1 /*-
2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
30 */
31
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
34
35 #include "opt_inet.h"
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38 #include "opt_tcpdebug.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/domain.h>
43 #include <sys/hhook.h>
44 #include <sys/kernel.h>
45 #include <sys/lock.h>
46 #include <sys/mbuf.h>
47 #include <sys/mutex.h>
48 #include <sys/protosw.h>
49 #include <sys/sdt.h>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
52 #include <sys/sysctl.h>
53
54 #include <net/if.h>
55 #include <net/route.h>
56 #include <net/vnet.h>
57
58 #include <netinet/in.h>
59 #include <netinet/in_kdtrace.h>
60 #include <netinet/in_systm.h>
61 #include <netinet/ip.h>
62 #include <netinet/in_pcb.h>
63 #include <netinet/ip_var.h>
64 #include <netinet/ip_options.h>
65 #ifdef INET6
66 #include <netinet6/in6_pcb.h>
67 #include <netinet/ip6.h>
68 #include <netinet6/ip6_var.h>
69 #endif
70 #ifdef TCP_RFC7413
71 #include <netinet/tcp_fastopen.h>
72 #endif
73 #include <netinet/tcp.h>
74 #define TCPOUTFLAGS
75 #include <netinet/tcp_fsm.h>
76 #include <netinet/tcp_seq.h>
77 #include <netinet/tcp_timer.h>
78 #include <netinet/tcp_var.h>
79 #include <netinet/tcpip.h>
80 #include <netinet/cc/cc.h>
81 #ifdef TCPPCAP
82 #include <netinet/tcp_pcap.h>
83 #endif
84 #ifdef TCPDEBUG
85 #include <netinet/tcp_debug.h>
86 #endif
87 #ifdef TCP_OFFLOAD
88 #include <netinet/tcp_offload.h>
89 #endif
90
91 #include <netipsec/ipsec_support.h>
92
93 #include <machine/in_cksum.h>
94
95 #include <security/mac/mac_framework.h>
96
97 VNET_DEFINE(int, path_mtu_discovery) = 1;
98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
99 &VNET_NAME(path_mtu_discovery), 1,
100 "Enable Path MTU Discovery");
101
102 VNET_DEFINE(int, tcp_do_tso) = 1;
103 #define V_tcp_do_tso VNET(tcp_do_tso)
104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
105 &VNET_NAME(tcp_do_tso), 0,
106 "Enable TCP Segmentation Offload");
107
108 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
109 #define V_tcp_sendspace VNET(tcp_sendspace)
110 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
111 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
112
113 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
114 #define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
116 &VNET_NAME(tcp_do_autosndbuf), 0,
117 "Enable automatic send buffer sizing");
118
119 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
120 #define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
121 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
122 &VNET_NAME(tcp_autosndbuf_inc), 0,
123 "Incrementor step size of automatic send buffer");
124
125 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
126 #define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
128 &VNET_NAME(tcp_autosndbuf_max), 0,
129 "Max size of automatic send buffer");
130
131 /*
132 * Make sure that either retransmit or persist timer is set for SYN, FIN and
133 * non-ACK.
134 */
135 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
136 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
137 tcp_timer_active((tp), TT_REXMT) || \
138 tcp_timer_active((tp), TT_PERSIST), \
139 ("neither rexmt nor persist timer is set"))
140
141 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
142 struct tcphdr *th, struct tcpopt *to,
143 long len, int tso);
144 static void inline cc_after_idle(struct tcpcb *tp);
145
146 /*
147 * Wrapper for the TCP established output helper hook.
148 */
149 static void inline
hhook_run_tcp_est_out(struct tcpcb * tp,struct tcphdr * th,struct tcpopt * to,long len,int tso)150 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
151 struct tcpopt *to, long len, int tso)
152 {
153 struct tcp_hhook_data hhook_data;
154
155 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
156 hhook_data.tp = tp;
157 hhook_data.th = th;
158 hhook_data.to = to;
159 hhook_data.len = len;
160 hhook_data.tso = tso;
161
162 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
163 tp->osd);
164 }
165 }
166
167 /*
168 * CC wrapper hook functions
169 */
170 static void inline
cc_after_idle(struct tcpcb * tp)171 cc_after_idle(struct tcpcb *tp)
172 {
173 INP_WLOCK_ASSERT(tp->t_inpcb);
174
175 if (CC_ALGO(tp)->after_idle != NULL)
176 CC_ALGO(tp)->after_idle(tp->ccv);
177 }
178
179 /*
180 * Tcp output routine: figure out what should be sent and send it.
181 */
182 int
tcp_output(struct tcpcb * tp)183 tcp_output(struct tcpcb *tp)
184 {
185 struct socket *so = tp->t_inpcb->inp_socket;
186 long len, recwin, sendwin;
187 int off, flags, error = 0; /* Keep compiler happy */
188 struct mbuf *m;
189 struct ip *ip = NULL;
190 struct ipovly *ipov = NULL;
191 struct tcphdr *th;
192 u_char opt[TCP_MAXOLEN];
193 unsigned ipoptlen, optlen, hdrlen;
194 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
195 unsigned ipsec_optlen = 0;
196 #endif
197 int idle, sendalot;
198 int sack_rxmit, sack_bytes_rxmt;
199 struct sackhole *p;
200 int tso, mtu;
201 struct tcpopt to;
202 #if 0
203 int maxburst = TCP_MAXBURST;
204 #endif
205 #ifdef INET6
206 struct ip6_hdr *ip6 = NULL;
207 int isipv6;
208
209 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
210 #endif
211
212 INP_WLOCK_ASSERT(tp->t_inpcb);
213
214 #ifdef TCP_OFFLOAD
215 if (tp->t_flags & TF_TOE)
216 return (tcp_offload_output(tp));
217 #endif
218
219 #ifdef TCP_RFC7413
220 /*
221 * For TFO connections in SYN_RECEIVED, only allow the initial
222 * SYN|ACK and those sent by the retransmit timer.
223 */
224 if ((tp->t_flags & TF_FASTOPEN) &&
225 (tp->t_state == TCPS_SYN_RECEIVED) &&
226 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN|ACK sent */
227 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */
228 return (0);
229 #endif
230 /*
231 * Determine length of data that should be transmitted,
232 * and flags that will be used.
233 * If there is some data or critical controls (SYN, RST)
234 * to send, then transmit; otherwise, investigate further.
235 */
236 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
237 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
238 cc_after_idle(tp);
239 tp->t_flags &= ~TF_LASTIDLE;
240 if (idle) {
241 if (tp->t_flags & TF_MORETOCOME) {
242 tp->t_flags |= TF_LASTIDLE;
243 idle = 0;
244 }
245 }
246 again:
247 /*
248 * If we've recently taken a timeout, snd_max will be greater than
249 * snd_nxt. There may be SACK information that allows us to avoid
250 * resending already delivered data. Adjust snd_nxt accordingly.
251 */
252 if ((tp->t_flags & TF_SACK_PERMIT) &&
253 SEQ_LT(tp->snd_nxt, tp->snd_max))
254 tcp_sack_adjust(tp);
255 sendalot = 0;
256 tso = 0;
257 mtu = 0;
258 off = tp->snd_nxt - tp->snd_una;
259 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
260
261 flags = tcp_outflags[tp->t_state];
262 /*
263 * Send any SACK-generated retransmissions. If we're explicitly trying
264 * to send out new data (when sendalot is 1), bypass this function.
