANK
+			 */
+			break;
+		}
+		break;
+	case ICMP_TIME_EXCEEDED:
+		if (code != ICMP_EXC_TTL)
+			return;
+		break;
+	}
+
+	read_lock(&ipgre_lock);
+	t = ipgre_tunnel_lookup(iph->daddr, iph->saddr, (flags&GRE_KEY) ? *(((u32*)p) + (grehlen>>2) - 1) : 0);
+	if (t == NULL || t->parms.iph.daddr == 0 || MULTICAST(t->parms.iph.daddr))
+		goto out;
+
+	if (t->parms.iph.ttl == 0 && type == ICMP_TIME_EXCEEDED)
+		goto out;
+
+	if (jiffies - t->err_time < IPTUNNEL_ERR_TIMEO)
+		t->err_count++;
+	else
+		t->err_count = 1;
+	t->err_time = jiffies;
+out:
+	read_unlock(&ipgre_lock);
+	return;
+#else
+	struct iphdr *iph = (struct iphdr*)dp;
+	struct iphdr *eiph;
+	u16	     *p = (u16*)(dp+(iph->ihl<<2));
+	int type = skb->h.icmph->type;
+	int code = skb->h.icmph->code;
+	int rel_type = 0;
+	int rel_code = 0;
+	int rel_info = 0;
+	u16 flags;
+	int grehlen = (iph->ihl<<2) + 4;
+	struct sk_buff *skb2;
+	struct flowi fl;
+	struct rtable *rt;
+
+	if (p[1] != htons(ETH_P_IP))
+		return;
+
+	flags = p[0];
+	if (flags&(GRE_CSUM|GRE_KEY|GRE_SEQ|GRE_ROUTING|GRE_VERSION)) {
+		if (flags&(GRE_VERSION|GRE_ROUTING))
+			return;
+		if (flags&GRE_CSUM)
+			grehlen += 4;
+		if (flags&GRE_KEY)
+			grehlen += 4;
+		if (flags&GRE_SEQ)
+			grehlen += 4;
+	}
+	if (len < grehlen + sizeof(struct iphdr))
+		return;
+	eiph = (struct iphdr*)(dp + grehlen);
+
+	switch (type) {
+	default:
+		return;
+	case ICMP_PARAMETERPROB:
+		if (skb->h.icmph->un.gateway < (iph->ihl<<2))
+			return;
+
+		/* So... This guy found something strange INSIDE encapsulated
+		   packet. Well, he is fool, but what can we do ?
+		 */
+		rel_type = ICMP_PARAMETERPROB;
+		rel_info = skb->h.icmph->un.gateway - grehlen;
+		break;
+
+	case ICMP_DEST_UNREACH:
+		switch (code) {
+		case ICMP_SR_FAILED:
+		case ICMP_PORT_UNREACH:
+			/* Impossible event. */
+			return;
+		case ICMP_FRAG_NEEDED:
+			/* And it is the only really necessary thing :-) */
+			rel_info = ntohs(skb->h.icmph->un.frag.mtu);
+			if (rel_info < grehlen+68)
+				return;
+			rel_info -= grehlen;
+			/* BSD 4.2 MORE DOES NOT EXIST IN NATURE. */
+			if (rel_info > ntohs(eiph->tot_len))
+				return;
+			break;
+		default:
+			/* All others are translated to HOST_UNREACH.
