net/ipv4/udp_offload.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *      IPV4 GSO/GRO offload support
   4  *      Linux INET implementation
   5  *
   6  *      UDPv4 GSO support
   7  */
   8
   9 #include <linux/skbuff.h>
  10 #include <net/udp.h>
  11 #include <net/protocol.h>
  12 #include <net/inet_common.h>
  13
  14 static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
  15         netdev_features_t features,
  16         struct sk_buff *(*gso_inner_segment)(struct sk_buff *skb,
  17                                              netdev_features_t features),
  18         __be16 new_protocol, bool is_ipv6)
  19 {
  20         int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
  21         bool remcsum, need_csum, offload_csum, gso_partial;
  22         struct sk_buff *segs = ERR_PTR(-EINVAL);
  23         struct udphdr *uh = udp_hdr(skb);
  24         u16 mac_offset = skb->mac_header;
  25         __be16 protocol = skb->protocol;
  26         u16 mac_len = skb->mac_len;
  27         int udp_offset, outer_hlen;
  28         __wsum partial;
  29         bool need_ipsec;
  30
  31         if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
  32                 goto out;
  33
  34         /* Adjust partial header checksum to negate old length.
  35          * We cannot rely on the value contained in uh->len as it is
  36          * possible that the actual value exceeds the boundaries of the
  37          * 16 bit length field due to the header being added outside of an
  38          * IP or IPv6 frame that was already limited to 64K - 1.
  39          */
  40         if (skb_shinfo(skb)->gso_type & SKB_GSO_PARTIAL)
  41                 partial = (__force __wsum)uh->len;
  42         else
  43                 partial = (__force __wsum)htonl(skb->len);
  44         partial = csum_sub(csum_unfold(uh->check), partial);
  45
  46         /* setup inner skb. */
  47         skb->encapsulation = 0;
  48         SKB_GSO_CB(skb)->encap_level = 0;
  49         __skb_pull(skb, tnl_hlen);
  50         skb_reset_mac_header(skb);
  51         skb_set_network_header(skb, skb_inner_network_offset(skb));
  52         skb->mac_len = skb_inner_network_offset(skb);
  53         skb->protocol = new_protocol;
  54
  55         need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL_CSUM);
  56         skb->encap_hdr_csum = need_csum;
  57
  58         remcsum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TUNNEL_REMCSUM);
  59         skb->remcsum_offload = remcsum;
  60
  61         need_ipsec = skb_dst(skb) && dst_xfrm(skb_dst(skb));
  62         /* Try to offload checksum if possible */
  63         offload_csum = !!(need_csum &&
  64                           !need_ipsec &&
  65                           (skb->dev->features &
  66                            (is_ipv6 ? (NETIF_F_HW_CSUM | NETIF_F_IPV6_CSUM) :
  67                                       (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM))));
  68
  69         features &= skb->dev->hw_enc_features;
  70
  71         /* The only checksum offload we care about from here on out is the
  72          * outer one so strip the existing checksum feature flags and
  73          * instead set the flag based on our outer checksum offload value.
  74          */
  75         if (remcsum) {
  76                 features &= ~NETIF_F_CSUM_MASK;
  77                 if (!need_csum || offload_csum)
  78                         features |= NETIF_F_HW_CSUM;
  79         }
  80
  81         /* segment inner packet. */
  82         segs = gso_inner_segment(skb, features);
  83         if (IS_ERR_OR_NULL(segs)) {
  84                 skb_gso_error_unwind(skb, protocol, tnl_hlen, mac_offset,
  85                                      mac_len);
  86                 goto out;
  87         }
  88
  89         gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
  90
  91         outer_hlen = skb_tnl_header_len(skb);
  92         udp_offset = outer_hlen - tnl_hlen;
  93         skb = segs;
  94         do {
  95                 unsigned int len;
  96
  97                 if (remcsum)
  98                         skb->ip_summed = CHECKSUM_NONE;
  99
 100                 /* Set up inner headers if we are offloading inner checksum */
 101                 if (skb->ip_summed == CHECKSUM_PARTIAL) {
 102                         skb_reset_inner_headers(skb);
 103                         skb->encapsulation = 1;
 104                 }
 105
 106                 skb->mac_len = mac_len;
 107                 skb->protocol = protocol;
 108
 109                 __skb_push(skb, outer_hlen);
 110                 skb_reset_mac_header(skb);
 111                 skb_set_network_header(skb, mac_len);
 112                 skb_set_transport_header(skb, udp_offset);
 113                 len = skb->len - udp_offset;
 114                 uh = udp_hdr(skb);
 115
 116                 /* If we are only performing partial GSO the inner header
 117                  * will be using a length value equal to only one MSS sized
 118                  * segment instead of the entire frame.
