merge branch 'eparis/pr-1216'

Closes #1216
LGTMs: @mrunalp @rhatdan @cyphar

libcontainer/selinux/selinux.go

@@ -32,33 +32,73 @@ const (
 	stRdOnly         = 0x01
 )
 
+type selinuxState struct {
+	enabledSet   bool
+	enabled      bool
+	selinuxfsSet bool
+	selinuxfs    string
+	mcsList      map[string]bool
+	sync.Mutex
+}
+
 var (
-	assignRegex           = regexp.MustCompile(`^([^=]+)=(.*)$`)
-	mcsList               = make(map[string]bool)
-	mcsLock               sync.Mutex
-	selinuxfs             = "unknown"
-	selinuxEnabled        = false // Stores whether selinux is currently enabled
-	selinuxEnabledChecked = false // Stores whether selinux enablement has been checked or established yet
+	assignRegex = regexp.MustCompile(`^([^=]+)=(.*)$`)
+	state       = selinuxState{
+		mcsList: make(map[string]bool),
+	}
 )
 
 type SELinuxContext map[string]string
 
+func (s *selinuxState) setEnable(enabled bool) bool {
+	s.Lock()
+	defer s.Unlock()
+	s.enabledSet = true
+	s.enabled = enabled
+	return s.enabled
+}
+
+func (s *selinuxState) getEnabled() bool {
+	s.Lock()
+	enabled := s.enabled
+	enabledSet := s.enabledSet
+	s.Unlock()
+	if enabledSet {
+		return enabled
+	}
+
+	enabled = false
+	if fs := getSelinuxMountPoint(); fs != "" {
+		if con, _ := Getcon(); con != "kernel" {
+			enabled = true
+		}
+	}
+	return s.setEnable(enabled)
+}
+
 // SetDisabled disables selinux support for the package
 func SetDisabled() {
-	selinuxEnabled, selinuxEnabledChecked = false, true
+	state.setEnable(false)
 }
 
-// getSelinuxMountPoint returns the path to the mountpoint of an selinuxfs
-// filesystem or an empty string if no mountpoint is found.  Selinuxfs is
-// a proc-like pseudo-filesystem that exposes the selinux policy API to
-// processes.  The existence of an selinuxfs mount is used to determine
-// whether selinux is currently enabled or not.
-func getSelinuxMountPoint() string {
-	if selinuxfs != "unknown" {
+func (s *selinuxState) setSELinuxfs(selinuxfs string) string {
+	s.Lock()
+	defer s.Unlock()
+	s.selinuxfsSet = true
+	s.selinuxfs = selinuxfs
+	return s.selinuxfs
+}
+
+func (s *selinuxState) getSELinuxfs() string {
+	s.Lock()
+	selinuxfs := s.selinuxfs
+	selinuxfsSet := s.selinuxfsSet
+	s.Unlock()
+	if selinuxfsSet {
 		return selinuxfs
 	}
-	selinuxfs = ""
 
+	selinuxfs = ""
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return selinuxfs
@@ -91,21 +131,21 @@ func getSelinuxMountPoint() string {
 			selinuxfs = ""
 		}
 	}
-	return selinuxfs
+	return s.setSELinuxfs(selinuxfs)
+}
+
+// getSelinuxMountPoint returns the path to the mountpoint of an selinuxfs
+// filesystem or an empty string if no mountpoint is found.  Selinuxfs is
+// a proc-like pseudo-filesystem that exposes the selinux policy API to
+// processes.  The existence of an selinuxfs mount is used to determine
+// whether selinux is currently enabled or not.
+func getSelinuxMountPoint() string {
+	return state.getSELinuxfs()
 }
 
 // SelinuxEnabled returns whether selinux is currently enabled.
 func SelinuxEnabled() bool {
-	if selinuxEnabledChecked {
-		return selinuxEnabled
-	}
-	selinuxEnabledChecked = true
-	if fs := getSelinuxMountPoint(); fs != "" {
-		if con, _ := Getcon(); con != "kernel" {
-			selinuxEnabled = true
-		}
-	}
-	return selinuxEnabled
+	return state.getEnabled()
 }
 
 func readConfig(target string) (value string) {
@@ -283,19 +323,19 @@ func SelinuxGetEnforceMode() int {
 }
 
 func mcsAdd(mcs string) error {
-	mcsLock.Lock()
-	defer mcsLock.Unlock()
-	if mcsList[mcs] {
+	state.Lock()
+	defer state.Unlock()
+	if state.mcsList[mcs] {
 		return fmt.Errorf("MCS Label already exists")
 	}
-	mcsList[mcs] = true
+	state.mcsList[mcs] = true
 	return nil
 }
 
 func mcsDelete(mcs string) {
-	mcsLock.Lock()
-	mcsList[mcs] = false
-	mcsLock.Unlock()
+	state.Lock()
+	defer state.Unlock()
+	state.mcsList[mcs] = false
 }
 
 func IntToMcs(id int, catRange uint32) string {