net/mptcp/options.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Multipath TCP
   3  *
   4  * Copyright (c) 2017 - 2019, Intel Corporation.
   5  */
   6
   7 #include <linux/kernel.h>
   8 #include <net/tcp.h>
   9 #include <net/mptcp.h>
  10 #include "protocol.h"
  11
  12 static bool mptcp_cap_flag_sha256(u8 flags)
  13 {
  14         return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
  15 }
  16
  17 void mptcp_parse_option(const struct sk_buff *skb, const unsigned char *ptr,
  18                         int opsize, struct tcp_options_received *opt_rx)
  19 {
  20         struct mptcp_options_received *mp_opt = &opt_rx->mptcp;
  21         u8 subtype = *ptr >> 4;
  22         int expected_opsize;
  23         u8 version;
  24         u8 flags;
  25
  26         switch (subtype) {
  27         case MPTCPOPT_MP_CAPABLE:
  28                 /* strict size checking */
  29                 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
  30                         if (skb->len > tcp_hdr(skb)->doff << 2)
  31                                 expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
  32                         else
  33                                 expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
  34                 } else {
  35                         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
  36                                 expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
  37                         else
  38                                 expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
  39                 }
  40                 if (opsize != expected_opsize)
  41                         break;
  42
  43                 /* try to be gentle vs future versions on the initial syn */
  44                 version = *ptr++ & MPTCP_VERSION_MASK;
  45                 if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
  46                         if (version != MPTCP_SUPPORTED_VERSION)
  47                                 break;
  48                 } else if (version < MPTCP_SUPPORTED_VERSION) {
  49                         break;
  50                 }
  51
  52                 flags = *ptr++;
  53                 if (!mptcp_cap_flag_sha256(flags) ||
  54                     (flags & MPTCP_CAP_EXTENSIBILITY))
  55                         break;
  56
  57                 /* RFC 6824, Section 3.1:
  58                  * "For the Checksum Required bit (labeled "A"), if either
  59                  * host requires the use of checksums, checksums MUST be used.
  60                  * In other words, the only way for checksums not to be used
  61                  * is if both hosts in their SYNs set A=0."
  62                  *
  63                  * Section 3.3.0:
  64                  * "If a checksum is not present when its use has been
  65                  * negotiated, the receiver MUST close the subflow with a RST as
  66                  * it is considered broken."
  67                  *
  68                  * We don't implement DSS checksum - fall back to TCP.
  69                  */
  70                 if (flags & MPTCP_CAP_CHECKSUM_REQD)
  71                         break;
  72
  73                 mp_opt->mp_capable = 1;
  74                 if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
  75                         mp_opt->sndr_key = get_unaligned_be64(ptr);
  76                         ptr += 8;
  77                 }
  78                 if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
  79                         mp_opt->rcvr_key = get_unaligned_be64(ptr);
  80                         ptr += 8;
  81                 }
  82                 if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA) {
  83                         /* Section 3.1.:
  84                          * "the data parameters in a MP_CAPABLE are semantically
  85                          * equivalent to those in a DSS option and can be used
  86                          * interchangeably."
  87                          */
  88                         mp_opt->dss = 1;
  89                         mp_opt->use_map = 1;
  90                         mp_opt->mpc_map = 1;
  91                         mp_opt->data_len = get_unaligned_be16(ptr);
  92                         ptr += 2;
  93                 }
  94                 pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d",
  95                          version, flags, opsize, mp_opt->sndr_key,
  96                          mp_opt->rcvr_key, mp_opt->data_len);
  97                 break;
  98
  99         case MPTCPOPT_DSS:
 100                 pr_debug("DSS");
 101                 ptr++;
 102
 103                 /* we must clear 'mpc_map' be able to detect MP_CAPABLE
 104                  * map vs DSS map in mptcp_incoming_options(), and reconstruct
 105                  * map info accordingly
 106                  */
 107                 mp_opt->mpc_map = 0;
 108                 flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
 109                 mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
 110                 mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
 111                 mp_opt->use_map = (flags & MPTCP_DSS_HAS_MAP) != 0;
 112                 mp_opt->ack64 = (flags & MPTCP_DSS_ACK64) != 0;
 113                 mp_opt->use_ack = (flags & MPTCP_DSS_HAS_ACK);
 114
 115                 pr_debug("data_fin=%d dsn64=%d use_map=%d ack64=%d use_ack=%d",
 116                          mp_opt->data_fin, mp_opt->dsn64,
 117                          mp_opt->use_map, mp_opt->ack64,
 118                          mp_opt->use_ack);
 119
 120                 expected_opsize = TCPOLEN_MPTCP_DSS_BASE;
 121
 122                 if (mp_opt->use_ack) {
 123                         if (mp_opt->ack64)
 124                                 expected_opsize += TCPOLEN_MPTCP_DSS_ACK64;
 125                         else
 126                                 expected_opsize += TCPOLEN_MPTCP_DSS_ACK32;
 127                 }
 128
 129                 if (mp_opt->use_map) {
 130                         if (mp_opt->dsn64)
 131                                 expected_opsize += TCPOLEN_MPTCP_DSS_MAP64;
 132                         else
 133                                 expected_opsize += TCPOLEN_MPTCP_DSS_MAP32;
 134                 }
 135
 136                 /* RFC 6824, Section 3.3:
 137                  * If a checksum is present, but its use had
 138                  * not been negotiated in the MP_CAPABLE handshake,
 139                  * the checksum field MUST be ignored.
