libcli: Add ads_dns_query_srv_send()/recv()

This issues the "query" for SRV records site-aware and siteless. If
there are SRV records returned without IP addresses, it will issue A
and AAAA requests, waiting up to async_dns_timeout seconds. If that
timeout is reached, ads_dns_query_srv_recv() returns whatever is
around.

Superdebug added by Jeremy <jra@samba.org> :-)

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

lib/addns/dnsquery_srv.c

@@ -0,0 +1,560 @@
+/*
+ *  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 "replace.h"
+#include "dnsquery.h"
+#include "dnsquery_srv.h"
+#include "lib/util/debug.h"
+#include "lib/util/tevent_ntstatus.h"
+#include "lib/util/talloc_stack.h"
+#include "lib/util/samba_util.h"
+#include "librpc/gen_ndr/dns.h"
+#include "librpc/ndr/libndr.h"
+
+/*
+ * For an array of dns_rr_srv records, issue A/AAAA queries for those
+ * records where the initial reply did not return IP addresses.
+ */
+
+struct dns_rr_srv_fill_state {
+	struct dns_rr_srv *srvs;
+	size_t num_srvs;
+
+	struct tevent_req **subreqs;
+	size_t num_outstanding;
+};
+
+static void dns_rr_srv_fill_done_a(struct tevent_req *subreq);
+#if defined(HAVE_IPV6)
+static void dns_rr_srv_fill_done_aaaa(struct tevent_req *subreq);
+#endif
+static void dns_rr_srv_fill_timedout(struct tevent_req *subreq);
+
+static struct tevent_req *dns_rr_srv_fill_send(
+	TALLOC_CTX *mem_ctx,
+	struct tevent_context *ev,
+	struct dns_rr_srv *srvs,
+	size_t num_srvs,
+	uint32_t timeout)
+{
+	struct tevent_req *req = NULL, *subreq = NULL;
+	struct dns_rr_srv_fill_state *state = NULL;
+	size_t i, num_subreqs;
+
+	req = tevent_req_create(mem_ctx, &state, struct dns_rr_srv_fill_state);
+	if (req == NULL) {
+		return NULL;
+	}
+	state->srvs = srvs;
+	state->num_srvs = num_srvs;
+
+	/*
+	 * Without IPv6 we only use half of this, but who does not
+	 * have IPv6 these days?
+	 */
+	num_subreqs = num_srvs * 2;
+
+	state->subreqs = talloc_zero_array(
+		state, struct tevent_req *, num_subreqs);
+	if (tevent_req_nomem(state->subreqs, req)) {
+		return tevent_req_post(req, ev);
+	}
+
+	for (i=0; i<num_srvs; i++) {
+
+		if (srvs[i].hostname == NULL) {
+			continue;
+		}
+		if (srvs[i].ss_s != NULL) {
+			/* IP address returned in SRV record. */
+			continue;
+		}
+
+		subreq = ads_dns_lookup_a_send(
+			state->subreqs, ev, srvs[i].hostname);
+		if (tevent_req_nomem(subreq, req)) {
+			TALLOC_FREE(state->subreqs);
+			return tevent_req_post(req, ev);
+		}
+		tevent_req_set_callback(
+			subreq, dns_rr_srv_fill_done_a, req);
+
+		state->subreqs[i*2] = subreq;
+		state->num_outstanding += 1;
+
+#if defined(HAVE_IPV6)
+		subreq = ads_dns_lookup_aaaa_send(
+			state->subreqs, ev, srvs[i].hostname);
+		if (tevent_req_nomem(subreq, req)) {
+			TALLOC_FREE(state->subreqs);
+			return tevent_req_post(req, ev);
+		}
+		tevent_req_set_callback(
+			subreq, dns_rr_srv_fill_done_aaaa, req);
+
+		state->subreqs[i*2+1] = subreq;
+		state->num_outstanding += 1;
+#endif
+	}
+
+	if (state->num_outstanding == 0) {
+		tevent_req_done(req);
+		return tevent_req_post(req, ev);
+	}
+
+	subreq = tevent_wakeup_send(
+		state->subreqs,
+		ev,
+		tevent_timeval_current_ofs(timeout, 0));
+	if (tevent_req_nomem(subreq, req)) {
+		return tevent_req_post(req, ev);
+	}
+	tevent_req_set_callback(subreq, dns_rr_srv_fill_timedout, req);
+
+	return req;
+}
+
+static void dns_rr_srv_fill_done(
+	struct tevent_req *subreq,
+	NTSTATUS (*recv_fn)(
+		struct tevent_req *req,
+		TALLOC_CTX *mem_ctx,
+		uint8_t *rcode_out,
