1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
5 * The Regents of the University of California. All rights reserved.
6 * Copyright (c) 2007-2008,2010
7 * Swinburne University of Technology, Melbourne, Australia.
8 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
9 * Copyright (c) 2010 The FreeBSD Foundation
10 * Copyright (c) 2010-2011 Juniper Networks, Inc.
11 * Copyright (c) 2019 Richard Scheffenegger <srichard@netapp.com>
12 * All rights reserved.
13 *
14 * Portions of this software were developed at the Centre for Advanced Internet
15 * Architectures, Swinburne University of Technology, by Lawrence Stewart,
16 * James Healy and David Hayes, made possible in part by a grant from the Cisco
17 * University Research Program Fund at Community Foundation Silicon Valley.
18 *
19 * Portions of this software were developed at the Centre for Advanced
20 * Internet Architectures, Swinburne University of Technology, Melbourne,
21 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
22 *
23 * Portions of this software were developed by Robert N. M. Watson under
24 * contract to Juniper Networks, Inc.
25 *
26 * Redistribution and use in source and binary forms, with or without
27 * modification, are permitted provided that the following conditions
28 * are met:
29 * 1. Redistributions of source code must retain the above copyright
30 * notice, this list of conditions and the following disclaimer.
31 * 2. Redistributions in binary form must reproduce the above copyright
32 * notice, this list of conditions and the following disclaimer in the
33 * documentation and/or other materials provided with the distribution.
34 * 3. Neither the name of the University nor the names of its contributors
35 * may be used to endorse or promote products derived from this software
36 * without specific prior written permission.
37 *
38 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
39 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
40 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
41 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
42 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
43 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
44 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
45 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
46 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
47 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48 * SUCH DAMAGE.
49 */
50
51 /*
52 * Utility functions to deal with Explicit Congestion Notification in TCP
53 * implementing the essential parts of the Accurate ECN extension
54 * https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-09
55 */
56
57 #include "opt_inet.h"
58 #include "opt_inet6.h"
59
60 #include <sys/param.h>
61 #include <sys/systm.h>
62 #include <sys/kernel.h>
63 #include <sys/sysctl.h>
64 #include <sys/malloc.h>
65 #include <sys/mbuf.h>
66 #include <sys/socket.h>
67 #include <sys/socketvar.h>
68
69 #include <machine/cpu.h>
70
71 #include <vm/uma.h>
72
73 #include <net/if.h>
74 #include <net/if_var.h>
75 #include <net/route.h>
76 #include <net/vnet.h>
77
78 #include <netinet/in.h>
79 #include <netinet/in_systm.h>
80 #include <netinet/ip.h>
81 #include <netinet/in_var.h>
82 #include <netinet/in_pcb.h>
83 #include <netinet/ip_var.h>
84 #include <netinet/ip6.h>
85 #include <netinet/icmp6.h>
86 #include <netinet6/nd6.h>
87 #include <netinet6/ip6_var.h>
88 #include <netinet6/in6_pcb.h>
89 #include <netinet/tcp.h>
90 #include <netinet/tcp_fsm.h>
91 #include <netinet/tcp_seq.h>
92 #include <netinet/tcp_var.h>
93 #include <netinet/tcp_syncache.h>
94 #include <netinet/tcp_timer.h>
95 #include <netinet/tcpip.h>
96 #include <netinet/tcp_ecn.h>
97
98 static inline int tcp_ecn_get_ace(uint16_t);
99 static inline void tcp_ecn_set_ace(uint16_t *, uint32_t);
100
101 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, ecn,
102 CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
103 "TCP ECN");
104
105 VNET_DEFINE(int, tcp_do_ecn) = 2;
106 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, enable,
107 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_do_ecn), 0,
108 "TCP ECN support");
109
110 VNET_DEFINE(int, tcp_ecn_maxretries) = 1;
111 SYSCTL_INT(_net_inet_tcp_ecn, OID_AUTO, maxretries,
112 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_ecn_maxretries), 0,
113 "Max retries before giving up on ECN");
114
115 /*
116 * Process incoming SYN,ACK packet
117 */
118 void
tcp_ecn_input_syn_sent(struct tcpcb * tp,uint16_t thflags,int iptos)119 tcp_ecn_input_syn_sent(struct tcpcb *tp, uint16_t thflags, int iptos)
120 {
121 switch (V_tcp_do_ecn) {
122 case 0:
123 return;
124 case 1:
125 /* FALLTHROUGH */
126 case 2:
127 /* RFC3168 ECN handling */
128 if ((thflags & (TH_CWR | TH_ECE)) == (0 | TH_ECE)) {
129 tp->t_flags2 |= TF2_ECN_PERMIT;
130 tp->t_flags2 &= ~TF2_ACE_PERMIT;
131 TCPSTAT_INC(tcps_ecn_shs);
132 }
133 break;
134 case 3:
135 /* FALLTHROUGH */
136 case 4:
137 /*
138 * Decoding Accurate ECN according to
139 * table in section 3.1.1
140 *
141 * On the SYN,ACK, process the AccECN
142 * flags indicating the state the SYN
143 * was delivered.
