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freebsd-skq/sys/netinet/tcp_input.c
Randall Stewart 13c0e198ca tcp: Fix bugs related to the PUSH bit and rack and an ack war 
Michaels testing with UDP tunneling found an issue with the push bit, which was only partly fixed
in the last commit. The problem is the left edge gets transmitted before the adjustments are done
to the send_map, this means that right edge bits must be considered to be added only if
the entire RSM is being retransmitted.

Now syzkaller also continued to find a crash, which Michael sent me the reproducer for. Turns
out that the reproducer on default (freebsd) stack made the stack get into an ack-war with itself.
After fixing the reference issues in rack the same ack-war was found in rack (and bbr). Basically
what happens is we go into the reassembly code and lose the FIN bit. The trick here is we
should not be going into the reassembly code if tlen == 0 i.e. the peer never sent you anything.
That then gets the proper action on the FIN bit but then you end up in LAST_ACK with no
timers running. This is because the usrclosed function gets called and the FIN's and such have
already been exchanged. So when we should be entering FIN_WAIT2 (or even FIN_WAIT1) we get
stuck in LAST_ACK. Fixing this means tweaking the usrclosed function so that we properly
recognize the condition and drop into FIN_WAIT2 where a timer will allow at least TP_MAXIDLE
before closing (to allow time for the peer to retransmit its FIN if the ack is lost). Setting the fast_finwait2
timer can speed this up in testing.

Reviewed by: mtuexen,rscheff
Sponsored by: Netflix Inc
Differential Revision:	https://reviews.freebsd.org/D30451
2021-05-25 13:23:31 -04:00

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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California. All rights reserved.
* Copyright (c) 2007-2008,2010
* Swinburne University of Technology, Melbourne, Australia.
* Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
* Copyright (c) 2010 The FreeBSD Foundation
* Copyright (c) 2010-2011 Juniper Networks, Inc.
* All rights reserved.
*
* Portions of this software were developed at the Centre for Advanced Internet
* Architectures, Swinburne University of Technology, by Lawrence Stewart,
* James Healy and David Hayes, made possible in part by a grant from the Cisco
* University Research Program Fund at Community Foundation Silicon Valley.
*
* Portions of this software were developed at the Centre for Advanced
* Internet Architectures, Swinburne University of Technology, Melbourne,
* Australia by David Hayes under sponsorship from the FreeBSD Foundation.
*
* Portions of this software were developed by Robert N. M. Watson under
* contract to Juniper Networks, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_tcpdebug.h"
#include <sys/param.h>
#include <sys/arb.h>
#include <sys/kernel.h>
#ifdef TCP_HHOOK
#include <sys/hhook.h>
#endif
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/proc.h> /* for proc0 declaration */
#include <sys/protosw.h>
#include <sys/qmath.h>
#include <sys/sdt.h>
#include <sys/signalvar.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#include <sys/stats.h>
#include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
#include <vm/uma.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/route.h>
#include <net/vnet.h>
#define TCPSTATES /* for logging */
#include <netinet/in.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h> /* required for icmp_var.h */
#include <netinet/icmp_var.h> /* for ICMP_BANDLIM */
#include <netinet/ip_var.h>
#include <netinet/ip_options.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/in6_var.h>
#include <netinet6/ip6_var.h>
#include <netinet6/nd6.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet6/tcp6_var.h>
#include <netinet/tcpip.h>
#include <netinet/cc/cc.h>
#include <netinet/tcp_fastopen.h>
#ifdef TCPPCAP
#include <netinet/tcp_pcap.h>
#endif
#include <netinet/tcp_syncache.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
#endif /* TCPDEBUG */
#ifdef TCP_OFFLOAD
#include <netinet/tcp_offload.h>
#endif
#include <netinet/udp.h>
#include <netipsec/ipsec_support.h>
#include <machine/in_cksum.h>
#include <security/mac/mac_framework.h>
const int tcprexmtthresh = 3;
VNET_DEFINE(int, tcp_log_in_vain) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_in_vain, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_log_in_vain), 0,
"Log all incoming TCP segments to closed ports");
VNET_DEFINE(int, blackhole) = 0;
#define V_blackhole VNET(blackhole)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, blackhole, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(blackhole), 0,
"Do not send RST on segments to closed ports");
VNET_DEFINE(int, tcp_delack_enabled) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, delayed_ack, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_delack_enabled), 0,
"Delay ACK to try and piggyback it onto a data packet");
VNET_DEFINE(int, drop_synfin) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(drop_synfin), 0,
"Drop TCP packets with SYN+FIN set");
VNET_DEFINE(int, tcp_do_prr_conservative) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr_conservative, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_prr_conservative), 0,
"Do conservative Proportional Rate Reduction");
VNET_DEFINE(int, tcp_do_prr) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_prr), 1,
"Enable Proportional Rate Reduction per RFC 6937");
VNET_DEFINE(int, tcp_do_lrd) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_lrd, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_lrd), 1,
"Perform Lost Retransmission Detection");
VNET_DEFINE(int, tcp_do_newcwv) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, newcwv, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_newcwv), 0,
"Enable New Congestion Window Validation per RFC7661");
VNET_DEFINE(int, tcp_do_rfc3042) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_rfc3042), 0,
"Enable RFC 3042 (Limited Transmit)");
VNET_DEFINE(int, tcp_do_rfc3390) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3390, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_rfc3390), 0,
"Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
VNET_DEFINE(int, tcp_initcwnd_segments) = 10;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, initcwnd_segments,
CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_initcwnd_segments), 0,
"Slow-start flight size (initial congestion window) in number of segments");
VNET_DEFINE(int, tcp_do_rfc3465) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_rfc3465), 0,
"Enable RFC 3465 (Appropriate Byte Counting)");
VNET_DEFINE(int, tcp_abc_l_var) = 2;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_abc_l_var), 2,
"Cap the max cwnd increment during slow-start to this number of segments");
static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
"TCP ECN");
VNET_DEFINE(int, tcp_do_ecn) = 2;
SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_ecn), 0,
"TCP ECN support");
VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_ecn_maxretries), 0,
"Max retries before giving up on ECN");
VNET_DEFINE(int, tcp_insecure_syn) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_syn, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_insecure_syn), 0,
"Follow RFC793 instead of RFC5961 criteria for accepting SYN packets");
VNET_DEFINE(int, tcp_insecure_rst) = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, insecure_rst, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_insecure_rst), 0,
"Follow RFC793 instead of RFC5961 criteria for accepting RST packets");
VNET_DEFINE(int, tcp_recvspace) = 1024*64;
#define V_tcp_recvspace VNET(tcp_recvspace)
SYSCTL_INT(_net_inet_tcp, TCPCTL_RECVSPACE, recvspace, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_recvspace), 0, "Initial receive socket buffer size");
VNET_DEFINE(int, tcp_do_autorcvbuf) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_do_autorcvbuf), 0,
"Enable automatic receive buffer sizing");
VNET_DEFINE(int, tcp_autorcvbuf_max) = 2*1024*1024;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, recvbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
&VNET_NAME(tcp_autorcvbuf_max), 0,
"Max size of automatic receive buffer");
VNET_DEFINE(struct inpcbhead, tcb);
#define tcb6 tcb /* for KAME src sync over BSD*'s */
VNET_DEFINE(struct inpcbinfo, tcbinfo);
/*
* TCP statistics are stored in an array of counter(9)s, which size matches
* size of struct tcpstat. TCP running connection count is a regular array.
*/
VNET_PCPUSTAT_DEFINE(struct tcpstat, tcpstat);
SYSCTL_VNET_PCPUSTAT(_net_inet_tcp, TCPCTL_STATS, stats, struct tcpstat,
tcpstat, "TCP statistics (struct tcpstat, netinet/tcp_var.h)");
VNET_DEFINE(counter_u64_t, tcps_states[TCP_NSTATES]);
SYSCTL_COUNTER_U64_ARRAY(_net_inet_tcp, TCPCTL_STATES, states, CTLFLAG_RD |
CTLFLAG_VNET, &VNET_NAME(tcps_states)[0], TCP_NSTATES,
"TCP connection counts by TCP state");
static void
tcp_vnet_init(const void *unused)
{
COUNTER_ARRAY_ALLOC(V_tcps_states, TCP_NSTATES, M_WAITOK);
VNET_PCPUSTAT_ALLOC(tcpstat, M_WAITOK);
}
VNET_SYSINIT(tcp_vnet_init, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
tcp_vnet_init, NULL);
#ifdef VIMAGE
static void
tcp_vnet_uninit(const void *unused)
{
COUNTER_ARRAY_FREE(V_tcps_states, TCP_NSTATES);
VNET_PCPUSTAT_FREE(tcpstat);
}
VNET_SYSUNINIT(tcp_vnet_uninit, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY,
tcp_vnet_uninit, NULL);
#endif /* VIMAGE */
/*
* Kernel module interface for updating tcpstat. The first argument is an index
* into tcpstat treated as an array.
*/
void
kmod_tcpstat_add(int statnum, int val)
{
counter_u64_add(VNET(tcpstat)[statnum], val);
}
#ifdef TCP_HHOOK
/*
* Wrapper for the TCP established input helper hook.
*/
void
hhook_run_tcp_est_in(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
{
struct tcp_hhook_data hhook_data;
if (V_tcp_hhh[HHOOK_TCP_EST_IN]->hhh_nhooks > 0) {
hhook_data.tp = tp;
hhook_data.th = th;
hhook_data.to = to;
hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_IN], &hhook_data,
tp->osd);
}
}
#endif
/*
* CC wrapper hook functions
*/
void
cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
uint16_t type)
{
#ifdef STATS
int32_t gput;
#endif
INP_WLOCK_ASSERT(tp->t_inpcb);
tp->ccv->nsegs = nsegs;
tp->ccv->bytes_this_ack = BYTES_THIS_ACK(tp, th);
if ((!V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd)) ||
(V_tcp_do_newcwv && (tp->snd_cwnd <= tp->snd_wnd) &&
(tp->snd_cwnd < (tcp_compute_pipe(tp) * 2))))
tp->ccv->flags |= CCF_CWND_LIMITED;
else
tp->ccv->flags &= ~CCF_CWND_LIMITED;
if (type == CC_ACK) {
#ifdef STATS
stats_voi_update_abs_s32(tp->t_stats, VOI_TCP_CALCFRWINDIFF,
((int32_t)tp->snd_cwnd) - tp->snd_wnd);
if (!IN_RECOVERY(tp->t_flags))
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_ACKLEN,
tp->ccv->bytes_this_ack / (tcp_maxseg(tp) * nsegs));
if ((tp->t_flags & TF_GPUTINPROG) &&
SEQ_GEQ(th->th_ack, tp->gput_ack)) {
/*
* Compute goodput in bits per millisecond.
*/
gput = (((int64_t)(th->th_ack - tp->gput_seq)) << 3) /
max(1, tcp_ts_getticks() - tp->gput_ts);
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_GPUT,
gput);
/*
* XXXLAS: This is a temporary hack, and should be
* chained off VOI_TCP_GPUT when stats(9) grows an API
* to deal with chained VOIs.
*/
if (tp->t_stats_gput_prev > 0)
stats_voi_update_abs_s32(tp->t_stats,
VOI_TCP_GPUT_ND,
((gput - tp->t_stats_gput_prev) * 100) /
tp->t_stats_gput_prev);
tp->t_flags &= ~TF_GPUTINPROG;
tp->t_stats_gput_prev = gput;
}
#endif /* STATS */
if (tp->snd_cwnd > tp->snd_ssthresh) {
tp->t_bytes_acked += tp->ccv->bytes_this_ack;
if (tp->t_bytes_acked >= tp->snd_cwnd) {
tp->t_bytes_acked -= tp->snd_cwnd;
tp->ccv->flags |= CCF_ABC_SENTAWND;
}
} else {
tp->ccv->flags &= ~CCF_ABC_SENTAWND;
tp->t_bytes_acked = 0;
}
}
if (CC_ALGO(tp)->ack_received != NULL) {
/* XXXLAS: Find a way to live without this */
tp->ccv->curack = th->th_ack;
CC_ALGO(tp)->ack_received(tp->ccv, type);
}
#ifdef STATS
stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_LCWIN, tp->snd_cwnd);
#endif
}
void
cc_conn_init(struct tcpcb *tp)
{
struct hc_metrics_lite metrics;
struct inpcb *inp = tp->t_inpcb;
u_int maxseg;
int rtt;
INP_WLOCK_ASSERT(tp->t_inpcb);
tcp_hc_get(&inp->inp_inc, &metrics);
maxseg = tcp_maxseg(tp);
if (tp->t_srtt == 0 && (rtt = metrics.rmx_rtt)) {
tp->t_srtt = rtt;
tp->t_rttbest = tp->t_srtt + TCP_RTT_SCALE;
TCPSTAT_INC(tcps_usedrtt);
if (metrics.rmx_rttvar) {
tp->t_rttvar = metrics.rmx_rttvar;
TCPSTAT_INC(tcps_usedrttvar);
} else {
/* default variation is +- 1 rtt */
tp->t_rttvar =
tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
}
TCPT_RANGESET(tp->t_rxtcur,
((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
tp->t_rttmin, TCPTV_REXMTMAX);
}
if (metrics.rmx_ssthresh) {
/*
* There's some sort of gateway or interface
* buffer limit on the path. Use this to set
* the slow start threshold, but set the
* threshold to no less than 2*mss.
*/
tp->snd_ssthresh = max(2 * maxseg, metrics.rmx_ssthresh);
TCPSTAT_INC(tcps_usedssthresh);
}
/*
* Set the initial slow-start flight size.
*
* If a SYN or SYN/ACK was lost and retransmitted, we have to
* reduce the initial CWND to one segment as congestion is likely
* requiring us to be cautious.
*/
if (tp->snd_cwnd == 1)
tp->snd_cwnd = maxseg; /* SYN(-ACK) lost */
else
tp->snd_cwnd = tcp_compute_initwnd(maxseg);
if (CC_ALGO(tp)->conn_init != NULL)
CC_ALGO(tp)->conn_init(tp->ccv);
}
void inline
cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
{
INP_WLOCK_ASSERT(tp->t_inpcb);
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_CSIG, type);
#endif
switch(type) {
case CC_NDUPACK:
if (!IN_FASTRECOVERY(tp->t_flags)) {
tp->snd_recover = tp->snd_max;
if (tp->t_flags2 & TF2_ECN_PERMIT)
tp->t_flags2 |= TF2_ECN_SND_CWR;
}
break;
case CC_ECN:
if (!IN_CONGRECOVERY(tp->t_flags) ||
/*
* Allow ECN reaction on ACK to CWR, if
* that data segment was also CE marked.
*/
SEQ_GEQ(th->th_ack, tp->snd_recover)) {
EXIT_CONGRECOVERY(tp->t_flags);
TCPSTAT_INC(tcps_ecn_rcwnd);
tp->snd_recover = tp->snd_max + 1;
if (tp->t_flags2 & TF2_ECN_PERMIT)
tp->t_flags2 |= TF2_ECN_SND_CWR;
}
break;
case CC_RTO:
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
EXIT_RECOVERY(tp->t_flags);
if (tp->t_flags2 & TF2_ECN_PERMIT)
tp->t_flags2 |= TF2_ECN_SND_CWR;
break;
case CC_RTO_ERR:
TCPSTAT_INC(tcps_sndrexmitbad);
/* RTO was unnecessary, so reset everything. */
tp->snd_cwnd = tp->snd_cwnd_prev;
tp->snd_ssthresh = tp->snd_ssthresh_prev;
tp->snd_recover = tp->snd_recover_prev;
if (tp->t_flags & TF_WASFRECOVERY)
ENTER_FASTRECOVERY(tp->t_flags);
if (tp->t_flags & TF_WASCRECOVERY)
ENTER_CONGRECOVERY(tp->t_flags);
tp->snd_nxt = tp->snd_max;
tp->t_flags &= ~TF_PREVVALID;
tp->t_badrxtwin = 0;
break;
}
if (CC_ALGO(tp)->cong_signal != NULL) {
if (th != NULL)
tp->ccv->curack = th->th_ack;
CC_ALGO(tp)->cong_signal(tp->ccv, type);
}
}
void inline
cc_post_recovery(struct tcpcb *tp, struct tcphdr *th)
{
INP_WLOCK_ASSERT(tp->t_inpcb);
/* XXXLAS: KASSERT that we're in recovery? */
if (CC_ALGO(tp)->post_recovery != NULL) {
tp->ccv->curack = th->th_ack;
CC_ALGO(tp)->post_recovery(tp->ccv);
}
/* XXXLAS: EXIT_RECOVERY ? */
tp->t_bytes_acked = 0;
tp->sackhint.delivered_data = 0;
tp->sackhint.prr_out = 0;
}
/*
* Indicate whether this ack should be delayed. We can delay the ack if
* following conditions are met:
* - There is no delayed ack timer in progress.
