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[Samba.git] / source4 / dns_server / dns_server.c

/*
   Unix SMB/CIFS implementation.

   DNS server startup

   Copyright (C) 2010 Kai Blin  <kai@samba.org>

   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 3 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, see <http://www.gnu.org/licenses/>.
*/

#include "includes.h"
#include "smbd/service_task.h"
#include "smbd/service.h"
#include "smbd/service_stream.h"
#include "smbd/process_model.h"
#include "lib/events/events.h"
#include "lib/socket/socket.h"
#include "lib/tsocket/tsocket.h"
#include "libcli/util/tstream.h"
#include "libcli/util/ntstatus.h"
#include "system/network.h"
#include "lib/stream/packet.h"
#include "lib/socket/netif.h"
#include "dns_server/dns_server.h"
#include "param/param.h"
#include "librpc/ndr/libndr.h"
#include "librpc/gen_ndr/ndr_dns.h"
#include "librpc/gen_ndr/ndr_dnsp.h"
#include <ldb.h>
#include "dsdb/samdb/samdb.h"
#include "dsdb/common/util.h"
#include "auth/session.h"
#include "lib/util/dlinklist.h"
#include "lib/util/tevent_werror.h"
#include "auth/auth.h"
#include "auth/credentials/credentials.h"

#undef DBGC_CLASS
#define DBGC_CLASS DBGC_DNS

NTSTATUS server_service_dns_init(void);

/* hold information about one dns socket */
struct dns_socket {
        struct dns_server *dns;
        struct tsocket_address *local_address;
};

struct dns_udp_socket {
        struct dns_socket *dns_socket;
        struct tdgram_context *dgram;
        struct tevent_queue *send_queue;
};

/*
  state of an open tcp connection
*/
struct dns_tcp_connection {
        /* stream connection we belong to */
        struct stream_connection *conn;

        /* the dns_server the connection belongs to */
        struct dns_socket *dns_socket;

        struct tstream_context *tstream;

        struct tevent_queue *send_queue;
};

static void dns_tcp_terminate_connection(struct dns_tcp_connection *dnsconn, const char *reason)
{
        stream_terminate_connection(dnsconn->conn, reason);
}

static void dns_tcp_recv(struct stream_connection *conn, uint16_t flags)
{
        struct dns_tcp_connection *dnsconn = talloc_get_type(conn->private_data,
                                                             struct dns_tcp_connection);
        /* this should never be triggered! */
        dns_tcp_terminate_connection(dnsconn, "dns_tcp_recv: called");
}

static void dns_tcp_send(struct stream_connection *conn, uint16_t flags)
{
        struct dns_tcp_connection *dnsconn = talloc_get_type(conn->private_data,
                                                             struct dns_tcp_connection);
        /* this should never be triggered! */
        dns_tcp_terminate_connection(dnsconn, "dns_tcp_send: called");
}

struct dns_process_state {
        DATA_BLOB *in;
        struct dns_server *dns;
        struct dns_name_packet in_packet;
        struct dns_request_state state;
        uint16_t dns_err;
        struct dns_name_packet out_packet;
        DATA_BLOB out;
};

static void dns_process_done(struct tevent_req *subreq);

static struct tevent_req *dns_process_send(TALLOC_CTX *mem_ctx,
                                           struct tevent_context *ev,
                                           struct dns_server *dns,
                                           DATA_BLOB *in)
{
        struct tevent_req *req, *subreq;
        struct dns_process_state *state;
        enum ndr_err_code ndr_err;
        WERROR ret;
        const char *forwarder = lpcfg_dns_forwarder(dns->task->lp_ctx);
        req = tevent_req_create(mem_ctx, &state, struct dns_process_state);
        if (req == NULL) {
                return NULL;
        }
        state->in = in;

        state->dns = dns;

        if (in->length < 12) {
                tevent_req_werror(req, WERR_INVALID_PARAM);
                return tevent_req_post(req, ev);
        }
        dump_data_dbgc(DBGC_DNS, 8, in->data, in->length);

        ndr_err = ndr_pull_struct_blob(
                in, state, &state->in_packet,
                (ndr_pull_flags_fn_t)ndr_pull_dns_name_packet);

        if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
                state->dns_err = DNS_RCODE_FORMERR;
                tevent_req_done(req);
                return tevent_req_post(req, ev);
        }
        if (DEBUGLVLC(DBGC_DNS, 8)) {
                NDR_PRINT_DEBUGC(DBGC_DNS, dns_name_packet, &state->in_packet);
        }

