sys/netinet/tcp_output.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  *
  31  *      @(#)tcp_output.c        8.4 (Berkeley) 5/24/95
  32  */
  33
  34 #include <sys/cdefs.h>
  35 #include "opt_inet.h"
  36 #include "opt_inet6.h"
  37 #include "opt_ipsec.h"
  38 #include "opt_kern_tls.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/systm.h>
  42 #include <sys/arb.h>
  43 #include <sys/domain.h>
  44 #ifdef TCP_HHOOK
  45 #include <sys/hhook.h>
  46 #endif
  47 #include <sys/kernel.h>
  48 #ifdef KERN_TLS
  49 #include <sys/ktls.h>
  50 #endif
  51 #include <sys/lock.h>
  52 #include <sys/mbuf.h>
  53 #include <sys/mutex.h>
  54 #include <sys/protosw.h>
  55 #include <sys/qmath.h>
  56 #include <sys/sdt.h>
  57 #include <sys/socket.h>
  58 #include <sys/socketvar.h>
  59 #include <sys/sysctl.h>
  60 #include <sys/stats.h>
  61
  62 #include <net/if.h>
  63 #include <net/route.h>
  64 #include <net/route/nhop.h>
  65 #include <net/vnet.h>
  66
  67 #include <netinet/in.h>
  68 #include <netinet/in_kdtrace.h>
  69 #include <netinet/in_systm.h>
  70 #include <netinet/ip.h>
  71 #include <netinet/in_pcb.h>
  72 #include <netinet/ip_var.h>
  73 #include <netinet/ip_options.h>
  74 #ifdef INET6
  75 #include <netinet6/in6_pcb.h>
  76 #include <netinet/ip6.h>
  77 #include <netinet6/ip6_var.h>
  78 #endif
  79 #include <netinet/tcp.h>
  80 #define TCPOUTFLAGS
  81 #include <netinet/tcp_fsm.h>
  82 #include <netinet/tcp_seq.h>
  83 #include <netinet/tcp_var.h>
  84 #include <netinet/tcp_log_buf.h>
  85 #include <netinet/tcp_syncache.h>
  86 #include <netinet/tcp_timer.h>
  87 #include <netinet/tcpip.h>
  88 #include <netinet/cc/cc.h>
  89 #include <netinet/tcp_fastopen.h>
  90 #ifdef TCPPCAP
  91 #include <netinet/tcp_pcap.h>
  92 #endif
  93 #ifdef TCP_OFFLOAD
  94 #include <netinet/tcp_offload.h>
  95 #endif
  96 #include <netinet/tcp_ecn.h>
  97
  98 #include <netipsec/ipsec_support.h>
  99
 100 #include <netinet/udp.h>
 101 #include <netinet/udp_var.h>
 102 #include <machine/in_cksum.h>
 103
 104 #include <security/mac/mac_framework.h>
 105
 106 VNET_DEFINE(int, path_mtu_discovery) = 1;
 107 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
 108         &VNET_NAME(path_mtu_discovery), 1,
 109         "Enable Path MTU Discovery");
 110
 111 VNET_DEFINE(int, tcp_do_tso) = 1;
 112 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
 113         &VNET_NAME(tcp_do_tso), 0,
 114         "Enable TCP Segmentation Offload");
 115
 116 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
 117 #define V_tcp_sendspace VNET(tcp_sendspace)
 118 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
 119         &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
 120
 121 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
 122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
 123         &VNET_NAME(tcp_do_autosndbuf), 0,
 124         "Enable automatic send buffer sizing");
 125
 126 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
 127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
 128         &VNET_NAME(tcp_autosndbuf_inc), 0,
 129         "Incrementor step size of automatic send buffer");
 130
 131 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
 132 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
 133         &VNET_NAME(tcp_autosndbuf_max), 0,
 134         "Max size of automatic send buffer");
 135
 136 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
 137 #define V_tcp_sendbuf_auto_lowat        VNET(tcp_sendbuf_auto_lowat)
 138 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
 139         &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
 140         "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
 141
 142 /*
 143  * Make sure that either retransmit or persist timer is set for SYN, FIN and
 144  * non-ACK.
 145  */
 146 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags)                        \
 147         KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
 148             tcp_timer_active((tp), TT_REXMT) ||                         \
 149             tcp_timer_active((tp), TT_PERSIST),                         \
 150             ("neither rexmt nor persist timer is set"))
 151
 152 #ifdef TCP_HHOOK
 153 /*
 154  * Wrapper for the TCP established output helper hook.
 155  */
 156 void
 157 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
 158     struct tcpopt *to, uint32_t len, int tso)
 159 {
 160         struct tcp_hhook_data hhook_data;
 161
 162         if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
 163                 hhook_data.tp = tp;
 164                 hhook_data.th = th;
 165                 hhook_data.to = to;
 166                 hhook_data.len = len;
 167                 hhook_data.tso = tso;
 168
 169                 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
 170                     &tp->t_osd);
 171         }
 172 }
 173 #endif
 174
 175 /*
 176  * CC wrapper hook functions
 177  */
 178 void
 179 cc_after_idle(struct tcpcb *tp)
 180 {
 181         INP_WLOCK_ASSERT(tptoinpcb(tp));
 182
 183         if (CC_ALGO(tp)->after_idle != NULL)
 184                 CC_ALGO(tp)->after_idle(&tp->t_ccv);
 185 }
 186
 187 /*
 188  * Tcp output routine: figure out what should be sent and send it.
 189  */
 190 int
 191 tcp_default_output(struct tcpcb *tp)
 192 {
 193         struct socket *so = tptosocket(tp);
 194         struct inpcb *inp = tptoinpcb(tp);
 195         int32_t len;
 196         uint32_t recwin, sendwin;
 197         uint16_t flags;
 198         int off, error = 0;     /* Keep compiler happy */
 199         u_int if_hw_tsomaxsegcount = 0;
 200         u_int if_hw_tsomaxsegsize = 0;
 201         struct mbuf *m;
 202         struct ip *ip = NULL;
 203         struct tcphdr *th;
 204         u_char opt[TCP_MAXOLEN];
 205         unsigned ipoptlen, optlen, hdrlen, ulen;
 206 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 207         unsigned ipsec_optlen = 0;
 208 #endif
 209         int idle, sendalot, curticks;
 210         int sack_rxmit, sack_bytes_rxmt;
 211         struct sackhole *p;
 212         int tso, mtu;
 213         struct tcpopt to;
 214         struct udphdr *udp = NULL;
 215         struct tcp_log_buffer *lgb;
 216         unsigned int wanted_cookie = 0;
 217         unsigned int dont_sendalot = 0;
 218 #if 0
 219         int maxburst = TCP_MAXBURST;
 220 #endif
 221 #ifdef INET6
 222         struct ip6_hdr *ip6 = NULL;
 223         const bool isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
 224 #endif
 225 #ifdef KERN_TLS
 226         const bool hw_tls = tp->t_nic_ktls_xmit != 0;
 227 #else
 228         const bool hw_tls = false;
 229 #endif
 230
 231         NET_EPOCH_ASSERT();
 232         INP_WLOCK_ASSERT(inp);
 233
 234 #ifdef TCP_OFFLOAD
 235         if (tp->t_flags & TF_TOE)
 236                 return (tcp_offload_output(tp));
 237 #endif
 238
 239         /*
 240          * For TFO connections in SYN_SENT or SYN_RECEIVED,
 241          * only allow the initial SYN or SYN|ACK and those sent
 242          * by the retransmit timer.
 243          */
 244         if (IS_FASTOPEN(tp->t_flags) &&
 245             ((tp->t_state == TCPS_SYN_SENT) ||
 246              (tp->t_state == TCPS_SYN_RECEIVED)) &&
 247             SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
 248             (tp->snd_nxt != tp->snd_una))       /* not a retransmit */
 249                 return (0);
 250
 251         /*
 252          * Determine length of data that should be transmitted,
 253          * and flags that will be used.
 254          * If there is some data or critical controls (SYN, RST)
 255          * to send, then transmit; otherwise, investigate further.
 256          */
 257         idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
 258         if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
 259             (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
 260                 cc_after_idle(tp);
 261         tp->t_flags &= ~TF_LASTIDLE;
 262         if (idle) {
 263                 if (tp->t_flags & TF_MORETOCOME) {
 264                         tp->t_flags |= TF_LASTIDLE;
 265                         idle = 0;
 266                 }
 267         }
 268 again:
 269         /*
 270          * If we've recently taken a timeout, snd_max will be greater than
 271          * snd_nxt.  There may be SACK information that allows us to avoid
 272          * resending already delivered data.  Adjust snd_nxt accordingly.
 273          */
 274         if ((tp->t_flags & TF_SACK_PERMIT) &&
 275             SEQ_LT(tp->snd_nxt, tp->snd_max))
 276                 tcp_sack_adjust(tp);
 277         sendalot = 0;
 278         tso = 0;
 279         mtu = 0;
 280         off = tp->snd_nxt - tp->snd_una;
 281         sendwin = min(tp->snd_wnd, tp->snd_cwnd);
 282
 283         flags = tcp_outflags[tp->t_state];
 284         /*
 285          * Send any SACK-generated retransmissions.  If we're explicitly trying
 286          * to send out new data (when sendalot is 1), bypass this function.
 287          * If we retransmit in fast recovery mode, decrement snd_cwnd, since
 288          * we're replacing a (future) new transmission with a retransmission
 289          * now, and we previously incremented snd_cwnd in tcp_input().
 290          */
 291         /*
 292          * Still in sack recovery , reset rxmit flag to zero.
 293          */
 294         sack_rxmit = 0;
 295         sack_bytes_rxmt = 0;
 296         len = 0;
 297         p = NULL;
 298         if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
 299             (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
 300                 uint32_t cwin;
 301
 302                 cwin =
 303                     imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
 304                 /* Do not retransmit SACK segments beyond snd_recover */
 305                 if (SEQ_GT(p->end, tp->snd_recover)) {
 306                         /*
 307                          * (At least) part of sack hole extends beyond
 308                          * snd_recover. Check to see if we can rexmit data
 309                          * for this hole.