* - Our last ack wasn't a 0-sized window. We never want to delay
* the ack that opens up a 0-sized window.
* - LRO wasn't used for this segment. We make sure by checking that the
* segment size is not larger than the MSS.
*/
#define DELAY_ACK(tp, tlen) \
((!tcp_timer_active(tp, TT_DELACK) && \
(tp->t_flags & TF_RXWIN0SENT) == 0) && \
(tlen <= tp->t_maxseg) && \
(V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
void inline
cc_ecnpkt_handler_flags(struct tcpcb *tp, uint16_t flags, uint8_t iptos)
{
INP_WLOCK_ASSERT(tp->t_inpcb);
if (CC_ALGO(tp)->ecnpkt_handler != NULL) {
switch (iptos & IPTOS_ECN_MASK) {
case IPTOS_ECN_CE:
tp->ccv->flags |= CCF_IPHDR_CE;
break;
case IPTOS_ECN_ECT0:
/* FALLTHROUGH */
case IPTOS_ECN_ECT1:
/* FALLTHROUGH */
case IPTOS_ECN_NOTECT:
tp->ccv->flags &= ~CCF_IPHDR_CE;
break;
}
if (flags & TH_CWR)
tp->ccv->flags |= CCF_TCPHDR_CWR;
else
tp->ccv->flags &= ~CCF_TCPHDR_CWR;
CC_ALGO(tp)->ecnpkt_handler(tp->ccv);
if (tp->ccv->flags & CCF_ACKNOW) {
tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
tp->t_flags |= TF_ACKNOW;
}
}
}
void inline
cc_ecnpkt_handler(struct tcpcb *tp, struct tcphdr *th, uint8_t iptos)
{
cc_ecnpkt_handler_flags(tp, th->th_flags, iptos);
}
/*
* TCP input handling is split into multiple parts:
* tcp6_input is a thin wrapper around tcp_input for the extended
* ip6_protox[] call format in ip6_input
* tcp_input handles primary segment validation, inpcb lookup and
* SYN processing on listen sockets
* tcp_do_segment processes the ACK and text of the segment for
* establishing, established and closing connections
*/
#ifdef INET6
int
tcp6_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
{
struct mbuf *m;
struct in6_ifaddr *ia6;
struct ip6_hdr *ip6;
m = *mp;
if (m->m_len < *offp + sizeof(struct tcphdr)) {
m = m_pullup(m, *offp + sizeof(struct tcphdr));
if (m == NULL) {
*mp = m;
TCPSTAT_INC(tcps_rcvshort);
return (IPPROTO_DONE);
}
}
/*
* draft-itojun-ipv6-tcp-to-anycast
* better place to put this in?
*/
ip6 = mtod(m, struct ip6_hdr *);
ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
if (ia6 && (ia6->ia6_flags & IN6_IFF_ANYCAST)) {
icmp6_error(m, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADDR,
(caddr_t)&ip6->ip6_dst - (caddr_t)ip6);
*mp = NULL;
return (IPPROTO_DONE);
}
*mp = m;
return (tcp_input_with_port(mp, offp, proto, port));
}
int
tcp6_input(struct mbuf **mp, int *offp, int proto)
{
return(tcp6_input_with_port(mp, offp, proto, 0));
}
#endif /* INET6 */
int
tcp_input_with_port(struct mbuf **mp, int *offp, int proto, uint16_t port)
{
struct mbuf *m = *mp;
struct tcphdr *th = NULL;
struct ip *ip = NULL;
struct inpcb *inp = NULL;
struct tcpcb *tp = NULL;
struct socket *so = NULL;
u_char *optp = NULL;
int off0;
int optlen = 0;
#ifdef INET
int len;
uint8_t ipttl;
#endif
int tlen = 0, off;
int drop_hdrlen;
int thflags;
int rstreason = 0; /* For badport_bandlim accounting purposes */
int lookupflag;
uint8_t iptos;
struct m_tag *fwd_tag = NULL;
#ifdef INET6
struct ip6_hdr *ip6 = NULL;
int isipv6;
#else
const void *ip6 = NULL;
#endif /* INET6 */
struct tcpopt to; /* options in this segment */
char *s = NULL; /* address and port logging */
#ifdef TCPDEBUG
/*
* The size of tcp_saveipgen must be the size of the max ip header,
* now IPv6.
*/
u_char tcp_saveipgen[IP6_HDR_LEN];
struct tcphdr tcp_savetcp;
short ostate = 0;
#endif
NET_EPOCH_ASSERT();
#ifdef INET6
isipv6 = (mtod(m, struct ip *)->ip_v == 6) ? 1 : 0;
#endif
off0 = *offp;
m = *mp;
*mp = NULL;
to.to_flags = 0;
TCPSTAT_INC(tcps_rcvtotal);
#ifdef INET6
if (isipv6) {
ip6 = mtod(m, struct ip6_hdr *);
th = (struct tcphdr *)((caddr_t)ip6 + off0);
tlen = sizeof(*ip6) + ntohs(ip6->ip6_plen) - off0;
if (port)
goto skip6_csum;
if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID_IPV6) {
if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
th->th_sum = m->m_pkthdr.csum_data;
else
th->th_sum = in6_cksum_pseudo(ip6, tlen,
IPPROTO_TCP, m->m_pkthdr.csum_data);
th->th_sum ^= 0xffff;
} else
th->th_sum = in6_cksum(m, IPPROTO_TCP, off0, tlen);
if (th->th_sum) {
TCPSTAT_INC(tcps_rcvbadsum);
goto drop;
}
skip6_csum:
/*
* Be proactive about unspecified IPv6 address in source.
* As we use all-zero to indicate unbounded/unconnected pcb,
* unspecified IPv6 address can be used to confuse us.
*
* Note that packets with unspecified IPv6 destination is
* already dropped in ip6_input.
*/
if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src)) {
/* XXX stat */
goto drop;
}
iptos = IPV6_TRAFFIC_CLASS(ip6);
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
/*
* Get IP and TCP header together in first mbuf.
* Note: IP leaves IP header in first mbuf.
*/
if (off0 > sizeof (struct ip)) {
ip_stripoptions(m);
off0 = sizeof(struct ip);
}
if (m->m_len < sizeof (struct tcpiphdr)) {
if ((m = m_pullup(m, sizeof (struct tcpiphdr)))
== NULL) {
TCPSTAT_INC(tcps_rcvshort);
return (IPPROTO_DONE);
}
}
ip = mtod(m, struct ip *);
th = (struct tcphdr *)((caddr_t)ip + off0);
tlen = ntohs(ip->ip_len) - off0;
iptos = ip->ip_tos;
if (port)
goto skip_csum;
if (m->m_pkthdr.csum_flags & CSUM_DATA_VALID) {
if (m->m_pkthdr.csum_flags & CSUM_PSEUDO_HDR)
th->th_sum = m->m_pkthdr.csum_data;
else
th->th_sum = in_pseudo(ip->ip_src.s_addr,
ip->ip_dst.s_addr,
htonl(m->m_pkthdr.csum_data + tlen +
IPPROTO_TCP));
th->th_sum ^= 0xffff;
} else {
struct ipovly *ipov = (struct ipovly *)ip;
/*
* Checksum extended TCP header and data.
*/
len = off0 + tlen;
ipttl = ip->ip_ttl;
bzero(ipov->ih_x1, sizeof(ipov->ih_x1));
ipov->ih_len = htons(tlen);
th->th_sum = in_cksum(m, len);
/* Reset length for SDT probes. */
ip->ip_len = htons(len);
/* Reset TOS bits */
ip->ip_tos = iptos;
/* Re-initialization for later version check */
ip->ip_ttl = ipttl;
ip->ip_v = IPVERSION;
ip->ip_hl = off0 >> 2;
}
skip_csum:
if (th->th_sum && (port == 0)) {
TCPSTAT_INC(tcps_rcvbadsum);
goto drop;
}
}
#endif /* INET */
/*
* Check that TCP offset makes sense,
* pull out TCP options and adjust length. XXX
*/
off = th->th_off << 2;
if (off < sizeof (struct tcphdr) || off > tlen) {
TCPSTAT_INC(tcps_rcvbadoff);
goto drop;
}
tlen -= off; /* tlen is used instead of ti->ti_len */
if (off > sizeof (struct tcphdr)) {
#ifdef INET6
if (isipv6) {
if (m->m_len < off0 + off) {
m = m_pullup(m, off0 + off);
if (m == NULL) {
TCPSTAT_INC(tcps_rcvshort);
return (IPPROTO_DONE);
}
}
ip6 = mtod(m, struct ip6_hdr *);
th = (struct tcphdr *)((caddr_t)ip6 + off0);
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
if (m->m_len < sizeof(struct ip) + off) {
if ((m = m_pullup(m, sizeof (struct ip) + off))
== NULL) {
TCPSTAT_INC(tcps_rcvshort);
return (IPPROTO_DONE);
}
ip = mtod(m, struct ip *);
th = (struct tcphdr *)((caddr_t)ip + off0);
}
}
#endif
optlen = off - sizeof (struct tcphdr);
optp = (u_char *)(th + 1);
}
thflags = th->th_flags;
/*
* Convert TCP protocol specific fields to host format.
*/
tcp_fields_to_host(th);
/*
* Delay dropping TCP, IP headers, IPv6 ext headers, and TCP options.
*/
drop_hdrlen = off0 + off;
/*
* Grab info from PACKET_TAG_IPFORWARD tag prepended to the chain.
*/
if (
#ifdef INET6
(isipv6 && (m->m_flags & M_IP6_NEXTHOP))
#ifdef INET
|| (!isipv6 && (m->m_flags & M_IP_NEXTHOP))
#endif
#endif
#if defined(INET) && !defined(INET6)
(m->m_flags & M_IP_NEXTHOP)
#endif
)
fwd_tag = m_tag_find(m, PACKET_TAG_IPFORWARD, NULL);
/*
* For initial SYN packets we don't need write lock on matching
* PCB, be it a listening one or a synchronized one. The packet
* shall not modify its state.
*/
lookupflag = (thflags & (TH_ACK|TH_SYN)) == TH_SYN ?
INPLOOKUP_RLOCKPCB : INPLOOKUP_WLOCKPCB;
findpcb:
#ifdef INET6
if (isipv6 && fwd_tag != NULL) {
struct sockaddr_in6 *next_hop6;
next_hop6 = (struct sockaddr_in6 *)(fwd_tag + 1);
/*
* Transparently forwarded. Pretend to be the destination.
* Already got one like this?
*/
inp = in6_pcblookup_mbuf(&V_tcbinfo,
&ip6->ip6_src, th->th_sport, &ip6->ip6_dst, th->th_dport,
lookupflag, m->m_pkthdr.rcvif, m);
if (!inp) {
/*
* It's new. Try to find the ambushing socket.
* Because we've rewritten the destination address,
* any hardware-generated hash is ignored.
*/
inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_src,
th->th_sport, &next_hop6->sin6_addr,
next_hop6->sin6_port ? ntohs(next_hop6->sin6_port) :
th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
m->m_pkthdr.rcvif);
}
} else if (isipv6) {
inp = in6_pcblookup_mbuf(&V_tcbinfo, &ip6->ip6_src,
th->th_sport, &ip6->ip6_dst, th->th_dport,
INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
}
#endif /* INET6 */
#if defined(INET6) && defined(INET)
else
#endif
#ifdef INET
if (fwd_tag != NULL) {
struct sockaddr_in *next_hop;
next_hop = (struct sockaddr_in *)(fwd_tag+1);
/*
* Transparently forwarded. Pretend to be the destination.
* already got one like this?
*/
inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src, th->th_sport,
ip->ip_dst, th->th_dport, lookupflag, m->m_pkthdr.rcvif, m);
if (!inp) {
/*
* It's new. Try to find the ambushing socket.
* Because we've rewritten the destination address,
* any hardware-generated hash is ignored.
*/
inp = in_pcblookup(&V_tcbinfo, ip->ip_src,
th->th_sport, next_hop->sin_addr,
next_hop->sin_port ? ntohs(next_hop->sin_port) :
th->th_dport, INPLOOKUP_WILDCARD | lookupflag,
m->m_pkthdr.rcvif);
}
} else
inp = in_pcblookup_mbuf(&V_tcbinfo, ip->ip_src,
th->th_sport, ip->ip_dst, th->th_dport,
INPLOOKUP_WILDCARD | lookupflag, m->m_pkthdr.rcvif, m);
#endif /* INET */
/*
* If the INPCB does not exist then all data in the incoming
* segment is discarded and an appropriate RST is sent back.
* XXX MRT Send RST using which routing table?
*/
if (inp == NULL) {
/*
* Log communication attempts to ports that are not
* in use.
*/
if ((V_tcp_log_in_vain == 1 && (thflags & TH_SYN)) ||
V_tcp_log_in_vain == 2) {
if ((s = tcp_log_vain(NULL, th, (void *)ip, ip6)))
log(LOG_INFO, "%s; %s: Connection attempt "
"to closed port\n", s, __func__);
}
/*
* When blackholing do not respond with a RST but
* completely ignore the segment and drop it.
*/
if ((V_blackhole == 1 && (thflags & TH_SYN)) ||
V_blackhole == 2)
goto dropunlock;
rstreason = BANDLIM_RST_CLOSEDPORT;
goto dropwithreset;
}
INP_LOCK_ASSERT(inp);
/*
* While waiting for inp lock during the lookup, another thread
* can have dropped the inpcb, in which case we need to loop back
* and try to find a new inpcb to deliver to.
*/
if (inp->inp_flags & INP_DROPPED) {
INP_UNLOCK(inp);
inp = NULL;
goto findpcb;
}
if ((inp->inp_flowtype == M_HASHTYPE_NONE) &&
(M_HASHTYPE_GET(m) != M_HASHTYPE_NONE) &&
((inp->inp_socket == NULL) ||
(inp->inp_socket->so_options & SO_ACCEPTCONN) == 0)) {
inp->inp_flowid = m->m_pkthdr.flowid;
inp->inp_flowtype = M_HASHTYPE_GET(m);
}
#if defined(IPSEC) || defined(IPSEC_SUPPORT)
#ifdef INET6
if (isipv6 && IPSEC_ENABLED(ipv6) &&
IPSEC_CHECK_POLICY(ipv6, m, inp) != 0) {
goto dropunlock;
}
#ifdef INET
else
#endif
#endif /* INET6 */
#ifdef INET
if (IPSEC_ENABLED(ipv4) &&
IPSEC_CHECK_POLICY(ipv4, m, inp) != 0) {
goto dropunlock;
}
#endif /* INET */
#endif /* IPSEC */
/*
* Check the minimum TTL for socket.
*/
if (inp->inp_ip_minttl != 0) {
#ifdef INET6
if (isipv6) {
if (inp->inp_ip_minttl > ip6->ip6_hlim)
goto dropunlock;
} else
#endif
if (inp->inp_ip_minttl > ip->ip_ttl)
goto dropunlock;
}
/*
* A previous connection in TIMEWAIT state is supposed to catch stray
* or duplicate segments arriving late. If this segment was a
* legitimate new connection attempt, the old INPCB gets removed and
* we can try again to find a listening socket.
*/
if (inp->inp_flags & INP_TIMEWAIT) {
tcp_dooptions(&to, optp, optlen,
(thflags & TH_SYN) ? TO_SYN : 0);
/*
* NB: tcp_twcheck unlocks the INP and frees the mbuf.
*/
if (tcp_twcheck(inp, &to, th, m, tlen))
goto findpcb;
return (IPPROTO_DONE);
}
/*
* The TCPCB may no longer exist if the connection is winding
* down or it is in the CLOSED state. Either way we drop the
* segment and send an appropriate response.