+			   rfc2003 contains "deep thoughts" about NET_UNREACH,
+			   I believe, it is just ether pollution. --ANK
+			 */
+			rel_type = ICMP_DEST_UNREACH;
+			rel_code = ICMP_HOST_UNREACH;
+			break;
+		}
+		break;
+	case ICMP_TIME_EXCEEDED:
+		if (code != ICMP_EXC_TTL)
+			return;
+		break;
+	}
+
+	/* Prepare fake skb to feed it to icmp_send */
+	skb2 = skb_clone(skb, GFP_ATOMIC);
+	if (skb2 == NULL)
+		return;
+	dst_release(skb2->dst);
+	skb2->dst = NULL;
+	skb_pull(skb2, skb->data - (u8*)eiph);
+	skb2->nh.raw = skb2->data;
+
+	/* Try to guess incoming interface */
+	memset(&fl, 0, sizeof(fl));
+	fl.fl4_dst = eiph->saddr;
+	fl.fl4_tos = RT_TOS(eiph->tos);
+	fl.proto = IPPROTO_GRE;
+	if (ip_route_output_key(&rt, &fl)) {
+		kfree_skb(skb2);
+		return;
+	}
+	skb2->dev = rt->u.dst.dev;
+
+	/* route "incoming" packet */
+	if (rt->rt_flags&RTCF_LOCAL) {
+		ip_rt_put(rt);
+		rt = NULL;
+		fl.fl4_dst = eiph->daddr;
+		fl.fl4_src = eiph->saddr;
+		fl.fl4_tos = eiph->tos;
+		if (ip_route_output_key(&rt, &fl) ||
+		    rt->u.dst.dev->type != ARPHRD_IPGRE) {
+			ip_rt_put(rt);
+			kfree_skb(skb2);
+			return;
+		}
+	} else {
+		ip_rt_put(rt);
+		if (ip_route_input(skb2, eiph->daddr, eiph->saddr, eiph->tos, skb2->dev) ||
+		    skb2->dst->dev->type != ARPHRD_IPGRE) {
+			kfree_skb(skb2);
+			return;
+		}
+	}
+
+	/* change mtu on this route */
+	if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
+		if (rel_info > dst_mtu(skb2->dst)) {
+			kfree_skb(skb2);
+			return;
+		}
+		skb2->dst->ops->update_pmtu(skb2->dst, rel_info);
+		rel_info = htonl(rel_info);
+	} else if (type == ICMP_TIME_EXCEEDED) {
+		struct ip_tunnel *t = (struct ip_tunnel*)skb2->dev->priv;
+		if (t->parms.iph.ttl) {
+			rel_type = ICMP_DEST_UNREACH;
+			rel_code = ICMP_HOST_UNREACH;
+		}
+	}
+
+	icmp_send(skb2, rel_type, rel_code, rel_info);
+	kfree_skb(skb2);
+#endif
+}
+
+static inline void ipgre_ecn_decapsulate(struct iphdr *iph, struct sk_buff *skb)
+{
+	if (INET_ECN_is_ce(iph->tos)) {
+		if (skb->protocol == htons(ETH_P_IP)) {
+			IP_ECN_set_ce(skb->nh.iph);
+		} else if (skb->protocol == htons(ETH_P_IPV6)) {
+			IP6_ECN_set_ce(skb->nh.ipv6h);
+		}
+	}
+}
+
+static inline u8
+ipgre_ecn_encapsulate(u8 tos, struct iphdr *old_iph, struct sk_buff *skb)
+{
+	u8 inner = 0;
+	if (skb->protocol == htons(ETH_P_IP))
+		inner = old_iph->tos;
+	else if (skb->protocol == htons(ETH_P_IPV6))
+		inner = ipv6_get_dsfield((struct ipv6hdr *)old_iph);
+	return INET_ECN_encapsulate(tos, inner);
+}
+
+static int ipgre_rcv(struct sk_buff *skb)
+{
+	struct iphdr *iph;
+	u8     *h;
+	u16    flags;
+	u16    csum = 0;
+	u32    key = 0;
+	u32    seqno = 0;
+	struct ip_tunnel *tunnel;
+	int    offset = 4;
+
+	if (!pskb_may_pull(skb, 16))
+		goto drop_nolock;
+
+	iph = skb->nh.iph;
+	h = skb->data;
+	flags = *(u16*)h;
+
+	if (flags&(GRE_CSUM|GRE_KEY|GRE_ROUTING|GRE_SEQ|GRE_VERSION)) {
+		/* - Version must be 0.
+		   - We do not support routing headers.
+		 */
+		if (flags&(GRE_VERSION|GRE_ROUTING))
+			goto drop_nolock;
+
+		if (flags&GRE_CSUM) {
+			if (skb->ip_summed == CHECKSUM_HW) {
+				csum = (u16)csum_fold(skb->csum);
+				if (csum)
+					skb->ip_summed = CHECKSUM_NONE;
+			}
+			if (skb->ip_summed == CHECKSUM_NONE) {
+				skb->csum = skb_checksum(skb, 0, skb->len, 0);
+				skb->ip_summed = CHECKSUM_HW;
+				csum = (u16)csum_fold(skb->csum);
+			}
+			offset += 4;
+		}
+		if (flags&GRE_KEY) {
+			key = *(u32*)(h + offset);
+			offset += 4;
+		}
+		if (flags&GRE_SEQ) {
+			seqno = ntohl(*(u32*)(h + offset));
+			offset += 4;
+		}
+	}
+
+	read_lock(&ipgre_lock);
+	if ((tunnel = ipgre_tunnel_lookup(iph->saddr, iph->daddr, key)) != NULL) {
+		secpath_reset(skb);
+
+		skb->protocol = *(u16*)(h + 2);
+		/* WCCP version 1 and 2 protocol decoding.
