net/core/lwt_bpf.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
   3  */
   4
   5 #include <linux/kernel.h>
   6 #include <linux/module.h>
   7 #include <linux/skbuff.h>
   8 #include <linux/types.h>
   9 #include <linux/bpf.h>
  10 #include <net/lwtunnel.h>
  11 #include <net/gre.h>
  12 #include <net/ip6_route.h>
  13 #include <net/ipv6_stubs.h>
  14
  15 struct bpf_lwt_prog {
  16         struct bpf_prog *prog;
  17         char *name;
  18 };
  19
  20 struct bpf_lwt {
  21         struct bpf_lwt_prog in;
  22         struct bpf_lwt_prog out;
  23         struct bpf_lwt_prog xmit;
  24         int family;
  25 };
  26
  27 #define MAX_PROG_NAME 256
  28
  29 static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
  30 {
  31         return (struct bpf_lwt *)lwt->data;
  32 }
  33
  34 #define NO_REDIRECT false
  35 #define CAN_REDIRECT true
  36
  37 static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
  38                        struct dst_entry *dst, bool can_redirect)
  39 {
  40         int ret;
  41
  42         /* Preempt disable is needed to protect per-cpu redirect_info between
  43          * BPF prog and skb_do_redirect(). The call_rcu in bpf_prog_put() and
  44          * access to maps strictly require a rcu_read_lock() for protection,
  45          * mixing with BH RCU lock doesn't work.
  46          */
  47         preempt_disable();
  48         bpf_compute_data_pointers(skb);
  49         ret = bpf_prog_run_save_cb(lwt->prog, skb);
  50
  51         switch (ret) {
  52         case BPF_OK:
  53         case BPF_LWT_REROUTE:
  54                 break;
  55
  56         case BPF_REDIRECT:
  57                 if (unlikely(!can_redirect)) {
  58                         pr_warn_once("Illegal redirect return code in prog %s\n",
  59                                      lwt->name ? : "<unknown>");
  60                         ret = BPF_OK;
  61                 } else {
  62                         skb_reset_mac_header(skb);
  63                         ret = skb_do_redirect(skb);
  64                         if (ret == 0)
  65                                 ret = BPF_REDIRECT;
  66                 }
  67                 break;
  68
  69         case BPF_DROP:
  70                 kfree_skb(skb);
  71                 ret = -EPERM;
  72                 break;
  73
  74         default:
  75                 pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
  76                 kfree_skb(skb);
  77                 ret = -EINVAL;
  78                 break;
  79         }
  80
  81         preempt_enable();
  82
  83         return ret;
  84 }
  85
  86 static int bpf_lwt_input_reroute(struct sk_buff *skb)
  87 {
  88         int err = -EINVAL;
  89
  90         if (skb->protocol == htons(ETH_P_IP)) {
  91                 struct iphdr *iph = ip_hdr(skb);
  92
  93                 err = ip_route_input_noref(skb, iph->daddr, iph->saddr,
  94                                            iph->tos, skb_dst(skb)->dev);
  95         } else if (skb->protocol == htons(ETH_P_IPV6)) {
  96                 err = ipv6_stub->ipv6_route_input(skb);
  97         } else {
  98                 err = -EAFNOSUPPORT;
  99         }
 100
 101         if (err)
 102                 goto err;
 103         return dst_input(skb);
 104
 105 err:
 106         kfree_skb(skb);
 107         return err;
 108 }
 109
 110 static int bpf_input(struct sk_buff *skb)
 111 {
 112         struct dst_entry *dst = skb_dst(skb);
 113         struct bpf_lwt *bpf;
 114         int ret;
 115
 116         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 117         if (bpf->in.prog) {
 118                 ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
 119                 if (ret < 0)
 120                         return ret;
 121                 if (ret == BPF_LWT_REROUTE)
 122                         return bpf_lwt_input_reroute(skb);
 123         }
 124
 125         if (unlikely(!dst->lwtstate->orig_input)) {
 126                 kfree_skb(skb);
 127                 return -EINVAL;
 128         }
 129
 130         return dst->lwtstate->orig_input(skb);
 131 }
 132
 133 static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 134 {
