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
29 static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
30
31 int 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 }
39 EXPORT_SYMBOL_GPL(gre_add_protocol);
40
41 int 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 }
57 EXPORT_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 */
62 int 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 gre_flags_to_tnl_flags(tpi->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 }
144 EXPORT_SYMBOL(gre_parse_header);
145
146 static 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
167 drop_unlock:
168 rcu_read_unlock();
169 drop:
170 kfree_skb(skb);
171 return NET_RX_DROP;
172 }
173
174 static 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
195 static const struct net_protocol net_gre_protocol = {
196 .handler = gre_rcv,
197 .err_handler = gre_err,
198 };
199
200 static 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
211 static void __exit gre_exit(void)
212 {
213 inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
214 }
215
216 module_init(gre_init);
217 module_exit(gre_exit);
218
219 MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
220 MODULE_AUTHOR("D. Kozlov <xeb@mail.ru>");
221 MODULE_LICENSE("GPL");
222
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