1 /* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21 #include <linux/module.h> 22 #include <linux/gfp.h> 23 #include <net/tcp.h> 24 25 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; 26 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 27 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 28 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 29 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 30 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 31 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 32 int sysctl_tcp_orphan_retries __read_mostly; 33 int sysctl_tcp_thin_linear_timeouts __read_mostly; 34 35 static void tcp_write_timer(unsigned long); 36 static void tcp_delack_timer(unsigned long); 37 static void tcp_keepalive_timer (unsigned long data); 38 39 void tcp_init_xmit_timers(struct sock *sk) 40 { 41 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 42 &tcp_keepalive_timer); 43 } 44 EXPORT_SYMBOL(tcp_init_xmit_timers); 45 46 static void tcp_write_err(struct sock *sk) 47 { 48 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 49 sk->sk_error_report(sk); 50 51 tcp_done(sk); 52 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 53 } 54 55 /* Do not allow orphaned sockets to eat all our resources. 56 * This is direct violation of TCP specs, but it is required 57 * to prevent DoS attacks. It is called when a retransmission timeout 58 * or zero probe timeout occurs on orphaned socket. 59 * 60 * Criteria is still not confirmed experimentally and may change. 61 * We kill the socket, if: 62 * 1. If number of orphaned sockets exceeds an administratively configured 63 * limit. 64 * 2. If we have strong memory pressure. 65 */ 66 static int tcp_out_of_resources(struct sock *sk, int do_reset) 67 { 68 struct tcp_sock *tp = tcp_sk(sk); 69 int shift = 0; 70 71 /* If peer does not open window for long time, or did not transmit 72 * anything for long time, penalize it. */ 73 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 74 shift++; 75 76 /* If some dubious ICMP arrived, penalize even more. */ 77 if (sk->sk_err_soft) 78 shift++; 79 80 if (tcp_too_many_orphans(sk, shift)) { 81 if (net_ratelimit()) 82 printk(KERN_INFO "Out of socket memory\n"); 83 84 /* Catch exceptional cases, when connection requires reset. 85 * 1. Last segment was sent recently. */ 86 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 87 /* 2. Window is closed. */ 88 (!tp->snd_wnd && !tp->packets_out)) 89 do_reset = 1; 90 if (do_reset) 91 tcp_send_active_reset(sk, GFP_ATOMIC); 92 tcp_done(sk); 93 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 94 return 1; 95 } 96 return 0; 97 } 98 99 /* Calculate maximal number or retries on an orphaned socket. */ 100 static int tcp_orphan_retries(struct sock *sk, int alive) 101 { 102 int retries = sysctl_tcp_orphan_retries; /* May be zero. */ 103 104 /* We know from an ICMP that something is wrong. */ 105 if (sk->sk_err_soft && !alive) 106 retries = 0; 107 108 /* However, if socket sent something recently, select some safe 109 * number of retries. 8 corresponds to >100 seconds with minimal 110 * RTO of 200msec. */ 111 if (retries == 0 && alive) 112 retries = 8; 113 return retries; 114 } 115 116 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 117 { 118 /* Black hole detection */ 119 if (sysctl_tcp_mtu_probing) { 120 if (!icsk->icsk_mtup.enabled) { 121 icsk->icsk_mtup.enabled = 1; 122 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 123 } else { 124 struct tcp_sock *tp = tcp_sk(sk); 125 int mss; 126 127 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 128 mss = min(sysctl_tcp_base_mss, mss); 129 mss = max(mss, 68 - tp->tcp_header_len); 130 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 131 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 132 } 133 } 134 } 135 136 /* This function calculates a "timeout" which is equivalent to the timeout of a 137 * TCP connection after "boundary" unsuccessful, exponentially backed-off 138 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if 139 * syn_set flag is set. 140 */ 141 static bool retransmits_timed_out(struct sock *sk, 142 unsigned int boundary, 143 unsigned int timeout, 144 bool syn_set) 145 { 146 unsigned int linear_backoff_thresh, start_ts; 147 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 148 149 if (!inet_csk(sk)->icsk_retransmits) 150 return false; 151 