libads/dns.c

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/* 
   Unix SMB/CIFS implementation.
   DNS utility library
   Copyright (C) Gerald (Jerry) Carter           2006.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "includes.h"

/* AIX resolv.h uses 'class' in struct ns_rr */

#if defined(AIX)
#  if defined(class)
#    undef class
#  endif
#endif  /* AIX */

/* resolver headers */

#include <sys/types.h>
#include <netinet/in.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <netdb.h>

#define MAX_DNS_PACKET_SIZE 0xffff

#ifdef NS_HFIXEDSZ      /* Bind 8/9 interface */
#if !defined(C_IN)      /* AIX 5.3 already defines C_IN */
#  define C_IN          ns_c_in
#endif
#if !defined(T_A)       /* AIX 5.3 already defines T_A */
#  define T_A           ns_t_a
#endif
#  define T_SRV         ns_t_srv
#if !defined(T_NS)      /* AIX 5.3 already defines T_NS */
#  define T_NS          ns_t_ns
#endif
#else
#  ifdef HFIXEDSZ
#    define NS_HFIXEDSZ HFIXEDSZ
#  else
#    define NS_HFIXEDSZ sizeof(HEADER)
#  endif        /* HFIXEDSZ */
#  ifdef PACKETSZ
#    define NS_PACKETSZ PACKETSZ
#  else /* 512 is usually the default */
#    define NS_PACKETSZ 512
#  endif        /* PACKETSZ */
#  define T_SRV         33
#endif

/*********************************************************************
*********************************************************************/

static BOOL ads_dns_parse_query( TALLOC_CTX *ctx, uint8 *start, uint8 *end,
                          uint8 **ptr, struct dns_query *q )
{
        uint8 *p = *ptr;
        pstring hostname;
        int namelen;

        ZERO_STRUCTP( q );
        
        if ( !start || !end || !q || !*ptr)
                return False;

        /* See RFC 1035 for details. If this fails, then return. */

        namelen = dn_expand( start, end, p, hostname, sizeof(hostname) );
        if ( namelen < 0 ) {
                return False;
        }
        p += namelen;
        q->hostname = talloc_strdup( ctx, hostname );

        /* check that we have space remaining */

        if ( PTR_DIFF(p+4, end) > 0 )
                return False;

        q->type     = RSVAL( p, 0 );
        q->in_class = RSVAL( p, 2 );
        p += 4;

        *ptr = p;

        return True;
}

/*********************************************************************
*********************************************************************/

static BOOL ads_dns_parse_rr( TALLOC_CTX *ctx, uint8 *start, uint8 *end,
                       uint8 **ptr, struct dns_rr *rr )
{
        uint8 *p = *ptr;
        pstring hostname;
        int namelen;

        if ( !start || !end || !rr || !*ptr)
                return -1;

        ZERO_STRUCTP( rr );
        /* pull the name from the answer */

        namelen = dn_expand( start, end, p, hostname, sizeof(hostname) );
        if ( namelen < 0 ) {
                return -1;
        }
        p += namelen;
        rr->hostname = talloc_strdup( ctx, hostname );

        /* check that we have space remaining */

        if ( PTR_DIFF(p+10, end) > 0 )
                return False;

        /* pull some values and then skip onto the string */

        rr->type     = RSVAL(p, 0);
        rr->in_class = RSVAL(p, 2);
        rr->ttl      = RIVAL(p, 4);
        rr->rdatalen = RSVAL(p, 8);
        
        p += 10;

        /* sanity check the available space */

        if ( PTR_DIFF(p+rr->rdatalen, end ) > 0 ) {
                return False;

        }

        /* save a point to the rdata for this section */

        rr->rdata = p;
        p += rr->rdatalen;

        *ptr = p;

        return True;
}

/*********************************************************************
*********************************************************************/

static BOOL ads_dns_parse_rr_srv( TALLOC_CTX *ctx, uint8 *start, uint8 *end,
                       uint8 **ptr, struct dns_rr_srv *srv )
{
        struct dns_rr rr;
        uint8 *p;
        pstring dcname;
        int namelen;

        if ( !start || !end || !srv || !*ptr)
                return -1;

