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 * Copyright (c) 1999-2004 The tcpdump.org project
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that: (1) source code distributions
9 * retain the above copyright notice and this paragraph in its entirety, (2)
10 * distributions including binary code include the above copyright notice and
11 * this paragraph in its entirety in the documentation or other materials
12 * provided with the distribution, and (3) all advertising materials mentioning
13 * features or use of this software display the following acknowledgement:
14 * ``This product includes software developed by the University of California,
15 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
16 * the University nor the names of its contributors may be used to endorse
17 * or promote products derived from this software without specific prior
18 * written permission.
19 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
20 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
21 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
22 */
23
24#ifndef lint
25static const char rcsid[] _U_ =
26    "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.120.2.3 2005/10/16 06:05:46 guy Exp $ (LBL)";
27#endif
28
29#ifdef HAVE_CONFIG_H
30#include "config.h"
31#endif
32
33#include <tcpdump-stdinc.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#include "rpc_auth.h"
51#include "rpc_msg.h"
52
53#include "nameser.h"
54
55#ifdef HAVE_LIBCRYPTO
56#include <openssl/md5.h>
57
58#define SIGNATURE_VALID		0
59#define SIGNATURE_INVALID	1
60#define CANT_CHECK_SIGNATURE	2
61
62static int tcp_verify_signature(const struct ip *ip, const struct tcphdr *tp,
63    const u_char *data, int length, const u_char *rcvsig);
64#endif
65
66static void print_tcp_rst_data(register const u_char *sp, u_int length);
67
68#define MAX_RST_DATA_LEN	30
69
70
71struct tha {
72#ifndef INET6
73	struct in_addr src;
74	struct in_addr dst;
75#else
76	struct in6_addr src;
77	struct in6_addr dst;
78#endif /*INET6*/
79	u_int port;
80};
81
82struct tcp_seq_hash {
83	struct tcp_seq_hash *nxt;
84	struct tha addr;
85	tcp_seq seq;
86	tcp_seq ack;
87};
88
89#define TSEQ_HASHSIZE 919
90
91/* These tcp optinos do not have the size octet */
92#define ZEROLENOPT(o) ((o) == TCPOPT_EOL || (o) == TCPOPT_NOP)
93
94static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];
95
96
97#ifndef TELNET_PORT
98#define TELNET_PORT	23
99#endif
100#ifndef BGP_PORT
101#define BGP_PORT	179
102#endif
103#define NETBIOS_SSN_PORT 139
104#ifndef PPTP_PORT
105#define PPTP_PORT	1723
106#endif
107#define BEEP_PORT        10288
108#ifndef NFS_PORT
109#define NFS_PORT	2049
110#endif
111#define MSDP_PORT	639
112#define LDP_PORT        646
113
114static int tcp_cksum(register const struct ip *ip,
115		     register const struct tcphdr *tp,
116		     register u_int len)
117{
118	union phu {
119		struct phdr {
120			u_int32_t src;
121			u_int32_t dst;
122			u_char mbz;
123			u_char proto;
124			u_int16_t len;
125		} ph;
126		u_int16_t pa[6];
127	} phu;
128	const u_int16_t *sp;
129
130	/* pseudo-header.. */
131	phu.ph.len = htons((u_int16_t)len);
132	phu.ph.mbz = 0;
133	phu.ph.proto = IPPROTO_TCP;
134	memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
135	if (IP_HL(ip) == 5)
136		memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
137	else
138		phu.ph.dst = ip_finddst(ip);
139
140	sp = &phu.pa[0];
141	return in_cksum((u_short *)tp, len,
142			sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
143}
144
145#ifdef INET6
146static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
147	u_int len)
148{
149	size_t i;
150	register const u_int16_t *sp;
151	u_int32_t sum;
152	union {
153		struct {
154			struct in6_addr ph_src;
155			struct in6_addr ph_dst;
156			u_int32_t	ph_len;
157			u_int8_t	ph_zero[3];
158			u_int8_t	ph_nxt;
159		} ph;
160		u_int16_t pa[20];
161	} phu;
162
163	/* pseudo-header */
164	memset(&phu, 0, sizeof(phu));
165	phu.ph.ph_src = ip6->ip6_src;
166	phu.ph.ph_dst = ip6->ip6_dst;
167	phu.ph.ph_len = htonl(len);
168	phu.ph.ph_nxt = IPPROTO_TCP;
169