        ret = dns_verify_tsig(dns, state, &state->state, &state->in_packet, in);
        if (!W_ERROR_IS_OK(ret)) {
                DEBUG(1, ("Failed to verify TSIG!\n"));
                state->dns_err = werr_to_dns_err(ret);
                tevent_req_done(req);
                return tevent_req_post(req, ev);
        }

        state->state.flags = state->in_packet.operation;
        state->state.flags |= DNS_FLAG_REPLY;

        
        if (forwarder && *forwarder) {
                state->state.flags |= DNS_FLAG_RECURSION_AVAIL;
        }

        state->out_packet = state->in_packet;

        switch (state->in_packet.operation & DNS_OPCODE) {
        case DNS_OPCODE_QUERY:
                subreq = dns_server_process_query_send(
                        state, ev, dns, &state->state, &state->in_packet);
                if (tevent_req_nomem(subreq, req)) {
                        return tevent_req_post(req, ev);
                }
                tevent_req_set_callback(subreq, dns_process_done, req);
                return req;
        case DNS_OPCODE_UPDATE:
                ret = dns_server_process_update(
                        dns, &state->state, state, &state->in_packet,
                        &state->out_packet.answers, &state->out_packet.ancount,
                        &state->out_packet.nsrecs,  &state->out_packet.nscount,
                        &state->out_packet.additional,
                        &state->out_packet.arcount);
                break;
        default:
                ret = WERR_DNS_ERROR_RCODE_NOT_IMPLEMENTED;
        }
        if (!W_ERROR_IS_OK(ret)) {
                state->dns_err = werr_to_dns_err(ret);
        }
        tevent_req_done(req);
        return tevent_req_post(req, ev);
}

static void dns_process_done(struct tevent_req *subreq)
{
        struct tevent_req *req = tevent_req_callback_data(
                subreq, struct tevent_req);
        struct dns_process_state *state = tevent_req_data(
                req, struct dns_process_state);
        WERROR ret;

        ret = dns_server_process_query_recv(
                subreq, state,
                &state->out_packet.answers, &state->out_packet.ancount,
                &state->out_packet.nsrecs,  &state->out_packet.nscount,
                &state->out_packet.additional, &state->out_packet.arcount);
        TALLOC_FREE(subreq);

        if (!W_ERROR_IS_OK(ret)) {
                state->dns_err = werr_to_dns_err(ret);
        }
        tevent_req_done(req);
}

static WERROR dns_process_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
                               DATA_BLOB *out)
{
        struct dns_process_state *state = tevent_req_data(
                req, struct dns_process_state);
        enum ndr_err_code ndr_err;
        WERROR ret;

        if (tevent_req_is_werror(req, &ret)) {
                return ret;
        }
        if (state->dns_err != DNS_RCODE_OK) {
                goto drop;
        }
        state->out_packet.operation |= state->state.flags;

        if (state->state.sign) {
                ret = dns_sign_tsig(state->dns, mem_ctx, &state->state,
                                    &state->out_packet, 0);
                if (!W_ERROR_IS_OK(ret)) {
                        state->dns_err = DNS_RCODE_SERVFAIL;
                        goto drop;
                }
        }

        if (DEBUGLVLC(DBGC_DNS, 8)) {
                NDR_PRINT_DEBUGC(DBGC_DNS, dns_name_packet, &state->out_packet);
        }

        ndr_err = ndr_push_struct_blob(
                out, mem_ctx, &state->out_packet,
                (ndr_push_flags_fn_t)ndr_push_dns_name_packet);
        if (!NDR_ERR_CODE_IS_SUCCESS(ndr_err)) {
                DEBUG(1, ("Failed to push packet: %s!\n",
                          ndr_errstr(ndr_err)));
                state->dns_err = DNS_RCODE_SERVFAIL;
                goto drop;
        }
        return WERR_OK;

drop:
        *out = data_blob_talloc(mem_ctx, state->in->data, state->in->length);
        if (out->data == NULL) {
                return WERR_NOMEM;
        }
        out->data[2] |= 0x80; /* Toggle DNS_FLAG_REPLY */
        out->data[3] |= state->dns_err;
        return WERR_OK;
}

