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/tcpip.h> 84 85 #include <netinet/udp.h> 86 #include <netinet/udp_var.h> 87 88 #include <netipsec/ipsec_support.h> 89 90 #include <machine/in_cksum.h> 91 92 #include <security/mac/mac_framework.h> 93 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"); 99 100 /* 101 * Move a TCP connection into TIME_WAIT state. 102 * inp is locked, and is unlocked before returning. 103 * 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. 109 */ 110 void 111 tcp_twstart(struct tcpcb *tp) 112 { 113 struct inpcb *inp = tptoinpcb(tp); 114 #ifdef INET6 115 bool isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6; 116 #endif 117 118 NET_EPOCH_ASSERT(); 119 INP_WLOCK_ASSERT(inp); 120 121 /* 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")); 124 125 tcp_state_change(tp, TCPS_TIME_WAIT); 126 soisdisconnected(inp->inp_socket); 127 128 if (tp->t_flags & TF_ACKNOW) 129 tcp_output(tp); 130 131 if (V_nolocaltimewait && ( 132 #ifdef INET6 133 isipv6 ? in6_localaddr(&inp->in6p_faddr) : 134 #endif 135 #ifdef INET 136 in_localip(inp->inp_faddr) 137 #else 138 false 139 #endif 140 )) { 141 if ((tp = tcp_close(tp)) != NULL) 142 INP_WUNLOCK(inp); 143 return; 144 } 145 146 tcp_timer_activate(tp, TT_2MSL, 2 * V_tcp_msl); 147 INP_WUNLOCK(inp); 148 } 149 150 /* 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 153 * the mbuf. 154 * 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. 157 */ 158 bool 159 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th, 160 struct mbuf *m, int tlen) 161 { 162 struct tcpcb *tp = intotcpcb(inp); 163 char *s; 164 int thflags; 165 tcp_seq seq; 166 167 NET_EPOCH_ASSERT(); 168 INP_LOCK_ASSERT(inp); 169 170 thflags = tcp_get_flags(th); 171 #ifdef INVARIANTS 172 if ((thflags & (TH_SYN | TH_ACK)) == TH_SYN) 173 INP_RLOCK_ASSERT(inp); 174 else { 175 INP_WLOCK_ASSERT(inp); 176 KASSERT(to != NULL, 177 ("%s: called without options on a non-SYN segment", 178 __func__)); 179 } 180 #endif 181 182 /* 183 * NOTE: for FIN_WAIT_2 (to be added later), 184 * must validate sequence number before accepting RST 185 */ 186 187 /* 188 * If the segment contains RST: 189 * Drop the segment - see Stevens, vol. 2, p. 964 and 190 * RFC 1337. 191 */ 192 if (thflags & TH_RST) 193 goto drop; 194 195 #if 0 196 /* PAWS not needed at the moment */ 197 /* 198 * RFC 1323 PAWS: If we have a timestamp reply on this segment 199 * and it's less than ts_recent, drop it. 200 */ 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) 204 goto drop; 205 goto ack; 206 } 207 /* 208 * ts_recent is never updated because we never accept new segments. 209 */ 210 #endif 211 212 /* 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__); 218 free(s, M_TCPLOG); 219 } 220 goto drop; 221 } 222 223 /* 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. 229 */ 230 if (((thflags & (TH_SYN | TH_ACK)) == TH_SYN) && 231 SEQ_GT(th->th_seq, tp->rcv_nxt)) { 232 /* 233 * In case we can't upgrade our lock just pretend we have 234 * lost this packet. 235 */ 236 if (INP_TRY_UPGRADE(inp) == 0) 237 goto drop; 238 if ((tp = tcp_close(tp)) != NULL) 239 INP_WUNLOCK(inp); 240 TCPSTAT_INC(tcps_tw_recycles); 241 return (true); 242 } 243 244 /* 245 * Send RST if UDP port numbers don't match 246 */ 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); 251 } else { 252 if (tcp_get_flags(th) & TH_SYN) 253 tlen++; 254 if (tcp_get_flags(th) & TH_FIN) 255 tlen++; 256 tcp_respond(tp, mtod(m, void *), th, m, 257 th->th_seq+tlen, (tcp_seq)0, TH_RST|TH_ACK); 258 } 259 INP_UNLOCK(inp); 260 TCPSTAT_INC(tcps_tw_resets); 261 return (false); 262 } 263 264 /* 265 * Drop the segment if it does not contain an ACK. 266 */ 267 if ((thflags & TH_ACK) == 0) 268 goto drop; 269 270 INP_WLOCK_ASSERT(inp); 271 272 /* 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. 277 */ 278 if (((to->to_flags & TOF_TS) == 0) && (tp->ts_recent != 0) && 279 (V_tcp_tolerate_missing_ts == 0)) { 280 goto drop; 281 } 282 283 /* 284 * Reset the 2MSL timer if this is a duplicate FIN. 285 */ 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); 290 } 291 292 /* 293 * Acknowledge the segment if it has data or is not a duplicate ACK. 294 */ 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); 300 INP_UNLOCK(inp); 301 TCPSTAT_INC(tcps_tw_responds); 302 return (false); 303 } 304 drop: 305 TCP_PROBE5(receive, NULL, NULL, m, NULL, th); 306 INP_UNLOCK(inp); 307 m_freem(m); 308 return (false); 309 } 310