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: releng/11.1/sys/netinet/tcp_output.c 319397 2017-06-01 08:19:45Z tuexen $");
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
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
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
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 = ((long)ulmin(cwin,
302 tp->snd_recover - p->rxmit));
303 } else
304 len = ((long)ulmin(cwin, p->end - p->rxmit));
305 off = p->rxmit - tp->snd_una;
306 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
307 __func__, off));
308 if (len > 0) {
309 sack_rxmit = 1;
310 sendalot = 1;
311 TCPSTAT_INC(tcps_sack_rexmits);
312 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
313 min(len, tp->t_maxseg));
314 }
315 }
316 after_sack_rexmit:
317 /*
318 * Get standard flags, and add SYN or FIN if requested by 'hidden'
319 * state flags.
320 */
321 if (tp->t_flags & TF_NEEDFIN)
322 flags |= TH_FIN;
323 if (tp->t_flags & TF_NEEDSYN)
324 flags |= TH_SYN;
325
326 SOCKBUF_LOCK(&so->so_snd);
327 /*
328 * If in persist timeout with window of 0, send 1 byte.
329 * Otherwise, if window is small but nonzero
330 * and timer expired, we will send what we can
331 * and go to transmit state.
332 */
333 if (tp->t_flags & TF_FORCEDATA) {
334 if (sendwin == 0) {
335 /*
336 * If we still have some data to send, then
337 * clear the FIN bit. Usually this would
338 * happen below when it realizes that we
339 * aren't sending all the data. However,
340 * if we have exactly 1 byte of unsent data,
341 * then it won't clear the FIN bit below,
342 * and if we are in persist state, we wind
343 * up sending the packet without recording
344 * that we sent the FIN bit.
345 *
346 * We can't just blindly clear the FIN bit,
347 * because if we don't have any more data
348 * to send then the probe will be the FIN
349 * itself.
350 */
351 if (off < sbused(&so->so_snd))
352 flags &= ~TH_FIN;
353 sendwin = 1;
354 } else {
355 tcp_timer_activate(tp, TT_PERSIST, 0);
356 tp->t_rxtshift = 0;
357 }
358 }
359
360 /*
361 * If snd_nxt == snd_max and we have transmitted a FIN, the
362 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
363 * a negative length. This can also occur when TCP opens up
364 * its congestion window while receiving additional duplicate
365 * acks after fast-retransmit because TCP will reset snd_nxt
366 * to snd_max after the fast-retransmit.
367 *
368 * In the normal retransmit-FIN-only case, however, snd_nxt will
369 * be set to snd_una, the offset will be 0, and the length may
370 * wind up 0.
371 *
372 * If sack_rxmit is true we are retransmitting from the scoreboard
373 * in which case len is already set.
374 */
375 if (sack_rxmit == 0) {
376 if (sack_bytes_rxmt == 0)
377 len = ((long)ulmin(sbavail(&so->so_snd), sendwin) -
378 off);
379 else {
380 long cwin;
381
382 /*
383 * We are inside of a SACK recovery episode and are
384 * sending new data, having retransmitted all the
385 * data possible in the scoreboard.
386 */
387 len = ((long)ulmin(sbavail(&so->so_snd), tp->snd_wnd) -
388 off);
389 /*
390 * Don't remove this (len > 0) check !
391 * We explicitly check for len > 0 here (although it
392 * isn't really necessary), to work around a gcc
393 * optimization issue - to force gcc to compute
394 * len above. Without this check, the computation
395 * of len is bungled by the optimizer.
396 */
397 if (len > 0) {
398 cwin = tp->snd_cwnd -
399 (tp->snd_nxt - tp->sack_newdata) -
400 sack_bytes_rxmt;
401 if (cwin < 0)
402 cwin = 0;
403 len = lmin(len, cwin);
404 }
405 }
406 }
407
408 /*
409 * Lop off SYN bit if it has already been sent. However, if this
410 * is SYN-SENT state and if segment contains data and if we don't
411 * know that foreign host supports TAO, suppress sending segment.
412 */
413 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
414 if (tp->t_state != TCPS_SYN_RECEIVED)
415 flags &= ~TH_SYN;
416 #ifdef TCP_RFC7413
417 /*
418 * When sending additional segments following a TFO SYN|ACK,
419 * do not include the SYN bit.
420 */
421 if ((tp->t_flags & TF_FASTOPEN) &&
422 (tp->t_state == TCPS_SYN_RECEIVED))
423 flags &= ~TH_SYN;
424 #endif
425 off--, len++;
426 }
427
428 /*
429 * Be careful not to send data and/or FIN on SYN segments.
430 * This measure is needed to prevent interoperability problems
431 * with not fully conformant TCP implementations.
432 */
433 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
434 len = 0;
435 flags &= ~TH_FIN;
436 }
437
438 #ifdef TCP_RFC7413
439 /*
440 * When retransmitting SYN|ACK on a passively-created TFO socket,
441 * don't include data, as the presence of data may have caused the
442 * original SYN|ACK to have been dropped by a middlebox.
443 */
444 if ((tp->t_flags & TF_FASTOPEN) &&
445 (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) ||
446 (flags & TH_RST)))
447 len = 0;
448 #endif
449 if (len <= 0) {
450 /*
451 * If FIN has been sent but not acked,
452 * but we haven't been called to retransmit,
453 * len will be < 0. Otherwise, window shrank
454 * after we sent into it. If window shrank to 0,
455 * cancel pending retransmit, pull snd_nxt back
456 * to (closed) window, and set the persist timer
457 * if it isn't already going. If the window didn't
458 * close completely, just wait for an ACK.
459 *
460 * We also do a general check here to ensure that
461 * we will set the persist timer when we have data
462 * to send, but a 0-byte window. This makes sure
463 * the persist timer is set even if the packet
464 * hits one of the "goto send" lines below.
465 */
466 len = 0;
467 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
468 (off < (int) sbavail(&so->so_snd))) {
469 tcp_timer_activate(tp, TT_REXMT, 0);
470 tp->t_rxtshift = 0;
471 tp->snd_nxt = tp->snd_una;
472 if (!tcp_timer_active(tp, TT_PERSIST))
473 tcp_setpersist(tp);
474 }
475 }
476
477 /* len will be >= 0 after this point. */
478 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
479
480 /*
481 * Automatic sizing of send socket buffer. Often the send buffer
482 * size is not optimally adjusted to the actual network conditions
483 * at hand (delay bandwidth product). Setting the buffer size too
484 * small limits throughput on links with high bandwidth and high
485 * delay (eg. trans-continental/oceanic links). Setting the
486 * buffer size too big consumes too much real kernel memory,
487 * especially with many connections on busy servers.