 140                  */
 141                 if (opsize != expected_opsize &&
 142                     opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
 143                         break;
 144
 145                 mp_opt->dss = 1;
 146
 147                 if (mp_opt->use_ack) {
 148                         if (mp_opt->ack64) {
 149                                 mp_opt->data_ack = get_unaligned_be64(ptr);
 150                                 ptr += 8;
 151                         } else {
 152                                 mp_opt->data_ack = get_unaligned_be32(ptr);
 153                                 ptr += 4;
 154                         }
 155
 156                         pr_debug("data_ack=%llu", mp_opt->data_ack);
 157                 }
 158
 159                 if (mp_opt->use_map) {
 160                         if (mp_opt->dsn64) {
 161                                 mp_opt->data_seq = get_unaligned_be64(ptr);
 162                                 ptr += 8;
 163                         } else {
 164                                 mp_opt->data_seq = get_unaligned_be32(ptr);
 165                                 ptr += 4;
 166                         }
 167
 168                         mp_opt->subflow_seq = get_unaligned_be32(ptr);
 169                         ptr += 4;
 170
 171                         mp_opt->data_len = get_unaligned_be16(ptr);
 172                         ptr += 2;
 173
 174                         pr_debug("data_seq=%llu subflow_seq=%u data_len=%u",
 175                                  mp_opt->data_seq, mp_opt->subflow_seq,
 176                                  mp_opt->data_len);
 177                 }
 178
 179                 break;
 180
 181         default:
 182                 break;
 183         }
 184 }
 185
 186 void mptcp_get_options(const struct sk_buff *skb,
 187                        struct tcp_options_received *opt_rx)
 188 {
 189         const unsigned char *ptr;
 190         const struct tcphdr *th = tcp_hdr(skb);
 191         int length = (th->doff * 4) - sizeof(struct tcphdr);
 192
 193         ptr = (const unsigned char *)(th + 1);
 194
 195         while (length > 0) {
 196                 int opcode = *ptr++;
 197                 int opsize;
 198
 199                 switch (opcode) {
 200                 case TCPOPT_EOL:
 201                         return;
 202                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 203                         length--;
 204                         continue;
 205                 default:
 206                         opsize = *ptr++;
 207                         if (opsize < 2) /* "silly options" */
 208                                 return;
 209                         if (opsize > length)
 210                                 return; /* don't parse partial options */
 211                         if (opcode == TCPOPT_MPTCP)
 212                                 mptcp_parse_option(skb, ptr, opsize, opt_rx);
 213                         ptr += opsize - 2;
 214                         length -= opsize;
 215                 }
 216         }
 217 }
 218
 219 bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 220                        unsigned int *size, struct mptcp_out_options *opts)
 221 {
 222         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 223
 224         /* we will use snd_isn to detect first pkt [re]transmission
 225          * in mptcp_established_options_mp()
 226          */
 227         subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
 228         if (subflow->request_mptcp) {
 229                 pr_debug("local_key=%llu", subflow->local_key);
 230                 opts->suboptions = OPTION_MPTCP_MPC_SYN;
 231                 opts->sndr_key = subflow->local_key;
 232                 *size = TCPOLEN_MPTCP_MPC_SYN;
 233                 return true;
