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 static struct gre_cisco_protocol __rcu *gre_cisco_proto_list[GRE_IP_PROTO_MAX];
  35
  36 int gre_add_protocol(const struct gre_protocol *proto, u8 version)
  37 {
  38         if (version >= GREPROTO_MAX)
  39                 return -EINVAL;
  40
  41         return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
  42                 0 : -EBUSY;
  43 }
  44 EXPORT_SYMBOL_GPL(gre_add_protocol);
  45
  46 int gre_del_protocol(const struct gre_protocol *proto, u8 version)
  47 {
  48         int ret;
  49
  50         if (version >= GREPROTO_MAX)
  51                 return -EINVAL;
  52
  53         ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
  54                 0 : -EBUSY;
  55
  56         if (ret)
  57                 return ret;
  58
  59         synchronize_rcu();
  60         return 0;
  61 }
  62 EXPORT_SYMBOL_GPL(gre_del_protocol);
  63
  64 void gre_build_header(struct sk_buff *skb, const struct tnl_ptk_info *tpi,
  65                       int hdr_len)
  66 {
  67         struct gre_base_hdr *greh;
  68
  69         skb_push(skb, hdr_len);
  70
  71         greh = (struct gre_base_hdr *)skb->data;
  72         greh->flags = tnl_flags_to_gre_flags(tpi->flags);
  73         greh->protocol = tpi->proto;
  74
  75         if (tpi->flags&(TUNNEL_KEY|TUNNEL_CSUM|TUNNEL_SEQ)) {
  76                 __be32 *ptr = (__be32 *)(((u8 *)greh) + hdr_len - 4);
  77
  78                 if (tpi->flags&TUNNEL_SEQ) {
  79                         *ptr = tpi->seq;
  80                         ptr--;
  81                 }
  82                 if (tpi->flags&TUNNEL_KEY) {
  83                         *ptr = tpi->key;
  84                         ptr--;
  85                 }
  86                 if (tpi->flags&TUNNEL_CSUM &&
  87                     !(skb_shinfo(skb)->gso_type & SKB_GSO_GRE)) {
  88                         *ptr = 0;
  89                         *(__sum16 *)ptr = csum_fold(skb_checksum(skb, 0,
  90                                                                  skb->len, 0));
  91                 }
  92         }
  93 }
  94 EXPORT_SYMBOL_GPL(gre_build_header);
  95
  96 struct sk_buff *gre_handle_offloads(struct sk_buff *skb, bool gre_csum)
  97 {
  98         int err;
  99
 100         if (likely(!skb->encapsulation)) {
 101                 skb_reset_inner_headers(skb);
 102                 skb->encapsulation = 1;
 103         }
 104
 105         if (skb_is_gso(skb)) {
 106                 err = skb_unclone(skb, GFP_ATOMIC);
 107                 if (unlikely(err))
 108                         goto error;
 109                 skb_shinfo(skb)->gso_type |= SKB_GSO_GRE;
 110                 return skb;
 111         } else if (skb->ip_summed == CHECKSUM_PARTIAL && gre_csum) {
 112                 err = skb_checksum_help(skb);
 113                 if (unlikely(err))
 114                         goto error;
 115         } else if (skb->ip_summed != CHECKSUM_PARTIAL)
 116                 skb->ip_summed = CHECKSUM_NONE;
 117
 118         return skb;
 119 error:
 120         kfree_skb(skb);
 121         return ERR_PTR(err);
 122 }
 123 EXPORT_SYMBOL_GPL(gre_handle_offloads);
 124
 125 static __sum16 check_checksum(struct sk_buff *skb)
 126 {
 127         __sum16 csum = 0;
 128
 129         switch (skb->ip_summed) {
 130         case CHECKSUM_COMPLETE:
 131                 csum = csum_fold(skb->csum);
 132
 133                 if (!csum)
 134                         break;
 135                 /* Fall through. */
 136
 137         case CHECKSUM_NONE:
 138                 skb->csum = 0;
 139                 csum = __skb_checksum_complete(skb);
 140                 skb->ip_summed = CHECKSUM_COMPLETE;
 141                 break;
 142         }
 143
 144         return csum;
 145 }
 146
 147 static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 148                             bool *csum_err)
 149 {
 150         unsigned int ip_hlen = ip_hdrlen(skb);
 151         const struct gre_base_hdr *greh;
 152         __be32 *options;
 153         int hdr_len;
 154
 155         if (unlikely(!pskb_may_pull(skb, sizeof(struct gre_base_hdr))))
 156                 return -EINVAL;
 157
 158         greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
 159         if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
 160                 return -EINVAL;
 161
 162         tpi->flags = gre_flags_to_tnl_flags(greh->flags);
 163         hdr_len = ip_gre_calc_hlen(tpi->flags);
 164
 165         if (!pskb_may_pull(skb, hdr_len))
 166                 return -EINVAL;
 167
 168         greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
 169         tpi->proto = greh->protocol;
 170
 171         options = (__be32 *)(greh + 1);
 172         if (greh->flags & GRE_CSUM) {
 173                 if (check_checksum(skb)) {
 174                         *csum_err = true;
 175                         return -EINVAL;
 176                 }
 177                 options++;
 178         }
 179
 180         if (greh->flags & GRE_KEY) {
 181                 tpi->key = *options;
 182                 options++;
 183         } else
 184                 tpi->key = 0;
 185
 186         if (unlikely(greh->flags & GRE_SEQ)) {
 187                 tpi->seq = *options;
 188                 options++;
 189         } else
 190                 tpi->seq = 0;
 191
 192         /* WCCP version 1 and 2 protocol decoding.