144 * Reactions to Path ECN mangling can
145 * come here.
146 */
147 switch (thflags & (TH_AE | TH_CWR | TH_ECE)) {
148 /* RFC3168 SYN */
149 case (0|0|TH_ECE):
150 tp->t_flags2 |= TF2_ECN_PERMIT;
151 tp->t_flags2 &= ~TF2_ACE_PERMIT;
152 TCPSTAT_INC(tcps_ecn_shs);
153 break;
154 /* non-ECT SYN */
155 case (0|TH_CWR|0):
156 tp->t_flags2 |= TF2_ACE_PERMIT;
157 tp->t_flags2 &= ~TF2_ECN_PERMIT;
158 tp->t_scep = 5;
159 TCPSTAT_INC(tcps_ecn_shs);
160 TCPSTAT_INC(tcps_ace_nect);
161 break;
162 /* ECT0 SYN */
163 case (TH_AE|0|0):
164 tp->t_flags2 |= TF2_ACE_PERMIT;
165 tp->t_flags2 &= ~TF2_ECN_PERMIT;
166 tp->t_scep = 5;
167 TCPSTAT_INC(tcps_ecn_shs);
168 TCPSTAT_INC(tcps_ace_ect0);
169 break;
170 /* ECT1 SYN */
171 case (0|TH_CWR|TH_ECE):
172 tp->t_flags2 |= TF2_ACE_PERMIT;
173 tp->t_flags2 &= ~TF2_ECN_PERMIT;
174 tp->t_scep = 5;
175 TCPSTAT_INC(tcps_ecn_shs);
176 TCPSTAT_INC(tcps_ace_ect1);
177 break;
178 /* CE SYN */
179 case (TH_AE|TH_CWR|0):
180 tp->t_flags2 |= TF2_ACE_PERMIT;
181 tp->t_flags2 &= ~TF2_ECN_PERMIT;
182 tp->t_scep = 6;
183 /*
184 * reduce the IW to 2 MSS (to
185 * account for delayed acks) if
186 * the SYN,ACK was CE marked
187 */
188 tp->snd_cwnd = 2 * tcp_maxseg(tp);
189 TCPSTAT_INC(tcps_ecn_shs);
190 TCPSTAT_INC(tcps_ace_nect);
191 break;
192 default:
193 tp->t_flags2 &= ~(TF2_ECN_PERMIT | TF2_ACE_PERMIT);
194 break;
195 }
196 /*
197 * Set the AccECN Codepoints on
198 * the outgoing <ACK> to the ECN
199 * state of the <SYN,ACK>
200 * according to table 3 in the
201 * AccECN draft
202 */
203 switch (iptos & IPTOS_ECN_MASK) {
204 case (IPTOS_ECN_NOTECT):
205 tp->t_rcep = 0b010;
206 break;
207 case (IPTOS_ECN_ECT0):
208 tp->t_rcep = 0b100;
209 break;
210 case (IPTOS_ECN_ECT1):
211 tp->t_rcep = 0b011;
212 break;
213 case (IPTOS_ECN_CE):
214 tp->t_rcep = 0b110;
215 break;
216 }
217 break;
218 }
219 }
220
221 /*
222 * Handle parallel SYN for ECN
223 */
224 void
tcp_ecn_input_parallel_syn(struct tcpcb * tp,uint16_t thflags,int iptos)225 tcp_ecn_input_parallel_syn(struct tcpcb *tp, uint16_t thflags, int iptos)
226 {
227 if (thflags & TH_ACK)
228 return;
229 switch (V_tcp_do_ecn) {
230 case 0:
231 return;
232 case 1:
233 /* FALLTHROUGH */
234 case 2:
235 /* RFC3168 ECN handling */
236 if ((thflags & (TH_CWR | TH_ECE)) == (TH_CWR | TH_ECE)) {
237 tp->t_flags2 |= TF2_ECN_PERMIT;
238 tp->t_flags2 &= ~TF2_ACE_PERMIT;
239 tp->t_flags2 |= TF2_ECN_SND_ECE;
240 TCPSTAT_INC(tcps_ecn_shs);
241 }
242 break;
243 case 3:
244 /* FALLTHROUGH */
245 case 4:
246 /* AccECN handling */
247 switch (thflags & (TH_AE | TH_CWR | TH_ECE)) {
248 default:
249 case (0|0|0):
250 tp->t_flags2 &= ~(TF2_ECN_PERMIT | TF2_ACE_PERMIT);
251 break;
252 case (0|TH_CWR|TH_ECE):
253 tp->t_flags2 |= TF2_ECN_PERMIT;
254 tp->t_flags2 &= ~TF2_ACE_PERMIT;
255 tp->t_flags2 |= TF2_ECN_SND_ECE;
256 TCPSTAT_INC(tcps_ecn_shs);
257 break;
258 case (TH_AE|TH_CWR|TH_ECE):
