/*	$OpenBSD: dns.c,v 1.63 2012/11/24 14:01:51 eric Exp $	*/

/*
 * Copyright (c) 2008 Gilles Chehade <gilles@openbsd.org>
 * Copyright (c) 2009 Jacek Masiulaniec <jacekm@dobremiasto.net>
 * Copyright (c) 2011 Eric Faurot <eric@faurot.net>
 *
 * 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 THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR 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/socket.h>
#include <sys/tree.h>
#include <sys/queue.h>
#include <sys/uio.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

#include <event.h>
#include <imsg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "asr.h"
#include "asr_private.h"
#include "smtpd.h"
#include "log.h"


struct mx {
	TAILQ_ENTRY(mx)	 entry;
	char		*host;
	int		 preference;
};

struct dnssession {
	uint64_t			 id;
	struct dns			 query;
	struct event			 ev;
	struct async			*as;
	int				 preference;
	size_t				 mxfound;
	TAILQ_HEAD(, mx)		 mx;
};

static struct dnssession *dnssession_init(struct dns *);
static void dnssession_destroy(struct dnssession *);
static void dnssession_mx_insert(struct dnssession *, const char *, int);
static void dns_asr_event_set(struct dnssession *, struct async_res *);
static void dns_asr_handler(int, short, void *);
static int  dns_asr_error(int);
static void dns_asr_dispatch_host(struct dnssession *);
static void dns_asr_dispatch_mx(struct dnssession *);
static void dns_asr_dispatch_cname(struct dnssession *);
static void dns_reply(struct dns *, int);

#define print_dname(a,b,c) asr_strdname(a, b, c)

/*
 * User interface.
 */

void
dns_query_host(char *host, int port, uint64_t id)
{
	struct dns	 query;

	bzero(&query, sizeof(query));
	strlcpy(query.host, host, sizeof(query.host));
	query.port = port;
	query.id = id;

	imsg_compose_event(env->sc_ievs[PROC_LKA], IMSG_DNS_HOST, 0, 0, -1,
	    &query, sizeof(query));
}

void
dns_query_mx(char *host, char *backup, int port, uint64_t id)
{
	struct dns	 query;

	bzero(&query, sizeof(query));
	strlcpy(query.host, host, sizeof(query.host));
	if (backup)
		strlcpy(query.backup, backup, sizeof(query.backup));
	query.port = port;
	query.id = id;

	imsg_compose_event(env->sc_ievs[PROC_LKA], IMSG_DNS_MX, 0, 0, -1,
	    &query, sizeof(query));
}

void
dns_query_ptr(struct sockaddr_storage *ss, uint64_t id)
{
	struct dns	 query;

	bzero(&query, sizeof(query));
	query.ss = *ss;
	query.id = id;

	imsg_compose_event(env->sc_ievs[PROC_LKA], IMSG_DNS_PTR, 0, 0, -1,
	    &query, sizeof(query));
}

/* LKA interface */
void
dns_async(struct imsgev *asker, int type, struct dns *query)
{
	struct dnssession *s;

	query->type  = type;
	query->asker = asker;
	s = dnssession_init(query);