struct dns_tcp_call {
        struct dns_tcp_connection *dns_conn;
        DATA_BLOB in;
        DATA_BLOB out;
        uint8_t out_hdr[4];
        struct iovec out_iov[2];
};

static void dns_tcp_call_process_done(struct tevent_req *subreq);
static void dns_tcp_call_writev_done(struct tevent_req *subreq);

static void dns_tcp_call_loop(struct tevent_req *subreq)
{
        struct dns_tcp_connection *dns_conn = tevent_req_callback_data(subreq,
                                      struct dns_tcp_connection);
        struct dns_server *dns = dns_conn->dns_socket->dns;
        struct dns_tcp_call *call;
        NTSTATUS status;

        call = talloc(dns_conn, struct dns_tcp_call);
        if (call == NULL) {
                dns_tcp_terminate_connection(dns_conn, "dns_tcp_call_loop: "
                                "no memory for dns_tcp_call");
                return;
        }
        call->dns_conn = dns_conn;

        status = tstream_read_pdu_blob_recv(subreq,
                                            call,
                                            &call->in);
        TALLOC_FREE(subreq);
        if (!NT_STATUS_IS_OK(status)) {
                const char *reason;

                reason = talloc_asprintf(call, "dns_tcp_call_loop: "
                                         "tstream_read_pdu_blob_recv() - %s",
                                         nt_errstr(status));
                if (!reason) {
                        reason = nt_errstr(status);
                }

                dns_tcp_terminate_connection(dns_conn, reason);
                return;
        }

        DEBUG(10,("Received DNS TCP packet of length %lu from %s\n",
                 (long) call->in.length,
                 tsocket_address_string(dns_conn->conn->remote_address, call)));

        /* skip length header */
        call->in.data += 2;
        call->in.length -= 2;

        subreq = dns_process_send(call, dns->task->event_ctx, dns,
                                  &call->in);
        if (subreq == NULL) {
                dns_tcp_terminate_connection(
                        dns_conn, "dns_tcp_call_loop: dns_process_send "
                        "failed\n");
                return;
        }
        tevent_req_set_callback(subreq, dns_tcp_call_process_done, call);

        /*
         * The dns tcp pdu's has the length as 2 byte (initial_read_size),
         * packet_full_request_u16 provides the pdu length then.
         */
        subreq = tstream_read_pdu_blob_send(dns_conn,
                                            dns_conn->conn->event.ctx,
                                            dns_conn->tstream,
                                            2, /* initial_read_size */
                                            packet_full_request_u16,
                                            dns_conn);
        if (subreq == NULL) {
                dns_tcp_terminate_connection(dns_conn, "dns_tcp_call_loop: "
                                "no memory for tstream_read_pdu_blob_send");
                return;
        }
        tevent_req_set_callback(subreq, dns_tcp_call_loop, dns_conn);
}

static void dns_tcp_call_process_done(struct tevent_req *subreq)
{
        struct dns_tcp_call *call = tevent_req_callback_data(subreq,
                        struct dns_tcp_call);
        struct dns_tcp_connection *dns_conn = call->dns_conn;
        WERROR err;

        err = dns_process_recv(subreq, call, &call->out);
        TALLOC_FREE(subreq);
        if (!W_ERROR_IS_OK(err)) {
                DEBUG(1, ("dns_process returned %s\n", win_errstr(err)));
                dns_tcp_terminate_connection(dns_conn,
                                "dns_tcp_call_loop: process function failed");
                return;
        }

        /* First add the length of the out buffer */
        RSSVAL(call->out_hdr, 0, call->out.length);
        call->out_iov[0].iov_base = (char *) call->out_hdr;
        call->out_iov[0].iov_len = 2;

        call->out_iov[1].iov_base = (char *) call->out.data;
        call->out_iov[1].iov_len = call->out.length;

        subreq = tstream_writev_queue_send(call,
                                           dns_conn->conn->event.ctx,
                                           dns_conn->tstream,
                                           dns_conn->send_queue,
                                           call->out_iov, 2);
        if (subreq == NULL) {
                dns_tcp_terminate_connection(dns_conn, "dns_tcp_call_loop: "
                                "no memory for tstream_writev_queue_send");
                return;
        }
        tevent_req_set_callback(subreq, dns_tcp_call_writev_done, call);
}

static void dns_tcp_call_writev_done(struct tevent_req *subreq)
{
        struct dns_tcp_call *call = tevent_req_callback_data(subreq,
                        struct dns_tcp_call);
        int sys_errno;
        int rc;

        rc = tstream_writev_queue_recv(subreq, &sys_errno);
        TALLOC_FREE(subreq);
        if (rc == -1) {
                const char *reason;

                reason = talloc_asprintf(call, "dns_tcp_call_writev_done: "
                                         "tstream_writev_queue_recv() - %d:%s",
                                         sys_errno, strerror(sys_errno));
                if (!reason) {
                        reason = "dns_tcp_call_writev_done: tstream_writev_queue_recv() failed";
                }

                dns_tcp_terminate_connection(call->dns_conn, reason);
                return;
        }

