dns.c

/*
 * Copyright (c) 2008-2014, Simon Schubert <[email protected]>.
 * Copyright (c) 2008 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Simon Schubert <[email protected]>.
 *
 * 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. Neither the name of The DragonFly Project 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 */

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

#include "dma.h"

static int
sort_pref(const void *a, const void *b)
{
	const struct mx_hostentry *ha = a, *hb = b;
	int v;

	/* sort increasing by preference primarily */
	v = ha->pref - hb->pref;
	if (v != 0)
		return (v);

	/* sort PF_INET6 before PF_INET */
	v = - (ha->ai.ai_family - hb->ai.ai_family);
	return (v);
}

static int
add_host(int pref, const char *host, int port, struct mx_hostentry **he, size_t *ps)
{
	struct addrinfo hints, *res, *res0 = NULL;
	char servname[10];
	struct mx_hostentry *p;
	const int count_inc = 10;

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = PF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_protocol = IPPROTO_TCP;

	snprintf(servname, sizeof(servname), "%d", port);
	switch (getaddrinfo(host, servname, &hints, &res0)) {
	case 0:
		break;
	case EAI_AGAIN:
	case EAI_NONAME:
		/*
		 * EAI_NONAME gets returned for:
		 * SMARTHOST set but DNS server not reachable -> defer
		 * SMARTHOST set but DNS server returns "host does not exist"
		 *           -> buggy configuration
		 *           -> either defer or bounce would be ok -> defer
		 * MX entry was returned by DNS server but name doesn't resolve
		 *           -> hopefully transient situation -> defer
		 * all other DNS problems should have been caught earlier
		 * in dns_get_mx_list().
		 */
		goto out;
	default:
		return(-1);
	}

	for (res = res0; res != NULL; res = res->ai_next) {
		if (*ps + 1 >= roundup(*ps, count_inc)) {
			size_t newsz = roundup(*ps + 2, count_inc);
			*he = reallocf(*he, newsz * sizeof(**he));
			if (*he == NULL)
				goto out;
		}

		p = &(*he)[*ps];
		strlcpy(p->host, host, sizeof(p->host));
		p->pref = pref;
		p->ai = *res;
		p->ai.ai_addr = NULL;
		bcopy(res->ai_addr, &p->sa, p->ai.ai_addrlen);

		getnameinfo((struct sockaddr *)&p->sa, p->ai.ai_addrlen,
			    p->addr, sizeof(p->addr),
			    NULL, 0, NI_NUMERICHOST);

		(*ps)++;
	}
	freeaddrinfo(res0);

	return (0);

out:
	if (res0 != NULL)
		freeaddrinfo(res0);
	return (1);
}

int
dns_get_mx_list(const char *host, int port, struct mx_hostentry **he, int no_mx)
{
	char outname[MAXDNAME];
	ns_msg msg;
	ns_rr rr;
	const char *searchhost;
	const unsigned char *cp;
	unsigned char *ans;
	struct mx_hostentry *hosts = NULL;
	size_t nhosts = 0;
	size_t anssz;
	int pref;
	int cname_recurse;
	int have_mx = 0;
	int err;
	int i;

	res_init();
	searchhost = host;
	cname_recurse = 0;

	anssz = 65536;
	ans = malloc(anssz);
	if (ans == NULL)
		return (1);

	if (no_mx)
		goto out;

repeat:
	err = res_search(searchhost, ns_c_in, ns_t_mx, ans, anssz);
	if (err < 0) {
		switch (h_errno) {
		case NO_DATA:
			/*
			 * Host exists, but no MX (or CNAME) entry.
			 * Not an error, use host name instead.
			 */
			goto out;
		case TRY_AGAIN:
			/* transient error */
			goto transerr;
		case NO_RECOVERY:
		case HOST_NOT_FOUND:
		default:
			errno = ENOENT;
			goto err;
		}
	}

	if (!ns_initparse(ans, anssz, &msg))
		goto transerr;

	switch (ns_msg_getflag(msg, ns_f_rcode)) {
	case ns_r_noerror:
		break;
	case ns_r_nxdomain:
		goto err;
	default:
		goto transerr;
	}

	for (i = 0; i < ns_msg_count(msg, ns_s_an); i++) {
		if (ns_parserr(&msg, ns_s_an, i, &rr))
			goto transerr;

		cp = ns_rr_rdata(rr);

		switch (ns_rr_type(rr)) {
		case ns_t_mx:
			have_mx = 1;
			pref = ns_get16(cp);
			cp += 2;
			err = ns_name_uncompress(ns_msg_base(msg), ns_msg_end(msg),
						 cp, outname, sizeof(outname));
			if (err < 0)
				goto transerr;

			err = add_host(pref, outname, port, &hosts, &nhosts);
			if (err == -1)
				goto err;
			break;

		case ns_t_cname:
			err = ns_name_uncompress(ns_msg_base(msg), ns_msg_end(msg),
						 cp, outname, sizeof(outname));
			if (err < 0)
				goto transerr;

			/* Prevent a CNAME loop */
			if (cname_recurse++ > 10)
				goto err;

			searchhost = outname;
			goto repeat;

		default:
			break;
		}
	}

out:
	err = 0;
	if (0) {
transerr:
		if (nhosts == 0)
			err = 1;
	}
	if (0) {
err:
		err = -1;
	}

	free(ans);

	if (err == 0) {
		if (!have_mx) {
			/*
			 * If we didn't find any MX, use the hostname instead.
			 */
			err = add_host(0, host, port, &hosts, &nhosts);
		} else if (nhosts == 0) {
			/*
			 * We did get MX, but couldn't resolve any of them
			 * due to transient errors.
			 */
			err = 1;
		}
	}

	if (nhosts > 0) {
		qsort(hosts, nhosts, sizeof(*hosts), sort_pref);
		/* terminate list */
		*hosts[nhosts].host = 0;
	} else {
		if (hosts != NULL)
			free(hosts);
		hosts = NULL;
	}

	*he = hosts;
	return (err);
}

#if defined(TESTING)
int
main(int argc, char **argv)
{
	struct mx_hostentry *he, *p;
	int err;

	err = dns_get_mx_list(argv[1], 53, &he, 0);
	if (err)
		return (err);

	for (p = he; *p->host != 0; p++) {
		printf("%d\t%s\t%s\n", p->pref, p->host, p->addr);
	}

	return (0);
}
#endif