domain.c revision 168516 
1/*
2 * Copyright (c) 1998-2004, 2006 Sendmail, Inc. and its suppliers.
3 *	All rights reserved.
4 * Copyright (c) 1986, 1995-1997 Eric P. Allman.  All rights reserved.
5 * Copyright (c) 1988, 1993
6 *	The Regents of the University of California.  All rights reserved.
7 *
8 * By using this file, you agree to the terms and conditions set
9 * forth in the LICENSE file which can be found at the top level of
10 * the sendmail distribution.
11 *
12 */
13
14#include <sendmail.h>
15#include "map.h"
16
17#if NAMED_BIND
18SM_RCSID("@(#)$Id: domain.c,v 8.202 2006/12/19 01:15:07 ca Exp $ (with name server)")
19#else /* NAMED_BIND */
20SM_RCSID("@(#)$Id: domain.c,v 8.202 2006/12/19 01:15:07 ca Exp $ (without name server)")
21#endif /* NAMED_BIND */
22
23#if NAMED_BIND
24
25# include <arpa/inet.h>
26
27
28/*
29**  The standard udp packet size PACKETSZ (512) is not sufficient for some
30**  nameserver answers containing very many resource records. The resolver
31**  may switch to tcp and retry if it detects udp packet overflow.
32**  Also note that the resolver routines res_query and res_search return
33**  the size of the *un*truncated answer in case the supplied answer buffer
34**  it not big enough to accommodate the entire answer.
35*/
36
37# ifndef MAXPACKET
38#  define MAXPACKET 8192	/* max packet size used internally by BIND */
39# endif /* ! MAXPACKET */
40
41typedef union
42{
43	HEADER		qb1;
44	unsigned char	qb2[MAXPACKET];
45} querybuf;
46
47# ifndef MXHOSTBUFSIZE
48#  define MXHOSTBUFSIZE	(128 * MAXMXHOSTS)
49# endif /* ! MXHOSTBUFSIZE */
50
51static char	MXHostBuf[MXHOSTBUFSIZE];
52#if (MXHOSTBUFSIZE < 2) || (MXHOSTBUFSIZE >= INT_MAX/2)
53	ERROR: _MXHOSTBUFSIZE is out of range
54#endif /* (MXHOSTBUFSIZE < 2) || (MXHOSTBUFSIZE >= INT_MAX/2) */
55
56# ifndef MAXDNSRCH
57#  define MAXDNSRCH	6	/* number of possible domains to search */
58# endif /* ! MAXDNSRCH */
59
60# ifndef RES_DNSRCH_VARIABLE
61#  define RES_DNSRCH_VARIABLE	_res.dnsrch
62# endif /* ! RES_DNSRCH_VARIABLE */
63
64# ifndef NO_DATA
65#  define NO_DATA	NO_ADDRESS
66# endif /* ! NO_DATA */
67
68# ifndef HFIXEDSZ
69#  define HFIXEDSZ	12	/* sizeof(HEADER) */
70# endif /* ! HFIXEDSZ */
71
72# define MAXCNAMEDEPTH	10	/* maximum depth of CNAME recursion */
73
74# if defined(__RES) && (__RES >= 19940415)
75#  define RES_UNC_T	char *
76# else /* defined(__RES) && (__RES >= 19940415) */
77#  define RES_UNC_T	unsigned char *
78# endif /* defined(__RES) && (__RES >= 19940415) */
79
80static int	mxrand __P((char *));
81static int	fallbackmxrr __P((int, unsigned short *, char **));
82
83/*
84**  GETFALLBACKMXRR -- get MX resource records for fallback MX host.
85**
86**	We have to initialize this once before doing anything else.
87**	Moreover, we have to repeat this from time to time to avoid
88**	stale data, e.g., in persistent queue runners.
89**	This should be done in a parent process so the child
90**	processes have the right data.
91**
92**	Parameters:
93**		host -- the name of the fallback MX host.
94**
95**	Returns:
96**		number of MX records.
97**
98**	Side Effects:
99**		Populates NumFallbackMXHosts and fbhosts.
100**		Sets renewal time (based on TTL).