488 *
489 * The criteria to step up the send buffer one notch are:
490 * 1. receive window of remote host is larger than send buffer
491 * (with a fudge factor of 5/4th);
492 * 2. send buffer is filled to 7/8th with data (so we actually
493 * have data to make use of it);
494 * 3. send buffer fill has not hit maximal automatic size;
495 * 4. our send window (slow start and cogestion controlled) is
496 * larger than sent but unacknowledged data in send buffer.
497 *
498 * The remote host receive window scaling factor may limit the
499 * growing of the send buffer before it reaches its allowed
500 * maximum.
501 *
502 * It scales directly with slow start or congestion window
503 * and does at most one step per received ACK. This fast
504 * scaling has the drawback of growing the send buffer beyond
505 * what is strictly necessary to make full use of a given
506 * delay*bandwidth product. However testing has shown this not
507 * to be much of an problem. At worst we are trading wasting
508 * of available bandwidth (the non-use of it) for wasting some
509 * socket buffer memory.
510 *
511 * TODO: Shrink send buffer during idle periods together
512 * with congestion window. Requires another timer. Has to
513 * wait for upcoming tcp timer rewrite.
514 *
515 * XXXGL: should there be used sbused() or sbavail()?
516 */
517 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
518 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
519 sbused(&so->so_snd) >= (so->so_snd.sb_hiwat / 8 * 7) &&
520 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
521 sendwin >= (sbused(&so->so_snd) -
522 (tp->snd_nxt - tp->snd_una))) {
523 if (!sbreserve_locked(&so->so_snd,
524 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
525 V_tcp_autosndbuf_max), so, curthread))
526 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
527 }
528 }
529
530 /*
531 * Decide if we can use TCP Segmentation Offloading (if supported by
532 * hardware).
533 *
534 * TSO may only be used if we are in a pure bulk sending state. The
535 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
536 * IP options prevent using TSO. With TSO the TCP header is the same
537 * (except for the sequence number) for all generated packets. This
538 * makes it impossible to transmit any options which vary per generated
539 * segment or packet.
540 *
541 * IPv4 handling has a clear separation of ip options and ip header
542 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
543 * the right thing below to provide length of just ip options and thus
544 * checking for ipoptlen is enough to decide if ip options are present.
545 */
546 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
547 /*
548 * Pre-calculate here as we save another lookup into the darknesses
549 * of IPsec that way and can actually decide if TSO is ok.
550 */
551 #ifdef INET6
552 if (isipv6 && IPSEC_ENABLED(ipv6))
553 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
554 #ifdef INET
555 else
556 #endif
557 #endif /* INET6 */
558 #ifdef INET
559 if (IPSEC_ENABLED(ipv4))
560 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
561 #endif /* INET */
562 #endif /* IPSEC */
563 #ifdef INET6
564 if (isipv6)
565 ipoptlen = ip6_optlen(tp->t_inpcb);
566 else
567 #endif
568 if (tp->t_inpcb->inp_options)
569 ipoptlen = tp->t_inpcb->inp_options->m_len -
570 offsetof(struct ipoption, ipopt_list);
571 else
572 ipoptlen = 0;
573 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
574 ipoptlen += ipsec_optlen;
575 #endif
576
577 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
578 ((tp->t_flags & TF_SIGNATURE) == 0) &&
579 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
580 ipoptlen == 0)
581 tso = 1;
582
583 if (sack_rxmit) {
584 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
585 flags &= ~TH_FIN;
586 } else {
587 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
588 sbused(&so->so_snd)))
589 flags &= ~TH_FIN;
590 }
591
592 recwin = sbspace(&so->so_rcv);
593
594 /*
595 * Sender silly window avoidance. We transmit under the following
596 * conditions when len is non-zero:
597 *
598 * - We have a full segment (or more with TSO)
599 * - This is the last buffer in a write()/send() and we are
600 * either idle or running NODELAY
601 * - we've timed out (e.g. persist timer)
602 * - we have more then 1/2 the maximum send window's worth of
603 * data (receiver may be limited the window size)
604 * - we need to retransmit
605 */
606 if (len) {
607 if (len >= tp->t_maxseg)
608 goto send;
609 /*
610 * NOTE! on localhost connections an 'ack' from the remote
611 * end may occur synchronously with the output and cause
612 * us to flush a buffer queued with moretocome. XXX
613 *
614 * note: the len + off check is almost certainly unnecessary.
615 */
616 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
617 (idle || (tp->t_flags & TF_NODELAY)) &&
618 len + off >= sbavail(&so->so_snd) &&
619 (tp->t_flags & TF_NOPUSH) == 0) {
620 goto send;
621 }
622 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
623 goto send;
624 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
625 goto send;
626 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
627 goto send;
628 if (sack_rxmit)
629 goto send;
630 }
631
632 /*
633 * Sending of standalone window updates.
634 *
635 * Window updates are important when we close our window due to a
636 * full socket buffer and are opening it again after the application
637 * reads data from it. Once the window has opened again and the
638 * remote end starts to send again the ACK clock takes over and
639 * provides the most current window information.
640 *
641 * We must avoid the silly window syndrome whereas every read
642 * from the receive buffer, no matter how small, causes a window
643 * update to be sent. We also should avoid sending a flurry of
644 * window updates when the socket buffer had queued a lot of data
645 * and the application is doing small reads.
646 *
647 * Prevent a flurry of pointless window updates by only sending
648 * an update when we can increase the advertized window by more
649 * than 1/4th of the socket buffer capacity. When the buffer is
650 * getting full or is very small be more aggressive and send an
651 * update whenever we can increase by two mss sized segments.
652 * In all other situations the ACK's to new incoming data will
653 * carry further window increases.
654 *
655 * Don't send an independent window update if a delayed
656 * ACK is pending (it will get piggy-backed on it) or the
657 * remote side already has done a half-close and won't send
658 * more data. Skip this if the connection is in T/TCP
659 * half-open state.