+		size_t *num_names_out,
+		char ***hostnames_out,
+		struct samba_sockaddr **addrs_out))
+{
+	struct tevent_req *req = tevent_req_callback_data(
+		subreq, struct tevent_req);
+	struct dns_rr_srv_fill_state *state = tevent_req_data(
+		req, struct dns_rr_srv_fill_state);
+	size_t num_subreqs = talloc_array_length(state->subreqs);
+	struct dns_rr_srv *srv = NULL;
+	size_t num_ips;
+	struct sockaddr_storage *tmp = NULL;
+	uint8_t rcode = 0;
+	char **hostnames_out = NULL;
+	struct samba_sockaddr *addrs = NULL;
+	size_t num_addrs = 0;
+	NTSTATUS status;
+	size_t i;
+	const char *ip_dbg_str = (recv_fn == ads_dns_lookup_a_recv) ?
+				 "A" : "AAAA";
+
+	/*
+	 * This loop walks all potential subreqs. Typical setups won't
+	 * have more than a few DCs. If you have really many DCs
+	 * (hundreds) and a DNS that doesn't return the DC IPs in the
+	 * SRV reply, you have bigger problems than this loop linearly
+	 * walking a pointer array. This is theoretically O(n^2), but
+	 * probably the DNS roundtrip time outweights this by a
+	 * lot. And we have a global timeout on this whole
+	 * dns_rr_srv_fill routine.
+	 */
+	for (i=0; i<num_subreqs; i++) {
+		if (state->subreqs[i] == subreq) {
+			state->subreqs[i] = NULL;
+			break;
+		}
+	}
+	if (i == num_subreqs) {
+		tevent_req_nterror(req, NT_STATUS_INTERNAL_ERROR);
+		return;
+	}
+
+	srv = &state->srvs[i/2]; /* 2 subreq per srv */
+
+	status = recv_fn(
+		subreq,
+		state,
+		&rcode,
+		&num_addrs,
+		&hostnames_out,
+		&addrs);
+	TALLOC_FREE(subreq);
+
+	if (!NT_STATUS_IS_OK(status)) {
+		DBG_INFO("async DNS %s lookup for %s returned %s\n",
+			 ip_dbg_str,
+			 srv->hostname,
+			 nt_errstr(status));
+		num_addrs = 0;
+		goto done;
+	}
+
+	if (rcode != DNS_RCODE_OK) {
+		DBG_INFO("async DNS %s lookup for %s returned DNS code "
+			 "%"PRIu8"\n",
+			 ip_dbg_str,
+			 srv->hostname,
+			 rcode);
+		num_addrs = 0;
+		goto done;
+	}
+
+	if (num_addrs == 0) {
+		DBG_INFO("async DNS %s lookup for %s returned 0 addresses.\n",
+			 ip_dbg_str,
+			 srv->hostname);
+		goto done;
+	}
+
+	num_ips = talloc_array_length(srv->ss_s);
+
+	if (num_ips + num_addrs < num_addrs) {
+		/* overflow */
+		goto done;
+	}
+
+	tmp = talloc_realloc(
+		state->srvs,
+		srv->ss_s,
+		struct sockaddr_storage,
+		num_ips + num_addrs);
+	if (tmp == NULL) {
+		goto done;
+	}
+
+	for (i=0; i<num_addrs; i++) {
+		char addr[INET6_ADDRSTRLEN];
+		DBG_INFO("async DNS %s lookup for %s [%zu] got %s -> %s\n",
+			 ip_dbg_str,
+			 srv->hostname,
+			 i,
+			 hostnames_out[i],
+			 print_sockaddr(addr, sizeof(addr), &addrs[i].u.ss));
+		tmp[num_ips + i] = addrs[i].u.ss;
+	}
+	srv->ss_s = tmp;
+	srv->num_ips = num_ips + num_addrs;
+
+done:
+	state->num_outstanding -= 1;
+	if (state->num_outstanding == 0) {
+		tevent_req_done(req);
+	}
+}
+
+static void dns_rr_srv_fill_done_a(struct tevent_req *subreq)
+{
+	dns_rr_srv_fill_done(subreq, ads_dns_lookup_a_recv);
+}
+
+#if defined(HAVE_IPV6)
+static void dns_rr_srv_fill_done_aaaa(struct tevent_req *subreq)
+{
+	dns_rr_srv_fill_done(subreq, ads_dns_lookup_aaaa_recv);
+}
+#endif
+
+static void dns_rr_srv_fill_timedout(struct tevent_req *subreq)
+{
+	struct tevent_req *req = tevent_req_callback_data(
+		subreq, struct tevent_req);
+	struct dns_rr_srv_fill_state *state = tevent_req_data(
+		req, struct dns_rr_srv_fill_state);
+	bool ok;
+
+	if (DEBUGLEVEL >= DBGLVL_INFO) {
+		size_t i, num_addrs = 0;
+
+		for (i=0; i<state->num_srvs; i++) {
+			/*
+			 * Count for the debug. Code that fills this