        /* Parse the RR entry.  Coming out of the this, ptr is at the beginning 
           of the next record */

        if ( !ads_dns_parse_rr( ctx, start, end, ptr, &rr ) ) {
                DEBUG(1,("ads_dns_parse_rr_srv: Failed to parse RR record\n"));
                return False;
        }

        if ( rr.type != T_SRV ) {
                DEBUG(1,("ads_dns_parse_rr_srv: Bad answer type (%d)\n", rr.type));
                return False;
        }

        p = rr.rdata;

        srv->priority = RSVAL(p, 0);
        srv->weight   = RSVAL(p, 2);
        srv->port     = RSVAL(p, 4);

        p += 6;

        namelen = dn_expand( start, end, p, dcname, sizeof(dcname) );
        if ( namelen < 0 ) {
                DEBUG(1,("ads_dns_parse_rr_srv: Failed to uncompress name!\n"));
                return False;
        }

        srv->hostname = talloc_strdup( ctx, dcname );

        DEBUG(10,("ads_dns_parse_rr_srv: Parsed %s [%u, %u, %u]\n", 
                  srv->hostname, 
                  srv->priority,
                  srv->weight,
                  srv->port));

        return True;
}

/*********************************************************************
*********************************************************************/

static BOOL ads_dns_parse_rr_ns( TALLOC_CTX *ctx, uint8 *start, uint8 *end,
                       uint8 **ptr, struct dns_rr_ns *nsrec )
{
        struct dns_rr rr;
        uint8 *p;
        pstring nsname;
        int namelen;

        if ( !start || !end || !nsrec || !*ptr)
                return -1;

        /* Parse the RR entry.  Coming out of the this, ptr is at the beginning 
           of the next record */

        if ( !ads_dns_parse_rr( ctx, start, end, ptr, &rr ) ) {
                DEBUG(1,("ads_dns_parse_rr_ns: Failed to parse RR record\n"));
                return False;
        }

        if ( rr.type != T_NS ) {
                DEBUG(1,("ads_dns_parse_rr_ns: Bad answer type (%d)\n", rr.type));
                return False;
        }

        p = rr.rdata;

        /* ame server hostname */
        
        namelen = dn_expand( start, end, p, nsname, sizeof(nsname) );
        if ( namelen < 0 ) {
                DEBUG(1,("ads_dns_parse_rr_ns: Failed to uncompress name!\n"));
                return False;
        }
        nsrec->hostname = talloc_strdup( ctx, nsname );

        return True;
}

/*********************************************************************
 Sort SRV record list based on weight and priority.  See RFC 2782.
*********************************************************************/

static int dnssrvcmp( struct dns_rr_srv *a, struct dns_rr_srv *b )
{
        if ( a->priority == b->priority ) {

                /* randomize entries with an equal weight and priority */
                if ( a->weight == b->weight ) 
                        return 0;

                /* higher weights should be sorted lower */ 
                if ( a->weight > b->weight )
                        return -1;
                else
                        return 1;
        }
                
        if ( a->priority < b->priority )
                return -1;

        return 1;
}

/*********************************************************************
 Simple wrapper for a DNS query
*********************************************************************/

static NTSTATUS dns_send_req( TALLOC_CTX *ctx, const char *name, int q_type, 
                              uint8 **buf, int *resp_length )
{
        uint8 *buffer = NULL;
        size_t buf_len = 0;
        int resp_len = NS_PACKETSZ;     
        
        do {
                if ( buffer )
                        TALLOC_FREE( buffer );
                
                buf_len = resp_len * sizeof(uint8);

                if (buf_len) {
                        if ( (buffer = TALLOC_ARRAY(ctx, uint8, buf_len)) == NULL ) {
                                DEBUG(0,("ads_dns_lookup_srv: talloc() failed!\n"));
                                return NT_STATUS_NO_MEMORY;
                        }
                } else {
                        buffer = NULL;
                }

                if ( (resp_len = res_query(name, C_IN, q_type, buffer, buf_len)) < 0 ) {
                        DEBUG(3,("ads_dns_lookup_srv: Failed to resolve %s (%s)\n", name, strerror(errno)));
                        TALLOC_FREE( buffer );
                        if (errno == ETIMEDOUT) {
                                return NT_STATUS_IO_TIMEOUT;
                        }
                        if (errno == ECONNREFUSED) {
                                return NT_STATUS_CONNECTION_REFUSED;
                        }
                        return NT_STATUS_UNSUCCESSFUL;
                }