660 */
661 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
662 !(tp->t_flags & TF_DELACK) &&
663 !TCPS_HAVERCVDFIN(tp->t_state)) {
664 /*
665 * "adv" is the amount we could increase the window,
666 * taking into account that we are limited by
667 * TCP_MAXWIN << tp->rcv_scale.
668 */
669 long adv;
670 int oldwin;
671
672 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
673 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
674 oldwin = (tp->rcv_adv - tp->rcv_nxt);
675 adv -= oldwin;
676 } else
677 oldwin = 0;
678
679 /*
680 * If the new window size ends up being the same as the old
681 * size when it is scaled, then don't force a window update.
682 */
683 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
684 goto dontupdate;
685
686 if (adv >= (long)(2 * tp->t_maxseg) &&
687 (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
688 recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
689 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
690 goto send;
691 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
692 goto send;
693 }
694 dontupdate:
695
696 /*
697 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
698 * is also a catch-all for the retransmit timer timeout case.
699 */
700 if (tp->t_flags & TF_ACKNOW)
701 goto send;
702 if ((flags & TH_RST) ||
703 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
704 goto send;
705 if (SEQ_GT(tp->snd_up, tp->snd_una))
706 goto send;
707 /*
708 * If our state indicates that FIN should be sent
709 * and we have not yet done so, then we need to send.
710 */
711 if (flags & TH_FIN &&
712 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
713 goto send;
714 /*
715 * In SACK, it is possible for tcp_output to fail to send a segment
716 * after the retransmission timer has been turned off. Make sure
717 * that the retransmission timer is set.
718 */
719 if ((tp->t_flags & TF_SACK_PERMIT) &&
720 SEQ_GT(tp->snd_max, tp->snd_una) &&
721 !tcp_timer_active(tp, TT_REXMT) &&
722 !tcp_timer_active(tp, TT_PERSIST)) {
723 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
724 goto just_return;
725 }
726 /*
727 * TCP window updates are not reliable, rather a polling protocol
728 * using ``persist'' packets is used to insure receipt of window
729 * updates. The three ``states'' for the output side are:
730 * idle not doing retransmits or persists
731 * persisting to move a small or zero window
732 * (re)transmitting and thereby not persisting
733 *
734 * tcp_timer_active(tp, TT_PERSIST)
735 * is true when we are in persist state.
736 * (tp->t_flags & TF_FORCEDATA)
737 * is set when we are called to send a persist packet.
738 * tcp_timer_active(tp, TT_REXMT)
739 * is set when we are retransmitting
740 * The output side is idle when both timers are zero.
741 *
742 * If send window is too small, there is data to transmit, and no
743 * retransmit or persist is pending, then go to persist state.
744 * If nothing happens soon, send when timer expires:
745 * if window is nonzero, transmit what we can,
746 * otherwise force out a byte.
747 */
748 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
749 !tcp_timer_active(tp, TT_PERSIST)) {
750 tp->t_rxtshift = 0;
751 tcp_setpersist(tp);
752 }
753
754 /*
755 * No reason to send a segment, just return.
756 */
757 just_return:
758 SOCKBUF_UNLOCK(&so->so_snd);
759 return (0);
760
761 send:
762 SOCKBUF_LOCK_ASSERT(&so->so_snd);
763 if (len > 0) {
764 if (len >= tp->t_maxseg)
765 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
766 else
767 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
768 }
769 /*
770 * Before ESTABLISHED, force sending of initial options
771 * unless TCP set not to do any options.
772 * NOTE: we assume that the IP/TCP header plus TCP options
773 * always fit in a single mbuf, leaving room for a maximum
774 * link header, i.e.
775 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
776 */
777 optlen = 0;
778 #ifdef INET6
779 if (isipv6)
780 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
781 else
782 #endif
783 hdrlen = sizeof (struct tcpiphdr);
784
785 /*
786 * Compute options for segment.
787 * We only have to care about SYN and established connection
788 * segments. Options for SYN-ACK segments are handled in TCP
789 * syncache.
790 */
791 to.to_flags = 0;
792 if ((tp->t_flags & TF_NOOPT) == 0) {
793 /* Maximum segment size. */
794 if (flags & TH_SYN) {
795 tp->snd_nxt = tp->iss;
796 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
797 to.to_flags |= TOF_MSS;
798 #ifdef TCP_RFC7413
799 /*
800 * Only include the TFO option on the first
801 * transmission of the SYN|ACK on a
802 * passively-created TFO socket, as the presence of
803 * the TFO option may have caused the original
804 * SYN|ACK to have been dropped by a middlebox.
805 */
806 if ((tp->t_flags & TF_FASTOPEN) &&
807 (tp->t_state == TCPS_SYN_RECEIVED) &&
808 (tp->t_rxtshift == 0)) {
809 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
810 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie;
811 to.to_flags |= TOF_FASTOPEN;
812 }
813 #endif
814 }
815 /* Window scaling. */
816 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
817 to.to_wscale = tp->request_r_scale;
818 to.to_flags |= TOF_SCALE;
819 }
820 /* Timestamps. */
821 if ((tp->t_flags & TF_RCVD_TSTMP) ||
822 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
823 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
824 to.to_tsecr = tp->ts_recent;
825 to.to_flags |= TOF_TS;
826 }
827
828 /* Set receive buffer autosizing timestamp. */
829 if (tp->rfbuf_ts == 0 &&
830 (so->so_rcv.sb_flags & SB_AUTOSIZE))
831 tp->rfbuf_ts = tcp_ts_getticks();
832
833 /* Selective ACK's. */
834 if (tp->t_flags & TF_SACK_PERMIT) {
835 if (flags & TH_SYN)
836 to.to_flags |= TOF_SACKPERM;
837 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
838 (tp->t_flags & TF_SACK_PERMIT) &&
839 tp->rcv_numsacks > 0) {
840 to.to_flags |= TOF_SACK;
841 to.to_nsacks = tp->rcv_numsacks;
842 to.to_sacks = (u_char *)tp->sackblks;
843 }
844 }
845 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
846 /* TCP-MD5 (RFC2385). */
847 /*
848 * Check that TCP_MD5SIG is enabled in tcpcb to
849 * account the size needed to set this TCP option.
