domain.c

< linux网络编程工具>>配套源码

/*
 * Copyright (c) 1998-2000 Sendmail, Inc. and its suppliers.
 *	All rights reserved.
 * Copyright (c) 1986, 1995-1997 Eric P. Allman.  All rights reserved.
 * Copyright (c) 1988, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * By using this file, you agree to the terms and conditions set
 * forth in the LICENSE file which can be found at the top level of
 * the sendmail distribution.
 *
 */

#include <sendmail.h>

#ifndef lint
# if NAMED_BIND
static char id[] = "@(#)$Id: domain.c,v 8.114.6.1.2.3 2000/06/13 18:00:08 gshapiro Exp $ (with name server)";
# else /* NAMED_BIND */
static char id[] = "@(#)$Id: domain.c,v 8.114.6.1.2.3 2000/06/13 18:00:08 gshapiro Exp $ (without name server)";
# endif /* NAMED_BIND */
#endif /* ! lint */


#if NAMED_BIND

# include <arpa/inet.h>

/*
**  The standard udp packet size PACKETSZ (512) is not sufficient for some
**  nameserver answers containing very many resource records. The resolver
**  may switch to tcp and retry if it detects udp packet overflow.
**  Also note that the resolver routines res_query and res_search return
**  the size of the *un*truncated answer in case the supplied answer buffer
**  it not big enough to accommodate the entire answer.
*/

# ifndef MAXPACKET
#  define MAXPACKET 8192	/* max packet size used internally by BIND */
# endif /* ! MAXPACKET */

typedef union
{
	HEADER	qb1;
	u_char	qb2[MAXPACKET];
} querybuf;

# ifndef MXHOSTBUFSIZE
#  define MXHOSTBUFSIZE	(128 * MAXMXHOSTS)
# endif /* ! MXHOSTBUFSIZE */

static char	MXHostBuf[MXHOSTBUFSIZE];

# ifndef MAXDNSRCH
#  define MAXDNSRCH	6	/* number of possible domains to search */
# endif /* ! MAXDNSRCH */

# ifndef RES_DNSRCH_VARIABLE
#  define RES_DNSRCH_VARIABLE	_res.dnsrch
# endif /* ! RES_DNSRCH_VARIABLE */

# ifndef MAX
#  define MAX(a, b)	((a) > (b) ? (a) : (b))
# endif /* ! MAX */

# ifndef NO_DATA
#  define NO_DATA	NO_ADDRESS
# endif /* ! NO_DATA */

# ifndef HFIXEDSZ
#  define HFIXEDSZ	12	/* sizeof(HEADER) */
# endif /* ! HFIXEDSZ */

# define MAXCNAMEDEPTH	10	/* maximum depth of CNAME recursion */

# if defined(__RES) && (__RES >= 19940415)
#  define RES_UNC_T	char *
# else /* defined(__RES) && (__RES >= 19940415) */
#  define RES_UNC_T	u_char *
# endif /* defined(__RES) && (__RES >= 19940415) */

static char	*gethostalias __P((char *));
static int	mxrand __P((char *));

/*
**  GETMXRR -- get MX resource records for a domain
**
**	Parameters:
**		host -- the name of the host to MX.
**		mxhosts -- a pointer to a return buffer of MX records.
**		mxprefs -- a pointer to a return buffer of MX preferences.
**			If NULL, don't try to populate.
**		droplocalhost -- If TRUE, all MX records less preferred
**			than the local host (as determined by $=w) will
**			be discarded.
**		rcode -- a pointer to an EX_ status code.
**
**	Returns:
**		The number of MX records found.
**		-1 if there is an internal failure.
**		If no MX records are found, mxhosts[0] is set to host
**			and 1 is returned.
*/

int
getmxrr(host, mxhosts, mxprefs, droplocalhost, rcode)
	char *host;
	char **mxhosts;
	u_short *mxprefs;
	bool droplocalhost;
	int *rcode;
{
	register u_char *eom, *cp;
	register int i, j, n;
	int nmx = 0;
	register char *bp;
	HEADER *hp;
	querybuf answer;
	int ancount, qdcount, buflen;
	bool seenlocal = FALSE;
	u_short pref, type;
	u_short localpref = 256;
	char *fallbackMX = FallBackMX;
	bool trycanon = FALSE;
	u_short *prefs;
	int (*resfunc)();
	u_short prefer[MAXMXHOSTS];
	int weight[MAXMXHOSTS];
	extern int res_query(), res_search();

	if (tTd(8, 2))
		dprintf("getmxrr(%s, droplocalhost=%d)\n",
			host, droplocalhost);

	if (fallbackMX != NULL && droplocalhost &&
	    wordinclass(fallbackMX, 'w'))
	{
		/* don't use fallback for this pass */
		fallbackMX = NULL;
	}

	*rcode = EX_OK;

	if (mxprefs != NULL)
		prefs = mxprefs;
	else
		prefs = prefer;


	/* efficiency hack -- numeric or non-MX lookups */
	if (host[0] == '[')
		goto punt;