                /* On AIX, Solaris, and possibly some older glibc systems (e.g. SLES8)
                   truncated replies never give back a resp_len > buflen
                   which ends up causing DNS resolve failures on large tcp DNS replies */

                if (buf_len == resp_len) {
                        if (resp_len == MAX_DNS_PACKET_SIZE) {
                                DEBUG(1,("dns_send_req: DNS reply too large when resolving %s\n",
                                        name));
                                TALLOC_FREE( buffer );
                                return NT_STATUS_BUFFER_TOO_SMALL;
                        }

                        resp_len = MIN(resp_len*2, MAX_DNS_PACKET_SIZE);
                }


        } while ( buf_len < resp_len && resp_len <= MAX_DNS_PACKET_SIZE );

        *buf = buffer;
        *resp_length = resp_len;

        return NT_STATUS_OK;
}

/*********************************************************************
 Simple wrapper for a DNS SRV query
*********************************************************************/

static NTSTATUS ads_dns_lookup_srv( TALLOC_CTX *ctx, const char *name, struct dns_rr_srv **dclist, int *numdcs )
{
        uint8 *buffer = NULL;
        int resp_len = 0;
        struct dns_rr_srv *dcs = NULL;
        int query_count, answer_count, auth_count, additional_count;
        uint8 *p = buffer;
        int rrnum;
        int idx = 0;
        NTSTATUS status;

        if ( !ctx || !name || !dclist ) {
                return NT_STATUS_INVALID_PARAMETER;
        }
        
        /* Send the request.  May have to loop several times in case 
           of large replies */

        status = dns_send_req( ctx, name, T_SRV, &buffer, &resp_len );
        if ( !NT_STATUS_IS_OK(status) ) {
                DEBUG(3,("ads_dns_lookup_srv: Failed to send DNS query (%s)\n",
                        nt_errstr(status)));
                return status;
        }
        p = buffer;

        /* For some insane reason, the ns_initparse() et. al. routines are only
           available in libresolv.a, and not the shared lib.  Who knows why....
           So we have to parse the DNS reply ourselves */

        /* Pull the answer RR's count from the header.  Use the NMB ordering macros */

        query_count      = RSVAL( p, 4 );
        answer_count     = RSVAL( p, 6 );
        auth_count       = RSVAL( p, 8 );
        additional_count = RSVAL( p, 10 );

        DEBUG(4,("ads_dns_lookup_srv: %d records returned in the answer section.\n", 
                answer_count));
                
        if (answer_count) {
                if ( (dcs = TALLOC_ZERO_ARRAY(ctx, struct dns_rr_srv, answer_count)) == NULL ) {
                        DEBUG(0,("ads_dns_lookup_srv: talloc() failure for %d char*'s\n", 
                                answer_count));
                        return NT_STATUS_NO_MEMORY;
                }
        } else {
                dcs = NULL;
        }

        /* now skip the header */

        p += NS_HFIXEDSZ;

        /* parse the query section */

        for ( rrnum=0; rrnum<query_count; rrnum++ ) {
                struct dns_query q;

                if (!ads_dns_parse_query(ctx, buffer,
                                        buffer+resp_len, &p, &q)) {
                        DEBUG(1,("ads_dns_lookup_srv: "
                                 "Failed to parse query record [%d]!\n", rrnum));
                        return NT_STATUS_UNSUCCESSFUL;
                }
        }

        /* now we are at the answer section */

        for ( rrnum=0; rrnum<answer_count; rrnum++ ) {
                if (!ads_dns_parse_rr_srv(ctx, buffer, buffer+resp_len,
                                        &p, &dcs[rrnum])) {
                        DEBUG(1,("ads_dns_lookup_srv: "
                                 "Failed to parse answer recordi [%d]!\n", rrnum));
                        return NT_STATUS_UNSUCCESSFUL;
                }               
        }
        idx = rrnum;