*/
tp = intotcpcb(inp);
if (tp == NULL || tp->t_state == TCPS_CLOSED) {
rstreason = BANDLIM_RST_CLOSEDPORT;
goto dropwithreset;
}
if ((tp->t_port != port) && (tp->t_state > TCPS_LISTEN)) {
rstreason = BANDLIM_RST_CLOSEDPORT;
goto dropwithreset;
}
#ifdef TCP_OFFLOAD
if (tp->t_flags & TF_TOE) {
tcp_offload_input(tp, m);
m = NULL; /* consumed by the TOE driver */
goto dropunlock;
}
#endif
#ifdef MAC
if (mac_inpcb_check_deliver(inp, m))
goto dropunlock;
#endif
so = inp->inp_socket;
KASSERT(so != NULL, ("%s: so == NULL", __func__));
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG) {
ostate = tp->t_state;
#ifdef INET6
if (isipv6) {
bcopy((char *)ip6, (char *)tcp_saveipgen, sizeof(*ip6));
} else
#endif
bcopy((char *)ip, (char *)tcp_saveipgen, sizeof(*ip));
tcp_savetcp = *th;
}
#endif /* TCPDEBUG */
/*
* When the socket is accepting connections (the INPCB is in LISTEN
* state) we look into the SYN cache if this is a new connection
* attempt or the completion of a previous one.
*/
KASSERT(tp->t_state == TCPS_LISTEN || !(so->so_options & SO_ACCEPTCONN),
("%s: so accepting but tp %p not listening", __func__, tp));
if (tp->t_state == TCPS_LISTEN && (so->so_options & SO_ACCEPTCONN)) {
struct in_conninfo inc;
bzero(&inc, sizeof(inc));
#ifdef INET6
if (isipv6) {
inc.inc_flags |= INC_ISIPV6;
if (inp->inp_inc.inc_flags & INC_IPV6MINMTU)
inc.inc_flags |= INC_IPV6MINMTU;
inc.inc6_faddr = ip6->ip6_src;
inc.inc6_laddr = ip6->ip6_dst;
} else
#endif
{
inc.inc_faddr = ip->ip_src;
inc.inc_laddr = ip->ip_dst;
}
inc.inc_fport = th->th_sport;
inc.inc_lport = th->th_dport;
inc.inc_fibnum = so->so_fibnum;
/*
* Check for an existing connection attempt in syncache if
* the flag is only ACK. A successful lookup creates a new
* socket appended to the listen queue in SYN_RECEIVED state.
*/
if ((thflags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK) {
/*
* Parse the TCP options here because
* syncookies need access to the reflected
* timestamp.
*/
tcp_dooptions(&to, optp, optlen, 0);
/*
* NB: syncache_expand() doesn't unlock
* inp and tcpinfo locks.
*/
rstreason = syncache_expand(&inc, &to, th, &so, m, port);
if (rstreason < 0) {
/*
* A failing TCP MD5 signature comparison
* must result in the segment being dropped
* and must not produce any response back
* to the sender.
*/
goto dropunlock;
} else if (rstreason == 0) {
/*
* No syncache entry or ACK was not
* for our SYN/ACK. Send a RST.
* NB: syncache did its own logging
* of the failure cause.
*/
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
tfo_socket_result:
if (so == NULL) {
/*
* We completed the 3-way handshake
* but could not allocate a socket
* either due to memory shortage,
* listen queue length limits or
* global socket limits. Send RST
* or wait and have the remote end
* retransmit the ACK for another
* try.
*/
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Socket allocation failed due to "
"limits or memory shortage, %s\n",
s, __func__,
V_tcp_sc_rst_sock_fail ?
"sending RST" : "try again");
if (V_tcp_sc_rst_sock_fail) {
rstreason = BANDLIM_UNLIMITED;
goto dropwithreset;
} else
goto dropunlock;
}
/*
* Socket is created in state SYN_RECEIVED.
* Unlock the listen socket, lock the newly
* created socket and update the tp variable.
* If we came here via jump to tfo_socket_result,
* then listening socket is read-locked.
*/
INP_UNLOCK(inp); /* listen socket */
inp = sotoinpcb(so);
/*
* New connection inpcb is already locked by
* syncache_expand().
*/
INP_WLOCK_ASSERT(inp);
tp = intotcpcb(inp);
KASSERT(tp->t_state == TCPS_SYN_RECEIVED,
("%s: ", __func__));
/*
* Process the segment and the data it
* contains. tcp_do_segment() consumes
* the mbuf chain and unlocks the inpcb.
*/
TCP_PROBE5(receive, NULL, tp, m, tp, th);
tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen,
iptos);
return (IPPROTO_DONE);
}
/*
* Segment flag validation for new connection attempts:
*
* Our (SYN|ACK) response was rejected.
* Check with syncache and remove entry to prevent
* retransmits.
*
* NB: syncache_chkrst does its own logging of failure
* causes.
*/
if (thflags & TH_RST) {
syncache_chkrst(&inc, th, m, port);
goto dropunlock;
}
/*
* We can't do anything without SYN.
*/
if ((thflags & TH_SYN) == 0) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"SYN is missing, segment ignored\n",
s, __func__);
TCPSTAT_INC(tcps_badsyn);
goto dropunlock;
}
/*
* (SYN|ACK) is bogus on a listen socket.
*/
if (thflags & TH_ACK) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"SYN|ACK invalid, segment rejected\n",
s, __func__);
syncache_badack(&inc, port); /* XXX: Not needed! */
TCPSTAT_INC(tcps_badsyn);
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
/*
* If the drop_synfin option is enabled, drop all
* segments with both the SYN and FIN bits set.
* This prevents e.g. nmap from identifying the
* TCP/IP stack.
* XXX: Poor reasoning. nmap has other methods
* and is constantly refining its stack detection
* strategies.
* XXX: This is a violation of the TCP specification
* and was used by RFC1644.
*/
if ((thflags & TH_FIN) && V_drop_synfin) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"SYN|FIN segment ignored (based on "
"sysctl setting)\n", s, __func__);
TCPSTAT_INC(tcps_badsyn);
goto dropunlock;
}
/*
* Segment's flags are (SYN) or (SYN|FIN).
*
* TH_PUSH, TH_URG, TH_ECE, TH_CWR are ignored
* as they do not affect the state of the TCP FSM.
* The data pointed to by TH_URG and th_urp is ignored.
*/
KASSERT((thflags & (TH_RST|TH_ACK)) == 0,
("%s: Listen socket: TH_RST or TH_ACK set", __func__));
KASSERT(thflags & (TH_SYN),
("%s: Listen socket: TH_SYN not set", __func__));
INP_RLOCK_ASSERT(inp);
#ifdef INET6
/*
* If deprecated address is forbidden,
* we do not accept SYN to deprecated interface
* address to prevent any new inbound connection from
* getting established.
* When we do not accept SYN, we send a TCP RST,
* with deprecated source address (instead of dropping
* it). We compromise it as it is much better for peer
* to send a RST, and RST will be the final packet
* for the exchange.
*
* If we do not forbid deprecated addresses, we accept
* the SYN packet. RFC2462 does not suggest dropping
* SYN in this case.
* If we decipher RFC2462 5.5.4, it says like this:
* 1. use of deprecated addr with existing
* communication is okay - "SHOULD continue to be
* used"
* 2. use of it with new communication:
* (2a) "SHOULD NOT be used if alternate address
* with sufficient scope is available"
* (2b) nothing mentioned otherwise.
* Here we fall into (2b) case as we have no choice in
* our source address selection - we must obey the peer.
*
* The wording in RFC2462 is confusing, and there are
* multiple description text for deprecated address
* handling - worse, they are not exactly the same.
* I believe 5.5.4 is the best one, so we follow 5.5.4.
*/
if (isipv6 && !V_ip6_use_deprecated) {
struct in6_ifaddr *ia6;
ia6 = in6ifa_ifwithaddr(&ip6->ip6_dst, 0 /* XXX */, false);
if (ia6 != NULL &&
(ia6->ia6_flags & IN6_IFF_DEPRECATED)) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt to deprecated "
"IPv6 address rejected\n",
s, __func__);
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
}
#endif /* INET6 */
/*
* Basic sanity checks on incoming SYN requests:
* Don't respond if the destination is a link layer
* broadcast according to RFC1122 4.2.3.10, p. 104.
* If it is from this socket it must be forged.
* Don't respond if the source or destination is a
* global or subnet broad- or multicast address.
* Note that it is quite possible to receive unicast
* link-layer packets with a broadcast IP address. Use
* in_broadcast() to find them.
*/
if (m->m_flags & (M_BCAST|M_MCAST)) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt from broad- or multicast "
"link layer address ignored\n", s, __func__);
goto dropunlock;
}
#ifdef INET6
if (isipv6) {
if (th->th_dport == th->th_sport &&
IN6_ARE_ADDR_EQUAL(&ip6->ip6_dst, &ip6->ip6_src)) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt to/from self "
"ignored\n", s, __func__);
goto dropunlock;
}
if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
IN6_IS_ADDR_MULTICAST(&ip6->ip6_src)) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt from/to multicast "
"address ignored\n", s, __func__);
goto dropunlock;
}
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
if (th->th_dport == th->th_sport &&
ip->ip_dst.s_addr == ip->ip_src.s_addr) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt from/to self "
"ignored\n", s, __func__);
goto dropunlock;
}
if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif)) {
if ((s = tcp_log_addrs(&inc, th, NULL, NULL)))
log(LOG_DEBUG, "%s; %s: Listen socket: "
"Connection attempt from/to broad- "
"or multicast address ignored\n",
s, __func__);
goto dropunlock;
}
}
#endif
/*
* SYN appears to be valid. Create compressed TCP state
* for syncache.
*/
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp,
(void *)tcp_saveipgen, &tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
tcp_dooptions(&to, optp, optlen, TO_SYN);
if ((so = syncache_add(&inc, &to, th, inp, so, m, NULL, NULL,
iptos, port)) != NULL)
goto tfo_socket_result;
/*
* Entry added to syncache and mbuf consumed.
* Only the listen socket is unlocked by syncache_add().
*/
return (IPPROTO_DONE);
} else if (tp->t_state == TCPS_LISTEN) {
/*
* When a listen socket is torn down the SO_ACCEPTCONN
* flag is removed first while connections are drained
* from the accept queue in a unlock/lock cycle of the
* ACCEPT_LOCK, opening a race condition allowing a SYN
* attempt go through unhandled.
*/
goto dropunlock;
}
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
if (tp->t_flags & TF_SIGNATURE) {
tcp_dooptions(&to, optp, optlen, thflags);
if ((to.to_flags & TOF_SIGNATURE) == 0) {
TCPSTAT_INC(tcps_sig_err_nosigopt);
goto dropunlock;
}
if (!TCPMD5_ENABLED() ||
TCPMD5_INPUT(m, th, to.to_signature) != 0)
goto dropunlock;
}
#endif
TCP_PROBE5(receive, NULL, tp, m, tp, th);
/*
* Segment belongs to a connection in SYN_SENT, ESTABLISHED or later
* state. tcp_do_segment() always consumes the mbuf chain, unlocks
* the inpcb, and unlocks pcbinfo.
*
* XXXGL: in case of a pure SYN arriving on existing connection
* TCP stacks won't need to modify the PCB, they would either drop
* the segment silently, or send a challenge ACK. However, we try
* to upgrade the lock, because calling convention for stacks is
* write-lock on PCB. If upgrade fails, drop the SYN.
*/
if (lookupflag == INPLOOKUP_RLOCKPCB && INP_TRY_UPGRADE(inp) == 0)
goto dropunlock;
tp->t_fb->tfb_tcp_do_segment(m, th, so, tp, drop_hdrlen, tlen, iptos);
return (IPPROTO_DONE);
dropwithreset:
TCP_PROBE5(receive, NULL, tp, m, tp, th);
if (inp != NULL) {
tcp_dropwithreset(m, th, tp, tlen, rstreason);
INP_UNLOCK(inp);
} else
tcp_dropwithreset(m, th, NULL, tlen, rstreason);
m = NULL; /* mbuf chain got consumed. */
goto drop;
dropunlock:
if (m != NULL)
TCP_PROBE5(receive, NULL, tp, m, tp, th);
if (inp != NULL)
INP_UNLOCK(inp);
drop:
if (s != NULL)
free(s, M_TCPLOG);
if (m != NULL)
m_freem(m);
return (IPPROTO_DONE);
}
/*
* Automatic sizing of receive socket buffer. Often the send
* buffer size is not optimally adjusted to the actual network
* conditions at hand (delay bandwidth product). Setting the
* buffer size too small limits throughput on links with high
* bandwidth and high delay (eg. trans-continental/oceanic links).
*
* On the receive side the socket buffer memory is only rarely
* used to any significant extent. This allows us to be much
* more aggressive in scaling the receive socket buffer. For
* the case that the buffer space is actually used to a large
* extent and we run out of kernel memory we can simply drop
* the new segments; TCP on the sender will just retransmit it
* later. Setting the buffer size too big may only consume too
* much kernel memory if the application doesn't read() from
* the socket or packet loss or reordering makes use of the
* reassembly queue.
*
* The criteria to step up the receive buffer one notch are:
* 1. Application has not set receive buffer size with
* SO_RCVBUF. Setting SO_RCVBUF clears SB_AUTOSIZE.
* 2. the number of bytes received during 1/2 of an sRTT
* is at least 3/8 of the current socket buffer size.
* 3. receive buffer size has not hit maximal automatic size;
*
* If all of the criteria are met we increaset the socket buffer
* by a 1/2 (bounded by the max). This allows us to keep ahead
* of slow-start but also makes it so our peer never gets limited
* by our rwnd which we then open up causing a burst.
*
* This algorithm does two steps per RTT at most and only if
* we receive a bulk stream w/o packet losses or reorderings.
* Shrinking the buffer during idle times is not necessary as
* it doesn't consume any memory when idle.
*
* TODO: Only step up if the application is actually serving
* the buffer to better manage the socket buffer resources.
*/
int
tcp_autorcvbuf(struct mbuf *m, struct tcphdr *th, struct socket *so,
struct tcpcb *tp, int tlen)
{
int newsize = 0;
if (V_tcp_do_autorcvbuf && (so->so_rcv.sb_flags & SB_AUTOSIZE) &&
tp->t_srtt != 0 && tp->rfbuf_ts != 0 &&
TCP_TS_TO_TICKS(tcp_ts_getticks() - tp->rfbuf_ts) >
((tp->t_srtt >> TCP_RTT_SHIFT)/2)) {
if (tp->rfbuf_cnt > ((so->so_rcv.sb_hiwat / 2)/ 4 * 3) &&
so->so_rcv.sb_hiwat < V_tcp_autorcvbuf_max) {
newsize = min((so->so_rcv.sb_hiwat + (so->so_rcv.sb_hiwat/2)), V_tcp_autorcvbuf_max);
}
TCP_PROBE6(receive__autoresize, NULL, tp, m, tp, th, newsize);
/* Start over with next RTT. */
tp->rfbuf_ts = 0;
tp->rfbuf_cnt = 0;
} else {
tp->rfbuf_cnt += tlen; /* add up */
}
return (newsize);
}
int
tcp_input(struct mbuf **mp, int *offp, int proto)
{
return(tcp_input_with_port(mp, offp, proto, 0));
}
void
tcp_handle_wakeup(struct tcpcb *tp, struct socket *so)
{
/*
* Since tp might be gone if the session entered
* the TIME_WAIT state before coming here, we need
* to check if the socket is still connected.
*/
if (tp == NULL) {
return;
}
if (so == NULL) {
return;
}
INP_LOCK_ASSERT(tp->t_inpcb);
if (tp->t_flags & TF_WAKESOR) {
tp->t_flags &= ~TF_WAKESOR;
SOCKBUF_LOCK_ASSERT(&so->so_rcv);
sorwakeup_locked(so);
}
}
void
tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
struct tcpcb *tp, int drop_hdrlen, int tlen, uint8_t iptos)
{
int thflags, acked, ourfinisacked, needoutput = 0, sack_changed;
int rstreason, todrop, win, incforsyn = 0;
uint32_t tiwin;
uint16_t nsegs;
char *s;
struct in_conninfo *inc;
struct mbuf *mfree;
struct tcpopt to;
int tfo_syn;
u_int maxseg;
#ifdef TCPDEBUG
/*
* The size of tcp_saveipgen must be the size of the max ip header,
* now IPv6.
