The Tcpdump Group git mirrors - tcpdump/blob - print-tcp.c

   1 /*
   2  * Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that: (1) source code distributions
   7  * retain the above copyright notice and this paragraph in its entirety, (2)
   8  * distributions including binary code include the above copyright notice and
   9  * this paragraph in its entirety in the documentation or other materials
  10  * provided with the distribution, and (3) all advertising materials mentioning
  11  * features or use of this software display the following acknowledgement:
  12  * ``This product includes software developed by the University of California,
  13  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  14  * the University nor the names of its contributors may be used to endorse
  15  * or promote products derived from this software without specific prior
  16  * written permission.
  17  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  18  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  20  */
  21
  22 #ifndef lint
  23 static const char rcsid[] _U_ =
  24     "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.107.2.5 2004-07-28 20:11:31 guy Exp $ (LBL)";
  25 #endif
  26
  27 #ifdef HAVE_CONFIG_H
  28 #include "config.h"
  29 #endif
  30
  31 #include <tcpdump-stdinc.h>
  32
  33 #include <rpc/rpc.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38
  39 #include "interface.h"
  40 #include "addrtoname.h"
  41 #include "extract.h"
  42
  43 #include "tcp.h"
  44
  45 #include "ip.h"
  46 #ifdef INET6
  47 #include "ip6.h"
  48 #endif
  49 #include "ipproto.h"
  50
  51 #include "nameser.h"
  52
  53 static void print_tcp_rst_data(register const u_char *sp, u_int length);
  54
  55 #define MAX_RST_DATA_LEN        30
  56
  57
  58 struct tha {
  59 #ifndef INET6
  60         struct in_addr src;
  61         struct in_addr dst;
  62 #else
  63         struct in6_addr src;
  64         struct in6_addr dst;
  65 #endif /*INET6*/
  66         u_int port;
  67 };
  68
  69 struct tcp_seq_hash {
  70         struct tcp_seq_hash *nxt;
  71         struct tha addr;
  72         tcp_seq seq;
  73         tcp_seq ack;
  74 };
  75
  76 #define TSEQ_HASHSIZE 919
  77
  78 /* These tcp optinos do not have the size octet */
  79 #define ZEROLENOPT(o) ((o) == TCPOPT_EOL || (o) == TCPOPT_NOP)
  80
  81 static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];
  82
  83
  84 #ifndef TELNET_PORT
  85 #define TELNET_PORT     23
  86 #endif
  87 #ifndef BGP_PORT
  88 #define BGP_PORT        179
  89 #endif
  90 #define NETBIOS_SSN_PORT 139
  91 #ifndef PPTP_PORT
  92 #define PPTP_PORT       1723
  93 #endif
  94 #define BEEP_PORT        10288
  95 #ifndef NFS_PORT
  96 #define NFS_PORT        2049
  97 #endif
  98 #define MSDP_PORT       639
  99 #define LDP_PORT        646
 100
 101 static int tcp_cksum(register const struct ip *ip,
 102                      register const struct tcphdr *tp,
 103                      register u_int len)
 104 {
 105         union phu {
 106                 struct phdr {
 107                         u_int32_t src;
 108                         u_int32_t dst;
 109                         u_char mbz;
 110                         u_char proto;
 111                         u_int16_t len;
 112                 } ph;
 113                 u_int16_t pa[6];
 114         } phu;
 115         const u_int16_t *sp;
 116
 117         /* pseudo-header.. */
 118         phu.ph.len = htons((u_int16_t)len);
 119         phu.ph.mbz = 0;
 120         phu.ph.proto = IPPROTO_TCP;
 121         memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
 122         if (IP_HL(ip) == 5)
 123                 memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
 124         else
 125                 phu.ph.dst = ip_finddst(ip);
 126
 127         sp = &phu.pa[0];
 128         return in_cksum((u_short *)tp, len,
 129                         sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
 130 }
 131
 132 #ifdef INET6
 133 static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
 134         u_int len)
 135 {
 136         size_t i;
 137         register const u_int16_t *sp;
 138         u_int32_t sum;
 139         union {
 140                 struct {
 141                         struct in6_addr ph_src;
 142                         struct in6_addr ph_dst;