        /* Parse the authority section */
        /* just skip these for now */

        for ( rrnum=0; rrnum<auth_count; rrnum++ ) {
                struct dns_rr rr;

                if (!ads_dns_parse_rr( ctx, buffer,
                                        buffer+resp_len, &p, &rr)) {
                        DEBUG(1,("ads_dns_lookup_srv: "
                                 "Failed to parse authority record! [%d]\n", rrnum));
                        return NT_STATUS_UNSUCCESSFUL;
                }
        }

        /* Parse the additional records section */

        for ( rrnum=0; rrnum<additional_count; rrnum++ ) {
                struct dns_rr rr;
                int i;

                if (!ads_dns_parse_rr(ctx, buffer, buffer+resp_len,
                                        &p, &rr)) {
                        DEBUG(1,("ads_dns_lookup_srv: Failed "
                                 "to parse additional records section! [%d]\n", rrnum));
                        return NT_STATUS_UNSUCCESSFUL;
                }

                /* only interested in A records as a shortcut for having to come 
                   back later and lookup the name.  For multi-homed hosts, the 
                   number of additional records and exceed the number of answer 
                   records. */
                  

                if ( (rr.type != T_A) || (rr.rdatalen != 4) ) 
                        continue;

                for ( i=0; i<idx; i++ ) {
                        if ( strcmp( rr.hostname, dcs[i].hostname ) == 0 ) {
                                int num_ips = dcs[i].num_ips;
                                uint8 *buf;
                                struct in_addr *tmp_ips;

                                /* allocate new memory */
                                
                                if ( dcs[i].num_ips == 0 ) {
                                        if ( (dcs[i].ips = TALLOC_ARRAY( dcs, 
                                                struct in_addr, 1 )) == NULL ) 
                                        {
                                                return NT_STATUS_NO_MEMORY;
                                        }
                                } else {
                                        if ( (tmp_ips = TALLOC_REALLOC_ARRAY( dcs, dcs[i].ips,
                                                struct in_addr, dcs[i].num_ips+1)) == NULL ) 
                                        {
                                                return NT_STATUS_NO_MEMORY;
                                        }
                                        
                                        dcs[i].ips = tmp_ips;
                                }
                                dcs[i].num_ips++;
                                
                                /* copy the new IP address */
                                
                                buf = (uint8*)&dcs[i].ips[num_ips].s_addr;
                                memcpy( buf, rr.rdata, 4 );
                        }
                }
        }

        qsort( dcs, idx, sizeof(struct dns_rr_srv), QSORT_CAST dnssrvcmp );
        
        *dclist = dcs;
        *numdcs = idx;
        
        return NT_STATUS_OK;
}

/*********************************************************************
 Simple wrapper for a DNS NS query
*********************************************************************/

NTSTATUS ads_dns_lookup_ns( TALLOC_CTX *ctx, const char *dnsdomain, struct dns_rr_ns **nslist, int *numns )
{
        uint8 *buffer = NULL;
        int resp_len = 0;
        struct dns_rr_ns *nsarray = NULL;
        int query_count, answer_count, auth_count, additional_count;
        uint8 *p;
        int rrnum;
        int idx = 0;
        NTSTATUS status;

        if ( !ctx || !dnsdomain || !nslist ) {
                return NT_STATUS_INVALID_PARAMETER;
        }
        
        /* Send the request.  May have to loop several times in case 
           of large replies */
           
        status = dns_send_req( ctx, dnsdomain, T_NS, &buffer, &resp_len );
        if ( !NT_STATUS_IS_OK(status) ) {
                DEBUG(3,("ads_dns_lookup_ns: Failed to send DNS query (%s)\n",
                        nt_errstr(status)));
                return status;
        }
        p = buffer;

        /* For some insane reason, the ns_initparse() et. al. routines are only
           available in libresolv.a, and not the shared lib.  Who knows why....
           So we have to parse the DNS reply ourselves */

        /* Pull the answer RR's count from the header.  Use the NMB ordering macros */

        query_count      = RSVAL( p, 4 );
        answer_count     = RSVAL( p, 6 );
        auth_count       = RSVAL( p, 8 );
        additional_count = RSVAL( p, 10 );