+		 * - Change protocol to IP
+		 * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
+		 */
+		if (flags == 0 &&
+		    skb->protocol == __constant_htons(ETH_P_WCCP)) {
+			skb->protocol = __constant_htons(ETH_P_IP);
+			if ((*(h + offset) & 0xF0) != 0x40) 
+				offset += 4;
+		}
+
+		skb->mac.raw = skb->nh.raw;
+		skb->nh.raw = __pskb_pull(skb, offset);
+		skb_postpull_rcsum(skb, skb->mac.raw, offset);
+		memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
+		skb->pkt_type = PACKET_HOST;
+#ifdef CONFIG_NET_IPGRE_BROADCAST
+		if (MULTICAST(iph->daddr)) {
+			/* Looped back packet, drop it! */
+			if (((struct rtable*)skb->dst)->fl.iif == 0)
+				goto drop;
+			tunnel->stat.multicast++;
+			skb->pkt_type = PACKET_BROADCAST;
+		}
+#endif
+
+		if (((flags&GRE_CSUM) && csum) ||
+		    (!(flags&GRE_CSUM) && tunnel->parms.i_flags&GRE_CSUM)) {
+			tunnel->stat.rx_crc_errors++;
+			tunnel->stat.rx_errors++;
+			goto drop;
+		}
+		if (tunnel->parms.i_flags&GRE_SEQ) {
+			if (!(flags&GRE_SEQ) ||
+			    (tunnel->i_seqno && (s32)(seqno - tunnel->i_seqno) < 0)) {
+				tunnel->stat.rx_fifo_errors++;
+				tunnel->stat.rx_errors++;
+				goto drop;
+			}
+			tunnel->i_seqno = seqno + 1;
+		}
+		tunnel->stat.rx_packets++;
+		tunnel->stat.rx_bytes += skb->len;
+		skb->dev = tunnel->dev;
+		dst_release(skb->dst);
+		skb->dst = NULL;
+		nf_reset(skb);
+		ipgre_ecn_decapsulate(iph, skb);
+		netif_rx(skb);
+		read_unlock(&ipgre_lock);
+		return(0);
+	}
+	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PROT_UNREACH, 0);
+
+drop:
+	read_unlock(&ipgre_lock);
+drop_nolock:
+	kfree_skb(skb);
+	return(0);
+}
+
+static int ipgre_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct ip_tunnel *tunnel = (struct ip_tunnel*)dev->priv;
+	struct net_device_stats *stats = &tunnel->stat;
+	struct iphdr  *old_iph = skb->nh.iph;
+	struct iphdr  *tiph;
+	u8     tos;
+	u16    df;
+	struct rtable *rt;     			/* Route to the other host */
+	struct net_device *tdev;			/* Device to other host */
+	struct iphdr  *iph;			/* Our new IP header */
+	int    max_headroom;			/* The extra header space needed */
+	int    gre_hlen;
+	u32    dst;
+	int    mtu;
+
+	if (tunnel->recursion++) {
+		tunnel->stat.collisions++;
+		goto tx_error;
+	}
+
+	if (dev->hard_header) {
+		gre_hlen = 0;
+		tiph = (struct iphdr*)skb->data;
+	} else {
+		gre_hlen = tunnel->hlen;
+		tiph = &tunnel->parms.iph;
+	}
+
+	if ((dst = tiph->daddr) == 0) {
+		/* NBMA tunnel */
+
+		if (skb->dst == NULL) {
+			tunnel->stat.tx_fifo_errors++;
+			goto tx_error;
+		}
+
+		if (skb->protocol == htons(ETH_P_IP)) {
+			rt = (struct rtable*)skb->dst;
+			if ((dst = rt->rt_gateway) == 0)
+				goto tx_error_icmp;
+		}
+#ifdef CONFIG_IPV6
+		else if (skb->protocol == htons(ETH_P_IPV6)) {
+			struct in6_addr *addr6;
+			int addr_type;
+			struct neighbour *neigh = skb->dst->neighbour;
+
+			if (neigh == NULL)
