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 #define pr_fmt(fmt) "MPTCP: " fmt
   8
   9 #include <linux/kernel.h>
  10 #include <crypto/sha2.h>
  11 #include <net/tcp.h>
  12 #include <net/mptcp.h>
  13 #include "protocol.h"
  14 #include "mib.h"
  15
  16 #include <trace/events/mptcp.h>
  17
  18 static bool mptcp_cap_flag_sha256(u8 flags)
  19 {
  20         return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
  21 }
  22
  23 static void mptcp_parse_option(const struct sk_buff *skb,
  24                                const unsigned char *ptr, int opsize,
  25                                struct mptcp_options_received *mp_opt)
  26 {
  27         u8 subtype = *ptr >> 4;
  28         int expected_opsize;
  29         u8 version;
  30         u8 flags;
  31         u8 i;
  32
  33         switch (subtype) {
  34         case MPTCPOPT_MP_CAPABLE:
  35                 /* strict size checking */
  36                 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
  37                         if (skb->len > tcp_hdr(skb)->doff << 2)
  38                                 expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
  39                         else
  40                                 expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
  41                 } else {
  42                         if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
  43                                 expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
  44                         else
  45                                 expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
  46                 }
  47
  48                 /* Cfr RFC 8684 Section 3.3.0:
  49                  * If a checksum is present but its use had
  50                  * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
  51                  * close the subflow with a RST, as it is not behaving as negotiated.
  52                  * If a checksum is not present when its use has been negotiated, the
  53                  * receiver MUST close the subflow with a RST, as it is considered
  54                  * broken
  55                  * We parse even option with mismatching csum presence, so that
  56                  * later in subflow_data_ready we can trigger the reset.
  57                  */
  58                 if (opsize != expected_opsize &&
  59                     (expected_opsize != TCPOLEN_MPTCP_MPC_ACK_DATA ||
  60                      opsize != TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM))
  61                         break;
  62
  63                 /* try to be gentle vs future versions on the initial syn */
  64                 version = *ptr++ & MPTCP_VERSION_MASK;
  65                 if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
  66                         if (version != MPTCP_SUPPORTED_VERSION)
  67                                 break;
  68                 } else if (version < MPTCP_SUPPORTED_VERSION) {
  69                         break;
  70                 }
  71
  72                 flags = *ptr++;
  73                 if (!mptcp_cap_flag_sha256(flags) ||
  74                     (flags & MPTCP_CAP_EXTENSIBILITY))
  75                         break;
  76
  77                 /* RFC 6824, Section 3.1:
  78                  * "For the Checksum Required bit (labeled "A"), if either
  79                  * host requires the use of checksums, checksums MUST be used.
  80                  * In other words, the only way for checksums not to be used
  81                  * is if both hosts in their SYNs set A=0."
  82                  */
  83                 if (flags & MPTCP_CAP_CHECKSUM_REQD)
  84                         mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
  85
  86                 mp_opt->deny_join_id0 = !!(flags & MPTCP_CAP_DENY_JOIN_ID0);
  87
  88                 mp_opt->suboptions |= OPTIONS_MPTCP_MPC;
  89                 if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
  90                         mp_opt->sndr_key = get_unaligned_be64(ptr);
  91                         ptr += 8;
  92                 }
  93                 if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
  94                         mp_opt->rcvr_key = get_unaligned_be64(ptr);
  95                         ptr += 8;
  96                 }
  97                 if (opsize >= TCPOLEN_MPTCP_MPC_ACK_DATA) {
  98                         /* Section 3.1.:
  99                          * "the data parameters in a MP_CAPABLE are semantically
 100                          * equivalent to those in a DSS option and can be used
 101                          * interchangeably."
 102                          */
 103                         mp_opt->suboptions |= OPTION_MPTCP_DSS;
 104                         mp_opt->use_map = 1;
 105                         mp_opt->mpc_map = 1;
 106                         mp_opt->data_len = get_unaligned_be16(ptr);
 107                         ptr += 2;
 108                 }
 109                 if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM) {
 110                         mp_opt->csum = get_unaligned((__force __sum16 *)ptr);
 111                         mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
 112                         ptr += 2;
 113                 }
 114                 pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d csum=%u",
 115                          version, flags, opsize, mp_opt->sndr_key,
 116                          mp_opt->rcvr_key, mp_opt->data_len, mp_opt->csum);
 117                 break;
 118
 119         case MPTCPOPT_MP_JOIN:
 120                 mp_opt->suboptions |= OPTIONS_MPTCP_MPJ;
 121                 if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
 122                         mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
 123                         mp_opt->join_id = *ptr++;
 124                         mp_opt->token = get_unaligned_be32(ptr);
 125                         ptr += 4;
 126                         mp_opt->nonce = get_unaligned_be32(ptr);
 127                         ptr += 4;
 128                         pr_debug("MP_JOIN bkup=%u, id=%u, token=%u, nonce=%u",
 129                                  mp_opt->backup, mp_opt->join_id,
 130                                  mp_opt->token, mp_opt->nonce);
 131                 } else if (opsize == TCPOLEN_MPTCP_MPJ_SYNACK) {
 132                         mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
 133                         mp_opt->join_id = *ptr++;
 134                         mp_opt->thmac = get_unaligned_be64(ptr);
 135                         ptr += 8;
 136                         mp_opt->nonce = get_unaligned_be32(ptr);
 137                         ptr += 4;
 138                         pr_debug("MP_JOIN bkup=%u, id=%u, thmac=%llu, nonce=%u",
 139                                  mp_opt->backup, mp_opt->join_id,
 140                                  mp_opt->thmac, mp_opt->nonce);
 141                 } else if (opsize == TCPOLEN_MPTCP_MPJ_ACK) {
 142                         ptr += 2;
 143                         memcpy(mp_opt->hmac, ptr, MPTCPOPT_HMAC_LEN);
 144                         pr_debug("MP_JOIN hmac");
 145                 } else {
 146                         mp_opt->suboptions &= ~OPTIONS_MPTCP_MPJ;
 147                 }
 148                 break;
 149
 150         case MPTCPOPT_DSS:
 151                 pr_debug("DSS");
 152                 ptr++;
 153
 154                 /* we must clear 'mpc_map' be able to detect MP_CAPABLE
 155                  * map vs DSS map in mptcp_incoming_options(), and reconstruct
 156                  * map info accordingly
 157                  */
 158                 mp_opt->mpc_map = 0;
 159                 flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
 160                 mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
 161                 mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
 162                 mp_opt->use_map = (flags & MPTCP_DSS_HAS_MAP) != 0;
 163                 mp_opt->ack64 = (flags & MPTCP_DSS_ACK64) != 0;
 164                 mp_opt->use_ack = (flags & MPTCP_DSS_HAS_ACK);
 165
 166                 pr_debug("data_fin=%d dsn64=%d use_map=%d ack64=%d use_ack=%d",
 167                          mp_opt->data_fin, mp_opt->dsn64,
 168                          mp_opt->use_map, mp_opt->ack64,
 169                          mp_opt->use_ack);
 170
 171                 expected_opsize = TCPOLEN_MPTCP_DSS_BASE;
 172
 173                 if (mp_opt->use_ack) {
 174                         if (mp_opt->ack64)
 175                                 expected_opsize += TCPOLEN_MPTCP_DSS_ACK64;
 176                         else
 177                                 expected_opsize += TCPOLEN_MPTCP_DSS_ACK32;
 178                 }
 179
 180                 if (mp_opt->use_map) {
 181                         if (mp_opt->dsn64)
 182                                 expected_opsize += TCPOLEN_MPTCP_DSS_MAP64;
 183                         else
 184                                 expected_opsize += TCPOLEN_MPTCP_DSS_MAP32;
 185                 }
 186
 187                 /* Always parse any csum presence combination, we will enforce
 188                  * RFC 8684 Section 3.3.0 checks later in subflow_data_ready
 189                  */
 190                 if (opsize != expected_opsize &&
 191                     opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
 192                         break;
 193
 194                 mp_opt->suboptions |= OPTION_MPTCP_DSS;
 195                 if (mp_opt->use_ack) {
 196                         if (mp_opt->ack64) {
 197                                 mp_opt->data_ack = get_unaligned_be64(ptr);
 198                                 ptr += 8;
 199                         } else {
 200                                 mp_opt->data_ack = get_unaligned_be32(ptr);
 201                                 ptr += 4;
 202                         }
 203
 204                         pr_debug("data_ack=%llu", mp_opt->data_ack);
 205                 }
 206
 207                 if (mp_opt->use_map) {
 208                         if (mp_opt->dsn64) {
 209                                 mp_opt->data_seq = get_unaligned_be64(ptr);
 210                                 ptr += 8;
 211                         } else {
 212                                 mp_opt->data_seq = get_unaligned_be32(ptr);
 213                                 ptr += 4;
 214                         }
 215
 216                         mp_opt->subflow_seq = get_unaligned_be32(ptr);
 217                         ptr += 4;
 218
 219                         mp_opt->data_len = get_unaligned_be16(ptr);
 220                         ptr += 2;
 221
