xref: /freebsd/sys/netinet/tcp_input.c (revision ae2f0b2611f112b400177db951f9bd992de72b4d)
1  /*-
2   * SPDX-License-Identifier: BSD-3-Clause
3   *
4   * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
5   *	The Regents of the University of California.  All rights reserved.
6   * Copyright (c) 2007-2008,2010
7   *	Swinburne University of Technology, Melbourne, Australia.
8   * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
9   * Copyright (c) 2010 The FreeBSD Foundation
10   * Copyright (c) 2010-2011 Juniper Networks, Inc.
11   * All rights reserved.
12   *
13   * Portions of this software were developed at the Centre for Advanced Internet
14   * Architectures, Swinburne University of Technology, by Lawrence Stewart,
15   * James Healy and David Hayes, made possible in part by a grant from the Cisco
16   * University Research Program Fund at Community Foundation Silicon Valley.
17   *
18   * Portions of this software were developed at the Centre for Advanced
19   * Internet Architectures, Swinburne University of Technology, Melbourne,
20   * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
21   *
22   * Portions of this software were developed by Robert N. M. Watson under
23   * contract to Juniper Networks, Inc.
24   *
25   * Redistribution and use in source and binary forms, with or without
26   * modification, are permitted provided that the following conditions
27   * are met:
28   * 1. Redistributions of source code must retain the above copyright
29   *    notice, this list of conditions and the following disclaimer.
30   * 2. Redistributions in binary form must reproduce the above copyright
31   *    notice, this list of conditions and the following disclaimer in the
32   *    documentation and/or other materials provided with the distribution.
33   * 3. Neither the name of the University nor the names of its contributors
34   *    may be used to endorse or promote products derived from this software
35   *    without specific prior written permission.
36   *
37   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
38   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
39   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
40   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
41   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
42   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
43   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
44   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
45   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
46   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
47   * SUCH DAMAGE.
48   *
49   *	@(#)tcp_input.c	8.12 (Berkeley) 5/24/95
50   */
51  
52  #include <sys/cdefs.h>
53  __FBSDID("$FreeBSD$");
54  
55  #include "opt_inet.h"
56  #include "opt_inet6.h"
57  #include "opt_ipsec.h"
58  
59  #include <sys/param.h>
60  #include <sys/arb.h>
61  #include <sys/kernel.h>
62  #ifdef TCP_HHOOK
63  #include <sys/hhook.h>
64  #endif
65  #include <sys/malloc.h>
66  #include <sys/mbuf.h>
67  #include <sys/proc.h>		/* for proc0 declaration */
68  #include <sys/protosw.h>
69  #include <sys/qmath.h>
70  #include <sys/sdt.h>
71  #include <sys/signalvar.h>
72  #include <sys/socket.h>
73  #include <sys/socketvar.h>
74  #include <sys/sysctl.h>
75  #include <sys/syslog.h>
76  #include <sys/systm.h>
77  #include <sys/stats.h>
78  
79  #include <machine/cpu.h>	/* before tcp_seq.h, for tcp_random18() */
80  
81  #include <vm/uma.h>
82  
83  #include <net/if.h>
84  #include <net/if_var.h>
85  #include <net/route.h>
86  #include <net/vnet.h>
87  
88  #define TCPSTATES		/* for logging */
89  
90  #include <netinet/in.h>
91  #include <netinet/in_kdtrace.h>
92  #include <netinet/in_pcb.h>
93  #include <netinet/in_systm.h>
94  #include <netinet/ip.h>
95  #include <netinet/ip_icmp.h>	/* required for icmp_var.h */
96  #include <netinet/icmp_var.h>	/* for ICMP_BANDLIM */
97  #include <netinet/ip_var.h>
98  #include <netinet/ip_options.h>
99  #include <netinet/ip6.h>
100  #include <netinet/icmp6.h>
101  #include <netinet6/in6_pcb.h>
102  #include <netinet6/in6_var.h>
103  #include <netinet6/ip6_var.h>
104  #include <netinet6/nd6.h>
105  #include <netinet/tcp.h>
106  #include <netinet/tcp_fsm.h>
107  #include <netinet/tcp_seq.h>
108  #include <netinet/tcp_timer.h>
109  #include <netinet/tcp_var.h>
110  #include <netinet/tcp_log_buf.h>
111  #include <netinet6/tcp6_var.h>
112  #include <netinet/tcpip.h>
113  #include <netinet/cc/cc.h>
114  #include <netinet/tcp_fastopen.h>
115  #ifdef TCPPCAP
116  #include <netinet/tcp_pcap.h>
117  #endif
118  #include <netinet/tcp_syncache.h>
119  #ifdef TCP_OFFLOAD
120  #include <netinet/tcp_offload.h>
121  #endif
122  #include <netinet/tcp_ecn.h>
123  #include <netinet/udp.h>
124  
125  #include <netipsec/ipsec_support.h>
126  
127  #include <machine/in_cksum.h>
128  
129  #include <security/mac/mac_framework.h>
130  
131  const int tcprexmtthresh = 3;
132  
133  VNET_DEFINE(int, tcp_log_in_vain) = 0;
134  SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_VNET | CTLFLAG_RW,
135      &VNET_NAME(tcp_log_in_vain), 0,
136      "Log all incoming TCP segments to closed ports");
137  
138  VNET_DEFINE(int, blackhole) = 0;
139  #define	V_blackhole		VNET(blackhole)
140  SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
141      &VNET_NAME(blackhole), 0,
142      "Do not send RST on segments to closed ports");
143  
144  VNET_DEFINE(bool, blackhole_local) = false;
145  #define	V_blackhole_local	VNET(blackhole_local)
146  SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, blackhole_local, CTLFLAG_VNET |
147      CTLFLAG_RW, &VNET_NAME(blackhole_local), false,
148      "Enforce net.inet.tcp.blackhole for locally originated packets");
149  
150  VNET_DEFINE(int, tcp_delack_enabled) = 1;
151  SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
152      &VNET_NAME(tcp_delack_enabled), 0,
153      "Delay ACK to try and piggyback it onto a data packet");
154  
155  VNET_DEFINE(int, drop_synfin) = 0;
156  SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
157      &VNET_NAME(drop_synfin), 0,
158      "Drop TCP packets with SYN+FIN set");
159  
160  VNET_DEFINE(int, tcp_do_prr_conservative) = 0;
161  SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr_conservative, CTLFLAG_VNET | CTLFLAG_RW,
162      &VNET_NAME(tcp_do_prr_conservative), 0,
163      "Do conservative Proportional Rate Reduction");
164  
165  VNET_DEFINE(int, tcp_do_prr) = 1;
166  SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr, CTLFLAG_VNET | CTLFLAG_RW,
167      &VNET_NAME(tcp_do_prr), 1,
168      "Enable Proportional Rate Reduction per RFC 6937");
169  
170  VNET_DEFINE(int, tcp_do_lrd) = 0;
171  SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_lrd, CTLFLAG_VNET | CTLFLAG_RW,
172      &VNET_NAME(tcp_do_lrd), 1,
173      "Perform Lost Retransmission Detection");
174  
175  VNET_DEFINE(int, tcp_do_newcwv) = 0;
176  SYSCTL_INT(_net_inet_tcp, OID_AUTO, newcwv, CTLFLAG_VNET | CTLFLAG_RW,
177      &VNET_NAME(tcp_do_newcwv), 0,
178      "Enable New Congestion Window Validation per RFC7661");
179  
180  VNET_DEFINE(int, tcp_do_rfc3042) = 1;
181  SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
182      &VNET_NAME(tcp_do_rfc3042), 0,
183      "Enable RFC 3042 (Limited Transmit)");
184  
185  VNET_DEFINE(int, tcp_do_rfc3390) = 1;
186  SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
187      &VNET_NAME(tcp_do_rfc3390), 0,
188      "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
189  
190  VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
191  SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
192      CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
193      "Slow-start flight size (initial congestion window) in number of segments");
194  
195  VNET_DEFINE(int, tcp_do_rfc3465) = 1;
196  SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
197      &VNET_NAME(tcp_do_rfc3465), 0,
198      "Enable RFC 3465 (Appropriate Byte Counting)");
199  
200  VNET_DEFINE(int, tcp_abc_l_var) = 2;
201  SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
202      &VNET_NAME(tcp_abc_l_var), 2,
203      "Cap the max cwnd increment during slow-start to this number of segments");
204  
205  VNET_DEFINE(int, tcp_insecure_syn) = 0;
206  SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
207      &VNET_NAME(tcp_insecure_syn), 0,
208      "Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
209  
210  VNET_DEFINE(int, tcp_insecure_rst) = 0;
211  SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
212      &VNET_NAME(tcp_insecure_rst), 0,
213      "Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
214  
215  VNET_DEFINE(int, tcp_recvspace) = 1024*64;
216  #define	V_tcp_recvspace	VNET(tcp_recvspace)
217  SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
218      &VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
219  
220  VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
221  SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
222      &VNET_NAME(tcp_do_autorcvbuf), 0,
223      "Enable automatic receive buffer sizing");
224  
225  VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
226  SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
227      &VNET_NAME(tcp_autorcvbuf_max), 0,
228      "Max size of automatic receive buffer");
229  
230  VNET_DEFINE(struct inpcbinfo, tcbinfo);
231  
232  /*
233   * TCP statistics are stored in an array of counter(9)s, which size matches
234   * size of struct tcpstat.  TCP running connection count is a regular array.
235   */
236  VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
237  SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
238      tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
239  VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
240  SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
241      CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
242      "TCP connection counts by TCP state");
243  
244  /*
245   * Kernel module interface for updating tcpstat.  The first argument is an index
246   * into tcpstat treated as an array.
247   */
248  void
249  kmod_tcpstat_add(int statnum, int val)
250  {
251  
252  	counter_u64_add(VNET(tcpstat)[statnum], val);
253  }
254  
255  /*
256   * Make sure that we only start a SACK loss recovery when
257   * receiving a duplicate ACK with a SACK block, and also
258   * complete SACK loss recovery in case the other end
259   * reneges.
260   */
261  static bool inline
262  tcp_is_sack_recovery(struct tcpcb *tp, struct tcpopt *to)
263  {
264  	return ((tp->t_flags & TF_SACK_PERMIT) &&
265  		((to->to_flags & TOF_SACK) ||
266  		(!TAILQ_EMPTY(&tp->snd_holes))));
267  }
268  
269  #ifdef TCP_HHOOK
270  /*
271   * Wrapper for the TCP established input helper hook.
272   */
273  void
274  hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
275  {
276  	struct tcp_hhook_data hhook_data;
277  
278  	if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
279  		hhook_data.tp = tp;
280  		hhook_data.th = th;
281  		hhook_data.to = to;
282  
283  		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
284  		    &tp->t_osd);
285  	}
286  }
287  #endif
288  
289  /*
290   * CC wrapper hook functions
291   */
292  void
293  cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
294      uint16_t type)
295  {
296  #ifdef STATS
297  	int32_t gput;
298  #endif
299  
300  	INP_WLOCK_ASSERT(tptoinpcb(tp));
301  
302  	tp->t_ccv.nsegs = nsegs;
303  	tp->t_ccv.bytes_this_ack = BYTES_THIS_ACK(tp, th);
304  	if ((!V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd)) ||
305  	    (V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd) &&
306  	     (tp->snd_cwnd < (tcp_compute_pipe(tp) * 2))))
307  		tp->t_ccv.flags |= CCF_CWND_LIMITED;
308  	else
309  		tp->t_ccv.flags &= ~CCF_CWND_LIMITED;
310  
311  	if (type == CC_ACK) {
312  #ifdef STATS
313  		stats_voi_update_abs_s32(tp->t_stats, VOI_TCP_CALCFRWINDIFF,
314  		    ((int32_t)tp->snd_cwnd) - tp->snd_wnd);
315  		if (!IN_RECOVERY(tp->t_flags))
316  			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_ACKLEN,
317  			   tp->t_ccv.bytes_this_ack / (tcp_maxseg(tp) * nsegs));
318  		if ((tp->t_flags & TF_GPUTINPROG) &&
319  		    SEQ_GEQ(th->th_ack, tp->gput_ack)) {
320  			/*
321  			 * Compute goodput in bits per millisecond.
322  			 */
323  			gput = (((int64_t)SEQ_SUB(th->th_ack, tp->gput_seq)) << 3) /
324  			    max(1, tcp_ts_getticks() - tp->gput_ts);
325  			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_GPUT,
326  			    gput);
327  			/*
328  			 * XXXLAS: This is a temporary hack, and should be
329  			 * chained off VOI_TCP_GPUT when stats(9) grows an API
330  			 * to deal with chained VOIs.
331  			 */
332  			if (tp->t_stats_gput_prev > 0)
333  				stats_voi_update_abs_s32(tp->t_stats,
334  				    VOI_TCP_GPUT_ND,
335  				    ((gput - tp->t_stats_gput_prev) * 100) /
336  				    tp->t_stats_gput_prev);
337  			tp->t_flags &= ~TF_GPUTINPROG;
338  			tp->t_stats_gput_prev = gput;
339  		}
340  #endif /* STATS */
341  		if (tp->snd_cwnd > tp->snd_ssthresh) {
342  			tp->t_bytes_acked += tp->t_ccv.bytes_this_ack;
343  			if (tp->t_bytes_acked >= tp->snd_cwnd) {
344  				tp->t_bytes_acked -= tp->snd_cwnd;
345  				tp->t_ccv.flags |= CCF_ABC_SENTAWND;
346  			}
347  		} else {
348  				tp->t_ccv.flags &= ~CCF_ABC_SENTAWND;
349  				tp->t_bytes_acked = 0;
350  		}
351  	}
352  
353  	if (CC_ALGO(tp)->ack_received != NULL) {
354  		/* XXXLAS: Find a way to live without this */
355  		tp->t_ccv.curack = th->th_ack;
356  		CC_ALGO(tp)->ack_received(&tp->t_ccv, type);
357  	}
358  #ifdef STATS
359  	stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_LCWIN, tp->snd_cwnd);
360  #endif
361  }
362  
363  void
364  cc_conn_init(struct tcpcb *tp)
365  {
366  	struct hc_metrics_lite metrics;
367  	struct inpcb *inp = tptoinpcb(tp);
368  	u_int maxseg;
369  	int rtt;
370  
371  	INP_WLOCK_ASSERT(inp);
372  
373  	tcp_hc_get(&inp->inp_inc, &metrics);
374  	maxseg = tcp_maxseg(tp);
375  
376  	if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
377  		tp->t_srtt = rtt;
378  		TCPSTAT_INC(tcps_usedrtt);
379  		if (metrics.rmx_rttvar) {
380  			tp->t_rttvar = metrics.rmx_rttvar;
381  			TCPSTAT_INC(tcps_usedrttvar);
382  		} else {
383  			/* default variation is +- 1 rtt */
384  			tp->t_rttvar =
385  			    tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
386  		}
387  		TCPT_RANGESET(tp->t_rxtcur,
388  		    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
389  		    tp->t_rttmin, TCPTV_REXMTMAX);
390  	}
391  	if (metrics.rmx_ssthresh) {
392  		/*
393  		 * There's some sort of gateway or interface
394  		 * buffer limit on the path.  Use this to set
395  		 * the slow start threshold, but set the
396  		 * threshold to no less than 2*mss.
397  		 */
398  		tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
399  		TCPSTAT_INC(tcps_usedssthresh);
400  	}
401  
402  	/*
403  	 * Set the initial slow-start flight size.
404  	 *
405  	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
406  	 * reduce the initial CWND to one segment as congestion is likely
407  	 * requiring us to be cautious.
408  	 */
409  	if (tp->snd_cwnd == 1)
410  		tp->snd_cwnd = maxseg;		/* SYN(-ACK) lost */
411  	else
412  		tp->snd_cwnd = tcp_compute_initwnd(maxseg);
413  
414  	if (CC_ALGO(tp)->conn_init != NULL)
415  		CC_ALGO(tp)->conn_init(&tp->t_ccv);
416  }
417  
418  void inline
419  cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
420  {
421  	INP_WLOCK_ASSERT(tptoinpcb(tp));
422  
423  #ifdef STATS
424  	stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_CSIG, type);
425  #endif
426  
427  	switch(type) {
428  	case CC_NDUPACK:
429  		if (!IN_FASTRECOVERY(tp->t_flags)) {
430  			tp->snd_recover = tp->snd_max;
431  			if (tp->t_flags2 & TF2_ECN_PERMIT)
432  				tp->t_flags2 |= TF2_ECN_SND_CWR;
433  		}
434  		break;
435  	case CC_ECN:
436  		if (!IN_CONGRECOVERY(tp->t_flags) ||
437  		    /*
438  		     * Allow ECN reaction on ACK to CWR, if
439  		     * that data segment was also CE marked.
440  		     */
441  		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
442  			EXIT_CONGRECOVERY(tp->t_flags);
443  			TCPSTAT_INC(tcps_ecn_rcwnd);
444  			tp->snd_recover = tp->snd_max + 1;
445  			if (tp->t_flags2 & TF2_ECN_PERMIT)
446  				tp->t_flags2 |= TF2_ECN_SND_CWR;
447  		}
448  		break;
449  	case CC_RTO:
450  		tp->t_dupacks = 0;
451  		tp->t_bytes_acked = 0;
452  		EXIT_RECOVERY(tp->t_flags);
453  		if (tp->t_flags2 & TF2_ECN_PERMIT)
454  			tp->t_flags2 |= TF2_ECN_SND_CWR;
455  		break;
456  	case CC_RTO_ERR:
457  		TCPSTAT_INC(tcps_sndrexmitbad);
458  		/* RTO was unnecessary, so reset everything. */
459  		tp->snd_cwnd = tp->snd_cwnd_prev;
460  		tp->snd_ssthresh = tp->snd_ssthresh_prev;
461  		tp->snd_recover = tp->snd_recover_prev;
462  		if (tp->t_flags & TF_WASFRECOVERY)
463  			ENTER_FASTRECOVERY(tp->t_flags);
464  		if (tp->t_flags & TF_WASCRECOVERY)
465  			ENTER_CONGRECOVERY(tp->t_flags);
466  		tp->snd_nxt = tp->snd_max;
467  		tp->t_flags &= ~TF_PREVVALID;
468  		tp->t_badrxtwin = 0;
469  		break;
470  	}
471  
472  	if (CC_ALGO(tp)->cong_signal != NULL) {
473  		if (th != NULL)
474  			tp->t_ccv.curack = th->th_ack;
475  		CC_ALGO(tp)->cong_signal(&tp->t_ccv, type);
476  	}
477  }
478  
479  void inline
480  cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
481  {
482  	INP_WLOCK_ASSERT(tptoinpcb(tp));
483  
484  	/* XXXLAS: KASSERT that we're in recovery? */
485  
486  	if (CC_ALGO(tp)->post_recovery != NULL) {
487  		tp->t_ccv.curack = th->th_ack;
488  		CC_ALGO(tp)->post_recovery(&tp->t_ccv);
489  	}
490  	/* XXXLAS: EXIT_RECOVERY ? */
491  	tp->t_bytes_acked = 0;
492  	tp->sackhint.delivered_data = 0;
493  	tp->sackhint.prr_out = 0;
494  }
495  
496  /*
497   * Indicate whether this ack should be delayed.  We can delay the ack if
498   * following conditions are met:
499   *	- There is no delayed ack timer in progress.
500   *	- Our last ack wasn't a 0-sized window. We never want to delay
501   *	  the ack that opens up a 0-sized window.
502   *	- LRO wasn't used for this segment. We make sure by checking that the
503   *	  segment size is not larger than the MSS.