265 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
266 * we're replacing a (future) new transmission with a retransmission
267 * now, and we previously incremented snd_cwnd in tcp_input().
268 */
269 /*
270 * Still in sack recovery , reset rxmit flag to zero.
271 */
272 sack_rxmit = 0;
273 sack_bytes_rxmt = 0;
274 len = 0;
275 p = NULL;
276 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
277 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
278 long cwin;
279
280 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
281 if (cwin < 0)
282 cwin = 0;
283 /* Do not retransmit SACK segments beyond snd_recover */
284 if (SEQ_GT(p->end, tp->snd_recover)) {
285 /*
286 * (At least) part of sack hole extends beyond
287 * snd_recover. Check to see if we can rexmit data
288 * for this hole.
289 */
290 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
291 /*
292 * Can't rexmit any more data for this hole.
293 * That data will be rexmitted in the next
294 * sack recovery episode, when snd_recover
295 * moves past p->rxmit.
296 */
297 p = NULL;
298 goto after_sack_rexmit;
299 } else {
300 /* Can rexmit part of the current hole */
301 len = ((int32_t)ulmin(cwin,
302 SEQ_SUB(tp->snd_recover, p->rxmit)));
303 }
304 } else {
305 len = ((int32_t)ulmin(cwin,
306 SEQ_SUB(p->end, p->rxmit)));
307 }
308 off = SEQ_SUB(p->rxmit, tp->snd_una);
309 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
310 __func__, off));
311 if (len > 0) {
312 sack_rxmit = 1;
313 sendalot = 1;
314 TCPSTAT_INC(tcps_sack_rexmits);
315 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
316 min(len, tp->t_maxseg));
317 }
318 }
319 after_sack_rexmit:
320 /*
321 * Get standard flags, and add SYN or FIN if requested by 'hidden'
322 * state flags.
323 */
324 if (tp->t_flags & TF_NEEDFIN)
325 flags |= TH_FIN;
326 if (tp->t_flags & TF_NEEDSYN)
327 flags |= TH_SYN;
328
329 SOCKBUF_LOCK(&so->so_snd);
330 /*
331 * If in persist timeout with window of 0, send 1 byte.
332 * Otherwise, if window is small but nonzero
333 * and timer expired, we will send what we can
334 * and go to transmit state.
335 */
336 if (tp->t_flags & TF_FORCEDATA) {
337 if (sendwin == 0) {
338 /*
339 * If we still have some data to send, then
340 * clear the FIN bit. Usually this would
341 * happen below when it realizes that we
342 * aren't sending all the data. However,
343 * if we have exactly 1 byte of unsent data,
344 * then it won't clear the FIN bit below,
345 * and if we are in persist state, we wind
346 * up sending the packet without recording
347 * that we sent the FIN bit.
348 *
349 * We can't just blindly clear the FIN bit,
350 * because if we don't have any more data
351 * to send then the probe will be the FIN
352 * itself.
353 */
354 if (off < sbused(&so->so_snd))
355 flags &= ~TH_FIN;
356 sendwin = 1;
357 } else {
358 tcp_timer_activate(tp, TT_PERSIST, 0);
359 tp->t_rxtshift = 0;
360 }
361 }
362
363 /*
364 * If snd_nxt == snd_max and we have transmitted a FIN, the
365 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
366 * a negative length. This can also occur when TCP opens up
367 * its congestion window while receiving additional duplicate
368 * acks after fast-retransmit because TCP will reset snd_nxt
369 * to snd_max after the fast-retransmit.
370 *
371 * In the normal retransmit-FIN-only case, however, snd_nxt will
372 * be set to snd_una, the offset will be 0, and the length may
373 * wind up 0.
374 *
375 * If sack_rxmit is true we are retransmitting from the scoreboard
376 * in which case len is already set.
377 */
378 if (sack_rxmit == 0) {
379 if (sack_bytes_rxmt == 0)
380 len = ((long)ulmin(sbavail(&so->so_snd), sendwin) -
381 off);
382 else {
383 long cwin;
384
385 /*
386 * We are inside of a SACK recovery episode and are
387 * sending new data, having retransmitted all the
388 * data possible in the scoreboard.
389 */
390 len = ((long)ulmin(sbavail(&so->so_snd), tp->snd_wnd) -
391 off);
392 /*
393 * Don't remove this (len > 0) check !
394 * We explicitly check for len > 0 here (although it
395 * isn't really necessary), to work around a gcc
396 * optimization issue - to force gcc to compute
397 * len above. Without this check, the computation
398 * of len is bungled by the optimizer.
399 */
400 if (len > 0) {
401 cwin = tp->snd_cwnd -
402 (tp->snd_nxt - tp->sack_newdata) -
403 sack_bytes_rxmt;
404 if (cwin < 0)
405 cwin = 0;
406 len = lmin(len, cwin);
407 }
408 }
409 }
410
411 /*
412 * Lop off SYN bit if it has already been sent. However, if this
413 * is SYN-SENT state and if segment contains data and if we don't
414 * know that foreign host supports TAO, suppress sending segment.
415 */
416 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
417 if (tp->t_state != TCPS_SYN_RECEIVED)
418 flags &= ~TH_SYN;
419 #ifdef TCP_RFC7413
420 /*
421 * When sending additional segments following a TFO SYN|ACK,
422 * do not include the SYN bit.
423 */
424 if ((tp->t_flags & TF_FASTOPEN) &&
425 (tp->t_state == TCPS_SYN_RECEIVED))
426 flags &= ~TH_SYN;
427 #endif
428 off--, len++;
429 }
430
431 /*
432 * Be careful not to send data and/or FIN on SYN segments.
433 * This measure is needed to prevent interoperability problems
434 * with not fully conformant TCP implementations.
435 */
436 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
437 len = 0;
438 flags &= ~TH_FIN;
439 }
440
441 #ifdef TCP_RFC7413
442 /*
443 * When retransmitting SYN|ACK on a passively-created TFO socket,
444 * don't include data, as the presence of data may have caused the
445 * original SYN|ACK to have been dropped by a middlebox.
446 */
447 if ((tp->t_flags & TF_FASTOPEN) &&
448 (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) ||
449 (flags & TH_RST)))
450 len = 0;
451 #endif
452 if (len <= 0) {
453 /*
454 * If FIN has been sent but not acked,
455 * but we haven't been called to retransmit,
456 * len will be < 0. Otherwise, window shrank
457 * after we sent into it. If window shrank to 0,
458 * cancel pending retransmit, pull snd_nxt back
459 * to (closed) window, and set the persist timer
460 * if it isn't already going. If the window didn't
461 * close completely, just wait for an ACK.
462 *
463 * We also do a general check here to ensure that
464 * we will set the persist timer when we have data
465 * to send, but a 0-byte window. This makes sure
466 * the persist timer is set even if the packet
467 * hits one of the "goto send" lines below.
468 */
469 len = 0;
470 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
471 (off < (int) sbavail(&so->so_snd))) {
472 tcp_timer_activate(tp, TT_REXMT, 0);
473 tp->t_rxtshift = 0;
474 tp->snd_nxt = tp->snd_una;
475 if (!tcp_timer_active(tp, TT_PERSIST))
476 tcp_setpersist(tp);
477 }
478 }
479
480 /* len will be >= 0 after this point. */
481 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
482
483 /*
484 * Automatic sizing of send socket buffer. Often the send buffer
485 * size is not optimally adjusted to the actual network conditions
486 * at hand (delay bandwidth product). Setting the buffer size too
487 * small limits throughput on links with high bandwidth and high
488 * delay (eg. trans-continental/oceanic links). Setting the
489 * buffer size too big consumes too much real kernel memory,
490 * especially with many connections on busy servers.