 222                         if (opsize == expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM) {
 223                                 mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
 224                                 mp_opt->csum = get_unaligned((__force __sum16 *)ptr);
 225                                 ptr += 2;
 226                         }
 227
 228                         pr_debug("data_seq=%llu subflow_seq=%u data_len=%u csum=%d:%u",
 229                                  mp_opt->data_seq, mp_opt->subflow_seq,
 230                                  mp_opt->data_len, !!(mp_opt->suboptions & OPTION_MPTCP_CSUMREQD),
 231                                  mp_opt->csum);
 232                 }
 233
 234                 break;
 235
 236         case MPTCPOPT_ADD_ADDR:
 237                 mp_opt->echo = (*ptr++) & MPTCP_ADDR_ECHO;
 238                 if (!mp_opt->echo) {
 239                         if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
 240                             opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT)
 241                                 mp_opt->addr.family = AF_INET;
 242 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 243                         else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6 ||
 244                                  opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT)
 245                                 mp_opt->addr.family = AF_INET6;
 246 #endif
 247                         else
 248                                 break;
 249                 } else {
 250                         if (opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE ||
 251                             opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT)
 252                                 mp_opt->addr.family = AF_INET;
 253 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 254                         else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE ||
 255                                  opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT)
 256                                 mp_opt->addr.family = AF_INET6;
 257 #endif
 258                         else
 259                                 break;
 260                 }
 261
 262                 mp_opt->suboptions |= OPTION_MPTCP_ADD_ADDR;
 263                 mp_opt->addr.id = *ptr++;
 264                 mp_opt->addr.port = 0;
 265                 mp_opt->ahmac = 0;
 266                 if (mp_opt->addr.family == AF_INET) {
 267                         memcpy((u8 *)&mp_opt->addr.addr.s_addr, (u8 *)ptr, 4);
 268                         ptr += 4;
 269                         if (opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT ||
 270                             opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT) {
 271                                 mp_opt->addr.port = htons(get_unaligned_be16(ptr));
 272                                 ptr += 2;
 273                         }
 274                 }
 275 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 276                 else {
 277                         memcpy(mp_opt->addr.addr6.s6_addr, (u8 *)ptr, 16);
 278                         ptr += 16;
 279                         if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT ||
 280                             opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT) {
 281                                 mp_opt->addr.port = htons(get_unaligned_be16(ptr));
 282                                 ptr += 2;
 283                         }
 284                 }
 285 #endif
 286                 if (!mp_opt->echo) {
 287                         mp_opt->ahmac = get_unaligned_be64(ptr);
 288                         ptr += 8;
 289                 }
 290                 pr_debug("ADD_ADDR%s: id=%d, ahmac=%llu, echo=%d, port=%d",
 291                          (mp_opt->addr.family == AF_INET6) ? "6" : "",
 292                          mp_opt->addr.id, mp_opt->ahmac, mp_opt->echo, ntohs(mp_opt->addr.port));
 293                 break;
 294
 295         case MPTCPOPT_RM_ADDR:
 296                 if (opsize < TCPOLEN_MPTCP_RM_ADDR_BASE + 1 ||
 297                     opsize > TCPOLEN_MPTCP_RM_ADDR_BASE + MPTCP_RM_IDS_MAX)
 298                         break;
 299
 300                 ptr++;
 301
 302                 mp_opt->suboptions |= OPTION_MPTCP_RM_ADDR;
 303                 mp_opt->rm_list.nr = opsize - TCPOLEN_MPTCP_RM_ADDR_BASE;
 304                 for (i = 0; i < mp_opt->rm_list.nr; i++)
 305                         mp_opt->rm_list.ids[i] = *ptr++;
 306                 pr_debug("RM_ADDR: rm_list_nr=%d", mp_opt->rm_list.nr);
 307                 break;
 308
 309         case MPTCPOPT_MP_PRIO:
 310                 if (opsize != TCPOLEN_MPTCP_PRIO)
 311                         break;
 312
 313                 mp_opt->suboptions |= OPTION_MPTCP_PRIO;
 314                 mp_opt->backup = *ptr++ & MPTCP_PRIO_BKUP;
 315                 pr_debug("MP_PRIO: prio=%d", mp_opt->backup);
 316                 break;
 317
 318         case MPTCPOPT_MP_FASTCLOSE:
 319                 if (opsize != TCPOLEN_MPTCP_FASTCLOSE)
 320                         break;
 321
 322                 ptr += 2;
 323                 mp_opt->rcvr_key = get_unaligned_be64(ptr);
 324                 ptr += 8;
 325                 mp_opt->suboptions |= OPTION_MPTCP_FASTCLOSE;
 326                 pr_debug("MP_FASTCLOSE: recv_key=%llu", mp_opt->rcvr_key);
 327                 break;
 328
 329         case MPTCPOPT_RST:
 330                 if (opsize != TCPOLEN_MPTCP_RST)
 331                         break;
 332
 333                 if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
 334                         break;
 335
 336                 mp_opt->suboptions |= OPTION_MPTCP_RST;
 337                 flags = *ptr++;
 338                 mp_opt->reset_transient = flags & MPTCP_RST_TRANSIENT;
 339                 mp_opt->reset_reason = *ptr;
 340                 pr_debug("MP_RST: transient=%u reason=%u",
 341                          mp_opt->reset_transient, mp_opt->reset_reason);
 342                 break;
 343
 344         case MPTCPOPT_MP_FAIL:
 345                 if (opsize != TCPOLEN_MPTCP_FAIL)
 346                         break;
 347
 348                 ptr += 2;
 349                 mp_opt->suboptions |= OPTION_MPTCP_FAIL;
 350                 mp_opt->fail_seq = get_unaligned_be64(ptr);
 351                 pr_debug("MP_FAIL: data_seq=%llu", mp_opt->fail_seq);
 352                 break;
 353
 354         default:
 355                 break;
 356         }
 357 }
 358
 359 void mptcp_get_options(const struct sk_buff *skb,
 360                        struct mptcp_options_received *mp_opt)
 361 {
 362         const struct tcphdr *th = tcp_hdr(skb);
 363         const unsigned char *ptr;
 364         int length;
 365
 366         /* initialize option status */
 367         mp_opt->suboptions = 0;
 368
 369         length = (th->doff * 4) - sizeof(struct tcphdr);
 370         ptr = (const unsigned char *)(th + 1);
 371
 372         while (length > 0) {
 373                 int opcode = *ptr++;
 374                 int opsize;
 375
 376                 switch (opcode) {
 377                 case TCPOPT_EOL:
 378                         return;
 379                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
 380                         length--;
 381                         continue;
 382                 default:
 383                         if (length < 2)
 384                                 return;
 385                         opsize = *ptr++;
 386                         if (opsize < 2) /* "silly options" */
 387                                 return;
 388                         if (opsize > length)
 389                                 return; /* don't parse partial options */
 390                         if (opcode == TCPOPT_MPTCP)
 391                                 mptcp_parse_option(skb, ptr, opsize, mp_opt);
 392                         ptr += opsize - 2;
 393                         length -= opsize;
 394                 }
 395         }
 396 }
 397
 398 bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 399                        unsigned int *size, struct mptcp_out_options *opts)
 400 {
 401         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 402
 403         /* we will use snd_isn to detect first pkt [re]transmission
 404          * in mptcp_established_options_mp()
 405          */
 406         subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
 407         if (subflow->request_mptcp) {
 408                 opts->suboptions = OPTION_MPTCP_MPC_SYN;
 409                 opts->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk));
 410                 opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
 411                 *size = TCPOLEN_MPTCP_MPC_SYN;
 412                 return true;
 413         } else if (subflow->request_join) {
 414                 pr_debug("remote_token=%u, nonce=%u", subflow->remote_token,
 415                          subflow->local_nonce);
 416                 opts->suboptions = OPTION_MPTCP_MPJ_SYN;
 417                 opts->join_id = subflow->local_id;
 418                 opts->token = subflow->remote_token;
 419                 opts->nonce = subflow->local_nonce;
 420                 opts->backup = subflow->request_bkup;
 421                 *size = TCPOLEN_MPTCP_MPJ_SYN;
 422                 return true;
 423         }
 424         return false;
 425 }
 426
 427 static void clear_3rdack_retransmission(struct sock *sk)
 428 {
 429         struct inet_connection_sock *icsk = inet_csk(sk);
 430
 431         sk_stop_timer(sk, &icsk->icsk_delack_timer);
 432         icsk->icsk_ack.timeout = 0;
 433         icsk->icsk_ack.ato = 0;
 434         icsk->icsk_ack.pending &= ~(ICSK_ACK_SCHED | ICSK_ACK_TIMER);
 435 }
 436
 437 static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
 438                                          bool snd_data_fin_enable,
 439                                          unsigned int *size,
 440                                          unsigned int remaining,
 441                                          struct mptcp_out_options *opts)
 442 {
 443         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 444         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 445         struct mptcp_ext *mpext;
 446         unsigned int data_len;
 447         u8 len;
 448
 449         /* When skb is not available, we better over-estimate the emitted
 450          * options len. A full DSS option (28 bytes) is longer than
 451          * TCPOLEN_MPTCP_MPC_ACK_DATA(22) or TCPOLEN_MPTCP_MPJ_ACK(24), so
 452          * tell the caller to defer the estimate to
 453          * mptcp_established_options_dss(), which will reserve enough space.