        /* We don't care about errors */

        talloc_free(call);
}

/*
  called when we get a new connection
*/
static void dns_tcp_accept(struct stream_connection *conn)
{
        struct dns_socket *dns_socket;
        struct dns_tcp_connection *dns_conn;
        struct tevent_req *subreq;
        int rc;

        dns_conn = talloc_zero(conn, struct dns_tcp_connection);
        if (dns_conn == NULL) {
                stream_terminate_connection(conn,
                                "dns_tcp_accept: out of memory");
                return;
        }

        dns_conn->send_queue = tevent_queue_create(conn, "dns_tcp_accept");
        if (dns_conn->send_queue == NULL) {
                stream_terminate_connection(conn,
                                "dns_tcp_accept: out of memory");
                return;
        }

        dns_socket = talloc_get_type(conn->private_data, struct dns_socket);

        TALLOC_FREE(conn->event.fde);

        rc = tstream_bsd_existing_socket(dns_conn,
                        socket_get_fd(conn->socket),
                        &dns_conn->tstream);
        if (rc < 0) {
                stream_terminate_connection(conn,
                                "dns_tcp_accept: out of memory");
                return;
        }

        dns_conn->conn = conn;
        dns_conn->dns_socket = dns_socket;
        conn->private_data = dns_conn;

        /*
         * The dns tcp pdu's has the length as 2 byte (initial_read_size),
         * packet_full_request_u16 provides the pdu length then.
         */
        subreq = tstream_read_pdu_blob_send(dns_conn,
                                            dns_conn->conn->event.ctx,
                                            dns_conn->tstream,
                                            2, /* initial_read_size */
                                            packet_full_request_u16,
                                            dns_conn);
        if (subreq == NULL) {
                dns_tcp_terminate_connection(dns_conn, "dns_tcp_accept: "
                                "no memory for tstream_read_pdu_blob_send");
                return;
        }
        tevent_req_set_callback(subreq, dns_tcp_call_loop, dns_conn);
}

static const struct stream_server_ops dns_tcp_stream_ops = {
        .name                   = "dns_tcp",
        .accept_connection      = dns_tcp_accept,
        .recv_handler           = dns_tcp_recv,
        .send_handler           = dns_tcp_send
};

struct dns_udp_call {
        struct dns_udp_socket *sock;
        struct tsocket_address *src;
        DATA_BLOB in;
        DATA_BLOB out;
};

static void dns_udp_call_process_done(struct tevent_req *subreq);
static void dns_udp_call_sendto_done(struct tevent_req *subreq);

static void dns_udp_call_loop(struct tevent_req *subreq)
{
        struct dns_udp_socket *sock = tevent_req_callback_data(subreq,
                                      struct dns_udp_socket);
        struct dns_server *dns = sock->dns_socket->dns;
        struct dns_udp_call *call;
        uint8_t *buf;
        ssize_t len;
        int sys_errno;

        call = talloc(sock, struct dns_udp_call);
        if (call == NULL) {
                talloc_free(call);
                goto done;
        }
        call->sock = sock;

        len = tdgram_recvfrom_recv(subreq, &sys_errno,
                                   call, &buf, &call->src);
        TALLOC_FREE(subreq);
        if (len == -1) {
                talloc_free(call);
                goto done;
        }

        call->in.data = buf;
        call->in.length = len;

