Upstream didn't accepted this patch and only replied that user should fix
the configuration. Since we believe that even if configuration is wrong,
program (especially daemon) shouldn't crash with segfault, we rather fix
this on our own to print a nice error when level of recursion exceeds 128.

diff -up ypserv-2.31/revnetgroup/getnetgrent.c.recursive ypserv-2.31/revnetgroup/getnetgrent.c
--- ypserv-2.31/revnetgroup/getnetgrent.c.recursive	2013-05-17 12:37:08.143675080 +0200
+++ ypserv-2.31/revnetgroup/getnetgrent.c	2013-05-17 14:20:49.376566354 +0200
@@ -31,6 +31,8 @@
 
 #include "hash.h"
 
+#define NETGROUPENTRY_RECURSION_LIMIT 128
+
 extern hash_t *input;
 
 void rev_setnetgrent (const char *);
@@ -53,7 +55,7 @@ struct netgrlist
   };
 
 
-static void rev_expand_netgroupentry (const char *, struct netgrlist *);
+static void rev_expand_netgroupentry (const char *, struct netgrlist *, int level);
 static void rev_parse_entry (char *, char *, struct netgrlist *);
 static void rev_netgr_free (struct netgrlist *);
 static struct netgrlist list = {0, 0, NULL};
@@ -83,7 +85,7 @@ rev_setnetgrent (const char *netgr)
     {
       rev_endnetgrent ();
       netgroup = strdup (netgr);
-      rev_expand_netgroupentry (netgr, &list);
+      rev_expand_netgroupentry (netgr, &list, 0);
     }
   first = 1;
 }
@@ -141,7 +143,7 @@ rev_netgr_free (struct netgrlist *list)
 }
 
 static void
-rev_expand_netgroupentry (const char *netgr, struct netgrlist *list)
+rev_expand_netgroupentry (const char *netgr, struct netgrlist *list, int level)
 {
   char *outval = NULL;
   char *outptr = NULL;
@@ -156,6 +158,14 @@ rev_expand_netgroupentry (const char *ne
   if (outptr == NULL)
     return;
 
+  /* check the recursion - return if we exceed the recursion limit */
+  if (level >= NETGROUPENTRY_RECURSION_LIMIT)
+    {
+      fprintf (stderr, "WARNING: level of recursion in netgroup %s reached"
+	       "%d, entry ignored\n", netgr, NETGROUPENTRY_RECURSION_LIMIT);
+      return;
+    }
+
   /* make a copy to work with */
   outval = strdup (outptr);
   if (outval == NULL)
@@ -198,7 +208,7 @@ rev_expand_netgroupentry (const char *ne
 	  *end = '\0';
 
 	  /* recursion */
-	  rev_expand_netgroupentry (start, list);
+	  rev_expand_netgroupentry (start, list, level+1);
 	}
 
       /* skip to the next entry */