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Linux/net/ipv4/gre_demux.c

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  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 
 33 static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
 34 
 35 int 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 }
 43 EXPORT_SYMBOL_GPL(gre_add_protocol);
 44 
 45 int 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 }
 61 EXPORT_SYMBOL_GPL(gre_del_protocol);
 62 
 63 /* Fills in tpi and returns header length to be pulled. */
 64 int 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 }
123 EXPORT_SYMBOL(gre_parse_header);
124 
125 static 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 
146 drop_unlock:
147         rcu_read_unlock();
148 drop:
149         kfree_skb(skb);
150         return NET_RX_DROP;
151 }
152 
153 static 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 
169 static const struct net_protocol net_gre_protocol = {
170         .handler     = gre_rcv,
171         .err_handler = gre_err,
172         .netns_ok    = 1,
173 };
174 
175 static 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 
186 static void __exit gre_exit(void)
187 {
188         inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
189 }
190 
191 module_init(gre_init);
192 module_exit(gre_exit);
193 
194 MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
195 MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
196 MODULE_LICENSE("GPL");
197 

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