pkg/ns: don't allow operations after Close()

ns/ns.go

@@ -58,6 +58,7 @@ type NetNS interface {
 type netNS struct {
 	file    *os.File
 	mounted bool
+	closed  bool
 }
 
 func getCurrentThreadNetNSPath() string {
@@ -165,8 +166,22 @@ func (ns *netNS) Fd() uintptr {
 	return ns.file.Fd()
 }
 
+func (ns *netNS) errorIfClosed() error {
+	if ns.closed {
+		return fmt.Errorf("%q has already been closed", ns.file.Name())
+	}
+	return nil
+}
+
 func (ns *netNS) Close() error {
-	ns.file.Close()
+	if err := ns.errorIfClosed(); err != nil {
+		return err
+	}
+
+	if err := ns.file.Close(); err != nil {
+		return fmt.Errorf("Failed to close %q: %v", ns.file.Name(), err)
+	}
+	ns.closed = true
 
 	if ns.mounted {
 		if err := unix.Unmount(ns.file.Name(), unix.MNT_DETACH); err != nil {
@@ -175,11 +190,17 @@ func (ns *netNS) Close() error {
 		if err := os.RemoveAll(ns.file.Name()); err != nil {
 			return fmt.Errorf("Failed to clean up namespace %s: %v", ns.file.Name(), err)
 		}
+		ns.mounted = false
 	}
+
 	return nil
 }
 
 func (ns *netNS) Do(toRun func(NetNS) error) error {
+	if err := ns.errorIfClosed(); err != nil {
+		return err
+	}
+
 	containedCall := func(hostNS NetNS) error {
 		threadNS, err := GetNS(getCurrentThreadNetNSPath())
 		if err != nil {
@@ -218,6 +239,10 @@ func (ns *netNS) Do(toRun func(NetNS) error) error {
 }
 
 func (ns *netNS) Set() error {
+	if err := ns.errorIfClosed(); err != nil {
+		return err
+	}
+
 	if _, _, err := unix.Syscall(unix.SYS_SETNS, ns.Fd(), uintptr(unix.CLONE_NEWNET), 0); err != 0 {
 		return fmt.Errorf("Error switching to ns %v: %v", ns.file.Name(), err)
 	}