152 if (unlikely(!tcp_sk(sk)->retrans_stamp)) 153 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when; 154 else 155 start_ts = tcp_sk(sk)->retrans_stamp; 156 157 if (likely(timeout == 0)) { 158 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 159 160 if (boundary <= linear_backoff_thresh) 161 timeout = ((2 << boundary) - 1) * rto_base; 162 else 163 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 164 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 165 } 166 return (tcp_time_stamp - start_ts) >= timeout; 167 } 168 169 /* A write timeout has occurred. Process the after effects. */ 170 static int tcp_write_timeout(struct sock *sk) 171 { 172 struct inet_connection_sock *icsk = inet_csk(sk); 173 int retry_until; 174 bool do_reset, syn_set = 0; 175 176 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 177 if (icsk->icsk_retransmits) 178 dst_negative_advice(sk); 179 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 180 syn_set = 1; 181 } else { 182 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { 183 /* Black hole detection */ 184 tcp_mtu_probing(icsk, sk); 185 186 dst_negative_advice(sk); 187 } 188 189 retry_until = sysctl_tcp_retries2; 190 if (sock_flag(sk, SOCK_DEAD)) { 191 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 192 193 retry_until = tcp_orphan_retries(sk, alive); 194 do_reset = alive || 195 !retransmits_timed_out(sk, retry_until, 0, 0); 196 197 if (tcp_out_of_resources(sk, do_reset)) 198 return 1; 199 } 200 } 201 202 if (retransmits_timed_out(sk, retry_until, 203 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 204 /* Has it gone just too far? */ 205 tcp_write_err(sk); 206 return 1; 207 } 208 return 0; 209 } 210 211 static void tcp_delack_timer(unsigned long data) 212 { 213 struct sock *sk = (struct sock *)data; 214 struct tcp_sock *tp = tcp_sk(sk); 215 struct inet_connection_sock *icsk = inet_csk(sk); 216 217 bh_lock_sock(sk); 218 if (sock_owned_by_user(sk)) { 219 /* Try again later. */ 220 icsk->icsk_ack.blocked = 1; 221 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 222 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); 223 goto out_unlock; 224 } 225 226 sk_mem_reclaim_partial(sk); 227 228 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 229 goto out; 230 231 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 232 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 233 goto out; 234 } 235 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 236 237 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 238 struct sk_buff *skb; 239 240 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 241 242 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 243 sk_backlog_rcv(sk, skb); 244 245 tp->ucopy.memory = 0; 246 } 247 248 if (inet_csk_ack_scheduled(sk)) { 249 if (!icsk->icsk_ack.pingpong) { 250 /* Delayed ACK missed: inflate ATO. */ 251 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 252 } else { 253 /* Delayed ACK missed: leave pingpong mode and 254 * deflate ATO. 255 */ 256 icsk->icsk_ack.pingpong = 0; 257 icsk->icsk_ack.ato = TCP_ATO_MIN; 258 } 259 tcp_send_ack(sk); 260 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 261 } 262 263 out: 264 if (tcp_memory_pressure) 265 sk_mem_reclaim(sk); 266 out_unlock: 267 bh_unlock_sock(sk); 268 sock_put(sk); 269 } 270 271 static void tcp_probe_timer(struct sock *sk) 272 { 273 struct inet_connection_sock *icsk = inet_csk(sk); 274 struct tcp_sock *tp = tcp_sk(sk); 275 int max_probes; 276 277 if (tp->packets_out || !tcp_send_head(sk)) { 278 icsk->icsk_probes_out = 0; 279 return; 280 } 281 282 /* *WARNING* RFC 1122 forbids this 283 * 284 * It doesn't AFAIK, because we kill the retransmit timer -AK 285 * 286 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 287 * this behaviour in Solaris down as a bug fix. [AC] 288 * 289 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 290 * even if they advertise zero window. Hence, connection is killed only 291 * if we received no ACKs for normal connection timeout. It is not killed 292 * only because window stays zero for some time, window may be zero 293 * until armageddon and even later. We are in full accordance 294 * with RFCs, only probe timer combines both retransmission timeout 295 * and probe timeout in one bottle. --ANK 296 */ 297 max_probes = sysctl_tcp_retries2; 298 299 if (sock_flag(sk, SOCK_DEAD)) { 300 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 301 302 max_probes = tcp_orphan_retries(sk, alive); 303 304 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 305 return; 306 } 307 308 if (icsk->icsk_probes_out > max_probes) { 309 tcp_write_err(sk); 310 } else { 311 /* Only send another probe if we didn't close things up. */ 312 tcp_send_probe0(sk); 313 } 314 } 315 316 /* 317 * The TCP retransmit timer. 