850 */
851 if (tp->t_flags & TF_SIGNATURE)
852 to.to_flags |= TOF_SIGNATURE;
853 #endif /* TCP_SIGNATURE */
854
855 /* Processing the options. */
856 hdrlen += optlen = tcp_addoptions(&to, opt);
857 }
858
859 /*
860 * Adjust data length if insertion of options will
861 * bump the packet length beyond the t_maxseg length.
862 * Clear the FIN bit because we cut off the tail of
863 * the segment.
864 */
865 if (len + optlen + ipoptlen > tp->t_maxseg) {
866 flags &= ~TH_FIN;
867
868 if (tso) {
869 u_int if_hw_tsomax;
870 u_int if_hw_tsomaxsegcount;
871 u_int if_hw_tsomaxsegsize;
872 struct mbuf *mb;
873 u_int moff;
874 int max_len;
875
876 /* extract TSO information */
877 if_hw_tsomax = tp->t_tsomax;
878 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
879 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
880
881 /*
882 * Limit a TSO burst to prevent it from
883 * overflowing or exceeding the maximum length
884 * allowed by the network interface:
885 */
886 KASSERT(ipoptlen == 0,
887 ("%s: TSO can't do IP options", __func__));
888
889 /*
890 * Check if we should limit by maximum payload
891 * length:
892 */
893 if (if_hw_tsomax != 0) {
894 /* compute maximum TSO length */
895 max_len = (if_hw_tsomax - hdrlen -
896 max_linkhdr);
897 if (max_len <= 0) {
898 len = 0;
899 } else if (len > max_len) {
900 sendalot = 1;
901 len = max_len;
902 }
903 }
904
905 /*
906 * Check if we should limit by maximum segment
907 * size and count:
908 */
909 if (if_hw_tsomaxsegcount != 0 &&
910 if_hw_tsomaxsegsize != 0) {
911 /*
912 * Subtract one segment for the LINK
913 * and TCP/IP headers mbuf that will
914 * be prepended to this mbuf chain
915 * after the code in this section
916 * limits the number of mbufs in the
917 * chain to if_hw_tsomaxsegcount.
918 */
919 if_hw_tsomaxsegcount -= 1;
920 max_len = 0;
921 mb = sbsndmbuf(&so->so_snd, off, &moff);
922
923 while (mb != NULL && max_len < len) {
924 u_int mlen;
925 u_int frags;
926
927 /*
928 * Get length of mbuf fragment
929 * and how many hardware frags,
930 * rounded up, it would use:
931 */
932 mlen = (mb->m_len - moff);
933 frags = howmany(mlen,
934 if_hw_tsomaxsegsize);
935
936 /* Handle special case: Zero Length Mbuf */
937 if (frags == 0)
938 frags = 1;
939
940 /*
941 * Check if the fragment limit
942 * will be reached or exceeded:
943 */
944 if (frags >= if_hw_tsomaxsegcount) {
945 max_len += min(mlen,
946 if_hw_tsomaxsegcount *
947 if_hw_tsomaxsegsize);
948 break;
949 }
950 max_len += mlen;
951 if_hw_tsomaxsegcount -= frags;
952 moff = 0;
953 mb = mb->m_next;
954 }
955 if (max_len <= 0) {
956 len = 0;
957 } else if (len > max_len) {
958 sendalot = 1;
959 len = max_len;
960 }
961 }
962
963 /*
964 * Prevent the last segment from being
965 * fractional unless the send sockbuf can be
966 * emptied:
967 */
968 max_len = (tp->t_maxseg - optlen);
969 if ((off + len) < sbavail(&so->so_snd)) {
970 moff = len % max_len;
971 if (moff != 0) {
972 len -= moff;
973 sendalot = 1;
974 }
975 }
976
977 /*
978 * In case there are too many small fragments
979 * don't use TSO:
980 */
981 if (len <= max_len) {
982 len = max_len;
983 sendalot = 1;
984 tso = 0;
985 }
986
987 /*
988 * Send the FIN in a separate segment
989 * after the bulk sending is done.
990 * We don't trust the TSO implementations
991 * to clear the FIN flag on all but the
992 * last segment.
993 */
994 if (tp->t_flags & TF_NEEDFIN)
995 sendalot = 1;
996
997 } else {
998 len = tp->t_maxseg - optlen - ipoptlen;
999 sendalot = 1;
1000 }
1001 } else
1002 tso = 0;
1003
1004 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1005 ("%s: len > IP_MAXPACKET", __func__));
1006
1007 /*#ifdef DIAGNOSTIC*/
1008 #ifdef INET6
1009 if (max_linkhdr + hdrlen > MCLBYTES)
1010 #else
1011 if (max_linkhdr + hdrlen > MHLEN)
1012 #endif
1013 panic("tcphdr too big");
1014 /*#endif*/
1015
1016 /*
1017 * This KASSERT is here to catch edge cases at a well defined place.
1018 * Before, those had triggered (random) panic conditions further down.
1019 */
1020 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1021
1022 /*
1023 * Grab a header mbuf, attaching a copy of data to
1024 * be transmitted, and initialize the header from
1025 * the template for sends on this connection.
1026 */
1027 if (len) {
1028 struct mbuf *mb;
1029 u_int moff;
1030
1031 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1032 TCPSTAT_INC(tcps_sndprobe);
1033 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1034 tp->t_sndrexmitpack++;
1035 TCPSTAT_INC(tcps_sndrexmitpack);
1036 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1037 } else {
1038 TCPSTAT_INC(tcps_sndpack);
1039 TCPSTAT_ADD(tcps_sndbyte, len);
1040 }
1041 #ifdef INET6
1042 if (MHLEN < hdrlen + max_linkhdr)
1043 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1044 else
1045 #endif
1046 m = m_gethdr(M_NOWAIT, MT_DATA);
1047
1048 if (m == NULL) {
1049 SOCKBUF_UNLOCK(&so->so_snd);
1050 error = ENOBUFS;
1051 sack_rxmit = 0;
1052 goto out;
1053 }
1054
1055 m->m_data += max_linkhdr;
1056 m->m_len = hdrlen;
1057
1058 /*
1059 * Start the m_copy functions from the closest mbuf
1060 * to the offset in the socket buffer chain.