*/
u_char tcp_saveipgen[IP6_HDR_LEN];
struct tcphdr tcp_savetcp;
short ostate = 0;
#endif
thflags = th->th_flags;
inc = &tp->t_inpcb->inp_inc;
tp->sackhint.last_sack_ack = 0;
sack_changed = 0;
nsegs = max(1, m->m_pkthdr.lro_nsegs);
NET_EPOCH_ASSERT();
INP_WLOCK_ASSERT(tp->t_inpcb);
KASSERT(tp->t_state > TCPS_LISTEN, ("%s: TCPS_LISTEN",
__func__));
KASSERT(tp->t_state != TCPS_TIME_WAIT, ("%s: TCPS_TIME_WAIT",
__func__));
#ifdef TCPPCAP
/* Save segment, if requested. */
tcp_pcap_add(th, m, &(tp->t_inpkts));
#endif
TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_IN, 0,
tlen, NULL, true);
if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
log(LOG_DEBUG, "%s; %s: "
"SYN|FIN segment ignored (based on "
"sysctl setting)\n", s, __func__);
free(s, M_TCPLOG);
}
goto drop;
}
/*
* If a segment with the ACK-bit set arrives in the SYN-SENT state
* check SEQ.ACK first.
*/
if ((tp->t_state == TCPS_SYN_SENT) && (thflags & TH_ACK) &&
(SEQ_LEQ(th->th_ack, tp->iss) || SEQ_GT(th->th_ack, tp->snd_max))) {
rstreason = BANDLIM_UNLIMITED;
goto dropwithreset;
}
/*
* Segment received on connection.
* Reset idle time and keep-alive timer.
* XXX: This should be done after segment
* validation to ignore broken/spoofed segs.
*/
tp->t_rcvtime = ticks;
/*
* Scale up the window into a 32-bit value.
* For the SYN_SENT state the scale is zero.
*/
tiwin = th->th_win << tp->snd_scale;
#ifdef STATS
stats_voi_update_abs_ulong(tp->t_stats, VOI_TCP_FRWIN, tiwin);
#endif
/*
* TCP ECN processing.
*/
if (tp->t_flags2 & TF2_ECN_PERMIT) {
if (thflags & TH_CWR) {
tp->t_flags2 &= ~TF2_ECN_SND_ECE;
tp->t_flags |= TF_ACKNOW;
}
switch (iptos & IPTOS_ECN_MASK) {
case IPTOS_ECN_CE:
tp->t_flags2 |= TF2_ECN_SND_ECE;
TCPSTAT_INC(tcps_ecn_ce);
break;
case IPTOS_ECN_ECT0:
TCPSTAT_INC(tcps_ecn_ect0);
break;
case IPTOS_ECN_ECT1:
TCPSTAT_INC(tcps_ecn_ect1);
break;
}
/* Process a packet differently from RFC3168. */
cc_ecnpkt_handler(tp, th, iptos);
/* Congestion experienced. */
if (thflags & TH_ECE) {
cc_cong_signal(tp, th, CC_ECN);
}
}
/*
* Parse options on any incoming segment.
*/
tcp_dooptions(&to, (u_char *)(th + 1),
(th->th_off << 2) - sizeof(struct tcphdr),
(thflags & TH_SYN) ? TO_SYN : 0);
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
if ((tp->t_flags & TF_SIGNATURE) != 0 &&
(to.to_flags & TOF_SIGNATURE) == 0) {
TCPSTAT_INC(tcps_sig_err_sigopt);
/* XXX: should drop? */
}
#endif
/*
* If echoed timestamp is later than the current time,
* fall back to non RFC1323 RTT calculation. Normalize
* timestamp if syncookies were used when this connection
* was established.
*/
if ((to.to_flags & TOF_TS) && (to.to_tsecr != 0)) {
to.to_tsecr -= tp->ts_offset;
if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks()))
to.to_tsecr = 0;
else if (tp->t_flags & TF_PREVVALID &&
tp->t_badrxtwin != 0 && SEQ_LT(to.to_tsecr, tp->t_badrxtwin))
cc_cong_signal(tp, th, CC_RTO_ERR);
}
/*
* Process options only when we get SYN/ACK back. The SYN case
* for incoming connections is handled in tcp_syncache.
* According to RFC1323 the window field in a SYN (i.e., a <SYN>
* or <SYN,ACK>) segment itself is never scaled.
* XXX this is traditional behavior, may need to be cleaned up.
*/
if (tp->t_state == TCPS_SYN_SENT && (thflags & TH_SYN)) {
/* Handle parallel SYN for ECN */
if (!(thflags & TH_ACK) &&
((thflags & (TH_CWR | TH_ECE)) == (TH_CWR | TH_ECE)) &&
((V_tcp_do_ecn == 1) || (V_tcp_do_ecn == 2))) {
tp->t_flags2 |= TF2_ECN_PERMIT;
tp->t_flags2 |= TF2_ECN_SND_ECE;
TCPSTAT_INC(tcps_ecn_shs);
}
if ((to.to_flags & TOF_SCALE) &&
(tp->t_flags & TF_REQ_SCALE) &&
!(tp->t_flags & TF_NOOPT)) {
tp->t_flags |= TF_RCVD_SCALE;
tp->snd_scale = to.to_wscale;
} else
tp->t_flags &= ~TF_REQ_SCALE;
/*
* Initial send window. It will be updated with
* the next incoming segment to the scaled value.
*/
tp->snd_wnd = th->th_win;
if ((to.to_flags & TOF_TS) &&
(tp->t_flags & TF_REQ_TSTMP) &&
!(tp->t_flags & TF_NOOPT)) {
tp->t_flags |= TF_RCVD_TSTMP;
tp->ts_recent = to.to_tsval;
tp->ts_recent_age = tcp_ts_getticks();
} else
tp->t_flags &= ~TF_REQ_TSTMP;
if (to.to_flags & TOF_MSS)
tcp_mss(tp, to.to_mss);
if ((tp->t_flags & TF_SACK_PERMIT) &&
(!(to.to_flags & TOF_SACKPERM) ||
(tp->t_flags & TF_NOOPT)))
tp->t_flags &= ~TF_SACK_PERMIT;
if (IS_FASTOPEN(tp->t_flags)) {
if ((to.to_flags & TOF_FASTOPEN) &&
!(tp->t_flags & TF_NOOPT)) {
uint16_t mss;
if (to.to_flags & TOF_MSS)
mss = to.to_mss;
else
if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
mss = TCP6_MSS;
else
mss = TCP_MSS;
tcp_fastopen_update_cache(tp, mss,
to.to_tfo_len, to.to_tfo_cookie);
} else
tcp_fastopen_disable_path(tp);
}
}
/*
* If timestamps were negotiated during SYN/ACK and a
* segment without a timestamp is received, silently drop
* the segment, unless it is a RST segment or missing timestamps are
* tolerated.
* See section 3.2 of RFC 7323.
*/
if ((tp->t_flags & TF_RCVD_TSTMP) && !(to.to_flags & TOF_TS)) {
if (((thflags & TH_RST) != 0) || V_tcp_tolerate_missing_ts) {
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
log(LOG_DEBUG, "%s; %s: Timestamp missing, "
"segment processed normally\n",
s, __func__);
free(s, M_TCPLOG);
}
} else {
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
log(LOG_DEBUG, "%s; %s: Timestamp missing, "
"segment silently dropped\n", s, __func__);
free(s, M_TCPLOG);
}
goto drop;
}
}
/*
* If timestamps were not negotiated during SYN/ACK and a
* segment with a timestamp is received, ignore the
* timestamp and process the packet normally.
* See section 3.2 of RFC 7323.
*/
if (!(tp->t_flags & TF_RCVD_TSTMP) && (to.to_flags & TOF_TS)) {
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
log(LOG_DEBUG, "%s; %s: Timestamp not expected, "
"segment processed normally\n", s, __func__);
free(s, M_TCPLOG);
}
}
/*
* Header prediction: check for the two common cases
* of a uni-directional data xfer. If the packet has
* no control flags, is in-sequence, the window didn't
* change and we're not retransmitting, it's a
* candidate. If the length is zero and the ack moved
* forward, we're the sender side of the xfer. Just
* free the data acked & wake any higher level process
* that was blocked waiting for space. If the length
* is non-zero and the ack didn't move, we're the
* receiver side. If we're getting packets in-order
* (the reassembly queue is empty), add the data to
* the socket buffer and note that we need a delayed ack.
* Make sure that the hidden state-flags are also off.
* Since we check for TCPS_ESTABLISHED first, it can only
* be TH_NEEDSYN.
*/
if (tp->t_state == TCPS_ESTABLISHED &&
th->th_seq == tp->rcv_nxt &&
(thflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
tp->snd_nxt == tp->snd_max &&
tiwin && tiwin == tp->snd_wnd &&
((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
SEGQ_EMPTY(tp) &&
((to.to_flags & TOF_TS) == 0 ||
TSTMP_GEQ(to.to_tsval, tp->ts_recent)) ) {
/*
* If last ACK falls within this segment's sequence numbers,
* record the timestamp.
* NOTE that the test is modified according to the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
*/
if ((to.to_flags & TOF_TS) != 0 &&
SEQ_LEQ(th->th_seq, tp->last_ack_sent)) {
tp->ts_recent_age = tcp_ts_getticks();
tp->ts_recent = to.to_tsval;
}
if (tlen == 0) {
if (SEQ_GT(th->th_ack, tp->snd_una) &&
SEQ_LEQ(th->th_ack, tp->snd_max) &&
!IN_RECOVERY(tp->t_flags) &&
(to.to_flags & TOF_SACK) == 0 &&
TAILQ_EMPTY(&tp->snd_holes)) {
/*
* This is a pure ack for outstanding data.
*/
TCPSTAT_INC(tcps_predack);
/*
* "bad retransmit" recovery without timestamps.
*/
if ((to.to_flags & TOF_TS) == 0 &&
tp->t_rxtshift == 1 &&
tp->t_flags & TF_PREVVALID &&
(int)(ticks - tp->t_badrxtwin) < 0) {
cc_cong_signal(tp, th, CC_RTO_ERR);
}
/*
* Recalculate the transmit timer / rtt.
*
* Some boxes send broken timestamp replies
* during the SYN+ACK phase, ignore
* timestamps of 0 or we could calculate a
* huge RTT and blow up the retransmit timer.
*/
if ((to.to_flags & TOF_TS) != 0 &&
to.to_tsecr) {
uint32_t t;
t = tcp_ts_getticks() - to.to_tsecr;
if (!tp->t_rttlow || tp->t_rttlow > t)
tp->t_rttlow = t;
tcp_xmit_timer(tp,
TCP_TS_TO_TICKS(t) + 1);
} else if (tp->t_rtttime &&
SEQ_GT(th->th_ack, tp->t_rtseq)) {
if (!tp->t_rttlow ||
tp->t_rttlow > ticks - tp->t_rtttime)
tp->t_rttlow = ticks - tp->t_rtttime;
tcp_xmit_timer(tp,
ticks - tp->t_rtttime);
}
acked = BYTES_THIS_ACK(tp, th);
#ifdef TCP_HHOOK
/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
hhook_run_tcp_est_in(tp, th, &to);
#endif
TCPSTAT_ADD(tcps_rcvackpack, nsegs);
TCPSTAT_ADD(tcps_rcvackbyte, acked);
sbdrop(&so->so_snd, acked);
if (SEQ_GT(tp->snd_una, tp->snd_recover) &&
SEQ_LEQ(th->th_ack, tp->snd_recover))
tp->snd_recover = th->th_ack - 1;
/*
* Let the congestion control algorithm update
* congestion control related information. This
* typically means increasing the congestion
* window.
*/
cc_ack_received(tp, th, nsegs, CC_ACK);
tp->snd_una = th->th_ack;
/*
* Pull snd_wl2 up to prevent seq wrap relative
* to th_ack.
*/
tp->snd_wl2 = th->th_ack;
tp->t_dupacks = 0;
m_freem(m);
/*
* If all outstanding data are acked, stop
* retransmit timer, otherwise restart timer
* using current (possibly backed-off) value.
* If process is waiting for space,
* wakeup/selwakeup/signal. If data
* are ready to send, let tcp_output
* decide between more output or persist.
*/
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp,
(void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
if (tp->snd_una == tp->snd_max)
tcp_timer_activate(tp, TT_REXMT, 0);
else if (!tcp_timer_active(tp, TT_PERSIST))
tcp_timer_activate(tp, TT_REXMT,
tp->t_rxtcur);
sowwakeup(so);
if (sbavail(&so->so_snd))
(void) tp->t_fb->tfb_tcp_output(tp);
goto check_delack;
}
} else if (th->th_ack == tp->snd_una &&
tlen <= sbspace(&so->so_rcv)) {
int newsize = 0; /* automatic sockbuf scaling */
/*
* This is a pure, in-sequence data packet with
* nothing on the reassembly queue and we have enough
* buffer space to take it.
*/
/* Clean receiver SACK report if present */
if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks)
tcp_clean_sackreport(tp);
TCPSTAT_INC(tcps_preddat);
tp->rcv_nxt += tlen;
if (tlen &&
((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
(tp->t_fbyte_in == 0)) {
tp->t_fbyte_in = ticks;
if (tp->t_fbyte_in == 0)
tp->t_fbyte_in = 1;
if (tp->t_fbyte_out && tp->t_fbyte_in)
tp->t_flags2 |= TF2_FBYTES_COMPLETE;
}
/*
* Pull snd_wl1 up to prevent seq wrap relative to
* th_seq.
*/
tp->snd_wl1 = th->th_seq;
/*
* Pull rcv_up up to prevent seq wrap relative to
* rcv_nxt.
*/
tp->rcv_up = tp->rcv_nxt;
TCPSTAT_ADD(tcps_rcvpack, nsegs);
TCPSTAT_ADD(tcps_rcvbyte, tlen);
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp,
(void *)tcp_saveipgen, &tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
newsize = tcp_autorcvbuf(m, th, so, tp, tlen);
/* Add data to socket buffer. */
SOCKBUF_LOCK(&so->so_rcv);
if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
m_freem(m);
} else {
/*
* Set new socket buffer size.
* Give up when limit is reached.
*/
if (newsize)
if (!sbreserve_locked(&so->so_rcv,
newsize, so, NULL))
so->so_rcv.sb_flags &= ~SB_AUTOSIZE;
m_adj(m, drop_hdrlen); /* delayed header drop */
sbappendstream_locked(&so->so_rcv, m, 0);
}
/* NB: sorwakeup_locked() does an implicit unlock. */
sorwakeup_locked(so);
if (DELAY_ACK(tp, tlen)) {
tp->t_flags |= TF_DELACK;
} else {
tp->t_flags |= TF_ACKNOW;
tp->t_fb->tfb_tcp_output(tp);
}
goto check_delack;
}
}
/*
* Calculate amount of space in receive window,
* and then do TCP input processing.
* Receive window is amount of space in rcv queue,
* but not less than advertised window.
*/
win = sbspace(&so->so_rcv);
if (win < 0)
win = 0;
tp->rcv_wnd = imax(win, (int)(tp->rcv_adv - tp->rcv_nxt));
switch (tp->t_state) {
/*
* If the state is SYN_RECEIVED:
* if seg contains an ACK, but not for our SYN/ACK, send a RST.
*/
case TCPS_SYN_RECEIVED:
if ((thflags & TH_ACK) &&
(SEQ_LEQ(th->th_ack, tp->snd_una) ||
SEQ_GT(th->th_ack, tp->snd_max))) {
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
if (IS_FASTOPEN(tp->t_flags)) {
/*
* When a TFO connection is in SYN_RECEIVED, the
* only valid packets are the initial SYN, a
* retransmit/copy of the initial SYN (possibly with
* a subset of the original data), a valid ACK, a
* FIN, or a RST.
*/
if ((thflags & (TH_SYN|TH_ACK)) == (TH_SYN|TH_ACK)) {
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
} else if (thflags & TH_SYN) {
/* non-initial SYN is ignored */
if ((tcp_timer_active(tp, TT_DELACK) ||
tcp_timer_active(tp, TT_REXMT)))
goto drop;
} else if (!(thflags & (TH_ACK|TH_FIN|TH_RST))) {
goto drop;
}
}
break;
/*
* If the state is SYN_SENT:
* if seg contains a RST with valid ACK (SEQ.ACK has already
* been verified), then drop the connection.
* if seg contains a RST without an ACK, drop the seg.
* if seg does not contain SYN, then drop the seg.
* Otherwise this is an acceptable SYN segment
* initialize tp->rcv_nxt and tp->irs
* if seg contains ack then advance tp->snd_una
* if seg contains an ECE and ECN support is enabled, the stream
* is ECN capable.