 193          * - Change protocol to IP
 194          * - When dealing with WCCPv2, Skip extra 4 bytes in GRE header
 195          */
 196         if (greh->flags == 0 && tpi->proto == htons(ETH_P_WCCP)) {
 197                 tpi->proto = htons(ETH_P_IP);
 198                 if ((*(u8 *)options & 0xF0) != 0x40) {
 199                         hdr_len += 4;
 200                         if (!pskb_may_pull(skb, hdr_len))
 201                                 return -EINVAL;
 202                 }
 203         }
 204
 205         return iptunnel_pull_header(skb, hdr_len, tpi->proto);
 206 }
 207
 208 static int gre_cisco_rcv(struct sk_buff *skb)
 209 {
 210         struct tnl_ptk_info tpi;
 211         int i;
 212         bool csum_err = false;
 213
 214 #ifdef CONFIG_NET_IPGRE_BROADCAST
 215         if (ipv4_is_multicast(ip_hdr(skb)->daddr)) {
 216                 /* Looped back packet, drop it! */
 217                 if (rt_is_output_route(skb_rtable(skb)))
 218                         goto drop;
 219         }
 220 #endif
 221
 222         if (parse_gre_header(skb, &tpi, &csum_err) < 0)
 223                 goto drop;
 224
 225         rcu_read_lock();
 226         for (i = 0; i < GRE_IP_PROTO_MAX; i++) {
 227                 struct gre_cisco_protocol *proto;
 228                 int ret;
 229
 230                 proto = rcu_dereference(gre_cisco_proto_list[i]);
 231                 if (!proto)
 232                         continue;
 233                 ret = proto->handler(skb, &tpi);
 234                 if (ret == PACKET_RCVD) {
 235                         rcu_read_unlock();
 236                         return 0;
 237                 }
 238         }
 239         rcu_read_unlock();
 240
 241         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);
 242 drop:
 243         kfree_skb(skb);
 244         return 0;
 245 }
 246
 247 static void gre_cisco_err(struct sk_buff *skb, u32 info)
 248 {
 249         /* All the routers (except for Linux) return only
 250          * 8 bytes of packet payload. It means, that precise relaying of
 251          * ICMP in the real Internet is absolutely infeasible.
 252          *
 253          * Moreover, Cisco "wise men" put GRE key to the third word
 254          * in GRE header. It makes impossible maintaining even soft
 255          * state for keyed
 256          * GRE tunnels with enabled checksum. Tell them "thank you".
 257          *
 258          * Well, I wonder, rfc1812 was written by Cisco employee,
 259          * what the hell these idiots break standards established
 260          * by themselves???