1061 */
1062 mb = sbsndptr(&so->so_snd, off, len, &moff);
1063
1064 if (len <= MHLEN - hdrlen - max_linkhdr) {
1065 m_copydata(mb, moff, (int)len,
1066 mtod(m, caddr_t) + hdrlen);
1067 m->m_len += len;
1068 } else {
1069 m->m_next = m_copy(mb, moff, (int)len);
1070 if (m->m_next == NULL) {
1071 SOCKBUF_UNLOCK(&so->so_snd);
1072 (void) m_free(m);
1073 error = ENOBUFS;
1074 sack_rxmit = 0;
1075 goto out;
1076 }
1077 }
1078
1079 /*
1080 * If we're sending everything we've got, set PUSH.
1081 * (This will keep happy those implementations which only
1082 * give data to the user when a buffer fills or
1083 * a PUSH comes in.)
1084 */
1085 if ((off + len == sbused(&so->so_snd)) && !(flags & TH_SYN))
1086 flags |= TH_PUSH;
1087 SOCKBUF_UNLOCK(&so->so_snd);
1088 } else {
1089 SOCKBUF_UNLOCK(&so->so_snd);
1090 if (tp->t_flags & TF_ACKNOW)
1091 TCPSTAT_INC(tcps_sndacks);
1092 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1093 TCPSTAT_INC(tcps_sndctrl);
1094 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1095 TCPSTAT_INC(tcps_sndurg);
1096 else
1097 TCPSTAT_INC(tcps_sndwinup);
1098
1099 m = m_gethdr(M_NOWAIT, MT_DATA);
1100 if (m == NULL) {
1101 error = ENOBUFS;
1102 sack_rxmit = 0;
1103 goto out;
1104 }
1105 #ifdef INET6
1106 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1107 MHLEN >= hdrlen) {
1108 M_ALIGN(m, hdrlen);
1109 } else
1110 #endif
1111 m->m_data += max_linkhdr;
1112 m->m_len = hdrlen;
1113 }
1114 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1115 m->m_pkthdr.rcvif = (struct ifnet *)0;
1116 #ifdef MAC
1117 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1118 #endif
1119 #ifdef INET6
1120 if (isipv6) {
1121 ip6 = mtod(m, struct ip6_hdr *);
1122 th = (struct tcphdr *)(ip6 + 1);
1123 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1124 } else
1125 #endif /* INET6 */
1126 {
1127 ip = mtod(m, struct ip *);
1128 ipov = (struct ipovly *)ip;
1129 th = (struct tcphdr *)(ip + 1);
1130 tcpip_fillheaders(tp->t_inpcb, ip, th);
1131 }
1132
1133 /*
1134 * Fill in fields, remembering maximum advertised
1135 * window for use in delaying messages about window sizes.
1136 * If resending a FIN, be sure not to use a new sequence number.
1137 */
1138 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1139 tp->snd_nxt == tp->snd_max)
1140 tp->snd_nxt--;
1141 /*
1142 * If we are starting a connection, send ECN setup
1143 * SYN packet. If we are on a retransmit, we may
1144 * resend those bits a number of times as per
1145 * RFC 3168.
1146 */
1147 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1148 if (tp->t_rxtshift >= 1) {
1149 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1150 flags |= TH_ECE|TH_CWR;
1151 } else
1152 flags |= TH_ECE|TH_CWR;
1153 }
1154
1155 if (tp->t_state == TCPS_ESTABLISHED &&
1156 (tp->t_flags & TF_ECN_PERMIT)) {
1157 /*
1158 * If the peer has ECN, mark data packets with
1159 * ECN capable transmission (ECT).
1160 * Ignore pure ack packets, retransmissions and window probes.
1161 */
1162 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1163 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1164 #ifdef INET6
1165 if (isipv6)
1166 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1167 else
1168 #endif
1169 ip->ip_tos |= IPTOS_ECN_ECT0;
1170 TCPSTAT_INC(tcps_ecn_ect0);
1171 }
1172
1173 /*
1174 * Reply with proper ECN notifications.
1175 */
1176 if (tp->t_flags & TF_ECN_SND_CWR) {
1177 flags |= TH_CWR;
1178 tp->t_flags &= ~TF_ECN_SND_CWR;
1179 }
1180 if (tp->t_flags & TF_ECN_SND_ECE)
1181 flags |= TH_ECE;
1182 }
1183
1184 /*
1185 * If we are doing retransmissions, then snd_nxt will
1186 * not reflect the first unsent octet. For ACK only
1187 * packets, we do not want the sequence number of the
1188 * retransmitted packet, we want the sequence number
1189 * of the next unsent octet. So, if there is no data
1190 * (and no SYN or FIN), use snd_max instead of snd_nxt
1191 * when filling in ti_seq. But if we are in persist
1192 * state, snd_max might reflect one byte beyond the
1193 * right edge of the window, so use snd_nxt in that
1194 * case, since we know we aren't doing a retransmission.
1195 * (retransmit and persist are mutually exclusive...)
1196 */
1197 if (sack_rxmit == 0) {
1198 if (len || (flags & (TH_SYN|TH_FIN)) ||
1199 tcp_timer_active(tp, TT_PERSIST))
1200 th->th_seq = htonl(tp->snd_nxt);
1201 else
1202 th->th_seq = htonl(tp->snd_max);
1203 } else {
1204 th->th_seq = htonl(p->rxmit);
1205 p->rxmit += len;
1206 tp->sackhint.sack_bytes_rexmit += len;
1207 }
1208 th->th_ack = htonl(tp->rcv_nxt);
1209 if (optlen) {
1210 bcopy(opt, th + 1, optlen);
1211 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1212 }
1213 th->th_flags = flags;
1214 /*
1215 * Calculate receive window. Don't shrink window,
1216 * but avoid silly window syndrome.
1217 */
1218 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1219 recwin < (long)tp->t_maxseg)
1220 recwin = 0;
1221 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1222 recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1223 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1224 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1225 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1226
1227 /*
1228 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1229 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1230 * case is handled in syncache.
1231 */
1232 if (flags & TH_SYN)
1233 th->th_win = htons((u_short)
1234 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1235 else
1236 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1237
1238 /*
1239 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1240 * a 0 window. This may cause the remote transmitter to stall. This
1241 * flag tells soreceive() to disable delayed acknowledgements when
1242 * draining the buffer. This can occur if the receiver is attempting
1243 * to read more data than can be buffered prior to transmitting on
1244 * the connection.
