net/ipv4/gre_demux.c

   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");