491 *
492 * The criteria to step up the send buffer one notch are:
493 * 1. receive window of remote host is larger than send buffer
494 * (with a fudge factor of 5/4th);
495 * 2. send buffer is filled to 7/8th with data (so we actually
496 * have data to make use of it);
497 * 3. send buffer fill has not hit maximal automatic size;
498 * 4. our send window (slow start and cogestion controlled) is
499 * larger than sent but unacknowledged data in send buffer.
500 *
501 * The remote host receive window scaling factor may limit the
502 * growing of the send buffer before it reaches its allowed
503 * maximum.
504 *
505 * It scales directly with slow start or congestion window
506 * and does at most one step per received ACK. This fast
507 * scaling has the drawback of growing the send buffer beyond
508 * what is strictly necessary to make full use of a given
509 * delay*bandwidth product. However testing has shown this not
510 * to be much of an problem. At worst we are trading wasting
511 * of available bandwidth (the non-use of it) for wasting some
512 * socket buffer memory.
513 *
514 * TODO: Shrink send buffer during idle periods together
515 * with congestion window. Requires another timer. Has to
516 * wait for upcoming tcp timer rewrite.
517 *
518 * XXXGL: should there be used sbused() or sbavail()?
519 */
520 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
521 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
522 sbused(&so->so_snd) >= (so->so_snd.sb_hiwat / 8 * 7) &&
523 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
524 sendwin >= (sbused(&so->so_snd) -
525 (tp->snd_nxt - tp->snd_una))) {
526 if (!sbreserve_locked(&so->so_snd,
527 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
528 V_tcp_autosndbuf_max), so, curthread))
529 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
530 }
531 }
532
533 /*
534 * Decide if we can use TCP Segmentation Offloading (if supported by
535 * hardware).
536 *
537 * TSO may only be used if we are in a pure bulk sending state. The
538 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
539 * IP options prevent using TSO. With TSO the TCP header is the same
540 * (except for the sequence number) for all generated packets. This
541 * makes it impossible to transmit any options which vary per generated
542 * segment or packet.
543 *
544 * IPv4 handling has a clear separation of ip options and ip header
545 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
546 * the right thing below to provide length of just ip options and thus
547 * checking for ipoptlen is enough to decide if ip options are present.
548 */
549 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
550 /*
551 * Pre-calculate here as we save another lookup into the darknesses
552 * of IPsec that way and can actually decide if TSO is ok.
553 */
554 #ifdef INET6
555 if (isipv6 && IPSEC_ENABLED(ipv6))
556 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
557 #ifdef INET
558 else
559 #endif
560 #endif /* INET6 */
561 #ifdef INET
562 if (IPSEC_ENABLED(ipv4))
563 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
564 #endif /* INET */
565 #endif /* IPSEC */
566 #ifdef INET6
567 if (isipv6)
568 ipoptlen = ip6_optlen(tp->t_inpcb);
569 else
570 #endif
571 if (tp->t_inpcb->inp_options)
572 ipoptlen = tp->t_inpcb->inp_options->m_len -
573 offsetof(struct ipoption, ipopt_list);
574 else
575 ipoptlen = 0;
576 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
577 ipoptlen += ipsec_optlen;
578 #endif
579
580 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
581 ((tp->t_flags & TF_SIGNATURE) == 0) &&
582 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
583 ipoptlen == 0)
584 tso = 1;
585
586 if (sack_rxmit) {
587 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
588 flags &= ~TH_FIN;
589 } else {
590 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
591 sbused(&so->so_snd)))
592 flags &= ~TH_FIN;
593 }
594
595 recwin = sbspace(&so->so_rcv);
596
597 /*
598 * Sender silly window avoidance. We transmit under the following
599 * conditions when len is non-zero:
600 *
601 * - We have a full segment (or more with TSO)
602 * - This is the last buffer in a write()/send() and we are
603 * either idle or running NODELAY
604 * - we've timed out (e.g. persist timer)
605 * - we have more then 1/2 the maximum send window's worth of
606 * data (receiver may be limited the window size)
607 * - we need to retransmit
608 */
609 if (len) {
610 if (len >= tp->t_maxseg)
611 goto send;
612 /*
613 * NOTE! on localhost connections an 'ack' from the remote
614 * end may occur synchronously with the output and cause
615 * us to flush a buffer queued with moretocome. XXX
616 *
617 * note: the len + off check is almost certainly unnecessary.
618 */
619 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
620 (idle || (tp->t_flags & TF_NODELAY)) &&
621 len + off >= sbavail(&so->so_snd) &&
622 (tp->t_flags & TF_NOPUSH) == 0) {
623 goto send;
624 }
625 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
626 goto send;
627 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
628 goto send;
629 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
630 goto send;
631 if (sack_rxmit)
632 goto send;
633 }
634
635 /*
636 * Sending of standalone window updates.
637 *
638 * Window updates are important when we close our window due to a
639 * full socket buffer and are opening it again after the application
640 * reads data from it. Once the window has opened again and the
641 * remote end starts to send again the ACK clock takes over and
642 * provides the most current window information.
643 *
644 * We must avoid the silly window syndrome whereas every read
645 * from the receive buffer, no matter how small, causes a window
646 * update to be sent. We also should avoid sending a flurry of
647 * window updates when the socket buffer had queued a lot of data
648 * and the application is doing small reads.
649 *
650 * Prevent a flurry of pointless window updates by only sending
651 * an update when we can increase the advertized window by more
652 * than 1/4th of the socket buffer capacity. When the buffer is
653 * getting full or is very small be more aggressive and send an
654 * update whenever we can increase by two mss sized segments.
655 * In all other situations the ACK's to new incoming data will
656 * carry further window increases.
657 *
658 * Don't send an independent window update if a delayed
659 * ACK is pending (it will get piggy-backed on it) or the
660 * remote side already has done a half-close and won't send
661 * more data. Skip this if the connection is in T/TCP
662 * half-open state.
663 */
664 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
665 !(tp->t_flags & TF_DELACK) &&
666 !TCPS_HAVERCVDFIN(tp->t_state)) {
667 /*
668 * "adv" is the amount we could increase the window,
669 * taking into account that we are limited by
670 * TCP_MAXWIN << tp->rcv_scale.
671 */
672 long adv;
673 int oldwin;
674
675 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
676 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
677 oldwin = (tp->rcv_adv - tp->rcv_nxt);
678 adv -= oldwin;
679 } else
680 oldwin = 0;
681
682 /*
683 * If the new window size ends up being the same as or less
684 * than the old size when it is scaled, then don't force
685 * a window update.
686 */
687 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
688 goto dontupdate;
689
690 if (adv >= (long)(2 * tp->t_maxseg) &&
691 (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
692 recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
693 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
694 goto send;
695 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
696 goto send;
697 }
698 dontupdate:
699
700 /*
701 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
702 * is also a catch-all for the retransmit timer timeout case.
703 */
704 if (tp->t_flags & TF_ACKNOW)
705 goto send;
706 if ((flags & TH_RST) ||
707 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
708 goto send;
709 if (SEQ_GT(tp->snd_up, tp->snd_una))
710 goto send;
711 /*
712 * If our state indicates that FIN should be sent
713 * and we have not yet done so, then we need to send.