	/*
	**  If we don't have MX records in our host switch, don't
	**  try for MX records.  Note that this really isn't "right",
	**  since we might be set up to try NIS first and then DNS;
	**  if the host is found in NIS we really shouldn't be doing
	**  MX lookups.  However, that should be a degenerate case.
	*/

	if (!UseNameServer)
		goto punt;
	if (HasWildcardMX && ConfigLevel >= 6)
		resfunc = res_query;
	else
		resfunc = res_search;

	errno = 0;
	n = (*resfunc)(host, C_IN, T_MX, (u_char *) &answer, sizeof(answer));
	if (n < 0)
	{
		if (tTd(8, 1))
			dprintf("getmxrr: res_search(%s) failed (errno=%d, h_errno=%d)\n",
			    (host == NULL) ? "<NULL>" : host, errno, h_errno);
		switch (h_errno)
		{
		  case NO_DATA:
			trycanon = TRUE;
			/* FALLTHROUGH */

		  case NO_RECOVERY:
			/* no MX data on this host */
			goto punt;

		  case HOST_NOT_FOUND:
# if BROKEN_RES_SEARCH
		  case 0:	/* Ultrix resolver retns failure w/ h_errno=0 */
# endif /* BROKEN_RES_SEARCH */
			/* host doesn't exist in DNS; might be in /etc/hosts */
			trycanon = TRUE;
			*rcode = EX_NOHOST;
			goto punt;

		  case TRY_AGAIN:
		  case -1:
			/* couldn't connect to the name server */
			if (fallbackMX != NULL)
			{
				/* name server is hosed -- push to fallback */
				if (nmx > 0)
					prefs[nmx] = prefs[nmx - 1] + 1;
				else
					prefs[nmx] = 0;
				mxhosts[nmx++] = fallbackMX;
				return nmx;
			}
			/* it might come up later; better queue it up */
			*rcode = EX_TEMPFAIL;
			break;

		  default:
			syserr("getmxrr: res_search (%s) failed with impossible h_errno (%d)\n",
				host, h_errno);
			*rcode = EX_OSERR;
			break;
		}

		/* irreconcilable differences */
		return -1;
	}

	/* avoid problems after truncation in tcp packets */
	if (n > sizeof(answer))
		n = sizeof(answer);

	/* find first satisfactory answer */
	hp = (HEADER *)&answer;
	cp = (u_char *)&answer + HFIXEDSZ;
	eom = (u_char *)&answer + n;
	for (qdcount = ntohs((u_short)hp->qdcount);
	     qdcount--;
	     cp += n + QFIXEDSZ)
	{
		if ((n = dn_skipname(cp, eom)) < 0)
			goto punt;
	}
	buflen = sizeof(MXHostBuf) - 1;
	bp = MXHostBuf;
	ancount = ntohs((u_short)hp->ancount);
	while (--ancount >= 0 && cp < eom && nmx < MAXMXHOSTS - 1)
	{
		if ((n = dn_expand((u_char *)&answer,
		    eom, cp, (RES_UNC_T) bp, buflen)) < 0)
			break;
		cp += n;
		GETSHORT(type, cp);
		cp += INT16SZ + INT32SZ;
		GETSHORT(n, cp);
		if (type != T_MX)
		{
			if (tTd(8, 8) || _res.options & RES_DEBUG)
				dprintf("unexpected answer type %d, size %d\n",
					type, n);
			cp += n;
			continue;
		}
		GETSHORT(pref, cp);
		if ((n = dn_expand((u_char *)&answer, eom, cp,
				   (RES_UNC_T) bp, buflen)) < 0)
			break;
		cp += n;
		if (wordinclass(bp, 'w'))
		{
			if (tTd(8, 3))
				dprintf("found localhost (%s) in MX list, pref=%d\n",
					bp, pref);
			if (droplocalhost)
			{
				if (!seenlocal || pref < localpref)
					localpref = pref;
				seenlocal = TRUE;
				continue;
			}
			weight[nmx] = 0;
		}
		else
			weight[nmx] = mxrand(bp);
		prefs[nmx] = pref;
		mxhosts[nmx++] = bp;
		n = strlen(bp);
		bp += n;
		if (bp[-1] != '.')
		{
			*bp++ = '.';
			n++;
		}
		*bp++ = '\0';
		buflen -= n + 1;
	}

	/* sort the records */
	for (i = 0; i < nmx; i++)
	{
		for (j = i + 1; j < nmx; j++)
		{
			if (prefs[i] > prefs[j] ||
			    (prefs[i] == prefs[j] && weight[i] > weight[j]))
			{
				register int temp;
				register char *temp1;

				temp = prefs[i];
				prefs[i] = prefs[j];
				prefs[j] = temp;
				temp1 = mxhosts[i];
				mxhosts[i] = mxhosts[j];
				mxhosts[j] = temp1;
				temp = weight[i];
				weight[i] = weight[j];
				weight[j] = temp;
			}
		}
		if (seenlocal && prefs[i] >= localpref)
		{
			/* truncate higher preference part of list */
			nmx = i;
		}
	}