 135         struct dst_entry *dst = skb_dst(skb);
 136         struct bpf_lwt *bpf;
 137         int ret;
 138
 139         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 140         if (bpf->out.prog) {
 141                 ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
 142                 if (ret < 0)
 143                         return ret;
 144         }
 145
 146         if (unlikely(!dst->lwtstate->orig_output)) {
 147                 pr_warn_once("orig_output not set on dst for prog %s\n",
 148                              bpf->out.name);
 149                 kfree_skb(skb);
 150                 return -EINVAL;
 151         }
 152
 153         return dst->lwtstate->orig_output(net, sk, skb);
 154 }
 155
 156 static int xmit_check_hhlen(struct sk_buff *skb)
 157 {
 158         int hh_len = skb_dst(skb)->dev->hard_header_len;
 159
 160         if (skb_headroom(skb) < hh_len) {
 161                 int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
 162
 163                 if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
 164                         return -ENOMEM;
 165         }
 166
 167         return 0;
 168 }
 169
 170 static int bpf_lwt_xmit_reroute(struct sk_buff *skb)
 171 {
 172         struct net_device *l3mdev = l3mdev_master_dev_rcu(skb_dst(skb)->dev);
 173         int oif = l3mdev ? l3mdev->ifindex : 0;
 174         struct dst_entry *dst = NULL;
 175         int err = -EAFNOSUPPORT;
 176         struct sock *sk;
 177         struct net *net;
 178         bool ipv4;
 179
 180         if (skb->protocol == htons(ETH_P_IP))
 181                 ipv4 = true;
 182         else if (skb->protocol == htons(ETH_P_IPV6))
 183                 ipv4 = false;
 184         else
 185                 goto err;
 186
 187         sk = sk_to_full_sk(skb->sk);
 188         if (sk) {
 189                 if (sk->sk_bound_dev_if)
 190                         oif = sk->sk_bound_dev_if;
 191                 net = sock_net(sk);
 192         } else {
 193                 net = dev_net(skb_dst(skb)->dev);
 194         }
 195
 196         if (ipv4) {
 197                 struct iphdr *iph = ip_hdr(skb);
 198                 struct flowi4 fl4 = {};
 199                 struct rtable *rt;
 200
 201                 fl4.flowi4_oif = oif;
 202                 fl4.flowi4_mark = skb->mark;
 203                 fl4.flowi4_uid = sock_net_uid(net, sk);
 204                 fl4.flowi4_tos = RT_TOS(iph->tos);
 205                 fl4.flowi4_flags = FLOWI_FLAG_ANYSRC;
 206                 fl4.flowi4_proto = iph->protocol;
 207                 fl4.daddr = iph->daddr;
 208                 fl4.saddr = iph->saddr;
 209
 210                 rt = ip_route_output_key(net, &fl4);
 211                 if (IS_ERR(rt)) {
 212                         err = PTR_ERR(rt);
 213                         goto err;
 214                 }
 215                 dst = &rt->dst;
 216         } else {
 217                 struct ipv6hdr *iph6 = ipv6_hdr(skb);
 218                 struct flowi6 fl6 = {};
 219
 220                 fl6.flowi6_oif = oif;
 221                 fl6.flowi6_mark = skb->mark;
 222                 fl6.flowi6_uid = sock_net_uid(net, sk);
 223                 fl6.flowlabel = ip6_flowinfo(iph6);
 224                 fl6.flowi6_proto = iph6->nexthdr;
 225                 fl6.daddr = iph6->daddr;
 226                 fl6.saddr = iph6->saddr;
 227
 228                 err = ipv6_stub->ipv6_dst_lookup(net, skb->sk, &dst, &fl6);
 229                 if (unlikely(err))
 230                         goto err;
 231                 if (IS_ERR(dst)) {
 232                         err = PTR_ERR(dst);
 233                         goto err;
 234                 }
 235         }
 236         if (unlikely(dst->error)) {
 237                 err = dst->error;
 238                 dst_release(dst);
 239                 goto err;
 240         }
 241
 242         /* Although skb header was reserved in bpf_lwt_push_ip_encap(), it
 243          * was done for the previous dst, so we are doing it here again, in
 244          * case the new dst needs much more space. The call below is a noop
 245          * if there is enough header space in skb.