504   */
505  #define DELAY_ACK(tp, tlen)						\
506  	((!tcp_timer_active(tp, TT_DELACK) &&				\
507  	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
508  	    (tlen <= tp->t_maxseg) &&					\
509  	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
510  
511  void inline
512  cc_ecnpkt_handler_flags(struct tcpcb *tp, uint16_t flags, uint8_t iptos)
513  {
514  	INP_WLOCK_ASSERT(tptoinpcb(tp));
515  
516  	if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
517  		switch (iptos & IPTOS_ECN_MASK) {
518  		case IPTOS_ECN_CE:
519  			tp->t_ccv.flags |= CCF_IPHDR_CE;
520  			break;
521  		case IPTOS_ECN_ECT0:
522  			/* FALLTHROUGH */
523  		case IPTOS_ECN_ECT1:
524  			/* FALLTHROUGH */
525  		case IPTOS_ECN_NOTECT:
526  			tp->t_ccv.flags &= ~CCF_IPHDR_CE;
527  			break;
528  		}
529  
530  		if (flags & TH_CWR)
531  			tp->t_ccv.flags |= CCF_TCPHDR_CWR;
532  		else
533  			tp->t_ccv.flags &= ~CCF_TCPHDR_CWR;
534  
535  		CC_ALGO(tp)->ecnpkt_handler(&tp->t_ccv);
536  
537  		if (tp->t_ccv.flags & CCF_ACKNOW) {
538  			tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
539  			tp->t_flags |= TF_ACKNOW;
540  		}
541  	}
542  }
543  
544  void inline
545  cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
546  {
547  	cc_ecnpkt_handler_flags(tp, tcp_get_flags(th), iptos);
548  }
549  
550  /*
551   * TCP input handling is split into multiple parts:
552   *   tcp6_input is a thin wrapper around tcp_input for the extended
553   *	ip6_protox[] call format in ip6_input
554   *   tcp_input handles primary segment validation, inpcb lookup and
555   *	SYN processing on listen sockets
556   *   tcp_do_segment processes the ACK and text of the segment for
557   *	establishing, established and closing connections
558   */
559  #ifdef INET6
560  int
561  tcp6_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
562  {
563  	struct mbuf *m;
564  	struct in6_ifaddr *ia6;
565  	struct ip6_hdr *ip6;
566  
567  	m = *mp;
568  	if (m->m_len < *offp + sizeof(struct tcphdr)) {
569  		m = m_pullup(m, *offp + sizeof(struct tcphdr));
570  		if (m == NULL) {
571  			*mp = m;
572  			TCPSTAT_INC(tcps_rcvshort);
573  			return (IPPROTO_DONE);
574  		}
575  	}
576  
577  	/*
578  	 * draft-itojun-ipv6-tcp-to-anycast
579  	 * better place to put this in?
580  	 */
581  	ip6 = mtod(m, struct ip6_hdr *);
582  	ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
583  	if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
584  		icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
585  			    (caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
586  		*mp = NULL;
587  		return (IPPROTO_DONE);
588  	}
589  
590  	*mp = m;
591  	return (tcp_input_with_port(mp, offp, proto, port));
592  }
593  
594  int
595  tcp6_input(struct mbuf **mp, int *offp, int proto)
596  {
597  
598  	return(tcp6_input_with_port(mp, offp, proto, 0));
599  }
600  #endif /* INET6 */
601  
602  int
603  tcp_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
604  {
605  	struct mbuf *m = *mp;
606  	struct tcphdr *th = NULL;
607  	struct ip *ip = NULL;
608  	struct inpcb *inp = NULL;
609  	struct tcpcb *tp = NULL;
610  	struct socket *so = NULL;
611  	u_char *optp = NULL;
612  	int off0;
613  	int optlen = 0;
614  #ifdef INET
615  	int len;
616  	uint8_t ipttl;
617  #endif
618  	int tlen = 0, off;
619  	int drop_hdrlen;
620  	int thflags;
621  	int rstreason = 0;	/* For badport_bandlim accounting purposes */
622  	int lookupflag;
623  	uint8_t iptos;
624  	struct m_tag *fwd_tag = NULL;
625  #ifdef INET6
626  	struct ip6_hdr *ip6 = NULL;
627  	int isipv6;
628  #else
629  	const void *ip6 = NULL;
630  #endif /* INET6 */
631  	struct tcpopt to;		/* options in this segment */
632  	char *s = NULL;			/* address and port logging */
633  
634  	NET_EPOCH_ASSERT();
635  
636  #ifdef INET6
637  	isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
638  #endif
639  
640  	off0 = *offp;
641  	m = *mp;
642  	*mp = NULL;
643  	to.to_flags = 0;
644  	TCPSTAT_INC(tcps_rcvtotal);
645  
646  #ifdef INET6
647  	if (isipv6) {
648  		ip6 = mtod(m, struct ip6_hdr *);
649  		th = (struct tcphdr *)((caddr_t)ip6 + off0);
650  		tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
651  		if (port)
652  			goto skip6_csum;
653  		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
654  			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
655  				th->th_sum = m->m_pkthdr.csum_data;
656  			else
657  				th->th_sum = in6_cksum_pseudo(ip6, tlen,
658  				    IPPROTO_TCP, m->m_pkthdr.csum_data);
659  			th->th_sum ^= 0xffff;
660  		} else
661  			th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
662  		if (th->th_sum) {
663  			TCPSTAT_INC(tcps_rcvbadsum);
664  			goto drop;
665  		}
666  	skip6_csum:
667  		/*
668  		 * Be proactive about unspecified IPv6 address in source.
669  		 * As we use all-zero to indicate unbounded/unconnected pcb,
670  		 * unspecified IPv6 address can be used to confuse us.
671  		 *
672  		 * Note that packets with unspecified IPv6 destination is
673  		 * already dropped in ip6_input.
674  		 */
675  		KASSERT(!IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_dst),
676  		    ("%s: unspecified destination v6 address", __func__));
677  		if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
678  			/* XXX stat */
679  			goto drop;
680  		}
681  		iptos = IPV6_TRAFFIC_CLASS(ip6);
682  	}
683  #endif
684  #if defined(INET) && defined(INET6)
685  	else
686  #endif
687  #ifdef INET
688  	{
689  		/*
690  		 * Get IP and TCP header together in first mbuf.
691  		 * Note: IP leaves IP header in first mbuf.
692  		 */
693  		if (off0 > sizeof (struct ip)) {
694  			ip_stripoptions(m);
695  			off0 = sizeof(struct ip);
696  		}
697  		if (m->m_len < sizeof (struct tcpiphdr)) {
698  			if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
699  			    == NULL) {
700  				TCPSTAT_INC(tcps_rcvshort);
701  				return (IPPROTO_DONE);
702  			}
703  		}
704  		ip = mtod(m, struct ip *);
705  		th = (struct tcphdr *)((caddr_t)ip + off0);
706  		tlen = ntohs(ip->ip_len) - off0;
707  
708  		iptos = ip->ip_tos;
709  		if (port)
710  			goto skip_csum;
711  		if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
712  			if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
713  				th->th_sum = m->m_pkthdr.csum_data;
714  			else
715  				th->th_sum = in_pseudo(ip->ip_src.s_addr,
716  				    ip->ip_dst.s_addr,
717  				    htonl(m->m_pkthdr.csum_data + tlen +
718  				    IPPROTO_TCP));
719  			th->th_sum ^= 0xffff;
720  		} else {
721  			struct ipovly *ipov = (struct ipovly *)ip;
722  
723  			/*
724  			 * Checksum extended TCP header and data.
725  			 */
726  			len = off0 + tlen;
727  			ipttl = ip->ip_ttl;
728  			bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
729  			ipov->ih_len = htons(tlen);
730  			th->th_sum = in_cksum(m, len);
731  			/* Reset length for SDT probes. */
732  			ip->ip_len = htons(len);
733  			/* Reset TOS bits */
734  			ip->ip_tos = iptos;
735  			/* Re-initialization for later version check */
736  			ip->ip_ttl = ipttl;
737  			ip->ip_v = IPVERSION;
738  			ip->ip_hl = off0 >> 2;
739  		}
740  	skip_csum:
741  		if (th->th_sum && (port == 0)) {
742  			TCPSTAT_INC(tcps_rcvbadsum);
743  			goto drop;
744  		}
745  		KASSERT(ip->ip_dst.s_addr != INADDR_ANY,
746  		    ("%s: unspecified destination v4 address", __func__));
747  		if (__predict_false(ip->ip_src.s_addr == INADDR_ANY)) {
748  			/* XXX stat */
749  			goto drop;
750  		}
751  	}
752  #endif /* INET */
753  
754  	/*
755  	 * Check that TCP offset makes sense,
756  	 * pull out TCP options and adjust length.		XXX
757  	 */
758  	off = th->th_off << 2;
759  	if (off < sizeof (struct tcphdr) || off > tlen) {
760  		TCPSTAT_INC(tcps_rcvbadoff);
761  		goto drop;
762  	}
763  	tlen -= off;	/* tlen is used instead of ti->ti_len */
764  	if (off > sizeof (struct tcphdr)) {
765  #ifdef INET6
766  		if (isipv6) {
767  			if (m->m_len < off0 + off) {
768  				m = m_pullup(m, off0 + off);
769  				if (m == NULL) {
770  					TCPSTAT_INC(tcps_rcvshort);
771  					return (IPPROTO_DONE);
772  				}
773  			}
774  			ip6 = mtod(m, struct ip6_hdr *);
775  			th = (struct tcphdr *)((caddr_t)ip6 + off0);
776  		}
777  #endif
778  #if defined(INET) && defined(INET6)
779  		else
780  #endif
781  #ifdef INET
782  		{
783  			if (m->m_len < sizeof(struct ip) + off) {
784  				if ((m = m_pullup(m, sizeof (struct ip) + off))
785  				    == NULL) {
786  					TCPSTAT_INC(tcps_rcvshort);
787  					return (IPPROTO_DONE);
788  				}
789  				ip = mtod(m, struct ip *);
790  				th = (struct tcphdr *)((caddr_t)ip + off0);
791  			}
792  		}
793  #endif
794  		optlen = off - sizeof (struct tcphdr);
795  		optp = (u_char *)(th + 1);
796  	}
797  	thflags = tcp_get_flags(th);
798  
799  	/*
800  	 * Convert TCP protocol specific fields to host format.
801  	 */
802  	tcp_fields_to_host(th);
803  
804  	/*
805  	 * Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
806  	 */
807  	drop_hdrlen = off0 + off;
808  
809  	/*
810  	 * Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
811  	 */
812          if (
813  #ifdef INET6
814  	    (isipv6 && (m->m_flags & M_IP6_NEXTHOP))
815  #ifdef INET
816  	    || (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
817  #endif
818  #endif
819  #if defined(INET) && !defined(INET6)
820  	    (m->m_flags & M_IP_NEXTHOP)
821  #endif
822  	    )
823  		fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
824  
825  	/*
826  	 * For initial SYN packets we don't need write lock on matching
827  	 * PCB, be it a listening one or a synchronized one.  The packet
828  	 * shall not modify its state.
829  	 */
830  	lookupflag = INPLOOKUP_WILDCARD |
831  	    ((thflags & (TH_ACK|TH_SYN)) == TH_SYN ?
832  	    INPLOOKUP_RLOCKPCB : INPLOOKUP_WLOCKPCB);
833  findpcb:
834  #ifdef INET6
835  	if (isipv6 && fwd_tag != NULL) {
836  		struct sockaddr_in6 *next_hop6;
837  
838  		next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
839  		/*
840  		 * Transparently forwarded. Pretend to be the destination.
841  		 * Already got one like this?
842  		 */
843  		inp = in6_pcblookup_mbuf(&V_tcbinfo,
844  		    &ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
845  		    lookupflag & ~INPLOOKUP_WILDCARD, m->m_pkthdr.rcvif, m);
846  		if (!inp) {
847  			/*
848  			 * It's new.  Try to find the ambushing socket.
849  			 * Because we've rewritten the destination address,
850  			 * any hardware-generated hash is ignored.
851  			 */
852  			inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
853  			    th->th_sport, &next_hop6->sin6_addr,
854  			    next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
855  			    th->th_dport, lookupflag, m->m_pkthdr.rcvif);
856  		}
857  	} else if (isipv6) {
858  		inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
859  		    th->th_sport, &ip6->ip6_dst, th->th_dport, lookupflag,
860  		    m->m_pkthdr.rcvif, m);
861  	}
862  #endif /* INET6 */
863  #if defined(INET6) && defined(INET)
864  	else
865  #endif
866  #ifdef INET
867  	if (fwd_tag != NULL) {
868  		struct sockaddr_in *next_hop;
869  
870  		next_hop = (struct sockaddr_in *)(fwd_tag+1);
871  		/*
872  		 * Transparently forwarded. Pretend to be the destination.
873  		 * already got one like this?
874  		 */
875  		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
876  		    ip->ip_dst, th->th_dport, lookupflag & ~INPLOOKUP_WILDCARD,
877  		    m->m_pkthdr.rcvif, m);
878  		if (!inp) {
879  			/*
880  			 * It's new.  Try to find the ambushing socket.
881  			 * Because we've rewritten the destination address,
882  			 * any hardware-generated hash is ignored.
883  			 */
884  			inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
885  			    th->th_sport, next_hop->sin_addr,
886  			    next_hop->sin_port ? ntohs(next_hop->sin_port) :
887  			    th->th_dport, lookupflag, m->m_pkthdr.rcvif);
888  		}
889  	} else
890  		inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
891  		    th->th_sport, ip->ip_dst, th->th_dport, lookupflag,
892  		    m->m_pkthdr.rcvif, m);
893  #endif /* INET */
894  
895  	/*
896  	 * If the INPCB does not exist then all data in the incoming
897  	 * segment is discarded and an appropriate RST is sent back.
898  	 * XXX MRT Send RST using which routing table?
899  	 */
900  	if (inp == NULL) {
901  		if (rstreason != 0) {
902  			/* We came here after second (safety) lookup. */
903  			MPASS((lookupflag & INPLOOKUP_WILDCARD) == 0);
904  			goto dropwithreset;
905  		}
906  		/*
907  		 * Log communication attempts to ports that are not
908  		 * in use.
909  		 */
910  		if ((V_tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
911  		    V_tcp_log_in_vain == 2) {
912  			if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
913  				log(LOG_INFO, "%s; %s: Connection attempt "
914  				    "to closed port\n", s, __func__);
915  		}
916  		/*
917  		 * When blackholing do not respond with a RST but
918  		 * completely ignore the segment and drop it.
919  		 */
920  		if (((V_blackhole == 1 && (thflags & TH_SYN)) ||
921  		    V_blackhole == 2) && (V_blackhole_local || (
922  #ifdef INET6
923  		    isipv6 ? !in6_localaddr(&ip6->ip6_src) :
924  #endif
925  #ifdef INET
926  		    !in_localip(ip->ip_src)
927  #else
928  		    true
929  #endif
930  		    )))
931  			goto dropunlock;
932  
933  		rstreason = BANDLIM_RST_CLOSEDPORT;
934  		goto dropwithreset;
935  	}
936  	INP_LOCK_ASSERT(inp);
937  
938  	if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
939  	    (M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
940  	    !SOLISTENING(inp->inp_socket)) {
941  		inp->inp_flowid = m->m_pkthdr.flowid;
942  		inp->inp_flowtype = M_HASHTYPE_GET(m);
943  	}
944  #if defined(IPSEC) || defined(IPSEC_SUPPORT)
945  #ifdef INET6
946  	if (isipv6 && IPSEC_ENABLED(ipv6) &&
947  	    IPSEC_CHECK_POLICY(ipv6, m, inp) != 0) {
948  		goto dropunlock;
949  	}
950  #ifdef INET
951  	else
952  #endif
953  #endif /* INET6 */
954  #ifdef INET
955  	if (IPSEC_ENABLED(ipv4) &&
956  	    IPSEC_CHECK_POLICY(ipv4, m, inp) != 0) {
957  		goto dropunlock;
958  	}
959  #endif /* INET */
960  #endif /* IPSEC */
961  
962  	/*
963  	 * Check the minimum TTL for socket.
964  	 */
965  	if (inp->inp_ip_minttl != 0) {
966  #ifdef INET6
967  		if (isipv6) {
968  			if (inp->inp_ip_minttl > ip6->ip6_hlim)
969  				goto dropunlock;
970  		} else
971  #endif
972  		if (inp->inp_ip_minttl > ip->ip_ttl)
973  			goto dropunlock;
974  	}
975  
976  	tp = intotcpcb(inp);
977  	switch (tp->t_state) {
978  	case TCPS_TIME_WAIT:
979  		/*
980  		 * A previous connection in TIMEWAIT state is supposed to catch
981  		 * stray or duplicate segments arriving late.  If this segment
982  		 * was a legitimate new connection attempt, the old INPCB gets
983  		 * removed and we can try again to find a listening socket.
984  		 */
985  		tcp_dooptions(&to, optp, optlen,
986  		    (thflags & TH_SYN) ? TO_SYN : 0);
987  		/*
988  		 * tcp_twcheck unlocks the inp always, and frees the m if fails.
989  		 */
990  		if (tcp_twcheck(inp, &to, th, m, tlen))
991  			goto findpcb;
992  		return (IPPROTO_DONE);
993  	case TCPS_CLOSED:
994  		/*
995  		 * The TCPCB may no longer exist if the connection is winding
996  		 * down or it is in the CLOSED state.  Either way we drop the
997  		 * segment and send an appropriate response.
998  		 */
999  		rstreason = BANDLIM_RST_CLOSEDPORT;
1000  		goto dropwithreset;
1001  	}
1002  
1003  	if ((tp->t_port != port) && (tp->t_state > TCPS_LISTEN)) {
1004  		rstreason = BANDLIM_RST_CLOSEDPORT;
1005  		goto dropwithreset;
1006  	}
1007  
1008  #ifdef TCP_OFFLOAD
1009  	if (tp->t_flags & TF_TOE) {
1010  		tcp_offload_input(tp, m);
1011  		m = NULL;	/* consumed by the TOE driver */
1012  		goto dropunlock;
1013  	}
1014  #endif
1015  
1016  #ifdef MAC
1017  	if (mac_inpcb_check_deliver(inp, m))
1018  		goto dropunlock;
1019  #endif
1020  	so = inp->inp_socket;
1021  	KASSERT(so != NULL, ("%s: so == NULL", __func__));
1022  	/*
1023  	 * When the socket is accepting connections (the INPCB is in LISTEN
1024  	 * state) we look into the SYN cache if this is a new connection
1025  	 * attempt or the completion of a previous one.
1026  	 */
1027  	KASSERT(tp->t_state == TCPS_LISTEN || !SOLISTENING(so),
1028  	    ("%s: so accepting but tp %p not listening", __func__, tp));
1029  	if (tp->t_state == TCPS_LISTEN && SOLISTENING(so)) {
1030  		struct in_conninfo inc;
1031  
1032  		bzero(&inc, sizeof(inc));
1033  #ifdef INET6
1034  		if (isipv6) {
1035  			inc.inc_flags |= INC_ISIPV6;
1036  			if (inp->inp_inc.inc_flags & INC_IPV6MINMTU)
1037  				inc.inc_flags |= INC_IPV6MINMTU;
1038  			inc.inc6_faddr = ip6->ip6_src;
1039  			inc.inc6_laddr = ip6->ip6_dst;
1040  		} else
1041  #endif
1042  		{
1043  			inc.inc_faddr = ip->ip_src;
1044  			inc.inc_laddr = ip->ip_dst;
1045  		}
1046  		inc.inc_fport = th->th_sport;
1047  		inc.inc_lport = th->th_dport;
1048  		inc.inc_fibnum = so->so_fibnum;
1049  
1050  		/*
1051  		 * Check for an existing connection attempt in syncache if
1052  		 * the flag is only ACK.  A successful lookup creates a new
1053  		 * socket appended to the listen queue in SYN_RECEIVED state.
1054  		 */
1055  		if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
1056  			/*
1057  			 * Parse the TCP options here because
1058  			 * syncookies need access to the reflected
1059  			 * timestamp.
1060  			 */
1061  			tcp_dooptions(&to, optp, optlen, 0);
1062  			/*
1063  			 * NB: syncache_expand() doesn't unlock inp.
1064  			 */
1065  			rstreason = syncache_expand(&inc, &to, th, &so, m, port);
1066  			if (rstreason < 0) {
1067  				/*
1068  				 * A failing TCP MD5 signature comparison
1069  				 * must result in the segment being dropped
1070  				 * and must not produce any response back
1071  				 * to the sender.