101*/
102
103int NumFallbackMXHosts = 0;	/* Number of fallback MX hosts (after MX expansion) */
104static char *fbhosts[MAXMXHOSTS + 1];
105
106int
107getfallbackmxrr(host)
108	char *host;
109{
110	int i, rcode;
111	int ttl;
112	static time_t renew = 0;
113
114#if 0
115	/* This is currently done before this function is called. */
116	if (host == NULL || *host == '\0')
117		return 0;
118#endif /* 0 */
119	if (NumFallbackMXHosts > 0 && renew > curtime())
120		return NumFallbackMXHosts;
121	if (host[0] == '[')
122	{
123		fbhosts[0] = host;
124		NumFallbackMXHosts = 1;
125	}
126	else
127	{
128		/* free old data */
129		for (i = 0; i < NumFallbackMXHosts; i++)
130			sm_free(fbhosts[i]);
131
132		/* get new data */
133		NumFallbackMXHosts = getmxrr(host, fbhosts, NULL, false,
134					     &rcode, false, &ttl);
135		renew = curtime() + ttl;
136		for (i = 0; i < NumFallbackMXHosts; i++)
137			fbhosts[i] = newstr(fbhosts[i]);
138	}
139	return NumFallbackMXHosts;
140}
141
142/*
143**  FALLBACKMXRR -- add MX resource records for fallback MX host to list.
144**
145**	Parameters:
146**		nmx -- current number of MX records.
147**		prefs -- array of preferences.
148**		mxhosts -- array of MX hosts (maximum size: MAXMXHOSTS)
149**
150**	Returns:
151**		new number of MX records.
152**
153**	Side Effects:
154**		If FallbackMX was set, it appends the MX records for
155**		that host to mxhosts (and modifies prefs accordingly).
156*/
157
158static int
159fallbackmxrr(nmx, prefs, mxhosts)
160	int nmx;
161	unsigned short *prefs;
162	char **mxhosts;
163{
164	int i;
165
166	for (i = 0; i < NumFallbackMXHosts && nmx < MAXMXHOSTS; i++)
167	{
168		if (nmx > 0)
169			prefs[nmx] = prefs[nmx - 1] + 1;
170		else
171			prefs[nmx] = 0;
172		mxhosts[nmx++] = fbhosts[i];
173	}
174	return nmx;
175}
176
177/*
178**  GETMXRR -- get MX resource records for a domain
179**
180**	Parameters:
181**		host -- the name of the host to MX.
182**		mxhosts -- a pointer to a return buffer of MX records.
183**		mxprefs -- a pointer to a return buffer of MX preferences.
184**			If NULL, don't try to populate.
185**		droplocalhost -- If true, all MX records less preferred
186**			than the local host (as determined by $=w) will
187**			be discarded.
188**		rcode -- a pointer to an EX_ status code.
189**		tryfallback -- add also fallback MX host?
190**		pttl -- pointer to return TTL (can be NULL).
191**
192**	Returns:
193**		The number of MX records found.
194**		-1 if there is an internal failure.
195**		If no MX records are found, mxhosts[0] is set to host
196**			and 1 is returned.
197**
198**	Side Effects:
199**		The entries made for mxhosts point to a static array
200**		MXHostBuf[MXHOSTBUFSIZE], so the data needs to be copied,
201**		if it must be preserved across calls to this function.
202*/
203
204int
205getmxrr(host, mxhosts, mxprefs, droplocalhost, rcode, tryfallback, pttl)
206	char *host;
207	char **mxhosts;
208	unsigned short *mxprefs;
209	bool droplocalhost;
210	int *rcode;
211	bool tryfallback;
212	int *pttl;
213{
214	register unsigned char *eom, *cp;
215	register int i, j, n;
216	int nmx = 0;
217	register char *bp;
218	HEADER *hp;
219	querybuf answer;
220	int ancount, qdcount, buflen;
221	bool seenlocal = false;
222	unsigned short pref, type;
223	unsigned short localpref = 256;
224	char *fallbackMX = FallbackMX;
225	bool trycanon = false;
226	unsigned short *prefs;
227	int (*resfunc) __P((const char *, int, int, u_char *, int));
228	unsigned short prefer[MAXMXHOSTS];
229	int weight[MAXMXHOSTS];
230	int ttl = 0;
231	extern int res_query(), res_search();
232
233	if (tTd(8, 2))
234		sm_dprintf("getmxrr(%s, droplocalhost=%d)\n",
235			   host, droplocalhost);
236	*rcode = EX_OK;
237	if (pttl != NULL)
238		*pttl = SM_DEFAULT_TTL;
239	if (*host == '\0')
240		return 0;
241
242	if ((fallbackMX != NULL && droplocalhost &&
243	     wordinclass(fallbackMX, 'w')) || !tryfallback)
244	{
245		/* don't use fallback for this pass */
246		fallbackMX = NULL;
247	}
248
249	if (mxprefs != NULL)
250		prefs = mxprefs;
251	else
252		prefs = prefer;
253
254	/* efficiency hack -- numeric or non-MX lookups */
255	if (host[0] == '[')
256		goto punt;
257
258	/*
259	**  If we don't have MX records in our host switch, don't
260	**  try for MX records.  Note that this really isn't "right",
261	**  since we might be set up to try NIS first and then DNS;
262	**  if the host is found in NIS we really shouldn't be doing
263	**  MX lookups.  However, that should be a degenerate case.