 143                         u_int32_t       ph_len;
 144                         u_int8_t        ph_zero[3];
 145                         u_int8_t        ph_nxt;
 146                 } ph;
 147                 u_int16_t pa[20];
 148         } phu;
 149
 150         /* pseudo-header */
 151         memset(&phu, 0, sizeof(phu));
 152         phu.ph.ph_src = ip6->ip6_src;
 153         phu.ph.ph_dst = ip6->ip6_dst;
 154         phu.ph.ph_len = htonl(len);
 155         phu.ph.ph_nxt = IPPROTO_TCP;
 156
 157         sum = 0;
 158         for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
 159                 sum += phu.pa[i];
 160
 161         sp = (const u_int16_t *)tp;
 162
 163         for (i = 0; i < (len & ~1); i += 2)
 164                 sum += *sp++;
 165
 166         if (len & 1)
 167                 sum += htons((*(const u_int8_t *)sp) << 8);
 168
 169         while (sum > 0xffff)
 170                 sum = (sum & 0xffff) + (sum >> 16);
 171         sum = ~sum & 0xffff;
 172
 173         return (sum);
 174 }
 175 #endif
 176
 177 void
 178 tcp_print(register const u_char *bp, register u_int length,
 179           register const u_char *bp2, int fragmented)
 180 {
 181         register const struct tcphdr *tp;
 182         register const struct ip *ip;
 183         register u_char flags;
 184         register u_int hlen;
 185         register char ch;
 186         u_int16_t sport, dport, win, urp;
 187         u_int32_t seq, ack, thseq, thack;
 188         int threv;
 189 #ifdef INET6
 190         register const struct ip6_hdr *ip6;
 191 #endif
 192
 193         tp = (struct tcphdr *)bp;
 194         ip = (struct ip *)bp2;
 195 #ifdef INET6
 196         if (IP_V(ip) == 6)
 197                 ip6 = (struct ip6_hdr *)bp2;
 198         else
 199                 ip6 = NULL;
 200 #endif /*INET6*/
 201         ch = '\0';
 202         if (!TTEST(tp->th_dport)) {
 203                 (void)printf("%s > %s: [|tcp]",
 204                         ipaddr_string(&ip->ip_src),
 205                         ipaddr_string(&ip->ip_dst));
 206                 return;
 207         }
 208
 209         sport = EXTRACT_16BITS(&tp->th_sport);
 210         dport = EXTRACT_16BITS(&tp->th_dport);
 211
 212         hlen = TH_OFF(tp) * 4;
 213
 214         /*
 215          * If data present, header length valid, and NFS port used,
 216          * assume NFS.
 217          * Pass offset of data plus 4 bytes for RPC TCP msg length
 218          * to NFS print routines.
 219          */
 220         if (!qflag && hlen >= sizeof(*tp) && hlen <= length) {
 221                 if ((u_char *)tp + 4 + sizeof(struct rpc_msg) <= snapend &&
 222                     dport == NFS_PORT) {
 223                         nfsreq_print((u_char *)tp + hlen + 4, length - hlen,
 224                                      (u_char *)ip);
 225                         return;
 226                 } else if ((u_char *)tp + 4 + sizeof(struct rpc_msg)
 227                            <= snapend &&
 228                            sport == NFS_PORT) {
 229                         nfsreply_print((u_char *)tp + hlen + 4, length - hlen,
 230                                        (u_char *)ip);
 231                         return;
 232                 }
 233         }
 234 #ifdef INET6
 235         if (ip6) {
 236                 if (ip6->ip6_nxt == IPPROTO_TCP) {
 237                         (void)printf("%s.%s > %s.%s: ",
 238                                 ip6addr_string(&ip6->ip6_src),
 239                                 tcpport_string(sport),
 240                                 ip6addr_string(&ip6->ip6_dst),
 241                                 tcpport_string(dport));
 242                 } else {
 243                         (void)printf("%s > %s: ",
 244                                 tcpport_string(sport), tcpport_string(dport));
 245                 }
 246         } else
 247 #endif /*INET6*/
 248         {
 249                 if (ip->ip_p == IPPROTO_TCP) {
 250                         (void)printf("%s.%s > %s.%s: ",
 251                                 ipaddr_string(&ip->ip_src),
 252                                 tcpport_string(sport),
 253                                 ipaddr_string(&ip->ip_dst),
 254                                 tcpport_string(dport));
 255                 } else {
 256                         (void)printf("%s > %s: ",