 310                          */
 311                         if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
 312                                 /*
 313                                  * Can't rexmit any more data for this hole.
 314                                  * That data will be rexmitted in the next
 315                                  * sack recovery episode, when snd_recover
 316                                  * moves past p->rxmit.
 317                                  */
 318                                 p = NULL;
 319                                 goto after_sack_rexmit;
 320                         } else {
 321                                 /* Can rexmit part of the current hole */
 322                                 len = ((int32_t)ulmin(cwin,
 323                                     SEQ_SUB(tp->snd_recover, p->rxmit)));
 324                         }
 325                 } else {
 326                         len = ((int32_t)ulmin(cwin,
 327                             SEQ_SUB(p->end, p->rxmit)));
 328                 }
 329                 if (len > 0) {
 330                         off = SEQ_SUB(p->rxmit, tp->snd_una);
 331                         KASSERT(off >= 0,("%s: sack block to the left of una : %d",
 332                             __func__, off));
 333                         sack_rxmit = 1;
 334                         sendalot = 1;
 335                         TCPSTAT_INC(tcps_sack_rexmits);
 336                         TCPSTAT_ADD(tcps_sack_rexmit_bytes,
 337                             min(len, tcp_maxseg(tp)));
 338                 }
 339         }
 340 after_sack_rexmit:
 341         /*
 342          * Get standard flags, and add SYN or FIN if requested by 'hidden'
 343          * state flags.
 344          */
 345         if (tp->t_flags & TF_NEEDFIN)
 346                 flags |= TH_FIN;
 347         if (tp->t_flags & TF_NEEDSYN)
 348                 flags |= TH_SYN;
 349
 350         SOCKBUF_LOCK(&so->so_snd);
 351         /*
 352          * If in persist timeout with window of 0, send 1 byte.
 353          * Otherwise, if window is small but nonzero
 354          * and timer expired, we will send what we can
 355          * and go to transmit state.
 356          */
 357         if (tp->t_flags & TF_FORCEDATA) {
 358                 if (sendwin == 0) {
 359                         /*
 360                          * If we still have some data to send, then
 361                          * clear the FIN bit.  Usually this would
 362                          * happen below when it realizes that we
 363                          * aren't sending all the data.  However,
 364                          * if we have exactly 1 byte of unsent data,
 365                          * then it won't clear the FIN bit below,
 366                          * and if we are in persist state, we wind
 367                          * up sending the packet without recording
 368                          * that we sent the FIN bit.
 369                          *
 370                          * We can't just blindly clear the FIN bit,
 371                          * because if we don't have any more data
 372                          * to send then the probe will be the FIN
 373                          * itself.
 374                          */
 375                         if (off < sbused(&so->so_snd))
 376                                 flags &= ~TH_FIN;
 377                         sendwin = 1;
 378                 } else {
 379                         tcp_timer_activate(tp, TT_PERSIST, 0);
 380                         tp->t_rxtshift = 0;
 381                 }
 382         }
 383
 384         /*
 385          * If snd_nxt == snd_max and we have transmitted a FIN, the
 386          * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
 387          * a negative length.  This can also occur when TCP opens up
 388          * its congestion window while receiving additional duplicate
 389          * acks after fast-retransmit because TCP will reset snd_nxt
 390          * to snd_max after the fast-retransmit.
 391          *
 392          * In the normal retransmit-FIN-only case, however, snd_nxt will
 393          * be set to snd_una, the offset will be 0, and the length may
 394          * wind up 0.
 395          *
 396          * If sack_rxmit is true we are retransmitting from the scoreboard
 397          * in which case len is already set.
 398          */
 399         if (sack_rxmit == 0) {
 400                 if (sack_bytes_rxmt == 0)
 401                         len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
 402                             off);
 403                 else {
 404                         int32_t cwin;
 405
 406                         /*
 407                          * We are inside of a SACK recovery episode and are
 408                          * sending new data, having retransmitted all the
 409                          * data possible in the scoreboard.
 410                          */
 411                         len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
 412                             off);
 413                         /*
 414                          * Don't remove this (len > 0) check !
 415                          * We explicitly check for len > 0 here (although it
 416                          * isn't really necessary), to work around a gcc
 417                          * optimization issue - to force gcc to compute
 418                          * len above. Without this check, the computation
 419                          * of len is bungled by the optimizer.
 420                          */
 421                         if (len > 0) {
 422                                 cwin = tp->snd_cwnd - imax(0, (int32_t)
 423                                         (tp->snd_nxt - tp->snd_recover)) -
 424                                         sack_bytes_rxmt;
 425                                 if (cwin < 0)
 426                                         cwin = 0;
 427                                 len = imin(len, cwin);
 428                         }
 429                 }
 430         }
 431
 432         /*
 433          * Lop off SYN bit if it has already been sent.  However, if this
 434          * is SYN-SENT state and if segment contains data and if we don't
 435          * know that foreign host supports TAO, suppress sending segment.
 436          */
 437         if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
 438                 if (tp->t_state != TCPS_SYN_RECEIVED)
 439                         flags &= ~TH_SYN;
 440                 /*
 441                  * When sending additional segments following a TFO SYN|ACK,
 442                  * do not include the SYN bit.
 443                  */
 444                 if (IS_FASTOPEN(tp->t_flags) &&
 445                     (tp->t_state == TCPS_SYN_RECEIVED))
 446                         flags &= ~TH_SYN;
 447                 off--, len++;
 448         }
 449
 450         /*
 451          * Be careful not to send data and/or FIN on SYN segments.
 452          * This measure is needed to prevent interoperability problems
 453          * with not fully conformant TCP implementations.
 454          */
 455         if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
 456                 len = 0;
 457                 flags &= ~TH_FIN;
 458         }
 459
 460         /*
 461          * On TFO sockets, ensure no data is sent in the following cases:
 462          *
 463          *  - When retransmitting SYN|ACK on a passively-created socket
 464          *
 465          *  - When retransmitting SYN on an actively created socket
 466          *
 467          *  - When sending a zero-length cookie (cookie request) on an
 468          *    actively created socket
 469          *
 470          *  - When the socket is in the CLOSED state (RST is being sent)
 471          */
 472         if (IS_FASTOPEN(tp->t_flags) &&
 473             (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
 474              ((tp->t_state == TCPS_SYN_SENT) &&
 475               (tp->t_tfo_client_cookie_len == 0)) ||
 476              (flags & TH_RST)))
 477                 len = 0;
 478         if (len <= 0) {
 479                 /*
 480                  * If FIN has been sent but not acked,
 481                  * but we haven't been called to retransmit,
 482                  * len will be < 0.  Otherwise, window shrank
 483                  * after we sent into it.  If window shrank to 0,
 484                  * cancel pending retransmit, pull snd_nxt back
 485                  * to (closed) window, and set the persist timer
 486                  * if it isn't already going.  If the window didn't
 487                  * close completely, just wait for an ACK.
 488                  *
 489                  * We also do a general check here to ensure that
 490                  * we will set the persist timer when we have data
 491                  * to send, but a 0-byte window. This makes sure
 492                  * the persist timer is set even if the packet
 493                  * hits one of the "goto send" lines below.
 494                  */
 495                 len = 0;
 496                 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
 497                     (off < (int) sbavail(&so->so_snd)) &&
 498                     !tcp_timer_active(tp, TT_PERSIST)) {
 499                         tcp_timer_activate(tp, TT_REXMT, 0);
 500                         tp->t_rxtshift = 0;
 501                         tp->snd_nxt = tp->snd_una;
 502                         if (!tcp_timer_active(tp, TT_PERSIST))
 503                                 tcp_setpersist(tp);
 504                 }
 505         }
 506
 507         /* len will be >= 0 after this point. */
 508         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
 509
 510         tcp_sndbuf_autoscale(tp, so, sendwin);
 511
 512         /*
 513          * Decide if we can use TCP Segmentation Offloading (if supported by
 514          * hardware).
 515          *
 516          * TSO may only be used if we are in a pure bulk sending state.  The
 517          * presence of TCP-MD5, SACK retransmits, SACK advertizements and
 518          * IP options prevent using TSO.  With TSO the TCP header is the same
 519          * (except for the sequence number) for all generated packets.  This
 520          * makes it impossible to transmit any options which vary per generated
 521          * segment or packet.
 522          *
 523          * IPv4 handling has a clear separation of ip options and ip header
 524          * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
 525          * the right thing below to provide length of just ip options and thus
 526          * checking for ipoptlen is enough to decide if ip options are present.
 527          */
 528 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 529         /*
 530          * Pre-calculate here as we save another lookup into the darknesses
 531          * of IPsec that way and can actually decide if TSO is ok.
