1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 * @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95
32 */
33
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36
37 #include "opt_inet.h"
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40
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>
47 #include <sys/mbuf.h>
48 #include <sys/priv.h>
49 #include <sys/proc.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>
55
56 #include <vm/uma.h>
57
58 #include <net/route.h>
59 #include <net/if.h>
60 #include <net/if_var.h>
61 #include <net/vnet.h>
62
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>
71 #ifdef INET6
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>
77 #endif
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/tcp_hpts.h>
84 #include <netinet/tcpip.h>
85
86 #include <netinet/udp.h>
87 #include <netinet/udp_var.h>
88
89 #include <netipsec/ipsec_support.h>
90
91 #include <machine/in_cksum.h>
92
93 #include <security/mac/mac_framework.h>
94
95 VNET_DEFINE_STATIC(bool, nolocaltimewait) = true;
96 #define V_nolocaltimewait VNET(nolocaltimewait)
97 SYSCTL_BOOL(_net_inet_tcp, OID_AUTO, nolocaltimewait,
98 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(nolocaltimewait), true,
99 "Do not create TCP TIME_WAIT state for local connections");
100
101 /*
102 * Move a TCP connection into TIME_WAIT state.
103 * inp is locked, and is unlocked before returning.
104 *
105 * This function used to free tcpcb and allocate a compressed TCP time-wait
106 * structure tcptw. This served well for 20 years but is no longer relevant
107 * on modern machines in the modern internet. However, the function remains
108 * so that TCP stacks require less modification and we don't burn the bridge
109 * to go back to using compressed time-wait.
110 */
111 void
112 tcp_twstart(struct tcpcb *tp)
113 {
114 struct inpcb *inp = tptoinpcb(tp);
115 #ifdef INET6
116 bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
117 #endif
118
119 NET_EPOCH_ASSERT();
120 INP_WLOCK_ASSERT(inp);
121
122 /* A dropped inp should never transition to TIME_WAIT state. */
123 KASSERT((inp->inp_flags & INP_DROPPED) == 0, ("tcp_twstart: "
124 "(inp->inp_flags & INP_DROPPED) != 0"));
125
126 tcp_state_change(tp, TCPS_TIME_WAIT);
127 soisdisconnected(inp->inp_socket);
128
129 if (tp->t_flags & TF_ACKNOW)
130 tcp_output(tp);
131
132 if (V_nolocaltimewait && (
133 #ifdef INET6
134 isipv6 ? in6_localaddr(&inp->in6p_faddr) :
135 #endif
136 #ifdef INET
137 in_localip(inp->inp_faddr)
138 #else
139 false
140 #endif
141 )) {
142 if ((tp = tcp_close(tp)) != NULL)
143 INP_WUNLOCK(inp);
144 return;
145 }
146
147 tcp_timer_activate(tp, TT_2MSL, 2 * V_tcp_msl);
148 INP_WUNLOCK(inp);
149 }
150
151 /*
152 * Returns true if the TIME_WAIT state was killed and we should start over,
153 * looking for a pcb in the listen state. Otherwise returns false and frees
154 * the mbuf.
155 *
156 * For pure SYN-segments the PCB shall be read-locked and the tcpopt pointer
157 * may be NULL. For the rest write-lock and valid tcpopt.
158 */
159 bool
160 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
161 struct mbuf *m, int tlen)
162 {
163 struct tcpcb *tp = intotcpcb(inp);
164 char *s;
165 int thflags;
166 tcp_seq seq;
167
168 NET_EPOCH_ASSERT();
169 INP_LOCK_ASSERT(inp);
170
171 thflags = tcp_get_flags(th);
172 #ifdef INVARIANTS
173 if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN)
174 INP_RLOCK_ASSERT(inp);
175 else {
176 INP_WLOCK_ASSERT(inp);
177 KASSERT(to != NULL,
178 ("%s: called without options on a non-SYN segment",
179 __func__));
180 }
181 #endif
182
183 /*
184 * NOTE: for FIN_WAIT_2 (to be added later),
185 * must validate sequence number before accepting RST
186 */
187
188 /*
189 * If the segment contains RST:
190 * Drop the segment - see Stevens, vol. 2, p. 964 and
191 * RFC 1337.