264	*/
265
266	if (!UseNameServer)
267		goto punt;
268	if (HasWildcardMX && ConfigLevel >= 6)
269		resfunc = res_query;
270	else
271		resfunc = res_search;
272
273	errno = 0;
274	n = (*resfunc)(host, C_IN, T_MX, (unsigned char *) &answer,
275		       sizeof(answer));
276	if (n < 0)
277	{
278		if (tTd(8, 1))
279			sm_dprintf("getmxrr: res_search(%s) failed (errno=%d, h_errno=%d)\n",
280				host, errno, h_errno);
281		switch (h_errno)
282		{
283		  case NO_DATA:
284			trycanon = true;
285			/* FALLTHROUGH */
286
287		  case NO_RECOVERY:
288			/* no MX data on this host */
289			goto punt;
290
291		  case HOST_NOT_FOUND:
292# if BROKEN_RES_SEARCH
293		  case 0:	/* Ultrix resolver retns failure w/ h_errno=0 */
294# endif /* BROKEN_RES_SEARCH */
295			/* host doesn't exist in DNS; might be in /etc/hosts */
296			trycanon = true;
297			*rcode = EX_NOHOST;
298			goto punt;
299
300		  case TRY_AGAIN:
301		  case -1:
302			/* couldn't connect to the name server */
303			if (fallbackMX != NULL)
304			{
305				/* name server is hosed -- push to fallback */
306				return fallbackmxrr(nmx, prefs, mxhosts);
307			}
308			/* it might come up later; better queue it up */
309			*rcode = EX_TEMPFAIL;
310			break;
311
312		  default:
313			syserr("getmxrr: res_search (%s) failed with impossible h_errno (%d)",
314				host, h_errno);
315			*rcode = EX_OSERR;
316			break;
317		}
318
319		/* irreconcilable differences */
320		return -1;
321	}
322
323	/* avoid problems after truncation in tcp packets */
324	if (n > sizeof(answer))
325		n = sizeof(answer);
326
327	/* find first satisfactory answer */
328	hp = (HEADER *)&answer;
329	cp = (unsigned char *)&answer + HFIXEDSZ;
330	eom = (unsigned char *)&answer + n;
331	for (qdcount = ntohs((unsigned short) hp->qdcount);
332	     qdcount--;
333	     cp += n + QFIXEDSZ)
334	{
335		if ((n = dn_skipname(cp, eom)) < 0)
336			goto punt;
337	}
338
339	/* NOTE: see definition of MXHostBuf! */
340	buflen = sizeof(MXHostBuf) - 1;
341	SM_ASSERT(buflen > 0);
342	bp = MXHostBuf;
343	ancount = ntohs((unsigned short) hp->ancount);
344
345	/* See RFC 1035 for layout of RRs. */
346	/* XXX leave room for FallbackMX ? */
347	while (--ancount >= 0 && cp < eom && nmx < MAXMXHOSTS - 1)
348	{
349		if ((n = dn_expand((unsigned char *)&answer, eom, cp,
350				   (RES_UNC_T) bp, buflen)) < 0)
351			break;
352		cp += n;
353		GETSHORT(type, cp);
354		cp += INT16SZ;		/* skip over class */
355		GETLONG(ttl, cp);
356		GETSHORT(n, cp);	/* rdlength */
357		if (type != T_MX)
358		{
359			if (tTd(8, 8) || _res.options & RES_DEBUG)
360				sm_dprintf("unexpected answer type %d, size %d\n",
361					type, n);
362			cp += n;
363			continue;
364		}
365		GETSHORT(pref, cp);
366		if ((n = dn_expand((unsigned char *)&answer, eom, cp,
367				   (RES_UNC_T) bp, buflen)) < 0)
368			break;
369		cp += n;
370		n = strlen(bp);
371# if 0
372		/* Can this happen? */
373		if (n == 0)
374		{
375			if (LogLevel > 4)
376				sm_syslog(LOG_ERR, NOQID,
377					  "MX records for %s contain empty string",
378					  host);
379			continue;
380		}
381# endif /* 0 */
382		if (wordinclass(bp, 'w'))
383		{
384			if (tTd(8, 3))
385				sm_dprintf("found localhost (%s) in MX list, pref=%d\n",
386					bp, pref);
387			if (droplocalhost)
388			{
389				if (!seenlocal || pref < localpref)
390					localpref = pref;
391				seenlocal = true;
392				continue;
393			}
394			weight[nmx] = 0;
395		}
396		else
397			weight[nmx] = mxrand(bp);
398		prefs[nmx] = pref;
399		mxhosts[nmx++] = bp;
400		bp += n;
401		if (bp[-1] != '.')
