From cbc033201863c9f67bde66ca22e4e0d9d1d1a414 Mon Sep 17 00:00:00 2001
From: bert hubert <bert.hubert@netherlabs.nl>
Date: Sat, 16 Jan 2016 12:48:53 +0100
Subject: [PATCH] found with the help of @mischapeters - turns out our recent
 'supply local address to lua' improvements triggered us to set the source
 address on all our replies explicitly, something FreeBSD did not like and was
 wasteful on Linux. Plus added some logging that would have helped debug this
 faster.

---
 pdns/pdns_recursor.cc | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/pdns/pdns_recursor.cc b/pdns/pdns_recursor.cc
index 5fdb7be88..4fff3ef50 100644
--- a/pdns/pdns_recursor.cc
+++ b/pdns/pdns_recursor.cc
@@ -141,6 +141,7 @@ unsigned int g_maxMThreads;
 __thread struct timeval g_now; // timestamp, updated (too) frequently
 typedef map<int, ComboAddress> listenSocketsAddresses_t; // is shared across all threads right now
 listenSocketsAddresses_t g_listenSocketsAddresses; // is shared across all threads right now
+set<int> g_fromtosockets; // listen sockets that use 'sendfromto()' mechanism
 
 __thread MT_t* MT; // the big MTasker
 
@@ -860,11 +861,13 @@ void startDoResolve(void *p)
       struct iovec iov;
       char cbuf[256];
       fillMSGHdr(&msgh, &iov, cbuf, 0, (char*)&*packet.begin(), packet.size(), &dc->d_remote);
-      if(dc->d_local.sin4.sin_family)
+      if(g_fromtosockets.count(dc->d_socket)) {
 	addCMsgSrcAddr(&msgh, cbuf, &dc->d_local, 0);
-      else
+      } else
         msgh.msg_control=NULL;
-      sendmsg(dc->d_socket, &msgh, 0);
+      if(sendmsg(dc->d_socket, &msgh, 0) < 0 && g_logCommonErrors) 
+        L<<Logger::Warning<<"Sending UDP reply to client "<<dc->d_remote.toStringWithPort()<<" failed with: "<<strerror(errno)<<endl;
+
       if(!SyncRes::s_nopacketcache && !variableAnswer && !sr.wasVariable() ) {
         t_packetCache->insertResponsePacket(string((const char*)&*packet.begin(), packet.size()),
                                             (edo.d_Z & EDNSOpts::DNSSECOK), // ponder filtering on dnssecmode here
@@ -1168,13 +1171,14 @@ string* doProcessUDPQuestion(const std::string& question, const ComboAddress& fr
       struct iovec iov;
       char cbuf[256];
       fillMSGHdr(&msgh, &iov, cbuf, 0, (char*)response.c_str(), response.length(), const_cast<ComboAddress*>(&fromaddr));
-      if(destaddr.sin4.sin_family) {
+      if(g_fromtosockets.count(fd)) {
 	addCMsgSrcAddr(&msgh, cbuf, &destaddr, 0);
       }
       else {
         msgh.msg_control=NULL;
       }
-      sendmsg(fd, &msgh, 0);
+      if(sendmsg(fd, &msgh, 0) < 0 && g_logCommonErrors)
+        L<<Logger::Warning<<"Sending UDP reply to client "<<fromaddr.toStringWithPort()<<" failed with: "<<strerror(errno)<<endl;
 
       if(response.length() >= sizeof(struct dnsheader)) {
         struct dnsheader dh;
@@ -1413,9 +1417,13 @@ void makeUDPServerSockets()
       L<<Logger::Warning<<"Unable to enable timestamp reporting for socket"<<endl;
 
     if(IsAnyAddress(sin)) {
-      setsockopt(fd, IPPROTO_IP, GEN_IP_PKTINFO, &one, sizeof(one));     // linux supports this, so why not - might fail on other systems
+      if(sin.sin4.sin_family == AF_INET)
+        if(!setsockopt(fd, IPPROTO_IP, GEN_IP_PKTINFO, &one, sizeof(one)))     // linux supports this, so why not - might fail on other systems
+          g_fromtosockets.insert(fd);
 #ifdef IPV6_RECVPKTINFO
-      setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
+      if(sin.sin4.sin_family == AF_INET6)
+        if(!setsockopt(fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one)))
+          g_fromtosockets.insert(fd);
 #endif
       if(sin.sin6.sin6_family == AF_INET6 && setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one)) < 0) {
 	L<<Logger::Error<<"Failed to set IPv6 socket to IPv6 only, continuing anyhow: "<<strerror(errno)<<endl;
-- 
2.40.0