+			 * in ensures no wrap.
+			 */
+			num_addrs += state->srvs[i].num_ips;
+		}
+
+		DBG_INFO("async DNS lookup timed out after %zu addresses "
+			 "returned (not an error)\n",
+			 num_addrs);
+	}
+
+	ok = tevent_wakeup_recv(subreq);
+	TALLOC_FREE(subreq);
+	TALLOC_FREE(state->subreqs);
+	if (!ok) {
+		tevent_req_oom(subreq);
+		return;
+	}
+
+	tevent_req_done(req);
+}
+
+static NTSTATUS dns_rr_srv_fill_recv(struct tevent_req *req)
+{
+	return tevent_req_simple_recv_ntstatus(req);
+}
+
+/*
+ * Request a SRV record and fill in the A/AAAA records if the SRV
+ * record did not carry them.
+ */
+
+struct ads_dns_query_srv_state {
+	struct tevent_context *ev;
+	uint32_t async_dns_timeout;
+	const char *query;
+
+	struct tevent_req *fill_req;
+	struct tevent_req *timeout_req;
+	struct dns_rr_srv *srvs;
+	size_t num_srvs;
+};
+
+static void ads_dns_query_srv_site_aware_done(struct tevent_req *subreq);
+static void ads_dns_query_srv_done(struct tevent_req *subreq);
+static void ads_dns_query_srv_filled(struct tevent_req *subreq);
+
+struct tevent_req *ads_dns_query_srv_send(
+	TALLOC_CTX *mem_ctx,
+	struct tevent_context *ev,
+	uint32_t async_dns_timeout,
+	const char *sitename,
+	const char *query)
+{
+	struct tevent_req *req = NULL, *subreq = NULL;
+	struct ads_dns_query_srv_state *state = NULL;
+
+	req = tevent_req_create(
+		mem_ctx, &state, struct ads_dns_query_srv_state);
+	if (req == NULL) {
+		return NULL;
+	}
+	state->ev = ev;
+	state->async_dns_timeout = async_dns_timeout;
+	state->query = query;
+
+	if ((sitename != NULL) && (sitename[0] != '\0')) {
+		char *after_tcp = NULL;
+		char *site_aware = NULL;
+
+		/*
+		 * ".<SITENAME>._sites" comes after "._tcp."
+		 */
+		after_tcp = strstr(state->query, "._tcp.");
+		if (after_tcp == NULL) {
+			tevent_req_nterror(req, NT_STATUS_INVALID_PARAMETER);
+			return tevent_req_post(req, ev);
+		}
+		after_tcp += 6; /* strlen("._tcp.") */
+
+		site_aware = talloc_asprintf(
+			state,
+			"%.*s%s._sites.%s",
+			(int)(after_tcp - state->query),
+			state->query,
+			sitename,
+			after_tcp);
+		if (tevent_req_nomem(site_aware, req)) {
+			return tevent_req_post(req, ev);
+		}
+
+		subreq = ads_dns_lookup_srv_send(state, ev, site_aware);
+		if (tevent_req_nomem(subreq, req)) {
+			return tevent_req_post(req, ev);
+		}
+		tevent_req_set_callback(
+			subreq, ads_dns_query_srv_site_aware_done, req);
+		return req;
+	}
+
+	subreq = ads_dns_lookup_srv_send(state, state->ev, state->query);
+	if (tevent_req_nomem(subreq, req)) {
+		return tevent_req_post(req, ev);
+	}
+	tevent_req_set_callback(subreq, ads_dns_query_srv_done, req);
+	return req;
+}
+
+static void ads_dns_query_srv_site_aware_done(struct tevent_req *subreq)
+{
+	struct tevent_req *req = tevent_req_callback_data(
+		subreq, struct tevent_req);
+	struct ads_dns_query_srv_state *state = tevent_req_data(
+		req, struct ads_dns_query_srv_state);
+	NTSTATUS status;
+
+	status = ads_dns_lookup_srv_recv(
+		subreq, state, &state->srvs, &state->num_srvs);
+	TALLOC_FREE(subreq);
+
+	if (NT_STATUS_EQUAL(status, NT_STATUS_IO_TIMEOUT) ||
+	    NT_STATUS_EQUAL(status, NT_STATUS_CONNECTION_REFUSED)) {
+		tevent_req_nterror(req, status);
+		return;
+	}
+
+	if (NT_STATUS_IS_OK(status) && (state->num_srvs != 0)) {
+		if (state->async_dns_timeout == 0) {
+			tevent_req_done(req);
+			return;
+		}
+
+		subreq = dns_rr_srv_fill_send(
+			state,
+			state->ev,
+			state->srvs,
+			state->num_srvs,
+			state->async_dns_timeout);
+		if (tevent_req_nomem(subreq, req)) {