714 */
715 if (flags & TH_FIN &&
716 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
717 goto send;
718 /*
719 * In SACK, it is possible for tcp_output to fail to send a segment
720 * after the retransmission timer has been turned off. Make sure
721 * that the retransmission timer is set.
722 */
723 if ((tp->t_flags & TF_SACK_PERMIT) &&
724 SEQ_GT(tp->snd_max, tp->snd_una) &&
725 !tcp_timer_active(tp, TT_REXMT) &&
726 !tcp_timer_active(tp, TT_PERSIST)) {
727 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
728 goto just_return;
729 }
730 /*
731 * TCP window updates are not reliable, rather a polling protocol
732 * using ``persist'' packets is used to insure receipt of window
733 * updates. The three ``states'' for the output side are:
734 * idle not doing retransmits or persists
735 * persisting to move a small or zero window
736 * (re)transmitting and thereby not persisting
737 *
738 * tcp_timer_active(tp, TT_PERSIST)
739 * is true when we are in persist state.
740 * (tp->t_flags & TF_FORCEDATA)
741 * is set when we are called to send a persist packet.
742 * tcp_timer_active(tp, TT_REXMT)
743 * is set when we are retransmitting
744 * The output side is idle when both timers are zero.
745 *
746 * If send window is too small, there is data to transmit, and no
747 * retransmit or persist is pending, then go to persist state.
748 * If nothing happens soon, send when timer expires:
749 * if window is nonzero, transmit what we can,
750 * otherwise force out a byte.
751 */
752 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
753 !tcp_timer_active(tp, TT_PERSIST)) {
754 tp->t_rxtshift = 0;
755 tcp_setpersist(tp);
756 }
757
758 /*
759 * No reason to send a segment, just return.
760 */
761 just_return:
762 SOCKBUF_UNLOCK(&so->so_snd);
763 return (0);
764
765 send:
766 SOCKBUF_LOCK_ASSERT(&so->so_snd);
767 if (len > 0) {
768 if (len >= tp->t_maxseg)
769 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
770 else
771 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
772 }
773 /*
774 * Before ESTABLISHED, force sending of initial options
775 * unless TCP set not to do any options.
776 * NOTE: we assume that the IP/TCP header plus TCP options
777 * always fit in a single mbuf, leaving room for a maximum
778 * link header, i.e.
779 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
780 */
781 optlen = 0;
782 #ifdef INET6
783 if (isipv6)
784 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
785 else
786 #endif
787 hdrlen = sizeof (struct tcpiphdr);
788
789 /*
790 * Compute options for segment.
791 * We only have to care about SYN and established connection
792 * segments. Options for SYN-ACK segments are handled in TCP
793 * syncache.
794 */
795 to.to_flags = 0;
796 if ((tp->t_flags & TF_NOOPT) == 0) {
797 /* Maximum segment size. */
798 if (flags & TH_SYN) {
799 tp->snd_nxt = tp->iss;
800 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
801 to.to_flags |= TOF_MSS;
802 #ifdef TCP_RFC7413
803 /*
804 * Only include the TFO option on the first
805 * transmission of the SYN|ACK on a
806 * passively-created TFO socket, as the presence of
807 * the TFO option may have caused the original
808 * SYN|ACK to have been dropped by a middlebox.
809 */
810 if ((tp->t_flags & TF_FASTOPEN) &&
811 (tp->t_state == TCPS_SYN_RECEIVED) &&
812 (tp->t_rxtshift == 0)) {
813 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
814 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie;
815 to.to_flags |= TOF_FASTOPEN;
816 }
817 #endif
818 }
819 /* Window scaling. */
820 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
821 to.to_wscale = tp->request_r_scale;
822 to.to_flags |= TOF_SCALE;
823 }
824 /* Timestamps. */
825 if ((tp->t_flags & TF_RCVD_TSTMP) ||
826 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
827 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
828 to.to_tsecr = tp->ts_recent;
829 to.to_flags |= TOF_TS;
830 }
831
832 /* Set receive buffer autosizing timestamp. */
833 if (tp->rfbuf_ts == 0 &&
834 (so->so_rcv.sb_flags & SB_AUTOSIZE))
835 tp->rfbuf_ts = tcp_ts_getticks();
836
837 /* Selective ACK's. */
838 if (tp->t_flags & TF_SACK_PERMIT) {
839 if (flags & TH_SYN)
840 to.to_flags |= TOF_SACKPERM;
841 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
842 (tp->t_flags & TF_SACK_PERMIT) &&
843 tp->rcv_numsacks > 0) {
844 to.to_flags |= TOF_SACK;
845 to.to_nsacks = tp->rcv_numsacks;
846 to.to_sacks = (u_char *)tp->sackblks;
847 }
848 }
849 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
850 /* TCP-MD5 (RFC2385). */
851 /*
852 * Check that TCP_MD5SIG is enabled in tcpcb to
853 * account the size needed to set this TCP option.
854 */
855 if (tp->t_flags & TF_SIGNATURE)
856 to.to_flags |= TOF_SIGNATURE;
857 #endif /* TCP_SIGNATURE */
858
859 /* Processing the options. */
860 hdrlen += optlen = tcp_addoptions(&to, opt);
861 }
862
863 /*
864 * Adjust data length if insertion of options will
865 * bump the packet length beyond the t_maxseg length.
866 * Clear the FIN bit because we cut off the tail of
867 * the segment.
868 */
869 if (len + optlen + ipoptlen > tp->t_maxseg) {
870 flags &= ~TH_FIN;
871
872 if (tso) {
873 u_int if_hw_tsomax;
874 u_int if_hw_tsomaxsegcount;
875 u_int if_hw_tsomaxsegsize;
876 struct mbuf *mb;
877 u_int moff;
878 int max_len;
879
880 /* extract TSO information */
881 if_hw_tsomax = tp->t_tsomax;
882 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
883 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
884
885 /*
886 * Limit a TSO burst to prevent it from
887 * overflowing or exceeding the maximum length
888 * allowed by the network interface:
889 */
890 KASSERT(ipoptlen == 0,
891 ("%s: TSO can't do IP options", __func__));
892
893 /*
894 * Check if we should limit by maximum payload
895 * length:
896 */
897 if (if_hw_tsomax != 0) {
898 /* compute maximum TSO length */
899 max_len = (if_hw_tsomax - hdrlen -
900 max_linkhdr);
901 if (max_len <= 0) {
902 len = 0;
903 } else if (len > max_len) {
904 sendalot = 1;
905 len = max_len;
906 }
907 }
908
909 /*
910 * Check if we should limit by maximum segment
911 * size and count:
912 */
913 if (if_hw_tsomaxsegcount != 0 &&
914 if_hw_tsomaxsegsize != 0) {
915 /*
916 * Subtract one segment for the LINK
917 * and TCP/IP headers mbuf that will
918 * be prepended to this mbuf chain
919 * after the code in this section
920 * limits the number of mbufs in the
921 * chain to if_hw_tsomaxsegcount.