	switch (type) {
	case IMSG_DNS_HOST:
		log_debug("debug: dns: lookup host \"%s\"", query->host);
		if (sockaddr_from_str((struct sockaddr*)&query->ss, PF_UNSPEC,
		    query->host) == 0) {
			log_debug("debug: dns:  \"%s\" is an IP address",
			    query->host);
			query->error = DNS_OK;
			dns_reply(query, IMSG_DNS_HOST);
			dns_reply(query, IMSG_DNS_HOST_END);
			dnssession_destroy(s);
			return;
		}
		dnssession_mx_insert(s, query->host, 0);
		stat_increment("lka.session.host", 1);
		query->error = DNS_ENOTFOUND; /* override later */
		dns_asr_dispatch_host(s);
		return;
	case IMSG_DNS_PTR:
		s->as = getnameinfo_async((struct sockaddr*)&query->ss,
		    query->ss.ss_len,
		    s->query.host, sizeof(s->query.host), NULL, 0, 0, NULL);
		stat_increment("lka.session.cname", 1);
		if (s->as == NULL) {
			log_debug("debug: dns_async: asr_query_cname error");
			break;
		}
		dns_asr_dispatch_cname(s);
		return;
	case IMSG_DNS_MX:
		log_debug("debug: dns: lookup mx \"%s\"", query->host);
		s->as = res_query_async(query->host, C_IN, T_MX, NULL, 0, NULL);
		stat_increment("lka.session.mx", 1);
		if (s->as == NULL) {
			log_debug("debug: dns_async: asr_query_dns error");
			break;
		}
		dns_asr_dispatch_mx(s);
		return;
	default:
		log_debug("debug: dns_async: bad request");
		break;
	}

	stat_increment("lka.failure", 1);
	dnssession_destroy(s);
}

static void
dns_reply(struct dns *query, int type)
{
	imsg_compose_event(query->asker, type, 0, 0, -1, query, sizeof(*query));
}

static void
dns_asr_event_set(struct dnssession *s, struct async_res *ar)
{
	struct timeval tv = { 0, 0 };

	tv.tv_usec = ar->ar_timeout * 1000;
	event_set(&s->ev, ar->ar_fd,
	    ar->ar_cond == ASYNC_READ ? EV_READ : EV_WRITE, dns_asr_handler, s);
	event_add(&s->ev, &tv);
}

static void
dns_asr_handler(int fd, short event, void *arg)
{
	struct dnssession *s = arg;

	switch (s->query.type) {
	case IMSG_DNS_HOST:
		dns_asr_dispatch_host(s);
		break;
	case IMSG_DNS_PTR:
		dns_asr_dispatch_cname(s);
		break;
	case IMSG_DNS_MX:
		dns_asr_dispatch_mx(s);
		break;
	default:
		fatalx("bad query type");
	}
}

static int
dns_asr_error(int ar_err)
{
	switch (ar_err) {
	case 0:
		return DNS_OK;
	case NO_DATA:
	case NO_RECOVERY:
		stat_increment("lka.failure", 1);
		return DNS_EINVAL;
	default:
		return DNS_RETRY;
	}
}

static void
dns_asr_dispatch_mx(struct dnssession *s)
{
	struct dns		*query = &s->query;
	struct async_res	 ar;
	struct unpack		 pack;
	struct header		 h;
	struct query		 q;
	struct rr		 rr;
	char			 buf[512];

	if (async_run(s->as, &ar) == ASYNC_COND) {
		dns_asr_event_set(s, &ar);
		return;
	}

	if (ar.ar_h_errno && ar.ar_h_errno != NO_DATA) {
		query->error = ar.ar_rcode == NXDOMAIN ? \
			DNS_ENONAME : dns_asr_error(ar.ar_h_errno);
		dns_reply(query, IMSG_DNS_HOST_END);
		dnssession_destroy(s);
		free(ar.ar_data);
		return;
	}

	unpack_init(&pack, ar.ar_data, ar.ar_datalen);
	unpack_header(&pack, &h);
	unpack_query(&pack, &q);

	for (; h.ancount; h.ancount--) {
		unpack_rr(&pack, &rr);
		if (rr.rr_type != T_MX)
			continue;
		print_dname(rr.rr.mx.exchange, buf, sizeof(buf));
		buf[strlen(buf) - 1] = '\0';
		dnssession_mx_insert(s, buf, rr.rr.mx.preference);
	}

	free(ar.ar_data);

	/* fallback to host if no MX is found. */
	if (TAILQ_EMPTY(&s->mx))
		dnssession_mx_insert(s, query->host, 0);