* if SYN has been acked change to ESTABLISHED else SYN_RCVD state
* arrange for segment to be acked (eventually)
* continue processing rest of data/controls, beginning with URG
*/
case TCPS_SYN_SENT:
if ((thflags & (TH_ACK|TH_RST)) == (TH_ACK|TH_RST)) {
TCP_PROBE5(connect__refused, NULL, tp,
m, tp, th);
tp = tcp_drop(tp, ECONNREFUSED);
}
if (thflags & TH_RST)
goto drop;
if (!(thflags & TH_SYN))
goto drop;
tp->irs = th->th_seq;
tcp_rcvseqinit(tp);
if (thflags & TH_ACK) {
int tfo_partial_ack = 0;
TCPSTAT_INC(tcps_connects);
soisconnected(so);
#ifdef MAC
mac_socketpeer_set_from_mbuf(m, so);
#endif
/* Do window scaling on this connection? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->rcv_scale = tp->request_r_scale;
}
tp->rcv_adv += min(tp->rcv_wnd,
TCP_MAXWIN << tp->rcv_scale);
tp->snd_una++; /* SYN is acked */
/*
* If not all the data that was sent in the TFO SYN
* has been acked, resend the remainder right away.
*/
if (IS_FASTOPEN(tp->t_flags) &&
(tp->snd_una != tp->snd_max)) {
tp->snd_nxt = th->th_ack;
tfo_partial_ack = 1;
}
/*
* If there's data, delay ACK; if there's also a FIN
* ACKNOW will be turned on later.
*/
if (DELAY_ACK(tp, tlen) && tlen != 0 && !tfo_partial_ack)
tcp_timer_activate(tp, TT_DELACK,
tcp_delacktime);
else
tp->t_flags |= TF_ACKNOW;
if (((thflags & (TH_CWR | TH_ECE)) == TH_ECE) &&
(V_tcp_do_ecn == 1)) {
tp->t_flags2 |= TF2_ECN_PERMIT;
TCPSTAT_INC(tcps_ecn_shs);
}
/*
* Received <SYN,ACK> in SYN_SENT[*] state.
* Transitions:
* SYN_SENT --> ESTABLISHED
* SYN_SENT* --> FIN_WAIT_1
*/
tp->t_starttime = ticks;
if (tp->t_flags & TF_NEEDFIN) {
tcp_state_change(tp, TCPS_FIN_WAIT_1);
tp->t_flags &= ~TF_NEEDFIN;
thflags &= ~TH_SYN;
} else {
tcp_state_change(tp, TCPS_ESTABLISHED);
TCP_PROBE5(connect__established, NULL, tp,
m, tp, th);
cc_conn_init(tp);
tcp_timer_activate(tp, TT_KEEP,
TP_KEEPIDLE(tp));
}
} else {
/*
* Received initial SYN in SYN-SENT[*] state =>
* simultaneous open.
* If it succeeds, connection is * half-synchronized.
* Otherwise, do 3-way handshake:
* SYN-SENT -> SYN-RECEIVED
* SYN-SENT* -> SYN-RECEIVED*
*/
tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
tcp_timer_activate(tp, TT_REXMT, 0);
tcp_state_change(tp, TCPS_SYN_RECEIVED);
}
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Advance th->th_seq to correspond to first data byte.
* If data, trim to stay within window,
* dropping FIN if necessary.
*/
th->th_seq++;
if (tlen > tp->rcv_wnd) {
todrop = tlen - tp->rcv_wnd;
m_adj(m, -todrop);
tlen = tp->rcv_wnd;
thflags &= ~TH_FIN;
TCPSTAT_INC(tcps_rcvpackafterwin);
TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
}
tp->snd_wl1 = th->th_seq - 1;
tp->rcv_up = th->th_seq;
/*
* Client side of transaction: already sent SYN and data.
* If the remote host used T/TCP to validate the SYN,
* our data will be ACK'd; if so, enter normal data segment
* processing in the middle of step 5, ack processing.
* Otherwise, goto step 6.
*/
if (thflags & TH_ACK)
goto process_ACK;
goto step6;
/*
* If the state is LAST_ACK or CLOSING or TIME_WAIT:
* do normal processing.
*
* NB: Leftover from RFC1644 T/TCP. Cases to be reused later.
*/
case TCPS_LAST_ACK:
case TCPS_CLOSING:
break; /* continue normal processing */
}
/*
* States other than LISTEN or SYN_SENT.
* First check the RST flag and sequence number since reset segments
* are exempt from the timestamp and connection count tests. This
* fixes a bug introduced by the Stevens, vol. 2, p. 960 bugfix
* below which allowed reset segments in half the sequence space
* to fall though and be processed (which gives forged reset
* segments with a random sequence number a 50 percent chance of
* killing a connection).
* Then check timestamp, if present.
* Then check the connection count, if present.
* Then check that at least some bytes of segment are within
* receive window. If segment begins before rcv_nxt,
* drop leading data (and SYN); if nothing left, just ack.
*/
if (thflags & TH_RST) {
/*
* RFC5961 Section 3.2
*
* - RST drops connection only if SEG.SEQ == RCV.NXT.
* - If RST is in window, we send challenge ACK.
*
* Note: to take into account delayed ACKs, we should
* test against last_ack_sent instead of rcv_nxt.
* Note 2: we handle special case of closed window, not
* covered by the RFC.
*/
if ((SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) ||
(tp->rcv_wnd == 0 && tp->last_ack_sent == th->th_seq)) {
KASSERT(tp->t_state != TCPS_SYN_SENT,
("%s: TH_RST for TCPS_SYN_SENT th %p tp %p",
__func__, th, tp));
if (V_tcp_insecure_rst ||
tp->last_ack_sent == th->th_seq) {
TCPSTAT_INC(tcps_drops);
/* Drop the connection. */
switch (tp->t_state) {
case TCPS_SYN_RECEIVED:
so->so_error = ECONNREFUSED;
goto close;
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
case TCPS_CLOSING:
case TCPS_LAST_ACK:
so->so_error = ECONNRESET;
close:
/* FALLTHROUGH */
default:
tp = tcp_close(tp);
}
} else {
TCPSTAT_INC(tcps_badrst);
/* Send challenge ACK. */
tcp_respond(tp, mtod(m, void *), th, m,
tp->rcv_nxt, tp->snd_nxt, TH_ACK);
tp->last_ack_sent = tp->rcv_nxt;
m = NULL;
}
}
goto drop;
}
/*
* RFC5961 Section 4.2
* Send challenge ACK for any SYN in synchronized state.
*/
if ((thflags & TH_SYN) && tp->t_state != TCPS_SYN_SENT &&
tp->t_state != TCPS_SYN_RECEIVED) {
TCPSTAT_INC(tcps_badsyn);
if (V_tcp_insecure_syn &&
SEQ_GEQ(th->th_seq, tp->last_ack_sent) &&
SEQ_LT(th->th_seq, tp->last_ack_sent + tp->rcv_wnd)) {
tp = tcp_drop(tp, ECONNRESET);
rstreason = BANDLIM_UNLIMITED;
} else {
/* Send challenge ACK. */
tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
tp->snd_nxt, TH_ACK);
tp->last_ack_sent = tp->rcv_nxt;
m = NULL;
}
goto drop;
}
/*
* RFC 1323 PAWS: If we have a timestamp reply on this segment
* and it's less than ts_recent, drop it.
*/
if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
TSTMP_LT(to.to_tsval, tp->ts_recent)) {
/* Check to see if ts_recent is over 24 days old. */
if (tcp_ts_getticks() - tp->ts_recent_age > TCP_PAWS_IDLE) {
/*
* Invalidate ts_recent. If this segment updates
* ts_recent, the age will be reset later and ts_recent
* will get a valid value. If it does not, setting
* ts_recent to zero will at least satisfy the
* requirement that zero be placed in the timestamp
* echo reply when ts_recent isn't valid. The
* age isn't reset until we get a valid ts_recent
* because we don't want out-of-order segments to be
* dropped when ts_recent is old.
*/
tp->ts_recent = 0;
} else {
TCPSTAT_INC(tcps_rcvduppack);
TCPSTAT_ADD(tcps_rcvdupbyte, tlen);
TCPSTAT_INC(tcps_pawsdrop);
if (tlen)
goto dropafterack;
goto drop;
}
}
/*
* In the SYN-RECEIVED state, validate that the packet belongs to
* this connection before trimming the data to fit the receive
* window. Check the sequence number versus IRS since we know
* the sequence numbers haven't wrapped. This is a partial fix
* for the "LAND" DoS attack.
*/
if (tp->t_state == TCPS_SYN_RECEIVED && SEQ_LT(th->th_seq, tp->irs)) {
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
todrop = tp->rcv_nxt - th->th_seq;
if (todrop > 0) {
if (thflags & TH_SYN) {
thflags &= ~TH_SYN;
th->th_seq++;
if (th->th_urp > 1)
th->th_urp--;
else
thflags &= ~TH_URG;
todrop--;
}
/*
* Following if statement from Stevens, vol. 2, p. 960.
*/
if (todrop > tlen
|| (todrop == tlen && (thflags & TH_FIN) == 0)) {
/*
* Any valid FIN must be to the left of the window.
* At this point the FIN must be a duplicate or out
* of sequence; drop it.
*/
thflags &= ~TH_FIN;
/*
* Send an ACK to resynchronize and drop any data.
* But keep on processing for RST or ACK.
*/
tp->t_flags |= TF_ACKNOW;
todrop = tlen;
TCPSTAT_INC(tcps_rcvduppack);
TCPSTAT_ADD(tcps_rcvdupbyte, todrop);
} else {
TCPSTAT_INC(tcps_rcvpartduppack);
TCPSTAT_ADD(tcps_rcvpartdupbyte, todrop);
}
/*
* DSACK - add SACK block for dropped range
*/
if ((todrop > 0) && (tp->t_flags & TF_SACK_PERMIT)) {
tcp_update_sack_list(tp, th->th_seq,
th->th_seq + todrop);
/*
* ACK now, as the next in-sequence segment
* will clear the DSACK block again
*/
tp->t_flags |= TF_ACKNOW;
}
drop_hdrlen += todrop; /* drop from the top afterwards */
th->th_seq += todrop;
tlen -= todrop;
if (th->th_urp > todrop)
th->th_urp -= todrop;
else {
thflags &= ~TH_URG;
th->th_urp = 0;
}
}
/*
* If new data are received on a connection after the
* user processes are gone, then RST the other end.
*/
if ((so->so_state & SS_NOFDREF) &&
tp->t_state > TCPS_CLOSE_WAIT && tlen) {
if ((s = tcp_log_addrs(inc, th, NULL, NULL))) {
log(LOG_DEBUG, "%s; %s: %s: Received %d bytes of data "
"after socket was closed, "
"sending RST and removing tcpcb\n",
s, __func__, tcpstates[tp->t_state], tlen);
free(s, M_TCPLOG);
}
tp = tcp_close(tp);
TCPSTAT_INC(tcps_rcvafterclose);
rstreason = BANDLIM_UNLIMITED;
goto dropwithreset;
}
/*
* If segment ends after window, drop trailing data
* (and PUSH and FIN); if nothing left, just ACK.
*/
todrop = (th->th_seq + tlen) - (tp->rcv_nxt + tp->rcv_wnd);
if (todrop > 0) {
TCPSTAT_INC(tcps_rcvpackafterwin);
if (todrop >= tlen) {
TCPSTAT_ADD(tcps_rcvbyteafterwin, tlen);
/*
* If window is closed can only take segments at
* window edge, and have to drop data and PUSH from
* incoming segments. Continue processing, but
* remember to ack. Otherwise, drop segment
* and ack.
*/
if (tp->rcv_wnd == 0 && th->th_seq == tp->rcv_nxt) {
tp->t_flags |= TF_ACKNOW;
TCPSTAT_INC(tcps_rcvwinprobe);
} else
goto dropafterack;
} else
TCPSTAT_ADD(tcps_rcvbyteafterwin, todrop);
m_adj(m, -todrop);
tlen -= todrop;
thflags &= ~(TH_PUSH|TH_FIN);
}
/*
* If last ACK falls within this segment's sequence numbers,
* record its timestamp.
* NOTE:
* 1) That the test incorporates suggestions from the latest
* proposal of the tcplw@cray.com list (Braden 1993/04/26).
* 2) That updating only on newer timestamps interferes with
* our earlier PAWS tests, so this check should be solely
* predicated on the sequence space of this segment.
* 3) That we modify the segment boundary check to be
* Last.ACK.Sent <= SEG.SEQ + SEG.Len
* instead of RFC1323's
* Last.ACK.Sent < SEG.SEQ + SEG.Len,
* This modified check allows us to overcome RFC1323's
* limitations as described in Stevens TCP/IP Illustrated
* Vol. 2 p.869. In such cases, we can still calculate the
* RTT correctly when RCV.NXT == Last.ACK.Sent.
*/
if ((to.to_flags & TOF_TS) != 0 &&
SEQ_LEQ(th->th_seq, tp->last_ack_sent) &&
SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen +
((thflags & (TH_SYN|TH_FIN)) != 0))) {
tp->ts_recent_age = tcp_ts_getticks();
tp->ts_recent = to.to_tsval;
}
/*
* If the ACK bit is off: if in SYN-RECEIVED state or SENDSYN
* flag is on (half-synchronized state), then queue data for
* later processing; else drop segment and return.
*/
if ((thflags & TH_ACK) == 0) {
if (tp->t_state == TCPS_SYN_RECEIVED ||
(tp->t_flags & TF_NEEDSYN)) {
if (tp->t_state == TCPS_SYN_RECEIVED &&
IS_FASTOPEN(tp->t_flags)) {
tp->snd_wnd = tiwin;
cc_conn_init(tp);
}
goto step6;
} else if (tp->t_flags & TF_ACKNOW)
goto dropafterack;
else
goto drop;
}
/*
* Ack processing.
*/
switch (tp->t_state) {
/*
* In SYN_RECEIVED state, the ack ACKs our SYN, so enter
* ESTABLISHED state and continue processing.
* The ACK was checked above.
*/
case TCPS_SYN_RECEIVED:
TCPSTAT_INC(tcps_connects);
soisconnected(so);
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->rcv_scale = tp->request_r_scale;
}
tp->snd_wnd = tiwin;
/*
* Make transitions:
* SYN-RECEIVED -> ESTABLISHED
* SYN-RECEIVED* -> FIN-WAIT-1
*/
tp->t_starttime = ticks;
if (IS_FASTOPEN(tp->t_flags) && tp->t_tfo_pending) {
tcp_fastopen_decrement_counter(tp->t_tfo_pending);
tp->t_tfo_pending = NULL;
}
if (tp->t_flags & TF_NEEDFIN) {
tcp_state_change(tp, TCPS_FIN_WAIT_1);
tp->t_flags &= ~TF_NEEDFIN;
} else {
tcp_state_change(tp, TCPS_ESTABLISHED);
TCP_PROBE5(accept__established, NULL, tp,
m, tp, th);
/*
* TFO connections call cc_conn_init() during SYN
* processing. Calling it again here for such
* connections is not harmless as it would undo the
* snd_cwnd reduction that occurs when a TFO SYN|ACK
* is retransmitted.
*/
if (!IS_FASTOPEN(tp->t_flags))
cc_conn_init(tp);
tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
}
/*
* Account for the ACK of our SYN prior to
* regular ACK processing below, except for
* simultaneous SYN, which is handled later.
*/
if (SEQ_GT(th->th_ack, tp->snd_una) && !(tp->t_flags & TF_NEEDSYN))
incforsyn = 1;
/*
* If segment contains data or ACK, will call tcp_reass()
* later; if not, do so now to pass queued data to user.
*/
if (tlen == 0 && (thflags & TH_FIN) == 0) {
(void) tcp_reass(tp, (struct tcphdr *)0, NULL, 0,
(struct mbuf *)0);
tcp_handle_wakeup(tp, so);
}
tp->snd_wl1 = th->th_seq - 1;
/* FALLTHROUGH */
/*
* In ESTABLISHED state: drop duplicate ACKs; ACK out of range
* ACKs. If the ack is in the range
* tp->snd_una < th->th_ack <= tp->snd_max
* then advance tp->snd_una to th->th_ack and drop
* data from the retransmission queue. If this ACK reflects
* more up to date window information we update our window information.