 532          */
 533 #ifdef INET6
 534         if (isipv6 && IPSEC_ENABLED(ipv6))
 535                 ipsec_optlen = IPSEC_HDRSIZE(ipv6, inp);
 536 #ifdef INET
 537         else
 538 #endif
 539 #endif /* INET6 */
 540 #ifdef INET
 541         if (IPSEC_ENABLED(ipv4))
 542                 ipsec_optlen = IPSEC_HDRSIZE(ipv4, inp);
 543 #endif /* INET */
 544 #endif /* IPSEC */
 545 #ifdef INET6
 546         if (isipv6)
 547                 ipoptlen = ip6_optlen(inp);
 548         else
 549 #endif
 550         if (inp->inp_options)
 551                 ipoptlen = inp->inp_options->m_len -
 552                                 offsetof(struct ipoption, ipopt_list);
 553         else
 554                 ipoptlen = 0;
 555 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
 556         ipoptlen += ipsec_optlen;
 557 #endif
 558
 559         if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
 560             (tp->t_port == 0) &&
 561             ((tp->t_flags & TF_SIGNATURE) == 0) &&
 562             tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
 563             ipoptlen == 0 && !(flags & TH_SYN))
 564                 tso = 1;
 565
 566         if (sack_rxmit) {
 567                 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
 568                         flags &= ~TH_FIN;
 569         } else {
 570                 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
 571                     sbused(&so->so_snd)))
 572                         flags &= ~TH_FIN;
 573         }
 574
 575         recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
 576             (long)TCP_MAXWIN << tp->rcv_scale);
 577
 578         /*
 579          * Sender silly window avoidance.   We transmit under the following
 580          * conditions when len is non-zero:
 581          *
 582          *      - We have a full segment (or more with TSO)
 583          *      - This is the last buffer in a write()/send() and we are
 584          *        either idle or running NODELAY
 585          *      - we've timed out (e.g. persist timer)
 586          *      - we have more then 1/2 the maximum send window's worth of
 587          *        data (receiver may be limited the window size)
 588          *      - we need to retransmit
 589          */
 590         if (len) {
 591                 if (len >= tp->t_maxseg)
 592                         goto send;
 593                 /*
 594                  * As the TCP header options are now
 595                  * considered when setting up the initial
 596                  * window, we would not send the last segment
 597                  * if we skip considering the option length here.
 598                  * Note: this may not work when tcp headers change
 599                  * very dynamically in the future.
 600                  */
 601                 if ((((tp->t_flags & TF_SIGNATURE) ?
 602                         PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
 603                     ((tp->t_flags & TF_RCVD_TSTMP) ?
 604                         PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
 605                     len) >= tp->t_maxseg)
 606                         goto send;
 607                 /*
 608                  * NOTE! on localhost connections an 'ack' from the remote
 609                  * end may occur synchronously with the output and cause
 610                  * us to flush a buffer queued with moretocome.  XXX
 611                  *
 612                  * note: the len + off check is almost certainly unnecessary.
 613                  */
 614                 if (!(tp->t_flags & TF_MORETOCOME) &&   /* normal case */
 615                     (idle || (tp->t_flags & TF_NODELAY)) &&
 616                     (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
 617                     (tp->t_flags & TF_NOPUSH) == 0) {
 618                         goto send;
 619                 }
 620                 if (tp->t_flags & TF_FORCEDATA)         /* typ. timeout case */
 621                         goto send;
 622                 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
 623                         goto send;
 624                 if (SEQ_LT(tp->snd_nxt, tp->snd_max))   /* retransmit case */
 625                         goto send;
 626                 if (sack_rxmit)
 627                         goto send;
 628         }
 629
 630         /*
 631          * Sending of standalone window updates.
 632          *
 633          * Window updates are important when we close our window due to a
 634          * full socket buffer and are opening it again after the application
 635          * reads data from it.  Once the window has opened again and the
 636          * remote end starts to send again the ACK clock takes over and
 637          * provides the most current window information.
 638          *
 639          * We must avoid the silly window syndrome whereas every read
 640          * from the receive buffer, no matter how small, causes a window
 641          * update to be sent.  We also should avoid sending a flurry of
 642          * window updates when the socket buffer had queued a lot of data
 643          * and the application is doing small reads.
 644          *
 645          * Prevent a flurry of pointless window updates by only sending
 646          * an update when we can increase the advertized window by more
 647          * than 1/4th of the socket buffer capacity.  When the buffer is
 648          * getting full or is very small be more aggressive and send an
 649          * update whenever we can increase by two mss sized segments.
 650          * In all other situations the ACK's to new incoming data will
 651          * carry further window increases.
 652          *
 653          * Don't send an independent window update if a delayed
 654          * ACK is pending (it will get piggy-backed on it) or the
 655          * remote side already has done a half-close and won't send
 656          * more data.  Skip this if the connection is in T/TCP
 657          * half-open state.
 658          */
 659         if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
 660             !(tp->t_flags & TF_DELACK) &&
 661             !TCPS_HAVERCVDFIN(tp->t_state)) {
 662                 /*
 663                  * "adv" is the amount we could increase the window,
 664                  * taking into account that we are limited by
 665                  * TCP_MAXWIN << tp->rcv_scale.
 666                  */
 667                 int32_t adv;
 668                 int oldwin;
 669
 670                 adv = recwin;
 671                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
 672                         oldwin = (tp->rcv_adv - tp->rcv_nxt);
 673                         if (adv > oldwin)
 674                                 adv -= oldwin;
 675                         else
 676                                 adv = 0;
 677                 } else
 678                         oldwin = 0;
 679
 680                 /*
 681                  * If the new window size ends up being the same as or less
 682                  * than the old size when it is scaled, then don't force
 683                  * a window update.
 684                  */
 685                 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
 686                         goto dontupdate;
 687
 688                 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
 689                     (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
 690                      recwin <= (so->so_rcv.sb_hiwat / 8) ||
 691                      so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
 692                      adv >= TCP_MAXWIN << tp->rcv_scale))
 693                         goto send;
 694                 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
 695                         goto send;
 696         }
 697 dontupdate:
 698
 699         /*
 700          * Send if we owe the peer an ACK, RST, SYN, or urgent data.  ACKNOW
 701          * is also a catch-all for the retransmit timer timeout case.
 702          */
 703         if (tp->t_flags & TF_ACKNOW)
 704                 goto send;
 705         if ((flags & TH_RST) ||
 706             ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
 707                 goto send;
 708         if (SEQ_GT(tp->snd_up, tp->snd_una))
 709                 goto send;
 710         /*
 711          * If our state indicates that FIN should be sent
 712          * and we have not yet done so, then we need to send.
 713          */
 714         if (flags & TH_FIN &&
 715             ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
 716                 goto send;
 717         /*
 718          * In SACK, it is possible for tcp_output to fail to send a segment
 719          * after the retransmission timer has been turned off.  Make sure
 720          * that the retransmission timer is set.
 721          */
 722         if ((tp->t_flags & TF_SACK_PERMIT) &&
 723             SEQ_GT(tp->snd_max, tp->snd_una) &&
 724             !tcp_timer_active(tp, TT_REXMT) &&
 725             !tcp_timer_active(tp, TT_PERSIST)) {
 726                 tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
 727                 goto just_return;
 728         }
 729         /*
 730          * TCP window updates are not reliable, rather a polling protocol
 731          * using ``persist'' packets is used to insure receipt of window
 732          * updates.  The three ``states'' for the output side are:
 733          *      idle                    not doing retransmits or persists
 734          *      persisting              to move a small or zero window
 735          *      (re)transmitting        and thereby not persisting
 736          *
 737          * tcp_timer_active(tp, TT_PERSIST)
 738          *      is true when we are in persist state.
 739          * (tp->t_flags & TF_FORCEDATA)
 740          *      is set when we are called to send a persist packet.
 741          * tcp_timer_active(tp, TT_REXMT)
 742          *      is set when we are retransmitting
 743          * The output side is idle when both timers are zero.
 744          *
 745          * If send window is too small, there is data to transmit, and no
 746          * retransmit or persist is pending, then go to persist state.
 747          * If nothing happens soon, send when timer expires:
 748          * if window is nonzero, transmit what we can,
 749          * otherwise force out a byte.
 750          */
 751         if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
 752             !tcp_timer_active(tp, TT_PERSIST)) {
 753                 tp->t_rxtshift = 0;
 754                 tcp_setpersist(tp);
 755         }
 756
 757         /*
 758          * No reason to send a segment, just return.
 759          */
 760 just_return:
 761         SOCKBUF_UNLOCK(&so->so_snd);
 762         return (0);
 763
 764 send:
 765         SOCKBUF_LOCK_ASSERT(&so->so_snd);
 766         if (len > 0) {
 767                 if (len >= tp->t_maxseg)
 768                         tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
 769                 else
 770                         tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
 771         }
 772         /*
 773          * Before ESTABLISHED, force sending of initial options
 774          * unless TCP set not to do any options.
 775          * NOTE: we assume that the IP/TCP header plus TCP options
 776          * always fit in a single mbuf, leaving room for a maximum
 777          * link header, i.e.
 778          *      max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
 779          */
 780         optlen = 0;
 781 #ifdef INET6
 782         if (isipv6)
 783                 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
 784         else
 785 #endif
 786                 hdrlen = sizeof (struct tcpiphdr);
 787
 788         if (flags & TH_SYN) {
 789                 tp->snd_nxt = tp->iss;
 790         }
 791
 792         /*
 793          * Compute options for segment.
 794          * We only have to care about SYN and established connection
 795          * segments.  Options for SYN-ACK segments are handled in TCP
 796          * syncache.
 797          */
 798         to.to_flags = 0;
 799         if ((tp->t_flags & TF_NOOPT) == 0) {
 800                 /* Maximum segment size. */
 801                 if (flags & TH_SYN) {
 802                         to.to_mss = tcp_mssopt(&inp->inp_inc);
 803                         if (tp->t_port)
 804                                 to.to_mss -= V_tcp_udp_tunneling_overhead;
 805                         to.to_flags |= TOF_MSS;
 806
 807                         /*
 808                          * On SYN or SYN|ACK transmits on TFO connections,
 809                          * only include the TFO option if it is not a
 810                          * retransmit, as the presence of the TFO option may
 811                          * have caused the original SYN or SYN|ACK to have
 812                          * been dropped by a middlebox.
