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31 * @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/callout.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
46 #include <sys/malloc.h>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
52 #include <sys/syslog.h>
53 #include <sys/protosw.h>
54 #include <sys/random.h>
58 #include <net/route.h>
60 #include <net/if_var.h>
63 #include <netinet/in.h>
64 #include <netinet/in_kdtrace.h>
65 #include <netinet/in_pcb.h>
66 #include <netinet/in_systm.h>
67 #include <netinet/in_var.h>
68 #include <netinet/ip.h>
69 #include <netinet/ip_icmp.h>
70 #include <netinet/ip_var.h>
72 #include <netinet/ip6.h>
73 #include <netinet6/in6_pcb.h>
74 #include <netinet6/ip6_var.h>
75 #include <netinet6/scope6_var.h>
76 #include <netinet6/nd6.h>
78 #include <netinet/tcp.h>
79 #include <netinet/tcp_fsm.h>
80 #include <netinet/tcp_seq.h>
81 #include <netinet/tcp_timer.h>
82 #include <netinet/tcp_var.h>
83 #include <netinet/tcpip.h>
85 #include <netinet/udp.h>
86 #include <netinet/udp_var.h>
88 #include <netipsec/ipsec_support.h>
90 #include <machine/in_cksum.h>
92 #include <security/mac/mac_framework.h>
94 VNET_DEFINE_STATIC(bool, nolocaltimewait) = true;
95 #define V_nolocaltimewait VNET(nolocaltimewait)
96 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, nolocaltimewait,
97 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(nolocaltimewait), true,
98 "Do not create TCP TIME_WAIT state for local connections");
101 * Move a TCP connection into TIME_WAIT state.
102 * inp is locked, and is unlocked before returning.
104 * This function used to free tcpcb and allocate a compressed TCP time-wait
105 * structure tcptw. This served well for 20 years but is no longer relevant
106 * on modern machines in the modern internet. However, the function remains
107 * so that TCP stacks require less modification and we don't burn the bridge
108 * to go back to using compressed time-wait.
111 tcp_twstart(struct tcpcb *tp)
113 struct inpcb *inp = tptoinpcb(tp);
115 bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
119 INP_WLOCK_ASSERT(inp);
121 /* A dropped inp should never transition to TIME_WAIT state. */
122 KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
123 "(inp->inp_flags & INP_DROPPED) != 0"));
125 tcp_state_change(tp, TCPS_TIME_WAIT);
126 soisdisconnected(inp->inp_socket);
128 if (tp->t_flags & TF_ACKNOW)
131 if (V_nolocaltimewait && (
133 isipv6 ? in6_localaddr(&inp->in6p_faddr) :
136 in_localip(inp->inp_faddr)
141 if ((tp = tcp_close(tp)) != NULL)
146 tcp_timer_activate(tp, TT_2MSL, 2 * V_tcp_msl);
151 * Returns true if the TIME_WAIT state was killed and we should start over,
152 * looking for a pcb in the listen state. Otherwise returns false and frees
155 * For pure SYN-segments the PCB shall be read-locked and the tcpopt pointer
156 * may be NULL. For the rest write-lock and valid tcpopt.
159 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
160 struct mbuf *m, int tlen)
162 struct tcpcb *tp = intotcpcb(inp);
168 INP_LOCK_ASSERT(inp);
170 thflags = tcp_get_flags(th);
172 if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN)
173 INP_RLOCK_ASSERT(inp);
175 INP_WLOCK_ASSERT(inp);
177 ("%s: called without options on a non-SYN segment",
183 * NOTE: for FIN_WAIT_2 (to be added later),
184 * must validate sequence number before accepting RST
188 * If the segment contains RST:
189 * Drop the segment - see Stevens, vol. 2, p. 964 and
192 if (thflags & TH_RST)
196 /* PAWS not needed at the moment */
198 * RFC 1323 PAWS: If we have a timestamp reply on this segment
199 * and it's less than ts_recent, drop it.
201 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
202 TSTMP_LT(to.to_tsval, tp->ts_recent)) {
203 if ((thflags & TH_ACK) == 0)
208 * ts_recent is never updated because we never accept new segments.
212 /* Honor the drop_synfin sysctl variable. */
213 if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
214 if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
215 log(LOG_DEBUG, "%s; %s: "
216 "SYN|FIN segment ignored (based on "
217 "sysctl setting)\n", s, __func__);
224 * If a new connection request is received
225 * while in TIME_WAIT, drop the old connection
226 * and start over if the sequence numbers
227 * are above the previous ones.
228 * Allow UDP port number changes in this case.
230 if (((thflags & (TH_SYN | TH_ACK)) == TH_SYN) &&
231 SEQ_GT(th->th_seq, tp->rcv_nxt)) {
233 * In case we can't upgrade our lock just pretend we have
236 if (INP_TRY_UPGRADE(inp) == 0)
238 if ((tp = tcp_close(tp)) != NULL)
240 TCPSTAT_INC(tcps_tw_recycles);
245 * Send RST if UDP port numbers don't match
247 if (tp->t_port != m->m_pkthdr.tcp_tun_port) {
248 if (tcp_get_flags(th) & TH_ACK) {
249 tcp_respond(tp, mtod(m, void *), th, m,
250 (tcp_seq)0, th->th_ack, TH_RST);
252 if (tcp_get_flags(th) & TH_SYN)
254 if (tcp_get_flags(th) & TH_FIN)
256 tcp_respond(tp, mtod(m, void *), th, m,
257 th->th_seq+tlen, (tcp_seq)0, TH_RST|TH_ACK);
260 TCPSTAT_INC(tcps_tw_resets);
265 * Drop the segment if it does not contain an ACK.
267 if ((thflags & TH_ACK) == 0)
270 INP_WLOCK_ASSERT(inp);
273 * If timestamps were negotiated during SYN/ACK and a
274 * segment without a timestamp is received, silently drop
275 * the segment, unless the missing timestamps are tolerated.
276 * See section 3.2 of RFC 7323.
278 if (((to->to_flags & TOF_TS) == 0) && (tp->ts_recent != 0) &&
279 (V_tcp_tolerate_missing_ts == 0)) {
284 * Reset the 2MSL timer if this is a duplicate FIN.
286 if (thflags & TH_FIN) {
287 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
288 if (seq + 1 == tp->rcv_nxt)
289 tcp_timer_activate(tp, TT_2MSL, 2 * V_tcp_msl);
293 * Acknowledge the segment if it has data or is not a duplicate ACK.
295 if (thflags != TH_ACK || tlen != 0 ||
296 th->th_seq != tp->rcv_nxt || th->th_ack != tp->snd_nxt) {
297 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
298 tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
299 tp->snd_nxt, TH_ACK);
301 TCPSTAT_INC(tcps_tw_responds);
305 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);