[master] Prevent dig INSIST failures and hangs in some failure modes

4756.	[bug]		Interrupting dig could lead to an INSIST failure after
			certain errors were encountered while querying a host
			whose name resolved to more than one address.  Change
			4537 increased the odds of triggering this issue by
			causing dig to hang indefinitely when certain error
			paths were evaluated.  dig now also retries TCP queries
			(once) if the server gracefully closes the connection
			before sending a response. [RT #42832, #45159]

CHANGES

@@ -1,3 +1,12 @@
+4756.	[bug]		Interrupting dig could lead to an INSIST failure after
+			certain errors were encountered while querying a host
+			whose name resolved to more than one address.  Change
+			4537 increased the odds of triggering this issue by
+			causing dig to hang indefinitely when certain error
+			paths were evaluated.  dig now also retries TCP queries
+			(once) if the server gracefully closes the connection
+			before sending a response. [RT #42832, #45159]
+
 4755.	[cleanup]	Silence unnecessary log message when NZF file doesn't
 			exist. [RT #46186]
 

bin/dig/dighost.c

@@ -646,6 +646,7 @@ make_empty_lookup(void) {
 	looknew->mapped = ISC_TRUE;
 	looknew->dscp = -1;
 	looknew->rrcomments = 0;
+	looknew->eoferr = 0;
 	dns_fixedname_init(&looknew->fdomain);
 	ISC_LINK_INIT(looknew, link);
 	ISC_LIST_INIT(looknew->q);
@@ -737,6 +738,7 @@ clone_lookup(dig_lookup_t *lookold, isc_boolean_t servers) {
 	looknew->done_as_is = lookold->done_as_is;
 	looknew->dscp = lookold->dscp;
 	looknew->rrcomments = lookold->rrcomments;
+	looknew->eoferr = lookold->eoferr;
 
 	if (lookold->ecs_addr != NULL) {
 		size_t len = sizeof(isc_sockaddr_t);
@@ -2775,9 +2777,12 @@ send_udp(dig_query_t *query) {
 			next = ISC_LIST_NEXT(query, link);
 			l = query->lookup;
 			clear_query(query);
-			if (next == NULL)
+			if (next == NULL) {
 				printf(";; No acceptable nameservers\n");
-			check_next_lookup(l);
+				check_next_lookup(l);
+			} else {
+				send_udp(next);
+			}
 			return;
 		}
 
@@ -2909,7 +2914,7 @@ tcp_length_done(isc_task_t *task, isc_event_t *event) {
 	isc_buffer_t *b = NULL;
 	isc_result_t result;
 	dig_query_t *query = NULL;
-	dig_lookup_t *l;
+	dig_lookup_t *l, *n;
 	isc_uint16_t length;
 
 	REQUIRE(event->ev_type == ISC_SOCKEVENT_RECVDONE);
@@ -2944,13 +2949,20 @@ tcp_length_done(isc_task_t *task, isc_event_t *event) {
 				    sizeof(sockstr));
 		printf(";; communications error to %s: %s\n",
 		       sockstr, isc_result_totext(sevent->result));
+		if (keep != NULL)
+			isc_socket_detach(&keep);
 		l = query->lookup;
 		isc_socket_detach(&query->sock);
 		sockcount--;
 		debug("sockcount=%d", sockcount);
 		INSIST(sockcount >= 0);
+		if (sevent->result == ISC_R_EOF && l->eoferr == 0U) {
+			n = requeue_lookup(l, ISC_TRUE);
+			n->eoferr++;
+		}
 		isc_event_free(&event);
 		clear_query(query);
+		cancel_lookup(l);
 		check_next_lookup(l);
 		UNLOCK_LOOKUP;
 		return;
@@ -3443,13 +3455,20 @@ recv_done(isc_task_t *task, isc_event_t *event) {
 		} else {
 			printf(";; communications error: %s\n",
 			       isc_result_totext(sevent->result));
+			if (keep != NULL)
+				isc_socket_detach(&keep);
 			isc_socket_detach(&query->sock);
 			sockcount--;
 			debug("sockcount=%d", sockcount);
 			INSIST(sockcount >= 0);
 		}
+		if (sevent->result == ISC_R_EOF && l->eoferr == 0U) {
+			n = requeue_lookup(l, ISC_TRUE);
+			n->eoferr++;
+		}
 		isc_event_free(&event);
 		clear_query(query);
+		cancel_lookup(l);
 		check_next_lookup(l);
 		UNLOCK_LOOKUP;
 		return;
@@ -3511,6 +3530,7 @@ recv_done(isc_task_t *task, isc_event_t *event) {
 			if (fail) {
 				isc_event_free(&event);
 				clear_query(query);
+				cancel_lookup(l);
 				check_next_lookup(l);
 				UNLOCK_LOOKUP;
 				return;
@@ -3614,6 +3634,7 @@ recv_done(isc_task_t *task, isc_event_t *event) {
 			if (l->tcp_mode) {
 				isc_event_free(&event);
 				clear_query(query);
+				cancel_lookup(l);
 				check_next_lookup(l);
 				UNLOCK_LOOKUP;
 				return;

bin/dig/include/dig/dig.h

@@ -168,6 +168,7 @@ struct dig_lookup {
 	unsigned int ednsflags;
 	dns_opcode_t opcode;
 	int rrcomments;
+	unsigned int eoferr;
 };
 
 /*% The dig_query structure */