From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Mon, 15 May 2023 12:10:55 +0000 (+0200)
Subject: dnsdist: Stop setting SO_REUSEADDR on outgoing UDP client sockets
X-Git-Tag: rec-4.9.0-beta1~8^2~1
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=b33f09f1989e938c503142a38c556df94254443a;p=thirdparty%2Fpdns.git

dnsdist: Stop setting SO_REUSEADDR on outgoing UDP client sockets

`SO_REUSEADDR` is useful on TCP server sockets to allow binding quickly
after restarting the process without waiting `TIME_WAIT` seconds, or
to allow some port reuse on BSD. It also allows reusing a port more
quickly for TCP client sockets.
For UDP sockets, however, Linux allows two sockets to be bound to the
same address and port, and will distribute all packets to the most
recent socket, which is very unexpected, to say the least.
---

diff --git a/pdns/dnsdistdist/dnsdist-backend.cc b/pdns/dnsdistdist/dnsdist-backend.cc
index 9113183c83..cfa6e5c7b6 100644
--- a/pdns/dnsdistdist/dnsdist-backend.cc
+++ b/pdns/dnsdistdist/dnsdist-backend.cc
@@ -72,7 +72,6 @@ bool DownstreamState::reconnect()
 #endif
 
     if (!IsAnyAddress(d_config.sourceAddr)) {
-      SSetsockopt(fd, SOL_SOCKET, SO_REUSEADDR, 1);
 #ifdef IP_BIND_ADDRESS_NO_PORT
       if (d_config.ipBindAddrNoPort) {
         SSetsockopt(fd, SOL_IP, IP_BIND_ADDRESS_NO_PORT, 1);
diff --git a/pdns/dnsdistdist/dnsdist-healthchecks.cc b/pdns/dnsdistdist/dnsdist-healthchecks.cc
index 1addf7583d..9ec50e3a5a 100644
--- a/pdns/dnsdistdist/dnsdist-healthchecks.cc
+++ b/pdns/dnsdistdist/dnsdist-healthchecks.cc
@@ -319,7 +319,9 @@ bool queueHealthCheck(std::unique_ptr<FDMultiplexer>& mplexer, const std::shared
 #endif
 
     if (!IsAnyAddress(ds->d_config.sourceAddr)) {
-      sock.setReuseAddr();
+      if (ds->doHealthcheckOverTCP()) {
+        sock.setReuseAddr();
+      }
 #ifdef IP_BIND_ADDRESS_NO_PORT
       if (ds->d_config.ipBindAddrNoPort) {
         SSetsockopt(sock.getHandle(), SOL_IP, IP_BIND_ADDRESS_NO_PORT, 1);