402		{
403			*bp++ = '.';
404			n++;
405		}
406		*bp++ = '\0';
407		if (buflen < n + 1)
408		{
409			/* don't want to wrap buflen */
410			break;
411		}
412		buflen -= n + 1;
413	}
414
415	/* return only one TTL entry, that should be sufficient */
416	if (ttl > 0 && pttl != NULL)
417		*pttl = ttl;
418
419	/* sort the records */
420	for (i = 0; i < nmx; i++)
421	{
422		for (j = i + 1; j < nmx; j++)
423		{
424			if (prefs[i] > prefs[j] ||
425			    (prefs[i] == prefs[j] && weight[i] > weight[j]))
426			{
427				register int temp;
428				register char *temp1;
429
430				temp = prefs[i];
431				prefs[i] = prefs[j];
432				prefs[j] = temp;
433				temp1 = mxhosts[i];
434				mxhosts[i] = mxhosts[j];
435				mxhosts[j] = temp1;
436				temp = weight[i];
437				weight[i] = weight[j];
438				weight[j] = temp;
439			}
440		}
441		if (seenlocal && prefs[i] >= localpref)
442		{
443			/* truncate higher preference part of list */
444			nmx = i;
445		}
446	}
447
448	/* delete duplicates from list (yes, some bozos have duplicates) */
449	for (i = 0; i < nmx - 1; )
450	{
451		if (sm_strcasecmp(mxhosts[i], mxhosts[i + 1]) != 0)
452			i++;
453		else
454		{
455			/* compress out duplicate */
456			for (j = i + 1; j < nmx; j++)
457			{
458				mxhosts[j] = mxhosts[j + 1];
459				prefs[j] = prefs[j + 1];
460			}
461			nmx--;
462		}
463	}
464
465	if (nmx == 0)
466	{
467punt:
468		if (seenlocal)
469		{
470			struct hostent *h = NULL;
471
472			/*
473			**  If we have deleted all MX entries, this is
474			**  an error -- we should NEVER send to a host that
475			**  has an MX, and this should have been caught
476			**  earlier in the config file.
477			**
478			**  Some sites prefer to go ahead and try the
479			**  A record anyway; that case is handled by
480			**  setting TryNullMXList.  I believe this is a
481			**  bad idea, but it's up to you....
482			*/
483
484			if (TryNullMXList)
485			{
486				SM_SET_H_ERRNO(0);
487				errno = 0;
488				h = sm_gethostbyname(host, AF_INET);
489				if (h == NULL)
490				{
491					if (errno == ETIMEDOUT ||
492					    h_errno == TRY_AGAIN ||
493					    (errno == ECONNREFUSED &&
494					     UseNameServer))
495					{
496						*rcode = EX_TEMPFAIL;
497						return -1;
498					}
499# if NETINET6
500					SM_SET_H_ERRNO(0);
501					errno = 0;
502					h = sm_gethostbyname(host, AF_INET6);
503					if (h == NULL &&
504					    (errno == ETIMEDOUT ||
505					     h_errno == TRY_AGAIN ||
506					     (errno == ECONNREFUSED &&
507					      UseNameServer)))
508					{
509						*rcode = EX_TEMPFAIL;
510						return -1;
511					}
512# endif /* NETINET6 */
513				}
514			}
515
516			if (h == NULL)
517			{
518				*rcode = EX_CONFIG;
519				syserr("MX list for %s points back to %s",
520				       host, MyHostName);
521				return -1;
522			}
523# if NETINET6
524			freehostent(h);
525			h = NULL;
526# endif /* NETINET6 */
527		}
528		if (strlen(host) >= sizeof(MXHostBuf))
529		{
530			*rcode = EX_CONFIG;
531			syserr("Host name %s too long",
532			       shortenstring(host, MAXSHORTSTR));
533			return -1;
534		}
535		(void) sm_strlcpy(MXHostBuf, host, sizeof(MXHostBuf));
536		mxhosts[0] = MXHostBuf;
537		prefs[0] = 0;
538		if (host[0] == '[')
539		{
540			register char *p;
541# if NETINET6
542			struct sockaddr_in6 tmp6;
543# endif /* NETINET6 */
544
545			/* this may be an MX suppression-style address */
546			p = strchr(MXHostBuf, ']');
547			if (p != NULL)
548			{
549				*p = '\0';
550
551				if (inet_addr(&MXHostBuf[1]) != INADDR_NONE)
552				{
553					nmx++;
554					*p = ']';
555				}
556# if NETINET6
557				else if (anynet_pton(AF_INET6, &MXHostBuf[1],
558						     &tmp6.sin6_addr) == 1)
559				{
560					nmx++;
561					*p = ']';
562				}
563# endif /* NETINET6 */
564				else
565				{
566					trycanon = true;
567					mxhosts[0]++;
568				}
569			}
570		}
571		if (trycanon &&
572		    getcanonname(mxhosts[0], sizeof(MXHostBuf) - 2, false, pttl))
573		{
574			/* XXX MXHostBuf == "" ?  is that possible? */
575			bp = &MXHostBuf[strlen(MXHostBuf)];
576			if (bp[-1] != '.')
