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mirror of https://github.com/samba-team/samba.git synced 2024-12-22 13:34:15 +03:00

libcli/dns: Add dns_lookup

Wrapper function to parse resolv.conf and talk to multiple nameservers. This is
the code where we might want to add a "working nameserver" cache. glibc always
looks at the first configured nameserver. If that's dead, glibc runs into a
timeout and only then asks the second one that might succeed. When more than
one dns query is to be performed, these timeouts add up.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
This commit is contained in:
Volker Lendecke 2018-01-02 13:56:56 +01:00
parent e9e4aeafc0
commit 5f393deb30
4 changed files with 435 additions and 0 deletions

326
libcli/dns/dns_lookup.c Normal file
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@ -0,0 +1,326 @@
/*
* Unix SMB/CIFS implementation.
* Internal DNS query structures
* Copyright (C) Volker Lendecke 2018
*
* 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 "libcli/dns/dns_lookup.h"
#include "libcli/dns/resolvconf.h"
#include "libcli/dns/libdns.h"
#include "lib/util/tevent_unix.h"
#include "lib/util/samba_util.h"
#include "lib/util/debug.h"
struct dns_lookup_state {
struct tevent_context *ev;
const char *name;
enum dns_qclass qclass;
enum dns_qtype qtype;
char **nameservers;
size_t num_nameservers;
size_t num_sent;
struct tevent_req **dns_subreqs;
struct tevent_req *wait_subreq;
struct dns_name_packet *reply;
};
static int dns_lookup_send_next(struct tevent_req *req);
static void dns_lookup_done(struct tevent_req *subreq);
static void dns_lookup_waited(struct tevent_req *subreq);
struct tevent_req *dns_lookup_send(TALLOC_CTX *mem_ctx,
struct tevent_context *ev,
FILE *resolv_conf_fp,
const char *name,
enum dns_qclass qclass,
enum dns_qtype qtype)
{
struct tevent_req *req;
struct dns_lookup_state *state;
FILE *fp = resolv_conf_fp;
int ret;
req = tevent_req_create(mem_ctx, &state, struct dns_lookup_state);
if (req == NULL) {
return NULL;
}
state->ev = ev;
state->name = name;
state->qclass = qclass;
state->qtype = qtype;
if (resolv_conf_fp == NULL) {
fp = fopen("/etc/resolv.conf", "r");
if (fp == NULL) {
tevent_req_error(req, errno);
return tevent_req_post(req, ev);
}
}
ret = parse_resolvconf_fp(
fp,
state,
&state->nameservers,
&state->num_nameservers);
if (resolv_conf_fp == NULL) {
fclose(fp);
}
if (ret != 0) {
tevent_req_error(req, ret);
return tevent_req_post(req, ev);
}
if (state->num_nameservers == 0) {
/*
* glibc's getaddrinfo returns EAI_AGAIN when no
* nameservers are configured. EAGAIN seems closest.
*/
tevent_req_error(req, EAGAIN);
return tevent_req_post(req, ev);
}
state->dns_subreqs = talloc_zero_array(
state,
struct tevent_req *,
state->num_nameservers);
if (tevent_req_nomem(state->dns_subreqs, req)) {
return tevent_req_post(req, ev);
}
ret = dns_lookup_send_next(req);
if (tevent_req_error(req, ret)) {
return tevent_req_post(req, ev);
}
return req;
}
static int dns_lookup_send_next(struct tevent_req *req)
{
struct dns_lookup_state *state = tevent_req_data(
req, struct dns_lookup_state);
DBG_DEBUG("Sending DNS request #%zu to %s\n",
state->num_sent,
state->nameservers[state->num_sent]);
state->dns_subreqs[state->num_sent] = dns_cli_request_send(
state->dns_subreqs,
state->ev,
state->nameservers[state->num_sent],
state->name,
state->qclass,
state->qtype);
if (state->dns_subreqs[state->num_sent] == NULL) {
return ENOMEM;
}
tevent_req_set_callback(state->dns_subreqs[state->num_sent],
dns_lookup_done,
req);
state->num_sent += 1;
if (state->num_sent == state->num_nameservers) {
/*
* No more nameservers left
*/
DBG_DEBUG("cancelling wait_subreq\n");
TALLOC_FREE(state->wait_subreq);
return 0;
}
if (state->wait_subreq != NULL) {
/*
* This can happen if we fire the next request upon
* dns_cli_request returning a network-level error
*/
return 0;
}
state->wait_subreq = tevent_wakeup_send(
state,
state->ev,
tevent_timeval_current_ofs(1, 0));
if (state->wait_subreq == NULL) {
return ENOMEM;
}
tevent_req_set_callback(state->wait_subreq, dns_lookup_waited, req);
return 0;
}
static void dns_lookup_done(struct tevent_req *subreq)
{
struct tevent_req *req = tevent_req_callback_data(
subreq, struct tevent_req);
struct dns_lookup_state *state = tevent_req_data(
req, struct dns_lookup_state);
int dns_cli_request_ret;
size_t i;
dns_cli_request_ret = dns_cli_request_recv(
subreq,
state,
&state->reply);
for (i = 0; i < state->num_nameservers; i++) {
if (state->dns_subreqs[i] == subreq) {
break;
}
}
TALLOC_FREE(subreq);
if (i == state->num_nameservers) {
/* should never happen */
DBG_WARNING("Failed to find subreq");
tevent_req_error(req, EINVAL);
return;
}
state->dns_subreqs[i] = NULL;
if (dns_cli_request_ret == 0) {
/*
* Success, cancel everything else
*/
TALLOC_FREE(state->dns_subreqs);
TALLOC_FREE(state->wait_subreq);
tevent_req_done(req);
return;
}
DBG_DEBUG("dns_cli_request[%zu] returned %s\n", i,
strerror(dns_cli_request_ret));
if (state->num_sent < state->num_nameservers) {
/*
* We have a nameserver left to try
*/
int ret;
ret = dns_lookup_send_next(req);
if (tevent_req_error(req, ret)) {
return;
}
}
DBG_DEBUG("looking for outstanding requests\n");
for (i = 0; i<state->num_nameservers; i++) {
if (state->dns_subreqs[i] != NULL) {
break;
}
}
DBG_DEBUG("i=%zu, num_nameservers=%zu\n",
i, state->num_nameservers);
if (i == state->num_nameservers) {
/*
* Report the lower-level error if we have nothing
* outstanding anymore
*/
tevent_req_error(req, dns_cli_request_ret);
return;
}
/*
* Do nothing: We have other nameservers that might come back
* with something good.
*/
}
static void dns_lookup_waited(struct tevent_req *subreq)
{
struct tevent_req *req = tevent_req_callback_data(
subreq, struct tevent_req);
struct dns_lookup_state *state = tevent_req_data(
req, struct dns_lookup_state);
int ret;
bool ok;
DBG_DEBUG("waited\n");
ok = tevent_wakeup_recv(subreq);
TALLOC_FREE(subreq);
if (!ok) {
tevent_req_oom(req);
return;
}
state->wait_subreq = NULL;
ret = dns_lookup_send_next(req);
if (tevent_req_error(req, ret)) {
return;
}
/*
* dns_lookup_send_next() has already triggered the next wakeup
*/
}
int dns_lookup_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
struct dns_name_packet **reply)
{
struct dns_lookup_state *state = tevent_req_data(
req, struct dns_lookup_state);
int err;
if (tevent_req_is_unix_error(req, &err)) {
return err;
}
*reply = talloc_move(mem_ctx, &state->reply);
tevent_req_received(req);
return 0;
}
int dns_lookup(FILE *resolv_conf_fp,
const char *name,
enum dns_qclass qclass,
enum dns_qtype qtype,
TALLOC_CTX *mem_ctx,
struct dns_name_packet **reply)
{
struct tevent_context *ev;
struct tevent_req *req;
int ret = ENOMEM;
ev = samba_tevent_context_init(mem_ctx);
if (ev == NULL) {
goto fail;
}
req = dns_lookup_send(ev, ev, resolv_conf_fp, name, qclass, qtype);
if (req == NULL) {
goto fail;
}
if (!tevent_req_poll_unix(req, ev, &ret)) {
goto fail;
}
ret = dns_lookup_recv(req, mem_ctx, reply);
fail:
TALLOC_FREE(ev);
return ret;
}