922 */
923 if_hw_tsomaxsegcount -= 1;
924 max_len = 0;
925 mb = sbsndmbuf(&so->so_snd, off, &moff);
926
927 while (mb != NULL && max_len < len) {
928 u_int mlen;
929 u_int frags;
930
931 /*
932 * Get length of mbuf fragment
933 * and how many hardware frags,
934 * rounded up, it would use:
935 */
936 mlen = (mb->m_len - moff);
937 frags = howmany(mlen,
938 if_hw_tsomaxsegsize);
939
940 /* Handle special case: Zero Length Mbuf */
941 if (frags == 0)
942 frags = 1;
943
944 /*
945 * Check if the fragment limit
946 * will be reached or exceeded:
947 */
948 if (frags >= if_hw_tsomaxsegcount) {
949 max_len += min(mlen,
950 if_hw_tsomaxsegcount *
951 if_hw_tsomaxsegsize);
952 break;
953 }
954 max_len += mlen;
955 if_hw_tsomaxsegcount -= frags;
956 moff = 0;
957 mb = mb->m_next;
958 }
959 if (max_len <= 0) {
960 len = 0;
961 } else if (len > max_len) {
962 sendalot = 1;
963 len = max_len;
964 }
965 }
966
967 /*
968 * Prevent the last segment from being
969 * fractional unless the send sockbuf can be
970 * emptied:
971 */
972 max_len = (tp->t_maxseg - optlen);
973 if ((off + len) < sbavail(&so->so_snd)) {
974 moff = len % max_len;
975 if (moff != 0) {
976 len -= moff;
977 sendalot = 1;
978 }
979 }
980
981 /*
982 * In case there are too many small fragments
983 * don't use TSO:
984 */
985 if (len <= max_len) {
986 len = max_len;
987 sendalot = 1;
988 tso = 0;
989 }
990
991 /*
992 * Send the FIN in a separate segment
993 * after the bulk sending is done.
994 * We don't trust the TSO implementations
995 * to clear the FIN flag on all but the
996 * last segment.
997 */
998 if (tp->t_flags & TF_NEEDFIN)
999 sendalot = 1;
1000
1001 } else {
1002 len = tp->t_maxseg - optlen - ipoptlen;
1003 sendalot = 1;
1004 }
1005 } else
1006 tso = 0;
1007
1008 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1009 ("%s: len > IP_MAXPACKET", __func__));
1010
1011 /*#ifdef DIAGNOSTIC*/
1012 #ifdef INET6
1013 if (max_linkhdr + hdrlen > MCLBYTES)
1014 #else
1015 if (max_linkhdr + hdrlen > MHLEN)
1016 #endif
1017 panic("tcphdr too big");
1018 /*#endif*/
1019
1020 /*
1021 * This KASSERT is here to catch edge cases at a well defined place.
1022 * Before, those had triggered (random) panic conditions further down.
1023 */
1024 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1025
1026 /*
1027 * Grab a header mbuf, attaching a copy of data to
1028 * be transmitted, and initialize the header from
1029 * the template for sends on this connection.
1030 */
1031 if (len) {
1032 struct mbuf *mb;
1033 u_int moff;
1034
1035 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1036 TCPSTAT_INC(tcps_sndprobe);
1037 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1038 tp->t_sndrexmitpack++;
1039 TCPSTAT_INC(tcps_sndrexmitpack);
1040 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1041 } else {
1042 TCPSTAT_INC(tcps_sndpack);
1043 TCPSTAT_ADD(tcps_sndbyte, len);
1044 }
1045 #ifdef INET6
1046 if (MHLEN < hdrlen + max_linkhdr)
1047 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1048 else
1049 #endif
1050 m = m_gethdr(M_NOWAIT, MT_DATA);
1051
1052 if (m == NULL) {
1053 SOCKBUF_UNLOCK(&so->so_snd);
1054 error = ENOBUFS;
1055 sack_rxmit = 0;
1056 goto out;
1057 }
1058
1059 m->m_data += max_linkhdr;
1060 m->m_len = hdrlen;
1061
1062 /*
1063 * Start the m_copy functions from the closest mbuf
1064 * to the offset in the socket buffer chain.
1065 */
1066 mb = sbsndptr(&so->so_snd, off, len, &moff);
1067
1068 if (len <= MHLEN - hdrlen - max_linkhdr) {
1069 m_copydata(mb, moff, (int)len,
1070 mtod(m, caddr_t) + hdrlen);
1071 m->m_len += len;
1072 } else {
1073 m->m_next = m_copy(mb, moff, (int)len);
1074 if (m->m_next == NULL) {
1075 SOCKBUF_UNLOCK(&so->so_snd);
1076 (void) m_free(m);
1077 error = ENOBUFS;
1078 sack_rxmit = 0;
1079 goto out;
1080 }
1081 }
1082
1083 /*
1084 * If we're sending everything we've got, set PUSH.
1085 * (This will keep happy those implementations which only
1086 * give data to the user when a buffer fills or
1087 * a PUSH comes in.)
1088 */
1089 if ((off + len == sbused(&so->so_snd)) && !(flags & TH_SYN))
1090 flags |= TH_PUSH;
1091 SOCKBUF_UNLOCK(&so->so_snd);
1092 } else {
1093 SOCKBUF_UNLOCK(&so->so_snd);
1094 if (tp->t_flags & TF_ACKNOW)
1095 TCPSTAT_INC(tcps_sndacks);
1096 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1097 TCPSTAT_INC(tcps_sndctrl);
1098 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1099 TCPSTAT_INC(tcps_sndurg);
1100 else
1101 TCPSTAT_INC(tcps_sndwinup);
1102
1103 m = m_gethdr(M_NOWAIT, MT_DATA);
1104 if (m == NULL) {
1105 error = ENOBUFS;
1106 sack_rxmit = 0;
1107 goto out;
1108 }
1109 #ifdef INET6
1110 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1111 MHLEN >= hdrlen) {
1112 M_ALIGN(m, hdrlen);
1113 } else
1114 #endif
1115 m->m_data += max_linkhdr;
1116 m->m_len = hdrlen;
1117 }
1118 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1119 m->m_pkthdr.rcvif = (struct ifnet *)0;
1120 #ifdef MAC
1121 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1122 #endif
1123 #ifdef INET6
1124 if (isipv6) {
1125 ip6 = mtod(m, struct ip6_hdr *);
1126 th = (struct tcphdr *)(ip6 + 1);
1127 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1128 } else
1129 #endif /* INET6 */
1130 {
1131 ip = mtod(m, struct ip *);
1132 ipov = (struct ipovly *)ip;
1133 th = (struct tcphdr *)(ip + 1);
1134 tcpip_fillheaders(tp->t_inpcb, ip, th);
1135 }
1136
1137 /*
1138 * Fill in fields, remembering maximum advertised
1139 * window for use in delaying messages about window sizes.
1140 * If resending a FIN, be sure not to use a new sequence number.
1141 */
1142 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1143 tp->snd_nxt == tp->snd_max)
1144 tp->snd_nxt--;
1145 /*
1146 * If we are starting a connection, send ECN setup
1147 * SYN packet. If we are on a retransmit, we may
1148 * resend those bits a number of times as per
1149 * RFC 3168.
1150 */
1151 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1152 if (tp->t_rxtshift >= 1) {
1153 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1154 flags |= TH_ECE|TH_CWR;
1155 } else
1156 flags |= TH_ECE|TH_CWR;
1157 }
1158
1159 if (TCPS_HAVEESTABLISHED(tp->t_state) &&
1160 (tp->t_flags & TF_ECN_PERMIT)) {
1161 /*
1162 * If the peer has ECN, mark data packets with
1163 * ECN capable transmission (ECT).
