3 files changed, 34 insertions, 7 deletions

diff --git a/sys/src/cmd/ndb/dn.c b/sys/src/cmd/ndb/dn.c
index 7383c9e4b..fcf262259 100644
--- a/sys/src/cmd/ndb/dn.c
+++ b/sys/src/cmd/ndb/dn.c
@@ -655,6 +655,7 @@ getactivity(Request *req, int recursive)
 	now = time(nil);
 	nowns = nsec();
 	req->id = ++dnvars.id;
+	req->aux = nil;
 	unlock(&dnvars);
 
 	return rv;
diff --git a/sys/src/cmd/ndb/dnresolve.c b/sys/src/cmd/ndb/dnresolve.c
index 6e8709e94..3c5942093 100644
--- a/sys/src/cmd/ndb/dnresolve.c
+++ b/sys/src/cmd/ndb/dnresolve.c
@@ -52,6 +52,8 @@ struct Query {
 	DN	*dp;		/* domain */
 	ushort	type;		/* and type to look up */
 	Request *req;
+	Query	*prev;		/* previous query */
+
 	RR	*nsrp;		/* name servers to consult */
 
 	/* dest must not be on the stack due to forking in slave() */
@@ -225,14 +227,18 @@ queryinit(Query *qp, DN *dp, int type, Request *req)
 	qp->type = type;
 	if (qp->type != type)
 		dnslog("queryinit: bogus type %d", type);
-	qp->req = req;
 	qp->nsrp = nil;
 	qp->dest = qp->curdest = nil;
+	qp->prev = req->aux;
+	qp->req = req;
+	req->aux = qp;
 }
 
 static void
 querydestroy(Query *qp)
 {
+	if(qp->req->aux == qp)
+		qp->req->aux = qp->prev;
 	/* leave udpfd open */
 	if (qp->tcpfd >= 0)
 		close(qp->tcpfd);
@@ -739,6 +745,30 @@ ipisbm(uchar *ip)
 	return 0;
 }
 
+static int
+queryloops(Query *qp, RR *rp)
+{
+	DN *ns;
+
+	ns = rp->host;
+
+	/*
+	 *  avoid loops looking up a server under itself
+	 */
+	if(subsume(rp->owner->name, ns->name))
+		return 1;
+
+	/*
+	 *  must not cycle on name servers refering
+	 *  to each another.
+	 */
+	for(qp = qp->prev; qp; qp = qp->prev)
+		for(rp = qp->nsrp; rp; rp = rp->next)
+			if(rp->host == ns)
+				return 1;
+	return 0;
+}
+
 /*
  *  Get next server address(es) into qp->dest[nd] and beyond
  */
@@ -787,13 +817,8 @@ serveraddrs(Query *qp, int nd, int depth)
 			if(rp->marker)
 				continue;
 			rp->marker = 1;
-
-			/*
-			 *  avoid loops looking up a server under itself
-			 */
-			if(subsume(rp->owner->name, rp->host->name))
+			if(queryloops(qp, rp))
 				continue;
-
 			arp = dnresolve(rp->host->name, Cin, Ta, qp->req, 0,
 				depth+1, Recurse, 1, 0);
 			if(arp == nil)
diff --git a/sys/src/cmd/ndb/dns.h b/sys/src/cmd/ndb/dns.h
index 1e0ae2e86..e14a20cdd 100644
--- a/sys/src/cmd/ndb/dns.h
+++ b/sys/src/cmd/ndb/dns.h
@@ -182,6 +182,7 @@ struct Request
 	jmp_buf	mret;		/* where master jumps to after starting a slave */
 	int	id;
 	char	*from;		/* who asked us? */
+	void	*aux;
 };
 
 /*