170	sum = 0;
171	for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
172		sum += phu.pa[i];
173
174	sp = (const u_int16_t *)tp;
175
176	for (i = 0; i < (len & ~1); i += 2)
177		sum += *sp++;
178
179	if (len & 1)
180		sum += htons((*(const u_int8_t *)sp) << 8);
181
182	while (sum > 0xffff)
183		sum = (sum & 0xffff) + (sum >> 16);
184	sum = ~sum & 0xffff;
185
186	return (sum);
187}
188#endif
189
190void
191tcp_print(register const u_char *bp, register u_int length,
192	  register const u_char *bp2, int fragmented)
193{
194	register const struct tcphdr *tp;
195	register const struct ip *ip;
196	register u_char flags;
197	register u_int hlen;
198	register char ch;
199	u_int16_t sport, dport, win, urp;
200	u_int32_t seq, ack, thseq, thack;
201	int threv;
202#ifdef INET6
203	register const struct ip6_hdr *ip6;
204#endif
205
206	tp = (struct tcphdr *)bp;
207	ip = (struct ip *)bp2;
208#ifdef INET6
209	if (IP_V(ip) == 6)
210		ip6 = (struct ip6_hdr *)bp2;
211	else
212		ip6 = NULL;
213#endif /*INET6*/
214	ch = '\0';
215	if (!TTEST(tp->th_dport)) {
216		(void)printf("%s > %s: [|tcp]",
217			ipaddr_string(&ip->ip_src),
218			ipaddr_string(&ip->ip_dst));
219		return;
220	}
221
222	sport = EXTRACT_16BITS(&tp->th_sport);
223	dport = EXTRACT_16BITS(&tp->th_dport);
224
225	hlen = TH_OFF(tp) * 4;
226
227	/*
228	 * If data present, header length valid, and NFS port used,
229	 * assume NFS.
230	 * Pass offset of data plus 4 bytes for RPC TCP msg length
231	 * to NFS print routines.
232	 */
233	if (!qflag && hlen >= sizeof(*tp) && hlen <= length) {
234		if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg) <= snapend &&
235		    dport == NFS_PORT) {
236			nfsreq_print((u_char *)tp + hlen + 4, length - hlen,
237				     (u_char *)ip);
238			return;
239		} else if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg)
240			   <= snapend &&
241			   sport == NFS_PORT) {
242			nfsreply_print((u_char *)tp + hlen + 4, length - hlen,
243				       (u_char *)ip);
244			return;
245		}
246	}
247#ifdef INET6
248	if (ip6) {
249		if (ip6->ip6_nxt == IPPROTO_TCP) {
250			(void)printf("%s.%s > %s.%s: ",
251				ip6addr_string(&ip6->ip6_src),
252				tcpport_string(sport),
253				ip6addr_string(&ip6->ip6_dst),
254				tcpport_string(dport));
255		} else {
256			(void)printf("%s > %s: ",
257				tcpport_string(sport), tcpport_string(dport));
258		}
259	} else
260#endif /*INET6*/
261	{
262		if (ip->ip_p == IPPROTO_TCP) {
263			(void)printf("%s.%s > %s.%s: ",
264				ipaddr_string(&ip->ip_src),
265				tcpport_string(sport),
266				ipaddr_string(&ip->ip_dst),
267				tcpport_string(dport));
268		} else {
269			(void)printf("%s > %s: ",
270				tcpport_string(sport), tcpport_string(dport));
271		}
272	}
273
274	if (hlen < sizeof(*tp)) {
275		(void)printf(" tcp %d [bad hdr length %u - too short, < %lu]",
276		    length - hlen, hlen, (unsigned long)sizeof(*tp));
277		return;
278	}
279
280	TCHECK(*tp);
281
282	seq = EXTRACT_32BITS(&tp->th_seq);
283	ack = EXTRACT_32BITS(&tp->th_ack);
284	win = EXTRACT_16BITS(&tp->th_win);
285	urp = EXTRACT_16BITS(&tp->th_urp);
286
287	if (qflag) {
288		(void)printf("tcp %d", length - hlen);
289		if (hlen > length) {
290			(void)printf(" [bad hdr length %u - too long, > %u]",
291			    hlen, length);
292		}
293		return;
294	}
295	if ((flags = tp->th_flags) & (TH_SYN|TH_FIN|TH_RST|TH_PUSH|
296				      TH_ECNECHO|TH_CWR)) {
297		if (flags & TH_SYN)
298			putchar('S');
299		if (flags & TH_FIN)
300			putchar('F');
301		if (flags & TH_RST)
302			putchar('R');
303		if (flags & TH_PUSH)
304			putchar('P');
305		if (flags & TH_CWR)
306			putchar('W');	/* congestion _W_indow reduced (ECN) */
307		if (flags & TH_ECNECHO)
308			putchar('E');	/* ecn _E_cho sent (ECN) */
309	} else
310		putchar('.');
311
312	if (!Sflag && (flags & TH_ACK)) {
313		register struct tcp_seq_hash *th;
314		const void *src, *dst;
315		register int rev;
316		struct tha tha;
317		/*
318		 * Find (or record) the initial sequence numbers for
319		 * this conversation.  (we pick an arbitrary
320		 * collating order so there's only one entry for
321		 * both directions).