+				goto tx_error;
+
+			addr6 = (struct in6_addr*)&neigh->primary_key;
+			addr_type = ipv6_addr_type(addr6);
+
+			if (addr_type == IPV6_ADDR_ANY) {
+				addr6 = &skb->nh.ipv6h->daddr;
+				addr_type = ipv6_addr_type(addr6);
+			}
+
+			if ((addr_type & IPV6_ADDR_COMPATv4) == 0)
+				goto tx_error_icmp;
+
+			dst = addr6->s6_addr32[3];
+		}
+#endif
+		else
+			goto tx_error;
+	}
+
+	tos = tiph->tos;
+	if (tos&1) {
+		if (skb->protocol == htons(ETH_P_IP))
+			tos = old_iph->tos;
+		tos &= ~1;
+	}
+
+	{
+		struct flowi fl = { .oif = tunnel->parms.link,
+				    .nl_u = { .ip4_u =
+					      { .daddr = dst,
+						.saddr = tiph->saddr,
+						.tos = RT_TOS(tos) } },
+				    .proto = IPPROTO_GRE };
+		if (ip_route_output_key(&rt, &fl)) {
+			tunnel->stat.tx_carrier_errors++;
+			goto tx_error;
+		}
+	}
+	tdev = rt->u.dst.dev;
+
+	if (tdev == dev) {
+		ip_rt_put(rt);
+		tunnel->stat.collisions++;
+		goto tx_error;
+	}
+
+	df = tiph->frag_off;
+	if (df)
+		mtu = dst_mtu(&rt->u.dst) - tunnel->hlen;
+	else
+		mtu = skb->dst ? dst_mtu(skb->dst) : dev->mtu;
+
+	if (skb->dst)
+		skb->dst->ops->update_pmtu(skb->dst, mtu);
+
+	if (skb->protocol == htons(ETH_P_IP)) {
+		df |= (old_iph->frag_off&htons(IP_DF));
+
+		if ((old_iph->frag_off&htons(IP_DF)) &&
+		    mtu < ntohs(old_iph->tot_len)) {
+			icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
+			ip_rt_put(rt);
+			goto tx_error;
+		}
+	}
+#ifdef CONFIG_IPV6
+	else if (skb->protocol == htons(ETH_P_IPV6)) {
+		struct rt6_info *rt6 = (struct rt6_info*)skb->dst;
+
+		if (rt6 && mtu < dst_mtu(skb->dst) && mtu >= IPV6_MIN_MTU) {
+			if ((tunnel->parms.iph.daddr && !MULTICAST(tunnel->parms.iph.daddr)) ||
+			    rt6->rt6i_dst.plen == 128) {
+				rt6->rt6i_flags |= RTF_MODIFIED;
+				skb->dst->metrics[RTAX_MTU-1] = mtu;
+			}
+		}
+
+		if (mtu >= IPV6_MIN_MTU && mtu < skb->len - tunnel->hlen + gre_hlen) {
+			icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, dev);
+			ip_rt_put(rt);
+			goto tx_error;
+		}
+	}
+#endif
+
+	if (tunnel->err_count > 0) {
+		if (jiffies - tunnel->err_time < IPTUNNEL_ERR_TIMEO) {
+			tunnel->err_count--;
+
+			dst_link_failure(skb);
+		} else
+			tunnel->err_count = 0;
+	}
+
+	max_headroom = LL_RESERVED_SPACE(tdev) + gre_hlen;
+
+	if (skb_headroom(skb) < max_headroom || skb_cloned(skb) || skb_shared(skb)) {
+		struct sk_buff *new_skb = skb_realloc_headroom(skb, max_headroom);
+		if (!new_skb) {
+			ip_rt_put(rt);
+  			stats->tx_dropped++;
+			dev_kfree_skb(skb);
+			tunnel->recursion--;
+			return 0;
+		}
+		if (skb->sk)
+			skb_set_owner_w(new_skb, skb->sk);
+		dev_kfree_skb(skb);
+		skb = new_skb;
+		old_iph = skb->nh.iph;
+	}
+
+	skb->h.raw = skb->nh.raw;
+	skb->nh.raw = skb_push(skb, gre_hlen);
+	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
+	dst_release(skb->dst);
+	skb->dst = &rt->u.dst;
+
+	/*
+	 *	Push down and install the IPIP header.