259 tp->t_flags2 |= TF2_ACE_PERMIT;
260 tp->t_flags2 &= ~TF2_ECN_PERMIT;
261 TCPSTAT_INC(tcps_ecn_shs);
262 /*
263 * Set the AccECN Codepoints on
264 * the outgoing <ACK> to the ECN
265 * state of the <SYN,ACK>
266 * according to table 3 in the
267 * AccECN draft
268 */
269 switch (iptos & IPTOS_ECN_MASK) {
270 case (IPTOS_ECN_NOTECT):
271 tp->t_rcep = 0b010;
272 break;
273 case (IPTOS_ECN_ECT0):
274 tp->t_rcep = 0b100;
275 break;
276 case (IPTOS_ECN_ECT1):
277 tp->t_rcep = 0b011;
278 break;
279 case (IPTOS_ECN_CE):
280 tp->t_rcep = 0b110;
281 break;
282 }
283 break;
284 }
285 break;
286 }
287 }
288
289 /*
290 * TCP ECN processing.
291 */
292 int
tcp_ecn_input_segment(struct tcpcb * tp,uint16_t thflags,int tlen,int pkts,int iptos)293 tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int tlen, int pkts, int iptos)
294 {
295 int delta_cep = 0;
296
297 switch (iptos & IPTOS_ECN_MASK) {
298 case IPTOS_ECN_CE:
299 TCPSTAT_INC(tcps_ecn_rcvce);
300 break;
301 case IPTOS_ECN_ECT0:
302 TCPSTAT_INC(tcps_ecn_rcvect0);
303 break;
304 case IPTOS_ECN_ECT1:
305 TCPSTAT_INC(tcps_ecn_rcvect1);
306 break;
307 }
308
309 if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
310 if (tp->t_flags2 & TF2_ACE_PERMIT) {
311 if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
312 tp->t_rcep += 1;
313 if (tp->t_flags2 & TF2_ECN_PERMIT) {
314 delta_cep = (tcp_ecn_get_ace(thflags) + 8 -
315 (tp->t_scep & 7)) & 7;
316 if (delta_cep < pkts)
317 delta_cep = pkts -
318 ((pkts - delta_cep) & 7);
319 tp->t_scep += delta_cep;
320 } else {
321 /*
322 * process the final ACK of the 3WHS
323 * see table 3 in draft-ietf-tcpm-accurate-ecn
324 */
325 switch (tcp_ecn_get_ace(thflags)) {
326 case 0b010:
327 /* nonECT SYN or SYN,ACK */
328 /* FALLTHROUGH */
329 case 0b011:
330 /* ECT1 SYN or SYN,ACK */
331 /* FALLTHROUGH */
332 case 0b100:
333 /* ECT0 SYN or SYN,ACK */
334 tp->t_scep = 5;
335 break;
336 case 0b110:
337 /* CE SYN or SYN,ACK */
338 tp->t_scep = 6;
339 tp->snd_cwnd = 2 * tcp_maxseg(tp);
340 break;
341 default:
342 /* mangled AccECN handshake */
343 tp->t_scep = 5;
344 break;
345 }
346 tp->t_flags2 |= TF2_ECN_PERMIT;
347 }
348 } else {
349 /* RFC3168 ECN handling */
350 if ((thflags & (TH_SYN | TH_ECE)) == TH_ECE) {
351 delta_cep = 1;
352 tp->t_scep++;
353 }
354 if (thflags & TH_CWR) {
355 tp->t_flags2 &= ~TF2_ECN_SND_ECE;
356 tp->t_flags |= TF_ACKNOW;
357 }
358 if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
359 tp->t_flags2 |= TF2_ECN_SND_ECE;
360 }
361
362 /* Process a packet differently from RFC3168. */
363 cc_ecnpkt_handler_flags(tp, thflags, iptos);
364 }
365
366 return delta_cep;
367 }
368
369 /*
370 * Send ECN setup <SYN> packet header flags
371 */
372 uint16_t
tcp_ecn_output_syn_sent(struct tcpcb * tp)373 tcp_ecn_output_syn_sent(struct tcpcb *tp)
374 {
375 uint16_t thflags = 0;
376
377 if (V_tcp_do_ecn == 0)
378 return thflags;
379 if (V_tcp_do_ecn == 1) {
