File:  [DragonFly] / src / lib / libc / net / res_query.c
Revision 1.3: download - view: text, annotated - select for diffs
Tue Apr 13 21:53:43 2004 UTC (10 years, 4 months ago) by dillon
Branches: MAIN
CVS tags: HEAD, DragonFly_Snap29Sep2004, DragonFly_Snap13Sep2004, DragonFly_1_0_REL, DragonFly_1_0_RC1, DragonFly_1_0A_REL
res_search only incremented got_servfail for h_errno == TRY_AGAIN *AND*
hp->rcode == SERVFAIL.  However, there are cases such as timeouts where
rcode is not always set to SERVFAIL.  This leads to inconsistent nameserver
operation during multi-domain and truncated dot searches, especially during
booting when portions of the network are being brought up simultanious with
dns lookups.

This patch attempts to correct the problem by unconditionally terminating
the search if TRY_AGAIN is returned (after res_query has gone through all
retries and name servers) instead of trying other domain elements in the
domain seach path.

This patch should fix reported problems (which I can reproduce) with some
NFS mounts failing during boot.  This occured because mount_nfs thought the
host name lookup returned a definitive failure using a non-dotted host name
when, in fact, it timed out on the first part (host.search.domain.name) and
got a definitive host-not-found response on the second part (host.).

Generally speaking, search path name server timeouts can exceed 60 seconds
per element and most machines which consistently timeout on earlier portions
of a search path are effectively non-operational due to the imposed delays.
It is more important for DNS lookups to return the proper error code then
to be able to recover a valid lookup in later portions of the search path
in these situations.

/*
 * Copyright (c) 1988, 1993
 *    The Regents of the University of California.  All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * 	This product includes software developed by the University of
 * 	California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * @(#)res_query.c	8.1 (Berkeley) 6/4/93
 * $From: Id: res_query.c,v 8.14 1997/06/09 17:47:05 halley Exp $
 * $FreeBSD: src/lib/libc/net/res_query.c,v 1.19.2.2 2002/07/07 11:34:42 robert Exp $
 * $DragonFly: src/lib/libc/net/res_query.c,v 1.3 2004/04/13 21:53:43 dillon Exp $
 */

/*
 * Portions Copyright (c) 1993 by Digital Equipment Corporation.
 * 
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies, and that
 * the name of Digital Equipment Corporation not be used in advertising or
 * publicity pertaining to distribution of the document or software without
 * specific, written prior permission.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
 * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Portions Copyright (c) 1996 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <ctype.h>
#include <errno.h>
#include <netdb.h>
#include <resolv.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "res_config.h"

#if PACKETSZ > 1024
#define MAXPACKET	PACKETSZ
#else
#define MAXPACKET	1024
#endif

/*
 * Formulate a normal query, send, and await answer.
 * Returned answer is placed in supplied buffer "answer".
 * Perform preliminary check of answer, returning success only
 * if no error is indicated and the answer count is nonzero.
 * Return the size of the response on success, -1 on error.
 * Error number is left in h_errno.
 *
 * Caller must parse answer and determine whether it answers the question.
 */
int
res_query(name, class, type, answer, anslen)
	const char *name;	/* domain name */
	int class, type;	/* class and type of query */
	u_char *answer;		/* buffer to put answer */
	int anslen;		/* size of answer buffer */
{
	u_char buf[MAXPACKET];
	HEADER *hp = (HEADER *) answer;
	int n;

	hp->rcode = NOERROR;	/* default */

	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
		h_errno = NETDB_INTERNAL;
		return (-1);
	}
#ifdef DEBUG
	if (_res.options & RES_DEBUG)
		printf(";; res_query(%s, %d, %d)\n", name, class, type);
#endif

	n = res_mkquery(QUERY, name, class, type, NULL, 0, NULL,
			buf, sizeof(buf));
	if (n > 0 && (_res.options & RES_USE_EDNS0) != 0)
		n = res_opt(n, buf, sizeof(buf), anslen);
	if (n <= 0) {
#ifdef DEBUG
		if (_res.options & RES_DEBUG)
			printf(";; res_query: mkquery failed\n");
#endif
		h_errno = NO_RECOVERY;
		return (n);
	}
	n = res_send(buf, n, answer, anslen);
	if (n < 0) {
#ifdef DEBUG
		if (_res.options & RES_DEBUG)
			printf(";; res_query: send error\n");
#endif
		h_errno = TRY_AGAIN;
		return (n);
	}