322		 */
323#ifdef INET6
324		memset(&tha, 0, sizeof(tha));
325		rev = 0;
326		if (ip6) {
327			src = &ip6->ip6_src;
328			dst = &ip6->ip6_dst;
329			if (sport > dport)
330				rev = 1;
331			else if (sport == dport) {
332				if (memcmp(src, dst, sizeof ip6->ip6_dst) > 0)
333					rev = 1;
334			}
335			if (rev) {
336				memcpy(&tha.src, dst, sizeof ip6->ip6_dst);
337				memcpy(&tha.dst, src, sizeof ip6->ip6_src);
338				tha.port = dport << 16 | sport;
339			} else {
340				memcpy(&tha.dst, dst, sizeof ip6->ip6_dst);
341				memcpy(&tha.src, src, sizeof ip6->ip6_src);
342				tha.port = sport << 16 | dport;
343			}
344		} else {
345			src = &ip->ip_src;
346			dst = &ip->ip_dst;
347			if (sport > dport)
348				rev = 1;
349			else if (sport == dport) {
350				if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
351					rev = 1;
352			}
353			if (rev) {
354				memcpy(&tha.src, dst, sizeof ip->ip_dst);
355				memcpy(&tha.dst, src, sizeof ip->ip_src);
356				tha.port = dport << 16 | sport;
357			} else {
358				memcpy(&tha.dst, dst, sizeof ip->ip_dst);
359				memcpy(&tha.src, src, sizeof ip->ip_src);
360				tha.port = sport << 16 | dport;
361			}
362		}
363#else
364		rev = 0;
365		src = &ip->ip_src;
366		dst = &ip->ip_dst;
367		if (sport > dport)
368			rev = 1;
369		else if (sport == dport) {
370			if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
371				rev = 1;
372		}
373		if (rev) {
374			memcpy(&tha.src, dst, sizeof ip->ip_dst);
375			memcpy(&tha.dst, src, sizeof ip->ip_src);
376			tha.port = dport << 16 | sport;
377		} else {
378			memcpy(&tha.dst, dst, sizeof ip->ip_dst);
379			memcpy(&tha.src, src, sizeof ip->ip_src);
380			tha.port = sport << 16 | dport;
381		}
382#endif
383
384		threv = rev;
385		for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
386		     th->nxt; th = th->nxt)
387			if (memcmp((char *)&tha, (char *)&th->addr,
388				  sizeof(th->addr)) == 0)
389				break;
390
391		if (!th->nxt || (flags & TH_SYN)) {
392			/* didn't find it or new conversation */
393			if (th->nxt == NULL) {
394				th->nxt = (struct tcp_seq_hash *)
395					calloc(1, sizeof(*th));
396				if (th->nxt == NULL)
397					error("tcp_print: calloc");
398			}
399			th->addr = tha;
400			if (rev)
401				th->ack = seq, th->seq = ack - 1;
402			else
403				th->seq = seq, th->ack = ack - 1;
404		} else {
405			if (rev)
406				seq -= th->ack, ack -= th->seq;
407			else
408				seq -= th->seq, ack -= th->ack;
409		}
410
411		thseq = th->seq;
412		thack = th->ack;
413	} else {
414		/*fool gcc*/
415		thseq = thack = threv = 0;
416	}
417	if (hlen > length) {
418		(void)printf(" [bad hdr length %u - too long, > %u]",
419		    hlen, length);
420		return;
421	}
422
423	if (IP_V(ip) == 4 && vflag && !fragmented) {
424		u_int16_t sum, tcp_sum;
425		if (TTEST2(tp->th_sport, length)) {
426			sum = tcp_cksum(ip, tp, length);
427
428                        (void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
429			if (sum != 0) {
430				tcp_sum = EXTRACT_16BITS(&tp->th_sum);
431				(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
432			} else
433				(void)printf(" (correct),");
434		}
435	}
436#ifdef INET6
437	if (IP_V(ip) == 6 && ip6->ip6_plen && vflag && !fragmented) {
438		u_int16_t sum,tcp_sum;
439		if (TTEST2(tp->th_sport, length)) {
440			sum = tcp6_cksum(ip6, tp, length);