192 */
193 if (thflags & TH_RST)
194 goto drop;
195
196 #if 0
197 /* PAWS not needed at the moment */
198 /*
199 * RFC 1323 PAWS: If we have a timestamp reply on this segment
200 * and it's less than ts_recent, drop it.
201 */
202 if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
203 TSTMP_LT(to.to_tsval, tp->ts_recent)) {
204 if ((thflags & TH_ACK) == 0)
205 goto drop;
206 goto ack;
207 }
208 /*
209 * ts_recent is never updated because we never accept new segments.
210 */
211 #endif
212
213 /* Honor the drop_synfin sysctl variable. */
214 if ((thflags & TH_SYN) && (thflags & TH_FIN) && V_drop_synfin) {
215 if ((s = tcp_log_addrs(&inp->inp_inc, th, NULL, NULL))) {
216 log(LOG_DEBUG, "%s; %s: "
217 "SYN|FIN segment ignored (based on "
218 "sysctl setting)\n", s, __func__);
219 free(s, M_TCPLOG);
220 }
221 goto drop;
222 }
223
224 /*
225 * If a new connection request is received
226 * while in TIME_WAIT, drop the old connection
227 * and start over if the sequence numbers
228 * are above the previous ones.
229 * Allow UDP port number changes in this case.
230 */
231 if (((thflags & (TH_SYN | TH_ACK)) == TH_SYN) &&
232 SEQ_GT(th->th_seq, tp->rcv_nxt)) {
233 /*
234 * In case we can't upgrade our lock just pretend we have
235 * lost this packet.
236 */
237 if (INP_TRY_UPGRADE(inp) == 0)
238 goto drop;
239 if ((tp = tcp_close(tp)) != NULL)
240 INP_WUNLOCK(inp);
241 TCPSTAT_INC(tcps_tw_recycles);
242 return (true);
243 }
244
245 /*
246 * Send RST if UDP port numbers don't match
247 */
248 if (tp->t_port != m->m_pkthdr.tcp_tun_port) {
249 if (tcp_get_flags(th) & TH_ACK) {
250 tcp_respond(tp, mtod(m, void *), th, m,
251 (tcp_seq)0, th->th_ack, TH_RST);
252 } else {
253 if (tcp_get_flags(th) & TH_SYN)
254 tlen++;
255 if (tcp_get_flags(th) & TH_FIN)
256 tlen++;
257 tcp_respond(tp, mtod(m, void *), th, m,
258 th->th_seq+tlen, (tcp_seq)0, TH_RST|TH_ACK);
259 }
260 INP_UNLOCK(inp);
261 TCPSTAT_INC(tcps_tw_resets);
262 return (false);
263 }
264
265 /*
266 * Drop the segment if it does not contain an ACK.
267 */
268 if ((thflags & TH_ACK) == 0)
269 goto drop;
270
271 INP_WLOCK_ASSERT(inp);
272
273 /*
274 * If timestamps were negotiated during SYN/ACK and a
275 * segment without a timestamp is received, silently drop
276 * the segment, unless the missing timestamps are tolerated.
277 * See section 3.2 of RFC 7323.
278 */
279 if (((to->to_flags & TOF_TS) == 0) && (tp->ts_recent != 0) &&
280 (V_tcp_tolerate_missing_ts == 0)) {
281 goto drop;
282 }
283
284 /*
285 * Reset the 2MSL timer if this is a duplicate FIN.
286 */
287 if (thflags & TH_FIN) {
288 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
289 if (seq + 1 == tp->rcv_nxt)
290 tcp_timer_activate(tp, TT_2MSL, 2 * V_tcp_msl);
291 }
292
293 /*
294 * Acknowledge the segment if it has data or is not a duplicate ACK.
295 */
296 if (thflags != TH_ACK || tlen != 0 ||
297 th->th_seq != tp->rcv_nxt || th->th_ack != tp->snd_nxt) {
298 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
299 tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
300 tp->snd_nxt, TH_ACK);
301 INP_UNLOCK(inp);
302 TCPSTAT_INC(tcps_tw_responds);
303 return (false);
304 }
305 drop:
306 TCP_PROBE5(receive, NULL, NULL, m, NULL, th);
307 INP_UNLOCK(inp);
308 m_freem(m);
309 return (false);
310 }
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