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         u8 tcp_fin;
 338
 339         if (skb) {
 340                 mpext = mptcp_get_ext(skb);
 341                 tcp_fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
 342         } else {
 343                 mpext = NULL;
 344                 tcp_fin = 0;
 345         }
 346
 347         if (!skb || (mpext && mpext->use_map) || tcp_fin) {
 348                 unsigned int map_size;
 349
 350                 map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;
 351
 352                 remaining -= map_size;
 353                 dss_size = map_size;
 354                 if (mpext)
 355                         opts->ext_copy = *mpext;
 356
 357                 if (skb && tcp_fin &&
 358                     subflow->conn->sk_state != TCP_ESTABLISHED)
 359                         mptcp_write_data_fin(subflow, &opts->ext_copy);
 360                 ret = true;
 361         }
 362
 363         opts->ext_copy.use_ack = 0;
 364         msk = mptcp_sk(subflow->conn);
 365         if (!msk || !READ_ONCE(msk->can_ack)) {
 366                 *size = ALIGN(dss_size, 4);
 367                 return ret;
 368         }
 369
 370         ack_size = TCPOLEN_MPTCP_DSS_ACK64;
 371
 372         /* Add kind/length/subtype/flag overhead if mapping is not populated */
 373         if (dss_size == 0)
 374                 ack_size += TCPOLEN_MPTCP_DSS_BASE;
 375
 376         dss_size += ack_size;
 377
 378         opts->ext_copy.data_ack = msk->ack_seq;
 379         opts->ext_copy.ack64 = 1;
 380         opts->ext_copy.use_ack = 1;
 381
 382         *size = ALIGN(dss_size, 4);
 383         return true;
 384 }
 385
 386 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 387                                unsigned int *size, unsigned int remaining,
 388                                struct mptcp_out_options *opts)
 389 {
 390         unsigned int opt_size = 0;
 391         bool ret = false;
 392
 393         if (mptcp_established_options_mp(sk, skb, &opt_size, remaining, opts))
 394                 ret = true;
 395         else if (mptcp_established_options_dss(sk, skb, &opt_size, remaining,
 396                                                opts))
 397                 ret = true;
 398
 399         /* we reserved enough space for the above options, and exceeding the
 400          * TCP option space would be fatal
 401          */
 402         if (WARN_ON_ONCE(opt_size > remaining))
 403                 return false;
 404
 405         *size += opt_size;
 406         remaining -= opt_size;
 407
 408         return ret;
 409 }
 410
 411 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
 412                           struct mptcp_out_options *opts)
 413 {
 414         struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
 415
 416         if (subflow_req->mp_capable) {
 417                 opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
 418                 opts->sndr_key = subflow_req->local_key;
 419                 *size = TCPOLEN_MPTCP_MPC_SYNACK;
 420                 pr_debug("subflow_req=%p, local_key=%llu",
 421                          subflow_req, subflow_req->local_key);
 422                 return true;
 423         }
 424         return false;
 425 }
 426
 427 static bool check_fourth_ack(struct mptcp_subflow_context *subflow,
 428                              struct sk_buff *skb,
 429                              struct mptcp_options_received *mp_opt)
 430 {
 431         /* here we can process OoO, in-window pkts, only in-sequence 4th ack
 432          * are relevant
 433          */
 434         if (likely(subflow->fourth_ack ||
 435                    TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1))
 436                 return true;
 437
 438         if (mp_opt->use_ack)
 439                 subflow->fourth_ack = 1;
 440
 441         if (subflow->can_ack)
 442                 return true;
 443
 444         /* If the first established packet does not contain MP_CAPABLE + data
 445          * then fallback to TCP
 446          */
 447         if (!mp_opt->mp_capable) {
 448                 subflow->mp_capable = 0;
 449                 tcp_sk(mptcp_subflow_tcp_sock(subflow))->is_mptcp = 0;
 450                 return false;
 451         }
 452         subflow->remote_key = mp_opt->sndr_key;
 453         subflow->can_ack = 1;
 454         return true;
 455 }
 456
 457 void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb,
 458                             struct tcp_options_received *opt_rx)
 459 {
 460         struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 461         struct mptcp_options_received *mp_opt;
 462         struct mptcp_ext *mpext;
 463
 464         mp_opt = &opt_rx->mptcp;
 465         if (!check_fourth_ack(subflow, skb, mp_opt))
 466                 return;
 467
 468         if (!mp_opt->dss)
 469                 return;
 470
 471         mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
 472         if (!mpext)