+	 */
+
+	iph 			=	skb->nh.iph;
+	iph->version		=	4;
+	iph->ihl		=	sizeof(struct iphdr) >> 2;
+	iph->frag_off		=	df;
+	iph->protocol		=	IPPROTO_GRE;
+	iph->tos		=	ipgre_ecn_encapsulate(tos, old_iph, skb);
+	iph->daddr		=	rt->rt_dst;
+	iph->saddr		=	rt->rt_src;
+
+	if ((iph->ttl = tiph->ttl) == 0) {
+		if (skb->protocol == htons(ETH_P_IP))
+			iph->ttl = old_iph->ttl;
+#ifdef CONFIG_IPV6
+		else if (skb->protocol == htons(ETH_P_IPV6))
+			iph->ttl = ((struct ipv6hdr*)old_iph)->hop_limit;
+#endif
+		else
+			iph->ttl = dst_metric(&rt->u.dst, RTAX_HOPLIMIT);
+	}
+
+	((u16*)(iph+1))[0] = tunnel->parms.o_flags;
+	((u16*)(iph+1))[1] = skb->protocol;
+
+	if (tunnel->parms.o_flags&(GRE_KEY|GRE_CSUM|GRE_SEQ)) {
+		u32 *ptr = (u32*)(((u8*)iph) + tunnel->hlen - 4);
+
+		if (tunnel->parms.o_flags&GRE_SEQ) {
+			++tunnel->o_seqno;
+			*ptr = htonl(tunnel->o_seqno);
+			ptr--;
+		}
+		if (tunnel->parms.o_flags&GRE_KEY) {
+			*ptr = tunnel->parms.o_key;
+			ptr--;
+		}
+		if (tunnel->parms.o_flags&GRE_CSUM) {
+			*ptr = 0;
+			*(__u16*)ptr = ip_compute_csum((void*)(iph+1), skb->len - sizeof(struct iphdr));
+		}
+	}
+
+	nf_reset(skb);
+
+	IPTUNNEL_XMIT();
+	tunnel->recursion--;
+	return 0;
+
+tx_error_icmp:
+	dst_link_failure(skb);
+
+tx_error:
+	stats->tx_errors++;
+	dev_kfree_skb(skb);
+	tunnel->recursion--;
+	return 0;
+}
+
+static int
+ipgre_tunnel_ioctl (struct net_device *dev, struct ifreq *ifr, int cmd)
+{
+	int err = 0;
+	struct ip_tunnel_parm p;
+	struct ip_tunnel *t;
+
+	switch (cmd) {
+	case SIOCGETTUNNEL:
+		t = NULL;
+		if (dev == ipgre_fb_tunnel_dev) {
+			if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p))) {
+				err = -EFAULT;
+				break;
+			}
+			t = ipgre_tunnel_locate(&p, 0);
+		}
+		if (t == NULL)
+			t = (struct ip_tunnel*)dev->priv;
+		memcpy(&p, &t->parms, sizeof(p));
+		if (copy_to_user(ifr->ifr_ifru.ifru_data, &p, sizeof(p)))
+			err = -EFAULT;
+		break;
+
+	case SIOCADDTUNNEL:
+	case SIOCCHGTUNNEL:
+		err = -EPERM;
+		if (!capable(CAP_NET_ADMIN))
+			goto done;
+
+		err = -EFAULT;
+		if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
+			goto done;
+
+		err = -EINVAL;
+		if (p.iph.version != 4 || p.iph.protocol != IPPROTO_GRE ||
+		    p.iph.ihl != 5 || (p.iph.frag_off&htons(~IP_DF)) ||
+		    ((p.i_flags|p.o_flags)&(GRE_VERSION|GRE_ROUTING)))
+			goto done;
+		if (p.iph.ttl)
+			p.iph.frag_off |= htons(IP_DF);
+
+		if (!(p.i_flags&GRE_KEY))
+			p.i_key = 0;
+		if (!(p.o_flags&GRE_KEY))
+			p.o_key = 0;
+
+		t = ipgre_tunnel_locate(&p, cmd == SIOCADDTUNNEL);
+
+		if (dev != ipgre_fb_tunnel_dev && cmd == SIOCCHGTUNNEL) {
+			if (t != NULL) {
+				if (t->dev != dev) {
+					err = -EEXIST;
+					break;
+				}
+			} else {
+				unsigned nflags=0;
+
+				t = (struct ip_tunnel*)dev->priv;
+
+				if (MULTICAST(p.iph.daddr))