1245 */
1246 if (th->th_win == 0) {
1247 tp->t_sndzerowin++;
1248 tp->t_flags |= TF_RXWIN0SENT;
1249 } else
1250 tp->t_flags &= ~TF_RXWIN0SENT;
1251 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1252 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1253 th->th_flags |= TH_URG;
1254 } else
1255 /*
1256 * If no urgent pointer to send, then we pull
1257 * the urgent pointer to the left edge of the send window
1258 * so that it doesn't drift into the send window on sequence
1259 * number wraparound.
1260 */
1261 tp->snd_up = tp->snd_una; /* drag it along */
1262
1263 /*
1264 * Put TCP length in extended header, and then
1265 * checksum extended header and data.
1266 */
1267 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1268 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1269
1270 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1271 if (to.to_flags & TOF_SIGNATURE) {
1272 /*
1273 * Calculate MD5 signature and put it into the place
1274 * determined before.
1275 * NOTE: since TCP options buffer doesn't point into
1276 * mbuf's data, calculate offset and use it.
1277 */
1278 if (!TCPMD5_ENABLED() || TCPMD5_OUTPUT(m, th,
1279 (u_char *)(th + 1) + (to.to_signature - opt)) != 0) {
1280 /*
1281 * Do not send segment if the calculation of MD5
1282 * digest has failed.
1283 */
1284 goto out;
1285 }
1286 }
1287 #endif
1288 #ifdef INET6
1289 if (isipv6) {
1290 /*
1291 * There is no need to fill in ip6_plen right now.
1292 * It will be filled later by ip6_output.
1293 */
1294 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1295 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1296 optlen + len, IPPROTO_TCP, 0);
1297 }
1298 #endif
1299 #if defined(INET6) && defined(INET)
1300 else
1301 #endif
1302 #ifdef INET
1303 {
1304 m->m_pkthdr.csum_flags = CSUM_TCP;
1305 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1306 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1307
1308 /* IP version must be set here for ipv4/ipv6 checking later */
1309 KASSERT(ip->ip_v == IPVERSION,
1310 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1311 }
1312 #endif
1313
1314 /*
1315 * Enable TSO and specify the size of the segments.
1316 * The TCP pseudo header checksum is always provided.
1317 */
1318 if (tso) {
1319 KASSERT(len > tp->t_maxseg - optlen,
1320 ("%s: len <= tso_segsz", __func__));
1321 m->m_pkthdr.csum_flags |= CSUM_TSO;
1322 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1323 }
1324
1325 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1326 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1327 ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
1328 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1329 #else
1330 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1331 ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
1332 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1333 #endif
1334
1335 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1336 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1337
1338 #ifdef TCPDEBUG
1339 /*
1340 * Trace.
1341 */
1342 if (so->so_options & SO_DEBUG) {
1343 u_short save = 0;
1344 #ifdef INET6
1345 if (!isipv6)
1346 #endif
1347 {
1348 save = ipov->ih_len;
1349 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1350 }
1351 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1352 #ifdef INET6
1353 if (!isipv6)
1354 #endif
1355 ipov->ih_len = save;
1356 }
1357 #endif /* TCPDEBUG */
1358 TCP_PROBE3(debug__output, tp, th, m);
1359
1360 /*
1361 * Fill in IP length and desired time to live and
1362 * send to IP level. There should be a better way
1363 * to handle ttl and tos; we could keep them in
1364 * the template, but need a way to checksum without them.
1365 */
1366 /*
1367 * m->m_pkthdr.len should have been set before checksum calculation,
1368 * because in6_cksum() need it.
1369 */
1370 #ifdef INET6
1371 if (isipv6) {
1372 /*
1373 * we separately set hoplimit for every segment, since the
1374 * user might want to change the value via setsockopt.
1375 * Also, desired default hop limit might be changed via
1376 * Neighbor Discovery.
1377 */
1378 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1379
1380 /*
1381 * Set the packet size here for the benefit of DTrace probes.
1382 * ip6_output() will set it properly; it's supposed to include
1383 * the option header lengths as well.
1384 */
1385 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1386
1387 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1388 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1389 else
1390 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1391
1392 if (tp->t_state == TCPS_SYN_SENT)
1393 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1394
1395 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1396
1397 #ifdef TCPPCAP
1398 /* Save packet, if requested. */
1399 tcp_pcap_add(th, m, &(tp->t_outpkts));
1400 #endif
1401
1402 /* TODO: IPv6 IP6TOS_ECT bit on */
1403 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1404 &tp->t_inpcb->inp_route6,
1405 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1406 NULL, NULL, tp->t_inpcb);
1407
1408 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL)
1409 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu;
1410 }
1411 #endif /* INET6 */
1412 #if defined(INET) && defined(INET6)
1413 else
1414 #endif
1415 #ifdef INET
1416 {
1417 ip->ip_len = htons(m->m_pkthdr.len);
1418 #ifdef INET6
1419 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1420 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1421 #endif /* INET6 */
1422 /*
1423 * If we do path MTU discovery, then we set DF on every packet.
1424 * This might not be the best thing to do according to RFC3390
1425 * Section 2. However the tcp hostcache migitates the problem
1426 * so it affects only the first tcp connection with a host.
1427 *
1428 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1429 */
1430 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1431 ip->ip_off |= htons(IP_DF);
1432 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1433 } else {
1434 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1435 }
1436
1437 if (tp->t_state == TCPS_SYN_SENT)
1438 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1439
1440 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1441
1442 #ifdef TCPPCAP
1443 /* Save packet, if requested. */
1444 tcp_pcap_add(th, m, &(tp->t_outpkts));
1445 #endif
1446
1447 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1448 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1449 tp->t_inpcb);
1450
1451 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1452 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1453 }
1454 #endif /* INET */
1455
1456 out:
1457 /*
1458 * In transmit state, time the transmission and arrange for
1459 * the retransmit. In persist state, just set snd_max.
1460 */
1461 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1462 !tcp_timer_active(tp, TT_PERSIST)) {
1463 tcp_seq startseq = tp->snd_nxt;
1464
1465 /*
1466 * Advance snd_nxt over sequence space of this segment.