 257                                 tcpport_string(sport), tcpport_string(dport));
 258                 }
 259         }
 260
 261         if (hlen < sizeof(*tp)) {
 262                 (void)printf(" tcp %d [bad hdr length %u - too short, < %lu]",
 263                     length - hlen, hlen, (unsigned long)sizeof(*tp));
 264                 return;
 265         }
 266
 267         TCHECK(*tp);
 268
 269         seq = EXTRACT_32BITS(&tp->th_seq);
 270         ack = EXTRACT_32BITS(&tp->th_ack);
 271         win = EXTRACT_16BITS(&tp->th_win);
 272         urp = EXTRACT_16BITS(&tp->th_urp);
 273
 274         if (qflag) {
 275                 (void)printf("tcp %d", length - hlen);
 276                 if (hlen > length) {
 277                         (void)printf(" [bad hdr length %u - too long, > %u]",
 278                             hlen, length);
 279                 }
 280                 return;
 281         }
 282         if ((flags = tp->th_flags) & (TH_SYN|TH_FIN|TH_RST|TH_PUSH|
 283                                       TH_ECNECHO|TH_CWR)) {
 284                 if (flags & TH_SYN)
 285                         putchar('S');
 286                 if (flags & TH_FIN)
 287                         putchar('F');
 288                 if (flags & TH_RST)
 289                         putchar('R');
 290                 if (flags & TH_PUSH)
 291                         putchar('P');
 292                 if (flags & TH_CWR)
 293                         putchar('W');   /* congestion _W_indow reduced (ECN) */
 294                 if (flags & TH_ECNECHO)
 295                         putchar('E');   /* ecn _E_cho sent (ECN) */
 296         } else
 297                 putchar('.');
 298
 299         if (!Sflag && (flags & TH_ACK)) {
 300                 register struct tcp_seq_hash *th;
 301                 const void *src, *dst;
 302                 register int rev;
 303                 struct tha tha;
 304                 /*
 305                  * Find (or record) the initial sequence numbers for
 306                  * this conversation.  (we pick an arbitrary
 307                  * collating order so there's only one entry for
 308                  * both directions).
 309                  */
 310 #ifdef INET6
 311                 memset(&tha, 0, sizeof(tha));
 312                 rev = 0;
 313                 if (ip6) {
 314                         src = &ip6->ip6_src;
 315                         dst = &ip6->ip6_dst;
 316                         if (sport > dport)
 317                                 rev = 1;
 318                         else if (sport == dport) {
 319                                 if (memcmp(src, dst, sizeof ip6->ip6_dst) > 0)
 320                                         rev = 1;
 321                         }
 322                         if (rev) {
 323                                 memcpy(&tha.src, dst, sizeof ip6->ip6_dst);
 324                                 memcpy(&tha.dst, src, sizeof ip6->ip6_src);
 325                                 tha.port = dport << 16 | sport;
 326                         } else {
 327                                 memcpy(&tha.dst, dst, sizeof ip6->ip6_dst);
 328                                 memcpy(&tha.src, src, sizeof ip6->ip6_src);
 329                                 tha.port = sport << 16 | dport;
 330                         }
 331                 } else {
 332                         src = &ip->ip_src;
 333                         dst = &ip->ip_dst;
 334                         if (sport > dport)
 335                                 rev = 1;
 336                         else if (sport == dport) {
 337                                 if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 338                                         rev = 1;
 339                         }
 340                         if (rev) {
 341                                 memcpy(&tha.src, dst, sizeof ip->ip_dst);
 342                                 memcpy(&tha.dst, src, sizeof ip->ip_src);
 343                                 tha.port = dport << 16 | sport;
 344                         } else {
 345                                 memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 346                                 memcpy(&tha.src, src, sizeof ip->ip_src);
 347                                 tha.port = sport << 16 | dport;
