From b5bf63168a223907f23512ac42d25f54007a8270 Mon Sep 17 00:00:00 2001
From: "Alex K." <8418476+fearful-symmetry@users.noreply.github.com>
Date: Fri, 27 Sep 2024 08:12:25 -0700
Subject: [PATCH] Fix nil pointer deref if the file output lacks a `path`
 setting. (#40992)

* fix nil pointer deref if the fileout lacks a path

* format

* fix tests

(cherry picked from commit bdcad1005accd9291875cac47fc1c11df60fdd75)
---
 libbeat/outputs/fileout/config.go                |  1 +
 libbeat/outputs/fileout/config_test.go           |  1 +
 libbeat/outputs/fileout/pathformatstring.go      |  4 ++++
 libbeat/outputs/fileout/pathformatstring_test.go | 12 ++++++++++++
 4 files changed, 18 insertions(+)

diff --git a/libbeat/outputs/fileout/config.go b/libbeat/outputs/fileout/config.go
index 69af40e4289b..9228430d6d9b 100644
--- a/libbeat/outputs/fileout/config.go
+++ b/libbeat/outputs/fileout/config.go
@@ -38,6 +38,7 @@ type fileOutConfig struct {
 
 func defaultConfig() fileOutConfig {
 	return fileOutConfig{
+		Path:            &PathFormatString{},
 		NumberOfFiles:   7,
 		RotateEveryKb:   10 * 1024,
 		Permissions:     0600,
diff --git a/libbeat/outputs/fileout/config_test.go b/libbeat/outputs/fileout/config_test.go
index 7e149173f6df..0bf0d6f7cc13 100644
--- a/libbeat/outputs/fileout/config_test.go
+++ b/libbeat/outputs/fileout/config_test.go
@@ -37,6 +37,7 @@ func TestConfig(t *testing.T) {
 			config: config.MustNewConfigFrom([]byte(`{ }`)),
 			assertion: func(t *testing.T, actual *fileOutConfig, err error) {
 				expectedConfig := &fileOutConfig{
+					Path:            &PathFormatString{},
 					NumberOfFiles:   7,
 					RotateEveryKb:   10 * 1024,
 					Permissions:     0600,
diff --git a/libbeat/outputs/fileout/pathformatstring.go b/libbeat/outputs/fileout/pathformatstring.go
index acd2a7605fe6..fdaff2177872 100644
--- a/libbeat/outputs/fileout/pathformatstring.go
+++ b/libbeat/outputs/fileout/pathformatstring.go
@@ -18,6 +18,7 @@
 package fileout
 
 import (
+	"fmt"
 	"os"
 	"strings"
 	"time"
@@ -44,6 +45,9 @@ func (fs *PathFormatString) Run(timestamp time.Time) (string, error) {
 	placeholderEvent := &beat.Event{
 		Timestamp: timestamp,
 	}
+	if fs.efs == nil {
+		return "", fmt.Errorf("path format string is nil; check if `path` option is configured correctly")
+	}
 	return fs.efs.Run(placeholderEvent)
 }
 
diff --git a/libbeat/outputs/fileout/pathformatstring_test.go b/libbeat/outputs/fileout/pathformatstring_test.go
index b8eee4e44eaa..fa3c9ee08fe0 100644
--- a/libbeat/outputs/fileout/pathformatstring_test.go
+++ b/libbeat/outputs/fileout/pathformatstring_test.go
@@ -22,8 +22,20 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/elastic/elastic-agent-libs/config"
 )
 
+func TestCheckNilDoesntPanic(t *testing.T) {
+	newCfg := config.NewConfig()
+	handler, err := readConfig(newCfg)
+	require.NoError(t, err)
+	_, err = handler.Path.Run(time.Now())
+	require.Error(t, err)
+
+}
+
 func TestPathFormatString(t *testing.T) {
 	tests := []struct {
 		title          string