 813                          */
 814                         if (IS_FASTOPEN(tp->t_flags) &&
 815                             (tp->t_rxtshift == 0)) {
 816                                 if (tp->t_state == TCPS_SYN_RECEIVED) {
 817                                         to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
 818                                         to.to_tfo_cookie =
 819                                             (u_int8_t *)&tp->t_tfo_cookie.server;
 820                                         to.to_flags |= TOF_FASTOPEN;
 821                                         wanted_cookie = 1;
 822                                 } else if (tp->t_state == TCPS_SYN_SENT) {
 823                                         to.to_tfo_len =
 824                                             tp->t_tfo_client_cookie_len;
 825                                         to.to_tfo_cookie =
 826                                             tp->t_tfo_cookie.client;
 827                                         to.to_flags |= TOF_FASTOPEN;
 828                                         wanted_cookie = 1;
 829                                         /*
 830                                          * If we wind up having more data to
 831                                          * send with the SYN than can fit in
 832                                          * one segment, don't send any more
 833                                          * until the SYN|ACK comes back from
 834                                          * the other end.
 835                                          */
 836                                         dont_sendalot = 1;
 837                                 }
 838                         }
 839                 }
 840                 /* Window scaling. */
 841                 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
 842                         to.to_wscale = tp->request_r_scale;
 843                         to.to_flags |= TOF_SCALE;
 844                 }
 845                 /* Timestamps. */
 846                 if ((tp->t_flags & TF_RCVD_TSTMP) ||
 847                     ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
 848                         curticks = tcp_ts_getticks();
 849                         to.to_tsval = curticks + tp->ts_offset;
 850                         to.to_tsecr = tp->ts_recent;
 851                         to.to_flags |= TOF_TS;
 852                         if (tp->t_rxtshift == 1)
 853                                 tp->t_badrxtwin = curticks;
 854                 }
 855
 856                 /* Set receive buffer autosizing timestamp. */
 857                 if (tp->rfbuf_ts == 0 &&
 858                     (so->so_rcv.sb_flags & SB_AUTOSIZE))
 859                         tp->rfbuf_ts = tcp_ts_getticks();
 860
 861                 /* Selective ACK's. */
 862                 if (tp->t_flags & TF_SACK_PERMIT) {
 863                         if (flags & TH_SYN)
 864                                 to.to_flags |= TOF_SACKPERM;
 865                         else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
 866                             tp->rcv_numsacks > 0) {
 867                                 to.to_flags |= TOF_SACK;
 868                                 to.to_nsacks = tp->rcv_numsacks;
 869                                 to.to_sacks = (u_char *)tp->sackblks;
 870                         }
 871                 }
 872 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
 873                 /* TCP-MD5 (RFC2385). */
 874                 /*
 875                  * Check that TCP_MD5SIG is enabled in tcpcb to
 876                  * account the size needed to set this TCP option.
 877                  */
 878                 if (tp->t_flags & TF_SIGNATURE)
 879                         to.to_flags |= TOF_SIGNATURE;
 880 #endif /* TCP_SIGNATURE */
 881
 882                 /* Processing the options. */
 883                 hdrlen += optlen = tcp_addoptions(&to, opt);
 884                 /*
 885                  * If we wanted a TFO option to be added, but it was unable
 886                  * to fit, ensure no data is sent.
 887                  */
 888                 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
 889                     !(to.to_flags & TOF_FASTOPEN))
 890                         len = 0;
 891         }
 892         if (tp->t_port) {
 893                 if (V_tcp_udp_tunneling_port == 0) {
 894                         /* The port was removed?? */
 895                         SOCKBUF_UNLOCK(&so->so_snd);
 896                         return (EHOSTUNREACH);
 897                 }
 898                 hdrlen += sizeof(struct udphdr);
 899         }
 900         /*
 901          * Adjust data length if insertion of options will
 902          * bump the packet length beyond the t_maxseg length.
 903          * Clear the FIN bit because we cut off the tail of
 904          * the segment.
 905          */
 906         if (len + optlen + ipoptlen > tp->t_maxseg) {
 907                 flags &= ~TH_FIN;
 908
 909                 if (tso) {
 910                         u_int if_hw_tsomax;
 911                         u_int moff;
 912                         int max_len;
 913
 914                         /* extract TSO information */
 915                         if_hw_tsomax = tp->t_tsomax;
 916                         if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
 917                         if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
 918
 919                         /*
 920                          * Limit a TSO burst to prevent it from
 921                          * overflowing or exceeding the maximum length
 922                          * allowed by the network interface:
 923                          */
 924                         KASSERT(ipoptlen == 0,
 925                             ("%s: TSO can't do IP options", __func__));
 926
 927                         /*
 928                          * Check if we should limit by maximum payload
 929                          * length:
 930                          */
 931                         if (if_hw_tsomax != 0) {
 932                                 /* compute maximum TSO length */
 933                                 max_len = (if_hw_tsomax - hdrlen -
 934                                     max_linkhdr);
 935                                 if (max_len <= 0) {
 936                                         len = 0;
 937                                 } else if (len > max_len) {
 938                                         sendalot = 1;
 939                                         len = max_len;
 940                                 }
 941                         }
 942
 943                         /*
 944                          * Prevent the last segment from being
 945                          * fractional unless the send sockbuf can be
 946                          * emptied:
 947                          */
 948                         max_len = (tp->t_maxseg - optlen);
 949                         if (((uint32_t)off + (uint32_t)len) <
 950                             sbavail(&so->so_snd)) {
 951                                 moff = len % max_len;
 952                                 if (moff != 0) {
 953                                         len -= moff;
 954                                         sendalot = 1;
 955                                 }
 956                         }
 957
 958                         /*
 959                          * In case there are too many small fragments
 960                          * don't use TSO:
 961                          */
 962                         if (len <= max_len) {
 963                                 len = max_len;
 964                                 sendalot = 1;
 965                                 tso = 0;
 966                         }
 967
 968                         /*
 969                          * Send the FIN in a separate segment
 970                          * after the bulk sending is done.
 971                          * We don't trust the TSO implementations
 972                          * to clear the FIN flag on all but the
 973                          * last segment.
 974                          */
 975                         if (tp->t_flags & TF_NEEDFIN)
 976                                 sendalot = 1;
 977                 } else {
 978                         if (optlen + ipoptlen >= tp->t_maxseg) {
 979                                 /*
 980                                  * Since we don't have enough space to put
 981                                  * the IP header chain and the TCP header in
 982                                  * one packet as required by RFC 7112, don't
 983                                  * send it. Also ensure that at least one
 984                                  * byte of the payload can be put into the
 985                                  * TCP segment.
 986                                  */
 987                                 SOCKBUF_UNLOCK(&so->so_snd);
 988                                 error = EMSGSIZE;
 989                                 sack_rxmit = 0;
 990                                 goto out;
 991                         }
 992                         len = tp->t_maxseg - optlen - ipoptlen;
 993                         sendalot = 1;
 994                         if (dont_sendalot)
 995                                 sendalot = 0;
 996                 }
 997         } else
 998                 tso = 0;
 999
1000         KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1001             ("%s: len > IP_MAXPACKET", __func__));
1002
1003 /*#ifdef DIAGNOSTIC*/
1004 #ifdef INET6
1005         if (max_linkhdr + hdrlen > MCLBYTES)
1006 #else
1007         if (max_linkhdr + hdrlen > MHLEN)
1008 #endif
1009                 panic("tcphdr too big");
1010 /*#endif*/
1011
1012         /*
1013          * This KASSERT is here to catch edge cases at a well defined place.
1014          * Before, those had triggered (random) panic conditions further down.
1015          */
1016         KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1017
1018         /*
1019          * Grab a header mbuf, attaching a copy of data to
1020          * be transmitted, and initialize the header from
1021          * the template for sends on this connection.
1022          */
1023         if (len) {
1024                 struct mbuf *mb;
1025                 struct sockbuf *msb;
1026                 u_int moff;
1027
1028                 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1029                         TCPSTAT_INC(tcps_sndprobe);
1030 #ifdef STATS
1031                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1032                                 stats_voi_update_abs_u32(tp->t_stats,
1033                                 VOI_TCP_RETXPB, len);
1034                         else
1035                                 stats_voi_update_abs_u64(tp->t_stats,
1036                                     VOI_TCP_TXPB, len);
1037 #endif /* STATS */
1038                 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1039                         tp->t_sndrexmitpack++;
1040                         TCPSTAT_INC(tcps_sndrexmitpack);
1041                         TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1042 #ifdef STATS
1043                         stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1044                             len);
1045 #endif /* STATS */
1046                 } else {
1047                         TCPSTAT_INC(tcps_sndpack);
1048                         TCPSTAT_ADD(tcps_sndbyte, len);
1049 #ifdef STATS
1050                         stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1051                             len);
1052 #endif /* STATS */
1053                 }
1054 #ifdef INET6
1055                 if (MHLEN < hdrlen + max_linkhdr)
1056                         m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1057                 else
1058 #endif
1059                         m = m_gethdr(M_NOWAIT, MT_DATA);
1060
1061                 if (m == NULL) {
1062                         SOCKBUF_UNLOCK(&so->so_snd);
1063                         error = ENOBUFS;
1064                         sack_rxmit = 0;
1065                         goto out;
1066                 }
1067
1068                 m->m_data += max_linkhdr;
1069                 m->m_len = hdrlen;
1070
1071                 /*
1072                  * Start the m_copy functions from the closest mbuf
1073                  * to the offset in the socket buffer chain.
1074                  */
1075                 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1076                 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1077                         m_copydata(mb, moff, len,
1078                             mtod(m, caddr_t) + hdrlen);
1079                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1080                                 sbsndptr_adv(&so->so_snd, mb, len);
1081                         m->m_len += len;
1082                 } else {
1083                         if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1084                                 msb = NULL;
1085                         else
1086                                 msb = &so->so_snd;
1087                         m->m_next = tcp_m_copym(mb, moff,
1088                             &len, if_hw_tsomaxsegcount,
1089                             if_hw_tsomaxsegsize, msb, hw_tls);
1090                         if (len <= (tp->t_maxseg - optlen)) {
1091                                 /*
1092                                  * Must have ran out of mbufs for the copy
1093                                  * shorten it to no longer need tso. Lets
1094                                  * not put on sendalot since we are low on
1095                                  * mbufs.