 246          */
 247         err = skb_cow_head(skb, LL_RESERVED_SPACE(dst->dev));
 248         if (unlikely(err))
 249                 goto err;
 250
 251         skb_dst_drop(skb);
 252         skb_dst_set(skb, dst);
 253
 254         err = dst_output(dev_net(skb_dst(skb)->dev), skb->sk, skb);
 255         if (unlikely(err))
 256                 return err;
 257
 258         /* ip[6]_finish_output2 understand LWTUNNEL_XMIT_DONE */
 259         return LWTUNNEL_XMIT_DONE;
 260
 261 err:
 262         kfree_skb(skb);
 263         return err;
 264 }
 265
 266 static int bpf_xmit(struct sk_buff *skb)
 267 {
 268         struct dst_entry *dst = skb_dst(skb);
 269         struct bpf_lwt *bpf;
 270
 271         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 272         if (bpf->xmit.prog) {
 273                 __be16 proto = skb->protocol;
 274                 int ret;
 275
 276                 ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
 277                 switch (ret) {
 278                 case BPF_OK:
 279                         /* If the header changed, e.g. via bpf_lwt_push_encap,
 280                          * BPF_LWT_REROUTE below should have been used if the
 281                          * protocol was also changed.
 282                          */
 283                         if (skb->protocol != proto) {
 284                                 kfree_skb(skb);
 285                                 return -EINVAL;
 286                         }
 287                         /* If the header was expanded, headroom might be too
 288                          * small for L2 header to come, expand as needed.
 289                          */
 290                         ret = xmit_check_hhlen(skb);
 291                         if (unlikely(ret))
 292                                 return ret;
 293
 294                         return LWTUNNEL_XMIT_CONTINUE;
 295                 case BPF_REDIRECT:
 296                         return LWTUNNEL_XMIT_DONE;
 297                 case BPF_LWT_REROUTE:
 298                         return bpf_lwt_xmit_reroute(skb);
 299                 default:
 300                         return ret;
 301                 }
 302         }
 303
 304         return LWTUNNEL_XMIT_CONTINUE;
 305 }
 306
 307 static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
 308 {
 309         if (prog->prog)
 310                 bpf_prog_put(prog->prog);
 311
 312         kfree(prog->name);
 313 }
 314
 315 static void bpf_destroy_state(struct lwtunnel_state *lwt)
 316 {
 317         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
 318
 319         bpf_lwt_prog_destroy(&bpf->in);
 320         bpf_lwt_prog_destroy(&bpf->out);
 321         bpf_lwt_prog_destroy(&bpf->xmit);
 322 }
 323
 324 static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
 325         [LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
 326         [LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
 327                                 .len = MAX_PROG_NAME },
 328 };
 329
 330 static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
 331                           enum bpf_prog_type type)
 332 {
 333         struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
 334         struct bpf_prog *p;
 335         int ret;
 336         u32 fd;
 337
 338         ret = nla_parse_nested_deprecated(tb, LWT_BPF_PROG_MAX, attr,
 339                                           bpf_prog_policy, NULL);
 340         if (ret < 0)
 341                 return ret;
 342
 343         if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
 344                 return -EINVAL;
 345
 346         prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
 347         if (!prog->name)
 348                 return -ENOMEM;
 349
 350         fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
 351         p = bpf_prog_get_type(fd, type);
 352         if (IS_ERR(p))
 353                 return PTR_ERR(p);
 354
 355         prog->prog = p;
 356
 357         return 0;
 358 }
 359
 360 static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
 361         [LWT_BPF_IN]            = { .type = NLA_NESTED, },
 362         [LWT_BPF_OUT]           = { .type = NLA_NESTED, },
 363         [LWT_BPF_XMIT]          = { .type = NLA_NESTED, },
 364         [LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
 365 };
 366
 367 static int bpf_build_state(struct nlattr *nla,
 368                            unsigned int family, const void *cfg,
 369                            struct lwtunnel_state **ts,
 370                            struct netlink_ext_ack *extack)
 371 {
 372         struct nlattr *tb[LWT_BPF_MAX + 1];
 373         struct lwtunnel_state *newts;
 374         struct bpf_lwt *bpf;
 375         int ret;
 376
 377         if (family != AF_INET && family != AF_INET6)
 378                 return -EAFNOSUPPORT;
 379
 380         ret = nla_parse_nested_deprecated(tb, LWT_BPF_MAX, nla, bpf_nl_policy,
 381                                           extack);
 382         if (ret < 0)
 383                 return ret;
 384
 385         if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
 386                 return -EINVAL;
 387
 388         newts = lwtunnel_state_alloc(sizeof(*bpf));
 389         if (!newts)
 390                 return -ENOMEM;
 391
