xref: /linux/net/ipv4/gre_demux.c (revision 621cde16e49b3ecf7d59a8106a20aaebfb4a59a9)
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 
gre_add_protocol(const struct gre_protocol * proto,u8 version)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 
gre_del_protocol(const struct gre_protocol * proto,u8 version)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  */
gre_parse_header(struct sk_buff * skb,struct tnl_ptk_info * tpi,bool * csum_err,__be16 proto,int nhs)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 
gre_rcv(struct sk_buff * skb)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 
gre_err(struct sk_buff * skb,u32 info)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 
gre_init(void)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 
gre_exit(void)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