 234         }
 235         return false;
 236 }
 237
 238 void mptcp_rcv_synsent(struct sock *sk)
 239 {
 240         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 241         struct tcp_sock *tp = tcp_sk(sk);
 242
 243         pr_debug("subflow=%p", subflow);
 244         if (subflow->request_mptcp && tp->rx_opt.mptcp.mp_capable) {
 245                 subflow->mp_capable = 1;
 246                 subflow->can_ack = 1;
 247                 subflow->remote_key = tp->rx_opt.mptcp.sndr_key;
 248         } else {
 249                 tcp_sk(sk)->is_mptcp = 0;
 250         }
 251 }
 252
 253 static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 254                                          unsigned int *size,
 255                                          unsigned int remaining,
 256                                          struct mptcp_out_options *opts)
 257 {
 258         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 259         struct mptcp_ext *mpext;
 260         unsigned int data_len;
 261
 262         pr_debug("subflow=%p fourth_ack=%d seq=%x:%x remaining=%d", subflow,
 263                  subflow->fourth_ack, subflow->snd_isn,
 264                  skb ? TCP_SKB_CB(skb)->seq : 0, remaining);
 265
 266         if (subflow->mp_capable && !subflow->fourth_ack && skb &&
 267             subflow->snd_isn == TCP_SKB_CB(skb)->seq) {
 268                 /* When skb is not available, we better over-estimate the
 269                  * emitted options len. A full DSS option is longer than
 270                  * TCPOLEN_MPTCP_MPC_ACK_DATA, so let's the caller try to fit
 271                  * that.
 272                  */
 273                 mpext = mptcp_get_ext(skb);
 274                 data_len = mpext ? mpext->data_len : 0;
 275
 276                 /* we will check ext_copy.data_len in mptcp_write_options() to
 277                  * discriminate between TCPOLEN_MPTCP_MPC_ACK_DATA and
 278                  * TCPOLEN_MPTCP_MPC_ACK
 279                  */
 280                 opts->ext_copy.data_len = data_len;
 281                 opts->suboptions = OPTION_MPTCP_MPC_ACK;
 282                 opts->sndr_key = subflow->local_key;
 283                 opts->rcvr_key = subflow->remote_key;
 284
 285                 /* Section 3.1.
 286                  * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
 287                  * packets that start the first subflow of an MPTCP connection,
 288                  * as well as the first packet that carries data
 289                  */
 290                 if (data_len > 0)
 291                         *size = ALIGN(TCPOLEN_MPTCP_MPC_ACK_DATA, 4);
 292                 else
 293                         *size = TCPOLEN_MPTCP_MPC_ACK;
 294
 295                 pr_debug("subflow=%p, local_key=%llu, remote_key=%llu map_len=%d",
 296                          subflow, subflow->local_key, subflow->remote_key,
 297                          data_len);
 298
 299                 return true;
 300         }
 301         return false;
 302 }
 303
 304 static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
 305                                  struct mptcp_ext *ext)
 306 {
 307         ext->data_fin = 1;
 308
 309         if (!ext->use_map) {
 310                 /* RFC6824 requires a DSS mapping with specific values
 311                  * if DATA_FIN is set but no data payload is mapped
 312                  */
 313                 ext->use_map = 1;
 314                 ext->dsn64 = 1;
 315                 ext->data_seq = mptcp_sk(subflow->conn)->write_seq;
 316                 ext->subflow_seq = 0;
 317                 ext->data_len = 1;
 318         } else {
 319                 /* If there's an existing DSS mapping, DATA_FIN consumes
 320                  * 1 additional byte of mapping space.
