1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 *	GRE over IPv4 demultiplexer driver
4 *
5 *	Authors: Dmitry Kozlov (xeb@mail.ru)
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/module.h>
11#include <linux/if.h>
12#include <linux/icmp.h>
13#include <linux/kernel.h>
14#include <linux/kmod.h>
15#include <linux/skbuff.h>
16#include <linux/in.h>
17#include <linux/ip.h>
18#include <linux/netdevice.h>
19#include <linux/if_tunnel.h>
20#include <linux/spinlock.h>
21#include <net/protocol.h>
22#include <net/gre.h>
23#include <net/erspan.h>
24
25#include <net/icmp.h>
26#include <net/route.h>
27#include <net/xfrm.h>
28
29static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
30
31int gre_add_protocol(const struct gre_protocol *proto, u8 version)
32{
33	if (version >= GREPROTO_MAX)
34		return -EINVAL;
35
36	return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
37		0 : -EBUSY;
38}
39EXPORT_SYMBOL_GPL(gre_add_protocol);
40
41int gre_del_protocol(const struct gre_protocol *proto, u8 version)
42{
43	int ret;
44
45	if (version >= GREPROTO_MAX)
46		return -EINVAL;
47
48	ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
49		0 : -EBUSY;
50
51	if (ret)
52		return ret;
53
54	synchronize_rcu();
55	return 0;
56}
57EXPORT_SYMBOL_GPL(gre_del_protocol);
58
59/* Fills in tpi and returns header length to be pulled.
60 * Note that caller must use pskb_may_pull() before pulling GRE header.
61 */
62int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
63		     bool *csum_err, __be16 proto, int nhs)
64{
65	const struct gre_base_hdr *greh;
66	__be32 *options;
67	int hdr_len;
68
69	if (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))
70		return -EINVAL;
71
72	greh = (struct gre_base_hdr *)(skb->data + nhs);
73	if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
74		return -EINVAL;
75
76	tpi->flags = gre_flags_to_tnl_flags(greh->flags);
77	hdr_len = gre_calc_hlen(tpi->flags);
78
79	if (!pskb_may_pull(skb, nhs + hdr_len))
80		return -EINVAL;
81
82	greh = (struct gre_base_hdr *)(skb->data + nhs);
83	tpi->proto = greh->protocol;
84
85	options = (__be32 *)(greh + 1);
86	if (greh->flags & GRE_CSUM) {
87		if (!skb_checksum_simple_validate(skb)) {
88			skb_checksum_try_convert(skb, IPPROTO_GRE,
89						 null_compute_pseudo);
90		} else if (csum_err) {
91			*csum_err = true;
92			return -EINVAL;
93		}
94
95		options++;
96	}
97
98	if (greh->flags & GRE_KEY) {
99		tpi->key = *options;
100		options++;
101	} else {
102		tpi->key = 0;
103	}
104	if (unlikely(greh->flags & GRE_SEQ)) {
105		tpi->seq = *options;
106		options++;
107	} else {
108		tpi->seq = 0;
109	}
110	/* WCCP version 1 and 2 protocol decoding.
111	 * - Change protocol to IPv4/IPv6
112	 * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
113	 */
114	if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
115		u8 _val, *val;
116
117		val = skb_header_pointer(skb, nhs + hdr_len,
118					 sizeof(_val), &_val);
119		if (!val)
120			return -EINVAL;
121		tpi->proto = proto;
122		if ((*val & 0xF0) != 0x40)
123			hdr_len += 4;
124	}
125	tpi->hdr_len = hdr_len;
126
127	/* ERSPAN ver 1 and 2 protocol sets GRE key field
128	 * to 0 and sets the configured key in the
129	 * inner erspan header field
130	 */
131	if ((greh->protocol == htons(ETH_P_ERSPAN) && hdr_len != 4) ||
132	    greh->protocol == htons(ETH_P_ERSPAN2)) {
133		struct erspan_base_hdr *ershdr;
134
135		if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
136			return -EINVAL;
137
138		ershdr = (struct erspan_base_hdr *)(skb->data + nhs + hdr_len);
139		tpi->key = cpu_to_be32(get_session_id(ershdr));
140	}
141
142	return hdr_len;
143}
144EXPORT_SYMBOL(gre_parse_header);
145
146static int gre_rcv(struct sk_buff *skb)
147{
148	const struct gre_protocol *proto;
149	u8 ver;
150	int ret;
151
152	if (!pskb_may_pull(skb, 12))
153		goto drop;
154
155	ver = skb->data[1]&0x7f;
156	if (ver >= GREPROTO_MAX)
157		goto drop;
158
159	rcu_read_lock();
160	proto = rcu_dereference(gre_proto[ver]);
161	if (!proto || !proto->handler)
162		goto drop_unlock;
163	ret = proto->handler(skb);
164	rcu_read_unlock();
165	return ret;
166
167drop_unlock:
168	rcu_read_unlock();
169drop:
170	kfree_skb(skb);
171	return NET_RX_DROP;
172}
173
174static int gre_err(struct sk_buff *skb, u32 info)
175{
176	const struct gre_protocol *proto;
177	const struct iphdr *iph = (const struct iphdr *)skb->data;
178	u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
179	int err = 0;
180
181	if (ver >= GREPROTO_MAX)
182		return -EINVAL;
183
184	rcu_read_lock();
185	proto = rcu_dereference(gre_proto[ver]);
186	if (proto && proto->err_handler)
187		proto->err_handler(skb, info);
188	else
189		err = -EPROTONOSUPPORT;
190	rcu_read_unlock();
191
192	return err;
193}
194
195static const struct net_protocol net_gre_protocol = {
196	.handler     = gre_rcv,
197	.err_handler = gre_err,
198};
199
200static int __init gre_init(void)
201{
202	pr_info("GRE over IPv4 demultiplexor driver\n");
203
204	if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
205		pr_err("can't add protocol\n");
206		return -EAGAIN;
207	}
208	return 0;
209}
210
211static void __exit gre_exit(void)
212{
213	inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
214}
215
216module_init(gre_init);
217module_exit(gre_exit);
218
219MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
220MODULE_AUTHOR("D. Kozlov <xeb@mail.ru>");
221MODULE_LICENSE("GPL");
222