 454          */
 455         if (!skb)
 456                 return false;
 457
 458         /* MPC/MPJ needed only on 3rd ack packet, DATA_FIN and TCP shutdown take precedence */
 459         if (subflow->fully_established || snd_data_fin_enable ||
 460             subflow->snd_isn != TCP_SKB_CB(skb)->seq ||
 461             sk->sk_state != TCP_ESTABLISHED)
 462                 return false;
 463
 464         if (subflow->mp_capable) {
 465                 mpext = mptcp_get_ext(skb);
 466                 data_len = mpext ? mpext->data_len : 0;
 467
 468                 /* we will check ops->data_len in mptcp_write_options() to
 469                  * discriminate between TCPOLEN_MPTCP_MPC_ACK_DATA and
 470                  * TCPOLEN_MPTCP_MPC_ACK
 471                  */
 472                 opts->data_len = data_len;
 473                 opts->suboptions = OPTION_MPTCP_MPC_ACK;
 474                 opts->sndr_key = subflow->local_key;
 475                 opts->rcvr_key = subflow->remote_key;
 476                 opts->csum_reqd = READ_ONCE(msk->csum_enabled);
 477                 opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
 478
 479                 /* Section 3.1.
 480                  * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
 481                  * packets that start the first subflow of an MPTCP connection,
 482                  * as well as the first packet that carries data
 483                  */
 484                 if (data_len > 0) {
 485                         len = TCPOLEN_MPTCP_MPC_ACK_DATA;
 486                         if (opts->csum_reqd) {
 487                                 /* we need to propagate more info to csum the pseudo hdr */
 488                                 opts->data_seq = mpext->data_seq;
 489                                 opts->subflow_seq = mpext->subflow_seq;
 490                                 opts->csum = mpext->csum;
 491                                 len += TCPOLEN_MPTCP_DSS_CHECKSUM;
 492                         }
 493                         *size = ALIGN(len, 4);
 494                 } else {
 495                         *size = TCPOLEN_MPTCP_MPC_ACK;
 496                 }
 497
 498                 pr_debug("subflow=%p, local_key=%llu, remote_key=%llu map_len=%d",
 499                          subflow, subflow->local_key, subflow->remote_key,
 500                          data_len);
 501
 502                 return true;
 503         } else if (subflow->mp_join) {
 504                 opts->suboptions = OPTION_MPTCP_MPJ_ACK;
 505                 memcpy(opts->hmac, subflow->hmac, MPTCPOPT_HMAC_LEN);
 506                 *size = TCPOLEN_MPTCP_MPJ_ACK;
 507                 pr_debug("subflow=%p", subflow);
 508
 509                 /* we can use the full delegate action helper only from BH context
 510                  * If we are in process context - sk is flushing the backlog at
 511                  * socket lock release time - just set the appropriate flag, will
 512                  * be handled by the release callback
 513                  */
 514                 if (sock_owned_by_user(sk))
 515                         set_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status);
 516                 else
 517                         mptcp_subflow_delegate(subflow, MPTCP_DELEGATE_ACK);
 518                 return true;
 519         }
 520         return false;
 521 }
 522
 523 static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
 524                                  struct sk_buff *skb, struct mptcp_ext *ext)
 525 {
 526         /* The write_seq value has already been incremented, so the actual
 527          * sequence number for the DATA_FIN is one less.
 528          */
 529         u64 data_fin_tx_seq = READ_ONCE(mptcp_sk(subflow->conn)->write_seq) - 1;
 530
 531         if (!ext->use_map || !skb->len) {
 532                 /* RFC6824 requires a DSS mapping with specific values
 533                  * if DATA_FIN is set but no data payload is mapped
 534                  */
 535                 ext->data_fin = 1;
 536                 ext->use_map = 1;
 537                 ext->dsn64 = 1;
 538                 ext->data_seq = data_fin_tx_seq;
 539                 ext->subflow_seq = 0;
 540                 ext->data_len = 1;
 541         } else if (ext->data_seq + ext->data_len == data_fin_tx_seq) {
 542                 /* If there's an existing DSS mapping and it is the
 543                  * final mapping, DATA_FIN consumes 1 additional byte of
 544                  * mapping space.