577			{
578				*bp++ = '.';
579				*bp = '\0';
580			}
581			nmx = 1;
582		}
583	}
584
585	/* if we have a default lowest preference, include that */
586	if (fallbackMX != NULL && !seenlocal)
587	{
588		nmx = fallbackmxrr(nmx, prefs, mxhosts);
589	}
590	return nmx;
591}
592/*
593**  MXRAND -- create a randomizer for equal MX preferences
594**
595**	If two MX hosts have equal preferences we want to randomize
596**	the selection.  But in order for signatures to be the same,
597**	we need to randomize the same way each time.  This function
598**	computes a pseudo-random hash function from the host name.
599**
600**	Parameters:
601**		host -- the name of the host.
602**
603**	Returns:
604**		A random but repeatable value based on the host name.
605*/
606
607static int
608mxrand(host)
609	register char *host;
610{
611	int hfunc;
612	static unsigned int seed;
613
614	if (seed == 0)
615	{
616		seed = (int) curtime() & 0xffff;
617		if (seed == 0)
618			seed++;
619	}
620
621	if (tTd(17, 9))
622		sm_dprintf("mxrand(%s)", host);
623
624	hfunc = seed;
625	while (*host != '\0')
626	{
627		int c = *host++;
628
629		if (isascii(c) && isupper(c))
630			c = tolower(c);
631		hfunc = ((hfunc << 1) ^ c) % 2003;
632	}
633
634	hfunc &= 0xff;
635	hfunc++;
636
637	if (tTd(17, 9))
638		sm_dprintf(" = %d\n", hfunc);
639	return hfunc;
640}
641/*
642**  BESTMX -- find the best MX for a name
643**
644**	This is really a hack, but I don't see any obvious way
645**	to generalize it at the moment.
646*/
647
648/* ARGSUSED3 */
649char *
650bestmx_map_lookup(map, name, av, statp)
651	MAP *map;
652	char *name;
653	char **av;
654	int *statp;
655{
656	int nmx;
657	int saveopts = _res.options;
658	int i;
659	ssize_t len = 0;
660	char *result;
661	char *mxhosts[MAXMXHOSTS + 1];
662#if _FFR_BESTMX_BETTER_TRUNCATION
663	char *buf;
664#else /* _FFR_BESTMX_BETTER_TRUNCATION */
665	char *p;
666	char buf[PSBUFSIZE / 2];
667#endif /* _FFR_BESTMX_BETTER_TRUNCATION */
668
669	_res.options &= ~(RES_DNSRCH|RES_DEFNAMES);
670	nmx = getmxrr(name, mxhosts, NULL, false, statp, false, NULL);
671	_res.options = saveopts;
672	if (nmx <= 0)
673		return NULL;
674	if (bitset(MF_MATCHONLY, map->map_mflags))
675		return map_rewrite(map, name, strlen(name), NULL);
676	if ((map->map_coldelim == '\0') || (nmx == 1))
677		return map_rewrite(map, mxhosts[0], strlen(mxhosts[0]), av);
678
679	/*
680	**  We were given a -z flag (return all MXs) and there are multiple
681	**  ones.  We need to build them all into a list.
682	*/
683
684#if _FFR_BESTMX_BETTER_TRUNCATION
685	for (i = 0; i < nmx; i++)
686	{
687		if (strchr(mxhosts[i], map->map_coldelim) != NULL)
688		{
689			syserr("bestmx_map_lookup: MX host %.64s includes map delimiter character 0x%02X",
690			       mxhosts[i], map->map_coldelim);
691			return NULL;
692		}
693		len += strlen(mxhosts[i]) + 1;
694		if (len < 0)
695		{
696			len -= strlen(mxhosts[i]) + 1;
697			break;
698		}
699	}
700	buf = (char *) sm_malloc(len);
701	if (buf == NULL)
702	{
703		*statp = EX_UNAVAILABLE;
704		return NULL;
705	}
706	*buf = '\0';
707	for (i = 0; i < nmx; i++)
708	{
709		int end;
710
711		end = sm_strlcat(buf, mxhosts[i], len);
712		if (i != nmx && end + 1 < len)
713		{
714			buf[end] = map->map_coldelim;
715			buf[end + 1] = '\0';
716		}
717	}
718
719	/* Cleanly truncate for rulesets */
720	truncate_at_delim(buf, PSBUFSIZE / 2, map->map_coldelim);
721#else /* _FFR_BESTMX_BETTER_TRUNCATION */
722	p = buf;
723	for (i = 0; i < nmx; i++)
724	{
725		size_t slen;
726
727		if (strchr(mxhosts[i], map->map_coldelim) != NULL)
728		{
729			syserr("bestmx_map_lookup: MX host %.64s includes map delimiter character 0x%02X",
730			       mxhosts[i], map->map_coldelim);
731			return NULL;
732		}
733		slen = strlen(mxhosts[i]);
734		if (len + slen + 2 > sizeof(buf))
735			break;
736		if (i > 0)
737		{
738			*p++ = map->map_coldelim;
739			len++;
740		}
741		(void) sm_strlcpy(p, mxhosts[i], sizeof(buf) - len);
742		p += slen;
743		len += slen;
744	}
745#endif /* _FFR_BESTMX_BETTER_TRUNCATION */
746
747	result = map_rewrite(map, buf, len, av);
748#if _FFR_BESTMX_BETTER_TRUNCATION
749	sm_free(buf);
750#endif /* _FFR_BESTMX_BETTER_TRUNCATION */
751	return result;
752}
753/*
754**  DNS_GETCANONNAME -- get the canonical name for named host using DNS
755**
756**	This algorithm tries to be smart about wildcard MX records.