+					nflags = IFF_BROADCAST;
+				else if (p.iph.daddr)
+					nflags = IFF_POINTOPOINT;
+
+				if ((dev->flags^nflags)&(IFF_POINTOPOINT|IFF_BROADCAST)) {
+					err = -EINVAL;
+					break;
+				}
+				ipgre_tunnel_unlink(t);
+				t->parms.iph.saddr = p.iph.saddr;
+				t->parms.iph.daddr = p.iph.daddr;
+				t->parms.i_key = p.i_key;
+				t->parms.o_key = p.o_key;
+				memcpy(dev->dev_addr, &p.iph.saddr, 4);
+				memcpy(dev->broadcast, &p.iph.daddr, 4);
+				ipgre_tunnel_link(t);
+				netdev_state_change(dev);
+			}
+		}
+
+		if (t) {
+			err = 0;
+			if (cmd == SIOCCHGTUNNEL) {
+				t->parms.iph.ttl = p.iph.ttl;
+				t->parms.iph.tos = p.iph.tos;
+				t->parms.iph.frag_off = p.iph.frag_off;
+			}
+			if (copy_to_user(ifr->ifr_ifru.ifru_data, &t->parms, sizeof(p)))
+				err = -EFAULT;
+		} else
+			err = (cmd == SIOCADDTUNNEL ? -ENOBUFS : -ENOENT);
+		break;
+
+	case SIOCDELTUNNEL:
+		err = -EPERM;
+		if (!capable(CAP_NET_ADMIN))
+			goto done;
+
+		if (dev == ipgre_fb_tunnel_dev) {
+			err = -EFAULT;
+			if (copy_from_user(&p, ifr->ifr_ifru.ifru_data, sizeof(p)))
+				goto done;
+			err = -ENOENT;
+			if ((t = ipgre_tunnel_locate(&p, 0)) == NULL)
+				goto done;
+			err = -EPERM;
+			if (t == ipgre_fb_tunnel_dev->priv)
+				goto done;
+			dev = t->dev;
+		}
+		err = unregister_netdevice(dev);
+		break;
+
+	default:
+		err = -EINVAL;
+	}
+
+done:
+	return err;
+}
+
+static struct net_device_stats *ipgre_tunnel_get_stats(struct net_device *dev)
+{
+	return &(((struct ip_tunnel*)dev->priv)->stat);
+}
+
+static int ipgre_tunnel_change_mtu(struct net_device *dev, int new_mtu)
+{
+	struct ip_tunnel *tunnel = (struct ip_tunnel*)dev->priv;
+	if (new_mtu < 68 || new_mtu > 0xFFF8 - tunnel->hlen)
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
+#ifdef CONFIG_NET_IPGRE_BROADCAST
+/* Nice toy. Unfortunately, useless in real life :-)
+   It allows to construct virtual multiprotocol broadcast "LAN"
+   over the Internet, provided multicast routing is tuned.
+
+
+   I have no idea was this bicycle invented before me,
+   so that I had to set ARPHRD_IPGRE to a random value.
+   I have an impression, that Cisco could make something similar,
+   but this feature is apparently missing in IOS<=11.2(8).
+   
+   I set up 10.66.66/24 and fec0:6666:6666::0/96 as virtual networks
+   with broadcast 224.66.66.66. If you have access to mbone, play with me :-)
+
+   ping -t 255 224.66.66.66
+
+   If nobody answers, mbone does not work.
+
+   ip tunnel add Universe mode gre remote 224.66.66.66 local <Your_real_addr> ttl 255
+   ip addr add 10.66.66.<somewhat>/24 dev Universe
+   ifconfig Universe up
+   ifconfig Universe add fe80::<Your_real_addr>/10
+   ifconfig Universe add fec0:6666:6666::<Your_real_addr>/96
+   ftp 10.66.66.66
+   ...