*/
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
case TCPS_CLOSING:
case TCPS_LAST_ACK:
if (SEQ_GT(th->th_ack, tp->snd_max)) {
TCPSTAT_INC(tcps_rcvacktoomuch);
goto dropafterack;
}
if ((tp->t_flags & TF_SACK_PERMIT) &&
((to.to_flags & TOF_SACK) ||
!TAILQ_EMPTY(&tp->snd_holes))) {
if (((sack_changed = tcp_sack_doack(tp, &to, th->th_ack)) != 0) &&
(tp->t_flags & TF_LRD)) {
tcp_sack_lost_retransmission(tp, th);
}
} else
/*
* Reset the value so that previous (valid) value
* from the last ack with SACK doesn't get used.
*/
tp->sackhint.sacked_bytes = 0;
#ifdef TCP_HHOOK
/* Run HHOOK_TCP_ESTABLISHED_IN helper hooks. */
hhook_run_tcp_est_in(tp, th, &to);
#endif
if (SEQ_LEQ(th->th_ack, tp->snd_una)) {
maxseg = tcp_maxseg(tp);
if (tlen == 0 &&
(tiwin == tp->snd_wnd ||
(tp->t_flags & TF_SACK_PERMIT))) {
/*
* If this is the first time we've seen a
* FIN from the remote, this is not a
* duplicate and it needs to be processed
* normally. This happens during a
* simultaneous close.
*/
if ((thflags & TH_FIN) &&
(TCPS_HAVERCVDFIN(tp->t_state) == 0)) {
tp->t_dupacks = 0;
break;
}
TCPSTAT_INC(tcps_rcvdupack);
/*
* If we have outstanding data (other than
* a window probe), this is a completely
* duplicate ack (ie, window info didn't
* change and FIN isn't set),
* the ack is the biggest we've
* seen and we've seen exactly our rexmt
* threshold of them, assume a packet
* has been dropped and retransmit it.
* Kludge snd_nxt & the congestion
* window so we send only this one
* packet.
*
* We know we're losing at the current
* window size so do congestion avoidance
* (set ssthresh to half the current window
* and pull our congestion window back to
* the new ssthresh).
*
* Dup acks mean that packets have left the
* network (they're now cached at the receiver)
* so bump cwnd by the amount in the receiver
* to keep a constant cwnd packets in the
* network.
*
* When using TCP ECN, notify the peer that
* we reduced the cwnd.
*/
/*
* Following 2 kinds of acks should not affect
* dupack counting:
* 1) Old acks
* 2) Acks with SACK but without any new SACK
* information in them. These could result from
* any anomaly in the network like a switch
* duplicating packets or a possible DoS attack.
*/
if (th->th_ack != tp->snd_una ||
((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK) &&
!sack_changed))
break;
else if (!tcp_timer_active(tp, TT_REXMT))
tp->t_dupacks = 0;
else if (++tp->t_dupacks > tcprexmtthresh ||
IN_FASTRECOVERY(tp->t_flags)) {
cc_ack_received(tp, th, nsegs,
CC_DUPACK);
if (V_tcp_do_prr &&
IN_FASTRECOVERY(tp->t_flags) &&
(tp->t_flags & TF_SACK_PERMIT)) {
tcp_do_prr_ack(tp, th, &to);
} else if ((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK) &&
IN_FASTRECOVERY(tp->t_flags)) {
int awnd;
/*
* Compute the amount of data in flight first.
* We can inject new data into the pipe iff
* we have less than 1/2 the original window's
* worth of data in flight.
*/
if (V_tcp_do_newsack)
awnd = tcp_compute_pipe(tp);
else
awnd = (tp->snd_nxt - tp->snd_fack) +
tp->sackhint.sack_bytes_rexmit;
if (awnd < tp->snd_ssthresh) {
tp->snd_cwnd += maxseg;
if (tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
}
} else
tp->snd_cwnd += maxseg;
(void) tp->t_fb->tfb_tcp_output(tp);
goto drop;
} else if (tp->t_dupacks == tcprexmtthresh ||
(tp->t_flags & TF_SACK_PERMIT &&
V_tcp_do_newsack &&
tp->sackhint.sacked_bytes >
(tcprexmtthresh - 1) * maxseg)) {
enter_recovery:
/*
* Above is the RFC6675 trigger condition of
* more than (dupthresh-1)*maxseg sacked data.
* If the count of holes in the
* scoreboard is >= dupthresh, we could
* also enter loss recovery, but don't
* have that value readily available.
*/
tp->t_dupacks = tcprexmtthresh;
tcp_seq onxt = tp->snd_nxt;
/*
* If we're doing sack, or prr, check
* to see if we're already in sack
* recovery. If we're not doing sack,
* check to see if we're in newreno
* recovery.
*/
if (V_tcp_do_prr ||
(tp->t_flags & TF_SACK_PERMIT)) {
if (IN_FASTRECOVERY(tp->t_flags)) {
tp->t_dupacks = 0;
break;
}
} else {
if (SEQ_LEQ(th->th_ack,
tp->snd_recover)) {
tp->t_dupacks = 0;
break;
}
}
/* Congestion signal before ack. */
cc_cong_signal(tp, th, CC_NDUPACK);
cc_ack_received(tp, th, nsegs,
CC_DUPACK);
tcp_timer_activate(tp, TT_REXMT, 0);
tp->t_rtttime = 0;
if (V_tcp_do_prr) {
/*
* snd_ssthresh is already updated by
* cc_cong_signal.
*/
tp->sackhint.prr_delivered =
tp->sackhint.sacked_bytes;
tp->sackhint.recover_fs = max(1,
tp->snd_nxt - tp->snd_una);
}
if ((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK)) {
TCPSTAT_INC(
tcps_sack_recovery_episode);
tp->snd_recover = tp->snd_nxt;
tp->snd_cwnd = maxseg;
(void) tp->t_fb->tfb_tcp_output(tp);
if (SEQ_GT(th->th_ack, tp->snd_una))
goto resume_partialack;
goto drop;
}
tp->snd_nxt = th->th_ack;
tp->snd_cwnd = maxseg;
(void) tp->t_fb->tfb_tcp_output(tp);
KASSERT(tp->snd_limited <= 2,
("%s: tp->snd_limited too big",
__func__));
tp->snd_cwnd = tp->snd_ssthresh +
maxseg *
(tp->t_dupacks - tp->snd_limited);
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
goto drop;
} else if (V_tcp_do_rfc3042) {
/*
* Process first and second duplicate
* ACKs. Each indicates a segment
* leaving the network, creating room
* for more. Make sure we can send a
* packet on reception of each duplicate
* ACK by increasing snd_cwnd by one
* segment. Restore the original
* snd_cwnd after packet transmission.
*/
cc_ack_received(tp, th, nsegs,
CC_DUPACK);
uint32_t oldcwnd = tp->snd_cwnd;
tcp_seq oldsndmax = tp->snd_max;
u_int sent;
int avail;
KASSERT(tp->t_dupacks == 1 ||
tp->t_dupacks == 2,
("%s: dupacks not 1 or 2",
__func__));
if (tp->t_dupacks == 1)
tp->snd_limited = 0;
tp->snd_cwnd =
(tp->snd_nxt - tp->snd_una) +
(tp->t_dupacks - tp->snd_limited) *
maxseg;
/*
* Only call tcp_output when there
* is new data available to be sent.
* Otherwise we would send pure ACKs.
*/
SOCKBUF_LOCK(&so->so_snd);
avail = sbavail(&so->so_snd) -
(tp->snd_nxt - tp->snd_una);
SOCKBUF_UNLOCK(&so->so_snd);
if (avail > 0)
(void) tp->t_fb->tfb_tcp_output(tp);
sent = tp->snd_max - oldsndmax;
if (sent > maxseg) {
KASSERT((tp->t_dupacks == 2 &&
tp->snd_limited == 0) ||
(sent == maxseg + 1 &&
tp->t_flags & TF_SENTFIN),
("%s: sent too much",
__func__));
tp->snd_limited = 2;
} else if (sent > 0)
++tp->snd_limited;
tp->snd_cwnd = oldcwnd;
goto drop;
}
}
break;
} else {
/*
* This ack is advancing the left edge, reset the
* counter.
*/
tp->t_dupacks = 0;
/*
* If this ack also has new SACK info, increment the
* counter as per rfc6675. The variable
* sack_changed tracks all changes to the SACK
* scoreboard, including when partial ACKs without
* SACK options are received, and clear the scoreboard
* from the left side. Such partial ACKs should not be
* counted as dupacks here.
*/
if ((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK) &&
sack_changed) {
tp->t_dupacks++;
/* limit overhead by setting maxseg last */
if (!IN_FASTRECOVERY(tp->t_flags) &&
(tp->sackhint.sacked_bytes >
((tcprexmtthresh - 1) *
(maxseg = tcp_maxseg(tp))))) {
goto enter_recovery;
}
}
}
resume_partialack:
KASSERT(SEQ_GT(th->th_ack, tp->snd_una),
("%s: th_ack <= snd_una", __func__));
/*
* If the congestion window was inflated to account
* for the other side's cached packets, retract it.
*/
if (IN_FASTRECOVERY(tp->t_flags)) {
if (SEQ_LT(th->th_ack, tp->snd_recover)) {
if (tp->t_flags & TF_SACK_PERMIT)
if (V_tcp_do_prr && to.to_flags & TOF_SACK) {
tcp_timer_activate(tp, TT_REXMT, 0);
tp->t_rtttime = 0;
tcp_do_prr_ack(tp, th, &to);
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
} else
tcp_sack_partialack(tp, th);
else
tcp_newreno_partial_ack(tp, th);
} else
cc_post_recovery(tp, th);
} else if (IN_CONGRECOVERY(tp->t_flags)) {
if (SEQ_LT(th->th_ack, tp->snd_recover)) {
if (V_tcp_do_prr) {
tp->sackhint.delivered_data = BYTES_THIS_ACK(tp, th);
tp->snd_fack = th->th_ack;
tcp_do_prr_ack(tp, th, &to);
(void) tcp_output(tp);
}
} else
cc_post_recovery(tp, th);
}
/*
* If we reach this point, ACK is not a duplicate,
* i.e., it ACKs something we sent.
*/
if (tp->t_flags & TF_NEEDSYN) {
/*
* T/TCP: Connection was half-synchronized, and our
* SYN has been ACK'd (so connection is now fully
* synchronized). Go to non-starred state,
* increment snd_una for ACK of SYN, and check if
* we can do window scaling.
*/
tp->t_flags &= ~TF_NEEDSYN;
tp->snd_una++;
/* Do window scaling? */
if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
(TF_RCVD_SCALE|TF_REQ_SCALE)) {
tp->rcv_scale = tp->request_r_scale;
/* Send window already scaled. */
}
}
process_ACK:
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Adjust for the SYN bit in sequence space,
* but don't account for it in cwnd calculations.
* This is for the SYN_RECEIVED, non-simultaneous
* SYN case. SYN_SENT and simultaneous SYN are
* treated elsewhere.
*/
if (incforsyn)
tp->snd_una++;
acked = BYTES_THIS_ACK(tp, th);
KASSERT(acked >= 0, ("%s: acked unexepectedly negative "
"(tp->snd_una=%u, th->th_ack=%u, tp=%p, m=%p)", __func__,
tp->snd_una, th->th_ack, tp, m));
TCPSTAT_ADD(tcps_rcvackpack, nsegs);
TCPSTAT_ADD(tcps_rcvackbyte, acked);
/*
* If we just performed our first retransmit, and the ACK
* arrives within our recovery window, then it was a mistake
* to do the retransmit in the first place. Recover our
* original cwnd and ssthresh, and proceed to transmit where
* we left off.
*/
if (tp->t_rxtshift == 1 &&
tp->t_flags & TF_PREVVALID &&
tp->t_badrxtwin &&
SEQ_LT(to.to_tsecr, tp->t_badrxtwin))
cc_cong_signal(tp, th, CC_RTO_ERR);
/*
* If we have a timestamp reply, update smoothed
* round trip time. If no timestamp is present but
* transmit timer is running and timed sequence
* number was acked, update smoothed round trip time.
* Since we now have an rtt measurement, cancel the
* timer backoff (cf., Phil Karn's retransmit alg.).
* Recompute the initial retransmit timer.
*
* Some boxes send broken timestamp replies
* during the SYN+ACK phase, ignore
* timestamps of 0 or we could calculate a
* huge RTT and blow up the retransmit timer.
*/
if ((to.to_flags & TOF_TS) != 0 && to.to_tsecr) {
uint32_t t;
t = tcp_ts_getticks() - to.to_tsecr;
if (!tp->t_rttlow || tp->t_rttlow > t)
tp->t_rttlow = t;
tcp_xmit_timer(tp, TCP_TS_TO_TICKS(t) + 1);
} else if (tp->t_rtttime && SEQ_GT(th->th_ack, tp->t_rtseq)) {
if (!tp->t_rttlow || tp->t_rttlow > ticks - tp->t_rtttime)
tp->t_rttlow = ticks - tp->t_rtttime;
tcp_xmit_timer(tp, ticks - tp->t_rtttime);
}
/*
* If all outstanding data is acked, stop retransmit
* timer and remember to restart (more output or persist).
* If there is more data to be acked, restart retransmit
* timer, using current (possibly backed-off) value.
*/
if (th->th_ack == tp->snd_max) {
tcp_timer_activate(tp, TT_REXMT, 0);
needoutput = 1;
} else if (!tcp_timer_active(tp, TT_PERSIST))
tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
/*
* If no data (only SYN) was ACK'd,
* skip rest of ACK processing.
*/
if (acked == 0)
goto step6;
/*
* Let the congestion control algorithm update congestion
* control related information. This typically means increasing
* the congestion window.
*/
cc_ack_received(tp, th, nsegs, CC_ACK);
SOCKBUF_LOCK(&so->so_snd);
if (acked > sbavail(&so->so_snd)) {
if (tp->snd_wnd >= sbavail(&so->so_snd))
tp->snd_wnd -= sbavail(&so->so_snd);
else
tp->snd_wnd = 0;
mfree = sbcut_locked(&so->so_snd,
(int)sbavail(&so->so_snd));
ourfinisacked = 1;
} else {
mfree = sbcut_locked(&so->so_snd, acked);
if (tp->snd_wnd >= (uint32_t) acked)
tp->snd_wnd -= acked;
else
tp->snd_wnd = 0;
ourfinisacked = 0;
}
/* NB: sowwakeup_locked() does an implicit unlock. */
sowwakeup_locked(so);
m_freem(mfree);
/* Detect una wraparound. */
if (!IN_RECOVERY(tp->t_flags) &&
SEQ_GT(tp->snd_una, tp->snd_recover) &&
SEQ_LEQ(th->th_ack, tp->snd_recover))
tp->snd_recover = th->th_ack - 1;
/* XXXLAS: Can this be moved up into cc_post_recovery? */
if (IN_RECOVERY(tp->t_flags) &&
SEQ_GEQ(th->th_ack, tp->snd_recover)) {
EXIT_RECOVERY(tp->t_flags);
}
tp->snd_una = th->th_ack;
if (tp->t_flags & TF_SACK_PERMIT) {
if (SEQ_GT(tp->snd_una, tp->snd_recover))
tp->snd_recover = tp->snd_una;
}
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
switch (tp->t_state) {
/*
* In FIN_WAIT_1 STATE in addition to the processing
* for the ESTABLISHED state if our FIN is now acknowledged
* then enter FIN_WAIT_2.
*/
case TCPS_FIN_WAIT_1:
if (ourfinisacked) {
/*
* If we can't receive any more
* data, then closing user can proceed.
* Starting the timer is contrary to the
* specification, but if we don't get a FIN
* we'll hang forever.
*
* XXXjl:
* we should release the tp also, and use a
* compressed state.
*/
if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
soisdisconnected(so);
tcp_timer_activate(tp, TT_2MSL,
(tcp_fast_finwait2_recycle ?
tcp_finwait2_timeout :
TP_MAXIDLE(tp)));
}
tcp_state_change(tp, TCPS_FIN_WAIT_2);
}
break;
/*
* In CLOSING STATE in addition to the processing for
* the ESTABLISHED state if the ACK acknowledges our FIN
* then enter the TIME-WAIT state, otherwise ignore
* the segment.
*/
case TCPS_CLOSING:
if (ourfinisacked) {
tcp_twstart(tp);
m_freem(m);
return;
}
break;
/*
* In LAST_ACK, we may still be waiting for data to drain
* and/or to be acked, as well as for the ack of our FIN.