 392         newts->type = LWTUNNEL_ENCAP_BPF;
 393         bpf = bpf_lwt_lwtunnel(newts);
 394
 395         if (tb[LWT_BPF_IN]) {
 396                 newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
 397                 ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
 398                                      BPF_PROG_TYPE_LWT_IN);
 399                 if (ret  < 0)
 400                         goto errout;
 401         }
 402
 403         if (tb[LWT_BPF_OUT]) {
 404                 newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
 405                 ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
 406                                      BPF_PROG_TYPE_LWT_OUT);
 407                 if (ret < 0)
 408                         goto errout;
 409         }
 410
 411         if (tb[LWT_BPF_XMIT]) {
 412                 newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
 413                 ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
 414                                      BPF_PROG_TYPE_LWT_XMIT);
 415                 if (ret < 0)
 416                         goto errout;
 417         }
 418
 419         if (tb[LWT_BPF_XMIT_HEADROOM]) {
 420                 u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);
 421
 422                 if (headroom > LWT_BPF_MAX_HEADROOM) {
 423                         ret = -ERANGE;
 424                         goto errout;
 425                 }
 426
 427                 newts->headroom = headroom;
 428         }
 429
 430         bpf->family = family;
 431         *ts = newts;
 432
 433         return 0;
 434
 435 errout:
 436         bpf_destroy_state(newts);
 437         kfree(newts);
 438         return ret;
 439 }
 440
 441 static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
 442                              struct bpf_lwt_prog *prog)
 443 {
 444         struct nlattr *nest;
 445
 446         if (!prog->prog)
 447                 return 0;
 448
 449         nest = nla_nest_start_noflag(skb, attr);
 450         if (!nest)
 451                 return -EMSGSIZE;
 452
 453         if (prog->name &&
 454             nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
 455                 return -EMSGSIZE;
 456
 457         return nla_nest_end(skb, nest);
 458 }
 459
 460 static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
 461 {
 462         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
 463
 464         if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
 465             bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
 466             bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
 467                 return -EMSGSIZE;
 468
 469         return 0;
 470 }
 471
 472 static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
 473 {
 474         int nest_len = nla_total_size(sizeof(struct nlattr)) +
 475                        nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
 476                        0;
 477
 478         return nest_len + /* LWT_BPF_IN */
 479                nest_len + /* LWT_BPF_OUT */
 480                nest_len + /* LWT_BPF_XMIT */
 481                0;
 482 }
 483
 484 static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
 485 {
 486         /* FIXME:
 487          * The LWT state is currently rebuilt for delete requests which
 488          * results in a new bpf_prog instance. Comparing names for now.
 489          */
 490         if (!a->name && !b->name)
 491                 return 0;
 492
 493         if (!a->name || !b->name)
 494                 return 1;
 495
 496         return strcmp(a->name, b->name);
 497 }
 498
 499 static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
 500 {
 501         struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
 502         struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);
 503
 504         return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
 505                bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
 506                bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
 507 }
 508
 509 static const struct lwtunnel_encap_ops bpf_encap_ops = {
 510         .build_state    = bpf_build_state,
 511         .destroy_state  = bpf_destroy_state,
 512         .input          = bpf_input,
 513         .output         = bpf_output,
 514         .xmit           = bpf_xmit,
 515         .fill_encap     = bpf_fill_encap_info,
 516         .get_encap_size = bpf_encap_nlsize,
 517         .cmp_encap      = bpf_encap_cmp,
 518         .owner          = THIS_MODULE,
 519 };
 520
 521 static int handle_gso_type(struct sk_buff *skb, unsigned int gso_type,
 522                            int encap_len)
 523 {
 524         struct skb_shared_info *shinfo = skb_shinfo(skb);
 525
 526         gso_type |= SKB_GSO_DODGY;
 527         shinfo->gso_type |= gso_type;
 528         skb_decrease_gso_size(shinfo, encap_len);
 529         shinfo->gso_segs = 0;
 530         return 0;
 531 }
 532
 533 static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len)
 534 {
 535         int next_hdr_offset;
 536         void *next_hdr;
 537         __u8 protocol;
 538
 539         /* SCTP and UDP_L4 gso need more nuanced handling than what
 540          * handle_gso_type() does above: skb_decrease_gso_size() is not enough.