 545                  */
 546                 ext->data_fin = 1;
 547                 ext->data_len++;
 548         }
 549 }
 550
 551 static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 552                                           bool snd_data_fin_enable,
 553                                           unsigned int *size,
 554                                           unsigned int remaining,
 555                                           struct mptcp_out_options *opts)
 556 {
 557         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 558         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 559         unsigned int dss_size = 0;
 560         struct mptcp_ext *mpext;
 561         unsigned int ack_size;
 562         bool ret = false;
 563         u64 ack_seq;
 564
 565         opts->csum_reqd = READ_ONCE(msk->csum_enabled);
 566         mpext = skb ? mptcp_get_ext(skb) : NULL;
 567
 568         if (!skb || (mpext && mpext->use_map) || snd_data_fin_enable) {
 569                 unsigned int map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;
 570
 571                 if (mpext) {
 572                         if (opts->csum_reqd)
 573                                 map_size += TCPOLEN_MPTCP_DSS_CHECKSUM;
 574
 575                         opts->ext_copy = *mpext;
 576                 }
 577
 578                 remaining -= map_size;
 579                 dss_size = map_size;
 580                 if (skb && snd_data_fin_enable)
 581                         mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
 582                 opts->suboptions = OPTION_MPTCP_DSS;
 583                 ret = true;
 584         }
 585
 586         /* passive sockets msk will set the 'can_ack' after accept(), even
 587          * if the first subflow may have the already the remote key handy
 588          */
 589         opts->ext_copy.use_ack = 0;
 590         if (!READ_ONCE(msk->can_ack)) {
 591                 *size = ALIGN(dss_size, 4);
 592                 return ret;
 593         }
 594
 595         ack_seq = READ_ONCE(msk->ack_seq);
 596         if (READ_ONCE(msk->use_64bit_ack)) {
 597                 ack_size = TCPOLEN_MPTCP_DSS_ACK64;
 598                 opts->ext_copy.data_ack = ack_seq;
 599                 opts->ext_copy.ack64 = 1;
 600         } else {
 601                 ack_size = TCPOLEN_MPTCP_DSS_ACK32;
 602                 opts->ext_copy.data_ack32 = (uint32_t)ack_seq;
 603                 opts->ext_copy.ack64 = 0;
 604         }
 605         opts->ext_copy.use_ack = 1;
 606         opts->suboptions = OPTION_MPTCP_DSS;
 607         WRITE_ONCE(msk->old_wspace, __mptcp_space((struct sock *)msk));
 608
 609         /* Add kind/length/subtype/flag overhead if mapping is not populated */
 610         if (dss_size == 0)
 611                 ack_size += TCPOLEN_MPTCP_DSS_BASE;
 612
 613         dss_size += ack_size;
 614
 615         *size = ALIGN(dss_size, 4);
 616         return true;
 617 }
 618
 619 static u64 add_addr_generate_hmac(u64 key1, u64 key2,
 620                                   struct mptcp_addr_info *addr)
 621 {
 622         u16 port = ntohs(addr->port);
 623         u8 hmac[SHA256_DIGEST_SIZE];
 624         u8 msg[19];
 625         int i = 0;
 626
 627         msg[i++] = addr->id;
 628         if (addr->family == AF_INET) {
 629                 memcpy(&msg[i], &addr->addr.s_addr, 4);
 630                 i += 4;
 631         }
 632 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
 633         else if (addr->family == AF_INET6) {
 634                 memcpy(&msg[i], &addr->addr6.s6_addr, 16);
 635                 i += 16;
 636         }
 637 #endif
 638         msg[i++] = port >> 8;
 639         msg[i++] = port & 0xFF;
 640
 641         mptcp_crypto_hmac_sha(key1, key2, msg, i, hmac);
 642
 643         return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
 644 }
 645
 646 static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff *skb,
 647                                                unsigned int *size,
 648                                                unsigned int remaining,
 649                                                struct mptcp_out_options *opts)
 650 {
 651         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 652         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 653         bool drop_other_suboptions = false;
 654         unsigned int opt_size = *size;
 655         bool echo;
 656         int len;
 657
 658         /* add addr will strip the existing options, be sure to avoid breaking
 659          * MPC/MPJ handshakes
 660          */
 661         if (!mptcp_pm_should_add_signal(msk) ||
 662             (opts->suboptions & (OPTION_MPTCP_MPJ_ACK | OPTION_MPTCP_MPC_ACK)) ||
 663             !mptcp_pm_add_addr_signal(msk, skb, opt_size, remaining, &opts->addr,
 664                     &echo, &drop_other_suboptions))
 665                 return false;
 666
 667         if (drop_other_suboptions)
 668                 remaining += opt_size;
 669         len = mptcp_add_addr_len(opts->addr.family, echo, !!opts->addr.port);
 670         if (remaining < len)
 671                 return false;
 672
 673         *size = len;
 674         if (drop_other_suboptions) {
 675                 pr_debug("drop other suboptions");
 676                 opts->suboptions = 0;
 677
 678                 /* note that e.g. DSS could have written into the memory
 679                  * aliased by ahmac, we must reset the field here
 680                  * to avoid appending the hmac even for ADD_ADDR echo
 681                  * options
 682                  */
 683                 opts->ahmac = 0;
 684                 *size -= opt_size;
 685         }
 686         opts->suboptions |= OPTION_MPTCP_ADD_ADDR;
 687         if (!echo) {
 688                 opts->ahmac = add_addr_generate_hmac(msk->local_key,
 689                                                      msk->remote_key,
 690                                                      &opts->addr);
 691         }
 692         pr_debug("addr_id=%d, ahmac=%llu, echo=%d, port=%d",
 693                  opts->addr.id, opts->ahmac, echo, ntohs(opts->addr.port));
 694
 695         return true;
 696 }
 697
 698 static bool mptcp_established_options_rm_addr(struct sock *sk,
 699                                               unsigned int *size,
 700                                               unsigned int remaining,
 701                                               struct mptcp_out_options *opts)
 702 {
 703         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 704         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 705         struct mptcp_rm_list rm_list;
 706         int i, len;
 707
 708         if (!mptcp_pm_should_rm_signal(msk) ||
 709             !(mptcp_pm_rm_addr_signal(msk, remaining, &rm_list)))
 710                 return false;
 711
 712         len = mptcp_rm_addr_len(&rm_list);
 713         if (len < 0)
 714                 return false;
 715         if (remaining < len)
 716                 return false;
 717
 718         *size = len;
 719         opts->suboptions |= OPTION_MPTCP_RM_ADDR;
 720         opts->rm_list = rm_list;
 721
 722         for (i = 0; i < opts->rm_list.nr; i++)
 723                 pr_debug("rm_list_ids[%d]=%d", i, opts->rm_list.ids[i]);
 724
 725         return true;
 726 }
 727
 728 static bool mptcp_established_options_mp_prio(struct sock *sk,
 729                                               unsigned int *size,
 730                                               unsigned int remaining,
 731                                               struct mptcp_out_options *opts)
 732 {
 733         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 734
 735         /* can't send MP_PRIO with MPC, as they share the same option space:
 736          * 'backup'. Also it makes no sense at all
 737          */
 738         if (!subflow->send_mp_prio || (opts->suboptions & OPTIONS_MPTCP_MPC))
 739                 return false;
 740
 741         /* account for the trailing 'nop' option */
 742         if (remaining < TCPOLEN_MPTCP_PRIO_ALIGN)
 743                 return false;
 744
 745         *size = TCPOLEN_MPTCP_PRIO_ALIGN;
 746         opts->suboptions |= OPTION_MPTCP_PRIO;
 747         opts->backup = subflow->request_bkup;
 748
 749         pr_debug("prio=%d", opts->backup);
 750
 751         return true;
 752 }
 753
 754 static noinline bool mptcp_established_options_rst(struct sock *sk, struct sk_buff *skb,
 755                                                    unsigned int *size,
 756                                                    unsigned int remaining,
 757                                                    struct mptcp_out_options *opts)
 758 {
 759         const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 760
 761         if (remaining < TCPOLEN_MPTCP_RST)
 762                 return false;
 763
 764         *size = TCPOLEN_MPTCP_RST;
 765         opts->suboptions |= OPTION_MPTCP_RST;
 766         opts->reset_transient = subflow->reset_transient;
 767         opts->reset_reason = subflow->reset_reason;
 768
 769         return true;
 770 }
 771
 772 static bool mptcp_established_options_fastclose(struct sock *sk,
 773                                                 unsigned int *size,
 774                                                 unsigned int remaining,
 775                                                 struct mptcp_out_options *opts)
 776 {
 777         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 778         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 779
 780         if (likely(!subflow->send_fastclose))
 781                 return false;
 782
 783         if (remaining < TCPOLEN_MPTCP_FASTCLOSE)
 784                 return false;
 785
 786         *size = TCPOLEN_MPTCP_FASTCLOSE;
 787         opts->suboptions |= OPTION_MPTCP_FASTCLOSE;
 788         opts->rcvr_key = msk->remote_key;
 789
 790         pr_debug("FASTCLOSE key=%llu", opts->rcvr_key);
 791         return true;
 792 }
 793
 794 static bool mptcp_established_options_mp_fail(struct sock *sk,
 795                                               unsigned int *size,
 796                                               unsigned int remaining,
 797                                               struct mptcp_out_options *opts)
 798 {
 799         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 800
 801         if (likely(!subflow->send_mp_fail))
 802                 return false;
 803
 804         if (remaining < TCPOLEN_MPTCP_FAIL)
 805                 return false;
 806
 807         *size = TCPOLEN_MPTCP_FAIL;
 808         opts->suboptions |= OPTION_MPTCP_FAIL;
 809         opts->fail_seq = subflow->map_seq;
 810
 811         pr_debug("MP_FAIL fail_seq=%llu", opts->fail_seq);
 812
 813         return true;
 814 }
 815
 816 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 817                                unsigned int *size, unsigned int remaining,