+   ftp fec0:6666:6666::193.233.7.65
+   ...
+
+ */
+
+static int ipgre_header(struct sk_buff *skb, struct net_device *dev, unsigned short type,
+			void *daddr, void *saddr, unsigned len)
+{
+	struct ip_tunnel *t = (struct ip_tunnel*)dev->priv;
+	struct iphdr *iph = (struct iphdr *)skb_push(skb, t->hlen);
+	u16 *p = (u16*)(iph+1);
+
+	memcpy(iph, &t->parms.iph, sizeof(struct iphdr));
+	p[0]		= t->parms.o_flags;
+	p[1]		= htons(type);
+
+	/*
+	 *	Set the source hardware address. 
+	 */
+	 
+	if (saddr)
+		memcpy(&iph->saddr, saddr, 4);
+
+	if (daddr) {
+		memcpy(&iph->daddr, daddr, 4);
+		return t->hlen;
+	}
+	if (iph->daddr && !MULTICAST(iph->daddr))
+		return t->hlen;
+	
+	return -t->hlen;
+}
+
+static int ipgre_open(struct net_device *dev)
+{
+	struct ip_tunnel *t = (struct ip_tunnel*)dev->priv;
+
+	if (MULTICAST(t->parms.iph.daddr)) {
+		struct flowi fl = { .oif = t->parms.link,
+				    .nl_u = { .ip4_u =
+					      { .daddr = t->parms.iph.daddr,
+						.saddr = t->parms.iph.saddr,
+						.tos = RT_TOS(t->parms.iph.tos) } },
+				    .proto = IPPROTO_GRE };
+		struct rtable *rt;
+		if (ip_route_output_key(&rt, &fl))
+			return -EADDRNOTAVAIL;
+		dev = rt->u.dst.dev;
+		ip_rt_put(rt);
+		if (__in_dev_get(dev) == NULL)
+			return -EADDRNOTAVAIL;
+		t->mlink = dev->ifindex;
+		ip_mc_inc_group(__in_dev_get(dev), t->parms.iph.daddr);
+	}
+	return 0;
+}
+
+static int ipgre_close(struct net_device *dev)
+{
+	struct ip_tunnel *t = (struct ip_tunnel*)dev->priv;
+	if (MULTICAST(t->parms.iph.daddr) && t->mlink) {
+		struct in_device *in_dev = inetdev_by_index(t->mlink);
+		if (in_dev) {
+			ip_mc_dec_group(in_dev, t->parms.iph.daddr);
+			in_dev_put(in_dev);
+		}
+	}
+	return 0;
+}
+
+#endif
+
+static void ipgre_tunnel_setup(struct net_device *dev)
+{
+	SET_MODULE_OWNER(dev);
+	dev->uninit		= ipgre_tunnel_uninit;
+	dev->destructor 	= free_netdev;
+	dev->hard_start_xmit	= ipgre_tunnel_xmit;
+	dev->get_stats		= ipgre_tunnel_get_stats;
+	dev->do_ioctl		= ipgre_tunnel_ioctl;
+	dev->change_mtu		= ipgre_tunnel_change_mtu;
+
+	dev->type		= ARPHRD_IPGRE;
+	dev->hard_header_len 	= LL_MAX_HEADER + sizeof(struct iphdr) + 4;
+	dev->mtu		= 1500 - sizeof(struct iphdr) - 4;
+	dev->flags		= IFF_NOARP;
+	dev->iflink		= 0;
+	dev->addr_len		= 4;
+}
+
+static int ipgre_tunnel_init(struct net_device *dev)
+{
+	struct net_device *tdev = NULL;
+	struct ip_tunnel *tunnel;
+	struct iphdr *iph;
+	int hlen = LL_MAX_HEADER;
+	int mtu = 1500;
+	int addend = sizeof(struct iphdr) + 4;
+
+	tunnel = (struct ip_tunnel*)dev->priv;
+	iph = &tunnel->parms.iph;
+
+	tunnel->dev = dev;
+	strcpy(tunnel->parms.name, dev->name);
+
+	memcpy(dev->dev_addr, &tunnel->parms.iph.saddr, 4);
+	memcpy(dev->broadcast, &tunnel->parms.iph.daddr, 4);
+
