xref: /illumos-gate/usr/src/cmd/sendmail/src/domain.c (revision fec46055)
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
18 SM_RCSID("@(#)$Id: domain.c,v 8.202 2006/12/19 01:15:07 ca Exp $ (with name server)")
19 #else /* NAMED_BIND */
20 SM_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 
41 typedef 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 
51 static 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 
80 static int	mxrand __P((char *));
81 static 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 
103 int NumFallbackMXHosts = 0;	/* Number of fallback MX hosts (after MX expansion) */
104 static char *fbhosts[MAXMXHOSTS + 1];
105 
106 int
getfallbackmxrr(host)107 getfallbackmxrr(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 
158 static int
fallbackmxrr(nmx,prefs,mxhosts)159 fallbackmxrr(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 
204 int
getmxrr(host,mxhosts,mxprefs,droplocalhost,rcode,tryfallback,pttl)205 getmxrr(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 	{
467 punt:
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 
607 static int
mxrand(host)608 mxrand(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 */
649 char *
bestmx_map_lookup(map,name,av,statp)650 bestmx_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 
784 bool
dns_getcanonname(host,hbsize,trymx,statp,pttl)785 dns_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;
836 cnameloop:
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 
945 nexttype:
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 
1045 # if NETINET6
1046 				/* FALLTHROUGH */
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