From 9b4ced98ec9ac964d6cd01219a1670b9c77aa492 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Fri, 11 Oct 2019 16:26:51 +0200
Subject: [PATCH] dnsdist: Don't call SO_BINDTODEVICE with an empty interface
 name

---
 pdns/dnsdist-tcp.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/pdns/dnsdist-tcp.cc b/pdns/dnsdist-tcp.cc
index a387bee4e7..c3906a49aa 100644
--- a/pdns/dnsdist-tcp.cc
+++ b/pdns/dnsdist-tcp.cc
@@ -81,9 +81,11 @@ static std::unique_ptr<Socket> setupTCPDownstream(shared_ptr<DownstreamState>& d
         }
 #endif
 #ifdef SO_BINDTODEVICE
-        int res = setsockopt(result->getHandle(), SOL_SOCKET, SO_BINDTODEVICE, ds->sourceItfName.c_str(), ds->sourceItfName.length());
-        if (res != 0) {
-          vinfolog("Error setting up the interface on backend TCP socket '%s': %s", ds->getNameWithAddr(), stringerror());
+        if (!ds->sourceItfName.empty()) {
+          int res = setsockopt(result->getHandle(), SOL_SOCKET, SO_BINDTODEVICE, ds->sourceItfName.c_str(), ds->sourceItfName.length());
+          if (res != 0) {
+            vinfolog("Error setting up the interface on backend TCP socket '%s': %s", ds->getNameWithAddr(), stringerror());
+          }
         }
 #endif
         result->bind(ds->sourceAddr, false);
-- 
2.47.2