441                        (void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
442			if (sum != 0) {
443				tcp_sum = EXTRACT_16BITS(&tp->th_sum);
444				(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
445			} else
446				(void)printf(" (correct),");
447
448		}
449	}
450#endif
451
452	length -= hlen;
453	if (vflag > 1 || length > 0 || flags & (TH_SYN | TH_FIN | TH_RST))
454		(void)printf(" %u:%u(%u)", seq, seq + length, length);
455	if (flags & TH_ACK)
456		(void)printf(" ack %u", ack);
457
458	(void)printf(" win %d", win);
459
460	if (flags & TH_URG)
461		(void)printf(" urg %d", urp);
462	/*
463	 * Handle any options.
464	 */
465	if (hlen > sizeof(*tp)) {
466		register const u_char *cp;
467		register u_int i, opt, datalen;
468		register u_int len;
469
470		hlen -= sizeof(*tp);
471		cp = (const u_char *)tp + sizeof(*tp);
472		putchar(' ');
473		ch = '<';
474		while (hlen > 0) {
475			putchar(ch);
476			TCHECK(*cp);
477			opt = *cp++;
478			if (ZEROLENOPT(opt))
479				len = 1;
480			else {
481				TCHECK(*cp);
482				len = *cp++;	/* total including type, len */
483				if (len < 2 || len > hlen)
484					goto bad;
485				--hlen;		/* account for length byte */
486			}
487			--hlen;			/* account for type byte */
488			datalen = 0;
489
490/* Bail if "l" bytes of data are not left or were not captured  */
491#define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }
492
493			switch (opt) {
494
495			case TCPOPT_MAXSEG:
496				(void)printf("mss");
497				datalen = 2;
498				LENCHECK(datalen);
499				(void)printf(" %u", EXTRACT_16BITS(cp));
500
501				break;
502
503			case TCPOPT_EOL:
504				(void)printf("eol");
505				break;
506
507			case TCPOPT_NOP:
508				(void)printf("nop");
509				break;
510
511			case TCPOPT_WSCALE:
512				(void)printf("wscale");
513				datalen = 1;
514				LENCHECK(datalen);
515				(void)printf(" %u", *cp);
516				break;
517
518			case TCPOPT_SACKOK:
519				(void)printf("sackOK");
520				break;
521
522			case TCPOPT_SACK:
523				datalen = len - 2;
524				if (datalen % 8 != 0) {
525					(void)printf("malformed sack");
526				} else {
527					u_int32_t s, e;
528
529					(void)printf("sack %d ", datalen / 8);
530					for (i = 0; i < datalen; i += 8) {
531						LENCHECK(i + 4);
532						s = EXTRACT_32BITS(cp + i);
533						LENCHECK(i + 8);
534						e = EXTRACT_32BITS(cp + i + 4);
535						if (threv) {
536							s -= thseq;
537							e -= thseq;
538						} else {
539							s -= thack;
540							e -= thack;
541						}
542						(void)printf("{%u:%u}", s, e);
543					}
544				}
545				break;
546
547			case TCPOPT_ECHO:
548				(void)printf("echo");
549				datalen = 4;
550				LENCHECK(datalen);
551				(void)printf(" %u", EXTRACT_32BITS(cp));
552				break;
553
554			case TCPOPT_ECHOREPLY:
555				(void)printf("echoreply");
556				datalen = 4;
557				LENCHECK(datalen);
558				(void)printf(" %u", EXTRACT_32BITS(cp));
559				break;
560
561			case TCPOPT_TIMESTAMP:
562				(void)printf("timestamp");
563				datalen = 8;
564				LENCHECK(4);
565				(void)printf(" %u", EXTRACT_32BITS(cp));
566				LENCHECK(datalen);
567				(void)printf(" %u", EXTRACT_32BITS(cp + 4));
568				break;
569
570			case TCPOPT_CC:
571				(void)printf("cc");
572				datalen = 4;
573				LENCHECK(datalen);
574				(void)printf(" %u", EXTRACT_32BITS(cp));
575				break;
576