 818                                struct mptcp_out_options *opts)
 819 {
 820         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 821         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
 822         unsigned int opt_size = 0;
 823         bool snd_data_fin;
 824         bool ret = false;
 825
 826         opts->suboptions = 0;
 827
 828         if (unlikely(__mptcp_check_fallback(msk) && !mptcp_check_infinite_map(skb)))
 829                 return false;
 830
 831         if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) {
 832                 if (mptcp_established_options_fastclose(sk, &opt_size, remaining, opts) ||
 833                     mptcp_established_options_mp_fail(sk, &opt_size, remaining, opts)) {
 834                         *size += opt_size;
 835                         remaining -= opt_size;
 836                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFASTCLOSETX);
 837                 }
 838                 /* MP_RST can be used with MP_FASTCLOSE and MP_FAIL if there is room */
 839                 if (mptcp_established_options_rst(sk, skb, &opt_size, remaining, opts)) {
 840                         *size += opt_size;
 841                         remaining -= opt_size;
 842                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPRSTTX);
 843                 }
 844                 return true;
 845         }
 846
 847         snd_data_fin = mptcp_data_fin_enabled(msk);
 848         if (mptcp_established_options_mp(sk, skb, snd_data_fin, &opt_size, remaining, opts))
 849                 ret = true;
 850         else if (mptcp_established_options_dss(sk, skb, snd_data_fin, &opt_size, remaining, opts)) {
 851                 unsigned int mp_fail_size;
 852
 853                 ret = true;
 854                 if (mptcp_established_options_mp_fail(sk, &mp_fail_size,
 855                                                       remaining - opt_size, opts)) {
 856                         *size += opt_size + mp_fail_size;
 857                         remaining -= opt_size - mp_fail_size;
 858                         return true;
 859                 }
 860         }
 861
 862         /* we reserved enough space for the above options, and exceeding the
 863          * TCP option space would be fatal
 864          */
 865         if (WARN_ON_ONCE(opt_size > remaining))
 866                 return false;
 867
 868         *size += opt_size;
 869         remaining -= opt_size;
 870         if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining, opts)) {
 871                 *size += opt_size;
 872                 remaining -= opt_size;
 873                 ret = true;
 874         } else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
 875                 *size += opt_size;
 876                 remaining -= opt_size;
 877                 ret = true;
 878         }
 879
 880         if (mptcp_established_options_mp_prio(sk, &opt_size, remaining, opts)) {
 881                 *size += opt_size;
 882                 remaining -= opt_size;
 883                 ret = true;
 884         }
 885
 886         return ret;
 887 }
 888
 889 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 890                           struct mptcp_out_options *opts)
 891 {
 892         struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
 893
 894         if (subflow_req->mp_capable) {
 895                 opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
 896                 opts->sndr_key = subflow_req->local_key;
 897                 opts->csum_reqd = subflow_req->csum_reqd;
 898                 opts->allow_join_id0 = subflow_req->allow_join_id0;
 899                 *size = TCPOLEN_MPTCP_MPC_SYNACK;
 900                 pr_debug("subflow_req=%p, local_key=%llu",
 901                          subflow_req, subflow_req->local_key);
 902                 return true;
 903         } else if (subflow_req->mp_join) {
 904                 opts->suboptions = OPTION_MPTCP_MPJ_SYNACK;
 905                 opts->backup = subflow_req->backup;
 906                 opts->join_id = subflow_req->local_id;
 907                 opts->thmac = subflow_req->thmac;
 908                 opts->nonce = subflow_req->local_nonce;
 909                 pr_debug("req=%p, bkup=%u, id=%u, thmac=%llu, nonce=%u",
 910                          subflow_req, opts->backup, opts->join_id,
 911                          opts->thmac, opts->nonce);
 912                 *size = TCPOLEN_MPTCP_MPJ_SYNACK;
 913                 return true;
 914         }
 915         return false;
 916 }
 917
 918 static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 919                                     struct mptcp_subflow_context *subflow,
 920                                     struct sk_buff *skb,
 921                                     struct mptcp_options_received *mp_opt)
 922 {
 923         /* here we can process OoO, in-window pkts, only in-sequence 4th ack
 924          * will make the subflow fully established
 925          */
 926         if (likely(subflow->fully_established)) {
 927                 /* on passive sockets, check for 3rd ack retransmission
 928                  * note that msk is always set by subflow_syn_recv_sock()
 929                  * for mp_join subflows
 930                  */
 931                 if (TCP_SKB_CB(skb)->seq == subflow->ssn_offset + 1 &&
 932                     TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq &&
 933                     subflow->mp_join && (mp_opt->suboptions & OPTIONS_MPTCP_MPJ) &&
 934                     !subflow->request_join)
 935                         tcp_send_ack(ssk);
 936                 goto fully_established;
 937         }
 938
 939         /* we must process OoO packets before the first subflow is fully
 940          * established. OoO packets are instead a protocol violation
 941          * for MP_JOIN subflows as the peer must not send any data
 942          * before receiving the forth ack - cfr. RFC 8684 section 3.2.
 943          */
 944         if (TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1) {
 945                 if (subflow->mp_join)
 946                         goto reset;
 947                 return subflow->mp_capable;
 948         }
 949
 950         if (((mp_opt->suboptions & OPTION_MPTCP_DSS) && mp_opt->use_ack) ||
 951             ((mp_opt->suboptions & OPTION_MPTCP_ADD_ADDR) && !mp_opt->echo)) {
 952                 /* subflows are fully established as soon as we get any
 953                  * additional ack, including ADD_ADDR.
 954                  */
 955                 subflow->fully_established = 1;
 956                 WRITE_ONCE(msk->fully_established, true);
 957                 goto fully_established;
 958         }
 959
 960         /* If the first established packet does not contain MP_CAPABLE + data
 961          * then fallback to TCP. Fallback scenarios requires a reset for
 962          * MP_JOIN subflows.
 963          */
 964         if (!(mp_opt->suboptions & OPTIONS_MPTCP_MPC)) {
 965                 if (subflow->mp_join)
 966                         goto reset;
 967                 subflow->mp_capable = 0;
 968                 pr_fallback(msk);
 969                 __mptcp_do_fallback(msk);
 970                 return false;
 971         }
 972
 973         if (mp_opt->deny_join_id0)
 974                 WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
 975
 976         if (unlikely(!READ_ONCE(msk->pm.server_side)))
 977                 pr_warn_once("bogus mpc option on established client sk");
 978         mptcp_subflow_fully_established(subflow, mp_opt);
 979
 980 fully_established:
 981         /* if the subflow is not already linked into the conn_list, we can't
 982          * notify the PM: this subflow is still on the listener queue
 983          * and the PM possibly acquiring the subflow lock could race with
 984          * the listener close
 985          */
 986         if (likely(subflow->pm_notified) || list_empty(&subflow->node))
 987                 return true;
 988
 989         subflow->pm_notified = 1;
 990         if (subflow->mp_join) {
 991                 clear_3rdack_retransmission(ssk);
 992                 mptcp_pm_subflow_established(msk);
 993         } else {
 994                 mptcp_pm_fully_established(msk, ssk, GFP_ATOMIC);
 995         }
 996         return true;
 997
 998 reset:
 999         mptcp_subflow_reset(ssk);
1000         return false;
1001 }
1002
1003 u64 __mptcp_expand_seq(u64 old_seq, u64 cur_seq)
1004 {
1005         u32 old_seq32, cur_seq32;
1006
1007         old_seq32 = (u32)old_seq;
1008         cur_seq32 = (u32)cur_seq;
1009         cur_seq = (old_seq & GENMASK_ULL(63, 32)) + cur_seq32;
1010         if (unlikely(cur_seq32 < old_seq32 && before(old_seq32, cur_seq32)))
1011                 return cur_seq + (1LL << 32);
1012
1013         /* reverse wrap could happen, too */
1014         if (unlikely(cur_seq32 > old_seq32 && after(old_seq32, cur_seq32)))
1015                 return cur_seq - (1LL << 32);
1016         return cur_seq;
1017 }
1018
1019 static void ack_update_msk(struct mptcp_sock *msk,
1020                            struct sock *ssk,
1021                            struct mptcp_options_received *mp_opt)
1022 {
1023         u64 new_wnd_end, new_snd_una, snd_nxt = READ_ONCE(msk->snd_nxt);
1024         struct sock *sk = (struct sock *)msk;
1025         u64 old_snd_una;
1026
1027         mptcp_data_lock(sk);
1028
1029         /* avoid ack expansion on update conflict, to reduce the risk of
1030          * wrongly expanding to a future ack sequence number, which is way
1031          * more dangerous than missing an ack
1032          */
1033         old_snd_una = msk->snd_una;
1034         new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
1035
1036         /* ACK for data not even sent yet? Ignore.*/
1037         if (unlikely(after64(new_snd_una, snd_nxt)))
1038                 new_snd_una = old_snd_una;
1039
1040         new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;
1041
1042         if (after64(new_wnd_end, msk->wnd_end))
1043                 msk->wnd_end = new_wnd_end;
1044
1045         /* this assumes mptcp_incoming_options() is invoked after tcp_ack() */
1046         if (after64(msk->wnd_end, READ_ONCE(msk->snd_nxt)))
1047                 __mptcp_check_push(sk, ssk);
1048
1049         if (after64(new_snd_una, old_snd_una)) {
1050                 msk->snd_una = new_snd_una;
1051                 __mptcp_data_acked(sk);
1052         }
1053         mptcp_data_unlock(sk);
1054
1055         trace_ack_update_msk(mp_opt->data_ack,
1056                              old_snd_una, new_snd_una,
1057                              new_wnd_end, msk->wnd_end);
1058 }
1059
1060 bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
1061 {
1062         /* Skip if DATA_FIN was already received.