1164 * Ignore pure ack packets, retransmissions and window probes.
1165 */
1166 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1167 !((tp->t_flags & TF_FORCEDATA) && len == 1 &&
1168 SEQ_LT(tp->snd_una, tp->snd_max))) {
1169 #ifdef INET6
1170 if (isipv6)
1171 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1172 else
1173 #endif
1174 ip->ip_tos |= IPTOS_ECN_ECT0;
1175 TCPSTAT_INC(tcps_ecn_ect0);
1176 /*
1177 * Reply with proper ECN notifications.
1178 * Only set CWR on new data segments.
1179 */
1180 if (tp->t_flags & TF_ECN_SND_CWR) {
1181 flags |= TH_CWR;
1182 tp->t_flags &= ~TF_ECN_SND_CWR;
1183 }
1184 }
1185 if (tp->t_flags & TF_ECN_SND_ECE)
1186 flags |= TH_ECE;
1187 }
1188
1189 /*
1190 * If we are doing retransmissions, then snd_nxt will
1191 * not reflect the first unsent octet. For ACK only
1192 * packets, we do not want the sequence number of the
1193 * retransmitted packet, we want the sequence number
1194 * of the next unsent octet. So, if there is no data
1195 * (and no SYN or FIN), use snd_max instead of snd_nxt
1196 * when filling in ti_seq. But if we are in persist
1197 * state, snd_max might reflect one byte beyond the
1198 * right edge of the window, so use snd_nxt in that
1199 * case, since we know we aren't doing a retransmission.
1200 * (retransmit and persist are mutually exclusive...)
1201 */
1202 if (sack_rxmit == 0) {
1203 if (len || (flags & (TH_SYN|TH_FIN)) ||
1204 tcp_timer_active(tp, TT_PERSIST))
1205 th->th_seq = htonl(tp->snd_nxt);
1206 else
1207 th->th_seq = htonl(tp->snd_max);
1208 } else {
1209 th->th_seq = htonl(p->rxmit);
1210 p->rxmit += len;
1211 tp->sackhint.sack_bytes_rexmit += len;
1212 }
1213 th->th_ack = htonl(tp->rcv_nxt);
1214 if (optlen) {
1215 bcopy(opt, th + 1, optlen);
1216 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1217 }
1218 th->th_flags = flags;
1219 /*
1220 * Calculate receive window. Don't shrink window,
1221 * but avoid silly window syndrome.
1222 */
1223 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1224 recwin < (long)tp->t_maxseg)
1225 recwin = 0;
1226 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1227 recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1228 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1229 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1230 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1231
1232 /*
1233 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1234 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1235 * case is handled in syncache.
1236 */
1237 if (flags & TH_SYN)
1238 th->th_win = htons((u_short)
1239 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1240 else
1241 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1242
1243 /*
1244 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1245 * a 0 window. This may cause the remote transmitter to stall. This
1246 * flag tells soreceive() to disable delayed acknowledgements when
1247 * draining the buffer. This can occur if the receiver is attempting
1248 * to read more data than can be buffered prior to transmitting on
1249 * the connection.
1250 */
1251 if (th->th_win == 0) {
1252 tp->t_sndzerowin++;
1253 tp->t_flags |= TF_RXWIN0SENT;
1254 } else
1255 tp->t_flags &= ~TF_RXWIN0SENT;
1256 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1257 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1258 th->th_flags |= TH_URG;
1259 } else
1260 /*
1261 * If no urgent pointer to send, then we pull
1262 * the urgent pointer to the left edge of the send window
1263 * so that it doesn't drift into the send window on sequence
1264 * number wraparound.
1265 */
1266 tp->snd_up = tp->snd_una; /* drag it along */
1267
1268 /*
1269 * Put TCP length in extended header, and then
1270 * checksum extended header and data.
1271 */
1272 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1273 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1274
1275 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1276 if (to.to_flags & TOF_SIGNATURE) {
1277 /*
1278 * Calculate MD5 signature and put it into the place
1279 * determined before.
1280 * NOTE: since TCP options buffer doesn't point into
1281 * mbuf's data, calculate offset and use it.
1282 */
1283 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1284 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1285 /*
1286 * Do not send segment if the calculation of MD5
1287 * digest has failed.
1288 */
1289 m_freem(m);
1290 goto out;
1291 }
1292 }
1293 #endif
1294 #ifdef INET6
1295 if (isipv6) {
1296 /*
1297 * There is no need to fill in ip6_plen right now.
1298 * It will be filled later by ip6_output.
1299 */
1300 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1301 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1302 optlen + len, IPPROTO_TCP, 0);
1303 }
1304 #endif
1305 #if defined(INET6) && defined(INET)
1306 else
1307 #endif
1308 #ifdef INET
1309 {
1310 m->m_pkthdr.csum_flags = CSUM_TCP;
1311 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1312 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1313
1314 /* IP version must be set here for ipv4/ipv6 checking later */
1315 KASSERT(ip->ip_v == IPVERSION,
1316 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1317 }
1318 #endif
1319
1320 /*
1321 * Enable TSO and specify the size of the segments.
1322 * The TCP pseudo header checksum is always provided.
1323 */
1324 if (tso) {
1325 KASSERT(len > tp->t_maxseg - optlen,
1326 ("%s: len <= tso_segsz", __func__));
1327 m->m_pkthdr.csum_flags |= CSUM_TSO;
1328 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1329 }
1330
1331 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1332 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1333 ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
1334 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1335 #else
1336 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1337 ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
1338 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1339 #endif
1340
1341 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1342 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1343
1344 #ifdef TCPDEBUG
1345 /*
1346 * Trace.
1347 */
1348 if (so->so_options & SO_DEBUG) {
1349 u_short save = 0;
1350 #ifdef INET6
1351 if (!isipv6)
1352 #endif
1353 {
1354 save = ipov->ih_len;
1355 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1356 }
1357 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1358 #ifdef INET6
1359 if (!isipv6)
1360 #endif
1361 ipov->ih_len = save;
1362 }
1363 #endif /* TCPDEBUG */
1364 TCP_PROBE3(debug__output, tp, th, m);
1365
1366 /*
1367 * Fill in IP length and desired time to live and
1368 * send to IP level. There should be a better way
1369 * to handle ttl and tos; we could keep them in
1370 * the template, but need a way to checksum without them.
1371 */
1372 /*
1373 * m->m_pkthdr.len should have been set before checksum calculation,
1374 * because in6_cksum() need it.
1375 */
1376 #ifdef INET6
1377 if (isipv6) {
1378 /*
1379 * we separately set hoplimit for every segment, since the
1380 * user might want to change the value via setsockopt.
1381 * Also, desired default hop limit might be changed via
1382 * Neighbor Discovery.
1383 */
1384 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1385
1386 /*
1387 * Set the packet size here for the benefit of DTrace probes.
1388 * ip6_output() will set it properly; it's supposed to include
1389 * the option header lengths as well.