577			case TCPOPT_CCNEW:
578				(void)printf("ccnew");
579				datalen = 4;
580				LENCHECK(datalen);
581				(void)printf(" %u", EXTRACT_32BITS(cp));
582				break;
583
584			case TCPOPT_CCECHO:
585				(void)printf("ccecho");
586				datalen = 4;
587				LENCHECK(datalen);
588				(void)printf(" %u", EXTRACT_32BITS(cp));
589				break;
590
591			case TCPOPT_SIGNATURE:
592				(void)printf("md5:");
593				datalen = TCP_SIGLEN;
594				LENCHECK(datalen);
595#ifdef HAVE_LIBCRYPTO
596				switch (tcp_verify_signature(ip, tp,
597				    bp + TH_OFF(tp) * 4, length, cp)) {
598
599				case SIGNATURE_VALID:
600					(void)printf("valid");
601					break;
602
603				case SIGNATURE_INVALID:
604					(void)printf("invalid");
605					break;
606
607				case CANT_CHECK_SIGNATURE:
608					(void)printf("can't check - ");
609					for (i = 0; i < TCP_SIGLEN; ++i)
610						(void)printf("%02x", cp[i]);
611					break;
612				}
613#else
614				for (i = 0; i < TCP_SIGLEN; ++i)
615					(void)printf("%02x", cp[i]);
616#endif
617				break;
618
619			default:
620				(void)printf("opt-%u:", opt);
621				datalen = len - 2;
622				for (i = 0; i < datalen; ++i) {
623					LENCHECK(i);
624					(void)printf("%02x", cp[i]);
625				}
626				break;
627			}
628
629			/* Account for data printed */
630			cp += datalen;
631			hlen -= datalen;
632
633			/* Check specification against observed length */
634			++datalen;			/* option octet */
635			if (!ZEROLENOPT(opt))
636				++datalen;		/* size octet */
637			if (datalen != len)
638				(void)printf("[len %d]", len);
639			ch = ',';
640			if (opt == TCPOPT_EOL)
641				break;
642		}
643		putchar('>');
644	}
645
646	if (length <= 0)
647		return;
648
649	/*
650	 * Decode payload if necessary.
651	 */
652	bp += TH_OFF(tp) * 4;
653	if (flags & TH_RST) {
654		if (vflag)
655			print_tcp_rst_data(bp, length);
656	} else {
657		if (sport == TELNET_PORT || dport == TELNET_PORT) {
658			if (!qflag && vflag)
659				telnet_print(bp, length);
660		} else if (sport == BGP_PORT || dport == BGP_PORT)
661			bgp_print(bp, length);
662		else if (sport == PPTP_PORT || dport == PPTP_PORT)
663			pptp_print(bp);
664#ifdef TCPDUMP_DO_SMB
665		else if (sport == NETBIOS_SSN_PORT || dport == NETBIOS_SSN_PORT)
666			nbt_tcp_print(bp, length);
667#endif
668		else if (sport == BEEP_PORT || dport == BEEP_PORT)
669			beep_print(bp, length);
670		else if (length > 2 &&
671		    (sport == NAMESERVER_PORT || dport == NAMESERVER_PORT ||
672		     sport == MULTICASTDNS_PORT || dport == MULTICASTDNS_PORT)) {
673			/*
674			 * TCP DNS query has 2byte length at the head.
675			 * XXX packet could be unaligned, it can go strange
676			 */
677			ns_print(bp + 2, length - 2, 0);
678		} else if (sport == MSDP_PORT || dport == MSDP_PORT) {
679			msdp_print(bp, length);
680		}
681                else if (length > 0 && (sport == LDP_PORT || dport == LDP_PORT)) {
682                        ldp_print(bp, length);
683		}
684	}
685	return;
686bad:
687	fputs("[bad opt]", stdout);
688	if (ch != '\0')
689		putchar('>');
690	return;
691trunc:
692	fputs("[|tcp]", stdout);
693	if (ch != '\0')
694		putchar('>');
695}
696
697/*
698 * RFC1122 says the following on data in RST segments:
699 *
700 *         4.2.2.12  RST Segment: RFC-793 Section 3.4
701 *
702 *            A TCP SHOULD allow a received RST segment to include data.
