net/ipv4/gre_demux.c

   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 int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
  61                      bool *csum_err, __be16 proto, int nhs)
  62 {
  63         const struct gre_base_hdr *greh;
  64         __be32 *options;
  65         int hdr_len;
  66
  67         if (unlikely(!pskb_may_pull(skb, nhs + sizeof(struct gre_base_hdr))))
  68                 return -EINVAL;
  69
  70         greh = (struct gre_base_hdr *)(skb->data + nhs);
  71         if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
  72                 return -EINVAL;
  73
  74         tpi->flags = gre_flags_to_tnl_flags(greh->flags);
  75         hdr_len = gre_calc_hlen(tpi->flags);
  76
  77         if (!pskb_may_pull(skb, nhs + hdr_len))
  78                 return -EINVAL;
  79
  80         greh = (struct gre_base_hdr *)(skb->data + nhs);
  81         tpi->proto = greh->protocol;
  82
  83         options = (__be32 *)(greh + 1);
  84         if (greh->flags & GRE_CSUM) {
  85                 if (!skb_checksum_simple_validate(skb)) {
  86                         skb_checksum_try_convert(skb, IPPROTO_GRE,
  87                                                  null_compute_pseudo);
  88                 } else if (csum_err) {
  89                         *csum_err = true;
  90                         return -EINVAL;
  91                 }
  92
  93                 options++;
  94         }
  95
  96         if (greh->flags & GRE_KEY) {
  97                 tpi->key = *options;
  98                 options++;
  99         } else {
 100                 tpi->key = 0;
 101         }
 102         if (unlikely(greh->flags & GRE_SEQ)) {
 103                 tpi->seq = *options;
 104                 options++;
 105         } else {
 106                 tpi->seq = 0;
 107         }
 108         /* WCCP version 1 and 2 protocol decoding.
 109          * - Change protocol to IPv4/IPv6
 110          * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
 111          */
 112         if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
 113                 tpi->proto = proto;
 114                 if ((*(u8 *)options & 0xF0) != 0x40)
 115                         hdr_len += 4;
 116         }
 117         tpi->hdr_len = hdr_len;
 118
 119         /* ERSPAN ver 1 and 2 protocol sets GRE key field
 120          * to 0 and sets the configured key in the
 121          * inner erspan header field
 122          */
 123         if (greh->protocol == htons(ETH_P_ERSPAN) ||
 124             greh->protocol == htons(ETH_P_ERSPAN2)) {
 125                 struct erspan_base_hdr *ershdr;
 126
 127                 if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
 128                         return -EINVAL;
 129
 130                 ershdr = (struct erspan_base_hdr *)options;
 131                 tpi->key = cpu_to_be32(get_session_id(ershdr));
 132         }
 133
 134         return hdr_len;
 135 }
 136 EXPORT_SYMBOL(gre_parse_header);
 137
 138 static int gre_rcv(struct sk_buff *skb)
 139 {
 140         const struct gre_protocol *proto;
 141         u8 ver;
 142         int ret;
 143
 144         if (!pskb_may_pull(skb, 12))
 145                 goto drop;
 146
 147         ver = skb->data[1]&0x7f;
 148         if (ver >= GREPROTO_MAX)
 149                 goto drop;
 150
 151         rcu_read_lock();
 152         proto = rcu_dereference(gre_proto[ver]);
 153         if (!proto || !proto->handler)
 154                 goto drop_unlock;
 155         ret = proto->handler(skb);
 156         rcu_read_unlock();
 157         return ret;
 158
 159 drop_unlock:
 160         rcu_read_unlock();
 161 drop:
 162         kfree_skb(skb);
 163         return NET_RX_DROP;
 164 }
 165
 166 static int gre_err(struct sk_buff *skb, u32 info)
 167 {
 168         const struct gre_protocol *proto;
 169         const struct iphdr *iph = (const struct iphdr *)skb->data;
 170         u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
 171         int err = 0;
 172
 173         if (ver >= GREPROTO_MAX)
 174                 return -EINVAL;
 175
 176         rcu_read_lock();
 177         proto = rcu_dereference(gre_proto[ver]);
 178         if (proto && proto->err_handler)
 179                 proto->err_handler(skb, info);
 180         else
 181                 err = -EPROTONOSUPPORT;
 182         rcu_read_unlock();
 183
 184         return err;
 185 }
 186
 187 static const struct net_protocol net_gre_protocol = {
 188         .handler     = gre_rcv,
 189         .err_handler = gre_err,
 190         .netns_ok    = 1,
 191 };
 192
 193 static int __init gre_init(void)
 194 {
 195         pr_info("GRE over IPv4 demultiplexor driver\n");
 196
 197         if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
 198                 pr_err("can't add protocol\n");
 199                 return -EAGAIN;
 200         }
 201         return 0;
 202 }
 203
 204 static void __exit gre_exit(void)
 205 {
 206         inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
 207 }
 208
 209 module_init(gre_init);
 210 module_exit(gre_exit);
 211
 212 MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
 213 MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
 214 MODULE_LICENSE("GPL");