1390 */
1391 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1392
1393 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1394 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1395 else
1396 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1397
1398 if (tp->t_state == TCPS_SYN_SENT)
1399 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1400
1401 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1402
1403 #ifdef TCPPCAP
1404 /* Save packet, if requested. */
1405 tcp_pcap_add(th, m, &(tp->t_outpkts));
1406 #endif
1407
1408 /* TODO: IPv6 IP6TOS_ECT bit on */
1409 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1410 &tp->t_inpcb->inp_route6,
1411 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1412 NULL, NULL, tp->t_inpcb);
1413
1414 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL)
1415 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu;
1416 }
1417 #endif /* INET6 */
1418 #if defined(INET) && defined(INET6)
1419 else
1420 #endif
1421 #ifdef INET
1422 {
1423 ip->ip_len = htons(m->m_pkthdr.len);
1424 #ifdef INET6
1425 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1426 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1427 #endif /* INET6 */
1428 /*
1429 * If we do path MTU discovery, then we set DF on every packet.
1430 * This might not be the best thing to do according to RFC3390
1431 * Section 2. However the tcp hostcache migitates the problem
1432 * so it affects only the first tcp connection with a host.
1433 *
1434 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1435 */
1436 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1437 ip->ip_off |= htons(IP_DF);
1438 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1439 } else {
1440 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1441 }
1442
1443 if (tp->t_state == TCPS_SYN_SENT)
1444 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1445
1446 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1447
1448 #ifdef TCPPCAP
1449 /* Save packet, if requested. */
1450 tcp_pcap_add(th, m, &(tp->t_outpkts));
1451 #endif
1452
1453 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1454 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1455 tp->t_inpcb);
1456
1457 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1458 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1459 }
1460 #endif /* INET */
1461
1462 out:
1463 /*
1464 * In transmit state, time the transmission and arrange for
1465 * the retransmit. In persist state, just set snd_max.
1466 */
1467 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1468 !tcp_timer_active(tp, TT_PERSIST)) {
1469 tcp_seq startseq = tp->snd_nxt;
1470
1471 /*
1472 * Advance snd_nxt over sequence space of this segment.
1473 */
1474 if (flags & (TH_SYN|TH_FIN)) {
1475 if (flags & TH_SYN)
1476 tp->snd_nxt++;
1477 if (flags & TH_FIN) {
1478 tp->snd_nxt++;
1479 tp->t_flags |= TF_SENTFIN;
1480 }
1481 }
1482 if (sack_rxmit)
1483 goto timer;
1484 tp->snd_nxt += len;
1485 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1486 tp->snd_max = tp->snd_nxt;
1487 /*
1488 * Time this transmission if not a retransmission and
1489 * not currently timing anything.
1490 */
1491 if (tp->t_rtttime == 0) {
1492 tp->t_rtttime = ticks;
1493 tp->t_rtseq = startseq;
1494 TCPSTAT_INC(tcps_segstimed);
1495 }
1496 }
1497
1498 /*
1499 * Set retransmit timer if not currently set,
1500 * and not doing a pure ack or a keep-alive probe.
1501 * Initial value for retransmit timer is smoothed
1502 * round-trip time + 2 * round-trip time variance.
1503 * Initialize shift counter which is used for backoff
1504 * of retransmit time.
1505 */
1506 timer:
1507 if (!tcp_timer_active(tp, TT_REXMT) &&
1508 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1509 (tp->snd_nxt != tp->snd_una))) {
1510 if (tcp_timer_active(tp, TT_PERSIST)) {
1511 tcp_timer_activate(tp, TT_PERSIST, 0);
1512 tp->t_rxtshift = 0;
1513 }
1514 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1515 } else if (len == 0 && sbavail(&so->so_snd) &&
1516 !tcp_timer_active(tp, TT_REXMT) &&
1517 !tcp_timer_active(tp, TT_PERSIST)) {
1518 /*
1519 * Avoid a situation where we do not set persist timer
1520 * after a zero window condition. For example:
1521 * 1) A -> B: packet with enough data to fill the window
1522 * 2) B -> A: ACK for #1 + new data (0 window
1523 * advertisement)
1524 * 3) A -> B: ACK for #2, 0 len packet
1525 *
1526 * In this case, A will not activate the persist timer,
1527 * because it chose to send a packet. Unless tcp_output
1528 * is called for some other reason (delayed ack timer,
1529 * another input packet from B, socket syscall), A will
1530 * not send zero window probes.
1531 *
1532 * So, if you send a 0-length packet, but there is data
1533 * in the socket buffer, and neither the rexmt or
1534 * persist timer is already set, then activate the
1535 * persist timer.
1536 */
1537 tp->t_rxtshift = 0;
1538 tcp_setpersist(tp);
1539 }
1540 } else {
1541 /*
1542 * Persist case, update snd_max but since we are in
1543 * persist mode (no window) we do not update snd_nxt.
1544 */
1545 int xlen = len;
1546 if (flags & TH_SYN)
1547 ++xlen;
1548 if (flags & TH_FIN) {
1549 ++xlen;
1550 tp->t_flags |= TF_SENTFIN;
1551 }
1552 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1553 tp->snd_max = tp->snd_nxt + xlen;
1554 }
1555 if ((error == 0) &&
1556 (TCPS_HAVEESTABLISHED(tp->t_state) &&
1557 (tp->t_flags & TF_SACK_PERMIT) &&
1558 tp->rcv_numsacks > 0)) {
1559 /* Clean up any DSACK's sent */
1560 tcp_clean_dsack_blocks(tp);
1561 }
1562 if (error) {
1563
1564 /*
1565 * We know that the packet was lost, so back out the
1566 * sequence number advance, if any.
1567 *
1568 * If the error is EPERM the packet got blocked by the
1569 * local firewall. Normally we should terminate the
1570 * connection but the blocking may have been spurious
1571 * due to a firewall reconfiguration cycle. So we treat
1572 * it like a packet loss and let the retransmit timer and
1573 * timeouts do their work over time.
1574 * XXX: It is a POLA question whether calling tcp_drop right
1575 * away would be the really correct behavior instead.
1576 */
1577 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1578 !tcp_timer_active(tp, TT_PERSIST)) &&
1579 ((flags & TH_SYN) == 0) &&
1580 (error != EPERM)) {
1581 if (sack_rxmit) {
1582 p->rxmit -= len;
1583 tp->sackhint.sack_bytes_rexmit -= len;
1584 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1585 ("sackhint bytes rtx >= 0"));
1586 } else
1587 tp->snd_nxt -= len;
1588 }
1589 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1590 switch (error) {
1591 case EACCES:
1592 case EPERM:
1593 tp->t_softerror = error;
1594 return (error);
1595 case ENOBUFS:
1596 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1597 tp->snd_cwnd = tp->t_maxseg;
1598 return (0);
1599 case EMSGSIZE:
1600 /*
1601 * For some reason the interface we used initially
1602 * to send segments changed to another or lowered
1603 * its MTU.
1604 * If TSO was active we either got an interface
1605 * without TSO capabilits or TSO was turned off.
1606 * If we obtained mtu from ip_output() then update
1607 * it and try again.
1608 */
1609 if (tso)
1610 tp->t_flags &= ~TF_TSO;
1611 if (mtu != 0) {
1612 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1613 goto again;
1614 }
1615 return (error);
1616 case EHOSTDOWN:
1617 case EHOSTUNREACH:
1618 case ENETDOWN:
1619 case ENETUNREACH:
1620 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1621 tp->t_softerror = error;
1622 return (0);
1623 }
1624 /* FALLTHROUGH */
1625 default:
1626 return (error);
1627 }
1628 }
1629 TCPSTAT_INC(tcps_sndtotal);
1630
1631 /*
1632 * Data sent (as far as we can tell).
1633 * If this advertises a larger window than any other segment,
1634 * then remember the size of the advertised window.
