8 files changed, 25 insertions, 24 deletions
diff --git a/pkg/sentry/control/proc.go b/pkg/sentry/control/proc.go
index 668f47802..1d88db12f 100644
--- a/pkg/sentry/control/proc.go
+++ b/pkg/sentry/control/proc.go
@@ -183,9 +183,9 @@ func (proc *Proc) execAsync(args *ExecArgs) (*kernel.ThreadGroup, kernel.ThreadI
 		if initArgs.MountNamespaceVFS2 == nil {
 			// Set initArgs so that 'ctx' returns the namespace.
 			//
-			// MountNamespaceVFS2 adds a reference to the namespace, which is
-			// transferred to the new process.
+			// Add a reference to the namespace, which is transferred to the new process.
 			initArgs.MountNamespaceVFS2 = proc.Kernel.GlobalInit().Leader().MountNamespaceVFS2()
+			initArgs.MountNamespaceVFS2.IncRef()
 		}
 	} else {
 		if initArgs.MountNamespace == nil {
diff --git a/pkg/sentry/fs/user/path.go b/pkg/sentry/fs/user/path.go
index 2f5a43b84..124bc95ed 100644
--- a/pkg/sentry/fs/user/path.go
+++ b/pkg/sentry/fs/user/path.go
@@ -121,6 +121,7 @@ func resolve(ctx context.Context, mns *fs.MountNamespace, paths []string, name s
 
 func resolveVFS2(ctx context.Context, creds *auth.Credentials, mns *vfs.MountNamespace, paths []string, name string) (string, error) {
 	root := mns.Root()
+	root.IncRef()
 	defer root.DecRef(ctx)
 	for _, p := range paths {
 		if !path.IsAbs(p) {
diff --git a/pkg/sentry/fs/user/user.go b/pkg/sentry/fs/user/user.go
index 936fd3932..1f8684dc6 100644
--- a/pkg/sentry/fs/user/user.go
+++ b/pkg/sentry/fs/user/user.go
@@ -105,6 +105,7 @@ func getExecUserHomeVFS2(ctx context.Context, mns *vfs.MountNamespace, uid auth.
 	const defaultHome = "/"
 
 	root := mns.Root()
+	root.IncRef()
 	defer root.DecRef(ctx)
 
 	creds := auth.CredentialsFromContext(ctx)
diff --git a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
index ed729e480..e6fe0fc0d 100644
--- a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
+++ b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
@@ -95,10 +95,13 @@ func NewAccessor(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *auth
 	if err != nil {
 		return nil, err
 	}
+	// Pass a reference on root to the Accessor.
+	root := mntns.Root()
+	root.IncRef()
 	return &Accessor{
 		vfsObj: vfsObj,
 		mntns:  mntns,
-		root:   mntns.Root(),
+		root:   root,
 		creds:  creds,
 	}, nil
 }
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index d635c9e73..675506269 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -841,14 +841,16 @@ func (ctx *createProcessContext) Value(key interface{}) interface{} {
 		if ctx.args.MountNamespaceVFS2 == nil {
 			return nil
 		}
-		// MountNamespaceVFS2.Root() takes a reference on the root dirent for us.
-		return ctx.args.MountNamespaceVFS2.Root()
+		root := ctx.args.MountNamespaceVFS2.Root()
+		root.IncRef()
+		return root
 	case vfs.CtxMountNamespace:
 		if ctx.k.globalInit == nil {
 			return nil
 		}
-		// MountNamespaceVFS2 takes a reference for us.
-		return ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
+		mntns := ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
+		mntns.IncRef()
+		return mntns
 	case fs.CtxDirentCacheLimiter:
 		return ctx.k.DirentCacheLimiter
 	case inet.CtxStack:
@@ -904,14 +906,13 @@ func (k *Kernel) CreateProcess(args CreateProcessArgs) (*ThreadGroup, ThreadID,
 	if VFS2Enabled {
 		mntnsVFS2 = args.MountNamespaceVFS2
 		if mntnsVFS2 == nil {
-			// MountNamespaceVFS2 adds a reference to the namespace, which is
-			// transferred to the new process.
+			// Add a reference to the namespace, which is transferred to the new process.
 			mntnsVFS2 = k.globalInit.Leader().MountNamespaceVFS2()
+			mntnsVFS2.IncRef()
 		}
 		// Get the root directory from the MountNamespace.
 		root := mntnsVFS2.Root()
-		// The call to newFSContext below will take a reference on root, so we
-		// don't need to hold this one.
+		root.IncRef()
 		defer root.DecRef(ctx)
 