        DEBUG(10,("Received DNS UDP packet of length %lu from %s\n",
                 (long)call->in.length,
                 tsocket_address_string(call->src, call)));

        subreq = dns_process_send(call, dns->task->event_ctx, dns,
                                  &call->in);
        if (subreq == NULL) {
                TALLOC_FREE(call);
                goto done;
        }
        tevent_req_set_callback(subreq, dns_udp_call_process_done, call);

done:
        subreq = tdgram_recvfrom_send(sock,
                                      sock->dns_socket->dns->task->event_ctx,
                                      sock->dgram);
        if (subreq == NULL) {
                task_server_terminate(sock->dns_socket->dns->task,
                                      "no memory for tdgram_recvfrom_send",
                                      true);
                return;
        }
        tevent_req_set_callback(subreq, dns_udp_call_loop, sock);
}

static void dns_udp_call_process_done(struct tevent_req *subreq)
{
        struct dns_udp_call *call = tevent_req_callback_data(
                subreq, struct dns_udp_call);
        struct dns_udp_socket *sock = call->sock;
        struct dns_server *dns = sock->dns_socket->dns;
        WERROR err;

        err = dns_process_recv(subreq, call, &call->out);
        TALLOC_FREE(subreq);
        if (!W_ERROR_IS_OK(err)) {
                DEBUG(1, ("dns_process returned %s\n", win_errstr(err)));
                TALLOC_FREE(call);
                return;
        }

        subreq = tdgram_sendto_queue_send(call,
                                          dns->task->event_ctx,
                                          sock->dgram,
                                          sock->send_queue,
                                          call->out.data,
                                          call->out.length,
                                          call->src);
        if (subreq == NULL) {
                talloc_free(call);
                return;
        }
        tevent_req_set_callback(subreq, dns_udp_call_sendto_done, call);

}
static void dns_udp_call_sendto_done(struct tevent_req *subreq)
{
        struct dns_udp_call *call = tevent_req_callback_data(subreq,
                                       struct dns_udp_call);
        int sys_errno;

        tdgram_sendto_queue_recv(subreq, &sys_errno);

        /* We don't care about errors */

        talloc_free(call);
}

/*
  start listening on the given address
*/
static NTSTATUS dns_add_socket(struct dns_server *dns,
                               const struct model_ops *model_ops,
                               const char *name,
                               const char *address,
                               uint16_t port)
{
        struct dns_socket *dns_socket;
        struct dns_udp_socket *dns_udp_socket;
        struct tevent_req *udpsubreq;
        NTSTATUS status;
        int ret;

        dns_socket = talloc(dns, struct dns_socket);
        NT_STATUS_HAVE_NO_MEMORY(dns_socket);

        dns_socket->dns = dns;

        ret = tsocket_address_inet_from_strings(dns_socket, "ip",
                                                address, port,
                                                &dns_socket->local_address);
        if (ret != 0) {
                status = map_nt_error_from_unix_common(errno);
                return status;
        }

        status = stream_setup_socket(dns->task,
                                     dns->task->event_ctx,
                                     dns->task->lp_ctx,
                                     model_ops,
                                     &dns_tcp_stream_ops,
                                     "ip", address, &port,
                                     lpcfg_socket_options(dns->task->lp_ctx),
                                     dns_socket);
        if (!NT_STATUS_IS_OK(status)) {
                DEBUG(0,("Failed to bind to %s:%u TCP - %s\n",
                         address, port, nt_errstr(status)));
                talloc_free(dns_socket);
                return status;
        }

        dns_udp_socket = talloc(dns_socket, struct dns_udp_socket);
        NT_STATUS_HAVE_NO_MEMORY(dns_udp_socket);

        dns_udp_socket->dns_socket = dns_socket;

        ret = tdgram_inet_udp_socket(dns_socket->local_address,
                                     NULL,
                                     dns_udp_socket,
                                     &dns_udp_socket->dgram);
        if (ret != 0) {
                status = map_nt_error_from_unix_common(errno);
                DEBUG(0,("Failed to bind to %s:%u UDP - %s\n",
                         address, port, nt_errstr(status)));
                return status;
        }

        dns_udp_socket->send_queue = tevent_queue_create(dns_udp_socket,
                                                         "dns_udp_send_queue");
        NT_STATUS_HAVE_NO_MEMORY(dns_udp_socket->send_queue);

        udpsubreq = tdgram_recvfrom_send(dns_udp_socket,
                                         dns->task->event_ctx,
                                         dns_udp_socket->dgram);
        NT_STATUS_HAVE_NO_MEMORY(udpsubreq);
        tevent_req_set_callback(udpsubreq, dns_udp_call_loop, dns_udp_socket);

        return NT_STATUS_OK;
}

/*
  setup our listening sockets on the configured network interfaces
*/
static NTSTATUS dns_startup_interfaces(struct dns_server *dns, struct loadparm_context *lp_ctx,
                                       struct interface *ifaces)
{
        const struct model_ops *model_ops;
        int num_interfaces;
        TALLOC_CTX *tmp_ctx = talloc_new(dns);
        NTSTATUS status;
        int i;

