dns: Support larger queries when asking forwarder

This should fix bug #9632

Signed-off-by: Kai Blin <kai@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org>

4 files changed, 40 insertions, 0 deletions

diff --git a/source4/dns_server/dns_query.c b/source4/dns_server/dns_query.c
index 4ad14b9a55..5414e1d9ee 100644
--- a/source4/dns_server/dns_query.c
+++ b/source4/dns_server/dns_query.c
@@ -138,14 +138,17 @@ struct ask_forwarder_state {
 static void ask_forwarder_done(struct tevent_req *subreq);
 
 static struct tevent_req *ask_forwarder_send(
+	struct dns_server *dns,
 	TALLOC_CTX *mem_ctx, struct tevent_context *ev,
 	const char *forwarder, struct dns_name_question *question)
 {
 	struct tevent_req *req, *subreq;
 	struct ask_forwarder_state *state;
+	struct dns_res_rec *options;
 	struct dns_name_packet out_packet = { 0, };
 	DATA_BLOB out_blob;
 	enum ndr_err_code ndr_err;
+	WERROR werr;
 
 	req = tevent_req_create(mem_ctx, &state, struct ask_forwarder_state);
 	if (req == NULL) {
@@ -166,6 +169,15 @@ static struct tevent_req *ask_forwarder_send(
 	out_packet.qdcount = 1;
 	out_packet.questions = question;
 
+	werr = dns_generate_options(dns, state, &options);
+	if (!W_ERROR_IS_OK(werr)) {
+		tevent_req_werror(req, werr);
+		return tevent_req_post(req, ev);
+	}
+
+	out_packet.arcount = 1;
+	out_packet.additional = options;
+
 	ndr_err = ndr_push_struct_blob(
 		&out_blob, state, &out_packet,
 		(ndr_push_flags_fn_t)ndr_push_dns_name_packet);
@@ -615,6 +627,7 @@ struct tevent_req *dns_server_process_query_send(
 			  in->questions[0].name));
 
 		subreq = ask_forwarder_send(
+			dns,
 			state, ev, lpcfg_dns_forwarder(dns->task->lp_ctx),
 			&in->questions[0]);
 		if (tevent_req_nomem(subreq, req)) {
diff --git a/source4/dns_server/dns_server.c b/source4/dns_server/dns_server.c
index bb4605f56a..7ad4acae7a 100644
--- a/source4/dns_server/dns_server.c
+++ b/source4/dns_server/dns_server.c
@@ -791,6 +791,8 @@ static void dns_task_init(struct task_server *task)
 	}
 
 	dns->task = task;
+	/*FIXME: Make this a configurable option */
+	dns->max_payload = 4096;
 
 	dns->server_credentials = cli_credentials_init(dns);
 	if (!dns->server_credentials) {
diff --git a/source4/dns_server/dns_server.h b/source4/dns_server/dns_server.h
index ef85730ff8..efe4db822f 100644
--- a/source4/dns_server/dns_server.h
+++ b/source4/dns_server/dns_server.h
@@ -56,6 +56,7 @@ struct dns_server {
 	struct dns_server_zone *zones;
 	struct dns_server_tkey_store *tkeys;
 	struct cli_credentials *server_credentials;
+	uint16_t max_payload;
 };
 
 struct dns_request_state {
@@ -107,6 +108,9 @@ WERROR dns_name2dn(struct dns_server *dns,
 		   TALLOC_CTX *mem_ctx,
 		   const char *name,
 		   struct ldb_dn **_dn);
+WERROR dns_generate_options(struct dns_server *dns,
+			    TALLOC_CTX *mem_ctx,
+			    struct dns_res_rec **options);
 struct dns_server_tkey *dns_find_tkey(struct dns_server_tkey_store *store,
 				      const char *name);
 WERROR dns_verify_tsig(struct dns_server *dns,
diff --git a/source4/dns_server/dns_utils.c b/source4/dns_server/dns_utils.c
index e03a409751..21c7f5a680 100644
--- a/source4/dns_server/dns_utils.c
+++ b/source4/dns_server/dns_utils.c
@@ -378,3 +378,24 @@ WERROR dns_name2dn(struct dns_server *dns,
 	*_dn = dn;
 	return WERR_OK;
 }
+
+WERROR dns_generate_options(struct dns_server *dns,
+			    TALLOC_CTX *mem_ctx,
+			    struct dns_res_rec **options)
+{
+	struct dns_res_rec *o;
+
+	o = talloc_zero(mem_ctx, struct dns_res_rec);
+	if (o == NULL) {
+		return WERR_NOMEM;
+	}
+	o->name = '\0';
+	o->rr_type = DNS_QTYPE_OPT;
+	/* This is ugly, but RFC2671 wants the payload size in this field */
+	o->rr_class = (enum dns_qclass) dns->max_payload;
+	o->ttl = 0;
+	o->length = 0;
+
+	*options = o;
+	return WERR_OK;
+}