1063          * If updating simultaneously with the recvmsg loop, values
1064          * should match. If they mismatch, the peer is misbehaving and
1065          * we will prefer the most recent information.
1066          */
1067         if (READ_ONCE(msk->rcv_data_fin))
1068                 return false;
1069
1070         WRITE_ONCE(msk->rcv_data_fin_seq,
1071                    mptcp_expand_seq(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
1072         WRITE_ONCE(msk->rcv_data_fin, 1);
1073
1074         return true;
1075 }
1076
1077 static bool add_addr_hmac_valid(struct mptcp_sock *msk,
1078                                 struct mptcp_options_received *mp_opt)
1079 {
1080         u64 hmac = 0;
1081
1082         if (mp_opt->echo)
1083                 return true;
1084
1085         hmac = add_addr_generate_hmac(msk->remote_key,
1086                                       msk->local_key,
1087                                       &mp_opt->addr);
1088
1089         pr_debug("msk=%p, ahmac=%llu, mp_opt->ahmac=%llu\n",
1090                  msk, hmac, mp_opt->ahmac);
1091
1092         return hmac == mp_opt->ahmac;
1093 }
1094
1095 /* Return false if a subflow has been reset, else return true */
1096 bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
1097 {
1098         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
1099         struct mptcp_sock *msk = mptcp_sk(subflow->conn);
1100         struct mptcp_options_received mp_opt;
1101         struct mptcp_ext *mpext;
1102
1103         if (__mptcp_check_fallback(msk)) {
1104                 /* Keep it simple and unconditionally trigger send data cleanup and
1105                  * pending queue spooling. We will need to acquire the data lock
1106                  * for more accurate checks, and once the lock is acquired, such
1107                  * helpers are cheap.
1108                  */
1109                 mptcp_data_lock(subflow->conn);
1110                 if (sk_stream_memory_free(sk))
1111                         __mptcp_check_push(subflow->conn, sk);
1112                 __mptcp_data_acked(subflow->conn);
1113                 mptcp_data_unlock(subflow->conn);
1114                 return true;
1115         }
1116
1117         mptcp_get_options(skb, &mp_opt);
1118
1119         /* The subflow can be in close state only if check_fully_established()
1120          * just sent a reset. If so, tell the caller to ignore the current packet.
1121          */
1122         if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
1123                 return sk->sk_state != TCP_CLOSE;
1124
1125         if (unlikely(mp_opt.suboptions != OPTION_MPTCP_DSS)) {
1126                 if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
1127                     msk->local_key == mp_opt.rcvr_key) {
1128                         WRITE_ONCE(msk->rcv_fastclose, true);
1129                         mptcp_schedule_work((struct sock *)msk);
1130                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFASTCLOSERX);
1131                 }
1132
1133                 if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) &&
1134                     add_addr_hmac_valid(msk, &mp_opt)) {
1135                         if (!mp_opt.echo) {
1136                                 mptcp_pm_add_addr_received(sk, &mp_opt.addr);
1137                                 MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
1138                         } else {
1139                                 mptcp_pm_add_addr_echoed(msk, &mp_opt.addr);
1140                                 mptcp_pm_del_add_timer(msk, &mp_opt.addr, true);
1141                                 MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
1142                         }
1143
1144                         if (mp_opt.addr.port)
1145                                 MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_PORTADD);
1146                 }
1147
1148                 if (mp_opt.suboptions & OPTION_MPTCP_RM_ADDR)
1149                         mptcp_pm_rm_addr_received(msk, &mp_opt.rm_list);
1150
1151                 if (mp_opt.suboptions & OPTION_MPTCP_PRIO) {
1152                         mptcp_pm_mp_prio_received(sk, mp_opt.backup);
1153                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIORX);
1154                 }
1155
1156                 if (mp_opt.suboptions & OPTION_MPTCP_FAIL) {
1157                         mptcp_pm_mp_fail_received(sk, mp_opt.fail_seq);
1158                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFAILRX);
1159                 }
1160
1161                 if (mp_opt.suboptions & OPTION_MPTCP_RST) {
1162                         subflow->reset_seen = 1;
1163                         subflow->reset_reason = mp_opt.reset_reason;
1164                         subflow->reset_transient = mp_opt.reset_transient;
1165                         MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPRSTRX);
1166                 }
1167
1168                 if (!(mp_opt.suboptions & OPTION_MPTCP_DSS))
1169                         return true;
1170         }
1171
1172         /* we can't wait for recvmsg() to update the ack_seq, otherwise
1173          * monodirectional flows will stuck
1174          */
1175         if (mp_opt.use_ack)
1176                 ack_update_msk(msk, sk, &mp_opt);
1177
1178         /* Zero-data-length packets are dropped by the caller and not
1179          * propagated to the MPTCP layer, so the skb extension does not
1180          * need to be allocated or populated. DATA_FIN information, if
1181          * present, needs to be updated here before the skb is freed.
1182          */
1183         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
1184                 if (mp_opt.data_fin && mp_opt.data_len == 1 &&
1185                     mptcp_update_rcv_data_fin(msk, mp_opt.data_seq, mp_opt.dsn64) &&
1186                     schedule_work(&msk->work))
1187                         sock_hold(subflow->conn);
1188
1189                 return true;
1190         }
1191
1192         mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
1193         if (!mpext)
1194                 return true;
1195
1196         memset(mpext, 0, sizeof(*mpext));
1197
1198         if (likely(mp_opt.use_map)) {
1199                 if (mp_opt.mpc_map) {
1200                         /* this is an MP_CAPABLE carrying MPTCP data
1201                          * we know this map the first chunk of data
1202                          */
1203                         mptcp_crypto_key_sha(subflow->remote_key, NULL,
1204                                              &mpext->data_seq);
1205                         mpext->data_seq++;
1206                         mpext->subflow_seq = 1;
1207                         mpext->dsn64 = 1;
1208                         mpext->mpc_map = 1;
1209                         mpext->data_fin = 0;
1210                 } else {
1211                         mpext->data_seq = mp_opt.data_seq;
1212                         mpext->subflow_seq = mp_opt.subflow_seq;
1213                         mpext->dsn64 = mp_opt.dsn64;
1214                         mpext->data_fin = mp_opt.data_fin;
1215                 }
1216                 mpext->data_len = mp_opt.data_len;
1217                 mpext->use_map = 1;
1218                 mpext->csum_reqd = !!(mp_opt.suboptions & OPTION_MPTCP_CSUMREQD);
1219
1220                 if (mpext->csum_reqd)
1221                         mpext->csum = mp_opt.csum;
1222         }
1223
1224         return true;
1225 }
1226
1227 static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th)
1228 {
1229         const struct sock *ssk = (const struct sock *)tp;
1230         struct mptcp_subflow_context *subflow;
1231         u64 ack_seq, rcv_wnd_old, rcv_wnd_new;
1232         struct mptcp_sock *msk;
1233         u32 new_win;
1234         u64 win;
1235
1236         subflow = mptcp_subflow_ctx(ssk);
1237         msk = mptcp_sk(subflow->conn);
1238
1239         ack_seq = READ_ONCE(msk->ack_seq);
1240         rcv_wnd_new = ack_seq + tp->rcv_wnd;
1241
1242         rcv_wnd_old = atomic64_read(&msk->rcv_wnd_sent);
1243         if (after64(rcv_wnd_new, rcv_wnd_old)) {
1244                 u64 rcv_wnd;
1245
1246                 for (;;) {
1247                         rcv_wnd = atomic64_cmpxchg(&msk->rcv_wnd_sent, rcv_wnd_old, rcv_wnd_new);
1248
1249                         if (rcv_wnd == rcv_wnd_old)
1250                                 break;
1251                         if (before64(rcv_wnd_new, rcv_wnd)) {
1252                                 MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICTUPDATE);
1253                                 goto raise_win;
1254                         }
1255                         MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICT);
1256                         rcv_wnd_old = rcv_wnd;
1257                 }
1258                 return;
1259         }
1260
1261         if (rcv_wnd_new != rcv_wnd_old) {
1262 raise_win:
1263                 win = rcv_wnd_old - ack_seq;
1264                 tp->rcv_wnd = min_t(u64, win, U32_MAX);
1265                 new_win = tp->rcv_wnd;
1266
1267                 /* Make sure we do not exceed the maximum possible
1268                  * scaled window.
