/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright (c) 1995, 1996
 *      Bill Paul <wpaul@ctr.columbia.edu>. 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 Bill Paul.
 * 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 Bill Paul 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 Bill Paul 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/cdefs.h>
/*
 * Do standard and reverse DNS lookups using the resolver library.
 * Take care of all the dirty work here so the main program only has to
 * pass us a pointer to an array of characters.
 *
 * We have to use direct resolver calls here otherwise the YP server
 * could end up looping by calling itself over and over again until
 * it disappeared up its own belly button.
 */

#include <sys/param.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <sys/fcntl.h>
#include <sys/queue.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

#include <ctype.h>
#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <resolv.h>
#include <unistd.h>

#include <rpcsvc/yp.h>
#include "yp_extern.h"

static char *
parse(struct hostent *hp)
{
        static char result[MAXHOSTNAMELEN * 2];
        int i;
        size_t len;
        char addr[46];

        if (hp == NULL)
                return(NULL);

        if (inet_ntop(hp->h_addrtype, hp->h_addr, addr, sizeof(addr)) == NULL)
                return(NULL);

        len = strlen(addr) + 1 + strlen(hp->h_name);
        for (i = 0; hp->h_aliases[i]; i++)
                len += strlen(hp->h_aliases[i]) + 1;
        len++;

        if (len > sizeof(result))
                return(NULL);

        bzero(result, sizeof(result));
        snprintf(result, sizeof(result), "%s %s", addr, hp->h_name);
        for (i = 0; hp->h_aliases[i]; i++) {
                strcat(result, " ");
                strcat(result, hp->h_aliases[i]);
        }

        return ((char *)&result);
}

#define MAXPACKET (64*1024)
#define DEF_TTL 50

#define BY_DNS_ID 1
#define BY_RPC_XID 2

extern struct hostent *__dns_getanswer(char *, int, char *, int);

static TAILQ_HEAD(dns_qhead, circleq_dnsentry) qhead;

struct circleq_dnsentry {
        SVCXPRT *xprt;
        unsigned long xid;
        struct sockaddr_in client_addr;
        unsigned long ypvers;
        unsigned long id;
        unsigned long ttl;
        unsigned long type;
        unsigned short prot_type;
        char **domain;
        char *name;
        int addrtype;
        int addrlen;
        uint32_t addr[4];       /* IPv4 or IPv6 */
        TAILQ_ENTRY(circleq_dnsentry) links;
};

static int pending = 0;

int
yp_init_resolver(void)
{
        TAILQ_INIT(&qhead);
        if (!(_res.options & RES_INIT) && res_init() == -1) {
                yp_error("res_init failed");
                return(1);
        }
        if ((resfd = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
                yp_error("couldn't create socket");
                return(1);
        }
        if (fcntl(resfd, F_SETFL, O_NONBLOCK) == -1) {
                yp_error("couldn't make resolver socket non-blocking");
                return(1);
        }
        return(0);
}

static struct
circleq_dnsentry *yp_malloc_dnsent(void)
{
        register struct circleq_dnsentry *q;

        q = malloc(sizeof(struct circleq_dnsentry));

        if (q == NULL) {
                yp_error("failed to malloc() circleq dns entry");
                return(NULL);
        }

        return(q);
}

/*
 * Transmit a query.
 */
static unsigned long
yp_send_dns_query(char *name, int type)
{
        char buf[MAXPACKET];
        int n;
        HEADER *hptr;
        int ns;
        int rval;
        unsigned long id;

        bzero(buf, sizeof(buf));

        n = res_mkquery(QUERY,name,C_IN,type,NULL,0,NULL,buf,sizeof(buf));

        if (n <= 0) {
                yp_error("res_mkquery failed for %s type %d", name, type);
                return(0);
        }

        hptr = (HEADER *)&buf;
        id = ntohs(hptr->id);

        for (ns = 0; ns < _res.nscount; ns++) {
                rval = sendto(resfd, buf, n, 0,
                        (struct sockaddr *)&_res.nsaddr_list[ns],
                                sizeof(struct sockaddr));
                if (rval == -1) {
                        yp_error("sendto failed");
                        return(0);
                }
        }

        return(id);
}

static struct circleq_dnsentry *
yp_find_dnsqent(unsigned long id, int type)
{
        register struct circleq_dnsentry *q;

        TAILQ_FOREACH(q, &qhead, links) {
                switch (type) {
                case BY_RPC_XID:
                        if (id == q->xid)
                                return(q);
                        break;
                case BY_DNS_ID:
                default:
                        if (id == q->id)
                                return(q);
                        break;
                }
        }
        return (NULL);
}

static void
yp_send_dns_reply(struct circleq_dnsentry *q, char *buf)
{
        ypresponse result_v1;
        ypresp_val result_v2;
        unsigned long xid;
        struct sockaddr_in client_addr;
        xdrproc_t xdrfunc;
        char *result;