1072  				 */
1073  				goto dropunlock;
1074  			} else if (rstreason == 0) {
1075  				/*
1076  				 * No syncache entry, or ACK was not for our
1077  				 * SYN/ACK.  Do our protection against double
1078  				 * ACK.  If peer sent us 2 ACKs, then for the
1079  				 * first one syncache_expand() successfully
1080  				 * converted syncache entry into a socket,
1081  				 * while we were waiting on the inpcb lock.  We
1082  				 * don't want to sent RST for the second ACK,
1083  				 * so we perform second lookup without wildcard
1084  				 * match, hoping to find the new socket.  If
1085  				 * the ACK is stray indeed, rstreason would
1086  				 * hint the above code that the lookup was a
1087  				 * second attempt.
1088  				 *
1089  				 * NB: syncache did its own logging
1090  				 * of the failure cause.
1091  				 */
1092  				INP_WUNLOCK(inp);
1093  				rstreason = BANDLIM_RST_OPENPORT;
1094  				lookupflag &= ~INPLOOKUP_WILDCARD;
1095  				goto findpcb;
1096  			}
1097  tfo_socket_result:
1098  			if (so == NULL) {
1099  				/*
1100  				 * We completed the 3-way handshake
1101  				 * but could not allocate a socket
1102  				 * either due to memory shortage,
1103  				 * listen queue length limits or
1104  				 * global socket limits.  Send RST
1105  				 * or wait and have the remote end
1106  				 * retransmit the ACK for another
1107  				 * try.
1108  				 */
1109  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1110  					log(LOG_DEBUG, "%s; %s: Listen socket: "
1111  					    "Socket allocation failed due to "
1112  					    "limits or memory shortage, %s\n",
1113  					    s, __func__,
1114  					    V_tcp_sc_rst_sock_fail ?
1115  					    "sending RST" : "try again");
1116  				if (V_tcp_sc_rst_sock_fail) {
1117  					rstreason = BANDLIM_UNLIMITED;
1118  					goto dropwithreset;
1119  				} else
1120  					goto dropunlock;
1121  			}
1122  			/*
1123  			 * Socket is created in state SYN_RECEIVED.
1124  			 * Unlock the listen socket, lock the newly
1125  			 * created socket and update the tp variable.
1126  			 * If we came here via jump to tfo_socket_result,
1127  			 * then listening socket is read-locked.
1128  			 */
1129  			INP_UNLOCK(inp);	/* listen socket */
1130  			inp = sotoinpcb(so);
1131  			/*
1132  			 * New connection inpcb is already locked by
1133  			 * syncache_expand().
1134  			 */
1135  			INP_WLOCK_ASSERT(inp);
1136  			tp = intotcpcb(inp);
1137  			KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
1138  			    ("%s: ", __func__));
1139  			/*
1140  			 * Process the segment and the data it
1141  			 * contains.  tcp_do_segment() consumes
1142  			 * the mbuf chain and unlocks the inpcb.
1143  			 */
1144  			TCP_PROBE5(receive, NULL, tp, m, tp, th);
1145  			tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
1146  			    iptos);
1147  			return (IPPROTO_DONE);
1148  		}
1149  		/*
1150  		 * Segment flag validation for new connection attempts:
1151  		 *
1152  		 * Our (SYN|ACK) response was rejected.
1153  		 * Check with syncache and remove entry to prevent
1154  		 * retransmits.
1155  		 *
1156  		 * NB: syncache_chkrst does its own logging of failure
1157  		 * causes.
1158  		 */
1159  		if (thflags & TH_RST) {
1160  			syncache_chkrst(&inc, th, m, port);
1161  			goto dropunlock;
1162  		}
1163  		/*
1164  		 * We can't do anything without SYN.
1165  		 */
1166  		if ((thflags & TH_SYN) == 0) {
1167  			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1168  				log(LOG_DEBUG, "%s; %s: Listen socket: "
1169  				    "SYN is missing, segment ignored\n",
1170  				    s, __func__);
1171  			TCPSTAT_INC(tcps_badsyn);
1172  			goto dropunlock;
1173  		}
1174  		/*
1175  		 * (SYN|ACK) is bogus on a listen socket.
1176  		 */
1177  		if (thflags & TH_ACK) {
1178  			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1179  				log(LOG_DEBUG, "%s; %s: Listen socket: "
1180  				    "SYN|ACK invalid, segment rejected\n",
1181  				    s, __func__);
1182  			syncache_badack(&inc, port);	/* XXX: Not needed! */
1183  			TCPSTAT_INC(tcps_badsyn);
1184  			rstreason = BANDLIM_RST_OPENPORT;
1185  			goto dropwithreset;
1186  		}
1187  		/*
1188  		 * If the drop_synfin option is enabled, drop all
1189  		 * segments with both the SYN and FIN bits set.
1190  		 * This prevents e.g. nmap from identifying the
1191  		 * TCP/IP stack.
1192  		 * XXX: Poor reasoning.  nmap has other methods
1193  		 * and is constantly refining its stack detection
1194  		 * strategies.
1195  		 * XXX: This is a violation of the TCP specification
1196  		 * and was used by RFC1644.
1197  		 */
1198  		if ((thflags & TH_FIN) && V_drop_synfin) {
1199  			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1200  				log(LOG_DEBUG, "%s; %s: Listen socket: "
1201  				    "SYN|FIN segment ignored (based on "
1202  				    "sysctl setting)\n", s, __func__);
1203  			TCPSTAT_INC(tcps_badsyn);
1204  			goto dropunlock;
1205  		}
1206  		/*
1207  		 * Segment's flags are (SYN) or (SYN|FIN).
1208  		 *
1209  		 * TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
1210  		 * as they do not affect the state of the TCP FSM.
1211  		 * The data pointed to by TH_URG and th_urp is ignored.
1212  		 */
1213  		KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
1214  		    ("%s: Listen socket: TH_RST or TH_ACK set", __func__));
1215  		KASSERT(thflags & (TH_SYN),
1216  		    ("%s: Listen socket: TH_SYN not set", __func__));
1217  		INP_RLOCK_ASSERT(inp);
1218  #ifdef INET6
1219  		/*
1220  		 * If deprecated address is forbidden,
1221  		 * we do not accept SYN to deprecated interface
1222  		 * address to prevent any new inbound connection from
1223  		 * getting established.
1224  		 * When we do not accept SYN, we send a TCP RST,
1225  		 * with deprecated source address (instead of dropping
1226  		 * it).  We compromise it as it is much better for peer
1227  		 * to send a RST, and RST will be the final packet
1228  		 * for the exchange.
1229  		 *
1230  		 * If we do not forbid deprecated addresses, we accept
1231  		 * the SYN packet.  RFC2462 does not suggest dropping
1232  		 * SYN in this case.
1233  		 * If we decipher RFC2462 5.5.4, it says like this:
1234  		 * 1. use of deprecated addr with existing
1235  		 *    communication is okay - "SHOULD continue to be
1236  		 *    used"
1237  		 * 2. use of it with new communication:
1238  		 *   (2a) "SHOULD NOT be used if alternate address
1239  		 *        with sufficient scope is available"
1240  		 *   (2b) nothing mentioned otherwise.
1241  		 * Here we fall into (2b) case as we have no choice in
1242  		 * our source address selection - we must obey the peer.
1243  		 *
1244  		 * The wording in RFC2462 is confusing, and there are
1245  		 * multiple description text for deprecated address
1246  		 * handling - worse, they are not exactly the same.
1247  		 * I believe 5.5.4 is the best one, so we follow 5.5.4.
1248  		 */
1249  		if (isipv6 && !V_ip6_use_deprecated) {
1250  			struct in6_ifaddr *ia6;
1251  
1252  			ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
1253  			if (ia6 != NULL &&
1254  			    (ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
1255  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1256  				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1257  					"Connection attempt to deprecated "
1258  					"IPv6 address rejected\n",
1259  					s, __func__);
1260  				rstreason = BANDLIM_RST_OPENPORT;
1261  				goto dropwithreset;
1262  			}
1263  		}
1264  #endif /* INET6 */
1265  		/*
1266  		 * Basic sanity checks on incoming SYN requests:
1267  		 *   Don't respond if the destination is a link layer
1268  		 *	broadcast according to RFC1122 4.2.3.10, p. 104.
1269  		 *   If it is from this socket it must be forged.
1270  		 *   Don't respond if the source or destination is a
1271  		 *	global or subnet broad- or multicast address.
1272  		 *   Note that it is quite possible to receive unicast
1273  		 *	link-layer packets with a broadcast IP address. Use
1274  		 *	in_broadcast() to find them.
1275  		 */
1276  		if (m->m_flags & (M_BCAST|M_MCAST)) {
1277  			if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1278  			    log(LOG_DEBUG, "%s; %s: Listen socket: "
1279  				"Connection attempt from broad- or multicast "
1280  				"link layer address ignored\n", s, __func__);
1281  			goto dropunlock;
1282  		}
1283  #ifdef INET6
1284  		if (isipv6) {
1285  			if (th->th_dport == th->th_sport &&
1286  			    IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
1287  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1288  				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1289  					"Connection attempt to/from self "
1290  					"ignored\n", s, __func__);
1291  				goto dropunlock;
1292  			}
1293  			if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
1294  			    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
1295  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1296  				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1297  					"Connection attempt from/to multicast "
1298  					"address ignored\n", s, __func__);
1299  				goto dropunlock;
1300  			}
1301  		}
1302  #endif
1303  #if defined(INET) && defined(INET6)
1304  		else
1305  #endif
1306  #ifdef INET
1307  		{
1308  			if (th->th_dport == th->th_sport &&
1309  			    ip->ip_dst.s_addr == ip->ip_src.s_addr) {
1310  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1311  				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1312  					"Connection attempt from/to self "
1313  					"ignored\n", s, __func__);
1314  				goto dropunlock;
1315  			}
1316  			if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
1317  			    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
1318  			    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
1319  			    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
1320  				if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
1321  				    log(LOG_DEBUG, "%s; %s: Listen socket: "
1322  					"Connection attempt from/to broad- "
1323  					"or multicast address ignored\n",
1324  					s, __func__);
1325  				goto dropunlock;
1326  			}
1327  		}
1328  #endif
1329  		/*
1330  		 * SYN appears to be valid.  Create compressed TCP state
1331  		 * for syncache.
1332  		 */
1333  		TCP_PROBE3(debug__input, tp, th, m);
1334  		tcp_dooptions(&to, optp, optlen, TO_SYN);
1335  		if ((so = syncache_add(&inc, &to, th, inp, so, m, NULL, NULL,
1336  		    iptos, port)) != NULL)
1337  			goto tfo_socket_result;
1338  
1339  		/*
1340  		 * Entry added to syncache and mbuf consumed.
1341  		 * Only the listen socket is unlocked by syncache_add().
1342  		 */
1343  		return (IPPROTO_DONE);
1344  	} else if (tp->t_state == TCPS_LISTEN) {
1345  		/*
1346  		 * When a listen socket is torn down the SO_ACCEPTCONN
1347  		 * flag is removed first while connections are drained
1348  		 * from the accept queue in a unlock/lock cycle of the
1349  		 * ACCEPT_LOCK, opening a race condition allowing a SYN
1350  		 * attempt go through unhandled.
1351  		 */
1352  		goto dropunlock;
1353  	}
1354  #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1355  	if (tp->t_flags & TF_SIGNATURE) {
1356  		tcp_dooptions(&to, optp, optlen, thflags);
1357  		if ((to.to_flags & TOF_SIGNATURE) == 0) {
1358  			TCPSTAT_INC(tcps_sig_err_nosigopt);
1359  			goto dropunlock;
1360  		}
1361  		if (!TCPMD5_ENABLED() ||
1362  		    TCPMD5_INPUT(m, th, to.to_signature) != 0)
1363  			goto dropunlock;
1364  	}
1365  #endif
1366  	TCP_PROBE5(receive, NULL, tp, m, tp, th);
1367  
1368  	/*
1369  	 * Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
1370  	 * state.  tcp_do_segment() always consumes the mbuf chain, unlocks
1371  	 * the inpcb, and unlocks pcbinfo.
1372  	 *
1373  	 * XXXGL: in case of a pure SYN arriving on existing connection
1374  	 * TCP stacks won't need to modify the PCB, they would either drop
1375  	 * the segment silently, or send a challenge ACK.  However, we try
1376  	 * to upgrade the lock, because calling convention for stacks is
1377  	 * write-lock on PCB.  If upgrade fails, drop the SYN.
1378  	 */
1379  	if ((lookupflag & INPLOOKUP_RLOCKPCB) && INP_TRY_UPGRADE(inp) == 0)
1380  		goto dropunlock;
1381  
1382  	tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos);
1383  	return (IPPROTO_DONE);
1384  
1385  dropwithreset:
1386  	TCP_PROBE5(receive, NULL, tp, m, tp, th);
1387  
1388  	if (inp != NULL) {
1389  		tcp_dropwithreset(m, th, tp, tlen, rstreason);
1390  		INP_UNLOCK(inp);
1391  	} else
1392  		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
1393  	m = NULL;	/* mbuf chain got consumed. */
1394  	goto drop;
1395  
1396  dropunlock:
1397  	if (m != NULL)
1398  		TCP_PROBE5(receive, NULL, tp, m, tp, th);
1399  
1400  	if (inp != NULL)
1401  		INP_UNLOCK(inp);
1402  
1403  drop:
1404  	if (s != NULL)
1405  		free(s, M_TCPLOG);
1406  	if (m != NULL)
1407  		m_freem(m);
1408  	return (IPPROTO_DONE);
1409  }
1410  
1411  /*
1412   * Automatic sizing of receive socket buffer.  Often the send
1413   * buffer size is not optimally adjusted to the actual network
1414   * conditions at hand (delay bandwidth product).  Setting the
1415   * buffer size too small limits throughput on links with high
1416   * bandwidth and high delay (eg. trans-continental/oceanic links).
1417   *
1418   * On the receive side the socket buffer memory is only rarely
1419   * used to any significant extent.  This allows us to be much
1420   * more aggressive in scaling the receive socket buffer.  For
1421   * the case that the buffer space is actually used to a large
1422   * extent and we run out of kernel memory we can simply drop
1423   * the new segments; TCP on the sender will just retransmit it
1424   * later.  Setting the buffer size too big may only consume too
1425   * much kernel memory if the application doesn't read() from
1426   * the socket or packet loss or reordering makes use of the
1427   * reassembly queue.
1428   *
1429   * The criteria to step up the receive buffer one notch are:
1430   *  1. Application has not set receive buffer size with
1431   *     SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
1432   *  2. the number of bytes received during 1/2 of an sRTT
1433   *     is at least 3/8 of the current socket buffer size.
1434   *  3. receive buffer size has not hit maximal automatic size;
1435   *
1436   * If all of the criteria are met we increaset the socket buffer
1437   * by a 1/2 (bounded by the max). This allows us to keep ahead
1438   * of slow-start but also makes it so our peer never gets limited
1439   * by our rwnd which we then open up causing a burst.
1440   *
1441   * This algorithm does two steps per RTT at most and only if
1442   * we receive a bulk stream w/o packet losses or reorderings.
1443   * Shrinking the buffer during idle times is not necessary as
1444   * it doesn't consume any memory when idle.
1445   *
1446   * TODO: Only step up if the application is actually serving
1447   * the buffer to better manage the socket buffer resources.
1448   */
1449  int
1450  tcp_autorcvbuf(struct mbuf *m, struct tcphdr *th, struct socket *so,
1451      struct tcpcb *tp, int tlen)
1452  {
1453  	int newsize = 0;
1454  
1455  	if (V_tcp_do_autorcvbuf && (so->so_rcv.sb_flags & SB_AUTOSIZE) &&
1456  	    tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
1457  	    TCP_TS_TO_TICKS(tcp_ts_getticks() - tp->rfbuf_ts) >
1458  	    ((tp->t_srtt >> TCP_RTT_SHIFT)/2)) {
1459  		if (tp->rfbuf_cnt > ((so->so_rcv.sb_hiwat / 2)/ 4 * 3) &&
1460  		    so->so_rcv.sb_hiwat < V_tcp_autorcvbuf_max) {
1461  			newsize = min((so->so_rcv.sb_hiwat + (so->so_rcv.sb_hiwat/2)), V_tcp_autorcvbuf_max);
1462  		}
1463  		TCP_PROBE6(receive__autoresize, NULL, tp, m, tp, th, newsize);
1464  
1465  		/* Start over with next RTT. */
1466  		tp->rfbuf_ts = 0;
1467  		tp->rfbuf_cnt = 0;
1468  	} else {
1469  		tp->rfbuf_cnt += tlen;	/* add up */
1470  	}
1471  	return (newsize);
1472  }
1473  
1474  int
1475  tcp_input(struct mbuf **mp, int *offp, int proto)
1476  {
1477  	return(tcp_input_with_port(mp, offp, proto, 0));
1478  }
1479  
1480  static void
1481  tcp_handle_wakeup(struct tcpcb *tp)
1482  {
1483  
1484  	INP_WLOCK_ASSERT(tptoinpcb(tp));
1485  
1486  	if (tp->t_flags & TF_WAKESOR) {
1487  		struct socket *so = tptosocket(tp);
1488  
1489  		tp->t_flags &= ~TF_WAKESOR;
1490  		SOCKBUF_LOCK_ASSERT(&so->so_rcv);
1491  		sorwakeup_locked(so);
1492  	}
1493  }
1494  
1495  void
1496  tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
1497      struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
1498  {
1499  	uint16_t thflags;
1500  	int acked, ourfinisacked, needoutput = 0, sack_changed;
1501  	int rstreason, todrop, win, incforsyn = 0;
1502  	uint32_t tiwin;
1503  	uint16_t nsegs;
1504  	char *s;
1505  	struct inpcb *inp = tptoinpcb(tp);
1506  	struct in_conninfo *inc = &inp->inp_inc;
1507  	struct mbuf *mfree;
1508  	struct tcpopt to;
1509  	int tfo_syn;
1510  	u_int maxseg;
1511  
1512  	thflags = tcp_get_flags(th);
1513  	tp->sackhint.last_sack_ack = 0;
1514  	sack_changed = 0;
1515  	nsegs = max(1, m->m_pkthdr.lro_nsegs);
1516  
1517  	NET_EPOCH_ASSERT();
1518  	INP_WLOCK_ASSERT(inp);
1519  	KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
1520  	    __func__));
1521  	KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
1522  	    __func__));
1523  
1524  #ifdef TCPPCAP
1525  	/* Save segment, if requested. */
1526  	tcp_pcap_add(th, m, &(tp->t_inpkts));
1527  #endif
1528  	TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
1529  	    tlen, NULL, true);
1530  
1531  	if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
1532  		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1533  			log(LOG_DEBUG, "%s; %s: "
1534  			    "SYN|FIN segment ignored (based on "
1535  			    "sysctl setting)\n", s, __func__);
1536  			free(s, M_TCPLOG);
1537  		}
1538  		goto drop;
1539  	}
1540  
1541  	/*
1542  	 * If a segment with the ACK-bit set arrives in the SYN-SENT state
1543  	 * check SEQ.ACK first.
1544  	 */
1545  	if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
1546  	    (SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
1547  		rstreason = BANDLIM_UNLIMITED;
1548  		tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
1549  		goto dropwithreset;
1550  	}
1551  
1552  	/*
1553  	 * Segment received on connection.
1554  	 * Reset idle time and keep-alive timer.
1555  	 * XXX: This should be done after segment
1556  	 * validation to ignore broken/spoofed segs.
1557  	 */
1558  	if  (tp->t_idle_reduce &&
1559  	     (tp->snd_max == tp->snd_una) &&
1560  	     ((ticks - tp->t_rcvtime) >= tp->t_rxtcur))
1561  		cc_after_idle(tp);
1562  	tp->t_rcvtime = ticks;
1563  
1564  	if (thflags & TH_FIN)
1565  		tcp_log_end_status(tp, TCP_EI_STATUS_CLIENT_FIN);
1566  	/*
1567  	 * Scale up the window into a 32-bit value.
1568  	 * For the SYN_SENT state the scale is zero.
1569  	 */
1570  	tiwin = th->th_win << tp->snd_scale;
1571  #ifdef STATS
1572  	stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_FRWIN, tiwin);
1573  #endif
1574  
1575  	/*
1576  	 * TCP ECN processing.