1467 */
1468 if (flags & (TH_SYN|TH_FIN)) {
1469 if (flags & TH_SYN)
1470 tp->snd_nxt++;
1471 if (flags & TH_FIN) {
1472 tp->snd_nxt++;
1473 tp->t_flags |= TF_SENTFIN;
1474 }
1475 }
1476 if (sack_rxmit)
1477 goto timer;
1478 tp->snd_nxt += len;
1479 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1480 tp->snd_max = tp->snd_nxt;
1481 /*
1482 * Time this transmission if not a retransmission and
1483 * not currently timing anything.
1484 */
1485 if (tp->t_rtttime == 0) {
1486 tp->t_rtttime = ticks;
1487 tp->t_rtseq = startseq;
1488 TCPSTAT_INC(tcps_segstimed);
1489 }
1490 }
1491
1492 /*
1493 * Set retransmit timer if not currently set,
1494 * and not doing a pure ack or a keep-alive probe.
1495 * Initial value for retransmit timer is smoothed
1496 * round-trip time + 2 * round-trip time variance.
1497 * Initialize shift counter which is used for backoff
1498 * of retransmit time.
1499 */
1500 timer:
1501 if (!tcp_timer_active(tp, TT_REXMT) &&
1502 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1503 (tp->snd_nxt != tp->snd_una))) {
1504 if (tcp_timer_active(tp, TT_PERSIST)) {
1505 tcp_timer_activate(tp, TT_PERSIST, 0);
1506 tp->t_rxtshift = 0;
1507 }
1508 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1509 } else if (len == 0 && sbavail(&so->so_snd) &&
1510 !tcp_timer_active(tp, TT_REXMT) &&
1511 !tcp_timer_active(tp, TT_PERSIST)) {
1512 /*
1513 * Avoid a situation where we do not set persist timer
1514 * after a zero window condition. For example:
1515 * 1) A -> B: packet with enough data to fill the window
1516 * 2) B -> A: ACK for #1 + new data (0 window
1517 * advertisement)
1518 * 3) A -> B: ACK for #2, 0 len packet
1519 *
1520 * In this case, A will not activate the persist timer,
1521 * because it chose to send a packet. Unless tcp_output
1522 * is called for some other reason (delayed ack timer,
1523 * another input packet from B, socket syscall), A will
1524 * not send zero window probes.
1525 *
1526 * So, if you send a 0-length packet, but there is data
1527 * in the socket buffer, and neither the rexmt or
1528 * persist timer is already set, then activate the
1529 * persist timer.
1530 */
1531 tp->t_rxtshift = 0;
1532 tcp_setpersist(tp);
1533 }
1534 } else {
1535 /*
1536 * Persist case, update snd_max but since we are in
1537 * persist mode (no window) we do not update snd_nxt.
1538 */
1539 int xlen = len;
1540 if (flags & TH_SYN)
1541 ++xlen;
1542 if (flags & TH_FIN) {
1543 ++xlen;
1544 tp->t_flags |= TF_SENTFIN;
1545 }
1546 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1547 tp->snd_max = tp->snd_nxt + len;
1548 }
1549
1550 if (error) {
1551
1552 /*
1553 * We know that the packet was lost, so back out the
1554 * sequence number advance, if any.
1555 *
1556 * If the error is EPERM the packet got blocked by the
1557 * local firewall. Normally we should terminate the
1558 * connection but the blocking may have been spurious
1559 * due to a firewall reconfiguration cycle. So we treat
1560 * it like a packet loss and let the retransmit timer and
1561 * timeouts do their work over time.
1562 * XXX: It is a POLA question whether calling tcp_drop right
1563 * away would be the really correct behavior instead.
1564 */
1565 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1566 !tcp_timer_active(tp, TT_PERSIST)) &&
1567 ((flags & TH_SYN) == 0) &&
1568 (error != EPERM)) {
1569 if (sack_rxmit) {
1570 p->rxmit -= len;
1571 tp->sackhint.sack_bytes_rexmit -= len;
1572 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1573 ("sackhint bytes rtx >= 0"));
1574 } else
1575 tp->snd_nxt -= len;
1576 }
1577 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1578 switch (error) {
1579 case EACCES:
1580 tp->t_softerror = error;
1581 return (0);
1582 case EPERM:
1583 tp->t_softerror = error;
1584 return (error);
1585 case ENOBUFS:
1586 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1587 tp->snd_cwnd = tp->t_maxseg;
1588 return (0);
1589 case EMSGSIZE:
1590 /*
1591 * For some reason the interface we used initially
1592 * to send segments changed to another or lowered
1593 * its MTU.
1594 * If TSO was active we either got an interface
1595 * without TSO capabilits or TSO was turned off.
1596 * If we obtained mtu from ip_output() then update
1597 * it and try again.
1598 */
1599 if (tso)
1600 tp->t_flags &= ~TF_TSO;
1601 if (mtu != 0) {
1602 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1603 goto again;
1604 }
1605 return (error);
1606 case EHOSTDOWN:
1607 case EHOSTUNREACH:
1608 case ENETDOWN:
1609 case ENETUNREACH:
1610 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1611 tp->t_softerror = error;
1612 return (0);
1613 }
1614 /* FALLTHROUGH */
1615 default:
1616 return (error);
1617 }
1618 }
1619 TCPSTAT_INC(tcps_sndtotal);
1620
1621 /*
1622 * Data sent (as far as we can tell).
1623 * If this advertises a larger window than any other segment,
1624 * then remember the size of the advertised window.
1625 * Any pending ACK has now been sent.
1626 */
1627 if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1628 tp->rcv_adv = tp->rcv_nxt + recwin;
1629 tp->last_ack_sent = tp->rcv_nxt;
1630 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1631 if (tcp_timer_active(tp, TT_DELACK))
1632 tcp_timer_activate(tp, TT_DELACK, 0);
1633 #if 0
1634 /*
1635 * This completely breaks TCP if newreno is turned on. What happens
1636 * is that if delayed-acks are turned on on the receiver, this code
1637 * on the transmitter effectively destroys the TCP window, forcing
1638 * it to four packets (1.5Kx4 = 6K window).
1639 */
1640 if (sendalot && --maxburst)
1641 goto again;
1642 #endif
1643 if (sendalot)
1644 goto again;
1645 return (0);
1646 }
1647
1648 void
1649 tcp_setpersist(struct tcpcb *tp)
1650 {
1651 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1652 int tt;
1653
1654 tp->t_flags &= ~TF_PREVVALID;
1655 if (tcp_timer_active(tp, TT_REXMT))
1656 panic("tcp_setpersist: retransmit pending");
1657 /*
1658 * Start/restart persistence timer.