* If our FIN is now acknowledged, delete the TCB,
* enter the closed state and return.
*/
case TCPS_LAST_ACK:
if (ourfinisacked) {
tp = tcp_close(tp);
goto drop;
}
break;
}
}
step6:
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Update window information.
* Don't look at window if no ACK: TAC's send garbage on first SYN.
*/
if ((thflags & TH_ACK) &&
(SEQ_LT(tp->snd_wl1, th->th_seq) ||
(tp->snd_wl1 == th->th_seq && (SEQ_LT(tp->snd_wl2, th->th_ack) ||
(tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd))))) {
/* keep track of pure window updates */
if (tlen == 0 &&
tp->snd_wl2 == th->th_ack && tiwin > tp->snd_wnd)
TCPSTAT_INC(tcps_rcvwinupd);
tp->snd_wnd = tiwin;
tp->snd_wl1 = th->th_seq;
tp->snd_wl2 = th->th_ack;
if (tp->snd_wnd > tp->max_sndwnd)
tp->max_sndwnd = tp->snd_wnd;
needoutput = 1;
}
/*
* Process segments with URG.
*/
if ((thflags & TH_URG) && th->th_urp &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
/*
* This is a kludge, but if we receive and accept
* random urgent pointers, we'll crash in
* soreceive. It's hard to imagine someone
* actually wanting to send this much urgent data.
*/
SOCKBUF_LOCK(&so->so_rcv);
if (th->th_urp + sbavail(&so->so_rcv) > sb_max) {
th->th_urp = 0; /* XXX */
thflags &= ~TH_URG; /* XXX */
SOCKBUF_UNLOCK(&so->so_rcv); /* XXX */
goto dodata; /* XXX */
}
/*
* If this segment advances the known urgent pointer,
* then mark the data stream. This should not happen
* in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
* a FIN has been received from the remote side.
* In these states we ignore the URG.
*
* According to RFC961 (Assigned Protocols),
* the urgent pointer points to the last octet
* of urgent data. We continue, however,
* to consider it to indicate the first octet
* of data past the urgent section as the original
* spec states (in one of two places).
*/
if (SEQ_GT(th->th_seq+th->th_urp, tp->rcv_up)) {
tp->rcv_up = th->th_seq + th->th_urp;
so->so_oobmark = sbavail(&so->so_rcv) +
(tp->rcv_up - tp->rcv_nxt) - 1;
if (so->so_oobmark == 0)
so->so_rcv.sb_state |= SBS_RCVATMARK;
sohasoutofband(so);
tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
}
SOCKBUF_UNLOCK(&so->so_rcv);
/*
* Remove out of band data so doesn't get presented to user.
* This can happen independent of advancing the URG pointer,
* but if two URG's are pending at once, some out-of-band
* data may creep in... ick.
*/
if (th->th_urp <= (uint32_t)tlen &&
!(so->so_options & SO_OOBINLINE)) {
/* hdr drop is delayed */
tcp_pulloutofband(so, th, m, drop_hdrlen);
}
} else {
/*
* If no out of band data is expected,
* pull receive urgent pointer along
* with the receive window.
*/
if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
tp->rcv_up = tp->rcv_nxt;
}
dodata: /* XXX */
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Process the segment text, merging it into the TCP sequencing queue,
* and arranging for acknowledgment of receipt if necessary.
* This process logically involves adjusting tp->rcv_wnd as data
* is presented to the user (this happens in tcp_usrreq.c,
* case PRU_RCVD). If a FIN has already been received on this
* connection then we just ignore the text.
*/
tfo_syn = ((tp->t_state == TCPS_SYN_RECEIVED) &&
IS_FASTOPEN(tp->t_flags));
if ((tlen || (thflags & TH_FIN) || (tfo_syn && tlen > 0)) &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
tcp_seq save_start = th->th_seq;
tcp_seq save_rnxt = tp->rcv_nxt;
int save_tlen = tlen;
m_adj(m, drop_hdrlen); /* delayed header drop */
/*
* Insert segment which includes th into TCP reassembly queue
* with control block tp. Set thflags to whether reassembly now
* includes a segment with FIN. This handles the common case
* inline (segment is the next to be received on an established
* connection, and the queue is empty), avoiding linkage into
* and removal from the queue and repetition of various
* conversions.
* Set DELACK for segments received in order, but ack
* immediately when segments are out of order (so
* fast retransmit can work).
*/
if (th->th_seq == tp->rcv_nxt &&
SEGQ_EMPTY(tp) &&
(TCPS_HAVEESTABLISHED(tp->t_state) ||
tfo_syn)) {
if (DELAY_ACK(tp, tlen) || tfo_syn)
tp->t_flags |= TF_DELACK;
else
tp->t_flags |= TF_ACKNOW;
tp->rcv_nxt += tlen;
if (tlen &&
((tp->t_flags2 & TF2_FBYTES_COMPLETE) == 0) &&
(tp->t_fbyte_in == 0)) {
tp->t_fbyte_in = ticks;
if (tp->t_fbyte_in == 0)
tp->t_fbyte_in = 1;
if (tp->t_fbyte_out && tp->t_fbyte_in)
tp->t_flags2 |= TF2_FBYTES_COMPLETE;
}
thflags = th->th_flags & TH_FIN;
TCPSTAT_INC(tcps_rcvpack);
TCPSTAT_ADD(tcps_rcvbyte, tlen);
SOCKBUF_LOCK(&so->so_rcv);
if (so->so_rcv.sb_state & SBS_CANTRCVMORE)
m_freem(m);
else
sbappendstream_locked(&so->so_rcv, m, 0);
tp->t_flags |= TF_WAKESOR;
} else {
/*
* XXX: Due to the header drop above "th" is
* theoretically invalid by now. Fortunately
* m_adj() doesn't actually frees any mbufs
* when trimming from the head.
*/
tcp_seq temp = save_start;
if (tlen) {
thflags = tcp_reass(tp, th, &temp, &tlen, m);
tp->t_flags |= TF_ACKNOW;
}
}
if ((tp->t_flags & TF_SACK_PERMIT) &&
(save_tlen > 0) &&
TCPS_HAVEESTABLISHED(tp->t_state)) {
if ((tlen == 0) && (SEQ_LT(save_start, save_rnxt))) {
/*
* DSACK actually handled in the fastpath
* above.
*/
tcp_update_sack_list(tp, save_start,
save_start + save_tlen);
} else if ((tlen > 0) && SEQ_GT(tp->rcv_nxt, save_rnxt)) {
if ((tp->rcv_numsacks >= 1) &&
(tp->sackblks[0].end == save_start)) {
/*
* Partial overlap, recorded at todrop
* above.
*/
tcp_update_sack_list(tp,
tp->sackblks[0].start,
tp->sackblks[0].end);
} else {
tcp_update_dsack_list(tp, save_start,
save_start + save_tlen);
}
} else if (tlen >= save_tlen) {
/* Update of sackblks. */
tcp_update_dsack_list(tp, save_start,
save_start + save_tlen);
} else if (tlen > 0) {
tcp_update_dsack_list(tp, save_start,
save_start + tlen);
}
}
tcp_handle_wakeup(tp, so);
#if 0
/*
* Note the amount of data that peer has sent into
* our window, in order to estimate the sender's
* buffer size.
* XXX: Unused.
*/
if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt))
len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
else
len = so->so_rcv.sb_hiwat;
#endif
} else {
m_freem(m);
thflags &= ~TH_FIN;
}
/*
* If FIN is received ACK the FIN and let the user know
* that the connection is closing.
*/
if (thflags & TH_FIN) {
if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
/* The socket upcall is handled by socantrcvmore. */
socantrcvmore(so);
/*
* If connection is half-synchronized
* (ie NEEDSYN flag on) then delay ACK,
* so it may be piggybacked when SYN is sent.
* Otherwise, since we received a FIN then no
* more input can be expected, send ACK now.
*/
if (tp->t_flags & TF_NEEDSYN)
tp->t_flags |= TF_DELACK;
else
tp->t_flags |= TF_ACKNOW;
tp->rcv_nxt++;
}
switch (tp->t_state) {
/*
* In SYN_RECEIVED and ESTABLISHED STATES
* enter the CLOSE_WAIT state.
*/
case TCPS_SYN_RECEIVED:
tp->t_starttime = ticks;
/* FALLTHROUGH */
case TCPS_ESTABLISHED:
tcp_state_change(tp, TCPS_CLOSE_WAIT);
break;
/*
* If still in FIN_WAIT_1 STATE FIN has not been acked so
* enter the CLOSING state.
*/
case TCPS_FIN_WAIT_1:
tcp_state_change(tp, TCPS_CLOSING);
break;
/*
* In FIN_WAIT_2 state enter the TIME_WAIT state,
* starting the time-wait timer, turning off the other
* standard timers.
*/
case TCPS_FIN_WAIT_2:
tcp_twstart(tp);
return;
}
}
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
/*
* Return any desired output.
*/
if (needoutput || (tp->t_flags & TF_ACKNOW))
(void) tp->t_fb->tfb_tcp_output(tp);
check_delack:
INP_WLOCK_ASSERT(tp->t_inpcb);
if (tp->t_flags & TF_DELACK) {
tp->t_flags &= ~TF_DELACK;
tcp_timer_activate(tp, TT_DELACK, tcp_delacktime);
}
INP_WUNLOCK(tp->t_inpcb);
return;
dropafterack:
/*
* Generate an ACK dropping incoming segment if it occupies
* sequence space, where the ACK reflects our state.
*
* We can now skip the test for the RST flag since all
* paths to this code happen after packets containing
* RST have been dropped.
*
* In the SYN-RECEIVED state, don't send an ACK unless the
* segment we received passes the SYN-RECEIVED ACK test.
* If it fails send a RST. This breaks the loop in the
* "LAND" DoS attack, and also prevents an ACK storm
* between two listening ports that have been sent forged
* SYN segments, each with the source address of the other.
*/
if (tp->t_state == TCPS_SYN_RECEIVED && (thflags & TH_ACK) &&
(SEQ_GT(tp->snd_una, th->th_ack) ||
SEQ_GT(th->th_ack, tp->snd_max)) ) {
rstreason = BANDLIM_RST_OPENPORT;
goto dropwithreset;
}
#ifdef TCPDEBUG
if (so->so_options & SO_DEBUG)
tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
tp->t_flags |= TF_ACKNOW;
(void) tp->t_fb->tfb_tcp_output(tp);
INP_WUNLOCK(tp->t_inpcb);
m_freem(m);
return;
dropwithreset:
if (tp != NULL) {
tcp_dropwithreset(m, th, tp, tlen, rstreason);
INP_WUNLOCK(tp->t_inpcb);
} else
tcp_dropwithreset(m, th, NULL, tlen, rstreason);
return;
drop:
/*
* Drop space held by incoming segment and return.
*/
#ifdef TCPDEBUG
if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
tcp_trace(TA_DROP, ostate, tp, (void *)tcp_saveipgen,
&tcp_savetcp, 0);
#endif
TCP_PROBE3(debug__input, tp, th, m);
if (tp != NULL) {
INP_WUNLOCK(tp->t_inpcb);
}
m_freem(m);
}
/*
* Issue RST and make ACK acceptable to originator of segment.
* The mbuf must still include the original packet header.
* tp may be NULL.
*/
void
tcp_dropwithreset(struct mbuf *m, struct tcphdr *th, struct tcpcb *tp,
int tlen, int rstreason)
{
#ifdef INET
struct ip *ip;
#endif
#ifdef INET6
struct ip6_hdr *ip6;
#endif
if (tp != NULL) {
INP_LOCK_ASSERT(tp->t_inpcb);
}
/* Don't bother if destination was broadcast/multicast. */
if ((th->th_flags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST))
goto drop;
#ifdef INET6
if (mtod(m, struct ip *)->ip_v == 6) {
ip6 = mtod(m, struct ip6_hdr *);
if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst) ||
IN6_IS_ADDR_MULTICAST(&ip6->ip6_src))
goto drop;
/* IPv6 anycast check is done at tcp6_input() */
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
ip = mtod(m, struct ip *);
if (IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) ||
IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
ip->ip_src.s_addr == htonl(INADDR_BROADCAST) ||
in_broadcast(ip->ip_dst, m->m_pkthdr.rcvif))
goto drop;
}
#endif
/* Perform bandwidth limiting. */
if (badport_bandlim(rstreason) < 0)
goto drop;
/* tcp_respond consumes the mbuf chain. */
if (th->th_flags & TH_ACK) {
tcp_respond(tp, mtod(m, void *), th, m, (tcp_seq)0,
th->th_ack, TH_RST);
} else {
if (th->th_flags & TH_SYN)
tlen++;
if (th->th_flags & TH_FIN)
tlen++;
tcp_respond(tp, mtod(m, void *), th, m, th->th_seq+tlen,
(tcp_seq)0, TH_RST|TH_ACK);
}
return;
drop:
m_freem(m);
}
/*
* Parse TCP options and place in tcpopt.
*/
void
tcp_dooptions(struct tcpopt *to, u_char *cp, int cnt, int flags)
{
int opt, optlen;
to->to_flags = 0;
for (; cnt > 0; cnt -= optlen, cp += optlen) {
opt = cp[0];
if (opt == TCPOPT_EOL)
break;
if (opt == TCPOPT_NOP)
optlen = 1;
else {
if (cnt < 2)
break;
optlen = cp[1];
if (optlen < 2 || optlen > cnt)
break;
}
switch (opt) {
case TCPOPT_MAXSEG:
if (optlen != TCPOLEN_MAXSEG)
continue;
if (!(flags & TO_SYN))
continue;
to->to_flags |= TOF_MSS;
bcopy((char *)cp + 2,
(char *)&to->to_mss, sizeof(to->to_mss));
to->to_mss = ntohs(to->to_mss);
break;
case TCPOPT_WINDOW:
if (optlen != TCPOLEN_WINDOW)
continue;
if (!(flags & TO_SYN))
continue;
to->to_flags |= TOF_SCALE;
to->to_wscale = min(cp[2], TCP_MAX_WINSHIFT);
break;
case TCPOPT_TIMESTAMP:
if (optlen != TCPOLEN_TIMESTAMP)
continue;
to->to_flags |= TOF_TS;
bcopy((char *)cp + 2,
(char *)&to->to_tsval, sizeof(to->to_tsval));
to->to_tsval = ntohl(to->to_tsval);
bcopy((char *)cp + 6,
(char *)&to->to_tsecr, sizeof(to->to_tsecr));
to->to_tsecr = ntohl(to->to_tsecr);
break;
case TCPOPT_SIGNATURE:
/*
* In order to reply to a host which has set the
* TCP_SIGNATURE option in its initial SYN, we have
* to record the fact that the option was observed
* here for the syncache code to perform the correct
* response.
*/
if (optlen != TCPOLEN_SIGNATURE)
continue;
to->to_flags |= TOF_SIGNATURE;
to->to_signature = cp + 2;
break;
case TCPOPT_SACK_PERMITTED:
if (optlen != TCPOLEN_SACK_PERMITTED)
continue;
if (!(flags & TO_SYN))
continue;
if (!V_tcp_do_sack)
continue;
to->to_flags |= TOF_SACKPERM;
break;
case TCPOPT_SACK:
if (optlen <= 2 || (optlen - 2) % TCPOLEN_SACK != 0)
continue;
if (flags & TO_SYN)
continue;
to->to_flags |= TOF_SACK;
to->to_nsacks = (optlen - 2) / TCPOLEN_SACK;
to->to_sacks = cp + 2;
TCPSTAT_INC(tcps_sack_rcv_blocks);
break;
case TCPOPT_FAST_OPEN:
/*
* Cookie length validation is performed by the
* server side cookie checking code or the client
* side cookie cache update code.
*/
if (!(flags & TO_SYN))
continue;
if (!V_tcp_fastopen_client_enable &&
!V_tcp_fastopen_server_enable)
continue;
to->to_flags |= TOF_FASTOPEN;
to->to_tfo_len = optlen - 2;
to->to_tfo_cookie = to->to_tfo_len ? cp + 2 : NULL;
break;
default:
continue;
}
}
}
/*
* Pull out of band byte out of a segment so
* it doesn't appear in the user's data queue.
* It is still reflected in the segment length for
* sequencing purposes.