1577  	 */
1578  	if (tcp_ecn_input_segment(tp, thflags, tlen,
1579  	    tcp_packets_this_ack(tp, th->th_ack),
1580  	    iptos))
1581  		cc_cong_signal(tp, th, CC_ECN);
1582  
1583  	/*
1584  	 * Parse options on any incoming segment.
1585  	 */
1586  	tcp_dooptions(&to, (u_char *)(th + 1),
1587  	    (th->th_off << 2) - sizeof(struct tcphdr),
1588  	    (thflags & TH_SYN) ? TO_SYN : 0);
1589  
1590  #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1591  	if ((tp->t_flags & TF_SIGNATURE) != 0 &&
1592  	    (to.to_flags & TOF_SIGNATURE) == 0) {
1593  		TCPSTAT_INC(tcps_sig_err_sigopt);
1594  		/* XXX: should drop? */
1595  	}
1596  #endif
1597  	/*
1598  	 * If echoed timestamp is later than the current time,
1599  	 * fall back to non RFC1323 RTT calculation.  Normalize
1600  	 * timestamp if syncookies were used when this connection
1601  	 * was established.
1602  	 */
1603  	if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
1604  		to.to_tsecr -= tp->ts_offset;
1605  		if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
1606  			to.to_tsecr = 0;
1607  		else if (tp->t_rxtshift == 1 &&
1608  			 tp->t_flags & TF_PREVVALID &&
1609  			 tp->t_badrxtwin != 0 &&
1610  			 TSTMP_LT(to.to_tsecr, tp->t_badrxtwin))
1611  			cc_cong_signal(tp, th, CC_RTO_ERR);
1612  	}
1613  	/*
1614  	 * Process options only when we get SYN/ACK back. The SYN case
1615  	 * for incoming connections is handled in tcp_syncache.
1616  	 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1617  	 * or <SYN,ACK>) segment itself is never scaled.
1618  	 * XXX this is traditional behavior, may need to be cleaned up.
1619  	 */
1620  	if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
1621  		/* Handle parallel SYN for ECN */
1622  		tcp_ecn_input_parallel_syn(tp, thflags, iptos);
1623  		if ((to.to_flags & TOF_SCALE) &&
1624  		    (tp->t_flags & TF_REQ_SCALE) &&
1625  		    !(tp->t_flags & TF_NOOPT)) {
1626  			tp->t_flags |= TF_RCVD_SCALE;
1627  			tp->snd_scale = to.to_wscale;
1628  		} else
1629  			tp->t_flags &= ~TF_REQ_SCALE;
1630  		/*
1631  		 * Initial send window.  It will be updated with
1632  		 * the next incoming segment to the scaled value.
1633  		 */
1634  		tp->snd_wnd = th->th_win;
1635  		if ((to.to_flags & TOF_TS) &&
1636  		    (tp->t_flags & TF_REQ_TSTMP) &&
1637  		    !(tp->t_flags & TF_NOOPT)) {
1638  			tp->t_flags |= TF_RCVD_TSTMP;
1639  			tp->ts_recent = to.to_tsval;
1640  			tp->ts_recent_age = tcp_ts_getticks();
1641  		} else
1642  			tp->t_flags &= ~TF_REQ_TSTMP;
1643  		if (to.to_flags & TOF_MSS)
1644  			tcp_mss(tp, to.to_mss);
1645  		if ((tp->t_flags & TF_SACK_PERMIT) &&
1646  		    (!(to.to_flags & TOF_SACKPERM) ||
1647  		    (tp->t_flags & TF_NOOPT)))
1648  			tp->t_flags &= ~TF_SACK_PERMIT;
1649  		if (IS_FASTOPEN(tp->t_flags)) {
1650  			if ((to.to_flags & TOF_FASTOPEN) &&
1651  			    !(tp->t_flags & TF_NOOPT)) {
1652  				uint16_t mss;
1653  
1654  				if (to.to_flags & TOF_MSS)
1655  					mss = to.to_mss;
1656  				else
1657  					if ((inp->inp_vflag & INP_IPV6) != 0)
1658  						mss = TCP6_MSS;
1659  					else
1660  						mss = TCP_MSS;
1661  				tcp_fastopen_update_cache(tp, mss,
1662  				    to.to_tfo_len, to.to_tfo_cookie);
1663  			} else
1664  				tcp_fastopen_disable_path(tp);
1665  		}
1666  	}
1667  
1668  	/*
1669  	 * If timestamps were negotiated during SYN/ACK and a
1670  	 * segment without a timestamp is received, silently drop
1671  	 * the segment, unless it is a RST segment or missing timestamps are
1672  	 * tolerated.
1673  	 * See section 3.2 of RFC 7323.
1674  	 */
1675  	if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
1676  		if (((thflags & TH_RST) != 0) || V_tcp_tolerate_missing_ts) {
1677  			if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1678  				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1679  				    "segment processed normally\n",
1680  				    s, __func__);
1681  				free(s, M_TCPLOG);
1682  			}
1683  		} else {
1684  			if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1685  				log(LOG_DEBUG, "%s; %s: Timestamp missing, "
1686  				    "segment silently dropped\n", s, __func__);
1687  				free(s, M_TCPLOG);
1688  			}
1689  			goto drop;
1690  		}
1691  	}
1692  	/*
1693  	 * If timestamps were not negotiated during SYN/ACK and a
1694  	 * segment with a timestamp is received, ignore the
1695  	 * timestamp and process the packet normally.
1696  	 * See section 3.2 of RFC 7323.
1697  	 */
1698  	if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
1699  		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
1700  			log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
1701  			    "segment processed normally\n", s, __func__);
1702  			free(s, M_TCPLOG);
1703  		}
1704  	}
1705  
1706  	/*
1707  	 * Header prediction: check for the two common cases
1708  	 * of a uni-directional data xfer.  If the packet has
1709  	 * no control flags, is in-sequence, the window didn't
1710  	 * change and we're not retransmitting, it's a
1711  	 * candidate.  If the length is zero and the ack moved
1712  	 * forward, we're the sender side of the xfer.  Just
1713  	 * free the data acked & wake any higher level process
1714  	 * that was blocked waiting for space.  If the length
1715  	 * is non-zero and the ack didn't move, we're the
1716  	 * receiver side.  If we're getting packets in-order
1717  	 * (the reassembly queue is empty), add the data to
1718  	 * the socket buffer and note that we need a delayed ack.
1719  	 * Make sure that the hidden state-flags are also off.
1720  	 * Since we check for TCPS_ESTABLISHED first, it can only
1721  	 * be TH_NEEDSYN.
1722  	 */
1723  	if (tp->t_state == TCPS_ESTABLISHED &&
1724  	    th->th_seq == tp->rcv_nxt &&
1725  	    (thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
1726  	    tp->snd_nxt == tp->snd_max &&
1727  	    tiwin && tiwin == tp->snd_wnd &&
1728  	    ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
1729  	    SEGQ_EMPTY(tp) &&
1730  	    ((to.to_flags & TOF_TS) == 0 ||
1731  	     TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
1732  		/*
1733  		 * If last ACK falls within this segment's sequence numbers,
1734  		 * record the timestamp.
1735  		 * NOTE that the test is modified according to the latest
1736  		 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
1737  		 */
1738  		if ((to.to_flags & TOF_TS) != 0 &&
1739  		    SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
1740  			tp->ts_recent_age = tcp_ts_getticks();
1741  			tp->ts_recent = to.to_tsval;
1742  		}
1743  
1744  		if (tlen == 0) {
1745  			if (SEQ_GT(th->th_ack, tp->snd_una) &&
1746  			    SEQ_LEQ(th->th_ack, tp->snd_max) &&
1747  			    !IN_RECOVERY(tp->t_flags) &&
1748  			    (to.to_flags & TOF_SACK) == 0 &&
1749  			    TAILQ_EMPTY(&tp->snd_holes)) {
1750  				/*
1751  				 * This is a pure ack for outstanding data.
1752  				 */
1753  				TCPSTAT_INC(tcps_predack);
1754  
1755  				/*
1756  				 * "bad retransmit" recovery without timestamps.
1757  				 */
1758  				if ((to.to_flags & TOF_TS) == 0 &&
1759  				    tp->t_rxtshift == 1 &&
1760  				    tp->t_flags & TF_PREVVALID &&
1761  				    tp->t_badrxtwin != 0 &&
1762  				    TSTMP_LT(ticks, tp->t_badrxtwin)) {
1763  					cc_cong_signal(tp, th, CC_RTO_ERR);
1764  				}
1765  
1766  				/*
1767  				 * Recalculate the transmit timer / rtt.
1768  				 *
1769  				 * Some boxes send broken timestamp replies
1770  				 * during the SYN+ACK phase, ignore
1771  				 * timestamps of 0 or we could calculate a
1772  				 * huge RTT and blow up the retransmit timer.
1773  				 */
1774  				if ((to.to_flags & TOF_TS) != 0 &&
1775  				    to.to_tsecr) {
1776  					uint32_t t;
1777  
1778  					t = tcp_ts_getticks() - to.to_tsecr;
1779  					if (!tp->t_rttlow || tp->t_rttlow > t)
1780  						tp->t_rttlow = t;
1781  					tcp_xmit_timer(tp,
1782  					    TCP_TS_TO_TICKS(t) + 1);
1783  				} else if (tp->t_rtttime &&
1784  				    SEQ_GT(th->th_ack, tp->t_rtseq)) {
1785  					if (!tp->t_rttlow ||
1786  					    tp->t_rttlow > ticks - tp->t_rtttime)
1787  						tp->t_rttlow = ticks - tp->t_rtttime;
1788  					tcp_xmit_timer(tp,
1789  							ticks - tp->t_rtttime);
1790  				}
1791  				acked = BYTES_THIS_ACK(tp, th);
1792  
1793  #ifdef TCP_HHOOK
1794  				/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
1795  				hhook_run_tcp_est_in(tp, th, &to);
1796  #endif
1797  
1798  				TCPSTAT_ADD(tcps_rcvackpack, nsegs);
1799  				TCPSTAT_ADD(tcps_rcvackbyte, acked);
1800  				sbdrop(&so->so_snd, acked);
1801  				if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
1802  				    SEQ_LEQ(th->th_ack, tp->snd_recover))
1803  					tp->snd_recover = th->th_ack - 1;
1804  
1805  				/*
1806  				 * Let the congestion control algorithm update
1807  				 * congestion control related information. This
1808  				 * typically means increasing the congestion
1809  				 * window.
1810  				 */
1811  				cc_ack_received(tp, th, nsegs, CC_ACK);
1812  
1813  				tp->snd_una = th->th_ack;
1814  				/*
1815  				 * Pull snd_wl2 up to prevent seq wrap relative
1816  				 * to th_ack.
1817  				 */
1818  				tp->snd_wl2 = th->th_ack;
1819  				tp->t_dupacks = 0;
1820  				m_freem(m);
1821  
1822  				/*
1823  				 * If all outstanding data are acked, stop
1824  				 * retransmit timer, otherwise restart timer
1825  				 * using current (possibly backed-off) value.
1826  				 * If process is waiting for space,
1827  				 * wakeup/selwakeup/signal.  If data
1828  				 * are ready to send, let tcp_output
1829  				 * decide between more output or persist.
1830  				 */
1831  				TCP_PROBE3(debug__input, tp, th, m);
1832  				/*
1833  				 * Clear t_acktime if remote side has ACKd
1834  				 * all data in the socket buffer.
1835  				 * Otherwise, update t_acktime if we received
1836  				 * a sufficiently large ACK.
1837  				 */
1838  				if (sbavail(&so->so_snd) == 0)
1839  					tp->t_acktime = 0;
1840  				else if (acked > 1)
1841  					tp->t_acktime = ticks;
1842  				if (tp->snd_una == tp->snd_max)
1843  					tcp_timer_activate(tp, TT_REXMT, 0);
1844  				else if (!tcp_timer_active(tp, TT_PERSIST))
1845  					tcp_timer_activate(tp, TT_REXMT,
1846  					    TP_RXTCUR(tp));
1847  				sowwakeup(so);
1848  				if (sbavail(&so->so_snd))
1849  					(void) tcp_output(tp);
1850  				goto check_delack;
1851  			}
1852  		} else if (th->th_ack == tp->snd_una &&
1853  		    tlen <= sbspace(&so->so_rcv)) {
1854  			int newsize = 0;	/* automatic sockbuf scaling */
1855  
1856  			/*
1857  			 * This is a pure, in-sequence data packet with
1858  			 * nothing on the reassembly queue and we have enough
1859  			 * buffer space to take it.
1860  			 */
1861  			/* Clean receiver SACK report if present */
1862  			if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
1863  				tcp_clean_sackreport(tp);
1864  			TCPSTAT_INC(tcps_preddat);
1865  			tp->rcv_nxt += tlen;
1866  			if (tlen &&
1867  			    ((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
1868  			    (tp->t_fbyte_in == 0)) {
1869  				tp->t_fbyte_in = ticks;
1870  				if (tp->t_fbyte_in == 0)
1871  					tp->t_fbyte_in = 1;
1872  				if (tp->t_fbyte_out && tp->t_fbyte_in)
1873  					tp->t_flags2 |= TF2_FBYTES_COMPLETE;
1874  			}
1875  			/*
1876  			 * Pull snd_wl1 up to prevent seq wrap relative to
1877  			 * th_seq.
1878  			 */
1879  			tp->snd_wl1 = th->th_seq;
1880  			/*
1881  			 * Pull rcv_up up to prevent seq wrap relative to
1882  			 * rcv_nxt.
1883  			 */
1884  			tp->rcv_up = tp->rcv_nxt;
1885  			TCPSTAT_ADD(tcps_rcvpack, nsegs);
1886  			TCPSTAT_ADD(tcps_rcvbyte, tlen);
1887  			TCP_PROBE3(debug__input, tp, th, m);
1888  
1889  			newsize = tcp_autorcvbuf(m, th, so, tp, tlen);
1890  
1891  			/* Add data to socket buffer. */
1892  			SOCKBUF_LOCK(&so->so_rcv);
1893  			if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1894  				m_freem(m);
1895  			} else {
1896  				/*
1897  				 * Set new socket buffer size.
1898  				 * Give up when limit is reached.
1899  				 */
1900  				if (newsize)
1901  					if (!sbreserve_locked(so, SO_RCV,
1902  					    newsize, NULL))
1903  						so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
1904  				m_adj(m, drop_hdrlen);	/* delayed header drop */
1905  				sbappendstream_locked(&so->so_rcv, m, 0);
1906  			}
1907  			/* NB: sorwakeup_locked() does an implicit unlock. */
1908  			sorwakeup_locked(so);
1909  			if (DELAY_ACK(tp, tlen)) {
1910  				tp->t_flags |= TF_DELACK;
1911  			} else {
1912  				tp->t_flags |= TF_ACKNOW;
1913  				tcp_output(tp);
1914  			}
1915  			goto check_delack;
1916  		}
1917  	}
1918  
1919  	/*
1920  	 * Calculate amount of space in receive window,
1921  	 * and then do TCP input processing.
1922  	 * Receive window is amount of space in rcv queue,
1923  	 * but not less than advertised window.
1924  	 */
1925  	win = sbspace(&so->so_rcv);
1926  	if (win < 0)
1927  		win = 0;
1928  	tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
1929  
1930  	switch (tp->t_state) {
1931  	/*
1932  	 * If the state is SYN_RECEIVED:
1933  	 *	if seg contains an ACK, but not for our SYN/ACK, send a RST.
1934  	 */
1935  	case TCPS_SYN_RECEIVED:
1936  		if ((thflags & TH_ACK) &&
1937  		    (SEQ_LEQ(th->th_ack, tp->snd_una) ||
1938  		     SEQ_GT(th->th_ack, tp->snd_max))) {
1939  				rstreason = BANDLIM_RST_OPENPORT;
1940  				tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
1941  				goto dropwithreset;
1942  		}
1943  		if (IS_FASTOPEN(tp->t_flags)) {
1944  			/*
1945  			 * When a TFO connection is in SYN_RECEIVED, the
1946  			 * only valid packets are the initial SYN, a
1947  			 * retransmit/copy of the initial SYN (possibly with
1948  			 * a subset of the original data), a valid ACK, a
1949  			 * FIN, or a RST.
1950  			 */
1951  			if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
1952  				rstreason = BANDLIM_RST_OPENPORT;
1953  				tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
1954  				goto dropwithreset;
1955  			} else if (thflags & TH_SYN) {
1956  				/* non-initial SYN is ignored */
1957  				if ((tcp_timer_active(tp, TT_DELACK) ||
1958  				     tcp_timer_active(tp, TT_REXMT)))
1959  					goto drop;
1960  			} else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
1961  				goto drop;
1962  			}
1963  		}
1964  		break;
1965  
1966  	/*
1967  	 * If the state is SYN_SENT:
1968  	 *	if seg contains a RST with valid ACK (SEQ.ACK has already
1969  	 *	    been verified), then drop the connection.
1970  	 *	if seg contains a RST without an ACK, drop the seg.
1971  	 *	if seg does not contain SYN, then drop the seg.
1972  	 * Otherwise this is an acceptable SYN segment
1973  	 *	initialize tp->rcv_nxt and tp->irs
1974  	 *	if seg contains ack then advance tp->snd_una
1975  	 *	if seg contains an ECE and ECN support is enabled, the stream
1976  	 *	    is ECN capable.
1977  	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
1978  	 *	arrange for segment to be acked (eventually)
1979  	 *	continue processing rest of data/controls, beginning with URG
1980  	 */
1981  	case TCPS_SYN_SENT:
1982  		if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
1983  			TCP_PROBE5(connect__refused, NULL, tp,
1984  			    m, tp, th);
1985  			tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
1986  			tp = tcp_drop(tp, ECONNREFUSED);
1987  		}
1988  		if (thflags & TH_RST)
1989  			goto drop;
1990  		if (!(thflags & TH_SYN))
1991  			goto drop;
1992  
1993  		tp->irs = th->th_seq;
1994  		tcp_rcvseqinit(tp);
1995  		if (thflags & TH_ACK) {
1996  			int tfo_partial_ack = 0;
1997  
1998  			TCPSTAT_INC(tcps_connects);
1999  			soisconnected(so);
2000  #ifdef MAC
2001  			mac_socketpeer_set_from_mbuf(m, so);
2002  #endif
2003  			/* Do window scaling on this connection? */
2004  			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2005  				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2006  				tp->rcv_scale = tp->request_r_scale;
2007  			}
2008  			tp->rcv_adv += min(tp->rcv_wnd,
2009  			    TCP_MAXWIN << tp->rcv_scale);
2010  			tp->snd_una++;		/* SYN is acked */
2011  			/*
2012  			 * If not all the data that was sent in the TFO SYN
2013  			 * has been acked, resend the remainder right away.
2014  			 */
2015  			if (IS_FASTOPEN(tp->t_flags) &&
2016  			    (tp->snd_una != tp->snd_max)) {
2017  				tp->snd_nxt = th->th_ack;
2018  				tfo_partial_ack = 1;
2019  			}
2020  			/*
2021  			 * If there's data, delay ACK; if there's also a FIN
2022  			 * ACKNOW will be turned on later.
2023  			 */
2024  			if (DELAY_ACK(tp, tlen) && tlen != 0 && !tfo_partial_ack)
2025  				tcp_timer_activate(tp, TT_DELACK,
2026  				    tcp_delacktime);
2027  			else
2028  				tp->t_flags |= TF_ACKNOW;
2029  
2030  			tcp_ecn_input_syn_sent(tp, thflags, iptos);
2031  
2032  			/*
2033  			 * Received <SYN,ACK> in SYN_SENT[*] state.
2034  			 * Transitions:
2035  			 *	SYN_SENT  --> ESTABLISHED
2036  			 *	SYN_SENT* --> FIN_WAIT_1
2037  			 */
2038  			tp->t_starttime = ticks;
2039  			if (tp->t_flags & TF_NEEDFIN) {
2040  				tp->t_acktime = ticks;
2041  				tcp_state_change(tp, TCPS_FIN_WAIT_1);
2042  				tp->t_flags &= ~TF_NEEDFIN;
2043  				thflags &= ~TH_SYN;
2044  			} else {
2045  				tcp_state_change(tp, TCPS_ESTABLISHED);
2046  				TCP_PROBE5(connect__established, NULL, tp,
2047  				    m, tp, th);
2048  				cc_conn_init(tp);
2049  				tcp_timer_activate(tp, TT_KEEP,
2050  				    TP_KEEPIDLE(tp));
2051  			}
2052  		} else {
2053  			/*
2054  			 * Received initial SYN in SYN-SENT[*] state =>
2055  			 * simultaneous open.
