From 13b0fa78c2d9137e4dd0011e00f21d703401e122 Mon Sep 17 00:00:00 2001
From: Jaime Soriano Pastor <jaime.soriano@elastic.co>
Date: Wed, 14 Apr 2021 17:44:15 +0200
Subject: [PATCH] Fix panic when Hearbeat monitor initialization fails twice
 (#25073)

Initialization was only tried once. Second time a nil object and a nil
error are returned, producing nil pointer dereferences later.

(cherry picked from commit 1d858bd37efe1444366cc8bdee0bf527eaff3fc0)
---
 CHANGELOG.next.asciidoc                   |  1 +
 heartbeat/monitors/active/icmp/stdloop.go | 21 +++++++++++++--------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.next.asciidoc b/CHANGELOG.next.asciidoc
index 76d286dc1da9..a94aecc9f829 100644
--- a/CHANGELOG.next.asciidoc
+++ b/CHANGELOG.next.asciidoc
@@ -247,6 +247,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fixed excessive memory usage introduced in 7.5 due to over-allocating memory for HTTP checks. {pull}15639[15639]
 - Fixed scheduler shutdown issues which would in rare situations cause a panic due to semaphore misuse. {pull}16397[16397]
 - Fixed TCP TLS checks to properly validate hostnames, this broke in 7.x and only worked for IP SANs. {pull}17549[17549]
+- Fix panic when initialization of ICMP monitors fail twice. {pull}25073[25073]
 
 *Journalbeat*
 
diff --git a/heartbeat/monitors/active/icmp/stdloop.go b/heartbeat/monitors/active/icmp/stdloop.go
index 932154c61ada..05858f5537fc 100644
--- a/heartbeat/monitors/active/icmp/stdloop.go
+++ b/heartbeat/monitors/active/icmp/stdloop.go
@@ -87,20 +87,25 @@ type requestResult struct {
 // These vars should not be used directly, but rather getStdLoop
 // should be invoked to initialize and return stdLoop.
 var (
-	stdICMPLoopInit      sync.Once
+	stdICMPLoopInit      sync.Mutex
 	stdICMPLoopSingleton *stdICMPLoop
 )
 
 func getStdLoop() (*stdICMPLoop, error) {
-	var loopErr error
-	stdICMPLoopInit.Do(func() {
+	stdICMPLoopInit.Lock()
+	defer stdICMPLoopInit.Unlock()
+
+	if stdICMPLoopSingleton == nil {
 		debugf("initializing ICMP loop")
-		stdICMPLoopSingleton, loopErr = newICMPLoop()
-		if loopErr == nil {
-			debugf("ICMP loop successfully initialized")
+		singleton, err := newICMPLoop()
+		if err != nil {
+			return nil, err
 		}
-	})
-	return stdICMPLoopSingleton, loopErr
+		stdICMPLoopSingleton = singleton
+		debugf("ICMP loop successfully initialized")
+	}
+
+	return stdICMPLoopSingleton, nil
 }
 
 func noPingCapabilityError(message string) error {