+	/* Guess output device to choose reasonable mtu and hard_header_len */
+
+	if (iph->daddr) {
+		struct flowi fl = { .oif = tunnel->parms.link,
+				    .nl_u = { .ip4_u =
+					      { .daddr = iph->daddr,
+						.saddr = iph->saddr,
+						.tos = RT_TOS(iph->tos) } },
+				    .proto = IPPROTO_GRE };
+		struct rtable *rt;
+		if (!ip_route_output_key(&rt, &fl)) {
+			tdev = rt->u.dst.dev;
+			ip_rt_put(rt);
+		}
+
+		dev->flags |= IFF_POINTOPOINT;
+
+#ifdef CONFIG_NET_IPGRE_BROADCAST
+		if (MULTICAST(iph->daddr)) {
+			if (!iph->saddr)
+				return -EINVAL;
+			dev->flags = IFF_BROADCAST;
+			dev->hard_header = ipgre_header;
+			dev->open = ipgre_open;
+			dev->stop = ipgre_close;
+		}
+#endif
+	}
+
+	if (!tdev && tunnel->parms.link)
+		tdev = __dev_get_by_index(tunnel->parms.link);
+
+	if (tdev) {
+		hlen = tdev->hard_header_len;
+		mtu = tdev->mtu;
+	}
+	dev->iflink = tunnel->parms.link;
+
+	/* Precalculate GRE options length */
+	if (tunnel->parms.o_flags&(GRE_CSUM|GRE_KEY|GRE_SEQ)) {
+		if (tunnel->parms.o_flags&GRE_CSUM)
+			addend += 4;
+		if (tunnel->parms.o_flags&GRE_KEY)
+			addend += 4;
+		if (tunnel->parms.o_flags&GRE_SEQ)
+			addend += 4;
+	}
+	dev->hard_header_len = hlen + addend;
+	dev->mtu = mtu - addend;
+	tunnel->hlen = addend;
+	return 0;
+}
+
+int __init ipgre_fb_tunnel_init(struct net_device *dev)
+{
+	struct ip_tunnel *tunnel = (struct ip_tunnel*)dev->priv;
+	struct iphdr *iph = &tunnel->parms.iph;
+
+	tunnel->dev = dev;
+	strcpy(tunnel->parms.name, dev->name);
+
+	iph->version		= 4;
+	iph->protocol		= IPPROTO_GRE;
+	iph->ihl		= 5;
+	tunnel->hlen		= sizeof(struct iphdr) + 4;
+
+	dev_hold(dev);
+	tunnels_wc[0]		= tunnel;
+	return 0;
+}
+
+
+static struct net_protocol ipgre_protocol = {
+	.handler	=	ipgre_rcv,
+	.err_handler	=	ipgre_err,
+};
+
+
+/*
+ *	And now the modules code and kernel interface.
+ */
+
+static int __init ipgre_init(void)
+{
+	int err;
+
+	printk(KERN_INFO "GRE over IPv4 tunneling driver\n");
+
+	if (inet_add_protocol(&ipgre_protocol, IPPROTO_GRE) < 0) {
+		printk(KERN_INFO "ipgre init: can't add protocol\n");
+		return -EAGAIN;
+	}
+
+	ipgre_fb_tunnel_dev = alloc_netdev(sizeof(struct ip_tunnel), "gre0",
+					   ipgre_tunnel_setup);
+	if (!ipgre_fb_tunnel_dev) {
+		err = -ENOMEM;
+		goto err1;
+	}
+
+	ipgre_fb_tunnel_dev->init = ipgre_fb_tunnel_init;
+
+	if ((err = register_netdev(ipgre_fb_tunnel_dev)))
+		goto err2;
+out:
+	return err;
+err2:
+	free_netdev(ipgre_fb_tunnel_dev);
+err1:
+	inet_del_protocol(&ipgre_protocol, IPPROTO_GRE);
+	goto out;
+}
+
+static void ipgre_fini(void)
+{
+	if (inet_del_protocol(&ipgre_protocol, IPPROTO_GRE) < 0)
+		printk(KERN_INFO "ipgre close: can't remove protocol\n");
+
+	unregister_netdev(ipgre_fb_tunnel_dev);
+}
+
+module_init(ipgre_init);
+module_exit(ipgre_fini);
+MODULE_LICENSE("GPL");