 321                  */
 322                 ext->data_len++;
 323         }
 324 }
 325
 326 static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 327                                           unsigned int *size,
 328                                           unsigned int remaining,
 329                                           struct mptcp_out_options *opts)
 330 {
 331         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 332         unsigned int dss_size = 0;
 333         struct mptcp_ext *mpext;
 334         struct mptcp_sock *msk;
 335         unsigned int ack_size;
 336         bool ret = false;
 337         bool can_ack;
 338         u64 ack_seq;
 339         u8 tcp_fin;
 340
 341         if (skb) {
 342                 mpext = mptcp_get_ext(skb);
 343                 tcp_fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
 344         } else {
 345                 mpext = NULL;
 346                 tcp_fin = 0;
 347         }
 348
 349         if (!skb || (mpext && mpext->use_map) || tcp_fin) {
 350                 unsigned int map_size;
 351
 352                 map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;
 353
 354                 remaining -= map_size;
 355                 dss_size = map_size;
 356                 if (mpext)
 357                         opts->ext_copy = *mpext;
 358
 359                 if (skb && tcp_fin &&
 360                     subflow->conn->sk_state != TCP_ESTABLISHED)
 361                         mptcp_write_data_fin(subflow, &opts->ext_copy);
 362                 ret = true;
 363         }
 364
 365         /* passive sockets msk will set the 'can_ack' after accept(), even
 366          * if the first subflow may have the already the remote key handy
 367          */
 368         can_ack = true;
 369         opts->ext_copy.use_ack = 0;
 370         msk = mptcp_sk(subflow->conn);
 371         if (likely(msk && READ_ONCE(msk->can_ack))) {
 372                 ack_seq = msk->ack_seq;
 373         } else if (subflow->can_ack) {
 374                 mptcp_crypto_key_sha(subflow->remote_key, NULL, &ack_seq);
 375                 ack_seq++;
 376         } else {
 377                 can_ack = false;
 378         }
 379
 380         if (unlikely(!can_ack)) {
 381                 *size = ALIGN(dss_size, 4);
 382                 return ret;
 383         }
 384
 385         ack_size = TCPOLEN_MPTCP_DSS_ACK64;
 386
 387         /* Add kind/length/subtype/flag overhead if mapping is not populated */
 388         if (dss_size == 0)
 389                 ack_size += TCPOLEN_MPTCP_DSS_BASE;
 390
 391         dss_size += ack_size;
 392
 393         opts->ext_copy.data_ack = ack_seq;
 394         opts->ext_copy.ack64 = 1;
 395         opts->ext_copy.use_ack = 1;
 396
 397         *size = ALIGN(dss_size, 4);
 398         return true;
 399 }
 400
 401 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 402                                unsigned int *size, unsigned int remaining,
 403                                struct mptcp_out_options *opts)
 404 {
 405         unsigned int opt_size = 0;
 406         bool ret = false;
 407
 408         if (mptcp_established_options_mp(sk, skb, &opt_size, remaining, opts))
 409                 ret = true;
 410         else if (mptcp_established_options_dss(sk, skb, &opt_size, remaining,
 411                                                opts))
 412                 ret = true;
 413
 414         /* we reserved enough space for the above options, and exceeding the
 415          * TCP option space would be fatal
 416          */
 417         if (WARN_ON_ONCE(opt_size > remaining))
 418                 return false;
 419
 420         *size += opt_size;
 421         remaining -= opt_size;
 422
 423         return ret;
 424 }
 425
 426 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 427                           struct mptcp_out_options *opts)
 428 {
 429         struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
 430
 431         if (subflow_req->mp_capable) {
 432                 opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
 433                 opts->sndr_key = subflow_req->local_key;
 434                 *size = TCPOLEN_MPTCP_MPC_SYNACK;
 435                 pr_debug("subflow_req=%p, local_key=%llu",
 436                          subflow_req, subflow_req->local_key);
 437                 return true;
 438         }
 439         return false;
 440 }
 441
 442 static bool check_fourth_ack(struct mptcp_subflow_context *subflow,
 443                              struct sk_buff *skb,
 444                              struct mptcp_options_received *mp_opt)
 445 {
 446         /* here we can process OoO, in-window pkts, only in-sequence 4th ack
 447          * are relevant
 448          */
 449         if (likely(subflow->fourth_ack ||
 450                    TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1))
 451                 return true;
 452
 453         if (mp_opt->use_ack)
 454                 subflow->fourth_ack = 1;
 455
 456         if (subflow->can_ack)
 457                 return true;
 458
 459         /* If the first established packet does not contain MP_CAPABLE + data
 460          * then fallback to TCP
 461          */
 462         if (!mp_opt->mp_capable) {
 463                 subflow->mp_capable = 0;
 464                 tcp_sk(mptcp_subflow_tcp_sock(subflow))->is_mptcp = 0;
 465                 return false;
 466         }
 467         subflow->remote_key = mp_opt->sndr_key;
 468         subflow->can_ack = 1;
 469         return true;
 470 }
 471