380 /* Send a RFC3168 ECN setup <SYN> packet */
381 if (tp->t_rxtshift >= 1) {
382 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
383 thflags = TH_ECE|TH_CWR;
384 } else
385 thflags = TH_ECE|TH_CWR;
386 } else if (V_tcp_do_ecn == 3) {
387 /* Send an Accurate ECN setup <SYN> packet */
388 if (tp->t_rxtshift >= 1) {
389 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
390 thflags = TH_ECE|TH_CWR|TH_AE;
391 } else
392 thflags = TH_ECE|TH_CWR|TH_AE;
393 }
394
395 return thflags;
396 }
397
398 /*
399 * output processing of ECN feature
400 * returning IP ECN header codepoint
401 */
402 int
tcp_ecn_output_established(struct tcpcb * tp,uint16_t * thflags,int len,bool rxmit)403 tcp_ecn_output_established(struct tcpcb *tp, uint16_t *thflags, int len, bool rxmit)
404 {
405 int ipecn = IPTOS_ECN_NOTECT;
406 bool newdata;
407
408 /*
409 * If the peer has ECN, mark data packets with
410 * ECN capable transmission (ECT).
411 * Ignore pure control packets, retransmissions
412 * and window probes.
413 */
414 newdata = (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
415 !rxmit &&
416 !((tp->t_flags & TF_FORCEDATA) && len == 1));
417 /* RFC3168 ECN marking, only new data segments */
418 if (newdata) {
419 if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
420 ipecn = IPTOS_ECN_ECT1;
421 TCPSTAT_INC(tcps_ecn_sndect1);
422 } else {
423 ipecn = IPTOS_ECN_ECT0;
424 TCPSTAT_INC(tcps_ecn_sndect0);
425 }
426 }
427 /*
428 * Reply with proper ECN notifications.
429 */
430 if (tp->t_flags2 & TF2_ACE_PERMIT) {
431 tcp_ecn_set_ace(thflags, tp->t_rcep);
432 if (!(tp->t_flags2 & TF2_ECN_PERMIT)) {
433 /*
434 * here we process the final
435 * ACK of the 3WHS
436 */
437 if (tp->t_rcep == 0b110) {
438 tp->t_rcep = 6;
439 } else {
440 tp->t_rcep = 5;
441 }
442 tp->t_flags2 |= TF2_ECN_PERMIT;
443 }
444 } else {
445 if (newdata &&
446 (tp->t_flags2 & TF2_ECN_SND_CWR)) {
447 *thflags |= TH_CWR;
448 tp->t_flags2 &= ~TF2_ECN_SND_CWR;
449 }
450 if (tp->t_flags2 & TF2_ECN_SND_ECE)
451 *thflags |= TH_ECE;
452 }
453
454 return ipecn;
455 }
456
457 /*
458 * Set up the ECN related tcpcb fields from
459 * a syncache entry
460 */
461 void
tcp_ecn_syncache_socket(struct tcpcb * tp,struct syncache * sc)462 tcp_ecn_syncache_socket(struct tcpcb *tp, struct syncache *sc)
463 {
464 if (sc->sc_flags & SCF_ECN_MASK) {
465 switch (sc->sc_flags & SCF_ECN_MASK) {
466 case SCF_ECN:
467 tp->t_flags2 |= TF2_ECN_PERMIT;
468 break;
469 case SCF_ACE_N:
470 /* FALLTHROUGH */
471 case SCF_ACE_0:
472 /* FALLTHROUGH */
473 case SCF_ACE_1:
474 tp->t_flags2 |= TF2_ACE_PERMIT;
475 tp->t_scep = 5;
476 tp->t_rcep = 5;
477 break;
478 case SCF_ACE_CE:
479 tp->t_flags2 |= TF2_ACE_PERMIT;
480 tp->t_scep = 6;
481 tp->t_rcep = 6;
482 break;
483 }
484 }
485 }
486
487 /*
488 * Process a <SYN> packets ECN information, and provide the
489 * syncache with the relevant information.
