gre_demux.c revision 4749c09c37030ccdc44aecebe0f71b02a377fc14 
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;
34static struct gre_cisco_protocol __rcu *gre_cisco_proto_list[GRE_IP_PROTO_MAX];
35
36int gre_add_protocol(const struct gre_protocol *proto, u8 version)
37{
38	if (version >= GREPROTO_MAX)
39		return -EINVAL;
40
41	return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
42		0 : -EBUSY;
43}
44EXPORT_SYMBOL_GPL(gre_add_protocol);
45
46int gre_del_protocol(const struct gre_protocol *proto, u8 version)
47{
48	int ret;
49
50	if (version >= GREPROTO_MAX)
51		return -EINVAL;
52
53	ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
54		0 : -EBUSY;
55
56	if (ret)
57		return ret;
58
59	synchronize_rcu();
60	return 0;
61}
62EXPORT_SYMBOL_GPL(gre_del_protocol);
63
64void gre_build_header(struct sk_buff *skb, const struct tnl_ptk_info *tpi,
65		      int hdr_len)
66{
67	struct gre_base_hdr *greh;
68
69	skb_push(skb, hdr_len);
70
71	greh = (struct gre_base_hdr *)skb->data;
72	greh->flags = tnl_flags_to_gre_flags(tpi->flags);
73	greh->protocol = tpi->proto;
74
75	if (tpi->flags&(TUNNEL_KEY|TUNNEL_CSUM|TUNNEL_SEQ)) {
76		__be32 *ptr = (__be32 *)(((u8 *)greh) + hdr_len - 4);
77
78		if (tpi->flags&TUNNEL_SEQ) {
79			*ptr = tpi->seq;
80			ptr--;
81		}
82		if (tpi->flags&TUNNEL_KEY) {
83			*ptr = tpi->key;
84			ptr--;
85		}
86		if (tpi->flags&TUNNEL_CSUM &&
87		    !(skb_shinfo(skb)->gso_type &
88		      (SKB_GSO_GRE|SKB_GSO_GRE_CSUM))) {
89			*ptr = 0;
90			*(__sum16 *)ptr = csum_fold(skb_checksum(skb, 0,
91								 skb->len, 0));
92		}
93	}
94}
95EXPORT_SYMBOL_GPL(gre_build_header);
96
97static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
98			    bool *csum_err)
99{
100	unsigned int ip_hlen = ip_hdrlen(skb);
101	const struct gre_base_hdr *greh;
102	__be32 *options;
103	int hdr_len;
104
105	if (unlikely(!pskb_may_pull(skb, sizeof(struct gre_base_hdr))))
106		return -EINVAL;
107
108	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
109	if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
110		return -EINVAL;
111
112	tpi->flags = gre_flags_to_tnl_flags(greh->flags);
113	hdr_len = ip_gre_calc_hlen(tpi->flags);
114
115	if (!pskb_may_pull(skb, hdr_len))
116		return -EINVAL;
117
118	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
119	tpi->proto = greh->protocol;
120
121	options = (__be32 *)(greh + 1);
122	if (greh->flags & GRE_CSUM) {
123		if (skb_checksum_simple_validate(skb)) {
124			*csum_err = true;
125			return -EINVAL;
126		}
127		options++;
128	}
129
130	if (greh->flags & GRE_KEY) {
131		tpi->key = *options;
132		options++;
133	} else
134		tpi->key = 0;
135
136	if (unlikely(greh->flags & GRE_SEQ)) {
137		tpi->seq = *options;
138		options++;
139	} else
140		tpi->seq = 0;
141
142	/* WCCP version 1 and 2 protocol decoding.
143	 * - Change protocol to IP
144	 * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
145	 */
146	if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
147		tpi->proto = htons(ETH_P_IP);
148		if ((*(u8 *)options & 0xF0) != 0x40) {
149			hdr_len += 4;
150			if (!pskb_may_pull(skb, hdr_len))
151				return -EINVAL;
152		}
153	}
154
155	return iptunnel_pull_header(skb, hdr_len, tpi->proto);
156}
157
158static int gre_cisco_rcv(struct sk_buff *skb)
159{
160	struct tnl_ptk_info tpi;
161	int i;
162	bool csum_err = false;
163
164#ifdef CONFIG_NET_IPGRE_BROADCAST
165	if (ipv4_is_multicast(ip_hdr(skb)->daddr)) {
166		/* Looped back packet, drop it! */
167		if (rt_is_output_route(skb_rtable(skb)))
168			goto drop;
169	}
170#endif
171
172	if (parse_gre_header(skb, &tpi, &csum_err) < 0)
173		goto drop;
174
175	rcu_read_lock();
176	for (i = 0; i < GRE_IP_PROTO_MAX; i++) {
177		struct gre_cisco_protocol *proto;
178		int ret;
179
180		proto = rcu_dereference(gre_cisco_proto_list[i]);
181		if (!proto)
182			continue;
183		ret = proto->handler(skb, &tpi);
184		if (ret == PACKET_RCVD) {
185			rcu_read_unlock();
186			return 0;
187		}
188	}
189	rcu_read_unlock();
190
191	icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
192drop:
193	kfree_skb(skb);
194	return 0;
195}
196
197static void gre_cisco_err(struct sk_buff *skb, u32 info)
198{
199	/* All the routers (except for Linux) return only
200	 * 8 bytes of packet payload. It means, that precise relaying of
201	 * ICMP in the real Internet is absolutely infeasible.