1096                                  */
1097                                 tso = 0;
1098                         }
1099                         if (m->m_next == NULL) {
1100                                 SOCKBUF_UNLOCK(&so->so_snd);
1101                                 (void) m_free(m);
1102                                 error = ENOBUFS;
1103                                 sack_rxmit = 0;
1104                                 goto out;
1105                         }
1106                 }
1107
1108                 /*
1109                  * If we're sending everything we've got, set PUSH.
1110                  * (This will keep happy those implementations which only
1111                  * give data to the user when a buffer fills or
1112                  * a PUSH comes in.)
1113                  */
1114                 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1115                     !(flags & TH_SYN))
1116                         flags |= TH_PUSH;
1117                 SOCKBUF_UNLOCK(&so->so_snd);
1118         } else {
1119                 SOCKBUF_UNLOCK(&so->so_snd);
1120                 if (tp->t_flags & TF_ACKNOW)
1121                         TCPSTAT_INC(tcps_sndacks);
1122                 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1123                         TCPSTAT_INC(tcps_sndctrl);
1124                 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1125                         TCPSTAT_INC(tcps_sndurg);
1126                 else
1127                         TCPSTAT_INC(tcps_sndwinup);
1128
1129                 m = m_gethdr(M_NOWAIT, MT_DATA);
1130                 if (m == NULL) {
1131                         error = ENOBUFS;
1132                         sack_rxmit = 0;
1133                         goto out;
1134                 }
1135 #ifdef INET6
1136                 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1137                     MHLEN >= hdrlen) {
1138                         M_ALIGN(m, hdrlen);
1139                 } else
1140 #endif
1141                 m->m_data += max_linkhdr;
1142                 m->m_len = hdrlen;
1143         }
1144         SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1145         m->m_pkthdr.rcvif = (struct ifnet *)0;
1146 #ifdef MAC
1147         mac_inpcb_create_mbuf(inp, m);
1148 #endif
1149 #ifdef INET6
1150         if (isipv6) {
1151                 ip6 = mtod(m, struct ip6_hdr *);
1152                 if (tp->t_port) {
1153                         udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1154                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1155                         udp->uh_dport = tp->t_port;
1156                         ulen = hdrlen + len - sizeof(struct ip6_hdr);
1157                         udp->uh_ulen = htons(ulen);
1158                         th = (struct tcphdr *)(udp + 1);
1159                 } else {
1160                         th = (struct tcphdr *)(ip6 + 1);
1161                 }
1162                 tcpip_fillheaders(inp, tp->t_port, ip6, th);
1163         } else
1164 #endif /* INET6 */
1165         {
1166                 ip = mtod(m, struct ip *);
1167                 if (tp->t_port) {
1168                         udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1169                         udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1170                         udp->uh_dport = tp->t_port;
1171                         ulen = hdrlen + len - sizeof(struct ip);
1172                         udp->uh_ulen = htons(ulen);
1173                         th = (struct tcphdr *)(udp + 1);
1174                 } else
1175                         th = (struct tcphdr *)(ip + 1);
1176                 tcpip_fillheaders(inp, tp->t_port, ip, th);
1177         }
1178
1179         /*
1180          * Fill in fields, remembering maximum advertised
1181          * window for use in delaying messages about window sizes.
1182          * If resending a FIN, be sure not to use a new sequence number.
1183          */
1184         if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1185             tp->snd_nxt == tp->snd_max)
1186                 tp->snd_nxt--;
1187         /*
1188          * If we are starting a connection, send ECN setup
1189          * SYN packet. If we are on a retransmit, we may
1190          * resend those bits a number of times as per
1191          * RFC 3168.
1192          */
1193         if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1194                 flags |= tcp_ecn_output_syn_sent(tp);
1195         }
1196         /* Also handle parallel SYN for ECN */
1197         if ((TCPS_HAVERCVDSYN(tp->t_state)) &&
1198             (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT))) {
1199                 int ect = tcp_ecn_output_established(tp, &flags, len, sack_rxmit);
1200                 if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1201                     (tp->t_flags2 & TF2_ECN_SND_ECE))
1202                         tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1203 #ifdef INET6
1204                 if (isipv6) {
1205                         ip6->ip6_flow &= ~htonl(IPTOS_ECN_MASK << IPV6_FLOWLABEL_LEN);
1206                         ip6->ip6_flow |= htonl(ect << IPV6_FLOWLABEL_LEN);
1207                 }
1208                 else
1209 #endif
1210                 {
1211                         ip->ip_tos &= ~IPTOS_ECN_MASK;
1212                         ip->ip_tos |= ect;
1213                 }
1214         }
1215
1216         /*
1217          * If we are doing retransmissions, then snd_nxt will
1218          * not reflect the first unsent octet.  For ACK only
1219          * packets, we do not want the sequence number of the
1220          * retransmitted packet, we want the sequence number
1221          * of the next unsent octet.  So, if there is no data
1222          * (and no SYN or FIN), use snd_max instead of snd_nxt
1223          * when filling in ti_seq.  But if we are in persist
1224          * state, snd_max might reflect one byte beyond the
1225          * right edge of the window, so use snd_nxt in that
1226          * case, since we know we aren't doing a retransmission.
1227          * (retransmit and persist are mutually exclusive...)
1228          */
1229         if (sack_rxmit == 0) {
1230                 if (len || (flags & (TH_SYN|TH_FIN)) ||
1231                     tcp_timer_active(tp, TT_PERSIST))
1232                         th->th_seq = htonl(tp->snd_nxt);
1233                 else
1234                         th->th_seq = htonl(tp->snd_max);
1235         } else {
1236                 th->th_seq = htonl(p->rxmit);
1237                 p->rxmit += len;
1238                 /*
1239                  * Lost Retransmission Detection
1240                  * trigger resending of a (then
1241                  * still existing) hole, when
1242                  * fack acks recoverypoint.
1243                  */
1244                 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1245                         p->rxmit = tp->snd_recover;
1246                 tp->sackhint.sack_bytes_rexmit += len;
1247         }
1248         if (IN_RECOVERY(tp->t_flags)) {
1249                 /*
1250                  * Account all bytes transmitted while
1251                  * IN_RECOVERY, simplifying PRR and
1252                  * Lost Retransmit Detection
1253                  */
1254                 tp->sackhint.prr_out += len;
1255         }
1256         th->th_ack = htonl(tp->rcv_nxt);
1257         if (optlen) {
1258                 bcopy(opt, th + 1, optlen);
1259                 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1260         }
1261         tcp_set_flags(th, flags);
1262         /*
1263          * Calculate receive window.  Don't shrink window,
1264          * but avoid silly window syndrome.
1265          * If a RST segment is sent, advertise a window of zero.
1266          */
1267         if (flags & TH_RST) {
1268                 recwin = 0;
1269         } else {
1270                 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1271                     recwin < tp->t_maxseg)
1272                         recwin = 0;
1273                 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1274                     recwin < (tp->rcv_adv - tp->rcv_nxt))
1275                         recwin = (tp->rcv_adv - tp->rcv_nxt);
1276         }
1277         /*
1278          * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1279          * or <SYN,ACK>) segment itself is never scaled.  The <SYN,ACK>
1280          * case is handled in syncache.
1281          */
1282         if (flags & TH_SYN)
1283                 th->th_win = htons((u_short)
1284                                 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1285         else {
1286                 /* Avoid shrinking window with window scaling. */
1287                 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1288                 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1289         }
1290
1291         /*
1292          * Adjust the RXWIN0SENT flag - indicate that we have advertised
1293          * a 0 window.  This may cause the remote transmitter to stall.  This
1294          * flag tells soreceive() to disable delayed acknowledgements when
1295          * draining the buffer.  This can occur if the receiver is attempting
1296          * to read more data than can be buffered prior to transmitting on
1297          * the connection.
1298          */
1299         if (th->th_win == 0) {
1300                 tp->t_sndzerowin++;
1301                 tp->t_flags |= TF_RXWIN0SENT;
1302         } else
1303                 tp->t_flags &= ~TF_RXWIN0SENT;
1304         if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1305                 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1306                 th->th_flags |= TH_URG;
1307         } else
1308                 /*
1309                  * If no urgent pointer to send, then we pull
1310                  * the urgent pointer to the left edge of the send window
1311                  * so that it doesn't drift into the send window on sequence
1312                  * number wraparound.
1313                  */
1314                 tp->snd_up = tp->snd_una;               /* drag it along */
1315
1316         /*
1317          * Put TCP length in extended header, and then
1318          * checksum extended header and data.
1319          */
1320         m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1321
1322 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1323         if (to.to_flags & TOF_SIGNATURE) {
1324                 /*
1325                  * Calculate MD5 signature and put it into the place
1326                  * determined before.
1327                  * NOTE: since TCP options buffer doesn't point into
1328                  * mbuf's data, calculate offset and use it.
1329                  */
1330                 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1331                     (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1332                         /*
1333                          * Do not send segment if the calculation of MD5
1334                          * digest has failed.
1335                          */
1336                         m_freem(m);
1337                         goto out;
1338                 }
1339         }
1340 #endif
1341 #ifdef INET6
1342         if (isipv6) {
1343                 /*
1344                  * There is no need to fill in ip6_plen right now.
1345                  * It will be filled later by ip6_output.