1269                  */
1270                 if (unlikely(th->syn))
1271                         new_win = min(new_win, 65535U) << tp->rx_opt.rcv_wscale;
1272                 if (!tp->rx_opt.rcv_wscale &&
1273                     sock_net(ssk)->ipv4.sysctl_tcp_workaround_signed_windows)
1274                         new_win = min(new_win, MAX_TCP_WINDOW);
1275                 else
1276                         new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
1277
1278                 /* RFC1323 scaling applied */
1279                 new_win >>= tp->rx_opt.rcv_wscale;
1280                 th->window = htons(new_win);
1281                 MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDSHARED);
1282         }
1283 }
1284
1285 __sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum)
1286 {
1287         struct csum_pseudo_header header;
1288         __wsum csum;
1289
1290         /* cfr RFC 8684 3.3.1.:
1291          * the data sequence number used in the pseudo-header is
1292          * always the 64-bit value, irrespective of what length is used in the
1293          * DSS option itself.
1294          */
1295         header.data_seq = cpu_to_be64(data_seq);
1296         header.subflow_seq = htonl(subflow_seq);
1297         header.data_len = htons(data_len);
1298         header.csum = 0;
1299
1300         csum = csum_partial(&header, sizeof(header), sum);
1301         return csum_fold(csum);
1302 }
1303
1304 static __sum16 mptcp_make_csum(const struct mptcp_ext *mpext)
1305 {
1306         return __mptcp_make_csum(mpext->data_seq, mpext->subflow_seq, mpext->data_len,
1307                                  ~csum_unfold(mpext->csum));
1308 }
1309
1310 static void put_len_csum(u16 len, __sum16 csum, void *data)
1311 {
1312         __sum16 *sumptr = data + 2;
1313         __be16 *ptr = data;
1314
1315         put_unaligned_be16(len, ptr);
1316
1317         put_unaligned(csum, sumptr);
1318 }
1319
1320 void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp,
1321                          struct mptcp_out_options *opts)
1322 {
1323         const struct sock *ssk = (const struct sock *)tp;
1324         struct mptcp_subflow_context *subflow;
1325
1326         /* Which options can be used together?
1327          *
1328          * X: mutually exclusive
1329          * O: often used together
1330          * C: can be used together in some cases
1331          * P: could be used together but we prefer not to (optimisations)
1332          *
1333          *  Opt: | MPC  | MPJ  | DSS  | ADD  |  RM  | PRIO | FAIL |  FC  |
1334          * ------|------|------|------|------|------|------|------|------|
1335          *  MPC  |------|------|------|------|------|------|------|------|
1336          *  MPJ  |  X   |------|------|------|------|------|------|------|
1337          *  DSS  |  X   |  X   |------|------|------|------|------|------|
1338          *  ADD  |  X   |  X   |  P   |------|------|------|------|------|
1339          *  RM   |  C   |  C   |  C   |  P   |------|------|------|------|
1340          *  PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|
1341          *  FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|
1342          *  FC   |  X   |  X   |  X   |  X   |  X   |  X   |  X   |------|
1343          *  RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |
1344          * ------|------|------|------|------|------|------|------|------|
1345          *
1346          * The same applies in mptcp_established_options() function.
1347          */
1348         if (likely(OPTION_MPTCP_DSS & opts->suboptions)) {
1349                 struct mptcp_ext *mpext = &opts->ext_copy;
1350                 u8 len = TCPOLEN_MPTCP_DSS_BASE;
1351                 u8 flags = 0;
1352
1353                 if (mpext->use_ack) {
1354                         flags = MPTCP_DSS_HAS_ACK;
1355                         if (mpext->ack64) {
1356                                 len += TCPOLEN_MPTCP_DSS_ACK64;
1357                                 flags |= MPTCP_DSS_ACK64;
1358                         } else {
1359                                 len += TCPOLEN_MPTCP_DSS_ACK32;
1360                         }
1361                 }
1362
1363                 if (mpext->use_map) {
1364                         len += TCPOLEN_MPTCP_DSS_MAP64;
1365
1366                         /* Use only 64-bit mapping flags for now, add
1367                          * support for optional 32-bit mappings later.
1368                          */
1369                         flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
1370                         if (mpext->data_fin)
1371                                 flags |= MPTCP_DSS_DATA_FIN;
1372
1373                         if (opts->csum_reqd)
1374                                 len += TCPOLEN_MPTCP_DSS_CHECKSUM;
1375                 }
1376
1377                 *ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);
1378
1379                 if (mpext->use_ack) {
1380                         if (mpext->ack64) {
1381                                 put_unaligned_be64(mpext->data_ack, ptr);
1382                                 ptr += 2;
1383                         } else {
1384                                 put_unaligned_be32(mpext->data_ack32, ptr);
1385                                 ptr += 1;
1386                         }
1387                 }
1388
1389                 if (mpext->use_map) {
1390                         put_unaligned_be64(mpext->data_seq, ptr);
1391                         ptr += 2;
1392                         put_unaligned_be32(mpext->subflow_seq, ptr);
1393                         ptr += 1;
1394                         if (opts->csum_reqd) {
1395                                 /* data_len == 0 is reserved for the infinite mapping,
1396                                  * the checksum will also be set to 0.