757**	This is hard to do because DNS doesn't tell is if we matched
758**	against a wildcard or a specific MX.
759**
760**	We always prefer A & CNAME records, since these are presumed
761**	to be specific.
762**
763**	If we match an MX in one pass and lose it in the next, we use
764**	the old one.  For example, consider an MX matching *.FOO.BAR.COM.
765**	A hostname bletch.foo.bar.com will match against this MX, but
766**	will stop matching when we try bletch.bar.com -- so we know
767**	that bletch.foo.bar.com must have been right.  This fails if
768**	there was also an MX record matching *.BAR.COM, but there are
769**	some things that just can't be fixed.
770**
771**	Parameters:
772**		host -- a buffer containing the name of the host.
773**			This is a value-result parameter.
774**		hbsize -- the size of the host buffer.
775**		trymx -- if set, try MX records as well as A and CNAME.
776**		statp -- pointer to place to store status.
777**		pttl -- pointer to return TTL (can be NULL).
778**
779**	Returns:
780**		true -- if the host matched.
781**		false -- otherwise.
782*/
783
784bool
785dns_getcanonname(host, hbsize, trymx, statp, pttl)
786	char *host;
787	int hbsize;
788	bool trymx;
789	int *statp;
790	int *pttl;
791{
792	register unsigned char *eom, *ap;
793	register char *cp;
794	register int n;
795	HEADER *hp;
796	querybuf answer;
797	int ancount, qdcount;
798	int ret;
799	char **domain;
800	int type;
801	int ttl = 0;
802	char **dp;
803	char *mxmatch;
804	bool amatch;
805	bool gotmx = false;
806	int qtype;
807	int initial;
808	int loopcnt;
809	char nbuf[SM_MAX(MAXPACKET, MAXDNAME*2+2)];
810	char *searchlist[MAXDNSRCH + 2];
811
812	if (tTd(8, 2))
813		sm_dprintf("dns_getcanonname(%s, trymx=%d)\n", host, trymx);
814
815	if ((_res.options & RES_INIT) == 0 && res_init() == -1)
816	{
817		*statp = EX_UNAVAILABLE;
818		return false;
819	}
820
821	*statp = EX_OK;
822
823	/*
824	**  Initialize domain search list.  If there is at least one
825	**  dot in the name, search the unmodified name first so we
826	**  find "vse.CS" in Czechoslovakia instead of in the local
827	**  domain (e.g., vse.CS.Berkeley.EDU).  Note that there is no
828	**  longer a country named Czechoslovakia but this type of problem
829	**  is still present.
830	**
831	**  Older versions of the resolver could create this
832	**  list by tearing apart the host name.
833	*/
834
835	loopcnt = 0;
836cnameloop:
837	/* Check for dots in the name */
838	for (cp = host, n = 0; *cp != '\0'; cp++)
839		if (*cp == '.')
840			n++;
841
842	/*
843	**  Build the search list.
844	**	If there is at least one dot in name, start with a null
845	**	domain to search the unmodified name first.
846	**	If name does not end with a dot and search up local domain
847	**	tree desired, append each local domain component to the
848	**	search list; if name contains no dots and default domain
849	**	name is desired, append default domain name to search list;
850	**	else if name ends in a dot, remove that dot.
851	*/
852
853	dp = searchlist;
854	if (n > 0)
855		*dp++ = "";
856	if (n >= 0 && *--cp != '.' && bitset(RES_DNSRCH, _res.options))
857	{
858		/* make sure there are less than MAXDNSRCH domains */
859		for (domain = RES_DNSRCH_VARIABLE, ret = 0;
860		     *domain != NULL && ret < MAXDNSRCH;
861		     ret++)
862			*dp++ = *domain++;
863	}
864	else if (n == 0 && bitset(RES_DEFNAMES, _res.options))
865	{
866		*dp++ = _res.defdname;
867	}
868	else if (*cp == '.')