1346                  */
1347                 if (tp->t_port) {
1348                         m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1349                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1350                         udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1351                         th->th_sum = htons(0);
1352                         UDPSTAT_INC(udps_opackets);
1353                 } else {
1354                         m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1355                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1356                         th->th_sum = in6_cksum_pseudo(ip6,
1357                             sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1358                             0);
1359                 }
1360         }
1361 #endif
1362 #if defined(INET6) && defined(INET)
1363         else
1364 #endif
1365 #ifdef INET
1366         {
1367                 if (tp->t_port) {
1368                         m->m_pkthdr.csum_flags = CSUM_UDP;
1369                         m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1370                         udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1371                            ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1372                         th->th_sum = htons(0);
1373                         UDPSTAT_INC(udps_opackets);
1374                 } else {
1375                         m->m_pkthdr.csum_flags = CSUM_TCP;
1376                         m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1377                         th->th_sum = in_pseudo(ip->ip_src.s_addr,
1378                             ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1379                             IPPROTO_TCP + len + optlen));
1380                 }
1381
1382                 /* IP version must be set here for ipv4/ipv6 checking later */
1383                 KASSERT(ip->ip_v == IPVERSION,
1384                     ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1385         }
1386 #endif
1387
1388         /*
1389          * Enable TSO and specify the size of the segments.
1390          * The TCP pseudo header checksum is always provided.
1391          */
1392         if (tso) {
1393                 KASSERT(len > tp->t_maxseg - optlen,
1394                     ("%s: len <= tso_segsz", __func__));
1395                 m->m_pkthdr.csum_flags |= CSUM_TSO;
1396                 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1397         }
1398
1399         KASSERT(len + hdrlen == m_length(m, NULL),
1400             ("%s: mbuf chain shorter than expected: %d + %u != %u",
1401             __func__, len, hdrlen, m_length(m, NULL)));
1402
1403 #ifdef TCP_HHOOK
1404         /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1405         hhook_run_tcp_est_out(tp, th, &to, len, tso);
1406 #endif
1407
1408         TCP_PROBE3(debug__output, tp, th, m);
1409
1410         /* We're getting ready to send; log now. */
1411         /* XXXMT: We are not honoring verbose logging. */
1412
1413         if (tcp_bblogging_on(tp))
1414                 lgb = tcp_log_event(tp, th, &so->so_rcv, &so->so_snd,
1415                     TCP_LOG_OUT, ERRNO_UNK, len, NULL, false, NULL, NULL, 0,
1416                     NULL);
1417         else
1418                 lgb = NULL;
1419
1420         /*
1421          * Fill in IP length and desired time to live and
1422          * send to IP level.  There should be a better way
1423          * to handle ttl and tos; we could keep them in
1424          * the template, but need a way to checksum without them.
1425          */
1426         /*
1427          * m->m_pkthdr.len should have been set before checksum calculation,
1428          * because in6_cksum() need it.
1429          */
1430 #ifdef INET6
1431         if (isipv6) {
1432                 /*
1433                  * we separately set hoplimit for every segment, since the
1434                  * user might want to change the value via setsockopt.
1435                  * Also, desired default hop limit might be changed via
1436                  * Neighbor Discovery.
1437                  */
1438                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
1439
1440                 /*
1441                  * Set the packet size here for the benefit of DTrace probes.
1442                  * ip6_output() will set it properly; it's supposed to include
1443                  * the option header lengths as well.
1444                  */
1445                 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1446
1447                 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1448                         tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1449                 else
1450                         tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1451
1452                 if (tp->t_state == TCPS_SYN_SENT)
1453                         TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1454
1455                 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1456
1457 #ifdef TCPPCAP
1458                 /* Save packet, if requested. */
1459                 tcp_pcap_add(th, m, &(tp->t_outpkts));
1460 #endif
1461
1462                 /* TODO: IPv6 IP6TOS_ECT bit on */
1463                 error = ip6_output(m, inp->in6p_outputopts, &inp->inp_route6,
1464                     ((so->so_options & SO_DONTROUTE) ?  IP_ROUTETOIF : 0),
1465                     NULL, NULL, inp);
1466
1467                 if (error == EMSGSIZE && inp->inp_route6.ro_nh != NULL)
1468                         mtu = inp->inp_route6.ro_nh->nh_mtu;
1469         }
1470 #endif /* INET6 */
1471 #if defined(INET) && defined(INET6)
1472         else
1473 #endif
1474 #ifdef INET
1475     {
1476         ip->ip_len = htons(m->m_pkthdr.len);
1477 #ifdef INET6
1478         if (inp->inp_vflag & INP_IPV6PROTO)
1479                 ip->ip_ttl = in6_selecthlim(inp, NULL);
1480 #endif /* INET6 */
1481         /*
1482          * If we do path MTU discovery, then we set DF on every packet.
1483          * This might not be the best thing to do according to RFC3390
1484          * Section 2. However the tcp hostcache migitates the problem
1485          * so it affects only the first tcp connection with a host.
1486          *
1487          * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1488          */
1489         if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1490                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1491                 if (tp->t_port == 0 || len < V_tcp_minmss) {
1492                         ip->ip_off |= htons(IP_DF);
1493                 }
1494         } else {
1495                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1496         }
1497
1498         if (tp->t_state == TCPS_SYN_SENT)
1499                 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1500
1501         TCP_PROBE5(send, NULL, tp, ip, tp, th);
1502
1503 #ifdef TCPPCAP
1504         /* Save packet, if requested. */
1505         tcp_pcap_add(th, m, &(tp->t_outpkts));
1506 #endif
1507
1508         error = ip_output(m, inp->inp_options, &inp->inp_route,
1509             ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0, inp);
1510
1511         if (error == EMSGSIZE && inp->inp_route.ro_nh != NULL)
1512                 mtu = inp->inp_route.ro_nh->nh_mtu;
1513     }
1514 #endif /* INET */
1515
1516         if (lgb != NULL) {
1517                 lgb->tlb_errno = error;
1518                 lgb = NULL;
1519         }
1520 out:
1521         if (error == 0)
1522                 tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1523         /*
1524          * In transmit state, time the transmission and arrange for
1525          * the retransmit.  In persist state, just set snd_max.
1526          */
1527         if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1528             !tcp_timer_active(tp, TT_PERSIST)) {
1529                 tcp_seq startseq = tp->snd_nxt;
1530
1531                 /*
1532                  * Advance snd_nxt over sequence space of this segment.
1533                  */
1534                 if (flags & (TH_SYN|TH_FIN)) {
1535                         if (flags & TH_SYN)
1536                                 tp->snd_nxt++;
1537                         if (flags & TH_FIN) {
1538                                 tp->snd_nxt++;
1539                                 tp->t_flags |= TF_SENTFIN;
1540                         }
1541                 }
1542                 if (sack_rxmit)
1543                         goto timer;
1544                 tp->snd_nxt += len;
1545                 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1546                         /*
1547                          * Update "made progress" indication if we just
1548                          * added new data to an empty socket buffer.
1549                          */
1550                         if (tp->snd_una == tp->snd_max)
1551                                 tp->t_acktime = ticks;
1552                         tp->snd_max = tp->snd_nxt;
1553                         /*
1554                          * Time this transmission if not a retransmission and
1555                          * not currently timing anything.
1556                          */
1557                         tp->t_sndtime = ticks;
1558                         if (tp->t_rtttime == 0) {
1559                                 tp->t_rtttime = ticks;
1560                                 tp->t_rtseq = startseq;
1561                                 TCPSTAT_INC(tcps_segstimed);
1562                         }
1563 #ifdef STATS
1564                         if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1565                                 tp->t_flags |= TF_GPUTINPROG;
1566                                 tp->gput_seq = startseq;
1567                                 tp->gput_ack = startseq +
1568                                     ulmin(sbavail(&so->so_snd) - off, sendwin);
1569                                 tp->gput_ts = tcp_ts_getticks();
1570                         }
1571 #endif /* STATS */
1572                 }
1573
1574                 /*
1575                  * Set retransmit timer if not currently set,
1576                  * and not doing a pure ack or a keep-alive probe.
1577                  * Initial value for retransmit timer is smoothed
1578                  * round-trip time + 2 * round-trip time variance.
1579                  * Initialize shift counter which is used for backoff
1580                  * of retransmit time.
1581                  */
1582 timer:
1583                 if (!tcp_timer_active(tp, TT_REXMT) &&
1584                     ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1585                      (tp->snd_nxt != tp->snd_una))) {
1586                         if (tcp_timer_active(tp, TT_PERSIST)) {
1587                                 tcp_timer_activate(tp, TT_PERSIST, 0);
1588                                 tp->t_rxtshift = 0;
1589                         }
1590                         tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
1591                 } else if (len == 0 && sbavail(&so->so_snd) &&
1592                     !tcp_timer_active(tp, TT_REXMT) &&
1593                     !tcp_timer_active(tp, TT_PERSIST)) {
1594                         /*
1595                          * Avoid a situation where we do not set persist timer
1596                          * after a zero window condition. For example:
1597                          * 1) A -> B: packet with enough data to fill the window
1598                          * 2) B -> A: ACK for #1 + new data (0 window
1599                          *    advertisement)
1600                          * 3) A -> B: ACK for #2, 0 len packet
1601                          *
1602                          * In this case, A will not activate the persist timer,
1603                          * because it chose to send a packet. Unless tcp_output
1604                          * is called for some other reason (delayed ack timer,
1605                          * another input packet from B, socket syscall), A will
1606                          * not send zero window probes.
1607                          *
1608                          * So, if you send a 0-length packet, but there is data
1609                          * in the socket buffer, and neither the rexmt or
1610                          * persist timer is already set, then activate the
1611                          * persist timer.
1612                          */
1613                         tp->t_rxtshift = 0;
1614                         tcp_setpersist(tp);
1615                 }
1616         } else {
1617                 /*
1618                  * Persist case, update snd_max but since we are in
1619                  * persist mode (no window) we do not update snd_nxt.
1620                  */
1621                 int xlen = len;
1622                 if (flags & TH_SYN)
1623                         ++xlen;
1624                 if (flags & TH_FIN) {
1625                         ++xlen;
1626                         tp->t_flags |= TF_SENTFIN;
1627                 }
1628                 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1629                         tp->snd_max = tp->snd_nxt + xlen;
1630         }
1631         if ((error == 0) &&
1632             (TCPS_HAVEESTABLISHED(tp->t_state) &&
1633              (tp->t_flags & TF_SACK_PERMIT) &&
1634              tp->rcv_numsacks > 0)) {
1635                     /* Clean up any DSACK's sent */
1636                     tcp_clean_dsack_blocks(tp);
1637         }
1638         if (error) {
1639                 /*
1640                  * We know that the packet was lost, so back out the
1641                  * sequence number advance, if any.
