commit 4c70f4747a6a49352130cf4e158cd6afbf373d5b
Author: Your Name <you@example.com>
Date:   Tue Dec 2 09:25:41 2014 +0000

    backport query limiter to 3.5.3

diff --git a/pdns_recursor.cc b/pdns_recursor.cc
index dcadf1b..3708137 100644
--- a/pdns_recursor.cc
+++ b/pdns_recursor.cc
@@ -533,7 +533,14 @@ void startDoResolve(void *p)
     bool variableAnswer = false;
     // if there is a RecursorLua active, and it 'took' the query in preResolve, we don't launch beginResolve
     if(!t_pdl->get() || !(*t_pdl)->preresolve(dc->d_remote, g_listenSocketsAddresses[dc->d_socket], dc->d_mdp.d_qname, QType(dc->d_mdp.d_qtype), ret, res, &variableAnswer)) {
-       res = sr.beginResolve(dc->d_mdp.d_qname, QType(dc->d_mdp.d_qtype), dc->d_mdp.d_qclass, ret);
+      try {
+        res = sr.beginResolve(dc->d_mdp.d_qname, QType(dc->d_mdp.d_qtype), dc->d_mdp.d_qclass, ret);
+      }
+      catch(ImmediateServFailException &e) {
+        L<<Logger::Error<<"Sending SERVFAIL during resolve of '"<<dc->d_mdp.d_qname<<"' because: "<<e.reason<<endl;
+
+        res = RCode::ServFail;
+      }
 
       if(t_pdl->get()) {
         if(res == RCode::NoError) {
diff --git a/syncres.cc b/syncres.cc
index afadfbc..f98f116 100644
--- a/syncres.cc
+++ b/syncres.cc
@@ -915,6 +915,7 @@ int SyncRes::doResolveAt(set<string, CIStringCompare> nameservers, string auth,
           }
           else {
             s_outqueries++; d_outqueries++;
+            if(d_outqueries > 50) throw ImmediateServFailException("more than 50 queries sent while resolving "+qname);
           TryTCP:
             if(doTCP) {
               LOG(prefix<<qname<<": using TCP with "<< remoteIP->toStringWithPort() <<endl);
diff --git a/syncres.hh b/syncres.hh
index 5ef7fc0..218bd2d 100644
--- a/syncres.hh
+++ b/syncres.hh
@@ -533,6 +533,13 @@ private:
   static AtomicCounter s_currentConnections; //!< total number of current TCP connections
 };
 
+class ImmediateServFailException
+{
+public:
+  ImmediateServFailException(string r){reason=r;};
+
+  string reason; //! Print this to tell the user what went wrong
+};
 
 struct RemoteKeeper
 {