 473                 return;
 474
 475         memset(mpext, 0, sizeof(*mpext));
 476
 477         if (mp_opt->use_map) {
 478                 if (mp_opt->mpc_map) {
 479                         /* this is an MP_CAPABLE carrying MPTCP data
 480                          * we know this map the first chunk of data
 481                          */
 482                         mptcp_crypto_key_sha(subflow->remote_key, NULL,
 483                                              &mpext->data_seq);
 484                         mpext->data_seq++;
 485                         mpext->subflow_seq = 1;
 486                         mpext->dsn64 = 1;
 487                         mpext->mpc_map = 1;
 488                 } else {
 489                         mpext->data_seq = mp_opt->data_seq;
 490                         mpext->subflow_seq = mp_opt->subflow_seq;
 491                         mpext->dsn64 = mp_opt->dsn64;
 492                 }
 493                 mpext->data_len = mp_opt->data_len;
 494                 mpext->use_map = 1;
 495         }
 496
 497         if (mp_opt->use_ack) {
 498                 mpext->data_ack = mp_opt->data_ack;
 499                 mpext->use_ack = 1;
 500                 mpext->ack64 = mp_opt->ack64;
 501         }
 502
 503         mpext->data_fin = mp_opt->data_fin;
 504 }
 505
 506 void mptcp_write_options(__be32 *ptr, struct mptcp_out_options *opts)
 507 {
 508         if ((OPTION_MPTCP_MPC_SYN | OPTION_MPTCP_MPC_SYNACK |
 509              OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
 510                 u8 len;
 511
 512                 if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
 513                         len = TCPOLEN_MPTCP_MPC_SYN;
 514                 else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions)
 515                         len = TCPOLEN_MPTCP_MPC_SYNACK;
 516                 else if (opts->ext_copy.data_len)
 517                         len = TCPOLEN_MPTCP_MPC_ACK_DATA;
 518                 else
 519                         len = TCPOLEN_MPTCP_MPC_ACK;
 520
 521                 *ptr++ = htonl((TCPOPT_MPTCP << 24) | (len << 16) |
 522                                (MPTCPOPT_MP_CAPABLE << 12) |
 523                                (MPTCP_SUPPORTED_VERSION << 8) |
 524                                MPTCP_CAP_HMAC_SHA256);
 525
 526                 if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
 527                     opts->suboptions))
 528                         goto mp_capable_done;
 529
 530                 put_unaligned_be64(opts->sndr_key, ptr);
 531                 ptr += 2;
 532                 if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
 533                         goto mp_capable_done;
 534
 535                 put_unaligned_be64(opts->rcvr_key, ptr);
 536                 ptr += 2;
 537                 if (!opts->ext_copy.data_len)
 538                         goto mp_capable_done;
 539
 540                 put_unaligned_be32(opts->ext_copy.data_len << 16 |
 541                                    TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
 542                 ptr += 1;
 543         }
 544
 545 mp_capable_done:
 546         if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
 547                 struct mptcp_ext *mpext = &opts->ext_copy;
 548                 u8 len = TCPOLEN_MPTCP_DSS_BASE;
 549                 u8 flags = 0;
 550
 551                 if (mpext->use_ack) {
 552                         len += TCPOLEN_MPTCP_DSS_ACK64;
 553                         flags = MPTCP_DSS_HAS_ACK | MPTCP_DSS_ACK64;
 554                 }
 555
 556                 if (mpext->use_map) {
 557                         len += TCPOLEN_MPTCP_DSS_MAP64;
 558
 559                         /* Use only 64-bit mapping flags for now, add
 560                          * support for optional 32-bit mappings later.
 561                          */
 562                         flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
 563                         if (mpext->data_fin)
 564                                 flags |= MPTCP_DSS_DATA_FIN;
 565                 }
 566
 567                 *ptr++ = htonl((TCPOPT_MPTCP << 24) |
 568                                (len  << 16) |
 569                                (MPTCPOPT_DSS << 12) |
 570                                (flags));
 571
 572                 if (mpext->use_ack) {
 573                         put_unaligned_be64(mpext->data_ack, ptr);
 574                         ptr += 2;
 575                 }
 576
 577                 if (mpext->use_map) {
 578                         put_unaligned_be64(mpext->data_seq, ptr);
 579                         ptr += 2;
 580                         put_unaligned_be32(mpext->subflow_seq, ptr);
 581                         ptr += 1;
 582                         put_unaligned_be32(mpext->data_len << 16 |
 583                                            TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
 584                 }
 585         }
 586 }