 119                  */
 120                 if (gso_partial && skb_is_gso(skb)) {
 121                         uh->len = htons(skb_shinfo(skb)->gso_size +
 122                                         SKB_GSO_CB(skb)->data_offset +
 123                                         skb->head - (unsigned char *)uh);
 124                 } else {
 125                         uh->len = htons(len);
 126                 }
 127
 128                 if (!need_csum)
 129                         continue;
 130
 131                 uh->check = ~csum_fold(csum_add(partial,
 132                                        (__force __wsum)htonl(len)));
 133
 134                 if (skb->encapsulation || !offload_csum) {
 135                         uh->check = gso_make_checksum(skb, ~uh->check);
 136                         if (uh->check == 0)
 137                                 uh->check = CSUM_MANGLED_0;
 138                 } else {
 139                         skb->ip_summed = CHECKSUM_PARTIAL;
 140                         skb->csum_start = skb_transport_header(skb) - skb->head;
 141                         skb->csum_offset = offsetof(struct udphdr, check);
 142                 }
 143         } while ((skb = skb->next));
 144 out:
 145         return segs;
 146 }
 147
 148 struct sk_buff *skb_udp_tunnel_segment(struct sk_buff *skb,
 149                                        netdev_features_t features,
 150                                        bool is_ipv6)
 151 {
 152         __be16 protocol = skb->protocol;
 153         const struct net_offload **offloads;
 154         const struct net_offload *ops;
 155         struct sk_buff *segs = ERR_PTR(-EINVAL);
 156         struct sk_buff *(*gso_inner_segment)(struct sk_buff *skb,
 157                                              netdev_features_t features);
 158
 159         rcu_read_lock();
 160
 161         switch (skb->inner_protocol_type) {
 162         case ENCAP_TYPE_ETHER:
 163                 protocol = skb->inner_protocol;
 164                 gso_inner_segment = skb_mac_gso_segment;
 165                 break;
 166         case ENCAP_TYPE_IPPROTO:
 167                 offloads = is_ipv6 ? inet6_offloads : inet_offloads;
 168                 ops = rcu_dereference(offloads[skb->inner_ipproto]);
 169                 if (!ops || !ops->callbacks.gso_segment)
 170                         goto out_unlock;
 171                 gso_inner_segment = ops->callbacks.gso_segment;
 172                 break;
 173         default:
 174                 goto out_unlock;
 175         }
 176
 177         segs = __skb_udp_tunnel_segment(skb, features, gso_inner_segment,
 178                                         protocol, is_ipv6);
 179
 180 out_unlock:
 181         rcu_read_unlock();
 182
 183         return segs;
 184 }
 185 EXPORT_SYMBOL(skb_udp_tunnel_segment);
 186
 187 static struct sk_buff *__udp_gso_segment_list(struct sk_buff *skb,
 188                                               netdev_features_t features)
 189 {
 190         unsigned int mss = skb_shinfo(skb)->gso_size;
 191
 192         skb = skb_segment_list(skb, features, skb_mac_header_len(skb));
 193         if (IS_ERR(skb))
 194                 return skb;
 195
 196         udp_hdr(skb)->len = htons(sizeof(struct udphdr) + mss);
 197
 198         return skb;
 199 }
 200
 201 struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 202                                   netdev_features_t features)
 203 {
 204         struct sock *sk = gso_skb->sk;