        DEBUG(4,("ads_dns_lookup_ns: %d records returned in the answer section.\n", 
                answer_count));
                
        if (answer_count) {
                if ( (nsarray = TALLOC_ARRAY(ctx, struct dns_rr_ns, answer_count)) == NULL ) {
                        DEBUG(0,("ads_dns_lookup_ns: talloc() failure for %d char*'s\n", 
                                answer_count));
                        return NT_STATUS_NO_MEMORY;
                }
        } else {
                nsarray = NULL;
        }

        /* now skip the header */

        p += NS_HFIXEDSZ;

        /* parse the query section */

        for ( rrnum=0; rrnum<query_count; rrnum++ ) {
                struct dns_query q;

                if ( !ads_dns_parse_query( ctx, buffer, buffer+resp_len, &p, &q ) ) {
                        DEBUG(1,("ads_dns_lookup_ns: Failed to parse query record!\n"));
                        return NT_STATUS_UNSUCCESSFUL;
                }
        }

        /* now we are at the answer section */

        for ( rrnum=0; rrnum<answer_count; rrnum++ ) {
                if ( !ads_dns_parse_rr_ns( ctx, buffer, buffer+resp_len, &p, &nsarray[rrnum] ) ) {
                        DEBUG(1,("ads_dns_lookup_ns: Failed to parse answer record!\n"));
                        return NT_STATUS_UNSUCCESSFUL;
                }               
        }
        idx = rrnum;

        /* Parse the authority section */
        /* just skip these for now */

        for ( rrnum=0; rrnum<auth_count; rrnum++ ) {
                struct dns_rr rr;

                if ( !ads_dns_parse_rr( ctx, buffer, buffer+resp_len, &p, &rr ) ) {
                        DEBUG(1,("ads_dns_lookup_ns: Failed to parse authority record!\n"));
                        return NT_STATUS_UNSUCCESSFUL;
                }
        }

        /* Parse the additional records section */

        for ( rrnum=0; rrnum<additional_count; rrnum++ ) {
                struct dns_rr rr;
                int i;

                if ( !ads_dns_parse_rr( ctx, buffer, buffer+resp_len, &p, &rr ) ) {
                        DEBUG(1,("ads_dns_lookup_ns: Failed to parse additional records section!\n"));
                        return NT_STATUS_UNSUCCESSFUL;
                }

                /* only interested in A records as a shortcut for having to come 
                   back later and lookup the name */

                if ( (rr.type != T_A) || (rr.rdatalen != 4) ) 
                        continue;

                for ( i=0; i<idx; i++ ) {
                        if ( strcmp( rr.hostname, nsarray[i].hostname ) == 0 ) {
                                uint8 *buf = (uint8*)&nsarray[i].ip.s_addr;
                                memcpy( buf, rr.rdata, 4 );
                        }
                }
        }
        
        *nslist = nsarray;
        *numns = idx;
        
        return NT_STATUS_OK;
}

/****************************************************************************
 Store and fetch the AD client sitename.
****************************************************************************/

#define SITENAME_KEY    "AD_SITENAME/DOMAIN/%s"

static char *sitename_key(const char *realm)
{
        char *keystr;
        
        if (asprintf(&keystr, SITENAME_KEY, strupper_static(realm)) == -1) {
                return NULL;
        }

        return keystr;
}


/****************************************************************************
 Store the AD client sitename.
 We store indefinately as every new CLDAP query will re-write this.
****************************************************************************/

BOOL sitename_store(const char *realm, const char *sitename)
{
        time_t expire;
        BOOL ret = False;
        char *key;

        if (!gencache_init()) {
                return False;
        }

        if (!realm || (strlen(realm) == 0)) {
                DEBUG(0,("sitename_store: no realm\n"));
                return False;
        }
        
        key = sitename_key(realm);

        if (!sitename || (sitename && !*sitename)) {
                DEBUG(5,("sitename_store: deleting empty sitename!\n"));
                ret = gencache_del(key);
                SAFE_FREE(key);
                return ret;
        }

        expire = get_time_t_max(); /* Store indefinately. */
        
        DEBUG(10,("sitename_store: realm = [%s], sitename = [%s], expire = [%u]\n",
                realm, sitename, (unsigned int)expire ));

        ret = gencache_set( key, sitename, expire );
        SAFE_FREE(key);
        return ret;
}