1397                                  */
1398                                 put_len_csum(mpext->data_len,
1399                                              (mpext->data_len ? mptcp_make_csum(mpext) : 0),
1400                                              ptr);
1401                         } else {
1402                                 put_unaligned_be32(mpext->data_len << 16 |
1403                                                    TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
1404                         }
1405                         ptr += 1;
1406                 }
1407
1408                 /* We might need to add MP_FAIL options in rare cases */
1409                 if (unlikely(OPTION_MPTCP_FAIL & opts->suboptions))
1410                         goto mp_fail;
1411         } else if (OPTIONS_MPTCP_MPC & opts->suboptions) {
1412                 u8 len, flag = MPTCP_CAP_HMAC_SHA256;
1413
1414                 if (OPTION_MPTCP_MPC_SYN & opts->suboptions) {
1415                         len = TCPOLEN_MPTCP_MPC_SYN;
1416                 } else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions) {
1417                         len = TCPOLEN_MPTCP_MPC_SYNACK;
1418                 } else if (opts->data_len) {
1419                         len = TCPOLEN_MPTCP_MPC_ACK_DATA;
1420                         if (opts->csum_reqd)
1421                                 len += TCPOLEN_MPTCP_DSS_CHECKSUM;
1422                 } else {
1423                         len = TCPOLEN_MPTCP_MPC_ACK;
1424                 }
1425
1426                 if (opts->csum_reqd)
1427                         flag |= MPTCP_CAP_CHECKSUM_REQD;
1428
1429                 if (!opts->allow_join_id0)
1430                         flag |= MPTCP_CAP_DENY_JOIN_ID0;
1431
1432                 *ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
1433                                       MPTCP_SUPPORTED_VERSION,
1434                                       flag);
1435
1436                 if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
1437                     opts->suboptions))
1438                         goto mp_capable_done;
1439
1440                 put_unaligned_be64(opts->sndr_key, ptr);
1441                 ptr += 2;
1442                 if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
1443                         goto mp_capable_done;
1444
1445                 put_unaligned_be64(opts->rcvr_key, ptr);
1446                 ptr += 2;
1447                 if (!opts->data_len)
1448                         goto mp_capable_done;
1449
1450                 if (opts->csum_reqd) {
1451                         put_len_csum(opts->data_len,
1452                                      __mptcp_make_csum(opts->data_seq,
1453                                                        opts->subflow_seq,
1454                                                        opts->data_len,
1455                                                        ~csum_unfold(opts->csum)),
1456                                      ptr);
1457                 } else {
1458                         put_unaligned_be32(opts->data_len << 16 |
1459                                            TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
1460                 }
1461                 ptr += 1;
1462
1463                 /* MPC is additionally mutually exclusive with MP_PRIO */
1464                 goto mp_capable_done;
1465         } else if (OPTIONS_MPTCP_MPJ & opts->suboptions) {
1466                 if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
1467                         *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
1468                                               TCPOLEN_MPTCP_MPJ_SYN,
1469                                               opts->backup, opts->join_id);
1470                         put_unaligned_be32(opts->token, ptr);
1471                         ptr += 1;
1472                         put_unaligned_be32(opts->nonce, ptr);
1473                         ptr += 1;
1474                 } else if (OPTION_MPTCP_MPJ_SYNACK & opts->suboptions) {
1475                         *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
1476                                               TCPOLEN_MPTCP_MPJ_SYNACK,
1477                                               opts->backup, opts->join_id);
1478                         put_unaligned_be64(opts->thmac, ptr);
1479                         ptr += 2;
1480                         put_unaligned_be32(opts->nonce, ptr);
1481                         ptr += 1;
1482                 } else {
1483                         *ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
1484                                               TCPOLEN_MPTCP_MPJ_ACK, 0, 0);
1485                         memcpy(ptr, opts->hmac, MPTCPOPT_HMAC_LEN);
1486                         ptr += 5;
1487                 }
1488         } else if (OPTION_MPTCP_ADD_ADDR & opts->suboptions) {
1489                 u8 len = TCPOLEN_MPTCP_ADD_ADDR_BASE;
1490                 u8 echo = MPTCP_ADDR_ECHO;
1491
1492 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
1493                 if (opts->addr.family == AF_INET6)
1494                         len = TCPOLEN_MPTCP_ADD_ADDR6_BASE;
1495 #endif
1496
1497                 if (opts->addr.port)
1498                         len += TCPOLEN_MPTCP_PORT_LEN;
1499
1500                 if (opts->ahmac) {
1501                         len += sizeof(opts->ahmac);
1502                         echo = 0;
1503                 }
1504
1505                 *ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
1506                                       len, echo, opts->addr.id);
1507                 if (opts->addr.family == AF_INET) {
1508                         memcpy((u8 *)ptr, (u8 *)&opts->addr.addr.s_addr, 4);
1509                         ptr += 1;
1510                 }
1511 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
1512                 else if (opts->addr.family == AF_INET6) {
1513                         memcpy((u8 *)ptr, opts->addr.addr6.s6_addr, 16);
1514                         ptr += 4;
1515                 }
1516 #endif
1517
1518                 if (!opts->addr.port) {
1519                         if (opts->ahmac) {
1520                                 put_unaligned_be64(opts->ahmac, ptr);
1521                                 ptr += 2;
1522                         }
1523                 } else {
1524                         u16 port = ntohs(opts->addr.port);
1525
1526                         if (opts->ahmac) {
1527                                 u8 *bptr = (u8 *)ptr;
1528
1529                                 put_unaligned_be16(port, bptr);
1530                                 bptr += 2;
1531                                 put_unaligned_be64(opts->ahmac, bptr);
1532                                 bptr += 8;
1533                                 put_unaligned_be16(TCPOPT_NOP << 8 |
1534                                                    TCPOPT_NOP, bptr);
1535
1536                                 ptr += 3;
1537                         } else {
1538                                 put_unaligned_be32(port << 16 |
1539                                                    TCPOPT_NOP << 8 |
1540                                                    TCPOPT_NOP, ptr);
1541                                 ptr += 1;
1542                         }
1543                 }
1544         } else if (unlikely(OPTION_MPTCP_FASTCLOSE & opts->suboptions)) {
1545                 /* FASTCLOSE is mutually exclusive with others except RST */
1546                 *ptr++ = mptcp_option(MPTCPOPT_MP_FASTCLOSE,
1547                                       TCPOLEN_MPTCP_FASTCLOSE,
1548                                       0, 0);
1549                 put_unaligned_be64(opts->rcvr_key, ptr);
1550                 ptr += 2;
1551
1552                 if (OPTION_MPTCP_RST & opts->suboptions)
1553                         goto mp_rst;
1554                 return;
1555         } else if (unlikely(OPTION_MPTCP_FAIL & opts->suboptions)) {
1556 mp_fail:
1557                 /* MP_FAIL is mutually exclusive with others except RST */
1558                 subflow = mptcp_subflow_ctx(ssk);
1559                 subflow->send_mp_fail = 0;
1560
1561                 *ptr++ = mptcp_option(MPTCPOPT_MP_FAIL,
1562                                       TCPOLEN_MPTCP_FAIL,
1563                                       0, 0);
1564                 put_unaligned_be64(opts->fail_seq, ptr);
1565                 ptr += 2;
1566
1567                 if (OPTION_MPTCP_RST & opts->suboptions)
1568                         goto mp_rst;
1569                 return;
1570         } else if (unlikely(OPTION_MPTCP_RST & opts->suboptions)) {
1571 mp_rst:
1572                 *ptr++ = mptcp_option(MPTCPOPT_RST,
1573                                       TCPOLEN_MPTCP_RST,
1574                                       opts->reset_transient,
1575                                       opts->reset_reason);
1576                 return;
1577         }
1578
1579         if (OPTION_MPTCP_PRIO & opts->suboptions) {
1580                 subflow = mptcp_subflow_ctx(ssk);
1581                 subflow->send_mp_prio = 0;
1582
1583                 *ptr++ = mptcp_option(MPTCPOPT_MP_PRIO,
1584                                       TCPOLEN_MPTCP_PRIO,
1585                                       opts->backup, TCPOPT_NOP);
1586         }
1587
1588 mp_capable_done:
1589         if (OPTION_MPTCP_RM_ADDR & opts->suboptions) {
1590                 u8 i = 1;
1591
1592                 *ptr++ = mptcp_option(MPTCPOPT_RM_ADDR,
1593                                       TCPOLEN_MPTCP_RM_ADDR_BASE + opts->rm_list.nr,
1594                                       0, opts->rm_list.ids[0]);
1595
1596                 while (i < opts->rm_list.nr) {
1597                         u8 id1, id2, id3, id4;
1598
1599                         id1 = opts->rm_list.ids[i];
1600                         id2 = i + 1 < opts->rm_list.nr ? opts->rm_list.ids[i + 1] : TCPOPT_NOP;
1601                         id3 = i + 2 < opts->rm_list.nr ? opts->rm_list.ids[i + 2] : TCPOPT_NOP;
1602                         id4 = i + 3 < opts->rm_list.nr ? opts->rm_list.ids[i + 3] : TCPOPT_NOP;
1603                         put_unaligned_be32(id1 << 24 | id2 << 16 | id3 << 8 | id4, ptr);
1604                         ptr += 1;
1605                         i += 4;
1606                 }
1607         }
1608
1609         if (tp)
1610                 mptcp_set_rwin(tp, th);
1611 }
1612
1613 __be32 mptcp_get_reset_option(const struct sk_buff *skb)
1614 {
1615         const struct mptcp_ext *ext = mptcp_get_ext(skb);
1616         u8 flags, reason;
1617
1618         if (ext) {
1619                 flags = ext->reset_transient;
1620                 reason = ext->reset_reason;
1621
1622                 return mptcp_option(MPTCPOPT_RST, TCPOLEN_MPTCP_RST,
1623                                     flags, reason);
1624         }
1625
1626         return htonl(0u);
1627 }
1628 EXPORT_SYMBOL_GPL(mptcp_get_reset_option);