1659 */
1660 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1661 tcp_persmin, tcp_persmax);
1662 tcp_timer_activate(tp, TT_PERSIST, tt);
1663 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1664 tp->t_rxtshift++;
1665 }
1666
1667 /*
1668 * Insert TCP options according to the supplied parameters to the place
1669 * optp in a consistent way. Can handle unaligned destinations.
1670 *
1671 * The order of the option processing is crucial for optimal packing and
1672 * alignment for the scarce option space.
1673 *
1674 * The optimal order for a SYN/SYN-ACK segment is:
1675 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1676 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1677 *
1678 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1679 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1680 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1681 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1682 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1683 */
1684 int
1685 tcp_addoptions(struct tcpopt *to, u_char *optp)
1686 {
1687 u_int32_t mask, optlen = 0;
1688
1689 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1690 if ((to->to_flags & mask) != mask)
1691 continue;
1692 if (optlen == TCP_MAXOLEN)
1693 break;
1694 switch (to->to_flags & mask) {
1695 case TOF_MSS:
1696 while (optlen % 4) {
1697 optlen += TCPOLEN_NOP;
1698 *optp++ = TCPOPT_NOP;
1699 }
1700 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1701 continue;
1702 optlen += TCPOLEN_MAXSEG;
1703 *optp++ = TCPOPT_MAXSEG;
1704 *optp++ = TCPOLEN_MAXSEG;
1705 to->to_mss = htons(to->to_mss);
1706 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1707 optp += sizeof(to->to_mss);
1708 break;
1709 case TOF_SCALE:
1710 while (!optlen || optlen % 2 != 1) {
1711 optlen += TCPOLEN_NOP;
1712 *optp++ = TCPOPT_NOP;
1713 }
1714 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1715 continue;
1716 optlen += TCPOLEN_WINDOW;
1717 *optp++ = TCPOPT_WINDOW;
1718 *optp++ = TCPOLEN_WINDOW;
1719 *optp++ = to->to_wscale;
1720 break;
1721 case TOF_SACKPERM:
1722 while (optlen % 2) {
1723 optlen += TCPOLEN_NOP;
1724 *optp++ = TCPOPT_NOP;
1725 }
1726 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1727 continue;
1728 optlen += TCPOLEN_SACK_PERMITTED;
1729 *optp++ = TCPOPT_SACK_PERMITTED;
1730 *optp++ = TCPOLEN_SACK_PERMITTED;
1731 break;
1732 case TOF_TS:
1733 while (!optlen || optlen % 4 != 2) {
1734 optlen += TCPOLEN_NOP;
1735 *optp++ = TCPOPT_NOP;
1736 }
1737 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1738 continue;
1739 optlen += TCPOLEN_TIMESTAMP;
1740 *optp++ = TCPOPT_TIMESTAMP;
1741 *optp++ = TCPOLEN_TIMESTAMP;
1742 to->to_tsval = htonl(to->to_tsval);
1743 to->to_tsecr = htonl(to->to_tsecr);
1744 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1745 optp += sizeof(to->to_tsval);
1746 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1747 optp += sizeof(to->to_tsecr);
1748 break;
1749 case TOF_SIGNATURE:
1750 {
1751 int siglen = TCPOLEN_SIGNATURE - 2;
1752
1753 while (!optlen || optlen % 4 != 2) {
1754 optlen += TCPOLEN_NOP;
1755 *optp++ = TCPOPT_NOP;
1756 }
1757 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1758 to->to_flags &= ~TOF_SIGNATURE;
1759 continue;
1760 }
1761 optlen += TCPOLEN_SIGNATURE;
1762 *optp++ = TCPOPT_SIGNATURE;
1763 *optp++ = TCPOLEN_SIGNATURE;
1764 to->to_signature = optp;
1765 while (siglen--)
1766 *optp++ = 0;
1767 break;
1768 }
1769 case TOF_SACK:
1770 {
1771 int sackblks = 0;
1772 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1773 tcp_seq sack_seq;
1774
1775 while (!optlen || optlen % 4 != 2) {
1776 optlen += TCPOLEN_NOP;
1777 *optp++ = TCPOPT_NOP;
1778 }
1779 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1780 continue;
1781 optlen += TCPOLEN_SACKHDR;
1782 *optp++ = TCPOPT_SACK;
1783 sackblks = min(to->to_nsacks,
1784 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1785 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1786 while (sackblks--) {
1787 sack_seq = htonl(sack->start);
1788 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1789 optp += sizeof(sack_seq);
1790 sack_seq = htonl(sack->end);
1791 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1792 optp += sizeof(sack_seq);
1793 optlen += TCPOLEN_SACK;
1794 sack++;
1795 }
1796 TCPSTAT_INC(tcps_sack_send_blocks);
1797 break;
1798 }
1799 #ifdef TCP_RFC7413
1800 case TOF_FASTOPEN:
1801 {
1802 int total_len;
1803
1804 /* XXX is there any point to aligning this option? */
1805 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1806 if (TCP_MAXOLEN - optlen < total_len)
1807 continue;
1808 *optp++ = TCPOPT_FAST_OPEN;
1809 *optp++ = total_len;
1810 if (to->to_tfo_len > 0) {
1811 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1812 optp += to->to_tfo_len;
1813 }
1814 optlen += total_len;
1815 break;
1816 }
1817 #endif
1818 default:
1819 panic("%s: unknown TCP option type", __func__);
1820 break;
1821 }
1822 }
1823
1824 /* Terminate and pad TCP options to a 4 byte boundary. */
1825 if (optlen % 4) {
1826 optlen += TCPOLEN_EOL;
1827 *optp++ = TCPOPT_EOL;
1828 }
1829 /*
1830 * According to RFC 793 (STD0007):
1831 * "The content of the header beyond the End-of-Option option
1832 * must be header padding (i.e., zero)."
1833 * and later: "The padding is composed of zeros."
1834 */
1835 while (optlen % 4) {
1836 optlen += TCPOLEN_PAD;
1837 *optp++ = TCPOPT_PAD;
1838 }
1839
1840 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1841 return (optlen);
1842 }
Cache object: 1abee23dc24bdb839e537e852365afc2
|