        /* within the dns task we want to be a single process, so
           ask for the single process model ops and pass these to the
           stream_setup_socket() call. */
        model_ops = process_model_startup("single");
        if (!model_ops) {
                DEBUG(0,("Can't find 'single' process model_ops\n"));
                return NT_STATUS_INTERNAL_ERROR;
        }

        if (ifaces != NULL) {
                num_interfaces = iface_list_count(ifaces);

                for (i=0; i<num_interfaces; i++) {
                        const char *address = talloc_strdup(tmp_ctx,
                                                            iface_list_n_ip(ifaces, i));

                        status = dns_add_socket(dns, model_ops, "dns", address,
                                                DNS_SERVICE_PORT);
                        NT_STATUS_NOT_OK_RETURN(status);
                }
        } else {
                const char **wcard;
                wcard = iface_list_wildcard(tmp_ctx, lp_ctx);
                if (wcard == NULL) {
                        DEBUG(0, ("No wildcard address available\n"));
                        return NT_STATUS_INTERNAL_ERROR;
                }
                for (i = 0; wcard[i] != NULL; i++) {
                        status = dns_add_socket(dns, model_ops, "dns", wcard[i],
                                                DNS_SERVICE_PORT);
                        NT_STATUS_NOT_OK_RETURN(status);
                }
        }

        talloc_free(tmp_ctx);

        return NT_STATUS_OK;
}

static int dns_server_sort_zones(struct ldb_message **m1, struct ldb_message **m2)
{
        const char *n1, *n2;
        size_t l1, l2;

        n1 = ldb_msg_find_attr_as_string(*m1, "name", NULL);
        n2 = ldb_msg_find_attr_as_string(*m2, "name", NULL);

        l1 = strlen(n1);
        l2 = strlen(n2);

        /* If the string lengths are not equal just sort by length */
        if (l1 != l2) {
                /* If m1 is the larger zone name, return it first */
                return l2 - l1;
        }

        /*TODO: We need to compare DNs here, we want the DomainDNSZones first */
        return 0;
}

static struct dns_server_tkey_store *tkey_store_init(TALLOC_CTX *mem_ctx,
                                                     uint16_t size)
{
        struct dns_server_tkey_store *buffer = talloc_zero(mem_ctx,
                                                struct dns_server_tkey_store);

        if (buffer == NULL) {
                return NULL;
        }

        buffer->size = size;
        buffer->next_idx = 0;

        buffer->tkeys = talloc_zero_array(buffer, struct dns_server_tkey *, size);
        if (buffer->tkeys == NULL) {
                TALLOC_FREE(buffer);
        }

        return buffer;
}

static void dns_task_init(struct task_server *task)
{
        struct dns_server *dns;
        NTSTATUS status;
        struct interface *ifaces = NULL;
        int ret;
        struct ldb_result *res;
        static const char * const attrs[] = { "name", NULL};
        static const char * const attrs_none[] = { NULL};
        unsigned int i;
        struct ldb_message *dns_acc;
        char *hostname_lower;
        char *dns_spn;

        switch (lpcfg_server_role(task->lp_ctx)) {
        case ROLE_STANDALONE:
                task_server_terminate(task, "dns: no DNS required in standalone configuration", false);
                return;
        case ROLE_DOMAIN_MEMBER:
                task_server_terminate(task, "dns: no DNS required in member server configuration", false);
                return;
        case ROLE_ACTIVE_DIRECTORY_DC:
                /* Yes, we want a DNS */
                break;
        }

        if (lpcfg_interfaces(task->lp_ctx) && lpcfg_bind_interfaces_only(task->lp_ctx)) {
                load_interface_list(task, task->lp_ctx, &ifaces);

                if (iface_list_count(ifaces) == 0) {
                        task_server_terminate(task, "dns: no network interfaces configured", false);
                        return;
                }
        }

        task_server_set_title(task, "task[dns]");

        dns = talloc_zero(task, struct dns_server);
        if (dns == NULL) {
                task_server_terminate(task, "dns: out of memory", true);
                return;
        }

        dns->task = task;
        /*FIXME: Make this a configurable option */
        dns->max_payload = 4096;