1635 * Any pending ACK has now been sent.
1636 */
1637 if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1638 tp->rcv_adv = tp->rcv_nxt + recwin;
1639 tp->last_ack_sent = tp->rcv_nxt;
1640 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1641 if (tcp_timer_active(tp, TT_DELACK))
1642 tcp_timer_activate(tp, TT_DELACK, 0);
1643 #if 0
1644 /*
1645 * This completely breaks TCP if newreno is turned on. What happens
1646 * is that if delayed-acks are turned on on the receiver, this code
1647 * on the transmitter effectively destroys the TCP window, forcing
1648 * it to four packets (1.5Kx4 = 6K window).
1649 */
1650 if (sendalot && --maxburst)
1651 goto again;
1652 #endif
1653 if (sendalot)
1654 goto again;
1655 return (0);
1656 }
1657
1658 void
tcp_setpersist(struct tcpcb * tp)1659 tcp_setpersist(struct tcpcb *tp)
1660 {
1661 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1662 int tt;
1663
1664 tp->t_flags &= ~TF_PREVVALID;
1665 if (tcp_timer_active(tp, TT_REXMT))
1666 panic("tcp_setpersist: retransmit pending");
1667 /*
1668 * Start/restart persistence timer.
1669 */
1670 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1671 tcp_persmin, tcp_persmax);
1672 tcp_timer_activate(tp, TT_PERSIST, tt);
1673 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1674 tp->t_rxtshift++;
1675 }
1676
1677 /*
1678 * Insert TCP options according to the supplied parameters to the place
1679 * optp in a consistent way. Can handle unaligned destinations.
1680 *
1681 * The order of the option processing is crucial for optimal packing and
1682 * alignment for the scarce option space.
1683 *
1684 * The optimal order for a SYN/SYN-ACK segment is:
1685 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1686 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1687 *
1688 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1689 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1690 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1691 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1692 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1693 */
1694 int
tcp_addoptions(struct tcpopt * to,u_char * optp)1695 tcp_addoptions(struct tcpopt *to, u_char *optp)
1696 {
1697 u_int32_t mask, optlen = 0;
1698
1699 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1700 if ((to->to_flags & mask) != mask)
1701 continue;
1702 if (optlen == TCP_MAXOLEN)
1703 break;
1704 switch (to->to_flags & mask) {
1705 case TOF_MSS:
1706 while (optlen % 4) {
1707 optlen += TCPOLEN_NOP;
1708 *optp++ = TCPOPT_NOP;
1709 }
1710 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1711 continue;
1712 optlen += TCPOLEN_MAXSEG;
1713 *optp++ = TCPOPT_MAXSEG;
1714 *optp++ = TCPOLEN_MAXSEG;
1715 to->to_mss = htons(to->to_mss);
1716 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1717 optp += sizeof(to->to_mss);
1718 break;
1719 case TOF_SCALE:
1720 while (!optlen || optlen % 2 != 1) {
1721 optlen += TCPOLEN_NOP;
1722 *optp++ = TCPOPT_NOP;
1723 }
1724 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1725 continue;
1726 optlen += TCPOLEN_WINDOW;
1727 *optp++ = TCPOPT_WINDOW;
1728 *optp++ = TCPOLEN_WINDOW;
1729 *optp++ = to->to_wscale;
1730 break;
1731 case TOF_SACKPERM:
1732 while (optlen % 2) {
1733 optlen += TCPOLEN_NOP;
1734 *optp++ = TCPOPT_NOP;
1735 }
1736 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1737 continue;
1738 optlen += TCPOLEN_SACK_PERMITTED;
1739 *optp++ = TCPOPT_SACK_PERMITTED;
1740 *optp++ = TCPOLEN_SACK_PERMITTED;
1741 break;
1742 case TOF_TS:
1743 while (!optlen || optlen % 4 != 2) {
1744 optlen += TCPOLEN_NOP;
1745 *optp++ = TCPOPT_NOP;
1746 }
1747 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1748 continue;
1749 optlen += TCPOLEN_TIMESTAMP;
1750 *optp++ = TCPOPT_TIMESTAMP;
1751 *optp++ = TCPOLEN_TIMESTAMP;
1752 to->to_tsval = htonl(to->to_tsval);
1753 to->to_tsecr = htonl(to->to_tsecr);
1754 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1755 optp += sizeof(to->to_tsval);
1756 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1757 optp += sizeof(to->to_tsecr);
1758 break;
1759 case TOF_SIGNATURE:
1760 {
1761 int siglen = TCPOLEN_SIGNATURE - 2;
1762
1763 while (!optlen || optlen % 4 != 2) {
1764 optlen += TCPOLEN_NOP;
1765 *optp++ = TCPOPT_NOP;
1766 }
1767 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1768 to->to_flags &= ~TOF_SIGNATURE;
1769 continue;
1770 }
1771 optlen += TCPOLEN_SIGNATURE;
1772 *optp++ = TCPOPT_SIGNATURE;
1773 *optp++ = TCPOLEN_SIGNATURE;
1774 to->to_signature = optp;
1775 while (siglen--)
1776 *optp++ = 0;
1777 break;
1778 }
1779 case TOF_SACK:
1780 {
1781 int sackblks = 0;
1782 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1783 tcp_seq sack_seq;
1784
1785 while (!optlen || optlen % 4 != 2) {
1786 optlen += TCPOLEN_NOP;
1787 *optp++ = TCPOPT_NOP;
1788 }
1789 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1790 continue;
1791 optlen += TCPOLEN_SACKHDR;
1792 *optp++ = TCPOPT_SACK;
1793 sackblks = min(to->to_nsacks,
1794 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1795 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1796 while (sackblks--) {
1797 sack_seq = htonl(sack->start);
1798 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1799 optp += sizeof(sack_seq);
1800 sack_seq = htonl(sack->end);
1801 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1802 optp += sizeof(sack_seq);
1803 optlen += TCPOLEN_SACK;
1804 sack++;
1805 }
1806 TCPSTAT_INC(tcps_sack_send_blocks);
1807 break;
1808 }
1809 #ifdef TCP_RFC7413
1810 case TOF_FASTOPEN:
1811 {
1812 int total_len;
1813
1814 /* XXX is there any point to aligning this option? */
1815 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1816 if (TCP_MAXOLEN - optlen < total_len)
1817 continue;
1818 *optp++ = TCPOPT_FAST_OPEN;
1819 *optp++ = total_len;
1820 if (to->to_tfo_len > 0) {
1821 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1822 optp += to->to_tfo_len;
1823 }
1824 optlen += total_len;
1825 break;
1826 }
1827 #endif
1828 default:
1829 panic("%s: unknown TCP option type", __func__);
1830 break;
1831 }
1832 }
1833
1834 /* Terminate and pad TCP options to a 4 byte boundary. */
1835 if (optlen % 4) {
1836 optlen += TCPOLEN_EOL;
1837 *optp++ = TCPOPT_EOL;
1838 }
1839 /*
1840 * According to RFC 793 (STD0007):
1841 * "The content of the header beyond the End-of-Option option
1842 * must be header padding (i.e., zero)."
1843 * and later: "The padding is composed of zeros."
1844 */
1845 while (optlen % 4) {
1846 optlen += TCPOLEN_PAD;
1847 *optp++ = TCPOPT_PAD;
1848 }
1849
1850 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1851 return (optlen);
1852 }
1853