318 */ 319 320 void tcp_retransmit_timer(struct sock *sk) 321 { 322 struct tcp_sock *tp = tcp_sk(sk); 323 struct inet_connection_sock *icsk = inet_csk(sk); 324 325 if (!tp->packets_out) 326 goto out; 327 328 WARN_ON(tcp_write_queue_empty(sk)); 329 330 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 331 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 332 /* Receiver dastardly shrinks window. Our retransmits 333 * become zero probes, but we should not timeout this 334 * connection. If the socket is an orphan, time it out, 335 * we cannot allow such beasts to hang infinitely. 336 */ 337 #ifdef TCP_DEBUG 338 struct inet_sock *inet = inet_sk(sk); 339 if (sk->sk_family == AF_INET) { 340 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 341 &inet->inet_daddr, ntohs(inet->inet_dport), 342 inet->inet_num, tp->snd_una, tp->snd_nxt); 343 } 344 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) 345 else if (sk->sk_family == AF_INET6) { 346 struct ipv6_pinfo *np = inet6_sk(sk); 347 LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 348 &np->daddr, ntohs(inet->inet_dport), 349 inet->inet_num, tp->snd_una, tp->snd_nxt); 350 } 351 #endif 352 #endif 353 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 354 tcp_write_err(sk); 355 goto out; 356 } 357 tcp_enter_loss(sk, 0); 358 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 359 __sk_dst_reset(sk); 360 goto out_reset_timer; 361 } 362 363 if (tcp_write_timeout(sk)) 364 goto out; 365 366 if (icsk->icsk_retransmits == 0) { 367 int mib_idx; 368 369 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 370 if (tcp_is_sack(tp)) 371 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 372 else 373 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 374 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 375 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 376 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 377 tp->sacked_out) { 378 if (tcp_is_sack(tp)) 379 mib_idx = LINUX_MIB_TCPSACKFAILURES; 380 else 381 mib_idx = LINUX_MIB_TCPRENOFAILURES; 382 } else { 383 mib_idx = LINUX_MIB_TCPTIMEOUTS; 384 } 385 NET_INC_STATS_BH(sock_net(sk), mib_idx); 386 } 387 388 if (tcp_use_frto(sk)) { 389 tcp_enter_frto(sk); 390 } else { 391 tcp_enter_loss(sk, 0); 392 } 393 394 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 395 /* Retransmission failed because of local congestion, 396 * do not backoff. 397 */ 398 if (!icsk->icsk_retransmits) 399 icsk->icsk_retransmits = 1; 400 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 401 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 402 TCP_RTO_MAX); 403 goto out; 404 } 405 406 /* Increase the timeout each time we retransmit. Note that 407 * we do not increase the rtt estimate. rto is initialized 408 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 409 * that doubling rto each time is the least we can get away with. 410 * In KA9Q, Karn uses this for the first few times, and then 411 * goes to quadratic. netBSD doubles, but only goes up to *64, 412 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 413 * defined in the protocol as the maximum possible RTT. I guess 414 * we'll have to use something other than TCP to talk to the 415 * University of Mars. 416 * 417 * PAWS allows us longer timeouts and large windows, so once 418 * implemented ftp to mars will work nicely. We will have to fix 419 * the 120 second clamps though! 