 348                         }
 349                 }
 350 #else
 351                 rev = 0;
 352                 src = &ip->ip_src;
 353                 dst = &ip->ip_dst;
 354                 if (sport > dport)
 355                         rev = 1;
 356                 else if (sport == dport) {
 357                         if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 358                                 rev = 1;
 359                 }
 360                 if (rev) {
 361                         memcpy(&tha.src, dst, sizeof ip->ip_dst);
 362                         memcpy(&tha.dst, src, sizeof ip->ip_src);
 363                         tha.port = dport << 16 | sport;
 364                 } else {
 365                         memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 366                         memcpy(&tha.src, src, sizeof ip->ip_src);
 367                         tha.port = sport << 16 | dport;
 368                 }
 369 #endif
 370
 371                 threv = rev;
 372                 for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
 373                      th->nxt; th = th->nxt)
 374                         if (memcmp((char *)&tha, (char *)&th->addr,
 375                                   sizeof(th->addr)) == 0)
 376                                 break;
 377
 378                 if (!th->nxt || (flags & TH_SYN)) {
 379                         /* didn't find it or new conversation */
 380                         if (th->nxt == NULL) {
 381                                 th->nxt = (struct tcp_seq_hash *)
 382                                         calloc(1, sizeof(*th));
 383                                 if (th->nxt == NULL)
 384                                         error("tcp_print: calloc");
 385                         }
 386                         th->addr = tha;
 387                         if (rev)
 388                                 th->ack = seq, th->seq = ack - 1;
 389                         else
 390                                 th->seq = seq, th->ack = ack - 1;
 391                 } else {
 392                         if (rev)
 393                                 seq -= th->ack, ack -= th->seq;
 394                         else
 395                                 seq -= th->seq, ack -= th->ack;
 396                 }
 397
 398                 thseq = th->seq;
 399                 thack = th->ack;
 400         } else {
 401                 /*fool gcc*/
 402                 thseq = thack = threv = 0;
 403         }
 404         if (hlen > length) {
 405                 (void)printf(" [bad hdr length %u - too long, > %u]",
 406                     hlen, length);
 407                 return;
 408         }
 409
 410         if (IP_V(ip) == 4 && vflag && !fragmented) {
 411                 u_int16_t sum, tcp_sum;
 412                 if (TTEST2(tp->th_sport, length)) {
 413                         sum = tcp_cksum(ip, tp, length);
 414                         if (sum != 0) {
 415                                 tcp_sum = EXTRACT_16BITS(&tp->th_sum);
 416                                 (void)printf(" [bad tcp cksum %x (->%x)!]",
 417                                     tcp_sum, in_cksum_shouldbe(tcp_sum, sum));
 418                         } else
 419                                 (void)printf(" [tcp sum ok]");
 420                 }
 421         }
 422 #ifdef INET6
 423         if (IP_V(ip) == 6 && ip6->ip6_plen && vflag && !fragmented) {
 424                 int sum;
 425                 if (TTEST2(tp->th_sport, length)) {
 426                         sum = tcp6_cksum(ip6, tp, length);
 427                         if (sum != 0)
 428                                 (void)printf(" [bad tcp cksum %x!]", sum);
 429                         else
 430                                 (void)printf(" [tcp sum ok]");
 431                 }
 432         }
 433 #endif
 434
 435         length -= hlen;
 436         if (vflag > 1 || length > 0 || flags & (TH_SYN | TH_FIN | TH_RST))
 437                 (void)printf(" %u:%u(%u)", seq, seq + length, length);
 438         if (flags & TH_ACK)
 439                 (void)printf(" ack %u", ack);
 440
 441         (void)printf(" win %d", win);
 442
 443         if (flags & TH_URG)
 444                 (void)printf(" urg %d", urp);
 445         /*
 446          * Handle any options.
