libcontainer/intelrdt: refactor path handling

libcontainer/intelrdt/intelrdt.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"sync"
 
+	securejoin "github.com/cyphar/filepath-securejoin"
 	"github.com/moby/sys/mountinfo"
 	"golang.org/x/sys/unix"
 
@@ -159,10 +160,25 @@ func NewManager(config *configs.Config, id string, path string) *Manager {
 	if config.IntelRdt == nil {
 		return nil
 	}
-	if _, err := Root(); err != nil {
-		// Intel RDT is not available.
+
+	rootPath, err := Root()
+	if err != nil {
 		return nil
 	}
+	// NOTE: Should we check if the path provided as arg matches the path
+	// constructed below? If not, we're screwed as we've effectively lost resctrl
+	// control of the container (e.g. because the resctrl fs was unmounted or
+	// remounted elsewhere). All operations are deemed to fail.
+	if path == "" {
+		clos := id
+		if config.IntelRdt.ClosID != "" {
+			clos = config.IntelRdt.ClosID
+		}
+		if path, err = securejoin.SecureJoin(rootPath, clos); err != nil {
+			return nil
+		}
+	}
+
 	return newManager(config, id, path)
 }
 
@@ -428,32 +444,14 @@ func IsMBAEnabled() bool {
 	return mbaEnabled
 }
 
-// Get the path of the clos group in "resource control" filesystem that the container belongs to
-func (m *Manager) getIntelRdtPath() (string, error) {
-	rootPath, err := Root()
-	if err != nil {
-		return "", err
-	}
-
-	clos := m.id
-	if m.config.IntelRdt != nil && m.config.IntelRdt.ClosID != "" {
-		clos = m.config.IntelRdt.ClosID
-	}
-
-	return filepath.Join(rootPath, clos), nil
-}
-
 // Apply applies Intel RDT configuration to the process with the specified pid.
 func (m *Manager) Apply(pid int) (err error) {
 	// If intelRdt is not specified in config, we do nothing
 	if m.config.IntelRdt == nil {
 		return nil
 	}
 
-	path, err := m.getIntelRdtPath()
-	if err != nil {
-		return err
-	}
+	path := m.GetPath()
 
 	m.mu.Lock()
 	defer m.mu.Unlock()
@@ -497,9 +495,6 @@ func (m *Manager) Destroy() error {
 // GetPath returns Intel RDT path to save in a state file and to be able to
 // restore the object later.
 func (m *Manager) GetPath() string {
-	if m.path == "" {
-		m.path, _ = m.getIntelRdtPath()
-	}
 	return m.path
 }
 

libcontainer/intelrdt/intelrdt_test.go

@@ -101,13 +101,14 @@ func TestApply(t *testing.T) {
 	helper := NewIntelRdtTestUtil(t)
 
 	const closID = "test-clos"
+	closPath := filepath.Join(helper.IntelRdtPath, closID)
 
 	helper.config.IntelRdt.ClosID = closID
-	intelrdt := newManager(helper.config, "", helper.IntelRdtPath)
+	intelrdt := newManager(helper.config, "container-1", closPath)
 	if err := intelrdt.Apply(1234); err == nil {
 		t.Fatal("unexpected success when applying pid")
 	}
-	if _, err := os.Stat(filepath.Join(helper.IntelRdtPath, closID)); err == nil {
+	if _, err := os.Stat(closPath); err == nil {
 		t.Fatal("closid dir should not exist")
 	}