869	{
870		*cp = '\0';
871	}
872	*dp = NULL;
873
874	/*
875	**  Now loop through the search list, appending each domain in turn
876	**  name and searching for a match.
877	*/
878
879	mxmatch = NULL;
880	initial = T_A;
881# if NETINET6
882	if (InetMode == AF_INET6)
883		initial = T_AAAA;
884# endif /* NETINET6 */
885	qtype = initial;
886
887	for (dp = searchlist; *dp != NULL; )
888	{
889		if (qtype == initial)
890			gotmx = false;
891		if (tTd(8, 5))
892			sm_dprintf("dns_getcanonname: trying %s.%s (%s)\n",
893				host, *dp,
894# if NETINET6
895				qtype == T_AAAA ? "AAAA" :
896# endif /* NETINET6 */
897				qtype == T_A ? "A" :
898				qtype == T_MX ? "MX" :
899				"???");
900		errno = 0;
901		ret = res_querydomain(host, *dp, C_IN, qtype,
902				      answer.qb2, sizeof(answer.qb2));
903		if (ret <= 0)
904		{
905			int save_errno = errno;
906
907			if (tTd(8, 7))
908				sm_dprintf("\tNO: errno=%d, h_errno=%d\n",
909					   save_errno, h_errno);
910
911			if (save_errno == ECONNREFUSED || h_errno == TRY_AGAIN)
912			{
913				/*
914				**  the name server seems to be down or broken.
915				*/
916
917				SM_SET_H_ERRNO(TRY_AGAIN);
918				if (**dp == '\0')
919				{
920					if (*statp == EX_OK)
921						*statp = EX_TEMPFAIL;
922					goto nexttype;
923				}
924				*statp = EX_TEMPFAIL;
925
926				if (WorkAroundBrokenAAAA)
927				{
928					/*
929					**  Only return if not TRY_AGAIN as an
930					**  attempt with a different qtype may
931					**  succeed (res_querydomain() calls
932					**  res_query() calls res_send() which
933					**  sets errno to ETIMEDOUT if the
934					**  nameservers could be contacted but
935					**  didn't give an answer).
936					*/
937
938					if (save_errno != ETIMEDOUT)
939						return false;
940				}
941				else
942					return false;
943			}
944
945nexttype:
946			if (h_errno != HOST_NOT_FOUND)
947			{
948				/* might have another type of interest */
949# if NETINET6
950				if (qtype == T_AAAA)
951				{
952					qtype = T_A;
953					continue;
954				}
955				else
956# endif /* NETINET6 */
957				if (qtype == T_A && !gotmx &&
958				    (trymx || **dp == '\0'))
959				{
960					qtype = T_MX;
961					continue;
962				}
963			}
964
965			/* definite no -- try the next domain */
966			dp++;
967			qtype = initial;
968			continue;
969		}
970		else if (tTd(8, 7))
971			sm_dprintf("\tYES\n");
972
973		/* avoid problems after truncation in tcp packets */
974		if (ret > sizeof(answer))
975			ret = sizeof(answer);
976		SM_ASSERT(ret >= 0);
977
978		/*
979		**  Appear to have a match.  Confirm it by searching for A or
980		**  CNAME records.  If we don't have a local domain
981		**  wild card MX record, we will accept MX as well.
982		*/
983
984		hp = (HEADER *) &answer;
985		ap = (unsigned char *) &answer + HFIXEDSZ;
986		eom = (unsigned char *) &answer + ret;
987
988		/* skip question part of response -- we know what we asked */
989		for (qdcount = ntohs((unsigned short) hp->qdcount);
990		     qdcount--;
991		     ap += ret + QFIXEDSZ)
992		{
993			if ((ret = dn_skipname(ap, eom)) < 0)
994			{
995				if (tTd(8, 20))
996					sm_dprintf("qdcount failure (%d)\n",
997						ntohs((unsigned short) hp->qdcount));
998				*statp = EX_SOFTWARE;
999				return false;		/* ???XXX??? */
1000			}
1001		}
1002
1003		amatch = false;
1004		for (ancount = ntohs((unsigned short) hp->ancount);
1005		     --ancount >= 0 && ap < eom;
1006		     ap += n)
1007		{
1008			n = dn_expand((unsigned char *) &answer, eom, ap,
1009				      (RES_UNC_T) nbuf, sizeof(nbuf));
1010			if (n < 0)
1011				break;
1012			ap += n;
1013			GETSHORT(type, ap);
1014			ap += INT16SZ;		/* skip over class */
1015			GETLONG(ttl, ap);
1016			GETSHORT(n, ap);	/* rdlength */
1017			switch (type)
1018			{
1019			  case T_MX:
1020				gotmx = true;
1021				if (**dp != '\0' && HasWildcardMX)
1022				{
1023					/*
1024					**  If we are using MX matches and have
1025					**  not yet gotten one, save this one
1026					**  but keep searching for an A or
1027					**  CNAME match.