1642                  *
1643                  * If the error is EPERM the packet got blocked by the
1644                  * local firewall.  Normally we should terminate the
1645                  * connection but the blocking may have been spurious
1646                  * due to a firewall reconfiguration cycle.  So we treat
1647                  * it like a packet loss and let the retransmit timer and
1648                  * timeouts do their work over time.
1649                  * XXX: It is a POLA question whether calling tcp_drop right
1650                  * away would be the really correct behavior instead.
1651                  */
1652                 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1653                     !tcp_timer_active(tp, TT_PERSIST)) &&
1654                     ((flags & TH_SYN) == 0) &&
1655                     (error != EPERM)) {
1656                         if (sack_rxmit) {
1657                                 p->rxmit -= len;
1658                                 tp->sackhint.sack_bytes_rexmit -= len;
1659                                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1660                                     ("sackhint bytes rtx >= 0"));
1661                                 KASSERT((flags & TH_FIN) == 0,
1662                                     ("error while FIN with SACK rxmit"));
1663                         } else {
1664                                 tp->snd_nxt -= len;
1665                                 if (flags & TH_FIN)
1666                                         tp->snd_nxt--;
1667                         }
1668                 }
1669                 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);     /* Check gotos. */
1670                 switch (error) {
1671                 case EACCES:
1672                 case EPERM:
1673                         tp->t_softerror = error;
1674                         return (error);
1675                 case ENOBUFS:
1676                         TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1677                         tp->snd_cwnd = tp->t_maxseg;
1678                         return (0);
1679                 case EMSGSIZE:
1680                         /*
1681                          * For some reason the interface we used initially
1682                          * to send segments changed to another or lowered
1683                          * its MTU.
1684                          * If TSO was active we either got an interface
1685                          * without TSO capabilits or TSO was turned off.
1686                          * If we obtained mtu from ip_output() then update
1687                          * it and try again.
1688                          */
1689                         if (tso)
1690                                 tp->t_flags &= ~TF_TSO;
1691                         if (mtu != 0) {
1692                                 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1693                                 goto again;
1694                         }
1695                         return (error);
1696                 case EHOSTDOWN:
1697                 case EHOSTUNREACH:
1698                 case ENETDOWN:
1699                 case ENETUNREACH:
1700                         if (TCPS_HAVERCVDSYN(tp->t_state)) {
1701                                 tp->t_softerror = error;
1702                                 return (0);
1703                         }
1704                         /* FALLTHROUGH */
1705                 default:
1706                         return (error);
1707                 }
1708         }
1709         TCPSTAT_INC(tcps_sndtotal);
1710
1711         /*
1712          * Data sent (as far as we can tell).
1713          * If this advertises a larger window than any other segment,
1714          * then remember the size of the advertised window.
1715          * Any pending ACK has now been sent.
1716          */
1717         if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1718                 tp->rcv_adv = tp->rcv_nxt + recwin;
1719         tp->last_ack_sent = tp->rcv_nxt;
1720         tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1721         if (tcp_timer_active(tp, TT_DELACK))
1722                 tcp_timer_activate(tp, TT_DELACK, 0);
1723 #if 0
1724         /*
1725          * This completely breaks TCP if newreno is turned on.  What happens
1726          * is that if delayed-acks are turned on on the receiver, this code
1727          * on the transmitter effectively destroys the TCP window, forcing
1728          * it to four packets (1.5Kx4 = 6K window).
1729          */
1730         if (sendalot && --maxburst)
1731                 goto again;
1732 #endif
1733         if (sendalot)
1734                 goto again;
1735         return (0);
1736 }
1737
1738 void
1739 tcp_setpersist(struct tcpcb *tp)
1740 {
1741         int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1742         int tt;
1743         int maxunacktime;
1744
1745         tp->t_flags &= ~TF_PREVVALID;
1746         if (tcp_timer_active(tp, TT_REXMT))
1747                 panic("tcp_setpersist: retransmit pending");
1748         /*
1749          * If the state is already closed, don't bother.
1750          */
1751         if (tp->t_state == TCPS_CLOSED)
1752                 return;
1753
1754         /*
1755          * Start/restart persistence timer.
1756          */
1757         TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1758                       tcp_persmin, tcp_persmax);
1759         if (TP_MAXUNACKTIME(tp) && tp->t_acktime) {
1760                 maxunacktime = tp->t_acktime + TP_MAXUNACKTIME(tp) - ticks;
1761                 if (maxunacktime < 1)
1762                         maxunacktime = 1;
1763                 if (maxunacktime < tt)
1764                         tt = maxunacktime;
1765         }
1766         tcp_timer_activate(tp, TT_PERSIST, tt);
1767         if (tp->t_rxtshift < V_tcp_retries)
1768                 tp->t_rxtshift++;
1769 }
1770
1771 /*
1772  * Insert TCP options according to the supplied parameters to the place
1773  * optp in a consistent way.  Can handle unaligned destinations.
1774  *
1775  * The order of the option processing is crucial for optimal packing and
1776  * alignment for the scarce option space.
1777  *
1778  * The optimal order for a SYN/SYN-ACK segment is:
1779  *   MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1780  *   Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1781  *
1782  * The SACK options should be last.  SACK blocks consume 8*n+2 bytes.
1783  * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1784  * At minimum we need 10 bytes (to generate 1 SACK block).  If both
1785  * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1786  * we only have 10 bytes for SACK options (40 - (12 + 18)).
1787  */
1788 int
1789 tcp_addoptions(struct tcpopt *to, u_char *optp)
1790 {
1791         u_int32_t mask, optlen = 0;
1792
1793         for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1794                 if ((to->to_flags & mask) != mask)
1795                         continue;
1796                 if (optlen == TCP_MAXOLEN)
1797                         break;
1798                 switch (to->to_flags & mask) {
1799                 case TOF_MSS:
1800                         while (optlen % 4) {
1801                                 optlen += TCPOLEN_NOP;
1802                                 *optp++ = TCPOPT_NOP;
1803                         }
1804                         if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1805                                 continue;
1806                         optlen += TCPOLEN_MAXSEG;
1807                         *optp++ = TCPOPT_MAXSEG;
1808                         *optp++ = TCPOLEN_MAXSEG;
1809                         to->to_mss = htons(to->to_mss);
1810                         bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1811                         optp += sizeof(to->to_mss);
1812                         break;
1813                 case TOF_SCALE:
1814                         while (!optlen || optlen % 2 != 1) {
1815                                 optlen += TCPOLEN_NOP;
1816                                 *optp++ = TCPOPT_NOP;
1817                         }
1818                         if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1819                                 continue;
1820                         optlen += TCPOLEN_WINDOW;
1821                         *optp++ = TCPOPT_WINDOW;
1822                         *optp++ = TCPOLEN_WINDOW;
1823                         *optp++ = to->to_wscale;
1824                         break;
1825                 case TOF_SACKPERM:
1826                         while (optlen % 2) {
1827                                 optlen += TCPOLEN_NOP;
1828                                 *optp++ = TCPOPT_NOP;
1829                         }
1830                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1831                                 continue;
1832                         optlen += TCPOLEN_SACK_PERMITTED;
1833                         *optp++ = TCPOPT_SACK_PERMITTED;
1834                         *optp++ = TCPOLEN_SACK_PERMITTED;
1835                         break;
1836                 case TOF_TS:
1837                         while (!optlen || optlen % 4 != 2) {
1838                                 optlen += TCPOLEN_NOP;
1839                                 *optp++ = TCPOPT_NOP;
1840                         }
1841                         if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1842                                 continue;
1843                         optlen += TCPOLEN_TIMESTAMP;
1844                         *optp++ = TCPOPT_TIMESTAMP;
1845                         *optp++ = TCPOLEN_TIMESTAMP;
1846                         to->to_tsval = htonl(to->to_tsval);
1847                         to->to_tsecr = htonl(to->to_tsecr);
1848                         bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1849                         optp += sizeof(to->to_tsval);
1850                         bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1851                         optp += sizeof(to->to_tsecr);
1852                         break;
1853                 case TOF_SIGNATURE:
1854                         {
1855                         int siglen = TCPOLEN_SIGNATURE - 2;
1856
1857                         while (!optlen || optlen % 4 != 2) {
1858                                 optlen += TCPOLEN_NOP;
1859                                 *optp++ = TCPOPT_NOP;
1860                         }
1861                         if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1862                                 to->to_flags &= ~TOF_SIGNATURE;
1863                                 continue;
1864                         }
1865                         optlen += TCPOLEN_SIGNATURE;
1866                         *optp++ = TCPOPT_SIGNATURE;
1867                         *optp++ = TCPOLEN_SIGNATURE;
1868                         to->to_signature = optp;
1869                         while (siglen--)
1870                                  *optp++ = 0;
1871                         break;
1872                         }
1873                 case TOF_SACK:
1874                         {
1875                         int sackblks = 0;
1876                         struct sackblk *sack = (struct sackblk *)to->to_sacks;
1877                         tcp_seq sack_seq;
1878
1879                         while (!optlen || optlen % 4 != 2) {
1880                                 optlen += TCPOLEN_NOP;
1881                                 *optp++ = TCPOPT_NOP;
1882                         }
1883                         if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1884                                 continue;
1885                         optlen += TCPOLEN_SACKHDR;
1886                         *optp++ = TCPOPT_SACK;
1887                         sackblks = min(to->to_nsacks,
1888                                         (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1889                         *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1890                         while (sackblks--) {
1891                                 sack_seq = htonl(sack->start);
1892                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1893                                 optp += sizeof(sack_seq);
1894                                 sack_seq = htonl(sack->end);
1895                                 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1896                                 optp += sizeof(sack_seq);
1897                                 optlen += TCPOLEN_SACK;
1898                                 sack++;
1899                         }
1900                         TCPSTAT_INC(tcps_sack_send_blocks);
1901                         break;
1902                         }
1903                 case TOF_FASTOPEN:
1904                         {
1905                         int total_len;
1906
1907                         /* XXX is there any point to aligning this option? */
1908                         total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1909                         if (TCP_MAXOLEN - optlen < total_len) {
1910                                 to->to_flags &= ~TOF_FASTOPEN;
1911                                 continue;
1912                         }
1913                         *optp++ = TCPOPT_FAST_OPEN;
1914                         *optp++ = total_len;
1915                         if (to->to_tfo_len > 0) {
1916                                 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1917                                 optp += to->to_tfo_len;
1918                         }
1919                         optlen += total_len;
1920                         break;
1921                         }
1922                 default:
1923                         panic("%s: unknown TCP option type", __func__);
1924                         break;
1925                 }
1926         }
1927
1928         /* Terminate and pad TCP options to a 4 byte boundary. */
1929         if (optlen % 4) {
1930                 optlen += TCPOLEN_EOL;
1931                 *optp++ = TCPOPT_EOL;
1932         }
1933         /*
1934          * According to RFC 793 (STD0007):
1935          *   "The content of the header beyond the End-of-Option option
1936          *    must be header padding (i.e., zero)."