 205         unsigned int sum_truesize = 0;
 206         struct sk_buff *segs, *seg;
 207         struct udphdr *uh;
 208         unsigned int mss;
 209         bool copy_dtor;
 210         __sum16 check;
 211         __be16 newlen;
 212
 213         if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
 214                 return __udp_gso_segment_list(gso_skb, features);
 215
 216         mss = skb_shinfo(gso_skb)->gso_size;
 217         if (gso_skb->len <= sizeof(*uh) + mss)
 218                 return ERR_PTR(-EINVAL);
 219
 220         skb_pull(gso_skb, sizeof(*uh));
 221
 222         /* clear destructor to avoid skb_segment assigning it to tail */
 223         copy_dtor = gso_skb->destructor == sock_wfree;
 224         if (copy_dtor)
 225                 gso_skb->destructor = NULL;
 226
 227         segs = skb_segment(gso_skb, features);
 228         if (IS_ERR_OR_NULL(segs)) {
 229                 if (copy_dtor)
 230                         gso_skb->destructor = sock_wfree;
 231                 return segs;
 232         }
 233
 234         /* GSO partial and frag_list segmentation only requires splitting
 235          * the frame into an MSS multiple and possibly a remainder, both
 236          * cases return a GSO skb. So update the mss now.
 237          */
 238         if (skb_is_gso(segs))
 239                 mss *= skb_shinfo(segs)->gso_segs;
 240
 241         seg = segs;
 242         uh = udp_hdr(seg);
 243
 244         /* preserve TX timestamp flags and TS key for first segment */
 245         skb_shinfo(seg)->tskey = skb_shinfo(gso_skb)->tskey;
 246         skb_shinfo(seg)->tx_flags |=
 247                         (skb_shinfo(gso_skb)->tx_flags & SKBTX_ANY_TSTAMP);
 248
 249         /* compute checksum adjustment based on old length versus new */
 250         newlen = htons(sizeof(*uh) + mss);
 251         check = csum16_add(csum16_sub(uh->check, uh->len), newlen);
 252
 253         for (;;) {
 254                 if (copy_dtor) {
 255                         seg->destructor = sock_wfree;
 256                         seg->sk = sk;
 257                         sum_truesize += seg->truesize;
 258                 }
 259
 260                 if (!seg->next)
 261                         break;
 262
 263                 uh->len = newlen;
 264                 uh->check = check;
 265
 266                 if (seg->ip_summed == CHECKSUM_PARTIAL)
 267                         gso_reset_checksum(seg, ~check);
 268                 else
 269                         uh->check = gso_make_checksum(seg, ~check) ? :
 270                                     CSUM_MANGLED_0;
 271
 272                 seg = seg->next;
 273                 uh = udp_hdr(seg);
 274         }
 275
 276         /* last packet can be partial gso_size, account for that in checksum */
 277         newlen = htons(skb_tail_pointer(seg) - skb_transport_header(seg) +
 278                        seg->data_len);
 279         check = csum16_add(csum16_sub(uh->check, uh->len), newlen);
 280
 281         uh->len = newlen;
 282         uh->check = check;
 283
 284         if (seg->ip_summed == CHECKSUM_PARTIAL)
 285                 gso_reset_checksum(seg, ~check);
 286         else
 287                 uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;
 288
 289         /* update refcount for the packet */
 290         if (copy_dtor) {
 291                 int delta = sum_truesize - gso_skb->truesize;
 292
 293                 /* In some pathological cases, delta can be negative.
