From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Fri, 23 Jun 2017 08:35:03 +0000 (+0200)
Subject: dnsdist: Fix TCP with Fast Open requested but unsupported
X-Git-Tag: rec-4.1.0-alpha1~48^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fpull%2F5454%2Fhead;p=thirdparty%2Fpdns.git

dnsdist: Fix TCP with Fast Open requested but unsupported

If `tcpFastOpen` is set on a backend, we used to skip the
`connect()` call regardless of `MSG_FASTOPEN` availability.
We then tried to call `sendmsg()` (without `MSG_FASTOPEN`)
on an unconnected TCP socket, which failed.
---

diff --git a/pdns/dnsdist-lua.cc b/pdns/dnsdist-lua.cc
index 8b4b094c1f..50c0b3537d 100644
--- a/pdns/dnsdist-lua.cc
+++ b/pdns/dnsdist-lua.cc
@@ -437,7 +437,14 @@ vector<std::function<void(void)>> setupLua(bool client, const std::string& confi
 			}
 
 			if(vars.count("tcpFastOpen")) {
-			  ret->tcpFastOpen=boost::get<bool>(vars["tcpFastOpen"]);
+			  bool fastOpen = boost::get<bool>(vars["tcpFastOpen"]);
+			  if (fastOpen) {
+#ifdef MSG_FASTOPEN
+			    ret->tcpFastOpen=true;
+#else
+			    warnlog("TCP Fast Open has been configured on downstream server %s but is not supported", boost::get<string>(vars["address"]));
+#endif
+			  }
 			}
 
 			if(vars.count("name")) {
diff --git a/pdns/dnsdist-tcp.cc b/pdns/dnsdist-tcp.cc
index 95e3ac2045..02fafc634b 100644
--- a/pdns/dnsdist-tcp.cc
+++ b/pdns/dnsdist-tcp.cc
@@ -61,9 +61,13 @@ static int setupTCPDownstream(shared_ptr<DownstreamState> ds, uint16_t& downstre
         SBind(sock, ds->sourceAddr);
       }
       setNonBlocking(sock);
+#ifdef MSG_FASTOPEN
       if (!ds->tcpFastOpen) {
         SConnectWithTimeout(sock, ds->remote, ds->tcpConnectTimeout);
       }
+#else
+      SConnectWithTimeout(sock, ds->remote, ds->tcpConnectTimeout);
+#endif /* MSG_FASTOPEN */
       return sock;
     }
     catch(const std::runtime_error& e) {