490 */
491 int
tcp_ecn_syncache_add(uint16_t thflags,int iptos)492 tcp_ecn_syncache_add(uint16_t thflags, int iptos)
493 {
494 int scflags = 0;
495
496 switch (iptos & IPTOS_ECN_MASK) {
497 case IPTOS_ECN_CE:
498 TCPSTAT_INC(tcps_ecn_rcvce);
499 break;
500 case IPTOS_ECN_ECT0:
501 TCPSTAT_INC(tcps_ecn_rcvect0);
502 break;
503 case IPTOS_ECN_ECT1:
504 TCPSTAT_INC(tcps_ecn_rcvect1);
505 break;
506 }
507
508 switch (thflags & (TH_AE|TH_CWR|TH_ECE)) {
509 /* no ECN */
510 case (0|0|0):
511 break;
512 /* legacy ECN */
513 case (0|TH_CWR|TH_ECE):
514 scflags = SCF_ECN;
515 break;
516 /* Accurate ECN */
517 case (TH_AE|TH_CWR|TH_ECE):
518 if ((V_tcp_do_ecn == 3) ||
519 (V_tcp_do_ecn == 4)) {
520 switch (iptos & IPTOS_ECN_MASK) {
521 case IPTOS_ECN_CE:
522 scflags = SCF_ACE_CE;
523 break;
524 case IPTOS_ECN_ECT0:
525 scflags = SCF_ACE_0;
526 break;
527 case IPTOS_ECN_ECT1:
528 scflags = SCF_ACE_1;
529 break;
530 case IPTOS_ECN_NOTECT:
531 scflags = SCF_ACE_N;
532 break;
533 }
534 } else
535 scflags = SCF_ECN;
536 break;
537 /* Default Case (section 3.1.2) */
538 default:
539 if ((V_tcp_do_ecn == 3) ||
540 (V_tcp_do_ecn == 4)) {
541 switch (iptos & IPTOS_ECN_MASK) {
542 case IPTOS_ECN_CE:
543 scflags = SCF_ACE_CE;
544 break;
545 case IPTOS_ECN_ECT0:
546 scflags = SCF_ACE_0;
547 break;
548 case IPTOS_ECN_ECT1:
549 scflags = SCF_ACE_1;
550 break;
551 case IPTOS_ECN_NOTECT:
552 scflags = SCF_ACE_N;
553 break;
554 }
555 }
556 break;
557 }
558 return scflags;
559 }
560
561 /*
562 * Set up the ECN information for the <SYN,ACK> from
563 * syncache information.
564 */
565 uint16_t
tcp_ecn_syncache_respond(uint16_t thflags,struct syncache * sc)566 tcp_ecn_syncache_respond(uint16_t thflags, struct syncache *sc)
567 {
568 if ((thflags & TH_SYN) &&
569 (sc->sc_flags & SCF_ECN_MASK)) {
570 switch (sc->sc_flags & SCF_ECN_MASK) {
571 case SCF_ECN:
572 thflags |= (0 | 0 | TH_ECE);
573 TCPSTAT_INC(tcps_ecn_shs);
574 break;
575 case SCF_ACE_N:
576 thflags |= (0 | TH_CWR | 0);
577 TCPSTAT_INC(tcps_ecn_shs);
578 TCPSTAT_INC(tcps_ace_nect);
579 break;
580 case SCF_ACE_0:
581 thflags |= (TH_AE | 0 | 0);
582 TCPSTAT_INC(tcps_ecn_shs);
583 TCPSTAT_INC(tcps_ace_ect0);
584 break;
585 case SCF_ACE_1:
586 thflags |= (0 | TH_ECE | TH_CWR);
587 TCPSTAT_INC(tcps_ecn_shs);
588 TCPSTAT_INC(tcps_ace_ect1);
589 break;
590 case SCF_ACE_CE:
591 thflags |= (TH_AE | TH_CWR | 0);
592 TCPSTAT_INC(tcps_ecn_shs);
593 TCPSTAT_INC(tcps_ace_ce);
594 break;
595 }
596 }
597 return thflags;
598 }
599
600 static inline int
tcp_ecn_get_ace(uint16_t thflags)601 tcp_ecn_get_ace(uint16_t thflags)
602 {
603 return ((thflags & (TH_AE|TH_CWR|TH_ECE)) >> TH_ACE_SHIFT);
604 }
605
606 static inline void
tcp_ecn_set_ace(uint16_t * thflags,uint32_t t_rcep)607 tcp_ecn_set_ace(uint16_t *thflags, uint32_t t_rcep)
608 {
609 *thflags &= ~(TH_AE|TH_CWR|TH_ECE);
610 *thflags |= ((t_rcep << TH_ACE_SHIFT) & (TH_AE|TH_CWR|TH_ECE));
611 }
612