2056  			 * If it succeeds, connection is * half-synchronized.
2057  			 * Otherwise, do 3-way handshake:
2058  			 *        SYN-SENT -> SYN-RECEIVED
2059  			 *        SYN-SENT* -> SYN-RECEIVED*
2060  			 */
2061  			tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN | TF_SONOTCONN);
2062  			tcp_timer_activate(tp, TT_REXMT, 0);
2063  			tcp_state_change(tp, TCPS_SYN_RECEIVED);
2064  		}
2065  
2066  		/*
2067  		 * Advance th->th_seq to correspond to first data byte.
2068  		 * If data, trim to stay within window,
2069  		 * dropping FIN if necessary.
2070  		 */
2071  		th->th_seq++;
2072  		if (tlen > tp->rcv_wnd) {
2073  			todrop = tlen - tp->rcv_wnd;
2074  			m_adj(m, -todrop);
2075  			tlen = tp->rcv_wnd;
2076  			thflags &= ~TH_FIN;
2077  			TCPSTAT_INC(tcps_rcvpackafterwin);
2078  			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2079  		}
2080  		tp->snd_wl1 = th->th_seq - 1;
2081  		tp->rcv_up = th->th_seq;
2082  		/*
2083  		 * Client side of transaction: already sent SYN and data.
2084  		 * If the remote host used T/TCP to validate the SYN,
2085  		 * our data will be ACK'd; if so, enter normal data segment
2086  		 * processing in the middle of step 5, ack processing.
2087  		 * Otherwise, goto step 6.
2088  		 */
2089  		if (thflags & TH_ACK)
2090  			goto process_ACK;
2091  
2092  		goto step6;
2093  	}
2094  
2095  	/*
2096  	 * States other than LISTEN or SYN_SENT.
2097  	 * First check the RST flag and sequence number since reset segments
2098  	 * are exempt from the timestamp and connection count tests.  This
2099  	 * fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
2100  	 * below which allowed reset segments in half the sequence space
2101  	 * to fall though and be processed (which gives forged reset
2102  	 * segments with a random sequence number a 50 percent chance of
2103  	 * killing a connection).
2104  	 * Then check timestamp, if present.
2105  	 * Then check the connection count, if present.
2106  	 * Then check that at least some bytes of segment are within
2107  	 * receive window.  If segment begins before rcv_nxt,
2108  	 * drop leading data (and SYN); if nothing left, just ack.
2109  	 */
2110  	if (thflags & TH_RST) {
2111  		/*
2112  		 * RFC5961 Section 3.2
2113  		 *
2114  		 * - RST drops connection only if SEG.SEQ == RCV.NXT.
2115  		 * - If RST is in window, we send challenge ACK.
2116  		 *
2117  		 * Note: to take into account delayed ACKs, we should
2118  		 *   test against last_ack_sent instead of rcv_nxt.
2119  		 * Note 2: we handle special case of closed window, not
2120  		 *   covered by the RFC.
2121  		 */
2122  		if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2123  		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
2124  		    (tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
2125  			KASSERT(tp->t_state != TCPS_SYN_SENT,
2126  			    ("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
2127  			    __func__, th, tp));
2128  
2129  			if (V_tcp_insecure_rst ||
2130  			    tp->last_ack_sent == th->th_seq) {
2131  				TCPSTAT_INC(tcps_drops);
2132  				/* Drop the connection. */
2133  				switch (tp->t_state) {
2134  				case TCPS_SYN_RECEIVED:
2135  					so->so_error = ECONNREFUSED;
2136  					goto close;
2137  				case TCPS_ESTABLISHED:
2138  				case TCPS_FIN_WAIT_1:
2139  				case TCPS_FIN_WAIT_2:
2140  				case TCPS_CLOSE_WAIT:
2141  				case TCPS_CLOSING:
2142  				case TCPS_LAST_ACK:
2143  					so->so_error = ECONNRESET;
2144  				close:
2145  					/* FALLTHROUGH */
2146  				default:
2147  					tcp_log_end_status(tp, TCP_EI_STATUS_CLIENT_RST);
2148  					tp = tcp_close(tp);
2149  				}
2150  			} else {
2151  				TCPSTAT_INC(tcps_badrst);
2152  				/* Send challenge ACK. */
2153  				tcp_respond(tp, mtod(m, void *), th, m,
2154  				    tp->rcv_nxt, tp->snd_nxt, TH_ACK);
2155  				tp->last_ack_sent = tp->rcv_nxt;
2156  				m = NULL;
2157  			}
2158  		}
2159  		goto drop;
2160  	}
2161  
2162  	/*
2163  	 * RFC5961 Section 4.2
2164  	 * Send challenge ACK for any SYN in synchronized state.
2165  	 */
2166  	if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
2167  	    tp->t_state != TCPS_SYN_RECEIVED) {
2168  		TCPSTAT_INC(tcps_badsyn);
2169  		if (V_tcp_insecure_syn &&
2170  		    SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
2171  		    SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
2172  			tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
2173  			tp = tcp_drop(tp, ECONNRESET);
2174  			rstreason = BANDLIM_UNLIMITED;
2175  		} else {
2176  			tcp_ecn_input_syn_sent(tp, thflags, iptos);
2177  			/* Send challenge ACK. */
2178  			tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
2179  			    tp->snd_nxt, TH_ACK);
2180  			tp->last_ack_sent = tp->rcv_nxt;
2181  			m = NULL;
2182  		}
2183  		goto drop;
2184  	}
2185  
2186  	/*
2187  	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
2188  	 * and it's less than ts_recent, drop it.
2189  	 */
2190  	if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
2191  	    TSTMP_LT(to.to_tsval, tp->ts_recent)) {
2192  		/* Check to see if ts_recent is over 24 days old.  */
2193  		if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
2194  			/*
2195  			 * Invalidate ts_recent.  If this segment updates
2196  			 * ts_recent, the age will be reset later and ts_recent
2197  			 * will get a valid value.  If it does not, setting
2198  			 * ts_recent to zero will at least satisfy the
2199  			 * requirement that zero be placed in the timestamp
2200  			 * echo reply when ts_recent isn't valid.  The
2201  			 * age isn't reset until we get a valid ts_recent
2202  			 * because we don't want out-of-order segments to be
2203  			 * dropped when ts_recent is old.
2204  			 */
2205  			tp->ts_recent = 0;
2206  		} else {
2207  			TCPSTAT_INC(tcps_rcvduppack);
2208  			TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
2209  			TCPSTAT_INC(tcps_pawsdrop);
2210  			if (tlen)
2211  				goto dropafterack;
2212  			goto drop;
2213  		}
2214  	}
2215  
2216  	/*
2217  	 * In the SYN-RECEIVED state, validate that the packet belongs to
2218  	 * this connection before trimming the data to fit the receive
2219  	 * window.  Check the sequence number versus IRS since we know
2220  	 * the sequence numbers haven't wrapped.  This is a partial fix
2221  	 * for the "LAND" DoS attack.
2222  	 */
2223  	if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
2224  		rstreason = BANDLIM_RST_OPENPORT;
2225  		tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
2226  		goto dropwithreset;
2227  	}
2228  
2229  	todrop = tp->rcv_nxt - th->th_seq;
2230  	if (todrop > 0) {
2231  		if (thflags & TH_SYN) {
2232  			thflags &= ~TH_SYN;
2233  			th->th_seq++;
2234  			if (th->th_urp > 1)
2235  				th->th_urp--;
2236  			else
2237  				thflags &= ~TH_URG;
2238  			todrop--;
2239  		}
2240  		/*
2241  		 * Following if statement from Stevens, vol. 2, p. 960.
2242  		 */
2243  		if (todrop > tlen
2244  		    || (todrop == tlen && (thflags & TH_FIN) == 0)) {
2245  			/*
2246  			 * Any valid FIN must be to the left of the window.
2247  			 * At this point the FIN must be a duplicate or out
2248  			 * of sequence; drop it.
2249  			 */
2250  			thflags &= ~TH_FIN;
2251  
2252  			/*
2253  			 * Send an ACK to resynchronize and drop any data.
2254  			 * But keep on processing for RST or ACK.
2255  			 */
2256  			tp->t_flags |= TF_ACKNOW;
2257  			todrop = tlen;
2258  			TCPSTAT_INC(tcps_rcvduppack);
2259  			TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
2260  		} else {
2261  			TCPSTAT_INC(tcps_rcvpartduppack);
2262  			TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
2263  		}
2264  		/*
2265  		 * DSACK - add SACK block for dropped range
2266  		 */
2267  		if ((todrop > 0) && (tp->t_flags & TF_SACK_PERMIT)) {
2268  			tcp_update_sack_list(tp, th->th_seq,
2269  			    th->th_seq + todrop);
2270  			/*
2271  			 * ACK now, as the next in-sequence segment
2272  			 * will clear the DSACK block again
2273  			 */
2274  			tp->t_flags |= TF_ACKNOW;
2275  		}
2276  		drop_hdrlen += todrop;	/* drop from the top afterwards */
2277  		th->th_seq += todrop;
2278  		tlen -= todrop;
2279  		if (th->th_urp > todrop)
2280  			th->th_urp -= todrop;
2281  		else {
2282  			thflags &= ~TH_URG;
2283  			th->th_urp = 0;
2284  		}
2285  	}
2286  
2287  	/*
2288  	 * If new data are received on a connection after the
2289  	 * user processes are gone, then RST the other end.
2290  	 */
2291  	if ((tp->t_flags & TF_CLOSED) && tlen) {
2292  		if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
2293  			log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
2294  			    "after socket was closed, "
2295  			    "sending RST and removing tcpcb\n",
2296  			    s, __func__, tcpstates[tp->t_state], tlen);
2297  			free(s, M_TCPLOG);
2298  		}
2299  		tcp_log_end_status(tp, TCP_EI_STATUS_DATA_A_CLOSE);
2300  		/* tcp_close will kill the inp pre-log the Reset */
2301  		tcp_log_end_status(tp, TCP_EI_STATUS_SERVER_RST);
2302  		tp = tcp_close(tp);
2303  		TCPSTAT_INC(tcps_rcvafterclose);
2304  		rstreason = BANDLIM_UNLIMITED;
2305  		goto dropwithreset;
2306  	}
2307  
2308  	/*
2309  	 * If segment ends after window, drop trailing data
2310  	 * (and PUSH and FIN); if nothing left, just ACK.
2311  	 */
2312  	todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
2313  	if (todrop > 0) {
2314  		TCPSTAT_INC(tcps_rcvpackafterwin);
2315  		if (todrop >= tlen) {
2316  			TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
2317  			/*
2318  			 * If window is closed can only take segments at
2319  			 * window edge, and have to drop data and PUSH from
2320  			 * incoming segments.  Continue processing, but
2321  			 * remember to ack.  Otherwise, drop segment
2322  			 * and ack.
2323  			 */
2324  			if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
2325  				tp->t_flags |= TF_ACKNOW;
2326  				TCPSTAT_INC(tcps_rcvwinprobe);
2327  			} else
2328  				goto dropafterack;
2329  		} else
2330  			TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
2331  		m_adj(m, -todrop);
2332  		tlen -= todrop;
2333  		thflags &= ~(TH_PUSH|TH_FIN);
2334  	}
2335  
2336  	/*
2337  	 * If last ACK falls within this segment's sequence numbers,
2338  	 * record its timestamp.
2339  	 * NOTE:
2340  	 * 1) That the test incorporates suggestions from the latest
2341  	 *    proposal of the tcplw@cray.com list (Braden 1993/04/26).
2342  	 * 2) That updating only on newer timestamps interferes with
2343  	 *    our earlier PAWS tests, so this check should be solely
2344  	 *    predicated on the sequence space of this segment.
2345  	 * 3) That we modify the segment boundary check to be
2346  	 *        Last.ACK.Sent <= SEG.SEQ + SEG.Len
2347  	 *    instead of RFC1323's
2348  	 *        Last.ACK.Sent < SEG.SEQ + SEG.Len,
2349  	 *    This modified check allows us to overcome RFC1323's
2350  	 *    limitations as described in Stevens TCP/IP Illustrated
2351  	 *    Vol. 2 p.869. In such cases, we can still calculate the
2352  	 *    RTT correctly when RCV.NXT == Last.ACK.Sent.
2353  	 */
2354  	if ((to.to_flags & TOF_TS) != 0 &&
2355  	    SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
2356  	    SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
2357  		((thflags & (TH_SYN|TH_FIN)) != 0))) {
2358  		tp->ts_recent_age = tcp_ts_getticks();
2359  		tp->ts_recent = to.to_tsval;
2360  	}
2361  
2362  	/*
2363  	 * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
2364  	 * flag is on (half-synchronized state), then queue data for
2365  	 * later processing; else drop segment and return.
2366  	 */
2367  	if ((thflags & TH_ACK) == 0) {
2368  		if (tp->t_state == TCPS_SYN_RECEIVED ||
2369  		    (tp->t_flags & TF_NEEDSYN)) {
2370  			if (tp->t_state == TCPS_SYN_RECEIVED &&
2371  			    IS_FASTOPEN(tp->t_flags)) {
2372  				tp->snd_wnd = tiwin;
2373  				cc_conn_init(tp);
2374  			}
2375  			goto step6;
2376  		} else if (tp->t_flags & TF_ACKNOW)
2377  			goto dropafterack;
2378  		else
2379  			goto drop;
2380  	}
2381  
2382  	/*
2383  	 * Ack processing.
2384  	 */
2385  	switch (tp->t_state) {
2386  	/*
2387  	 * In SYN_RECEIVED state, the ack ACKs our SYN, so enter
2388  	 * ESTABLISHED state and continue processing.
2389  	 * The ACK was checked above.
2390  	 */
2391  	case TCPS_SYN_RECEIVED:
2392  
2393  		TCPSTAT_INC(tcps_connects);
2394  		if (tp->t_flags & TF_SONOTCONN) {
2395  			/*
2396  			 * Usually SYN_RECEIVED had been created from a LISTEN,
2397  			 * and solisten_enqueue() has already marked the socket
2398  			 * layer as connected.  If it didn't, which can happen
2399  			 * only with an accept_filter(9), then the tp is marked
2400  			 * with TF_SONOTCONN.  The other reason for this mark
2401  			 * to be set is a simultaneous open, a SYN_RECEIVED
2402  			 * that had been created from SYN_SENT.
2403  			 */
2404  			tp->t_flags &= ~TF_SONOTCONN;
2405  			soisconnected(so);
2406  		}
2407  		/* Do window scaling? */
2408  		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2409  			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2410  			tp->rcv_scale = tp->request_r_scale;
2411  		}
2412  		tp->snd_wnd = tiwin;
2413  		/*
2414  		 * Make transitions:
2415  		 *      SYN-RECEIVED  -> ESTABLISHED
2416  		 *      SYN-RECEIVED* -> FIN-WAIT-1
2417  		 */
2418  		tp->t_starttime = ticks;
2419  		if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
2420  			tcp_fastopen_decrement_counter(tp->t_tfo_pending);
2421  			tp->t_tfo_pending = NULL;
2422  		}
2423  		if (tp->t_flags & TF_NEEDFIN) {
2424  			tp->t_acktime = ticks;
2425  			tcp_state_change(tp, TCPS_FIN_WAIT_1);
2426  			tp->t_flags &= ~TF_NEEDFIN;
2427  		} else {
2428  			tcp_state_change(tp, TCPS_ESTABLISHED);
2429  			TCP_PROBE5(accept__established, NULL, tp,
2430  			    m, tp, th);
2431  			/*
2432  			 * TFO connections call cc_conn_init() during SYN
2433  			 * processing.  Calling it again here for such
2434  			 * connections is not harmless as it would undo the
2435  			 * snd_cwnd reduction that occurs when a TFO SYN|ACK
2436  			 * is retransmitted.
2437  			 */
2438  			if (!IS_FASTOPEN(tp->t_flags))
2439  				cc_conn_init(tp);
2440  			tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
2441  		}
2442  		/*
2443  		 * Account for the ACK of our SYN prior to
2444  		 * regular ACK processing below, except for
2445  		 * simultaneous SYN, which is handled later.
2446  		 */
2447  		if (SEQ_GT(th->th_ack, tp->snd_una) && !(tp->t_flags & TF_NEEDSYN))
2448  			incforsyn = 1;
2449  		/*
2450  		 * If segment contains data or ACK, will call tcp_reass()
2451  		 * later; if not, do so now to pass queued data to user.
2452  		 */
2453  		if (tlen == 0 && (thflags & TH_FIN) == 0) {
2454  			(void) tcp_reass(tp, (struct tcphdr *)0, NULL, 0,
2455  			    (struct mbuf *)0);
2456  			tcp_handle_wakeup(tp);
2457  		}
2458  		tp->snd_wl1 = th->th_seq - 1;
2459  		/* FALLTHROUGH */
2460  
2461  	/*
2462  	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
2463  	 * ACKs.  If the ack is in the range
2464  	 *	tp->snd_una < th->th_ack <= tp->snd_max
2465  	 * then advance tp->snd_una to th->th_ack and drop
2466  	 * data from the retransmission queue.  If this ACK reflects
2467  	 * more up to date window information we update our window information.
2468  	 */
2469  	case TCPS_ESTABLISHED:
2470  	case TCPS_FIN_WAIT_1:
2471  	case TCPS_FIN_WAIT_2:
2472  	case TCPS_CLOSE_WAIT:
2473  	case TCPS_CLOSING:
2474  	case TCPS_LAST_ACK:
2475  		if (SEQ_GT(th->th_ack, tp->snd_max)) {
2476  			TCPSTAT_INC(tcps_rcvacktoomuch);
2477  			goto dropafterack;
2478  		}
2479  		if (tcp_is_sack_recovery(tp, &to)) {
2480  			if (((sack_changed = tcp_sack_doack(tp, &to, th->th_ack)) != 0) &&
2481  			    (tp->t_flags & TF_LRD)) {
2482  				tcp_sack_lost_retransmission(tp, th);
2483  			}
2484  		} else
2485  			/*
2486  			 * Reset the value so that previous (valid) value
2487  			 * from the last ack with SACK doesn't get used.
2488  			 */
2489  			tp->sackhint.sacked_bytes = 0;
2490  
2491  #ifdef TCP_HHOOK
2492  		/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
2493  		hhook_run_tcp_est_in(tp, th, &to);
2494  #endif
2495  
2496  		if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
2497  			maxseg = tcp_maxseg(tp);
2498  			if (tlen == 0 &&
2499  			    (tiwin == tp->snd_wnd ||
2500  			    (tp->t_flags & TF_SACK_PERMIT))) {
2501  				/*
2502  				 * If this is the first time we've seen a
2503  				 * FIN from the remote, this is not a
2504  				 * duplicate and it needs to be processed
2505  				 * normally.  This happens during a
2506  				 * simultaneous close.
2507  				 */
2508  				if ((thflags & TH_FIN) &&
2509  				    (TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
2510  					tp->t_dupacks = 0;
2511  					break;
2512  				}
2513  				TCPSTAT_INC(tcps_rcvdupack);
2514  				/*
2515  				 * If we have outstanding data (other than
2516  				 * a window probe), this is a completely
2517  				 * duplicate ack (ie, window info didn't
2518  				 * change and FIN isn't set),
2519  				 * the ack is the biggest we've
2520  				 * seen and we've seen exactly our rexmt
2521  				 * threshold of them, assume a packet
2522  				 * has been dropped and retransmit it.
2523  				 * Kludge snd_nxt & the congestion
2524  				 * window so we send only this one
2525  				 * packet.
2526  				 *
2527  				 * We know we're losing at the current
2528  				 * window size so do congestion avoidance
2529  				 * (set ssthresh to half the current window
2530  				 * and pull our congestion window back to
2531  				 * the new ssthresh).
2532  				 *
2533  				 * Dup acks mean that packets have left the
2534  				 * network (they're now cached at the receiver)
2535  				 * so bump cwnd by the amount in the receiver
2536  				 * to keep a constant cwnd packets in the
2537  				 * network.