	if (hp->rcode != NOERROR || ntohs(hp->ancount) == 0) {
#ifdef DEBUG
		if (_res.options & RES_DEBUG)
			printf(";; rcode = %d, ancount=%d\n", hp->rcode,
			    ntohs(hp->ancount));
#endif
		switch (hp->rcode) {
		case NXDOMAIN:
			h_errno = HOST_NOT_FOUND;
			break;
		case SERVFAIL:
			h_errno = TRY_AGAIN;
			break;
		case NOERROR:
			h_errno = NO_DATA;
			break;
		case FORMERR:
		case NOTIMP:
		case REFUSED:
		default:
			h_errno = NO_RECOVERY;
			break;
		}
		return (-1);
	}
	return (n);
}

/*
 * Formulate a normal query, send, and retrieve answer in supplied buffer.
 * Return the size of the response on success, -1 on error.
 * If enabled, implement search rules until answer or unrecoverable failure
 * is detected.  Error code, if any, is left in h_errno.
 */
int
res_search(name, class, type, answer, anslen)
	const char *name;	/* domain name */
	int class, type;	/* class and type of query */
	u_char *answer;		/* buffer to put answer */
	int anslen;		/* size of answer */
{
	const char *cp, * const *domain;
	HEADER *hp = (HEADER *) answer;
	u_int dots;
	int trailing_dot, ret, saved_herrno;
	int got_nodata = 0, got_servfail = 0, tried_as_is = 0;

	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
		h_errno = NETDB_INTERNAL;
		return (-1);
	}
	errno = 0;
	h_errno = HOST_NOT_FOUND;	/* default, if we never query */
	dots = 0;
	for (cp = name; *cp; cp++)
		dots += (*cp == '.');
	trailing_dot = 0;
	if (cp > name && *--cp == '.')
		trailing_dot++;

	/* If there aren't any dots, it could be a user-level alias */
	if (!dots && (cp = hostalias(name)) != NULL)
		return (res_query(cp, class, type, answer, anslen));

	/*
	 * If there are dots in the name already, let's just give it a try
	 * 'as is'.  The threshold can be set with the "ndots" option.
	 */
	saved_herrno = -1;
	if (dots >= _res.ndots) {
		ret = res_querydomain(name, NULL, class, type, answer, anslen);
		if (ret > 0)
			return (ret);
		saved_herrno = h_errno;
		tried_as_is++;
	}

	/*
	 * We do at least one level of search if
	 *	- there is no dot and RES_DEFNAME is set, or
	 *	- there is at least one dot, there is no trailing dot,
	 *	  and RES_DNSRCH is set.
	 */
	if ((!dots && (_res.options & RES_DEFNAMES)) ||
	    (dots && !trailing_dot && (_res.options & RES_DNSRCH))) {
		int done = 0;

		for (domain = (const char * const *)_res.dnsrch;
		     *domain && !done;
		     domain++) {

			ret = res_querydomain(name, *domain, class, type,
					      answer, anslen);
			if (ret > 0)
				return (ret);

			/*
			 * If no server present, give up.
			 * If name isn't found in this domain,
			 * keep trying higher domains in the search list
			 * (if that's enabled).
			 * On a NO_DATA error, keep trying, otherwise
			 * a wildcard entry of another type could keep us
			 * from finding this entry higher in the domain.
			 * If we get some other error (negative answer or
			 * server failure), then stop searching up,
			 * but try the input name below in case it's
			 * fully-qualified.
			 */
			if (errno == ECONNREFUSED) {
				h_errno = TRY_AGAIN;
				return (-1);
			}

			switch (h_errno) {
			case NO_DATA:
				got_nodata++;
				/* FALLTHROUGH */
			case HOST_NOT_FOUND:
				/* keep trying */
				break;
			case TRY_AGAIN:
				/*
				 * This can occur due to a server failure
				 * (that is, all listed servers have failed),
				 * or all listed servers have timed out.
				 * hp->rcode may not be set to SERVFAIL in the
				 * case of a timeout.
				 *
				 * Either way we must terminate the search
				 * and return TRY_AGAIN in order to avoid
				 * non-deterministic return codes.  For
				 * example, loaded name servers or races
				 * against network startup/validation (dhcp,
				 * ppp, etc) can cause the search to timeout
				 * on one search element, e.g. 'fu.bar.com',
				 * and return a definitive failure on the
				 * next search element, e.g. 'fu.'.
				 */
				++got_servfail;
				/* FALLTHROUGH */
			default:
				/* anything else implies that we're done */
				done++;
			}