	/* delete duplicates from list (yes, some bozos have duplicates) */
	for (i = 0; i < nmx - 1; )
	{
		if (strcasecmp(mxhosts[i], mxhosts[i + 1]) != 0)
			i++;
		else
		{
			/* compress out duplicate */
			for (j = i + 1; j < nmx; j++)
			{
				mxhosts[j] = mxhosts[j + 1];
				prefs[j] = prefs[j + 1];
			}
			nmx--;
		}
	}

	if (nmx == 0)
	{
punt:
		if (seenlocal)
		{
			struct hostent *h = NULL;

			/*
			**  If we have deleted all MX entries, this is
			**  an error -- we should NEVER send to a host that
			**  has an MX, and this should have been caught
			**  earlier in the config file.
			**
			**  Some sites prefer to go ahead and try the
			**  A record anyway; that case is handled by
			**  setting TryNullMXList.  I believe this is a
			**  bad idea, but it's up to you....
			*/

			if (TryNullMXList)
			{
				h_errno = 0;
				errno = 0;
				h = sm_gethostbyname(host, AF_INET);
				if (h == NULL)
				{
					if (errno == ETIMEDOUT ||
					    h_errno == TRY_AGAIN ||
					    (errno == ECONNREFUSED &&
					     UseNameServer))
					{
						*rcode = EX_TEMPFAIL;
						return -1;
					}
# if NETINET6
					h_errno = 0;
					errno = 0;
					h = sm_gethostbyname(host, AF_INET6);
					if (h == NULL &&
					    (errno == ETIMEDOUT ||
					     h_errno == TRY_AGAIN ||
					     (errno == ECONNREFUSED &&
					      UseNameServer)))
					{
						*rcode = EX_TEMPFAIL;
						return -1;
					}
# endif /* NETINET6 */
				}
			}

			if (h == NULL)
			{
				*rcode = EX_CONFIG;
				syserr("MX list for %s points back to %s",
				       host, MyHostName);
				return -1;
			}
		}
		if (strlen(host) >= (SIZE_T) sizeof MXHostBuf)
		{
			*rcode = EX_CONFIG;
			syserr("Host name %s too long",
			       shortenstring(host, MAXSHORTSTR));
			return -1;
		}
		snprintf(MXHostBuf, sizeof MXHostBuf, "%s", host);
		mxhosts[0] = MXHostBuf;
		prefs[0] = 0;
		if (host[0] == '[')
		{
			register char *p;
# if NETINET6
			struct sockaddr_in6 tmp6;
# endif /* NETINET6 */

			/* this may be an MX suppression-style address */
			p = strchr(MXHostBuf, ']');
			if (p != NULL)
			{
				*p = '\0';

				if (inet_addr(&MXHostBuf[1]) != INADDR_NONE)
				{
					nmx++;
					*p = ']';
				}
# if NETINET6
				else if (inet_pton(AF_INET6, &MXHostBuf[1],
						   &tmp6.sin6_addr) == 1)
				{
					nmx++;
					*p = ']';
				}
# endif /* NETINET6 */
				else
				{
					trycanon = TRUE;
					mxhosts[0]++;
				}
			}
		}
		if (trycanon &&
		    getcanonname(mxhosts[0], sizeof MXHostBuf - 2, FALSE))
		{
			bp = &MXHostBuf[strlen(MXHostBuf)];
			if (bp[-1] != '.')
			{
				*bp++ = '.';
				*bp = '\0';
			}
			nmx = 1;
		}
	}

	/* if we have a default lowest preference, include that */
	if (fallbackMX != NULL && !seenlocal)
	{
		if (nmx > 0)
			prefs[nmx] = prefs[nmx - 1] + 1;
		else
			prefs[nmx] = 0;
		mxhosts[nmx++] = fallbackMX;
	}

	return nmx;
}
/*
**  MXRAND -- create a randomizer for equal MX preferences
**
**	If two MX hosts have equal preferences we want to randomize
**	the selection.  But in order for signatures to be the same,
**	we need to randomize the same way each time.  This function
**	computes a pseudo-random hash function from the host name.
**
**	Parameters:
**		host -- the name of the host.
**
**	Returns:
**		A random but repeatable value based on the host name.
**
**	Side Effects:
**		none.
*/

static int
mxrand(host)
	register char *host;
{
	int hfunc;
	static unsigned int seed;

	if (seed == 0)
	{
		seed = (int) curtime() & 0xffff;
		if (seed == 0)
			seed++;
	}

	if (tTd(17, 9))
		dprintf("mxrand(%s)", host);

	hfunc = seed;
	while (*host != '\0')
	{
		int c = *host++;

		if (isascii(c) && isupper(c))
			c = tolower(c);
		hfunc = ((hfunc << 1) ^ c) % 2003;
	}

	hfunc &= 0xff;
	hfunc++;

	if (tTd(17, 9))
		dprintf(" = %d\n", hfunc);
	return hfunc;
}
/*
**  BESTMX -- find the best MX for a name
**
**	This is really a hack, but I don't see any obvious way
**	to generalize it at the moment.
*/

/* ARGSUSED3 */
char *