2538  				 *
2539  				 * When using TCP ECN, notify the peer that
2540  				 * we reduced the cwnd.
2541  				 */
2542  				/*
2543  				 * Following 2 kinds of acks should not affect
2544  				 * dupack counting:
2545  				 * 1) Old acks
2546  				 * 2) Acks with SACK but without any new SACK
2547  				 * information in them. These could result from
2548  				 * any anomaly in the network like a switch
2549  				 * duplicating packets or a possible DoS attack.
2550  				 */
2551  				if (th->th_ack != tp->snd_una ||
2552  				    (tcp_is_sack_recovery(tp, &to) &&
2553  				    !sack_changed))
2554  					break;
2555  				else if (!tcp_timer_active(tp, TT_REXMT))
2556  					tp->t_dupacks = 0;
2557  				else if (++tp->t_dupacks > tcprexmtthresh ||
2558  				     IN_FASTRECOVERY(tp->t_flags)) {
2559  					cc_ack_received(tp, th, nsegs,
2560  					    CC_DUPACK);
2561  					if (V_tcp_do_prr &&
2562  					    IN_FASTRECOVERY(tp->t_flags)) {
2563  						tcp_do_prr_ack(tp, th, &to);
2564  					} else if (tcp_is_sack_recovery(tp, &to) &&
2565  					    IN_FASTRECOVERY(tp->t_flags)) {
2566  						int awnd;
2567  
2568  						/*
2569  						 * Compute the amount of data in flight first.
2570  						 * We can inject new data into the pipe iff
2571  						 * we have less than 1/2 the original window's
2572  						 * worth of data in flight.
2573  						 */
2574  						if (V_tcp_do_newsack)
2575  							awnd = tcp_compute_pipe(tp);
2576  						else
2577  							awnd = (tp->snd_nxt - tp->snd_fack) +
2578  								tp->sackhint.sack_bytes_rexmit;
2579  
2580  						if (awnd < tp->snd_ssthresh) {
2581  							tp->snd_cwnd += maxseg;
2582  							if (tp->snd_cwnd > tp->snd_ssthresh)
2583  								tp->snd_cwnd = tp->snd_ssthresh;
2584  						}
2585  					} else
2586  						tp->snd_cwnd += maxseg;
2587  					(void) tcp_output(tp);
2588  					goto drop;
2589  				} else if (tp->t_dupacks == tcprexmtthresh ||
2590  					    (tp->t_flags & TF_SACK_PERMIT &&
2591  					     V_tcp_do_newsack &&
2592  					     tp->sackhint.sacked_bytes >
2593  					     (tcprexmtthresh - 1) * maxseg)) {
2594  enter_recovery:
2595  					/*
2596  					 * Above is the RFC6675 trigger condition of
2597  					 * more than (dupthresh-1)*maxseg sacked data.
2598  					 * If the count of holes in the
2599  					 * scoreboard is >= dupthresh, we could
2600  					 * also enter loss recovery, but don't
2601  					 * have that value readily available.
2602  					 */
2603  					tp->t_dupacks = tcprexmtthresh;
2604  					tcp_seq onxt = tp->snd_nxt;
2605  
2606  					/*
2607  					 * If we're doing sack, or prr, check
2608  					 * to see if we're already in sack
2609  					 * recovery. If we're not doing sack,
2610  					 * check to see if we're in newreno
2611  					 * recovery.
2612  					 */
2613  					if (V_tcp_do_prr ||
2614  					    (tp->t_flags & TF_SACK_PERMIT)) {
2615  						if (IN_FASTRECOVERY(tp->t_flags)) {
2616  							tp->t_dupacks = 0;
2617  							break;
2618  						}
2619  					} else {
2620  						if (SEQ_LEQ(th->th_ack,
2621  						    tp->snd_recover)) {
2622  							tp->t_dupacks = 0;
2623  							break;
2624  						}
2625  					}
2626  					/* Congestion signal before ack. */
2627  					cc_cong_signal(tp, th, CC_NDUPACK);
2628  					cc_ack_received(tp, th, nsegs,
2629  					    CC_DUPACK);
2630  					tcp_timer_activate(tp, TT_REXMT, 0);
2631  					tp->t_rtttime = 0;
2632  					if (V_tcp_do_prr) {
2633  						/*
2634  						 * snd_ssthresh is already updated by
2635  						 * cc_cong_signal.
2636  						 */
2637  						if (tcp_is_sack_recovery(tp, &to)) {
2638  							tp->sackhint.prr_delivered =
2639  							    tp->sackhint.sacked_bytes;
2640  						} else {
2641  							tp->sackhint.prr_delivered =
2642  							    imin(tp->snd_max - tp->snd_una,
2643  							    imin(INT_MAX / 65536,
2644  								tp->t_dupacks) * maxseg);
2645  						}
2646  						tp->sackhint.recover_fs = max(1,
2647  						    tp->snd_nxt - tp->snd_una);
2648  					}
2649  					if (tcp_is_sack_recovery(tp, &to)) {
2650  						TCPSTAT_INC(
2651  						    tcps_sack_recovery_episode);
2652  						tp->snd_recover = tp->snd_nxt;
2653  						tp->snd_cwnd = maxseg;
2654  						(void) tcp_output(tp);
2655  						if (SEQ_GT(th->th_ack, tp->snd_una))
2656  							goto resume_partialack;
2657  						goto drop;
2658  					}
2659  					tp->snd_nxt = th->th_ack;
2660  					tp->snd_cwnd = maxseg;
2661  					(void) tcp_output(tp);
2662  					KASSERT(tp->snd_limited <= 2,
2663  					    ("%s: tp->snd_limited too big",
2664  					    __func__));
2665  					tp->snd_cwnd = tp->snd_ssthresh +
2666  					     maxseg *
2667  					     (tp->t_dupacks - tp->snd_limited);
2668  					if (SEQ_GT(onxt, tp->snd_nxt))
2669  						tp->snd_nxt = onxt;
2670  					goto drop;
2671  				} else if (V_tcp_do_rfc3042) {
2672  					/*
2673  					 * Process first and second duplicate
2674  					 * ACKs. Each indicates a segment
2675  					 * leaving the network, creating room
2676  					 * for more. Make sure we can send a
2677  					 * packet on reception of each duplicate
2678  					 * ACK by increasing snd_cwnd by one
2679  					 * segment. Restore the original
2680  					 * snd_cwnd after packet transmission.
2681  					 */
2682  					cc_ack_received(tp, th, nsegs,
2683  					    CC_DUPACK);
2684  					uint32_t oldcwnd = tp->snd_cwnd;
2685  					tcp_seq oldsndmax = tp->snd_max;
2686  					u_int sent;
2687  					int avail;
2688  
2689  					KASSERT(tp->t_dupacks == 1 ||
2690  					    tp->t_dupacks == 2,
2691  					    ("%s: dupacks not 1 or 2",
2692  					    __func__));
2693  					if (tp->t_dupacks == 1)
2694  						tp->snd_limited = 0;
2695  					tp->snd_cwnd =
2696  					    (tp->snd_nxt - tp->snd_una) +
2697  					    (tp->t_dupacks - tp->snd_limited) *
2698  					    maxseg;
2699  					/*
2700  					 * Only call tcp_output when there
2701  					 * is new data available to be sent
2702  					 * or we need to send an ACK.
2703  					 */
2704  					SOCKBUF_LOCK(&so->so_snd);
2705  					avail = sbavail(&so->so_snd) -
2706  					    (tp->snd_nxt - tp->snd_una);
2707  					SOCKBUF_UNLOCK(&so->so_snd);
2708  					if (avail > 0 || tp->t_flags & TF_ACKNOW)
2709  						(void) tcp_output(tp);
2710  					sent = tp->snd_max - oldsndmax;
2711  					if (sent > maxseg) {
2712  						KASSERT((tp->t_dupacks == 2 &&
2713  						    tp->snd_limited == 0) ||
2714  						   (sent == maxseg + 1 &&
2715  						    tp->t_flags & TF_SENTFIN),
2716  						    ("%s: sent too much",
2717  						    __func__));
2718  						tp->snd_limited = 2;
2719  					} else if (sent > 0)
2720  						++tp->snd_limited;
2721  					tp->snd_cwnd = oldcwnd;
2722  					goto drop;
2723  				}
2724  			}
2725  			break;
2726  		} else {
2727  			/*
2728  			 * This ack is advancing the left edge, reset the
2729  			 * counter.
2730  			 */
2731  			tp->t_dupacks = 0;
2732  			/*
2733  			 * If this ack also has new SACK info, increment the
2734  			 * counter as per rfc6675. The variable
2735  			 * sack_changed tracks all changes to the SACK
2736  			 * scoreboard, including when partial ACKs without
2737  			 * SACK options are received, and clear the scoreboard
2738  			 * from the left side. Such partial ACKs should not be
2739  			 * counted as dupacks here.
2740  			 */
2741  			if (tcp_is_sack_recovery(tp, &to) &&
2742  			    sack_changed) {
2743  				tp->t_dupacks++;
2744  				/* limit overhead by setting maxseg last */
2745  				if (!IN_FASTRECOVERY(tp->t_flags) &&
2746  				    (tp->sackhint.sacked_bytes >
2747  				    ((tcprexmtthresh - 1) *
2748  				    (maxseg = tcp_maxseg(tp))))) {
2749  					goto enter_recovery;
2750  				}
2751  			}
2752  		}
2753  
2754  resume_partialack:
2755  		KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
2756  		    ("%s: th_ack <= snd_una", __func__));
2757  
2758  		/*
2759  		 * If the congestion window was inflated to account
2760  		 * for the other side's cached packets, retract it.
2761  		 */
2762  		if (IN_FASTRECOVERY(tp->t_flags)) {
2763  			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2764  				if (tp->t_flags & TF_SACK_PERMIT)
2765  					if (V_tcp_do_prr && to.to_flags & TOF_SACK) {
2766  						tcp_timer_activate(tp, TT_REXMT, 0);
2767  						tp->t_rtttime = 0;
2768  						tcp_do_prr_ack(tp, th, &to);
2769  						tp->t_flags |= TF_ACKNOW;
2770  						(void) tcp_output(tp);
2771  					} else
2772  						tcp_sack_partialack(tp, th);
2773  				else
2774  					tcp_newreno_partial_ack(tp, th);
2775  			} else
2776  				cc_post_recovery(tp, th);
2777  		} else if (IN_CONGRECOVERY(tp->t_flags)) {
2778  			if (SEQ_LT(th->th_ack, tp->snd_recover)) {
2779  				if (V_tcp_do_prr) {
2780  					tp->sackhint.delivered_data = BYTES_THIS_ACK(tp, th);
2781  					tp->snd_fack = th->th_ack;
2782  					tcp_do_prr_ack(tp, th, &to);
2783  					(void) tcp_output(tp);
2784  				}
2785  			} else
2786  				cc_post_recovery(tp, th);
2787  		}
2788  		/*
2789  		 * If we reach this point, ACK is not a duplicate,
2790  		 *     i.e., it ACKs something we sent.
2791  		 */
2792  		if (tp->t_flags & TF_NEEDSYN) {
2793  			/*
2794  			 * T/TCP: Connection was half-synchronized, and our
2795  			 * SYN has been ACK'd (so connection is now fully
2796  			 * synchronized).  Go to non-starred state,
2797  			 * increment snd_una for ACK of SYN, and check if
2798  			 * we can do window scaling.
2799  			 */
2800  			tp->t_flags &= ~TF_NEEDSYN;
2801  			tp->snd_una++;
2802  			/* Do window scaling? */
2803  			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
2804  				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
2805  				tp->rcv_scale = tp->request_r_scale;
2806  				/* Send window already scaled. */
2807  			}
2808  		}
2809  
2810  process_ACK:
2811  		INP_WLOCK_ASSERT(inp);
2812  
2813  		/*
2814  		 * Adjust for the SYN bit in sequence space,
2815  		 * but don't account for it in cwnd calculations.
2816  		 * This is for the SYN_RECEIVED, non-simultaneous
2817  		 * SYN case. SYN_SENT and simultaneous SYN are
2818  		 * treated elsewhere.
2819  		 */
2820  		if (incforsyn)
2821  			tp->snd_una++;
2822  		acked = BYTES_THIS_ACK(tp, th);
2823  		KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
2824  		    "(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
2825  		    tp->snd_una, th->th_ack, tp, m));
2826  		TCPSTAT_ADD(tcps_rcvackpack, nsegs);
2827  		TCPSTAT_ADD(tcps_rcvackbyte, acked);
2828  
2829  		/*
2830  		 * If we just performed our first retransmit, and the ACK
2831  		 * arrives within our recovery window, then it was a mistake
2832  		 * to do the retransmit in the first place.  Recover our
2833  		 * original cwnd and ssthresh, and proceed to transmit where
2834  		 * we left off.
2835  		 */
2836  		if (tp->t_rxtshift == 1 &&
2837  		    tp->t_flags & TF_PREVVALID &&
2838  		    tp->t_badrxtwin != 0 &&
2839  		    to.to_flags & TOF_TS &&
2840  		    to.to_tsecr != 0 &&
2841  		    TSTMP_LT(to.to_tsecr, tp->t_badrxtwin))
2842  			cc_cong_signal(tp, th, CC_RTO_ERR);
2843  
2844  		/*
2845  		 * If we have a timestamp reply, update smoothed
2846  		 * round trip time.  If no timestamp is present but
2847  		 * transmit timer is running and timed sequence
2848  		 * number was acked, update smoothed round trip time.
2849  		 * Since we now have an rtt measurement, cancel the
2850  		 * timer backoff (cf., Phil Karn's retransmit alg.).
2851  		 * Recompute the initial retransmit timer.
2852  		 *
2853  		 * Some boxes send broken timestamp replies
2854  		 * during the SYN+ACK phase, ignore
2855  		 * timestamps of 0 or we could calculate a
2856  		 * huge RTT and blow up the retransmit timer.
2857  		 */
2858  		if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
2859  			uint32_t t;
2860  
2861  			t = tcp_ts_getticks() - to.to_tsecr;
2862  			if (!tp->t_rttlow || tp->t_rttlow > t)
2863  				tp->t_rttlow = t;
2864  			tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
2865  		} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
2866  			if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
2867  				tp->t_rttlow = ticks - tp->t_rtttime;
2868  			tcp_xmit_timer(tp, ticks - tp->t_rtttime);
2869  		}
2870  
2871  		SOCKBUF_LOCK(&so->so_snd);
2872  		/*
2873  		 * Clear t_acktime if remote side has ACKd all data in the
2874  		 * socket buffer and FIN (if applicable).
2875  		 * Otherwise, update t_acktime if we received a sufficiently
2876  		 * large ACK.
2877  		 */
2878  		if ((tp->t_state <= TCPS_CLOSE_WAIT &&
2879  		    acked == sbavail(&so->so_snd)) ||
2880  		    acked > sbavail(&so->so_snd))
2881  			tp->t_acktime = 0;
2882  		else if (acked > 1)
2883  			tp->t_acktime = ticks;
2884  
2885  		/*
2886  		 * If all outstanding data is acked, stop retransmit
2887  		 * timer and remember to restart (more output or persist).
2888  		 * If there is more data to be acked, restart retransmit
2889  		 * timer, using current (possibly backed-off) value.
2890  		 */
2891  		if (th->th_ack == tp->snd_max) {
2892  			tcp_timer_activate(tp, TT_REXMT, 0);
2893  			needoutput = 1;
2894  		} else if (!tcp_timer_active(tp, TT_PERSIST))
2895  			tcp_timer_activate(tp, TT_REXMT, TP_RXTCUR(tp));
2896  
2897  		/*
2898  		 * If no data (only SYN) was ACK'd,
2899  		 *    skip rest of ACK processing.
2900  		 */
2901  		if (acked == 0) {
2902  			SOCKBUF_UNLOCK(&so->so_snd);
2903  			goto step6;
2904  		}
2905  
2906  		/*
2907  		 * Let the congestion control algorithm update congestion
2908  		 * control related information. This typically means increasing
2909  		 * the congestion window.
2910  		 */
2911  		cc_ack_received(tp, th, nsegs, CC_ACK);
2912  
2913  		if (acked > sbavail(&so->so_snd)) {
2914  			if (tp->snd_wnd >= sbavail(&so->so_snd))
2915  				tp->snd_wnd -= sbavail(&so->so_snd);
2916  			else
2917  				tp->snd_wnd = 0;
2918  			mfree = sbcut_locked(&so->so_snd,
2919  			    (int)sbavail(&so->so_snd));
2920  			ourfinisacked = 1;
2921  		} else {
2922  			mfree = sbcut_locked(&so->so_snd, acked);
2923  			if (tp->snd_wnd >= (uint32_t) acked)
2924  				tp->snd_wnd -= acked;
2925  			else
2926  				tp->snd_wnd = 0;
2927  			ourfinisacked = 0;
2928  		}
2929  		/* NB: sowwakeup_locked() does an implicit unlock. */
2930  		sowwakeup_locked(so);
2931  		m_freem(mfree);
2932  		/* Detect una wraparound. */
2933  		if (!IN_RECOVERY(tp->t_flags) &&
2934  		    SEQ_GT(tp->snd_una, tp->snd_recover) &&
2935  		    SEQ_LEQ(th->th_ack, tp->snd_recover))
2936  			tp->snd_recover = th->th_ack - 1;
2937  		/* XXXLAS: Can this be moved up into cc_post_recovery? */
2938  		if (IN_RECOVERY(tp->t_flags) &&
2939  		    SEQ_GEQ(th->th_ack, tp->snd_recover)) {
2940  			EXIT_RECOVERY(tp->t_flags);
2941  		}
2942  		tp->snd_una = th->th_ack;
2943  		if (tp->t_flags & TF_SACK_PERMIT) {
2944  			if (SEQ_GT(tp->snd_una, tp->snd_recover))
2945  				tp->snd_recover = tp->snd_una;
2946  		}
2947  		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
2948  			tp->snd_nxt = tp->snd_una;
2949  
2950  		switch (tp->t_state) {
2951  		/*
2952  		 * In FIN_WAIT_1 STATE in addition to the processing
2953  		 * for the ESTABLISHED state if our FIN is now acknowledged
2954  		 * then enter FIN_WAIT_2.
2955  		 */
2956  		case TCPS_FIN_WAIT_1:
2957  			if (ourfinisacked) {
2958  				/*
2959  				 * If we can't receive any more
2960  				 * data, then closing user can proceed.
2961  				 * Starting the timer is contrary to the
2962  				 * specification, but if we don't get a FIN
2963  				 * we'll hang forever.
2964  				 */
2965  				if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
2966  					soisdisconnected(so);
2967  					tcp_timer_activate(tp, TT_2MSL,
2968  					    (tcp_fast_finwait2_recycle ?
2969  					    tcp_finwait2_timeout :
2970  					    TP_MAXIDLE(tp)));
2971  				}
2972  				tcp_state_change(tp, TCPS_FIN_WAIT_2);
2973  			}
2974  			break;
2975  
2976  		/*
2977  		 * In CLOSING STATE in addition to the processing for
2978  		 * the ESTABLISHED state if the ACK acknowledges our FIN
2979  		 * then enter the TIME-WAIT state, otherwise ignore
2980  		 * the segment.
2981  		 */
2982  		case TCPS_CLOSING:
2983  			if (ourfinisacked) {
2984  				tcp_twstart(tp);
2985  				m_freem(m);
2986  				return;
2987  			}
2988  			break;
2989  
2990  		/*
2991  		 * In LAST_ACK, we may still be waiting for data to drain
2992  		 * and/or to be acked, as well as for the ack of our FIN.
2993  		 * If our FIN is now acknowledged, delete the TCB,
2994  		 * enter the closed state and return.
2995  		 */
2996  		case TCPS_LAST_ACK:
2997  			if (ourfinisacked) {
2998  				tp = tcp_close(tp);
2999  				goto drop;
3000  			}
3001  			break;
3002  		}
3003  	}
3004  
3005  step6:
3006  	INP_WLOCK_ASSERT(inp);
3007  
3008  	/*
3009  	 * Update window information.