*/
void
tcp_pulloutofband(struct socket *so, struct tcphdr *th, struct mbuf *m,
int off)
{
int cnt = off + th->th_urp - 1;
while (cnt >= 0) {
if (m->m_len > cnt) {
char *cp = mtod(m, caddr_t) + cnt;
struct tcpcb *tp = sototcpcb(so);
INP_WLOCK_ASSERT(tp->t_inpcb);
tp->t_iobc = *cp;
tp->t_oobflags |= TCPOOB_HAVEDATA;
bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
m->m_len--;
if (m->m_flags & M_PKTHDR)
m->m_pkthdr.len--;
return;
}
cnt -= m->m_len;
m = m->m_next;
if (m == NULL)
break;
}
panic("tcp_pulloutofband");
}
/*
* Collect new round-trip time estimate
* and update averages and current timeout.
*/
void
tcp_xmit_timer(struct tcpcb *tp, int rtt)
{
int delta;
INP_WLOCK_ASSERT(tp->t_inpcb);
TCPSTAT_INC(tcps_rttupdated);
tp->t_rttupdated++;
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT,
imax(0, rtt * 1000 / hz));
#endif
if ((tp->t_srtt != 0) && (tp->t_rxtshift <= TCP_RTT_INVALIDATE)) {
/*
* srtt is stored as fixed point with 5 bits after the
* binary point (i.e., scaled by 8). The following magic
* is equivalent to the smoothing algorithm in rfc793 with
* an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
* point). Adjust rtt to origin 0.
*/
delta = ((rtt - 1) << TCP_DELTA_SHIFT)
- (tp->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT));
if ((tp->t_srtt += delta) <= 0)
tp->t_srtt = 1;
/*
* We accumulate a smoothed rtt variance (actually, a
* smoothed mean difference), then set the retransmit
* timer to smoothed rtt + 4 times the smoothed variance.
* rttvar is stored as fixed point with 4 bits after the
* binary point (scaled by 16). The following is
* equivalent to rfc793 smoothing with an alpha of .75
* (rttvar = rttvar*3/4 + |delta| / 4). This replaces
* rfc793's wired-in beta.
*/
if (delta < 0)
delta = -delta;
delta -= tp->t_rttvar >> (TCP_RTTVAR_SHIFT - TCP_DELTA_SHIFT);
if ((tp->t_rttvar += delta) <= 0)
tp->t_rttvar = 1;
if (tp->t_rttbest > tp->t_srtt + tp->t_rttvar)
tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
} else {
/*
* No rtt measurement yet - use the unsmoothed rtt.
* Set the variance to half the rtt (so our first
* retransmit happens at 3*rtt).
*/
tp->t_srtt = rtt << TCP_RTT_SHIFT;
tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
}
tp->t_rtttime = 0;
tp->t_rxtshift = 0;
/*
* the retransmit should happen at rtt + 4 * rttvar.
* Because of the way we do the smoothing, srtt and rttvar
* will each average +1/2 tick of bias. When we compute
* the retransmit timer, we want 1/2 tick of rounding and
* 1 extra tick because of +-1/2 tick uncertainty in the
* firing of the timer. The bias will give us exactly the
* 1.5 tick we need. But, because the bias is
* statistical, we have to test that we don't drop below
* the minimum feasible timer (which is 2 ticks).
*/
TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
max(tp->t_rttmin, rtt + 2), TCPTV_REXMTMAX);
/*
* We received an ack for a packet that wasn't retransmitted;
* it is probably safe to discard any error indications we've
* received recently. This isn't quite right, but close enough
* for now (a route might have failed after we sent a segment,
* and the return path might not be symmetrical).
*/
tp->t_softerror = 0;
}
/*
* Determine a reasonable value for maxseg size.
* If the route is known, check route for mtu.
* If none, use an mss that can be handled on the outgoing interface
* without forcing IP to fragment. If no route is found, route has no mtu,
* or the destination isn't local, use a default, hopefully conservative
* size (usually 512 or the default IP max size, but no more than the mtu
* of the interface), as we can't discover anything about intervening
* gateways or networks. We also initialize the congestion/slow start
* window to be a single segment if the destination isn't local.
* While looking at the routing entry, we also initialize other path-dependent
* parameters from pre-set or cached values in the routing entry.
*
* NOTE that resulting t_maxseg doesn't include space for TCP options or
* IP options, e.g. IPSEC data, since length of this data may vary, and
* thus it is calculated for every segment separately in tcp_output().
*
* NOTE that this routine is only called when we process an incoming
* segment, or an ICMP need fragmentation datagram. Outgoing SYN/ACK MSS
* settings are handled in tcp_mssopt().
*/
void
tcp_mss_update(struct tcpcb *tp, int offer, int mtuoffer,
struct hc_metrics_lite *metricptr, struct tcp_ifcap *cap)
{
int mss = 0;
uint32_t maxmtu = 0;
struct inpcb *inp = tp->t_inpcb;
struct hc_metrics_lite metrics;
#ifdef INET6
int isipv6 = ((inp->inp_vflag & INP_IPV6) != 0) ? 1 : 0;
size_t min_protoh = isipv6 ?
sizeof (struct ip6_hdr) + sizeof (struct tcphdr) :
sizeof (struct tcpiphdr);
#else
size_t min_protoh = sizeof(struct tcpiphdr);
#endif
INP_WLOCK_ASSERT(tp->t_inpcb);
if (tp->t_port)
min_protoh += V_tcp_udp_tunneling_overhead;
if (mtuoffer != -1) {
KASSERT(offer == -1, ("%s: conflict", __func__));
offer = mtuoffer - min_protoh;
}
/* Initialize. */
#ifdef INET6
if (isipv6) {
maxmtu = tcp_maxmtu6(&inp->inp_inc, cap);
tp->t_maxseg = V_tcp_v6mssdflt;
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
maxmtu = tcp_maxmtu(&inp->inp_inc, cap);
tp->t_maxseg = V_tcp_mssdflt;
}
#endif
/*
* No route to sender, stay with default mss and return.
*/
if (maxmtu == 0) {
/*
* In case we return early we need to initialize metrics
* to a defined state as tcp_hc_get() would do for us
* if there was no cache hit.
*/
if (metricptr != NULL)
bzero(metricptr, sizeof(struct hc_metrics_lite));
return;
}
/* What have we got? */
switch (offer) {
case 0:
/*
* Offer == 0 means that there was no MSS on the SYN
* segment, in this case we use tcp_mssdflt as
* already assigned to t_maxseg above.
*/
offer = tp->t_maxseg;
break;
case -1:
/*
* Offer == -1 means that we didn't receive SYN yet.
*/
/* FALLTHROUGH */
default:
/*
* Prevent DoS attack with too small MSS. Round up
* to at least minmss.
*/
offer = max(offer, V_tcp_minmss);
}
/*
* rmx information is now retrieved from tcp_hostcache.
*/
tcp_hc_get(&inp->inp_inc, &metrics);
if (metricptr != NULL)
bcopy(&metrics, metricptr, sizeof(struct hc_metrics_lite));
/*
* If there's a discovered mtu in tcp hostcache, use it.
* Else, use the link mtu.
*/
if (metrics.rmx_mtu)
mss = min(metrics.rmx_mtu, maxmtu) - min_protoh;
else {
#ifdef INET6
if (isipv6) {
mss = maxmtu - min_protoh;
if (!V_path_mtu_discovery &&
!in6_localaddr(&inp->in6p_faddr))
mss = min(mss, V_tcp_v6mssdflt);
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
mss = maxmtu - min_protoh;
if (!V_path_mtu_discovery &&
!in_localaddr(inp->inp_faddr))
mss = min(mss, V_tcp_mssdflt);
}
#endif
/*
* XXX - The above conditional (mss = maxmtu - min_protoh)
* probably violates the TCP spec.
* The problem is that, since we don't know the
* other end's MSS, we are supposed to use a conservative
* default. But, if we do that, then MTU discovery will
* never actually take place, because the conservative
* default is much less than the MTUs typically seen
* on the Internet today. For the moment, we'll sweep
* this under the carpet.
*
* The conservative default might not actually be a problem
* if the only case this occurs is when sending an initial
* SYN with options and data to a host we've never talked
* to before. Then, they will reply with an MSS value which
* will get recorded and the new parameters should get
* recomputed. For Further Study.
*/
}
mss = min(mss, offer);
/*
* Sanity check: make sure that maxseg will be large
* enough to allow some data on segments even if the
* all the option space is used (40bytes). Otherwise
* funny things may happen in tcp_output.
*
* XXXGL: shouldn't we reserve space for IP/IPv6 options?
*/
mss = max(mss, 64);
tp->t_maxseg = mss;
}
void
tcp_mss(struct tcpcb *tp, int offer)
{
int mss;
uint32_t bufsize;
struct inpcb *inp;
struct socket *so;
struct hc_metrics_lite metrics;
struct tcp_ifcap cap;
KASSERT(tp != NULL, ("%s: tp == NULL", __func__));
bzero(&cap, sizeof(cap));
tcp_mss_update(tp, offer, -1, &metrics, &cap);
mss = tp->t_maxseg;
inp = tp->t_inpcb;
/*
* If there's a pipesize, change the socket buffer to that size,
* don't change if sb_hiwat is different than default (then it
* has been changed on purpose with setsockopt).
* Make the socket buffers an integral number of mss units;
* if the mss is larger than the socket buffer, decrease the mss.
*/
so = inp->inp_socket;
SOCKBUF_LOCK(&so->so_snd);
if ((so->so_snd.sb_hiwat == V_tcp_sendspace) && metrics.rmx_sendpipe)
bufsize = metrics.rmx_sendpipe;
else
bufsize = so->so_snd.sb_hiwat;
if (bufsize < mss)
mss = bufsize;
else {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
if (bufsize > so->so_snd.sb_hiwat)
(void)sbreserve_locked(&so->so_snd, bufsize, so, NULL);
}
SOCKBUF_UNLOCK(&so->so_snd);
/*
* Sanity check: make sure that maxseg will be large
* enough to allow some data on segments even if the
* all the option space is used (40bytes). Otherwise
* funny things may happen in tcp_output.
*
* XXXGL: shouldn't we reserve space for IP/IPv6 options?
*/
tp->t_maxseg = max(mss, 64);
SOCKBUF_LOCK(&so->so_rcv);
if ((so->so_rcv.sb_hiwat == V_tcp_recvspace) && metrics.rmx_recvpipe)
bufsize = metrics.rmx_recvpipe;
else
bufsize = so->so_rcv.sb_hiwat;
if (bufsize > mss) {
bufsize = roundup(bufsize, mss);
if (bufsize > sb_max)
bufsize = sb_max;
if (bufsize > so->so_rcv.sb_hiwat)
(void)sbreserve_locked(&so->so_rcv, bufsize, so, NULL);
}
SOCKBUF_UNLOCK(&so->so_rcv);
/* Check the interface for TSO capabilities. */
if (cap.ifcap & CSUM_TSO) {
tp->t_flags |= TF_TSO;
tp->t_tsomax = cap.tsomax;
tp->t_tsomaxsegcount = cap.tsomaxsegcount;
tp->t_tsomaxsegsize = cap.tsomaxsegsize;
}
}
/*
* Determine the MSS option to send on an outgoing SYN.
*/
int
tcp_mssopt(struct in_conninfo *inc)
{
int mss = 0;
uint32_t thcmtu = 0;
uint32_t maxmtu = 0;
size_t min_protoh;
KASSERT(inc != NULL, ("tcp_mssopt with NULL in_conninfo pointer"));
#ifdef INET6
if (inc->inc_flags & INC_ISIPV6) {
mss = V_tcp_v6mssdflt;
maxmtu = tcp_maxmtu6(inc, NULL);
min_protoh = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
}
#endif
#if defined(INET) && defined(INET6)
else
#endif
#ifdef INET
{
mss = V_tcp_mssdflt;
maxmtu = tcp_maxmtu(inc, NULL);
min_protoh = sizeof(struct tcpiphdr);
}
#endif
#if defined(INET6) || defined(INET)
thcmtu = tcp_hc_getmtu(inc); /* IPv4 and IPv6 */
#endif
if (maxmtu && thcmtu)
mss = min(maxmtu, thcmtu) - min_protoh;
else if (maxmtu || thcmtu)
mss = max(maxmtu, thcmtu) - min_protoh;
return (mss);
}
void
tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
{
int snd_cnt = 0, limit = 0, del_data = 0, pipe = 0;
int maxseg = tcp_maxseg(tp);
INP_WLOCK_ASSERT(tp->t_inpcb);
/*
* Compute the amount of data that this ACK is indicating
* (del_data) and an estimate of how many bytes are in the
* network.
*/
del_data = tp->sackhint.delivered_data;
if (V_tcp_do_newsack)
pipe = tcp_compute_pipe(tp);
else
pipe = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit;
tp->sackhint.prr_delivered += del_data;
/*
* Proportional Rate Reduction
*/
if (pipe >= tp->snd_ssthresh) {
if (tp->sackhint.recover_fs == 0)
tp->sackhint.recover_fs =
imax(1, tp->snd_nxt - tp->snd_una);
snd_cnt = howmany((long)tp->sackhint.prr_delivered *
tp->snd_ssthresh, tp->sackhint.recover_fs) -
tp->sackhint.prr_out;
} else {
if (V_tcp_do_prr_conservative)
limit = tp->sackhint.prr_delivered -
tp->sackhint.prr_out;
else
limit = imax(tp->sackhint.prr_delivered -
tp->sackhint.prr_out, del_data) +
maxseg;
snd_cnt = imin((tp->snd_ssthresh - pipe), limit);
}
snd_cnt = imax(snd_cnt, 0) / maxseg;
/*
* Send snd_cnt new data into the network in response to this ack.
* If there is going to be a SACK retransmission, adjust snd_cwnd
* accordingly.
*/
if (IN_FASTRECOVERY(tp->t_flags)) {
tp->snd_cwnd = imax(maxseg, tp->snd_nxt - tp->snd_recover +
tp->sackhint.sack_bytes_rexmit + (snd_cnt * maxseg));
} else if (IN_CONGRECOVERY(tp->t_flags))
tp->snd_cwnd = imax(maxseg, pipe - del_data +
(snd_cnt * maxseg));
}
/*
* On a partial ack arrives, force the retransmission of the
* next unacknowledged segment. Do not clear tp->t_dupacks.
* By setting snd_nxt to ti_ack, this forces retransmission timer to
* be started again.
*/
void
tcp_newreno_partial_ack(struct tcpcb *tp, struct tcphdr *th)
{
tcp_seq onxt = tp->snd_nxt;
uint32_t ocwnd = tp->snd_cwnd;
u_int maxseg = tcp_maxseg(tp);
INP_WLOCK_ASSERT(tp->t_inpcb);
tcp_timer_activate(tp, TT_REXMT, 0);
tp->t_rtttime = 0;
tp->snd_nxt = th->th_ack;
/*
* Set snd_cwnd to one segment beyond acknowledged offset.
* (tp->snd_una has not yet been updated when this function is called.)
*/
tp->snd_cwnd = maxseg + BYTES_THIS_ACK(tp, th);
tp->t_flags |= TF_ACKNOW;
(void) tp->t_fb->tfb_tcp_output(tp);
tp->snd_cwnd = ocwnd;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
/*
* Partial window deflation. Relies on fact that tp->snd_una
* not updated yet.
*/
if (tp->snd_cwnd > BYTES_THIS_ACK(tp, th))
tp->snd_cwnd -= BYTES_THIS_ACK(tp, th);
else
tp->snd_cwnd = 0;
tp->snd_cwnd += maxseg;
}
int
tcp_compute_pipe(struct tcpcb *tp)
{
return (tp->snd_max - tp->snd_una +
tp->sackhint.sack_bytes_rexmit -
tp->sackhint.sacked_bytes);
}
uint32_t
tcp_compute_initwnd(uint32_t maxseg)
{
/*
* Calculate the Initial Window, also used as Restart Window
*
* RFC5681 Section 3.1 specifies the default conservative values.
* RFC3390 specifies slightly more aggressive values.
* RFC6928 increases it to ten segments.
* Support for user specified value for initial flight size.
*/
if (V_tcp_initcwnd_segments)
return min(V_tcp_initcwnd_segments * maxseg,
max(2 * maxseg, V_tcp_initcwnd_segments * 1460));
else if (V_tcp_do_rfc3390)
return min(4 * maxseg, max(2 * maxseg, 4380));
else {
/* Per RFC5681 Section 3.1 */
if (maxseg > 2190)
return (2 * maxseg);
else if (maxseg > 1095)
return (3 * maxseg);
else
return (4 * maxseg);
}
}
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