 472 void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb,
 473                             struct tcp_options_received *opt_rx)
 474 {
 475         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 476         struct mptcp_options_received *mp_opt;
 477         struct mptcp_ext *mpext;
 478
 479         mp_opt = &opt_rx->mptcp;
 480         if (!check_fourth_ack(subflow, skb, mp_opt))
 481                 return;
 482
 483         if (!mp_opt->dss)
 484                 return;
 485
 486         mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
 487         if (!mpext)
 488                 return;
 489
 490         memset(mpext, 0, sizeof(*mpext));
 491
 492         if (mp_opt->use_map) {
 493                 if (mp_opt->mpc_map) {
 494                         /* this is an MP_CAPABLE carrying MPTCP data
 495                          * we know this map the first chunk of data
 496                          */
 497                         mptcp_crypto_key_sha(subflow->remote_key, NULL,
 498                                              &mpext->data_seq);
 499                         mpext->data_seq++;
 500                         mpext->subflow_seq = 1;
 501                         mpext->dsn64 = 1;
 502                         mpext->mpc_map = 1;
 503                 } else {
 504                         mpext->data_seq = mp_opt->data_seq;
 505                         mpext->subflow_seq = mp_opt->subflow_seq;
 506                         mpext->dsn64 = mp_opt->dsn64;
 507                 }
 508                 mpext->data_len = mp_opt->data_len;
 509                 mpext->use_map = 1;
 510         }
 511
 512         if (mp_opt->use_ack) {
 513                 mpext->data_ack = mp_opt->data_ack;
 514                 mpext->use_ack = 1;
 515                 mpext->ack64 = mp_opt->ack64;
 516         }
 517
 518         mpext->data_fin = mp_opt->data_fin;
 519 }
 520
 521 void mptcp_write_options(__be32 *ptr, struct mptcp_out_options *opts)
 522 {
 523         if ((OPTION_MPTCP_MPC_SYN | OPTION_MPTCP_MPC_SYNACK |
 524              OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
 525                 u8 len;
 526
 527                 if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
 528                         len = TCPOLEN_MPTCP_MPC_SYN;
 529                 else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions)
 530                         len = TCPOLEN_MPTCP_MPC_SYNACK;
 531                 else if (opts->ext_copy.data_len)
 532                         len = TCPOLEN_MPTCP_MPC_ACK_DATA;
 533                 else
 534                         len = TCPOLEN_MPTCP_MPC_ACK;
 535
 536                 *ptr++ = htonl((TCPOPT_MPTCP << 24) | (len << 16) |
 537                                (MPTCPOPT_MP_CAPABLE << 12) |
 538                                (MPTCP_SUPPORTED_VERSION << 8) |
 539                                MPTCP_CAP_HMAC_SHA256);
 540
 541                 if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
 542                     opts->suboptions))
 543                         goto mp_capable_done;
 544
 545                 put_unaligned_be64(opts->sndr_key, ptr);
 546                 ptr += 2;
 547                 if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
 548                         goto mp_capable_done;
 549
 550                 put_unaligned_be64(opts->rcvr_key, ptr);
 551                 ptr += 2;
 552                 if (!opts->ext_copy.data_len)
 553                         goto mp_capable_done;
 554
 555                 put_unaligned_be32(opts->ext_copy.data_len << 16 |
 556                                    TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
 557                 ptr += 1;
 558         }
 559
 560 mp_capable_done:
 561         if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
 562                 struct mptcp_ext *mpext = &opts->ext_copy;
 563                 u8 len = TCPOLEN_MPTCP_DSS_BASE;
 564                 u8 flags = 0;
 565
 566                 if (mpext->use_ack) {
 567                         len += TCPOLEN_MPTCP_DSS_ACK64;
 568                         flags = MPTCP_DSS_HAS_ACK | MPTCP_DSS_ACK64;
 569                 }
 570
 571                 if (mpext->use_map) {
 572                         len += TCPOLEN_MPTCP_DSS_MAP64;
 573
 574                         /* Use only 64-bit mapping flags for now, add
 575                          * support for optional 32-bit mappings later.
 576                          */
 577                         flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
 578                         if (mpext->data_fin)
 579                                 flags |= MPTCP_DSS_DATA_FIN;
 580                 }
 581
 582                 *ptr++ = htonl((TCPOPT_MPTCP << 24) |
 583                                (len  << 16) |
 584                                (MPTCPOPT_DSS << 12) |
 585                                (flags));
 586
 587                 if (mpext->use_ack) {
 588                         put_unaligned_be64(mpext->data_ack, ptr);
 589                         ptr += 2;
 590                 }
 591
 592                 if (mpext->use_map) {
 593                         put_unaligned_be64(mpext->data_seq, ptr);
 594                         ptr += 2;
 595                         put_unaligned_be32(mpext->subflow_seq, ptr);
 596                         ptr += 1;
 597                         put_unaligned_be32(mpext->data_len << 16 |
 598                                            TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
 599                 }
 600         }
 601 }