3010  	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
3011  	 */
3012  	if ((thflags & TH_ACK) &&
3013  	    (SEQ_LT(tp->snd_wl1, th->th_seq) ||
3014  	    (tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
3015  	     (tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
3016  		/* keep track of pure window updates */
3017  		if (tlen == 0 &&
3018  		    tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
3019  			TCPSTAT_INC(tcps_rcvwinupd);
3020  		tp->snd_wnd = tiwin;
3021  		tp->snd_wl1 = th->th_seq;
3022  		tp->snd_wl2 = th->th_ack;
3023  		if (tp->snd_wnd > tp->max_sndwnd)
3024  			tp->max_sndwnd = tp->snd_wnd;
3025  		needoutput = 1;
3026  	}
3027  
3028  	/*
3029  	 * Process segments with URG.
3030  	 */
3031  	if ((thflags & TH_URG) && th->th_urp &&
3032  	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3033  		/*
3034  		 * This is a kludge, but if we receive and accept
3035  		 * random urgent pointers, we'll crash in
3036  		 * soreceive.  It's hard to imagine someone
3037  		 * actually wanting to send this much urgent data.
3038  		 */
3039  		SOCKBUF_LOCK(&so->so_rcv);
3040  		if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
3041  			th->th_urp = 0;			/* XXX */
3042  			thflags &= ~TH_URG;		/* XXX */
3043  			SOCKBUF_UNLOCK(&so->so_rcv);	/* XXX */
3044  			goto dodata;			/* XXX */
3045  		}
3046  		/*
3047  		 * If this segment advances the known urgent pointer,
3048  		 * then mark the data stream.  This should not happen
3049  		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
3050  		 * a FIN has been received from the remote side.
3051  		 * In these states we ignore the URG.
3052  		 *
3053  		 * According to RFC961 (Assigned Protocols),
3054  		 * the urgent pointer points to the last octet
3055  		 * of urgent data.  We continue, however,
3056  		 * to consider it to indicate the first octet
3057  		 * of data past the urgent section as the original
3058  		 * spec states (in one of two places).
3059  		 */
3060  		if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
3061  			tp->rcv_up = th->th_seq + th->th_urp;
3062  			so->so_oobmark = sbavail(&so->so_rcv) +
3063  			    (tp->rcv_up - tp->rcv_nxt) - 1;
3064  			if (so->so_oobmark == 0)
3065  				so->so_rcv.sb_state |= SBS_RCVATMARK;
3066  			sohasoutofband(so);
3067  			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
3068  		}
3069  		SOCKBUF_UNLOCK(&so->so_rcv);
3070  		/*
3071  		 * Remove out of band data so doesn't get presented to user.
3072  		 * This can happen independent of advancing the URG pointer,
3073  		 * but if two URG's are pending at once, some out-of-band
3074  		 * data may creep in... ick.
3075  		 */
3076  		if (th->th_urp <= (uint32_t)tlen &&
3077  		    !(so->so_options & SO_OOBINLINE)) {
3078  			/* hdr drop is delayed */
3079  			tcp_pulloutofband(so, th, m, drop_hdrlen);
3080  		}
3081  	} else {
3082  		/*
3083  		 * If no out of band data is expected,
3084  		 * pull receive urgent pointer along
3085  		 * with the receive window.
3086  		 */
3087  		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
3088  			tp->rcv_up = tp->rcv_nxt;
3089  	}
3090  dodata:							/* XXX */
3091  	INP_WLOCK_ASSERT(inp);
3092  
3093  	/*
3094  	 * Process the segment text, merging it into the TCP sequencing queue,
3095  	 * and arranging for acknowledgment of receipt if necessary.
3096  	 * This process logically involves adjusting tp->rcv_wnd as data
3097  	 * is presented to the user (this happens in tcp_usrreq.c,
3098  	 * case PRU_RCVD).  If a FIN has already been received on this
3099  	 * connection then we just ignore the text.
3100  	 */
3101  	tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
3102  		   IS_FASTOPEN(tp->t_flags));
3103  	if ((tlen || (thflags & TH_FIN) || (tfo_syn && tlen > 0)) &&
3104  	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3105  		tcp_seq save_start = th->th_seq;
3106  		tcp_seq save_rnxt  = tp->rcv_nxt;
3107  		int     save_tlen  = tlen;
3108  		m_adj(m, drop_hdrlen);	/* delayed header drop */
3109  		/*
3110  		 * Insert segment which includes th into TCP reassembly queue
3111  		 * with control block tp.  Set thflags to whether reassembly now
3112  		 * includes a segment with FIN.  This handles the common case
3113  		 * inline (segment is the next to be received on an established
3114  		 * connection, and the queue is empty), avoiding linkage into
3115  		 * and removal from the queue and repetition of various
3116  		 * conversions.
3117  		 * Set DELACK for segments received in order, but ack
3118  		 * immediately when segments are out of order (so
3119  		 * fast retransmit can work).
3120  		 */
3121  		if (th->th_seq == tp->rcv_nxt &&
3122  		    SEGQ_EMPTY(tp) &&
3123  		    (TCPS_HAVEESTABLISHED(tp->t_state) ||
3124  		     tfo_syn)) {
3125  			if (DELAY_ACK(tp, tlen) || tfo_syn)
3126  				tp->t_flags |= TF_DELACK;
3127  			else
3128  				tp->t_flags |= TF_ACKNOW;
3129  			tp->rcv_nxt += tlen;
3130  			if (tlen &&
3131  			    ((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
3132  			    (tp->t_fbyte_in == 0)) {
3133  				tp->t_fbyte_in = ticks;
3134  				if (tp->t_fbyte_in == 0)
3135  					tp->t_fbyte_in = 1;
3136  				if (tp->t_fbyte_out && tp->t_fbyte_in)
3137  					tp->t_flags2 |= TF2_FBYTES_COMPLETE;
3138  			}
3139  			thflags = tcp_get_flags(th) & TH_FIN;
3140  			TCPSTAT_INC(tcps_rcvpack);
3141  			TCPSTAT_ADD(tcps_rcvbyte, tlen);
3142  			SOCKBUF_LOCK(&so->so_rcv);
3143  			if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
3144  				m_freem(m);
3145  			else
3146  				sbappendstream_locked(&so->so_rcv, m, 0);
3147  			tp->t_flags |= TF_WAKESOR;
3148  		} else {
3149  			/*
3150  			 * XXX: Due to the header drop above "th" is
3151  			 * theoretically invalid by now.  Fortunately
3152  			 * m_adj() doesn't actually frees any mbufs
3153  			 * when trimming from the head.
3154  			 */
3155  			tcp_seq temp = save_start;
3156  
3157  			thflags = tcp_reass(tp, th, &temp, &tlen, m);
3158  			tp->t_flags |= TF_ACKNOW;
3159  		}
3160  		if ((tp->t_flags & TF_SACK_PERMIT) &&
3161  		    (save_tlen > 0) &&
3162  		    TCPS_HAVEESTABLISHED(tp->t_state)) {
3163  			if ((tlen == 0) && (SEQ_LT(save_start, save_rnxt))) {
3164  				/*
3165  				 * DSACK actually handled in the fastpath
3166  				 * above.
3167  				 */
3168  				tcp_update_sack_list(tp, save_start,
3169  				    save_start + save_tlen);
3170  			} else if ((tlen > 0) && SEQ_GT(tp->rcv_nxt, save_rnxt)) {
3171  				if ((tp->rcv_numsacks >= 1) &&
3172  				    (tp->sackblks[0].end == save_start)) {
3173  					/*
3174  					 * Partial overlap, recorded at todrop
3175  					 * above.
3176  					 */
3177  					tcp_update_sack_list(tp,
3178  					    tp->sackblks[0].start,
3179  					    tp->sackblks[0].end);
3180  				} else {
3181  					tcp_update_dsack_list(tp, save_start,
3182  					    save_start + save_tlen);
3183  				}
3184  			} else if (tlen >= save_tlen) {
3185  				/* Update of sackblks. */
3186  				tcp_update_dsack_list(tp, save_start,
3187  				    save_start + save_tlen);
3188  			} else if (tlen > 0) {
3189  				tcp_update_dsack_list(tp, save_start,
3190  				    save_start + tlen);
3191  			}
3192  		}
3193  		tcp_handle_wakeup(tp);
3194  #if 0
3195  		/*
3196  		 * Note the amount of data that peer has sent into
3197  		 * our window, in order to estimate the sender's
3198  		 * buffer size.
3199  		 * XXX: Unused.
3200  		 */
3201  		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
3202  			len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
3203  		else
3204  			len = so->so_rcv.sb_hiwat;
3205  #endif
3206  	} else {
3207  		m_freem(m);
3208  		thflags &= ~TH_FIN;
3209  	}
3210  
3211  	/*
3212  	 * If FIN is received ACK the FIN and let the user know
3213  	 * that the connection is closing.
3214  	 */
3215  	if (thflags & TH_FIN) {
3216  		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
3217  			/* The socket upcall is handled by socantrcvmore. */
3218  			socantrcvmore(so);
3219  			/*
3220  			 * If connection is half-synchronized
3221  			 * (ie NEEDSYN flag on) then delay ACK,
3222  			 * so it may be piggybacked when SYN is sent.
3223  			 * Otherwise, since we received a FIN then no
3224  			 * more input can be expected, send ACK now.
3225  			 */
3226  			if (tp->t_flags & TF_NEEDSYN)
3227  				tp->t_flags |= TF_DELACK;
3228  			else
3229  				tp->t_flags |= TF_ACKNOW;
3230  			tp->rcv_nxt++;
3231  		}
3232  		switch (tp->t_state) {
3233  		/*
3234  		 * In SYN_RECEIVED and ESTABLISHED STATES
3235  		 * enter the CLOSE_WAIT state.
3236  		 */
3237  		case TCPS_SYN_RECEIVED:
3238  			tp->t_starttime = ticks;
3239  			/* FALLTHROUGH */
3240  		case TCPS_ESTABLISHED:
3241  			tcp_state_change(tp, TCPS_CLOSE_WAIT);
3242  			break;
3243  
3244  		/*
3245  		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
3246  		 * enter the CLOSING state.
3247  		 */
3248  		case TCPS_FIN_WAIT_1:
3249  			tcp_state_change(tp, TCPS_CLOSING);
3250  			break;
3251  
3252  		/*
3253  		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
3254  		 * starting the time-wait timer, turning off the other
3255  		 * standard timers.
3256  		 */
3257  		case TCPS_FIN_WAIT_2:
3258  			tcp_twstart(tp);
3259  			return;
3260  		}
3261  	}
3262  	TCP_PROBE3(debug__input, tp, th, m);
3263  
3264  	/*
3265  	 * Return any desired output.
3266  	 */
3267  	if (needoutput || (tp->t_flags & TF_ACKNOW))
3268  		(void) tcp_output(tp);
3269  
3270  check_delack:
3271  	INP_WLOCK_ASSERT(inp);
3272  
3273  	if (tp->t_flags & TF_DELACK) {
3274  		tp->t_flags &= ~TF_DELACK;
3275  		tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
3276  	}
3277  	INP_WUNLOCK(inp);
3278  	return;
3279  
3280  dropafterack:
3281  	/*
3282  	 * Generate an ACK dropping incoming segment if it occupies
3283  	 * sequence space, where the ACK reflects our state.
3284  	 *
3285  	 * We can now skip the test for the RST flag since all
3286  	 * paths to this code happen after packets containing
3287  	 * RST have been dropped.
3288  	 *
3289  	 * In the SYN-RECEIVED state, don't send an ACK unless the
3290  	 * segment we received passes the SYN-RECEIVED ACK test.
3291  	 * If it fails send a RST.  This breaks the loop in the
3292  	 * "LAND" DoS attack, and also prevents an ACK storm
3293  	 * between two listening ports that have been sent forged
3294  	 * SYN segments, each with the source address of the other.
3295  	 */
3296  	if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
3297  	    (SEQ_GT(tp->snd_una, th->th_ack) ||
3298  	     SEQ_GT(th->th_ack, tp->snd_max)) ) {
3299  		rstreason = BANDLIM_RST_OPENPORT;
3300  		tcp_log_end_status(tp, TCP_EI_STATUS_RST_IN_FRONT);
3301  		goto dropwithreset;
3302  	}
3303  	TCP_PROBE3(debug__input, tp, th, m);
3304  	tp->t_flags |= TF_ACKNOW;
3305  	(void) tcp_output(tp);
3306  	INP_WUNLOCK(inp);
3307  	m_freem(m);
3308  	return;
3309  
3310  dropwithreset:
3311  	if (tp != NULL) {
3312  		tcp_dropwithreset(m, th, tp, tlen, rstreason);
3313  		INP_WUNLOCK(inp);
3314  	} else
3315  		tcp_dropwithreset(m, th, NULL, tlen, rstreason);
3316  	return;
3317  
3318  drop:
3319  	/*
3320  	 * Drop space held by incoming segment and return.
3321  	 */
3322  	TCP_PROBE3(debug__input, tp, th, m);
3323  	if (tp != NULL) {
3324  		INP_WUNLOCK(inp);
3325  	}
3326  	m_freem(m);
3327  }
3328  
3329  /*
3330   * Issue RST and make ACK acceptable to originator of segment.
3331   * The mbuf must still include the original packet header.
3332   * tp may be NULL.
3333   */
3334  void
3335  tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
3336      int tlen, int rstreason)
3337  {
3338  #ifdef INET
3339  	struct ip *ip;
3340  #endif
3341  #ifdef INET6
3342  	struct ip6_hdr *ip6;
3343  #endif
3344  
3345  	if (tp != NULL) {
3346  		INP_LOCK_ASSERT(tptoinpcb(tp));
3347  	}
3348  
3349  	/* Don't bother if destination was broadcast/multicast. */
3350  	if ((tcp_get_flags(th) & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
3351  		goto drop;
3352  #ifdef INET6
3353  	if (mtod(m, struct ip *)->ip_v == 6) {
3354  		ip6 = mtod(m, struct ip6_hdr *);
3355  		if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
3356  		    IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
3357  			goto drop;
3358  		/* IPv6 anycast check is done at tcp6_input() */
3359  	}
3360  #endif
3361  #if defined(INET) && defined(INET6)
3362  	else
3363  #endif
3364  #ifdef INET
3365  	{
3366  		ip = mtod(m, struct ip *);
3367  		if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
3368  		    IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
3369  		    ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
3370  		    in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
3371  			goto drop;
3372  	}
3373  #endif
3374  
3375  	/* Perform bandwidth limiting. */
3376  	if (badport_bandlim(rstreason) < 0)
3377  		goto drop;
3378  
3379  	/* tcp_respond consumes the mbuf chain. */
3380  	if (tcp_get_flags(th) & TH_ACK) {
3381  		tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
3382  		    th->th_ack, TH_RST);
3383  	} else {
3384  		if (tcp_get_flags(th) & TH_SYN)
3385  			tlen++;
3386  		if (tcp_get_flags(th) & TH_FIN)
3387  			tlen++;
3388  		tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
3389  		    (tcp_seq)0, TH_RST|TH_ACK);
3390  	}
3391  	return;
3392  drop:
3393  	m_freem(m);
3394  }
3395  
3396  /*
3397   * Parse TCP options and place in tcpopt.
3398   */
3399  void
3400  tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
3401  {
3402  	int opt, optlen;
3403  
3404  	to->to_flags = 0;
3405  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
3406  		opt = cp[0];
3407  		if (opt == TCPOPT_EOL)
3408  			break;
3409  		if (opt == TCPOPT_NOP)
3410  			optlen = 1;
3411  		else {
3412  			if (cnt < 2)
3413  				break;
3414  			optlen = cp[1];
3415  			if (optlen < 2 || optlen > cnt)
3416  				break;
3417  		}
3418  		switch (opt) {
3419  		case TCPOPT_MAXSEG:
3420  			if (optlen != TCPOLEN_MAXSEG)
3421  				continue;
3422  			if (!(flags & TO_SYN))
3423  				continue;
3424  			to->to_flags |= TOF_MSS;
3425  			bcopy((char *)cp + 2,
3426  			    (char *)&to->to_mss, sizeof(to->to_mss));
3427  			to->to_mss = ntohs(to->to_mss);
3428  			break;
3429  		case TCPOPT_WINDOW:
3430  			if (optlen != TCPOLEN_WINDOW)
3431  				continue;
3432  			if (!(flags & TO_SYN))
3433  				continue;
3434  			to->to_flags |= TOF_SCALE;
3435  			to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
3436  			break;
3437  		case TCPOPT_TIMESTAMP:
3438  			if (optlen != TCPOLEN_TIMESTAMP)
3439  				continue;
3440  			to->to_flags |= TOF_TS;
3441  			bcopy((char *)cp + 2,
3442  			    (char *)&to->to_tsval, sizeof(to->to_tsval));
3443  			to->to_tsval = ntohl(to->to_tsval);
3444  			bcopy((char *)cp + 6,
3445  			    (char *)&to->to_tsecr, sizeof(to->to_tsecr));
3446  			to->to_tsecr = ntohl(to->to_tsecr);
3447  			break;
3448  		case TCPOPT_SIGNATURE:
3449  			/*
3450  			 * In order to reply to a host which has set the
3451  			 * TCP_SIGNATURE option in its initial SYN, we have
3452  			 * to record the fact that the option was observed
3453  			 * here for the syncache code to perform the correct
3454  			 * response.
3455  			 */
3456  			if (optlen != TCPOLEN_SIGNATURE)
3457  				continue;
3458  			to->to_flags |= TOF_SIGNATURE;
3459  			to->to_signature = cp + 2;
3460  			break;
3461  		case TCPOPT_SACK_PERMITTED:
3462  			if (optlen != TCPOLEN_SACK_PERMITTED)
3463  				continue;
3464  			if (!(flags & TO_SYN))
3465  				continue;
3466  			if (!V_tcp_do_sack)
3467  				continue;
3468  			to->to_flags |= TOF_SACKPERM;
3469  			break;
3470  		case TCPOPT_SACK:
3471  			if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
3472  				continue;
3473  			if (flags & TO_SYN)
3474  				continue;
3475  			to->to_flags |= TOF_SACK;
3476  			to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
3477  			to->to_sacks = cp + 2;
3478  			TCPSTAT_INC(tcps_sack_rcv_blocks);
3479  			break;
3480  		case TCPOPT_FAST_OPEN:
3481  			/*
3482  			 * Cookie length validation is performed by the
3483  			 * server side cookie checking code or the client
3484  			 * side cookie cache update code.
3485  			 */
3486  			if (!(flags & TO_SYN))
3487  				continue;
3488  			if (!V_tcp_fastopen_client_enable &&
3489  			    !V_tcp_fastopen_server_enable)
3490  				continue;
3491  			to->to_flags |= TOF_FASTOPEN;
3492  			to->to_tfo_len = optlen - 2;
3493  			to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
3494  			break;
3495  		default:
3496  			continue;
3497  		}
3498  	}
3499  }
3500  
3501  /*
3502   * Pull out of band byte out of a segment so
3503   * it doesn't appear in the user's data queue.
3504   * It is still reflected in the segment length for
3505   * sequencing purposes.
3506   */
3507  void
3508  tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
3509      int off)
3510  {
3511  	int cnt = off + th->th_urp - 1;
3512  
3513  	while (cnt >= 0) {
3514  		if (m->m_len > cnt) {
3515  			char *cp = mtod(m, caddr_t) + cnt;
3516  			struct tcpcb *tp = sototcpcb(so);
3517  
3518  			INP_WLOCK_ASSERT(tptoinpcb(tp));
3519  
3520  			tp->t_iobc = *cp;
3521  			tp->t_oobflags |= TCPOOB_HAVEDATA;
3522  			bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
3523  			m->m_len--;
3524  			if (m->m_flags & M_PKTHDR)
3525  				m->m_pkthdr.len--;
3526  			return;
3527  		}
3528  		cnt -= m->m_len;
3529  		m = m->m_next;
3530  		if (m == NULL)
3531  			break;
3532  	}
3533  	panic("tcp_pulloutofband");
3534  }
3535  
3536  /*
3537   * Collect new round-trip time estimate
3538   * and update averages and current timeout.