 294                  * We need to either use refcount_add() or refcount_sub_and_test()
 295                  */
 296                 if (likely(delta >= 0))
 297                         refcount_add(delta, &sk->sk_wmem_alloc);
 298                 else
 299                         WARN_ON_ONCE(refcount_sub_and_test(-delta, &sk->sk_wmem_alloc));
 300         }
 301         return segs;
 302 }
 303 EXPORT_SYMBOL_GPL(__udp_gso_segment);
 304
 305 static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 306                                          netdev_features_t features)
 307 {
 308         struct sk_buff *segs = ERR_PTR(-EINVAL);
 309         unsigned int mss;
 310         __wsum csum;
 311         struct udphdr *uh;
 312         struct iphdr *iph;
 313
 314         if (skb->encapsulation &&
 315             (skb_shinfo(skb)->gso_type &
 316              (SKB_GSO_UDP_TUNNEL|SKB_GSO_UDP_TUNNEL_CSUM))) {
 317                 segs = skb_udp_tunnel_segment(skb, features, false);
 318                 goto out;
 319         }
 320
 321         if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4)))
 322                 goto out;
 323
 324         if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 325                 goto out;
 326
 327         if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 328                 return __udp_gso_segment(skb, features);
 329
 330         mss = skb_shinfo(skb)->gso_size;
 331         if (unlikely(skb->len <= mss))
 332                 goto out;
 333
 334         /* Do software UFO. Complete and fill in the UDP checksum as
 335          * HW cannot do checksum of UDP packets sent as multiple
 336          * IP fragments.
 337          */
 338
 339         uh = udp_hdr(skb);
 340         iph = ip_hdr(skb);
 341
 342         uh->check = 0;
 343         csum = skb_checksum(skb, 0, skb->len, 0);
 344         uh->check = udp_v4_check(skb->len, iph->saddr, iph->daddr, csum);
 345         if (uh->check == 0)
 346                 uh->check = CSUM_MANGLED_0;
 347
 348         skb->ip_summed = CHECKSUM_UNNECESSARY;
 349
 350         /* If there is no outer header we can fake a checksum offload
 351          * due to the fact that we have already done the checksum in
 352          * software prior to segmenting the frame.
 353          */
 354         if (!skb->encap_hdr_csum)
 355                 features |= NETIF_F_HW_CSUM;
 356
 357         /* Fragment the skb. IP headers of the fragments are updated in
 358          * inet_gso_segment()
 359          */
 360         segs = skb_segment(skb, features);
 361 out:
 362         return segs;
 363 }
 364
 365 #define UDP_GRO_CNT_MAX 64
 366 static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
 367                                                struct sk_buff *skb)
 368 {
 369         struct udphdr *uh = udp_hdr(skb);
 370         struct sk_buff *pp = NULL;
 371         struct udphdr *uh2;
 372         struct sk_buff *p;
 373         unsigned int ulen;
 374         int ret = 0;
 375
 376         /* requires non zero csum, for symmetry with GSO */
 377         if (!uh->check) {
 378                 NAPI_GRO_CB(skb)->flush = 1;
 379                 return NULL;
 380         }
 381
 382         /* Do not deal with padded or malicious packets, sorry ! */
 383         ulen = ntohs(uh->len);
 384         if (ulen <= sizeof(*uh) || ulen != skb_gro_len(skb)) {
 385                 NAPI_GRO_CB(skb)->flush = 1;
 386                 return NULL;
 387         }
 388         /* pull encapsulating udp header */
 389         skb_gro_pull(skb, sizeof(struct udphdr));
 390
 391         list_for_each_entry(p, head, list) {
 392                 if (!NAPI_GRO_CB(p)->same_flow)
 393                         continue;
 394
 395                 uh2 = udp_hdr(p);
 396
 397                 /* Match ports only, as csum is always non zero */
 398                 if ((*(u32 *)&uh->source != *(u32 *)&uh2->source)) {
 399                         NAPI_GRO_CB(p)->same_flow = 0;
 400                         continue;
 401                 }
 402
 403                 if (NAPI_GRO_CB(skb)->is_flist != NAPI_GRO_CB(p)->is_flist) {
 404                         NAPI_GRO_CB(skb)->flush = 1;
 405                         return p;
 406                 }
 407
 408                 /* Terminate the flow on len mismatch or if it grow "too much".
 409                  * Under small packet flood GRO count could elsewhere grow a lot
 410                  * leading to excessive truesize values.
 411                  * On len mismatch merge the first packet shorter than gso_size,
 412                  * otherwise complete the GRO packet.