 447          */
 448         if (hlen > sizeof(*tp)) {
 449                 register const u_char *cp;
 450                 register u_int i, opt, datalen;
 451                 register u_int len;
 452
 453                 hlen -= sizeof(*tp);
 454                 cp = (const u_char *)tp + sizeof(*tp);
 455                 putchar(' ');
 456                 ch = '<';
 457                 while (hlen > 0) {
 458                         putchar(ch);
 459                         TCHECK(*cp);
 460                         opt = *cp++;
 461                         if (ZEROLENOPT(opt))
 462                                 len = 1;
 463                         else {
 464                                 TCHECK(*cp);
 465                                 len = *cp++;    /* total including type, len */
 466                                 if (len < 2 || len > hlen)
 467                                         goto bad;
 468                                 --hlen;         /* account for length byte */
 469                         }
 470                         --hlen;                 /* account for type byte */
 471                         datalen = 0;
 472
 473 /* Bail if "l" bytes of data are not left or were not captured  */
 474 #define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }
 475
 476                         switch (opt) {
 477
 478                         case TCPOPT_MAXSEG:
 479                                 (void)printf("mss");
 480                                 datalen = 2;
 481                                 LENCHECK(datalen);
 482                                 (void)printf(" %u", EXTRACT_16BITS(cp));
 483
 484                                 break;
 485
 486                         case TCPOPT_EOL:
 487                                 (void)printf("eol");
 488                                 break;
 489
 490                         case TCPOPT_NOP:
 491                                 (void)printf("nop");
 492                                 break;
 493
 494                         case TCPOPT_WSCALE:
 495                                 (void)printf("wscale");
 496                                 datalen = 1;
 497                                 LENCHECK(datalen);
 498                                 (void)printf(" %u", *cp);
 499                                 break;
 500
 501                         case TCPOPT_SACKOK:
 502                                 (void)printf("sackOK");
 503                                 break;
 504
 505                         case TCPOPT_SACK:
 506                                 (void)printf("sack");
 507                                 datalen = len - 2;
 508                                 if (datalen % 8 != 0) {
 509                                         (void)printf(" malformed sack ");
 510                                 } else {
 511                                         u_int32_t s, e;
 512
 513                                         (void)printf(" sack %d ", datalen / 8);
 514                                         for (i = 0; i < datalen; i += 8) {
 515                                                 LENCHECK(i + 4);
 516                                                 s = EXTRACT_32BITS(cp + i);
 517                                                 LENCHECK(i + 8);
 518                                                 e = EXTRACT_32BITS(cp + i + 4);
 519                                                 if (threv) {
 520                                                         s -= thseq;
 521                                                         e -= thseq;
 522                                                 } else {
 523                                                         s -= thack;
 524                                                         e -= thack;
 525                                                 }
 526                                                 (void)printf("{%u:%u}", s, e);
 527                                         }
 528                                         (void)printf(" ");
 529                                 }
 530                                 break;
 531
 532                         case TCPOPT_ECHO:
 533                                 (void)printf("echo");
 534                                 datalen = 4;
 535                                 LENCHECK(datalen);
 536                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 537                                 break;
 538
 539                         case TCPOPT_ECHOREPLY:
 540                                 (void)printf("echoreply");
 541                                 datalen = 4;
 542                                 LENCHECK(datalen);
 543                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 544                                 break;
 545
 546                         case TCPOPT_TIMESTAMP:
 547                                 (void)printf("timestamp");
 548                                 datalen = 8;
 549                                 LENCHECK(4);
 550                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 551                                 LENCHECK(datalen);
 552                                 (void)printf(" %u", EXTRACT_32BITS(cp + 4));
 553                                 break;
 554
 555                         case TCPOPT_CC:
 556                                 (void)printf("cc");
 557                                 datalen = 4;
 558                                 LENCHECK(datalen);
 559                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 560                                 break;
 561
 562                         case TCPOPT_CCNEW:
 563                                 (void)printf("ccnew");
 564                                 datalen = 4;
 565                                 LENCHECK(datalen);
 566                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 567                                 break;
 568
 569                         case TCPOPT_CCECHO:
 570                                 (void)printf("ccecho");
 571                                 datalen = 4;
 572                                 LENCHECK(datalen);
 573                                 (void)printf(" %u", EXTRACT_32BITS(cp));
 574                                 break;
 575
 576                         default:
 577                                 (void)printf("opt-%u:", opt);
 578                                 datalen = len - 2;
 579                                 for (i = 0; i < datalen; ++i) {
 580                                         LENCHECK(i);
 581                                         (void)printf("%02x", cp[i]);
 582                                 }
 583                                 break;
 584                         }
 585
 586                         /* Account for data printed */
 587                         cp += datalen;
 588                         hlen -= datalen;
 589
 590                         /* Check specification against observed length */
 591                         ++datalen;                      /* option octet */
 592                         if (!ZEROLENOPT(opt))
 593                                 ++datalen;              /* size octet */
 594                         if (datalen != len)
 595                                 (void)printf("[len %d]", len);
 596                         ch = ',';
 597                         if (opt == TCPOPT_EOL)
 598                                 break;
 599                 }
 600                 putchar('>');
 601         }
 602
 603         if (length <= 0)
 604                 return;
 605
 606         /*
 607          * Decode payload if necessary.