        /*
         * Set up correct reply struct and
         * XDR filter depending on ypvers.
         */
        switch (q->ypvers) {
        case YPVERS:
                bzero((char *)&result_v2, sizeof(result_v2));

                if (buf == NULL)
                        result_v2.stat = YP_NOKEY;
                else {
                        result_v2.val.valdat_len = strlen(buf);
                        result_v2.val.valdat_val = buf;
                        result_v2.stat = YP_TRUE;
                }
                result = (char *)&result_v2;
                xdrfunc = (xdrproc_t)xdr_ypresp_val;
                break;
        case YPOLDVERS:
                /*
                 * The odds are we will _never_ execute this
                 * particular code, but we include it anyway
                 * for the sake of completeness.
                 */
                bzero((char *)&result_v1, sizeof(result_v1));
                result_v1.yp_resptype = YPRESP_VAL;

#define YPVAL ypresponse_u.yp_resp_valtype
                if (buf == NULL)
                        result_v1.YPVAL.stat = YP_NOKEY;
                else {
                        result_v1.YPVAL.val.valdat_len = strlen(buf);
                        result_v1.YPVAL.val.valdat_val = buf;
                        result_v1.YPVAL.stat = YP_TRUE;
                }
                result = (char *)&result_v1;
                xdrfunc = (xdrproc_t)xdr_ypresponse;
                break;
        default:
                yp_error("bad YP program version (%lu)!", q->ypvers);
                        return;
                break;
        }

        if (debug)
                yp_error("sending dns reply to %s (%lu)",
                        inet_ntoa(q->client_addr.sin_addr), q->id);
        /*
         * XXX This is disgusting. There's basically one transport
         * handle for UDP, but we're holding off on replying to a
         * client until we're ready, by which time we may have received
         * several other queries from other clients with different
         * transaction IDs. So to make the delayed response thing work,
         * we have to save the transaction ID and client address of
         * each request, then jam them into the transport handle when
         * we're ready to send a reply. Then after we've send the reply,
         * we put the old transaction ID and remote address back the
         * way we found 'em. This is _INCREDIBLY_ non-portable; it's
         * not even supported by the RPC library.
         */
        /*
         * XXX Don't frob the transaction ID for TCP handles.
         */
        if (q->prot_type == SOCK_DGRAM)
                xid = svcudp_set_xid(q->xprt, q->xid);
        client_addr = q->xprt->xp_raddr;
        q->xprt->xp_raddr = q->client_addr;

        if (!svc_sendreply(q->xprt, xdrfunc, result))
                yp_error("svc_sendreply failed");

        /*
         * Now that we sent the reply,
         * put the handle back the way it was.
         */
        if (q->prot_type == SOCK_DGRAM)
                svcudp_set_xid(q->xprt, xid);
        q->xprt->xp_raddr = client_addr;
}

/*
 * Decrement TTL on all queue entries, possibly nuking
 * any that have been around too long without being serviced.
 */
void
yp_prune_dnsq(void)
{
        register struct circleq_dnsentry *q, *n;

        q = TAILQ_FIRST(&qhead);
        while (q != NULL) {
                q->ttl--;
                n = TAILQ_NEXT(q, links);
                if (!q->ttl) {
                        TAILQ_REMOVE(&qhead, q, links);
                        free(q->name);
                        free(q);
                        pending--;
                }
                q = n;
        }

        if (pending < 0)
                pending = 0;
}

/*
 * Data is pending on the DNS socket; check for valid replies
 * to our queries and dispatch them to waiting clients.
 */
void
yp_run_dnsq(void)
{
        register struct circleq_dnsentry *q;
        char buf[sizeof(HEADER) + MAXPACKET];
        struct sockaddr_in sin;
        socklen_t len;
        int rval;
        HEADER *hptr;
        struct hostent *hent;

        if (debug)
                yp_error("running dns queue");

        bzero(buf, sizeof(buf));

        len = sizeof(struct sockaddr_in);
        rval = recvfrom(resfd, buf, sizeof(buf), 0,
                        (struct sockaddr *)&sin, &len);

        if (rval == -1) {
                yp_error("recvfrom failed: %s", strerror(errno));
                return;
        }

        /*
         * We may have data left in the socket that represents
         * replies to earlier queries that we don't care about
         * anymore. If there are no lookups pending or the packet
         * ID doesn't match any of the queue IDs, just drop it
         * on the floor.
         */
        hptr = (HEADER *)&buf;
        if (!pending ||
                (q = yp_find_dnsqent(ntohs(hptr->id), BY_DNS_ID)) == NULL) {
                /* ignore */
                return;
        }

        if (debug)
                yp_error("got dns reply from %s", inet_ntoa(sin.sin_addr));

        hent = __dns_getanswer(buf, rval, q->name, q->type);

        if (hent != NULL) {
                if (q->type == T_PTR) {
                        hent->h_addr = (char *)q->addr;
                        hent->h_addrtype = q->addrtype;
                        hent->h_length = q->addrlen;
                }
        }

        /* Got an answer ready for a client -- send it off. */
        yp_send_dns_reply(q, parse(hent));
        pending--;
        TAILQ_REMOVE(&qhead, q, links);
        free(q->name);
        free(q);

        /* Decrement TTLs on other entries while we're here. */
        yp_prune_dnsq();
}