 261          */
 262
 263         const int type = icmp_hdr(skb)->type;
 264         const int code = icmp_hdr(skb)->code;
 265         struct tnl_ptk_info tpi;
 266         bool csum_err = false;
 267         int i;
 268
 269         if (parse_gre_header(skb, &tpi, &csum_err)) {
 270                 if (!csum_err)          /* ignore csum errors. */
 271                         return;
 272         }
 273
 274         if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
 275                 ipv4_update_pmtu(skb, dev_net(skb->dev), info,
 276                                 skb->dev->ifindex, 0, IPPROTO_GRE, 0);
 277                 return;
 278         }
 279         if (type == ICMP_REDIRECT) {
 280                 ipv4_redirect(skb, dev_net(skb->dev), skb->dev->ifindex, 0,
 281                                 IPPROTO_GRE, 0);
 282                 return;
 283         }
 284
 285         rcu_read_lock();
 286         for (i = 0; i < GRE_IP_PROTO_MAX; i++) {
 287                 struct gre_cisco_protocol *proto;
 288
 289                 proto = rcu_dereference(gre_cisco_proto_list[i]);
 290                 if (!proto)
 291                         continue;
 292
 293                 if (proto->err_handler(skb, info, &tpi) == PACKET_RCVD)
 294                         goto out;
 295
 296         }
 297 out:
 298         rcu_read_unlock();
 299 }
 300
 301 static int gre_rcv(struct sk_buff *skb)
 302 {
 303         const struct gre_protocol *proto;
 304         u8 ver;
 305         int ret;
 306
 307         if (!pskb_may_pull(skb, 12))
 308                 goto drop;
 309
 310         ver = skb->data[1]&0x7f;
 311         if (ver >= GREPROTO_MAX)
 312                 goto drop;
 313
 314         rcu_read_lock();
 315         proto = rcu_dereference(gre_proto[ver]);
 316         if (!proto || !proto->handler)
 317                 goto drop_unlock;
 318         ret = proto->handler(skb);
 319         rcu_read_unlock();
 320         return ret;
 321
 322 drop_unlock:
 323         rcu_read_unlock();
 324 drop:
 325         kfree_skb(skb);
 326         return NET_RX_DROP;
 327 }
 328
 329 static void gre_err(struct sk_buff *skb, u32 info)
 330 {
 331         const struct gre_protocol *proto;
 332         const struct iphdr *iph = (const struct iphdr *)skb->data;
 333         u8 ver = skb->data[(iph->ihl<<2) + 1]&0x7f;
 334
 335         if (ver >= GREPROTO_MAX)
 336                 return;
 337
 338         rcu_read_lock();
 339         proto = rcu_dereference(gre_proto[ver]);
 340         if (proto && proto->err_handler)
 341                 proto->err_handler(skb, info);
 342         rcu_read_unlock();
 343 }
 344
 345 static const struct net_protocol net_gre_protocol = {
 346         .handler     = gre_rcv,
 347         .err_handler = gre_err,
 348         .netns_ok    = 1,
 349 };
 350
 351 static const struct gre_protocol ipgre_protocol = {
 352         .handler     = gre_cisco_rcv,
 353         .err_handler = gre_cisco_err,
 354 };
 355
 356 int gre_cisco_register(struct gre_cisco_protocol *newp)
 357 {
 358         struct gre_cisco_protocol **proto = (struct gre_cisco_protocol **)
 359                                             &gre_cisco_proto_list[newp->priority];
 360
 361         return (cmpxchg(proto, NULL, newp) == NULL) ? 0 : -EBUSY;
 362 }
 363 EXPORT_SYMBOL_GPL(gre_cisco_register);
 364
 365 int gre_cisco_unregister(struct gre_cisco_protocol *del_proto)
 366 {
 367         struct gre_cisco_protocol **proto = (struct gre_cisco_protocol **)
 368                                             &gre_cisco_proto_list[del_proto->priority];
 369         int ret;
 370
 371         ret = (cmpxchg(proto, del_proto, NULL) == del_proto) ? 0 : -EINVAL;
 372
 373         if (ret)
 374                 return ret;
 375
 376         synchronize_net();
 377         return 0;
 378 }
 379 EXPORT_SYMBOL_GPL(gre_cisco_unregister);
 380
 381 static int __init gre_init(void)
 382 {
 383         pr_info("GRE over IPv4 demultiplexor driver\n");
 384
 385         if (inet_add_protocol(&net_gre_protocol, IPPROTO_GRE) < 0) {
 386                 pr_err("can't add protocol\n");
 387                 goto err;
 388         }
 389
 390         if (gre_add_protocol(&ipgre_protocol, GREPROTO_CISCO) < 0) {
 391                 pr_info("%s: can't add ipgre handler\n", __func__);
 392                 goto err_gre;
 393         }
 394
 395         if (gre_offload_init()) {
 396                 pr_err("can't add protocol offload\n");
 397                 goto err_gso;
 398         }
 399
 400         return 0;
 401 err_gso:
 402         gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
 403 err_gre:
 404         inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
 405 err:
 406         return -EAGAIN;
 407 }
 408
 409 static void __exit gre_exit(void)
 410 {
 411         gre_offload_exit();
 412
 413         gre_del_protocol(&ipgre_protocol, GREPROTO_CISCO);
 414         inet_del_protocol(&net_gre_protocol, IPPROTO_GRE);
 415 }
 416
 417 module_init(gre_init);
 418 module_exit(gre_exit);
 419
 420 MODULE_DESCRIPTION("GRE over IPv4 demultiplexer driver");
 421 MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
 422 MODULE_LICENSE("GPL");