 413                  */
 414                 if (ulen > ntohs(uh2->len)) {
 415                         pp = p;
 416                 } else {
 417                         if (NAPI_GRO_CB(skb)->is_flist) {
 418                                 if (!pskb_may_pull(skb, skb_gro_offset(skb))) {
 419                                         NAPI_GRO_CB(skb)->flush = 1;
 420                                         return NULL;
 421                                 }
 422                                 if ((skb->ip_summed != p->ip_summed) ||
 423                                     (skb->csum_level != p->csum_level)) {
 424                                         NAPI_GRO_CB(skb)->flush = 1;
 425                                         return NULL;
 426                                 }
 427                                 ret = skb_gro_receive_list(p, skb);
 428                         } else {
 429                                 skb_gro_postpull_rcsum(skb, uh,
 430                                                        sizeof(struct udphdr));
 431
 432                                 ret = skb_gro_receive(p, skb);
 433                         }
 434                 }
 435
 436                 if (ret || ulen != ntohs(uh2->len) ||
 437                     NAPI_GRO_CB(p)->count >= UDP_GRO_CNT_MAX)
 438                         pp = p;
 439
 440                 return pp;
 441         }
 442
 443         /* mismatch, but we never need to flush */
 444         return NULL;
 445 }
 446
 447 struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
 448                                 struct udphdr *uh, struct sock *sk)
 449 {
 450         struct sk_buff *pp = NULL;
 451         struct sk_buff *p;
 452         struct udphdr *uh2;
 453         unsigned int off = skb_gro_offset(skb);
 454         int flush = 1;
 455
 456         NAPI_GRO_CB(skb)->is_flist = 0;
 457         if (skb->dev->features & NETIF_F_GRO_FRAGLIST)
 458                 NAPI_GRO_CB(skb)->is_flist = sk ? !udp_sk(sk)->gro_enabled: 1;
 459
 460         if ((sk && udp_sk(sk)->gro_enabled) || NAPI_GRO_CB(skb)->is_flist) {
 461                 pp = call_gro_receive(udp_gro_receive_segment, head, skb);
 462                 return pp;
 463         }
 464
 465         if (!sk || NAPI_GRO_CB(skb)->encap_mark ||
 466             (skb->ip_summed != CHECKSUM_PARTIAL &&
 467              NAPI_GRO_CB(skb)->csum_cnt == 0 &&
 468              !NAPI_GRO_CB(skb)->csum_valid) ||
 469             !udp_sk(sk)->gro_receive)
 470                 goto out;
 471
 472         /* mark that this skb passed once through the tunnel gro layer */
 473         NAPI_GRO_CB(skb)->encap_mark = 1;
 474
 475         flush = 0;
 476
 477         list_for_each_entry(p, head, list) {
 478                 if (!NAPI_GRO_CB(p)->same_flow)
 479                         continue;
 480
 481                 uh2 = (struct udphdr   *)(p->data + off);
 482
 483                 /* Match ports and either checksums are either both zero
 484                  * or nonzero.