/****************************************************************************
 Fetch the AD client sitename.
 Caller must free.
****************************************************************************/

char *sitename_fetch(const char *realm)
{
        char *sitename = NULL;
        time_t timeout;
        BOOL ret = False;
        const char *query_realm;
        char *key;
        
        if (!gencache_init()) {
                return NULL;
        }

        if (!realm || (strlen(realm) == 0)) {
                query_realm = lp_realm(); 
        } else {
                query_realm = realm;
        }

        key = sitename_key(query_realm);

        ret = gencache_get( key, &sitename, &timeout );
        SAFE_FREE(key);
        if ( !ret ) {
                DEBUG(5,("sitename_fetch: No stored sitename for %s\n",
                        query_realm));
        } else {
                DEBUG(5,("sitename_fetch: Returning sitename for %s: \"%s\"\n",
                        query_realm, sitename ));
        }
        return sitename;
}

/****************************************************************************
 Did the sitename change ?
****************************************************************************/

BOOL stored_sitename_changed(const char *realm, const char *sitename)
{
        BOOL ret = False;

        char *new_sitename;

        if (!realm || (strlen(realm) == 0)) {
                DEBUG(0,("stored_sitename_changed: no realm\n"));
                return False;
        }

        new_sitename = sitename_fetch(realm);

        if (sitename && new_sitename && !strequal(sitename, new_sitename)) {
                ret = True;
        } else if ((sitename && !new_sitename) ||
                        (!sitename && new_sitename)) {
                ret = True;
        }
        SAFE_FREE(new_sitename);
        return ret;
}

/********************************************************************
 Query with optional sitename.
********************************************************************/

NTSTATUS ads_dns_query_internal(TALLOC_CTX *ctx,
                                const char *servicename,
                                const char *realm,
                                const char *sitename,
                                struct dns_rr_srv **dclist,
                                int *numdcs )
{
        char *name;
        if (sitename) {
                name = talloc_asprintf(ctx, "%s._tcp.%s._sites.dc._msdcs.%s",
                                servicename, sitename, realm );
        } else {
                name = talloc_asprintf(ctx, "%s._tcp.dc._msdcs.%s",
                                servicename, realm );
        }
        if (!name) {
                return NT_STATUS_NO_MEMORY;
        }
        return ads_dns_lookup_srv( ctx, name, dclist, numdcs );
}

/********************************************************************
 Query for AD DC's.
********************************************************************/

NTSTATUS ads_dns_query_dcs(TALLOC_CTX *ctx,
                        const char *realm,
                        const char *sitename,
                        struct dns_rr_srv **dclist,
                        int *numdcs )
{
        NTSTATUS status;

        status = ads_dns_query_internal(ctx, "_ldap", realm, sitename,
                                        dclist, numdcs);

        if (NT_STATUS_EQUAL(status, NT_STATUS_IO_TIMEOUT) ||
            NT_STATUS_EQUAL(status, NT_STATUS_CONNECTION_REFUSED)) {
                return status;
        }

        if (sitename && !NT_STATUS_IS_OK(status)) {
                /* Sitename DNS query may have failed. Try without. */
                status = ads_dns_query_internal(ctx, "_ldap", realm, NULL,
                                                dclist, numdcs);
        }
        return status;
}

/********************************************************************
 Query for AD KDC's.
 Even if our underlying kerberos libraries are UDP only, this
 is pretty safe as it's unlikely that a KDC supports TCP and not UDP.
********************************************************************/

NTSTATUS ads_dns_query_kdcs(TALLOC_CTX *ctx,
                        const char *realm,
                        const char *sitename,
                        struct dns_rr_srv **dclist,
                        int *numdcs )
{
        NTSTATUS status;

        status = ads_dns_query_internal(ctx, "_kerberos", realm, sitename,
                                        dclist, numdcs);

        if (NT_STATUS_EQUAL(status, NT_STATUS_IO_TIMEOUT) ||
            NT_STATUS_EQUAL(status, NT_STATUS_CONNECTION_REFUSED)) {
                return status;
        }

        if (sitename && !NT_STATUS_IS_OK(status)) {
                /* Sitename DNS query may have failed. Try without. */
                status = ads_dns_query_internal(ctx, "_kerberos", realm, NULL,
                                                dclist, numdcs);
        }
        return status;
}

---