        dns->server_credentials = cli_credentials_init(dns);
        if (!dns->server_credentials) {
                task_server_terminate(task, "Failed to init server credentials\n", true);
                return;
        }

        dns->samdb = samdb_connect(dns, dns->task->event_ctx, dns->task->lp_ctx,
                              system_session(dns->task->lp_ctx), 0);
        if (!dns->samdb) {
                task_server_terminate(task, "dns: samdb_connect failed", true);
                return;
        }

        cli_credentials_set_conf(dns->server_credentials, task->lp_ctx);

        hostname_lower = strlower_talloc(dns, lpcfg_netbios_name(task->lp_ctx));
        dns_spn = talloc_asprintf(dns, "DNS/%s.%s",
                                  hostname_lower,
                                  lpcfg_dnsdomain(task->lp_ctx));
        TALLOC_FREE(hostname_lower);

        ret = dsdb_search_one(dns->samdb, dns, &dns_acc,
                              ldb_get_default_basedn(dns->samdb), LDB_SCOPE_SUBTREE,
                              attrs_none, 0, "(servicePrincipalName=%s)",
                              dns_spn);
        if (ret == LDB_SUCCESS) {
                TALLOC_FREE(dns_acc);
                if (!dns_spn) {
                        task_server_terminate(task, "dns: talloc_asprintf failed", true);
                        return;
                }
                status = cli_credentials_set_stored_principal(dns->server_credentials, task->lp_ctx, dns_spn);
                if (!NT_STATUS_IS_OK(status)) {
                        task_server_terminate(task,
                                              talloc_asprintf(task, "Failed to obtain server credentials for DNS, "
                                                              "despite finding it in the samdb! %s\n",
                                                              nt_errstr(status)),
                                              true);
                        return;
                }
        } else {
                TALLOC_FREE(dns_spn);
                status = cli_credentials_set_machine_account(dns->server_credentials, task->lp_ctx);
                if (!NT_STATUS_IS_OK(status)) {
                        task_server_terminate(task,
                                              talloc_asprintf(task, "Failed to obtain server credentials, perhaps a standalone server?: %s\n",
                                                              nt_errstr(status)),
                                              true);
                        return;
                }
        }

        dns->tkeys = tkey_store_init(dns, TKEY_BUFFER_SIZE);
        if (!dns->tkeys) {
                task_server_terminate(task, "Failed to allocate tkey storage\n", true);
                return;
        }

        // TODO: this search does not work against windows
        ret = dsdb_search(dns->samdb, dns, &res, NULL, LDB_SCOPE_SUBTREE,
                          attrs, DSDB_SEARCH_SEARCH_ALL_PARTITIONS, "(objectClass=dnsZone)");
        if (ret != LDB_SUCCESS) {
                task_server_terminate(task,
                                      "dns: failed to look up root DNS zones",
                                      true);
                return;
        }

        TYPESAFE_QSORT(res->msgs, res->count, dns_server_sort_zones);

        for (i=0; i < res->count; i++) {
                struct dns_server_zone *z;

                z = talloc_zero(dns, struct dns_server_zone);
                if (z == NULL) {
                        task_server_terminate(task, "dns failed to allocate memory", true);
                }

                z->name = ldb_msg_find_attr_as_string(res->msgs[i], "name", NULL);
                z->dn = talloc_move(z, &res->msgs[i]->dn);
                /*
                 * Ignore the RootDNSServers zone and zones that we don't support yet
                 * RootDNSServers should never be returned (Windows DNS server don't)
                 * ..TrustAnchors should never be returned as is, (Windows returns
                 * TrustAnchors) and for the moment we don't support DNSSEC so we'd better
                 * not return this zone.
                 */
                if ((strcmp(z->name, "RootDNSServers") == 0) ||
                    (strcmp(z->name, "..TrustAnchors") == 0))
                {
                        DEBUG(10, ("Ignoring zone %s\n", z->name));
                        talloc_free(z);
                        continue;
                }
                DLIST_ADD_END(dns->zones, z, NULL);
        }

        status = dns_startup_interfaces(dns, task->lp_ctx, ifaces);
        if (!NT_STATUS_IS_OK(status)) {
                task_server_terminate(task, "dns failed to setup interfaces", true);
                return;
        }
}

NTSTATUS server_service_dns_init(void)
{
        return register_server_service("dns", dns_task_init);
}