202	 *
203	 * Moreover, Cisco "wise men" put GRE key to the third word
204	 * in GRE header. It makes impossible maintaining even soft
205	 * state for keyed
206	 * GRE tunnels with enabled checksum. Tell them "thank you".
207	 *
208	 * Well, I wonder, rfc1812 was written by Cisco employee,
209	 * what the hell these idiots break standards established
210	 * by themselves???
211	 */
212
213	const int type = icmp_hdr(skb)->type;
214	const int code = icmp_hdr(skb)->code;
215	struct tnl_ptk_info tpi;
216	bool csum_err = false;
217	int i;
218
219	if (parse_gre_header(skb, &tpi, &csum_err)) {
220		if (!csum_err)		/* ignore csum errors. */
221			return;
222	}
223
224	if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
225		ipv4_update_pmtu(skb, dev_net(skb->dev), info,
226				skb->dev->ifindex, 0, IPPROTO_GRE, 0);
227		return;
228	}
229	if (type == ICMP_REDIRECT) {
230		ipv4_redirect(skb, dev_net(skb->dev), skb->dev->ifindex, 0,
231				IPPROTO_GRE, 0);
232		return;
233	}
234
235	rcu_read_lock();
236	for (i = 0; i < GRE_IP_PROTO_MAX; i++) {
237		struct gre_cisco_protocol *proto;
238
239		proto = rcu_dereference(gre_cisco_proto_list[i]);
240		if (!proto)
241			continue;
242
243		if (proto->err_handler(skb, info, &tpi) == PACKET_RCVD)
244			goto out;
245
246	}
247out:
248	rcu_read_unlock();
249}
250
251static int gre_rcv(struct sk_buff *skb)
252{
253	const struct gre_protocol *proto;
254	u8 ver;
255	int ret;
256
257	if (!pskb_may_pull(skb, 12))
258		goto drop;
259
260	ver = skb->data[1]&0x7f;
261	if (ver >= GREPROTO_MAX)
262		goto drop;
263
264	rcu_read_lock();
265	proto = rcu_dereference(gre_proto[ver]);
266	if (!proto || !proto->handler)
267		goto drop_unlock;
268	ret = proto->handler(skb);
269	rcu_read_unlock();
270	return ret;
271
272drop_unlock:
273	rcu_read_unlock();
274drop:
275	kfree_skb(skb);
276	return NET_RX_DROP;
277}
278
279static void gre_err(struct sk_buff *skb, u32 info)
280{
281	const struct gre_protocol *proto;
282	const struct iphdr *iph = (const struct iphdr *)skb->data;
283	u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
284
285	if (ver >= GREPROTO_MAX)
286		return;
287
288	rcu_read_lock();
289	proto = rcu_dereference(gre_proto[ver]);
290	if (proto && proto->err_handler)
291		proto->err_handler(skb, info);
292	rcu_read_unlock();
293}
294
295static const struct net_protocol net_gre_protocol = {
296	.handler     = gre_rcv,
297	.err_handler = gre_err,
298	.netns_ok    = 1,
299};
300
301static const struct gre_protocol ipgre_protocol = {
302	.handler     = gre_cisco_rcv,
303	.err_handler = gre_cisco_err,
304};
305
306int gre_cisco_register(struct gre_cisco_protocol *newp)
307{
308	struct gre_cisco_protocol **proto = (struct gre_cisco_protocol **)
309					    &gre_cisco_proto_list[newp->priority];
310
311	return (cmpxchg(proto, NULL, newp) == NULL) ? 0 : -EBUSY;
312}
313EXPORT_SYMBOL_GPL(gre_cisco_register);
314
315int gre_cisco_unregister(struct gre_cisco_protocol *del_proto)
316{
317	struct gre_cisco_protocol **proto = (struct gre_cisco_protocol **)
318					    &gre_cisco_proto_list[del_proto->priority];
319	int ret;
320
321	ret = (cmpxchg(proto, del_proto, NULL) == del_proto) ? 0 : -EINVAL;
322
323	if (ret)
324		return ret;
325
326	synchronize_net();
327	return 0;
328}
329EXPORT_SYMBOL_GPL(gre_cisco_unregister);
330
331static int __init gre_init(void)
332{
333	pr_info("GRE over IPv4 demultiplexor driver\n");
334
335	if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
336		pr_err("can't add protocol\n");
337		goto err;
338	}
339
340	if (gre_add_protocol(&ipgre_protocol, GREPROTO_CISCO) < 0) {
341		pr_info("%s: can't add ipgre handler\n", __func__);
342		goto err_gre;
343	}
344
345	return 0;
346err_gre:
347	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
348err:
349	return -EAGAIN;
350}
351
352static void __exit gre_exit(void)
353{
354	gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
355	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
356}
357
358module_init(gre_init);
359module_exit(gre_exit);
360
361MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
362MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
363MODULE_LICENSE("GPL");
364