 541          * So at the moment only TCP GSO packets are let through.
 542          */
 543         if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6)))
 544                 return -ENOTSUPP;
 545
 546         if (ipv4) {
 547                 protocol = ip_hdr(skb)->protocol;
 548                 next_hdr_offset = sizeof(struct iphdr);
 549                 next_hdr = skb_network_header(skb) + next_hdr_offset;
 550         } else {
 551                 protocol = ipv6_hdr(skb)->nexthdr;
 552                 next_hdr_offset = sizeof(struct ipv6hdr);
 553                 next_hdr = skb_network_header(skb) + next_hdr_offset;
 554         }
 555
 556         switch (protocol) {
 557         case IPPROTO_GRE:
 558                 next_hdr_offset += sizeof(struct gre_base_hdr);
 559                 if (next_hdr_offset > encap_len)
 560                         return -EINVAL;
 561
 562                 if (((struct gre_base_hdr *)next_hdr)->flags & GRE_CSUM)
 563                         return handle_gso_type(skb, SKB_GSO_GRE_CSUM,
 564                                                encap_len);
 565                 return handle_gso_type(skb, SKB_GSO_GRE, encap_len);
 566
 567         case IPPROTO_UDP:
 568                 next_hdr_offset += sizeof(struct udphdr);
 569                 if (next_hdr_offset > encap_len)
 570                         return -EINVAL;
 571
 572                 if (((struct udphdr *)next_hdr)->check)
 573                         return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL_CSUM,
 574                                                encap_len);
 575                 return handle_gso_type(skb, SKB_GSO_UDP_TUNNEL, encap_len);
 576
 577         case IPPROTO_IP:
 578         case IPPROTO_IPV6:
 579                 if (ipv4)
 580                         return handle_gso_type(skb, SKB_GSO_IPXIP4, encap_len);
 581                 else
 582                         return handle_gso_type(skb, SKB_GSO_IPXIP6, encap_len);
 583
 584         default:
 585                 return -EPROTONOSUPPORT;
 586         }
 587 }
 588
 589 int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress)
 590 {
 591         struct iphdr *iph;
 592         bool ipv4;
 593         int err;
 594
 595         if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM))
 596                 return -EINVAL;
 597
 598         /* validate protocol and length */
 599         iph = (struct iphdr *)hdr;
 600         if (iph->version == 4) {
 601                 ipv4 = true;
 602                 if (unlikely(len < iph->ihl * 4))
 603                         return -EINVAL;
 604         } else if (iph->version == 6) {
 605                 ipv4 = false;
 606                 if (unlikely(len < sizeof(struct ipv6hdr)))
 607                         return -EINVAL;
 608         } else {
 609                 return -EINVAL;
 610         }
 611
 612         if (ingress)
 613                 err = skb_cow_head(skb, len + skb->mac_len);
 614         else
 615                 err = skb_cow_head(skb,
 616                                    len + LL_RESERVED_SPACE(skb_dst(skb)->dev));
 617         if (unlikely(err))
 618                 return err;
 619
 620         /* push the encap headers and fix pointers */
 621         skb_reset_inner_headers(skb);
 622         skb_reset_inner_mac_header(skb);  /* mac header is not yet set */
 623         skb_set_inner_protocol(skb, skb->protocol);
 624         skb->encapsulation = 1;
 625         skb_push(skb, len);
 626         if (ingress)
 627                 skb_postpush_rcsum(skb, iph, len);
 628         skb_reset_network_header(skb);
 629         memcpy(skb_network_header(skb), hdr, len);
 630         bpf_compute_data_pointers(skb);
 631         skb_clear_hash(skb);
 632
 633         if (ipv4) {
 634                 skb->protocol = htons(ETH_P_IP);
 635                 iph = ip_hdr(skb);
 636
 637                 if (!iph->check)
 638                         iph->check = ip_fast_csum((unsigned char *)iph,
 639                                                   iph->ihl);
 640         } else {
 641                 skb->protocol = htons(ETH_P_IPV6);
 642         }
 643
 644         if (skb_is_gso(skb))
 645                 return handle_gso_encap(skb, ipv4, len);
 646
 647         return 0;
 648 }
 649
 650 static int __init bpf_lwt_init(void)
 651 {
 652         return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
 653 }
 654
 655 subsys_initcall(bpf_lwt_init)