/*
 * Queue and transmit an asynchronous DNS hostname lookup.
 */
ypstat
yp_async_lookup_name(struct svc_req *rqstp, char *name, int af)
{
        register struct circleq_dnsentry *q;
        socklen_t len;
        int type;

        /* Check for SOCK_DGRAM or SOCK_STREAM -- we need to know later */
        type = -1;
        len = sizeof(type);
        if (getsockopt(rqstp->rq_xprt->xp_fd, SOL_SOCKET,
                                        SO_TYPE, &type, &len) == -1) {
                yp_error("getsockopt failed: %s", strerror(errno));
                return(YP_YPERR);
        }

        /* Avoid transmitting dupe requests. */
        if (type == SOCK_DGRAM &&
            yp_find_dnsqent(svcudp_get_xid(rqstp->rq_xprt),BY_RPC_XID) != NULL)
                return(YP_TRUE);

        if ((q = yp_malloc_dnsent()) == NULL)
                return(YP_YPERR);

        q->type = (af == AF_INET) ? T_A : T_AAAA;
        q->ttl = DEF_TTL;
        q->xprt = rqstp->rq_xprt;
        q->ypvers = rqstp->rq_vers;
        q->prot_type = type;
        if (q->prot_type == SOCK_DGRAM)
                q->xid = svcudp_get_xid(q->xprt);
        q->client_addr = q->xprt->xp_raddr;
        q->domain = _res.dnsrch;
        q->id = yp_send_dns_query(name, q->type);

        if (q->id == 0) {
                yp_error("DNS query failed");
                free(q);
                return(YP_YPERR);
        }

        q->name = strdup(name);
        TAILQ_INSERT_HEAD(&qhead, q, links);
        pending++;

        if (debug)
                yp_error("queueing async DNS name lookup (%lu)", q->id);

        yp_prune_dnsq();
        return(YP_TRUE);
}

/*
 * Queue and transmit an asynchronous DNS IP address lookup.
 */
ypstat
yp_async_lookup_addr(struct svc_req *rqstp, char *addr, int af)
{
        register struct circleq_dnsentry *q;
        char buf[MAXHOSTNAMELEN], *qp;
        uint32_t abuf[4];       /* IPv4 or IPv6 */
        u_char *uaddr = (u_char *)abuf;
        socklen_t len;
        int type, n;

        /* Check for SOCK_DGRAM or SOCK_STREAM -- we need to know later */
        type = -1;
        len = sizeof(type);
        if (getsockopt(rqstp->rq_xprt->xp_fd, SOL_SOCKET,
                                        SO_TYPE, &type, &len) == -1) {
                yp_error("getsockopt failed: %s", strerror(errno));
                return(YP_YPERR);
        }

        /* Avoid transmitting dupe requests. */
        if (type == SOCK_DGRAM &&
            yp_find_dnsqent(svcudp_get_xid(rqstp->rq_xprt),BY_RPC_XID) != NULL)
                return(YP_TRUE);

        switch (af) {
        case AF_INET:
                if (inet_aton(addr, (struct in_addr *)uaddr) != 1)
                        return(YP_NOKEY);
                snprintf(buf, sizeof(buf), "%u.%u.%u.%u.in-addr.arpa",
                    (uaddr[3] & 0xff), (uaddr[2] & 0xff),
                    (uaddr[1] & 0xff), (uaddr[0] & 0xff));
                len = INADDRSZ;
                break;
        case AF_INET6:
                if (inet_pton(af, addr, uaddr) != 1)
                        return(YP_NOKEY);
                qp = buf;
                for (n = IN6ADDRSZ - 1; n >= 0; n--) {
                        qp += (size_t)sprintf(qp, "%x.%x.", uaddr[n] & 0xf,
                            (uaddr[n] >> 4) & 0xf);
                }
                strlcat(buf, "ip6.arpa", sizeof(buf));
                len = IN6ADDRSZ;
                break;
        default:
                return(YP_YPERR);
        }

        if ((q = yp_malloc_dnsent()) == NULL)
                return(YP_YPERR);

        if (debug)
                yp_error("DNS address is: %s", buf);

        q->type = T_PTR;
        q->ttl = DEF_TTL;
        q->xprt = rqstp->rq_xprt;
        q->ypvers = rqstp->rq_vers;
        q->domain = NULL;
        q->prot_type = type;
        if (q->prot_type == SOCK_DGRAM)
                q->xid = svcudp_get_xid(q->xprt);
        q->client_addr = q->xprt->xp_raddr;
        q->id = yp_send_dns_query(buf, q->type);

        if (q->id == 0) {
                yp_error("DNS query failed");
                free(q);
                return(YP_YPERR);
        }

        memcpy(q->addr, uaddr, len);
        q->addrlen = len;
        q->addrtype = af;
        q->name = strdup(buf);
        TAILQ_INSERT_HEAD(&qhead, q, links);
        pending++;

        if (debug)
                yp_error("queueing async DNS address lookup (%lu)", q->id);

        yp_prune_dnsq();
        return(YP_TRUE);
}