	/* Now we have a sorted list of MX to resolve. Simply "turn" this
	 * MX session into a regular host session.
	 */
	s->as = NULL;
	s->query.type = IMSG_DNS_HOST;
	s->query.error = DNS_ENOTFOUND; /* override later */
	dns_asr_dispatch_host(s);
}

static void
dns_asr_dispatch_host(struct dnssession *s)
{
	struct dns		*query = &s->query;
	struct mx		*mx;
	struct async_res	 ar;
	struct addrinfo		 hints, *ai;

next:
	/* query all listed hosts in turn */
	while (s->as == NULL) {

		mx = TAILQ_FIRST(&s->mx);
		if (mx == NULL || (s->preference != -1
		    && s->preference <= mx->preference)) {
			if (mx)
				log_debug("debug: dns: ignoring mx with < pri");
			if (s->mxfound)
				query->error = DNS_OK;
			dns_reply(query, IMSG_DNS_HOST_END);
			dnssession_destroy(s);
			return;
		}

		log_debug("debug: dns: resolving address for \"%s\"", mx->host);

		memset(&hints, 0, sizeof(hints));
		hints.ai_family = PF_UNSPEC;
		hints.ai_socktype = SOCK_STREAM;
		s->as = getaddrinfo_async(mx->host, NULL, &hints, NULL);
		TAILQ_REMOVE(&s->mx, mx, entry);
		free(mx->host);
		free(mx);
	}

	if (async_run(s->as, &ar) == ASYNC_COND) {
		dns_asr_event_set(s, &ar);
		return;
	}

	if (ar.ar_gai_errno == 0) {
		for (ai = ar.ar_addrinfo; ai; ai = ai->ai_next) {
			memcpy(&query->ss, ai->ai_addr, ai->ai_addrlen);
			log_debug("debug: dns: got address %s",
			    ss_to_text(&query->ss));
			dns_reply(query, IMSG_DNS_HOST);
			s->mxfound++;
		}
		freeaddrinfo(ar.ar_addrinfo);
	}

	s->as = NULL;
	goto next;
}

static void
dns_asr_dispatch_cname(struct dnssession *s)
{
	struct dns		*query = &s->query;
	struct async_res	 ar;

	if (async_run(s->as, &ar) == ASYNC_COND) {
		dns_asr_event_set(s, &ar);
		return;
	}

	/* the error code could be more precise, but we don't currently care */
	query->error = ar.ar_gai_errno ? DNS_ENOTFOUND : DNS_OK;
	dns_reply(query, IMSG_DNS_PTR);
	dnssession_destroy(s);
}

static struct dnssession *
dnssession_init(struct dns *query)
{
	struct dnssession *s;

	s = xcalloc(1, sizeof(struct dnssession), "dnssession_init");

	stat_increment("lka.session", 1);

	s->id = query->id;
	s->query = *query;
	s->preference = -1;

	TAILQ_INIT(&s->mx);

	return (s);
}

static void
dnssession_destroy(struct dnssession *s)
{
	struct mx	*mx;

	stat_decrement("lka.session", 1);
	event_del(&s->ev);

	while ((mx = TAILQ_FIRST(&s->mx))) {
		TAILQ_REMOVE(&s->mx, mx, entry);
		free(mx->host);
		free(mx);
	}

	free(s);
}

static void
dnssession_mx_insert(struct dnssession *s, const char *host, int preference)
{
	struct mx	*mx, *e;

	mx = xcalloc(1, sizeof *mx, "dnssession_mx_insert");
	mx->host = xstrdup(host, "dnssession_mx_insert");
	mx->preference = preference;

	log_debug("debug: dns: found mx \"%s\" with preference %i",
	    host, preference);

	TAILQ_FOREACH(e, &s->mx, entry) {
		if (mx->preference <= e->preference) {
			TAILQ_INSERT_BEFORE(e, mx, entry);
			goto end;
		}
	}

	TAILQ_INSERT_TAIL(&s->mx, mx, entry);

end:
	if (s->preference == -1 && s->query.backup[0]
	    && !strcasecmp(host, s->query.backup)) {
		log_debug("debug: dns: found our backup preference");
		s->preference = preference;
	}
}