From dbca186a6456b73e747bb665159ea03d212b8cd6 Mon Sep 17 00:00:00 2001
From: David Anderson <dave@natulte.net>
Date: Wed, 25 Mar 2020 23:11:22 -0700
Subject: [PATCH] stunner: fix data race.

In very low-latency conditions, a STUN request can complete before
the startup loop has finished firing off goroutines, leading to
a concurrent map mutation.
---
 stunner/stunner.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/stunner/stunner.go b/stunner/stunner.go
index 534f617f9..41cb868e8 100644
--- a/stunner/stunner.go
+++ b/stunner/stunner.go
@@ -184,6 +184,7 @@ func (s *Stunner) Run(ctx context.Context) error {
 		defer cancel()
 		need[server] = sender{ctx, cancel}
 	}
+	needMu.Lock()
 	for server, sender := range need {
 		wg.Add(1)
 		server, ctx := server, sender.ctx
@@ -192,6 +193,7 @@ func (s *Stunner) Run(ctx context.Context) error {
 			s.sendPackets(ctx, server)
 		}()
 	}
+	needMu.Unlock()
 	var err error
 	select {
 	case <-ctx.Done():