1/*
  2 *	GRE over IPv4 demultiplexer driver
  3 *
  4 *	Authors: Dmitry Kozlov (xeb@mail.ru)
  5 *
  6 *	This program is free software; you can redistribute it and/or
  7 *	modify it under the terms of the GNU General Public License
  8 *	as published by the Free Software Foundation; either version
  9 *	2 of the License, or (at your option) any later version.
 10 *
 11 */
 12
 13#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 14
 15#include <linux/module.h>
 16#include <linux/kernel.h>
 17#include <linux/kmod.h>
 18#include <linux/skbuff.h>
 19#include <linux/in.h>
 20#include <linux/ip.h>
 21#include <linux/netdevice.h>
 22#include <linux/spinlock.h>
 23#include <net/protocol.h>
 24#include <net/gre.h>
 25
 26
 27static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
 28static DEFINE_SPINLOCK(gre_proto_lock);
 29
 30int gre_add_protocol(const struct gre_protocol *proto, u8 version)
 31{
 32	if (version >= GREPROTO_MAX)
 33		goto err_out;
 34
 35	spin_lock(&gre_proto_lock);
 36	if (gre_proto[version])
 37		goto err_out_unlock;
 38
 39	RCU_INIT_POINTER(gre_proto[version], proto);
 40	spin_unlock(&gre_proto_lock);
 41	return 0;
 42
 43err_out_unlock:
 44	spin_unlock(&gre_proto_lock);
 45err_out:
 46	return -1;
 47}
 48EXPORT_SYMBOL_GPL(gre_add_protocol);
 49
 50int gre_del_protocol(const struct gre_protocol *proto, u8 version)
 51{
 52	if (version >= GREPROTO_MAX)
 53		goto err_out;
 54
 55	spin_lock(&gre_proto_lock);
 56	if (rcu_dereference_protected(gre_proto[version],
 57			lockdep_is_held(&gre_proto_lock)) != proto)
 58		goto err_out_unlock;
 59	RCU_INIT_POINTER(gre_proto[version], NULL);
 60	spin_unlock(&gre_proto_lock);
 61	synchronize_rcu();
 62	return 0;
 63
 64err_out_unlock:
 65	spin_unlock(&gre_proto_lock);
 66err_out:
 67	return -1;
 68}
 69EXPORT_SYMBOL_GPL(gre_del_protocol);
 70
 71static int gre_rcv(struct sk_buff *skb)
 72{
 73	const struct gre_protocol *proto;
 74	u8 ver;
 75	int ret;
 76
 77	if (!pskb_may_pull(skb, 12))
 78		goto drop;
 79
 80	ver = skb->data[1]&0x7f;
 81	if (ver >= GREPROTO_MAX)
 82		goto drop;
 83
 84	rcu_read_lock();
 85	proto = rcu_dereference(gre_proto[ver]);
 86	if (!proto || !proto->handler)
 87		goto drop_unlock;
 88	ret = proto->handler(skb);
 89	rcu_read_unlock();
 90	return ret;
 91
 92drop_unlock:
 93	rcu_read_unlock();
 94drop:
 95	kfree_skb(skb);
 96	return NET_RX_DROP;
 97}
 98
 99static void gre_err(struct sk_buff *skb, u32 info)
100{
101	const struct gre_protocol *proto;
102	const struct iphdr *iph = (const struct iphdr *)skb->data;
103	u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
104
105	if (ver >= GREPROTO_MAX)
106		return;
107
108	rcu_read_lock();
109	proto = rcu_dereference(gre_proto[ver]);
110	if (proto && proto->err_handler)
111		proto->err_handler(skb, info);
112	rcu_read_unlock();
113}
114
115static const struct net_protocol net_gre_protocol = {
116	.handler     = gre_rcv,
117	.err_handler = gre_err,
118	.netns_ok    = 1,
119};
120
121static int __init gre_init(void)
122{
123	pr_info("GRE over IPv4 demultiplexor driver\n");
124
125	if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
126		pr_err("can't add protocol\n");
127		return -EAGAIN;
128	}
129
130	return 0;
131}
132
133static void __exit gre_exit(void)
134{
135	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
136}
137
138module_init(gre_init);
139module_exit(gre_exit);
140
141MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
142MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
143MODULE_LICENSE("GPL");
144