703 *
704 *            DISCUSSION
705 *                 It has been suggested that a RST segment could contain
706 *                 ASCII text that encoded and explained the cause of the
707 *                 RST.  No standard has yet been established for such
708 *                 data.
709 *
710 */
711
712static void
713print_tcp_rst_data(register const u_char *sp, u_int length)
714{
715	int c;
716
717	if (TTEST2(*sp, length))
718		printf(" [RST");
719	else
720		printf(" [!RST");
721	if (length > MAX_RST_DATA_LEN) {
722		length = MAX_RST_DATA_LEN;	/* can use -X for longer */
723		putchar('+');			/* indicate we truncate */
724	}
725	putchar(' ');
726	while (length-- && sp <= snapend) {
727		c = *sp++;
728		safeputchar(c);
729	}
730	putchar(']');
731}
732
733#ifdef HAVE_LIBCRYPTO
734static int
735tcp_verify_signature(const struct ip *ip, const struct tcphdr *tp,
736    const u_char *data, int length, const u_char *rcvsig)
737{
738        struct tcphdr tp1;
739	u_char sig[TCP_SIGLEN];
740	char zero_proto = 0;
741	MD5_CTX ctx;
742	u_int16_t savecsum, tlen;
743#ifdef INET6
744	struct ip6_hdr *ip6;
745#endif
746	u_int32_t len32;
747	u_int8_t nxt;
748
749	tp1 = *tp;
750
751	if (tcpmd5secret == NULL)
752		return (CANT_CHECK_SIGNATURE);
753
754	MD5_Init(&ctx);
755	/*
756	 * Step 1: Update MD5 hash with IP pseudo-header.
757	 */
758	if (IP_V(ip) == 4) {
759		MD5_Update(&ctx, (char *)&ip->ip_src, sizeof(ip->ip_src));
760		MD5_Update(&ctx, (char *)&ip->ip_dst, sizeof(ip->ip_dst));
761		MD5_Update(&ctx, (char *)&zero_proto, sizeof(zero_proto));
762		MD5_Update(&ctx, (char *)&ip->ip_p, sizeof(ip->ip_p));
763		tlen = EXTRACT_16BITS(&ip->ip_len) - IP_HL(ip) * 4;
764		tlen = htons(tlen);
765		MD5_Update(&ctx, (char *)&tlen, sizeof(tlen));
766#ifdef INET6
767	} else if (IP_V(ip) == 6) {
768		ip6 = (struct ip6_hdr *)ip;
769		MD5_Update(&ctx, (char *)&ip6->ip6_src, sizeof(ip6->ip6_src));
770		MD5_Update(&ctx, (char *)&ip6->ip6_dst, sizeof(ip6->ip6_dst));
771		len32 = htonl(ntohs(ip6->ip6_plen));
772		MD5_Update(&ctx, (char *)&len32, sizeof(len32));
773		nxt = 0;
774		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
775		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
776		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
777		nxt = IPPROTO_TCP;
778		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
779#endif
780	} else
781		return (CANT_CHECK_SIGNATURE);
782
783	/*
784	 * Step 2: Update MD5 hash with TCP header, excluding options.
785	 * The TCP checksum must be set to zero.
786	 */
787	savecsum = tp1.th_sum;
788	tp1.th_sum = 0;
789	MD5_Update(&ctx, (char *)&tp1, sizeof(struct tcphdr));
790	tp1.th_sum = savecsum;
791	/*
792	 * Step 3: Update MD5 hash with TCP segment data, if present.
793	 */
794	if (length > 0)
795		MD5_Update(&ctx, data, length);
796	/*
797	 * Step 4: Update MD5 hash with shared secret.
798	 */
799	MD5_Update(&ctx, tcpmd5secret, strlen(tcpmd5secret));
800	MD5_Final(sig, &ctx);
801
802	if (memcmp(rcvsig, sig, TCP_SIGLEN) == 0)
803		return (SIGNATURE_VALID);
804	else
805		return (SIGNATURE_INVALID);
806}
807#endif /* HAVE_LIBCRYPTO */
808