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/if.h>
 17#include <linux/icmp.h>
 18#include <linux/kernel.h>
 19#include <linux/kmod.h>
 20#include <linux/skbuff.h>
 21#include <linux/in.h>
 22#include <linux/ip.h>
 23#include <linux/netdevice.h>
 24#include <linux/if_tunnel.h>
 25#include <linux/spinlock.h>
 26#include <net/protocol.h>
 27#include <net/gre.h>
 28
 29#include <net/icmp.h>
 30#include <net/route.h>
 31#include <net/xfrm.h>
 32
 33static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
 34
 35int gre_add_protocol(const struct gre_protocol *proto, u8 version)
 36{
 37	if (version >= GREPROTO_MAX)
 38		return -EINVAL;
 39
 40	return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
 41		0 : -EBUSY;
 42}
 43EXPORT_SYMBOL_GPL(gre_add_protocol);
 44
 45int gre_del_protocol(const struct gre_protocol *proto, u8 version)
 46{
 47	int ret;
 48
 49	if (version >= GREPROTO_MAX)
 50		return -EINVAL;
 51
 52	ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
 53		0 : -EBUSY;
 54
 55	if (ret)
 56		return ret;
 57
 58	synchronize_rcu();
 59	return 0;
 60}
 61EXPORT_SYMBOL_GPL(gre_del_protocol);
 62
 63/* Fills in tpi and returns header length to be pulled. */
 64int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 65		     bool *csum_err, __be16 proto, int nhs)
 66{
 67	const struct gre_base_hdr *greh;
 68	__be32 *options;
 69	int hdr_len;
 70
 71	if (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))
 72		return -EINVAL;
 73
 74	greh = (struct gre_base_hdr *)(skb->data + nhs);
 75	if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
 76		return -EINVAL;
 77
 78	tpi->flags = gre_flags_to_tnl_flags(greh->flags);
 79	hdr_len = gre_calc_hlen(tpi->flags);
 80
 81	if (!pskb_may_pull(skb, nhs + hdr_len))
 82		return -EINVAL;
 83
 84	greh = (struct gre_base_hdr *)(skb->data + nhs);
 85	tpi->proto = greh->protocol;
 86
 87	options = (__be32 *)(greh + 1);
 88	if (greh->flags & GRE_CSUM) {
 89		if (skb_checksum_simple_validate(skb)) {
 90			*csum_err = true;
 91			return -EINVAL;
 92		}
 93
 94		skb_checksum_try_convert(skb, IPPROTO_GRE, 0,
 95					 null_compute_pseudo);
 96		options++;
 97	}
 98
 99	if (greh->flags & GRE_KEY) {
100		tpi->key = *options;
101		options++;
102	} else {
103		tpi->key = 0;
104	}
105	if (unlikely(greh->flags & GRE_SEQ)) {
106		tpi->seq = *options;
107		options++;
108	} else {
109		tpi->seq = 0;
110	}
111	/* WCCP version 1 and 2 protocol decoding.
112	 * - Change protocol to IPv4/IPv6
113	 * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
114	 */
115	if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
116		tpi->proto = proto;
117		if ((*(u8 *)options & 0xF0) != 0x40)
118			hdr_len += 4;
119	}
120	tpi->hdr_len = hdr_len;
121	return hdr_len;
122}
123EXPORT_SYMBOL(gre_parse_header);
124
125static int gre_rcv(struct sk_buff *skb)
126{
127	const struct gre_protocol *proto;
128	u8 ver;
129	int ret;
130
131	if (!pskb_may_pull(skb, 12))
132		goto drop;
133
134	ver = skb->data[1]&0x7f;
135	if (ver >= GREPROTO_MAX)
136		goto drop;
137
138	rcu_read_lock();
139	proto = rcu_dereference(gre_proto[ver]);
140	if (!proto || !proto->handler)
141		goto drop_unlock;
142	ret = proto->handler(skb);
143	rcu_read_unlock();
144	return ret;
145
146drop_unlock:
147	rcu_read_unlock();
148drop:
149	kfree_skb(skb);
150	return NET_RX_DROP;
151}
152
153static void gre_err(struct sk_buff *skb, u32 info)
154{
155	const struct gre_protocol *proto;
156	const struct iphdr *iph = (const struct iphdr *)skb->data;
157	u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
158
159	if (ver >= GREPROTO_MAX)
160		return;
161
162	rcu_read_lock();
163	proto = rcu_dereference(gre_proto[ver]);
164	if (proto && proto->err_handler)
165		proto->err_handler(skb, info);
166	rcu_read_unlock();
167}
168
169static const struct net_protocol net_gre_protocol = {
170	.handler     = gre_rcv,
171	.err_handler = gre_err,
172	.netns_ok    = 1,
173};
174
175static int __init gre_init(void)
176{
177	pr_info("GRE over IPv4 demultiplexor driver\n");
178
179	if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
180		pr_err("can't add protocol\n");
181		return -EAGAIN;
182	}
183	return 0;
184}
185
186static void __exit gre_exit(void)
187{
188	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
189}
190
191module_init(gre_init);
192module_exit(gre_exit);
193
194MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
195MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
196MODULE_LICENSE("GPL");