+			return;
+		}
+		tevent_req_set_callback(
+			subreq, ads_dns_query_srv_filled, req);
+		return;
+	}
+
+	subreq = ads_dns_lookup_srv_send(state, state->ev, state->query);
+	if (tevent_req_nomem(subreq, req)) {
+		return;
+	}
+	tevent_req_set_callback(subreq, ads_dns_query_srv_done, req);
+}
+
+static void ads_dns_query_srv_done(struct tevent_req *subreq)
+{
+	struct tevent_req *req = tevent_req_callback_data(
+		subreq, struct tevent_req);
+	struct ads_dns_query_srv_state *state = tevent_req_data(
+		req, struct ads_dns_query_srv_state);
+	NTSTATUS status;
+
+	status = ads_dns_lookup_srv_recv(
+		subreq, state, &state->srvs, &state->num_srvs);
+	if (tevent_req_nterror(req, status)) {
+		return;
+	}
+
+	if ((state->num_srvs == 0) || (state->async_dns_timeout == 0)) {
+		tevent_req_done(req);
+		return;
+	}
+
+	subreq = dns_rr_srv_fill_send(
+		state,
+		state->ev,
+		state->srvs,
+		state->num_srvs,
+		state->async_dns_timeout);
+	if (tevent_req_nomem(subreq, req)) {
+		return;
+	}
+	tevent_req_set_callback(subreq, ads_dns_query_srv_filled, req);
+}
+
+static void ads_dns_query_srv_filled(struct tevent_req *subreq)
+{
+	NTSTATUS status = dns_rr_srv_fill_recv(subreq);
+	return tevent_req_simple_finish_ntstatus(subreq, status);
+}
+
+NTSTATUS ads_dns_query_srv_recv(
+	struct tevent_req *req,
+	TALLOC_CTX *mem_ctx,
+	struct dns_rr_srv **srvs,
+	size_t *num_srvs)
+{
+	struct ads_dns_query_srv_state *state = tevent_req_data(
+		req, struct ads_dns_query_srv_state);
+	NTSTATUS status;
+
+	if (tevent_req_is_nterror(req, &status)) {
+		tevent_req_received(req);
+		return status;
+	}
+	if (srvs != NULL) {
+		*srvs = talloc_move(mem_ctx, &state->srvs);
+	}
+	if (num_srvs != NULL) {
+		*num_srvs = state->num_srvs;
+	}
+	tevent_req_received(req);
+	return NT_STATUS_OK;
+}
+
+NTSTATUS ads_dns_query_srv(
+	TALLOC_CTX *mem_ctx,
+	uint32_t async_dns_timeout,
+	const char *sitename,
+	const char *query,
+	struct dns_rr_srv **srvs,
+	size_t *num_srvs)
+{
+	TALLOC_CTX *frame = talloc_stackframe();
+	struct tevent_context *ev = NULL;
+	struct tevent_req *req = NULL;
+	NTSTATUS status = NT_STATUS_NO_MEMORY;
+
+	ev = samba_tevent_context_init(frame);
+	if (ev == NULL) {
+		goto fail;
+	}
+	req = ads_dns_query_srv_send(
+		frame, ev, async_dns_timeout, sitename, query);
+	if (req == NULL) {
+		goto fail;
+	}
+	if (!tevent_req_poll_ntstatus(req, ev, &status)) {
+		goto fail;
+	}
+	status = ads_dns_query_srv_recv(req, mem_ctx, srvs, num_srvs);
+fail:
+	TALLOC_FREE(frame);
+	return status;
+}
+
+char *ads_dns_query_string_dcs(TALLOC_CTX *mem_ctx, const char *realm)
+{
+	char *ret = talloc_asprintf(mem_ctx, "_ldap._tcp.dc._msdcs.%s", realm);
+	return ret;
+}
+
+char *ads_dns_query_string_gcs(TALLOC_CTX *mem_ctx, const char *realm)
+{
+	char *ret = talloc_asprintf(mem_ctx, "_ldap._tcp.gc._msdcs.%s", realm);
+	return ret;
+}
+
+char *ads_dns_query_string_kdcs(TALLOC_CTX *mem_ctx, const char *realm)
+{
+	char *ret = talloc_asprintf(
+		mem_ctx, "_kerberos._tcp.dc._msdcs.%s", realm);
+	return ret;
+}
+
+char *ads_dns_query_string_pdc(TALLOC_CTX *mem_ctx, const char *realm)
+{
+	char *ret = talloc_asprintf(
+		mem_ctx, "_ldap._tcp.pdc._msdcs.%s", realm);
+	return ret;
+}
+
+char *ads_dns_query_string_dcs_guid(
+	TALLOC_CTX *mem_ctx,
+	const struct GUID *domain_guid,
+	const char *realm)
+{
+	struct GUID_txt_buf buf;
+	char *ret = NULL;
+
+	talloc_asprintf(
+		mem_ctx,
+		"_ldap._tcp.%s.domains._msdcs.%s",
+		GUID_buf_string(domain_guid, &buf),
+		realm);
+	return ret;
+}

