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dns: modify dns forwarder param to be multi-valued

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This allows a secondary DNS forwarder for a trivial failover. Requests
which fail/timeout at the primary DNS forwarder will be restarted
entirely with the next forwarder in the list.

Signed-off-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
This commit is contained in:
Garming Sam 2016-02-17 11:30:21 +13:00 committed by Garming Sam
parent 870b74d73e
commit 5caebde11d
3 changed files with 94 additions and 17 deletions
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5
docs-xml/smbdotconf/domain/dnsforwarder.xml
View File

@ -1,10 +1,9 @@
<samba:parameter name="dns forwarder"
context="G"
type="string"
constant="1"
type="cmdlist"
xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
<description>
<para>This option specifies the DNS server that DNS requests will be
<para>This option specifies the list of DNS servers that DNS requests will be
forwarded to if they can not be handled by Samba itself.
</para>

100
source4/dns_server/dns_query.c
View File

@ -31,6 +31,7 @@
#include "dsdb/common/util.h"
#include "dns_server/dns_server.h"
#include "libcli/dns/libdns.h"
#include "lib/util/dlinklist.h"
#include "lib/util/util_net.h"
#include "lib/util/tevent_werror.h"
#include "auth/auth.h"
@ -40,6 +41,11 @@
#undef DBGC_CLASS
#define DBGC_CLASS DBGC_DNS
struct forwarder_string {
const char *forwarder;
struct forwarder_string *prev, *next;
};
static WERROR add_response_rr(const char *name,
const struct dnsp_DnssrvRpcRecord *rec,
struct dns_res_rec **answers)
@ -912,12 +918,17 @@ static WERROR handle_tkey(struct dns_server *dns,
}
struct dns_server_process_query_state {
struct tevent_context *ev;
struct dns_server *dns;
struct dns_name_question *question;
struct dns_res_rec *answers;
uint16_t ancount;
struct dns_res_rec *nsrecs;
uint16_t nscount;
struct dns_res_rec *additional;
uint16_t arcount;
struct forwarder_string *forwarders;
};
static void dns_server_process_query_got_auth(struct tevent_req *subreq);
@ -930,6 +941,8 @@ struct tevent_req *dns_server_process_query_send(
{
struct tevent_req *req, *subreq;
struct dns_server_process_query_state *state;
const char **forwarders = NULL;
unsigned int i;
req = tevent_req_create(mem_ctx, &state,
struct dns_server_process_query_state);
@ -959,6 +972,18 @@ struct tevent_req *dns_server_process_query_send(
return tevent_req_post(req, ev);
}
state->dns = dns;
state->ev = ev;
state->question = &in->questions[0];
forwarders = lpcfg_dns_forwarder(dns->task->lp_ctx);
for (i = 0; forwarders != NULL && forwarders[i] != NULL; i++) {
struct forwarder_string *f = talloc_zero(state,
struct forwarder_string);
f->forwarder = forwarders[i];
DLIST_ADD_END(state->forwarders, f);
}
if (dns_authorative_for_zone(dns, in->questions[0].name)) {
req_state->flags |= DNS_FLAG_AUTHORITATIVE;
@ -978,7 +1003,7 @@ struct tevent_req *dns_server_process_query_send(
}
subreq = handle_authoritative_send(
state, ev, dns, lpcfg_dns_forwarder(dns->task->lp_ctx),
state, ev, dns, (forwarders == NULL ? NULL : forwarders[0]),
&in->questions[0], &state->answers, &state->nsrecs);
if (tevent_req_nomem(subreq, req)) {
return tevent_req_post(req, ev);
@ -993,9 +1018,9 @@ struct tevent_req *dns_server_process_query_send(
DEBUG(2, ("Not authoritative for '%s', forwarding\n",
in->questions[0].name));
subreq = ask_forwarder_send(
state, ev, dns, lpcfg_dns_forwarder(dns->task->lp_ctx),
&in->questions[0]);
subreq = ask_forwarder_send(state, ev, dns,
(forwarders == NULL ? NULL : forwarders[0]),
&in->questions[0]);
if (tevent_req_nomem(subreq, req)) {
return tevent_req_post(req, ev);
}
@ -1014,16 +1039,42 @@ static void dns_server_process_query_got_response(struct tevent_req *subreq)
subreq, struct tevent_req);
struct dns_server_process_query_state *state = tevent_req_data(
req, struct dns_server_process_query_state);
WERROR err;
WERROR werr;
err = ask_forwarder_recv(subreq, state,
&state->answers, &state->ancount,
&state->nsrecs, &state->nscount,
&state->additional, &state->arcount);
werr = ask_forwarder_recv(subreq, state,
&state->answers, &state->ancount,
&state->nsrecs, &state->nscount,
&state->additional, &state->arcount);
TALLOC_FREE(subreq);
if (tevent_req_werror(req, err)) {
/* If you get an error, attempt a different forwarder */
if (!W_ERROR_IS_OK(werr)) {
if (state->forwarders != NULL) {
DLIST_REMOVE(state->forwarders, state->forwarders);
}
/* If you have run out of forwarders, simply finish */
if (state->forwarders == NULL) {
tevent_req_werror(req, werr);
return;
}
DEBUG(5, ("DNS query returned %s, trying another forwarder.\n",
win_errstr(werr)));
subreq = ask_forwarder_send(state, state->ev, state->dns,
state->forwarders->forwarder,
state->question);
if (tevent_req_nomem(subreq, req)) {
return;
}
tevent_req_set_callback(subreq,
dns_server_process_query_got_response,
req);
return;
}
tevent_req_done(req);
}
@ -1037,9 +1088,36 @@ static void dns_server_process_query_got_auth(struct tevent_req *subreq)
werr = handle_authoritative_recv(subreq);
TALLOC_FREE(subreq);
if (tevent_req_werror(req, werr)) {
/* If you get an error, attempt a different forwarder */
if (!W_ERROR_IS_OK(werr)) {
if (state->forwarders != NULL) {
DLIST_REMOVE(state->forwarders, state->forwarders);
}
/* If you have run out of forwarders, simply finish */
if (state->forwarders == NULL) {
tevent_req_werror(req, werr);
return;
}
DEBUG(5, ("Error: %s, trying a different forwarder.\n",
win_errstr(werr)));
subreq = handle_authoritative_send(state, state->ev, state->dns,
state->forwarders->forwarder,
state->question, &state->answers,
&state->nsrecs);
if (tevent_req_nomem(subreq, req)) {
return;
}
tevent_req_set_callback(subreq,
dns_server_process_query_got_auth,
req);
return;
}
state->ancount = talloc_array_length(state->answers);
state->nscount = talloc_array_length(state->nsrecs);
state->arcount = talloc_array_length(state->additional);

6
source4/dns_server/dns_server.c
View File

@ -123,7 +123,7 @@ static struct tevent_req *dns_process_send(TALLOC_CTX *mem_ctx,
struct dns_process_state *state;
enum ndr_err_code ndr_err;
WERROR ret;
const char *forwarder = lpcfg_dns_forwarder(dns->task->lp_ctx);
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;
@ -169,8 +169,8 @@ static struct tevent_req *dns_process_send(TALLOC_CTX *mem_ctx,
state->state.flags = state->in_packet.operation;
state->state.flags |= DNS_FLAG_REPLY;
if (forwarder && *forwarder) {
if (forwarder && *forwarder && **forwarder) {
state->state.flags |= DNS_FLAG_RECURSION_AVAIL;
}