1937          *   and later: "The padding is composed of zeros."
1938          */
1939         while (optlen % 4) {
1940                 optlen += TCPOLEN_PAD;
1941                 *optp++ = TCPOPT_PAD;
1942         }
1943
1944         KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1945         return (optlen);
1946 }
1947
1948 /*
1949  * This is a copy of m_copym(), taking the TSO segment size/limit
1950  * constraints into account, and advancing the sndptr as it goes.
1951  */
1952 struct mbuf *
1953 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1954     int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1955 {
1956 #ifdef KERN_TLS
1957         struct ktls_session *tls, *ntls;
1958         struct mbuf *start __diagused;
1959 #endif
1960         struct mbuf *n, **np;
1961         struct mbuf *top;
1962         int32_t off = off0;
1963         int32_t len = *plen;
1964         int32_t fragsize;
1965         int32_t len_cp = 0;
1966         int32_t *pkthdrlen;
1967         uint32_t mlen, frags;
1968         bool copyhdr;
1969
1970         KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1971         KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1972         if (off == 0 && m->m_flags & M_PKTHDR)
1973                 copyhdr = true;
1974         else
1975                 copyhdr = false;
1976         while (off > 0) {
1977                 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1978                 if (off < m->m_len)
1979                         break;
1980                 off -= m->m_len;
1981                 if ((sb) && (m == sb->sb_sndptr)) {
1982                         sb->sb_sndptroff += m->m_len;
1983                         sb->sb_sndptr = m->m_next;
1984                 }
1985                 m = m->m_next;
1986         }
1987         np = &top;
1988         top = NULL;
1989         pkthdrlen = NULL;
1990 #ifdef KERN_TLS
1991         if (hw_tls && (m->m_flags & M_EXTPG))
1992                 tls = m->m_epg_tls;
1993         else
1994                 tls = NULL;
1995         start = m;
1996 #endif
1997         while (len > 0) {
1998                 if (m == NULL) {
1999                         KASSERT(len == M_COPYALL,
2000                             ("tcp_m_copym, length > size of mbuf chain"));
2001                         *plen = len_cp;
2002                         if (pkthdrlen != NULL)
2003                                 *pkthdrlen = len_cp;
2004                         break;
2005                 }
2006 #ifdef KERN_TLS
2007                 if (hw_tls) {
2008                         if (m->m_flags & M_EXTPG)
2009                                 ntls = m->m_epg_tls;
2010                         else
2011                                 ntls = NULL;
2012
2013                         /*
2014                          * Avoid mixing TLS records with handshake
2015                          * data or TLS records from different
2016                          * sessions.
2017                          */
2018                         if (tls != ntls) {
2019                                 MPASS(m != start);
2020                                 *plen = len_cp;
2021                                 if (pkthdrlen != NULL)
2022                                         *pkthdrlen = len_cp;
2023                                 break;
2024                         }
2025                 }
2026 #endif
2027                 mlen = min(len, m->m_len - off);
2028                 if (seglimit) {
2029                         /*
2030                          * For M_EXTPG mbufs, add 3 segments
2031                          * + 1 in case we are crossing page boundaries
2032                          * + 2 in case the TLS hdr/trailer are used
2033                          * It is cheaper to just add the segments
2034                          * than it is to take the cache miss to look
2035                          * at the mbuf ext_pgs state in detail.
2036                          */
2037                         if (m->m_flags & M_EXTPG) {
2038                                 fragsize = min(segsize, PAGE_SIZE);
2039                                 frags = 3;
2040                         } else {
2041                                 fragsize = segsize;
2042                                 frags = 0;
2043                         }
2044
2045                         /* Break if we really can't fit anymore. */
2046                         if ((frags + 1) >= seglimit) {
2047                                 *plen = len_cp;
2048                                 if (pkthdrlen != NULL)
2049                                         *pkthdrlen = len_cp;
2050                                 break;
2051                         }
2052
2053                         /*
2054                          * Reduce size if you can't copy the whole
2055                          * mbuf. If we can't copy the whole mbuf, also
2056                          * adjust len so the loop will end after this
2057                          * mbuf.
2058                          */
2059                         if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2060                                 mlen = (seglimit - frags - 1) * fragsize;
2061                                 len = mlen;
2062                                 *plen = len_cp + len;
2063                                 if (pkthdrlen != NULL)
2064                                         *pkthdrlen = *plen;
2065                         }
2066                         frags += howmany(mlen, fragsize);
2067                         if (frags == 0)
2068                                 frags++;
2069                         seglimit -= frags;
2070                         KASSERT(seglimit > 0,
2071                             ("%s: seglimit went too low", __func__));
2072                 }
2073                 if (copyhdr)
2074                         n = m_gethdr(M_NOWAIT, m->m_type);
2075                 else
2076                         n = m_get(M_NOWAIT, m->m_type);
2077                 *np = n;
2078                 if (n == NULL)
2079                         goto nospace;
2080                 if (copyhdr) {
2081                         if (!m_dup_pkthdr(n, m, M_NOWAIT))
2082                                 goto nospace;
2083                         if (len == M_COPYALL)
2084                                 n->m_pkthdr.len -= off0;
2085                         else
2086                                 n->m_pkthdr.len = len;
2087                         pkthdrlen = &n->m_pkthdr.len;
2088                         copyhdr = false;
2089                 }
2090                 n->m_len = mlen;
2091                 len_cp += n->m_len;
2092                 if (m->m_flags & (M_EXT|M_EXTPG)) {
2093                         n->m_data = m->m_data + off;
2094                         mb_dupcl(n, m);
2095                 } else
2096                         bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2097                             (u_int)n->m_len);
2098
2099                 if (sb && (sb->sb_sndptr == m) &&
2100                     ((n->m_len + off) >= m->m_len) && m->m_next) {
2101                         sb->sb_sndptroff += m->m_len;
2102                         sb->sb_sndptr = m->m_next;
2103                 }
2104                 off = 0;
2105                 if (len != M_COPYALL) {
2106                         len -= n->m_len;
2107                 }
2108                 m = m->m_next;
2109                 np = &n->m_next;
2110         }
2111         return (top);
2112 nospace:
2113         m_freem(top);
2114         return (NULL);
2115 }
2116
2117 void
2118 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2119 {
2120
2121         /*
2122          * Automatic sizing of send socket buffer.  Often the send buffer
2123          * size is not optimally adjusted to the actual network conditions
2124          * at hand (delay bandwidth product).  Setting the buffer size too
2125          * small limits throughput on links with high bandwidth and high
2126          * delay (eg. trans-continental/oceanic links).  Setting the
2127          * buffer size too big consumes too much real kernel memory,
2128          * especially with many connections on busy servers.
2129          *
2130          * The criteria to step up the send buffer one notch are:
2131          *  1. receive window of remote host is larger than send buffer
2132          *     (with a fudge factor of 5/4th);
2133          *  2. send buffer is filled to 7/8th with data (so we actually
2134          *     have data to make use of it);
2135          *  3. send buffer fill has not hit maximal automatic size;
2136          *  4. our send window (slow start and cogestion controlled) is
2137          *     larger than sent but unacknowledged data in send buffer.
2138          *
2139          * The remote host receive window scaling factor may limit the
2140          * growing of the send buffer before it reaches its allowed
2141          * maximum.
2142          *
2143          * It scales directly with slow start or congestion window
2144          * and does at most one step per received ACK.  This fast
2145          * scaling has the drawback of growing the send buffer beyond
2146          * what is strictly necessary to make full use of a given
2147          * delay*bandwidth product.  However testing has shown this not
2148          * to be much of an problem.  At worst we are trading wasting
2149          * of available bandwidth (the non-use of it) for wasting some
2150          * socket buffer memory.
2151          *
2152          * TODO: Shrink send buffer during idle periods together
2153          * with congestion window.  Requires another timer.  Has to
2154          * wait for upcoming tcp timer rewrite.
2155          *
2156          * XXXGL: should there be used sbused() or sbavail()?
2157          */
2158         if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2159                 int lowat;
2160
2161                 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2162                 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2163                     sbused(&so->so_snd) >=
2164                     (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2165                     sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2166                     sendwin >= (sbused(&so->so_snd) -
2167                     (tp->snd_nxt - tp->snd_una))) {
2168                         if (!sbreserve_locked(so, SO_SND,
2169                             min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2170                              V_tcp_autosndbuf_max), curthread))
2171                                 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
2172                 }
2173         }
2174 }