 608          */
 609         bp += TH_OFF(tp) * 4;
 610         if (flags & TH_RST) {
 611                 if (vflag)
 612                         print_tcp_rst_data(bp, length);
 613         } else {
 614                 if (sport == TELNET_PORT || dport == TELNET_PORT) {
 615                         if (!qflag && vflag)
 616                                 telnet_print(bp, length);
 617                 } else if (sport == BGP_PORT || dport == BGP_PORT)
 618                         bgp_print(bp, length);
 619                 else if (sport == PPTP_PORT || dport == PPTP_PORT)
 620                         pptp_print(bp);
 621 #ifdef TCPDUMP_DO_SMB
 622                 else if (sport == NETBIOS_SSN_PORT || dport == NETBIOS_SSN_PORT)
 623                         nbt_tcp_print(bp, length);
 624 #endif
 625                 else if (sport == BEEP_PORT || dport == BEEP_PORT)
 626                         beep_print(bp, length);
 627                 else if (length > 2 &&
 628                     (sport == NAMESERVER_PORT || dport == NAMESERVER_PORT ||
 629                      sport == MULTICASTDNS_PORT || dport == MULTICASTDNS_PORT)) {
 630                         /*
 631                          * TCP DNS query has 2byte length at the head.
 632                          * XXX packet could be unaligned, it can go strange
 633                          */
 634                         ns_print(bp + 2, length - 2, 0);
 635                 } else if (sport == MSDP_PORT || dport == MSDP_PORT) {
 636                         msdp_print(bp, length);
 637                 }
 638                 else if (sport == LDP_PORT || dport == LDP_PORT)
 639                         printf(": LDP, length: %u", length);
 640         }
 641         return;
 642 bad:
 643         fputs("[bad opt]", stdout);
 644         if (ch != '\0')
 645                 putchar('>');
 646         return;
 647 trunc:
 648         fputs("[|tcp]", stdout);
 649         if (ch != '\0')
 650                 putchar('>');
 651 }
 652
 653 /*
 654  * RFC1122 says the following on data in RST segments:
 655  *
 656  *         4.2.2.12  RST Segment: RFC-793 Section 3.4
 657  *
 658  *            A TCP SHOULD allow a received RST segment to include data.
 659  *
 660  *            DISCUSSION
 661  *                 It has been suggested that a RST segment could contain
 662  *                 ASCII text that encoded and explained the cause of the
 663  *                 RST.  No standard has yet been established for such
 664  *                 data.
 665  *
 666  */
 667
 668 static void
 669 print_tcp_rst_data(register const u_char *sp, u_int length)
 670 {
 671         int c;
 672
 673         if (TTEST2(*sp, length))
 674                 printf(" [RST");
 675         else
 676                 printf(" [!RST");
 677         if (length > MAX_RST_DATA_LEN) {
 678                 length = MAX_RST_DATA_LEN;      /* can use -X for longer */
 679                 putchar('+');                   /* indicate we truncate */
 680         }
 681         putchar(' ');
 682         while (length-- && sp <= snapend) {
 683                 c = *sp++;
 684                 safeputchar(c);
 685         }
 686         putchar(']');
 687 }