3539   */
3540  void
3541  tcp_xmit_timer(struct tcpcb *tp, int rtt)
3542  {
3543  	int delta;
3544  
3545  	INP_WLOCK_ASSERT(tptoinpcb(tp));
3546  
3547  	TCPSTAT_INC(tcps_rttupdated);
3548  	if (tp->t_rttupdated < UCHAR_MAX)
3549  		tp->t_rttupdated++;
3550  #ifdef STATS
3551  	stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT,
3552  	    imax(0, rtt * 1000 / hz));
3553  #endif
3554  	if ((tp->t_srtt != 0) && (tp->t_rxtshift <= TCP_RTT_INVALIDATE)) {
3555  		/*
3556  		 * srtt is stored as fixed point with 5 bits after the
3557  		 * binary point (i.e., scaled by 8).  The following magic
3558  		 * is equivalent to the smoothing algorithm in rfc793 with
3559  		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
3560  		 * point).  Adjust rtt to origin 0.
3561  		 */
3562  		delta = ((rtt - 1) << TCP_DELTA_SHIFT)
3563  			- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
3564  
3565  		if ((tp->t_srtt += delta) <= 0)
3566  			tp->t_srtt = 1;
3567  
3568  		/*
3569  		 * We accumulate a smoothed rtt variance (actually, a
3570  		 * smoothed mean difference), then set the retransmit
3571  		 * timer to smoothed rtt + 4 times the smoothed variance.
3572  		 * rttvar is stored as fixed point with 4 bits after the
3573  		 * binary point (scaled by 16).  The following is
3574  		 * equivalent to rfc793 smoothing with an alpha of .75
3575  		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
3576  		 * rfc793's wired-in beta.
3577  		 */
3578  		if (delta < 0)
3579  			delta = -delta;
3580  		delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
3581  		if ((tp->t_rttvar += delta) <= 0)
3582  			tp->t_rttvar = 1;
3583  	} else {
3584  		/*
3585  		 * No rtt measurement yet - use the unsmoothed rtt.
3586  		 * Set the variance to half the rtt (so our first
3587  		 * retransmit happens at 3*rtt).
3588  		 */
3589  		tp->t_srtt = rtt << TCP_RTT_SHIFT;
3590  		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
3591  	}
3592  	tp->t_rtttime = 0;
3593  	tp->t_rxtshift = 0;
3594  
3595  	/*
3596  	 * the retransmit should happen at rtt + 4 * rttvar.
3597  	 * Because of the way we do the smoothing, srtt and rttvar
3598  	 * will each average +1/2 tick of bias.  When we compute
3599  	 * the retransmit timer, we want 1/2 tick of rounding and
3600  	 * 1 extra tick because of +-1/2 tick uncertainty in the
3601  	 * firing of the timer.  The bias will give us exactly the
3602  	 * 1.5 tick we need.  But, because the bias is
3603  	 * statistical, we have to test that we don't drop below
3604  	 * the minimum feasible timer (which is 2 ticks).
3605  	 */
3606  	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
3607  		      max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
3608  
3609  	/*
3610  	 * We received an ack for a packet that wasn't retransmitted;
3611  	 * it is probably safe to discard any error indications we've
3612  	 * received recently.  This isn't quite right, but close enough
3613  	 * for now (a route might have failed after we sent a segment,
3614  	 * and the return path might not be symmetrical).
3615  	 */
3616  	tp->t_softerror = 0;
3617  }
3618  
3619  /*
3620   * Determine a reasonable value for maxseg size.
3621   * If the route is known, check route for mtu.
3622   * If none, use an mss that can be handled on the outgoing interface
3623   * without forcing IP to fragment.  If no route is found, route has no mtu,
3624   * or the destination isn't local, use a default, hopefully conservative
3625   * size (usually 512 or the default IP max size, but no more than the mtu
3626   * of the interface), as we can't discover anything about intervening
3627   * gateways or networks.  We also initialize the congestion/slow start
3628   * window to be a single segment if the destination isn't local.
3629   * While looking at the routing entry, we also initialize other path-dependent
3630   * parameters from pre-set or cached values in the routing entry.
3631   *
3632   * NOTE that resulting t_maxseg doesn't include space for TCP options or
3633   * IP options, e.g. IPSEC data, since length of this data may vary, and
3634   * thus it is calculated for every segment separately in tcp_output().
3635   *
3636   * NOTE that this routine is only called when we process an incoming
3637   * segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
3638   * settings are handled in tcp_mssopt().
3639   */
3640  void
3641  tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
3642      struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
3643  {
3644  	int mss = 0;
3645  	uint32_t maxmtu = 0;
3646  	struct inpcb *inp = tptoinpcb(tp);
3647  	struct hc_metrics_lite metrics;
3648  #ifdef INET6
3649  	int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
3650  	size_t min_protoh = isipv6 ?
3651  			    sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
3652  			    sizeof (struct tcpiphdr);
3653  #else
3654  	 size_t min_protoh = sizeof(struct tcpiphdr);
3655  #endif
3656  
3657  	INP_WLOCK_ASSERT(inp);
3658  
3659  	if (tp->t_port)
3660  		min_protoh += V_tcp_udp_tunneling_overhead;
3661  	if (mtuoffer != -1) {
3662  		KASSERT(offer == -1, ("%s: conflict", __func__));
3663  		offer = mtuoffer - min_protoh;
3664  	}
3665  
3666  	/* Initialize. */
3667  #ifdef INET6
3668  	if (isipv6) {
3669  		maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
3670  		tp->t_maxseg = V_tcp_v6mssdflt;
3671  	}
3672  #endif
3673  #if defined(INET) && defined(INET6)
3674  	else
3675  #endif
3676  #ifdef INET
3677  	{
3678  		maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
3679  		tp->t_maxseg = V_tcp_mssdflt;
3680  	}
3681  #endif
3682  
3683  	/*
3684  	 * No route to sender, stay with default mss and return.
3685  	 */
3686  	if (maxmtu == 0) {
3687  		/*
3688  		 * In case we return early we need to initialize metrics
3689  		 * to a defined state as tcp_hc_get() would do for us
3690  		 * if there was no cache hit.
3691  		 */
3692  		if (metricptr != NULL)
3693  			bzero(metricptr, sizeof(struct hc_metrics_lite));
3694  		return;
3695  	}
3696  
3697  	/* What have we got? */
3698  	switch (offer) {
3699  		case 0:
3700  			/*
3701  			 * Offer == 0 means that there was no MSS on the SYN
3702  			 * segment, in this case we use tcp_mssdflt as
3703  			 * already assigned to t_maxseg above.
3704  			 */
3705  			offer = tp->t_maxseg;
3706  			break;
3707  
3708  		case -1:
3709  			/*
3710  			 * Offer == -1 means that we didn't receive SYN yet.
3711  			 */
3712  			/* FALLTHROUGH */
3713  
3714  		default:
3715  			/*
3716  			 * Prevent DoS attack with too small MSS. Round up
3717  			 * to at least minmss.
3718  			 */
3719  			offer = max(offer, V_tcp_minmss);
3720  	}
3721  
3722  	/*
3723  	 * rmx information is now retrieved from tcp_hostcache.
3724  	 */
3725  	tcp_hc_get(&inp->inp_inc, &metrics);
3726  	if (metricptr != NULL)
3727  		bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
3728  
3729  	/*
3730  	 * If there's a discovered mtu in tcp hostcache, use it.
3731  	 * Else, use the link mtu.
3732  	 */
3733  	if (metrics.rmx_mtu)
3734  		mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
3735  	else {
3736  #ifdef INET6
3737  		if (isipv6) {
3738  			mss = maxmtu - min_protoh;
3739  			if (!V_path_mtu_discovery &&
3740  			    !in6_localaddr(&inp->in6p_faddr))
3741  				mss = min(mss, V_tcp_v6mssdflt);
3742  		}
3743  #endif
3744  #if defined(INET) && defined(INET6)
3745  		else
3746  #endif
3747  #ifdef INET
3748  		{
3749  			mss = maxmtu - min_protoh;
3750  			if (!V_path_mtu_discovery &&
3751  			    !in_localaddr(inp->inp_faddr))
3752  				mss = min(mss, V_tcp_mssdflt);
3753  		}
3754  #endif
3755  		/*
3756  		 * XXX - The above conditional (mss = maxmtu - min_protoh)
3757  		 * probably violates the TCP spec.
3758  		 * The problem is that, since we don't know the
3759  		 * other end's MSS, we are supposed to use a conservative
3760  		 * default.  But, if we do that, then MTU discovery will
3761  		 * never actually take place, because the conservative
3762  		 * default is much less than the MTUs typically seen
3763  		 * on the Internet today.  For the moment, we'll sweep
3764  		 * this under the carpet.
3765  		 *
3766  		 * The conservative default might not actually be a problem
3767  		 * if the only case this occurs is when sending an initial
3768  		 * SYN with options and data to a host we've never talked
3769  		 * to before.  Then, they will reply with an MSS value which
3770  		 * will get recorded and the new parameters should get
3771  		 * recomputed.  For Further Study.
3772  		 */
3773  	}
3774  	mss = min(mss, offer);
3775  
3776  	/*
3777  	 * Sanity check: make sure that maxseg will be large
3778  	 * enough to allow some data on segments even if the
3779  	 * all the option space is used (40bytes).  Otherwise
3780  	 * funny things may happen in tcp_output.
3781  	 *
3782  	 * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3783  	 */
3784  	mss = max(mss, 64);
3785  
3786  	tp->t_maxseg = mss;
3787  }
3788  
3789  void
3790  tcp_mss(struct tcpcb *tp, int offer)
3791  {
3792  	int mss;
3793  	uint32_t bufsize;
3794  	struct inpcb *inp = tptoinpcb(tp);
3795  	struct socket *so;
3796  	struct hc_metrics_lite metrics;
3797  	struct tcp_ifcap cap;
3798  
3799  	KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
3800  
3801  	bzero(&cap, sizeof(cap));
3802  	tcp_mss_update(tp, offer, -1, &metrics, &cap);
3803  
3804  	mss = tp->t_maxseg;
3805  
3806  	/*
3807  	 * If there's a pipesize, change the socket buffer to that size,
3808  	 * don't change if sb_hiwat is different than default (then it
3809  	 * has been changed on purpose with setsockopt).
3810  	 * Make the socket buffers an integral number of mss units;
3811  	 * if the mss is larger than the socket buffer, decrease the mss.
3812  	 */
3813  	so = inp->inp_socket;
3814  	SOCKBUF_LOCK(&so->so_snd);
3815  	if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
3816  		bufsize = metrics.rmx_sendpipe;
3817  	else
3818  		bufsize = so->so_snd.sb_hiwat;
3819  	if (bufsize < mss)
3820  		mss = bufsize;
3821  	else {
3822  		bufsize = roundup(bufsize, mss);
3823  		if (bufsize > sb_max)
3824  			bufsize = sb_max;
3825  		if (bufsize > so->so_snd.sb_hiwat)
3826  			(void)sbreserve_locked(so, SO_SND, bufsize, NULL);
3827  	}
3828  	SOCKBUF_UNLOCK(&so->so_snd);
3829  	/*
3830  	 * Sanity check: make sure that maxseg will be large
3831  	 * enough to allow some data on segments even if the
3832  	 * all the option space is used (40bytes).  Otherwise
3833  	 * funny things may happen in tcp_output.
3834  	 *
3835  	 * XXXGL: shouldn't we reserve space for IP/IPv6 options?
3836  	 */
3837  	tp->t_maxseg = max(mss, 64);
3838  
3839  	SOCKBUF_LOCK(&so->so_rcv);
3840  	if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
3841  		bufsize = metrics.rmx_recvpipe;
3842  	else
3843  		bufsize = so->so_rcv.sb_hiwat;
3844  	if (bufsize > mss) {
3845  		bufsize = roundup(bufsize, mss);
3846  		if (bufsize > sb_max)
3847  			bufsize = sb_max;
3848  		if (bufsize > so->so_rcv.sb_hiwat)
3849  			(void)sbreserve_locked(so, SO_RCV, bufsize, NULL);
3850  	}
3851  	SOCKBUF_UNLOCK(&so->so_rcv);
3852  
3853  	/* Check the interface for TSO capabilities. */
3854  	if (cap.ifcap & CSUM_TSO) {
3855  		tp->t_flags |= TF_TSO;
3856  		tp->t_tsomax = cap.tsomax;
3857  		tp->t_tsomaxsegcount = cap.tsomaxsegcount;
3858  		tp->t_tsomaxsegsize = cap.tsomaxsegsize;
3859  	}
3860  }
3861  
3862  /*
3863   * Determine the MSS option to send on an outgoing SYN.
3864   */
3865  int
3866  tcp_mssopt(struct in_conninfo *inc)
3867  {
3868  	int mss = 0;
3869  	uint32_t thcmtu = 0;
3870  	uint32_t maxmtu = 0;
3871  	size_t min_protoh;
3872  
3873  	KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
3874  
3875  #ifdef INET6
3876  	if (inc->inc_flags & INC_ISIPV6) {
3877  		mss = V_tcp_v6mssdflt;
3878  		maxmtu = tcp_maxmtu6(inc, NULL);
3879  		min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
3880  	}
3881  #endif
3882  #if defined(INET) && defined(INET6)
3883  	else
3884  #endif
3885  #ifdef INET
3886  	{
3887  		mss = V_tcp_mssdflt;
3888  		maxmtu = tcp_maxmtu(inc, NULL);
3889  		min_protoh = sizeof(struct tcpiphdr);
3890  	}
3891  #endif
3892  #if defined(INET6) || defined(INET)
3893  	thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
3894  #endif
3895  
3896  	if (maxmtu && thcmtu)
3897  		mss = min(maxmtu, thcmtu) - min_protoh;
3898  	else if (maxmtu || thcmtu)
3899  		mss = max(maxmtu, thcmtu) - min_protoh;
3900  
3901  	return (mss);
3902  }
3903  
3904  void
3905  tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
3906  {
3907  	int snd_cnt = 0, limit = 0, del_data = 0, pipe = 0;
3908  	int maxseg = tcp_maxseg(tp);
3909  
3910  	INP_WLOCK_ASSERT(tptoinpcb(tp));
3911  
3912  	/*
3913  	 * Compute the amount of data that this ACK is indicating
3914  	 * (del_data) and an estimate of how many bytes are in the
3915  	 * network.
3916  	 */
3917  	if (tcp_is_sack_recovery(tp, to) ||
3918  	    (IN_CONGRECOVERY(tp->t_flags) &&
3919  	     !IN_FASTRECOVERY(tp->t_flags))) {
3920  		del_data = tp->sackhint.delivered_data;
3921  		if (V_tcp_do_newsack)
3922  			pipe = tcp_compute_pipe(tp);
3923  		else
3924  			pipe = (tp->snd_nxt - tp->snd_fack) +
3925  				tp->sackhint.sack_bytes_rexmit;
3926  	} else {
3927  		if (tp->sackhint.prr_delivered < (tcprexmtthresh * maxseg +
3928  					     tp->snd_recover - tp->snd_una))
3929  			del_data = maxseg;
3930  		pipe = imax(0, tp->snd_max - tp->snd_una -
3931  			    imin(INT_MAX / 65536, tp->t_dupacks) * maxseg);
3932  	}
3933  	tp->sackhint.prr_delivered += del_data;
3934  	/*
3935  	 * Proportional Rate Reduction
3936  	 */
3937  	if (pipe >= tp->snd_ssthresh) {
3938  		if (tp->sackhint.recover_fs == 0)
3939  			tp->sackhint.recover_fs =
3940  			    imax(1, tp->snd_nxt - tp->snd_una);
3941  		snd_cnt = howmany((long)tp->sackhint.prr_delivered *
3942  			    tp->snd_ssthresh, tp->sackhint.recover_fs) -
3943  			    tp->sackhint.prr_out;
3944  	} else {
3945  		if (V_tcp_do_prr_conservative || (del_data == 0))
3946  			limit = tp->sackhint.prr_delivered -
3947  				tp->sackhint.prr_out;
3948  		else
3949  			limit = imax(tp->sackhint.prr_delivered -
3950  				    tp->sackhint.prr_out, del_data) +
3951  				    maxseg;
3952  		snd_cnt = imin((tp->snd_ssthresh - pipe), limit);
3953  	}
3954  	snd_cnt = imax(snd_cnt, 0) / maxseg;
3955  	/*
3956  	 * Send snd_cnt new data into the network in response to this ack.
3957  	 * If there is going to be a SACK retransmission, adjust snd_cwnd
3958  	 * accordingly.
3959  	 */
3960  	if (IN_FASTRECOVERY(tp->t_flags)) {
3961  		if (tcp_is_sack_recovery(tp, to)) {
3962  			tp->snd_cwnd = tp->snd_nxt - tp->snd_recover +
3963  					    tp->sackhint.sack_bytes_rexmit +
3964  					    (snd_cnt * maxseg);
3965  		} else {
3966  			tp->snd_cwnd = (tp->snd_max - tp->snd_una) +
3967  					    (snd_cnt * maxseg);
3968  		}
3969  	} else if (IN_CONGRECOVERY(tp->t_flags))
3970  		tp->snd_cwnd = pipe - del_data + (snd_cnt * maxseg);
3971  	tp->snd_cwnd = imax(maxseg, tp->snd_cwnd);
3972  }
3973  
3974  /*
3975   * On a partial ack arrives, force the retransmission of the
3976   * next unacknowledged segment.  Do not clear tp->t_dupacks.
3977   * By setting snd_nxt to ti_ack, this forces retransmission timer to
3978   * be started again.
3979   */
3980  void
3981  tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
3982  {
3983  	tcp_seq onxt = tp->snd_nxt;
3984  	uint32_t ocwnd = tp->snd_cwnd;
3985  	u_int maxseg = tcp_maxseg(tp);
3986  
3987  	INP_WLOCK_ASSERT(tptoinpcb(tp));
3988  
3989  	tcp_timer_activate(tp, TT_REXMT, 0);
3990  	tp->t_rtttime = 0;
3991  	tp->snd_nxt = th->th_ack;
3992  	/*
3993  	 * Set snd_cwnd to one segment beyond acknowledged offset.
3994  	 * (tp->snd_una has not yet been updated when this function is called.)
3995  	 */
3996  	tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
3997  	tp->t_flags |= TF_ACKNOW;
3998  	(void) tcp_output(tp);
3999  	tp->snd_cwnd = ocwnd;
4000  	if (SEQ_GT(onxt, tp->snd_nxt))
4001  		tp->snd_nxt = onxt;
4002  	/*
4003  	 * Partial window deflation.  Relies on fact that tp->snd_una
4004  	 * not updated yet.
4005  	 */
4006  	if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
4007  		tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
4008  	else
4009  		tp->snd_cwnd = 0;
4010  	tp->snd_cwnd += maxseg;
4011  }
4012  
4013  int
4014  tcp_compute_pipe(struct tcpcb *tp)
4015  {
4016  	if (tp->t_fb->tfb_compute_pipe == NULL) {
4017  		return (tp->snd_max - tp->snd_una +
4018  			tp->sackhint.sack_bytes_rexmit -
4019  			tp->sackhint.sacked_bytes);
4020  	} else {
4021  		return((*tp->t_fb->tfb_compute_pipe)(tp));
4022  	}
4023  }
4024  
4025  uint32_t
4026  tcp_compute_initwnd(uint32_t maxseg)
4027  {
4028  	/*
4029  	 * Calculate the Initial Window, also used as Restart Window
4030  	 *
4031  	 * RFC5681 Section 3.1 specifies the default conservative values.
4032  	 * RFC3390 specifies slightly more aggressive values.
4033  	 * RFC6928 increases it to ten segments.
4034  	 * Support for user specified value for initial flight size.
4035  	 */
4036  	if (V_tcp_initcwnd_segments)
4037  		return min(V_tcp_initcwnd_segments * maxseg,
4038  		    max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
4039  	else if (V_tcp_do_rfc3390)
4040  		return min(4 * maxseg, max(2 * maxseg, 4380));
4041  	else {
4042  		/* Per RFC5681 Section 3.1 */
4043  		if (maxseg > 2190)
4044  			return (2 * maxseg);
4045  		else if (maxseg > 1095)
4046  			return (3 * maxseg);
4047  		else
4048  			return (4 * maxseg);
4049  	}
4050  }
4051