1028					*/
1029
1030					if (trymx && mxmatch == NULL)
1031						mxmatch = *dp;
1032					continue;
1033				}
1034
1035				/*
1036				**  If we did not append a domain name, this
1037				**  must have been a canonical name to start
1038				**  with.  Even if we did append a domain name,
1039				**  in the absence of a wildcard MX this must
1040				**  still be a real MX match.
1041				**  Such MX matches are as good as an A match,
1042				**  fall through.
1043				*/
1044				/* FALLTHROUGH */
1045
1046# if NETINET6
1047			  case T_AAAA:
1048# endif /* NETINET6 */
1049			  case T_A:
1050				/* Flag that a good match was found */
1051				amatch = true;
1052
1053				/* continue in case a CNAME also exists */
1054				continue;
1055
1056			  case T_CNAME:
1057				if (DontExpandCnames)
1058				{
1059					/* got CNAME -- guaranteed canonical */
1060					amatch = true;
1061					break;
1062				}
1063
1064				if (loopcnt++ > MAXCNAMEDEPTH)
1065				{
1066					/*XXX should notify postmaster XXX*/
1067					message("DNS failure: CNAME loop for %s",
1068						host);
1069					if (CurEnv->e_message == NULL)
1070					{
1071						char ebuf[MAXLINE];
1072
1073						(void) sm_snprintf(ebuf,
1074							sizeof(ebuf),
1075							"Deferred: DNS failure: CNAME loop for %.100s",
1076							host);
1077						CurEnv->e_message =
1078						    sm_rpool_strdup_x(
1079							CurEnv->e_rpool, ebuf);
1080					}
1081					SM_SET_H_ERRNO(NO_RECOVERY);
1082					*statp = EX_CONFIG;
1083					return false;
1084				}
1085
1086				/* value points at name */
1087				if ((ret = dn_expand((unsigned char *)&answer,
1088						     eom, ap, (RES_UNC_T) nbuf,
1089						     sizeof(nbuf))) < 0)
1090					break;
1091				(void) sm_strlcpy(host, nbuf, hbsize);
1092
1093				/*
1094				**  RFC 1034 section 3.6 specifies that CNAME
1095				**  should point at the canonical name -- but
1096				**  urges software to try again anyway.
1097				*/
1098
1099				goto cnameloop;
1100
1101			  default:
1102				/* not a record of interest */
1103				continue;
1104			}
1105		}
1106
1107		if (amatch)
1108		{
1109			/*
1110			**  Got a good match -- either an A, CNAME, or an
1111			**  exact MX record.  Save it and get out of here.
1112			*/
1113
1114			mxmatch = *dp;
1115			break;
1116		}
1117
1118		/*
1119		**  Nothing definitive yet.
1120		**	If this was a T_A query and we haven't yet found a MX
1121		**		match, try T_MX if allowed to do so.
1122		**	Otherwise, try the next domain.
1123		*/
1124
1125# if NETINET6
1126		if (qtype == T_AAAA)
1127			qtype = T_A;
1128		else
1129# endif /* NETINET6 */
1130		if (qtype == T_A && !gotmx && (trymx || **dp == '\0'))
1131			qtype = T_MX;
1132		else
1133		{
1134			qtype = initial;
1135			dp++;
1136		}
1137	}
1138
1139	/* if nothing was found, we are done */
1140	if (mxmatch == NULL)
1141	{
1142		if (*statp == EX_OK)
1143			*statp = EX_NOHOST;
1144		return false;
1145	}
1146
1147	/*
1148	**  Create canonical name and return.
1149	**  If saved domain name is null, name was already canonical.
1150	**  Otherwise append the saved domain name.
1151	*/
1152
1153	(void) sm_snprintf(nbuf, sizeof(nbuf), "%.*s%s%.*s", MAXDNAME, host,
1154			   *mxmatch == '\0' ? "" : ".",
1155			   MAXDNAME, mxmatch);
1156	(void) sm_strlcpy(host, nbuf, hbsize);
1157	if (tTd(8, 5))
1158		sm_dprintf("dns_getcanonname: %s\n", host);
1159	*statp = EX_OK;
1160
1161	/* return only one TTL entry, that should be sufficient */
1162	if (ttl > 0 && pttl != NULL)
1163		*pttl = ttl;
1164	return true;
1165}
1166#endif /* NAMED_BIND */
1167