			/* if we got here for some reason other than DNSRCH,
			 * we only wanted one iteration of the loop, so stop.
			 */
			if (!(_res.options & RES_DNSRCH))
				done++;
		}
	}

	/*
	 * If we have not already tried the name "as is", do that now.
	 * note that we do this regardless of how many dots were in the
	 * name or whether it ends with a dot unless NOTLDQUERY is set.
	 */
	if (!tried_as_is && (dots || !(_res.options & RES_NOTLDQUERY))) {
		ret = res_querydomain(name, NULL, class, type, answer, anslen);
		if (ret > 0)
			return (ret);
	}

	/* if we got here, we didn't satisfy the search.
	 * if we did an initial full query, return that query's h_errno
	 * (note that we wouldn't be here if that query had succeeded).
	 * else if we ever got a nodata, send that back as the reason.
	 * else send back meaningless h_errno, that being the one from
	 * the last DNSRCH we did.
	 */
	if (saved_herrno != -1)
		h_errno = saved_herrno;
	else if (got_nodata)
		h_errno = NO_DATA;
	else if (got_servfail)
		h_errno = TRY_AGAIN;
	return (-1);
}

/*
 * Perform a call on res_query on the concatenation of name and domain,
 * removing a trailing dot from name if domain is NULL.
 */
int
res_querydomain(name, domain, class, type, answer, anslen)
	const char *name, *domain;
	int class, type;	/* class and type of query */
	u_char *answer;		/* buffer to put answer */
	int anslen;		/* size of answer */
{
	char nbuf[MAXDNAME];
	const char *longname = nbuf;
	int n, d;

	if ((_res.options & RES_INIT) == 0 && res_init() == -1) {
		h_errno = NETDB_INTERNAL;
		return (-1);
	}
#ifdef DEBUG
	if (_res.options & RES_DEBUG)
		printf(";; res_querydomain(%s, %s, %d, %d)\n",
		       name, domain?domain:"<Nil>", class, type);
#endif
	if (domain == NULL) {
		/*
		 * Check for trailing '.';
		 * copy without '.' if present.
		 */
		n = strlen(name);
		if (n >= MAXDNAME) {
			h_errno = NO_RECOVERY;
			return (-1);
		}
		n--;
		if (n >= 0 && name[n] == '.') {
			strncpy(nbuf, name, n);
			nbuf[n] = '\0';
		} else
			longname = name;
	} else {
		n = strlen(name);
		d = strlen(domain);
		if (n + d + 1 >= MAXDNAME) {
			h_errno = NO_RECOVERY;
			return (-1);
		}
		sprintf(nbuf, "%s.%s", name, domain);
	}
	return (res_query(longname, class, type, answer, anslen));
}

const char *
hostalias(name)
	const char *name;
{
	register char *cp1, *cp2;
	FILE *fp;
	char *file;
	char buf[BUFSIZ];
	static char abuf[MAXDNAME];

	if (_res.options & RES_NOALIASES)
		return (NULL);
	if (issetugid())
		return (NULL);
	file = getenv("HOSTALIASES");
	if (file == NULL || (fp = fopen(file, "r")) == NULL)
		return (NULL);
	setbuf(fp, NULL);
	buf[sizeof(buf) - 1] = '\0';
	while (fgets(buf, sizeof(buf), fp)) {
		for (cp1 = buf; *cp1 && !isspace((unsigned char)*cp1); ++cp1)
			;
		if (!*cp1)
			break;
		*cp1 = '\0';
		if (!strcasecmp(buf, name)) {
			while (isspace((unsigned char)*++cp1))
				;
			if (!*cp1)
				break;
			for (cp2 = cp1 + 1; *cp2 && !isspace((unsigned char)*cp2); ++cp2)
				;
			abuf[sizeof(abuf) - 1] = *cp2 = '\0';
			strncpy(abuf, cp1, sizeof(abuf) - 1);
			fclose(fp);
			return (abuf);
		}
	}
	fclose(fp);
	return (NULL);
}

/*
 * Weak aliases for applications that use certain private entry points,
 * and fail to include <resolv.h>.
 */
#undef res_query
__weak_reference(__res_query, res_query);
#undef res_search
__weak_reference(__res_search, res_search);
#undef res_querydomain
__weak_reference(__res_querydomain, res_querydomain);