420 */ 421 icsk->icsk_backoff++; 422 icsk->icsk_retransmits++; 423 424 out_reset_timer: 425 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 426 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 427 * might be increased if the stream oscillates between thin and thick, 428 * thus the old value might already be too high compared to the value 429 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 430 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 431 * exponential backoff behaviour to avoid continue hammering 432 * linear-timeout retransmissions into a black hole 433 */ 434 if (sk->sk_state == TCP_ESTABLISHED && 435 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 436 tcp_stream_is_thin(tp) && 437 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 438 icsk->icsk_backoff = 0; 439 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 440 } else { 441 /* Use normal (exponential) backoff */ 442 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 443 } 444 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 445 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0)) 446 __sk_dst_reset(sk); 447 448 out:; 449 } 450 451 static void tcp_write_timer(unsigned long data) 452 { 453 struct sock *sk = (struct sock *)data; 454 struct inet_connection_sock *icsk = inet_csk(sk); 455 int event; 456 457 bh_lock_sock(sk); 458 if (sock_owned_by_user(sk)) { 459 /* Try again later */ 460 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); 461 goto out_unlock; 462 } 463 464 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 465 goto out; 466 467 if (time_after(icsk->icsk_timeout, jiffies)) { 468 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 469 goto out; 470 } 471 472 event = icsk->icsk_pending; 473 icsk->icsk_pending = 0; 474 475 switch (event) { 476 case ICSK_TIME_RETRANS: 477 tcp_retransmit_timer(sk); 478 break; 479 case ICSK_TIME_PROBE0: 480 tcp_probe_timer(sk); 481 break; 482 } 483 484 out: 485 sk_mem_reclaim(sk); 486 out_unlock: 487 bh_unlock_sock(sk); 488 sock_put(sk); 489 } 490 491 /* 492 * Timer for listening sockets 493 */ 494 495 static void tcp_synack_timer(struct sock *sk) 496 { 497 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 498 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 499 } 500 501 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req) 502 { 503 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS); 504 } 505 EXPORT_SYMBOL(tcp_syn_ack_timeout); 506 507 void tcp_set_keepalive(struct sock *sk, int val) 508 { 509 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 510 return; 511 512 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 513 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 514 else if (!val) 515 inet_csk_delete_keepalive_timer(sk); 516 } 517 518 519 static void tcp_keepalive_timer (unsigned long data) 520 { 521 struct sock *sk = (struct sock *) data; 522 struct inet_connection_sock *icsk = inet_csk(sk); 523 struct tcp_sock *tp = tcp_sk(sk); 524 u32 elapsed; 525 526 /* Only process if socket is not in use. */ 527 bh_lock_sock(sk); 528 if (sock_owned_by_user(sk)) { 529 /* Try again later. */ 530 inet_csk_reset_keepalive_timer (sk, HZ/20); 531 goto out; 532 } 533 534 if (sk->sk_state == TCP_LISTEN) { 535 tcp_synack_timer(sk); 536 goto out; 537 } 538 539 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 540 if (tp->linger2 >= 0) { 541 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 542 543 if (tmo > 0) { 544 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 545 goto out; 546 } 547 } 548 tcp_send_active_reset(sk, GFP_ATOMIC); 549 goto death; 550 } 551 552 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 553 goto out; 554 555 elapsed = keepalive_time_when(tp); 556 557 /* It is alive without keepalive 8) */ 558 if (tp->packets_out || tcp_send_head(sk)) 559 goto resched; 560 561 elapsed = keepalive_time_elapsed(tp); 562 563 if (elapsed >= keepalive_time_when(tp)) { 564 /* If the TCP_USER_TIMEOUT option is enabled, use that 565 * to determine when to timeout instead. 566 */ 567 if ((icsk->icsk_user_timeout != 0 && 568 elapsed >= icsk->icsk_user_timeout && 569 icsk->icsk_probes_out > 0) || 570 (icsk->icsk_user_timeout == 0 && 571 icsk->icsk_probes_out >= keepalive_probes(tp))) { 572 tcp_send_active_reset(sk, GFP_ATOMIC); 573 tcp_write_err(sk); 574 goto out; 575 } 576 if (tcp_write_wakeup(sk) <= 0) { 577 icsk->icsk_probes_out++; 578 elapsed = keepalive_intvl_when(tp); 579 } else { 580 /* If keepalive was lost due to local congestion, 581 * try harder. 582 */ 583 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 584 } 585 } else { 586 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 587 elapsed = keepalive_time_when(tp) - elapsed; 588 } 589 590 sk_mem_reclaim(sk); 591 592 resched: 593 inet_csk_reset_keepalive_timer (sk, elapsed); 594 goto out; 595 596 death: 597 tcp_done(sk); 598 599 out: 600 bh_unlock_sock(sk); 601 sock_put(sk); 602 } 603