lib/addns/dnsquery_srv.h

@@ -0,0 +1,54 @@
+/*
+ *  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/>.
+ */
+
+#ifndef __LIB_ADDNS_DNSQUERY_SRV_H__
+#define __LIB_ADDNS_DNSQUERY_SRV_H__
+
+#include "replace.h"
+#include <tevent.h>
+#include "libcli/util/ntstatus.h"
+#include "libcli/dns/dns.h"
+
+struct tevent_req *ads_dns_query_srv_send(
+	TALLOC_CTX *mem_ctx,
+	struct tevent_context *ev,
+	uint32_t async_dns_timeout,
+	const char *sitename,
+	const char *query);
+NTSTATUS ads_dns_query_srv_recv(
+	struct tevent_req *req,
+	TALLOC_CTX *mem_ctx,
+	struct dns_rr_srv **srvs,
+	size_t *num_srvs);
+NTSTATUS ads_dns_query_srv(
+	TALLOC_CTX *mem_ctx,
+	uint32_t async_dns_timeout,
+	const char *sitename,
+	const char *query,
+	struct dns_rr_srv **srvs,
+	size_t *num_srvs);
+
+char *ads_dns_query_string_dcs(TALLOC_CTX *mem_ctx, const char *realm);
+char *ads_dns_query_string_gcs(TALLOC_CTX *mem_ctx, const char *realm);
+char *ads_dns_query_string_kdcs(TALLOC_CTX *mem_ctx, const char *realm);
+char *ads_dns_query_string_pdc(TALLOC_CTX *mem_ctx, const char *realm);
+
+struct GUID;
+char *ads_dns_query_string_dcs_guid(
+	TALLOC_CTX *mem_ctx,
+	const struct GUID *domain_guid,
+	const char *realm);
+
+#endif	/* _ADS_DNS_H */

lib/addns/wscript_build

@@ -9,6 +9,7 @@ bld.SAMBA_LIBRARY('addns',
                        dnsgss.c
                        dnsmarshall.c
                        error.c
+                       dnsquery_srv.c
                    ''',
                    public_deps='samba-util gssapi ndr resolv dns_lookup',
                    private_library=True,