45
libcli/dns/dns_lookup.h Normal file
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@ -0,0 +1,45 @@
/*
* Unix SMB/CIFS implementation.
* Internal DNS query structures
* Copyright (C) Volker Lendecke 2018
*
* 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 __LIBCLI_DNS_DNS_LOOKUP_H__
#define __LIBCLI_DNS_DNS_LOOKUP_H__
#include "replace.h"
#include "system/network.h"
#include <tevent.h>
#include "lib/util/data_blob.h"
#include "lib/util/time.h"
#include "librpc/gen_ndr/dns.h"
struct tevent_req *dns_lookup_send(TALLOC_CTX *mem_ctx,
struct tevent_context *ev,
FILE *resolv_conf_fp,
const char *name,
enum dns_qclass qclass,
enum dns_qtype qtype);
int dns_lookup_recv(struct tevent_req *req, TALLOC_CTX *mem_ctx,
struct dns_name_packet **reply);
int dns_lookup(FILE *resolv_conf_fp,
const char *name,
enum dns_qclass qclass,
enum dns_qtype qtype,
TALLOC_CTX *mem_ctx,
struct dns_name_packet **reply);
#endif

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@ -0,0 +1,55 @@
/*
* Unix SMB/CIFS implementation.
* Internal DNS query structures
* Copyright (C) Volker Lendecke 2018
*
* 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 <stdio.h>
#include <string.h>
#include <talloc.h>
#include <errno.h>
#include "libcli/dns/dns_lookup.h"
#include "lib/util/debug.h"
static int dns_lookuptest1(void)
{
struct dns_name_packet *reply = NULL;
int ret;
ret = dns_lookup(NULL, "www.samba.org", DNS_QCLASS_IN, DNS_QTYPE_A,
NULL, &reply);
if (ret != 0) {
fprintf(stderr, "dns_lookup failed: %s\n", strerror(ret));
return ret;
}
TALLOC_FREE(reply);
return 0;
}
int main(int argc, const char *argv[]) {
int ret;
setup_logging(argv[0], DEBUG_DEFAULT_STDERR);
debug_parse_levels("10");
ret = dns_lookuptest1();
if (ret != 0) {
return 1;
}
return 0;
}

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@ -8,3 +8,12 @@ bld.SAMBA_BINARY('resolvconftest',
source='resolvconftest.c',
deps='clidns',
install=False)
bld.SAMBA_SUBSYSTEM('dns_lookup',
source='dns_lookup.c',
public_deps='clidns')
bld.SAMBA_BINARY('dns_lookuptest',
source='dns_lookuptest.c',
deps='dns_lookup',
install=False)