 485                  */
 486                 if ((*(u32 *)&uh->source != *(u32 *)&uh2->source) ||
 487                     (!uh->check ^ !uh2->check)) {
 488                         NAPI_GRO_CB(p)->same_flow = 0;
 489                         continue;
 490                 }
 491         }
 492
 493         skb_gro_pull(skb, sizeof(struct udphdr)); /* pull encapsulating udp header */
 494         skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
 495         pp = call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);
 496
 497 out:
 498         skb_gro_flush_final(skb, pp, flush);
 499         return pp;
 500 }
 501 EXPORT_SYMBOL(udp_gro_receive);
 502
 503 INDIRECT_CALLABLE_SCOPE
 504 struct sk_buff *udp4_gro_receive(struct list_head *head, struct sk_buff *skb)
 505 {
 506         struct udphdr *uh = udp_gro_udphdr(skb);
 507         struct sk_buff *pp;
 508         struct sock *sk;
 509
 510         if (unlikely(!uh))
 511                 goto flush;
 512
 513         /* Don't bother verifying checksum if we're going to flush anyway. */
 514         if (NAPI_GRO_CB(skb)->flush)
 515                 goto skip;
 516
 517         if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
 518                                                  inet_gro_compute_pseudo))
 519                 goto flush;
 520         else if (uh->check)
 521                 skb_gro_checksum_try_convert(skb, IPPROTO_UDP,
 522                                              inet_gro_compute_pseudo);
 523 skip:
 524         NAPI_GRO_CB(skb)->is_ipv6 = 0;
 525         rcu_read_lock();
 526         sk = static_branch_unlikely(&udp_encap_needed_key) ? udp4_lib_lookup_skb(skb, uh->source, uh->dest) : NULL;
 527         pp = udp_gro_receive(head, skb, uh, sk);
 528         rcu_read_unlock();
 529         return pp;
 530
 531 flush:
 532         NAPI_GRO_CB(skb)->flush = 1;
 533         return NULL;
 534 }
 535
 536 static int udp_gro_complete_segment(struct sk_buff *skb)
 537 {
 538         struct udphdr *uh = udp_hdr(skb);
 539
 540         skb->csum_start = (unsigned char *)uh - skb->head;
 541         skb->csum_offset = offsetof(struct udphdr, check);
 542         skb->ip_summed = CHECKSUM_PARTIAL;
 543
 544         skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
 545         skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_L4;
 546         return 0;
 547 }
 548
 549 int udp_gro_complete(struct sk_buff *skb, int nhoff,
 550                      udp_lookup_t lookup)
 551 {
 552         __be16 newlen = htons(skb->len - nhoff);
 553         struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
 554         int err = -ENOSYS;
 555         struct sock *sk;
 556
 557         uh->len = newlen;
 558
 559         rcu_read_lock();
 560         sk = INDIRECT_CALL_INET(lookup, udp6_lib_lookup_skb,
 561                                 udp4_lib_lookup_skb, skb, uh->source, uh->dest);
 562         if (sk && udp_sk(sk)->gro_complete) {
 563                 skb_shinfo(skb)->gso_type = uh->check ? SKB_GSO_UDP_TUNNEL_CSUM
 564                                         : SKB_GSO_UDP_TUNNEL;
 565
 566                 /* Set encapsulation before calling into inner gro_complete()
 567                  * functions to make them set up the inner offsets.
 568                  */
 569                 skb->encapsulation = 1;
 570                 err = udp_sk(sk)->gro_complete(sk, skb,
 571                                 nhoff + sizeof(struct udphdr));
 572         } else {
 573                 err = udp_gro_complete_segment(skb);
 574         }
 575         rcu_read_unlock();
 576
 577         if (skb->remcsum_offload)
 578                 skb_shinfo(skb)->gso_type |= SKB_GSO_TUNNEL_REMCSUM;
 579
 580         return err;
 581 }
 582 EXPORT_SYMBOL(udp_gro_complete);
 583
 584 INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
 585 {
 586         const struct iphdr *iph = ip_hdr(skb);
 587         struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
 588
 589         if (NAPI_GRO_CB(skb)->is_flist) {
 590                 uh->len = htons(skb->len - nhoff);
 591
 592                 skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
 593                 skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
 594
 595                 if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
 596                         if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
 597                                 skb->csum_level++;
 598                 } else {
 599                         skb->ip_summed = CHECKSUM_UNNECESSARY;
 600                         skb->csum_level = 0;
 601                 }
 602
 603                 return 0;
 604         }
 605
 606         if (uh->check)
 607                 uh->check = ~udp_v4_check(skb->len - nhoff, iph->saddr,
 608                                           iph->daddr, 0);
 609
 610         return udp_gro_complete(skb, nhoff, udp4_lib_lookup_skb);
 611 }
 612
 613 static const struct net_offload udpv4_offload = {
 614         .callbacks = {
 615                 .gso_segment = udp4_ufo_fragment,
 616                 .gro_receive  = udp4_gro_receive,
 617                 .gro_complete = udp4_gro_complete,
 618         },
 619 };
 620
 621 int __init udpv4_offload_init(void)
 622 {
 623         return inet_add_offload(&udpv4_offload, IPPROTO_UDP);
 624 }