 		// Grab the working directory.
@@ -1648,16 +1649,16 @@ func (ctx supervisorContext) Value(key interface{}) interface{} {
 		if ctx.k.globalInit == nil {
 			return vfs.VirtualDentry{}
 		}
-		mntns := ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
-		defer mntns.DecRef(ctx)
-		// Root() takes a reference on the root dirent for us.
-		return mntns.Root()
+		root := ctx.k.GlobalInit().Leader().MountNamespaceVFS2().Root()
+		root.IncRef()
+		return root
 	case vfs.CtxMountNamespace:
 		if ctx.k.globalInit == nil {
 			return nil
 		}
-		// MountNamespaceVFS2() takes a reference for us.
-		return ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
+		mntns := ctx.k.GlobalInit().Leader().MountNamespaceVFS2()
+		mntns.IncRef()
+		return mntns
 	case fs.CtxDirentCacheLimiter:
 		return ctx.k.DirentCacheLimiter
 	case inet.CtxStack:
diff --git a/pkg/sentry/kernel/task.go b/pkg/sentry/kernel/task.go
index f796e0fa3..e90a19cfb 100644
--- a/pkg/sentry/kernel/task.go
+++ b/pkg/sentry/kernel/task.go
@@ -735,7 +735,6 @@ func (t *Task) SyscallRestartBlock() SyscallRestartBlock {
 func (t *Task) IsChrooted() bool {
 	if VFS2Enabled {
 		realRoot := t.mountNamespaceVFS2.Root()
-		defer realRoot.DecRef(t)
 		root := t.fsContext.RootDirectoryVFS2()
 		defer root.DecRef(t)
 		return root != realRoot
@@ -868,7 +867,6 @@ func (t *Task) MountNamespace() *fs.MountNamespace {
 func (t *Task) MountNamespaceVFS2() *vfs.MountNamespace {
 	t.mu.Lock()
 	defer t.mu.Unlock()
-	t.mountNamespaceVFS2.IncRef()
 	return t.mountNamespaceVFS2
 }
 
diff --git a/pkg/sentry/syscalls/linux/vfs2/execve.go b/pkg/sentry/syscalls/linux/vfs2/execve.go
index 066ee0863..c8ce2aabc 100644
--- a/pkg/sentry/syscalls/linux/vfs2/execve.go
+++ b/pkg/sentry/syscalls/linux/vfs2/execve.go
@@ -110,8 +110,7 @@ func execveat(t *kernel.Task, dirfd int32, pathnameAddr, argvAddr, envvAddr user
 	}
 
 	// Load the new TaskContext.
-	mntns := t.MountNamespaceVFS2() // FIXME(jamieliu): useless refcount change
-	defer mntns.DecRef(t)
+	mntns := t.MountNamespaceVFS2()
 	wd := t.FSContext().WorkingDirectoryVFS2()
 	defer wd.DecRef(t)
 	remainingTraversals := uint(linux.MaxSymlinkTraversals)
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index 79a2d8c41..78f115bfa 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -727,14 +727,12 @@ func (mnt *Mount) Root() *Dentry {
 	return mnt.root
 }
 
-// Root returns mntns' root. A reference is taken on the returned
-// VirtualDentry.
+// Root returns mntns' root. It does not take a reference on the returned Dentry.
 func (mntns *MountNamespace) Root() VirtualDentry {
 	vd := VirtualDentry{
 		mount:  mntns.root,
 		dentry: mntns.root.root,
 	}
-	vd.IncRef()
 	return vd
 }