config: protect global configOpts with a mutex (#296)

There is a race condition in configOpts when one goroutine calls
OverwriteConfigOpts while another reads the variable. This is common, as
almost every method in config.C reads this global variable.

Fix the data race by using a mutex. Since this variable is mostly read,
optimize it with a sync.RWMutex.

Author: mauri870

config/config.go

@@ -22,6 +22,7 @@ import (
 	"errors"
 	"fmt"
 	"strings"
+	"sync"
 
 	"github.com/elastic/elastic-agent-libs/str"
 	ucfg "github.com/elastic/go-ucfg"
@@ -41,7 +42,8 @@ type Namespace struct {
 const mask = "xxxxx"
 
 var (
-	configOpts = []ucfg.Option{
+	configOptsMu sync.RWMutex
+	configOpts   = []ucfg.Option{
 		ucfg.PathSep("."),
 		ucfg.ResolveEnv,
 		ucfg.VarExp,
@@ -62,6 +64,18 @@ var (
 	)
 )
 
+func getGlobalConfigOpts() []ucfg.Option {
+	configOptsMu.RLock()
+	defer configOptsMu.RUnlock()
+	return configOpts
+}
+
+func setGlobalConfigOpts(opts []ucfg.Option) {
+	configOptsMu.Lock()
+	defer configOptsMu.Unlock()
+	configOpts = opts
+}
+
 func NewConfig() *C {
 	return fromConfig(ucfg.New())
 }
@@ -74,11 +88,11 @@ func NewConfig() *C {
 // result.
 func NewConfigFrom(from interface{}) (*C, error) {
 	if str, ok := from.(string); ok {
-		c, err := yaml.NewConfig([]byte(str), configOpts...)
+		c, err := yaml.NewConfig([]byte(str), getGlobalConfigOpts()...)
 		return fromConfig(c), err
 	}
 
-	c, err := ucfg.NewFrom(from, configOpts...)
+	c, err := ucfg.NewFrom(from, getGlobalConfigOpts()...)
 	return fromConfig(c), err
 }
 
@@ -130,33 +144,33 @@ func NewConfigWithYAML(in []byte, source string) (*C, error) {
 		[]ucfg.Option{
 			ucfg.MetaData(ucfg.Meta{Source: source}),
 		},
-		configOpts...,
+		getGlobalConfigOpts()...,
 	)
 	c, err := yaml.NewConfig(in, opts...)
 	return fromConfig(c), err
 }
 
 // OverwriteConfigOpts allow to change the globally set config option
 func OverwriteConfigOpts(options []ucfg.Option) {
-	configOpts = options
+	setGlobalConfigOpts(options)
 }
 
 // Merge merges the parameter into the C object.
 func (c *C) Merge(from interface{}) error {
-	return c.access().Merge(from, configOpts...)
+	return c.access().Merge(from, getGlobalConfigOpts()...)
 }
 
 // Merge merges the parameter into the C object based on the provided options.
 func (c *C) MergeWithOpts(from interface{}, opts ...ucfg.Option) error {
-	o := configOpts
+	o := getGlobalConfigOpts()
 	if opts != nil {
 		o = append(o, opts...)
 	}
 	return c.access().Merge(from, o...)
 }
 
 func (c *C) Unpack(to interface{}) error {
-	return c.access().Unpack(to, configOpts...)
+	return c.access().Unpack(to, getGlobalConfigOpts()...)
 }
 
 func (c *C) Path() string {
@@ -168,11 +182,11 @@ func (c *C) PathOf(field string) string {
 }
 
 func (c *C) Remove(name string, idx int) (bool, error) {
-	return c.access().Remove(name, idx, configOpts...)
+	return c.access().Remove(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) Has(name string, idx int) (bool, error) {
-	return c.access().Has(name, idx, configOpts...)
+	return c.access().Has(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) HasField(name string) bool {
@@ -184,44 +198,44 @@ func (c *C) CountField(name string) (int, error) {
 }
 
 func (c *C) Bool(name string, idx int) (bool, error) {
-	return c.access().Bool(name, idx, configOpts...)
+	return c.access().Bool(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) String(name string, idx int) (string, error) {
-	return c.access().String(name, idx, configOpts...)
+	return c.access().String(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) Int(name string, idx int) (int64, error) {
-	return c.access().Int(name, idx, configOpts...)
+	return c.access().Int(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) Float(name string, idx int) (float64, error) {
-	return c.access().Float(name, idx, configOpts...)
+	return c.access().Float(name, idx, getGlobalConfigOpts()...)
 }
 
 func (c *C) Child(name string, idx int) (*C, error) {
-	sub, err := c.access().Child(name, idx, configOpts...)
+	sub, err := c.access().Child(name, idx, getGlobalConfigOpts()...)
 	return fromConfig(sub), err
 }
 
 func (c *C) SetBool(name string, idx int, value bool) error {
-	return c.access().SetBool(name, idx, value, configOpts...)
+	return c.access().SetBool(name, idx, value, getGlobalConfigOpts()...)
 }
 
 func (c *C) SetInt(name string, idx int, value int64) error {
-	return c.access().SetInt(name, idx, value, configOpts...)
+	return c.access().SetInt(name, idx, value, getGlobalConfigOpts()...)
 }
 
 func (c *C) SetFloat(name string, idx int, value float64) error {
-	return c.access().SetFloat(name, idx, value, configOpts...)
+	return c.access().SetFloat(name, idx, value, getGlobalConfigOpts()...)
 }
 
 func (c *C) SetString(name string, idx int, value string) error {
-	return c.access().SetString(name, idx, value, configOpts...)
+	return c.access().SetString(name, idx, value, getGlobalConfigOpts()...)
 }
 
 func (c *C) SetChild(name string, idx int, value *C) error {
-	return c.access().SetChild(name, idx, value.access(), configOpts...)
+	return c.access().SetChild(name, idx, value.access(), getGlobalConfigOpts()...)
 }
 
 func (c *C) IsDict() bool {
@@ -234,7 +248,7 @@ func (c *C) IsArray() bool {
 
 // FlattenedKeys return a sorted flattened views of the set keys in the configuration.
 func (c *C) FlattenedKeys() []string {
-	return c.access().FlattenedKeys(configOpts...)
+	return c.access().FlattenedKeys(getGlobalConfigOpts()...)
 }
 
 // Enabled return the configured enabled value or true by default.