[vfs2] Don't take reference in Task.MountNamespaceVFS2 and MountNamespace.Root.

This fixes reference leaks related to accidentally forgetting to DecRef()
after calling one or the other.

PiperOrigin-RevId: 336918922

11 files changed, 26 insertions, 9 deletions

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/fsimpl/devtmpfs/devtmpfs_test.go b/pkg/sentry/fsimpl/devtmpfs/devtmpfs_test.go
index 3a38b8bb4..e058eda7a 100644
--- a/pkg/sentry/fsimpl/devtmpfs/devtmpfs_test.go
+++ b/pkg/sentry/fsimpl/devtmpfs/devtmpfs_test.go
@@ -53,6 +53,7 @@ func setupDevtmpfs(t *testing.T) (context.Context, *auth.Credentials, *vfs.Virtu
 		t.Fatalf("failed to create tmpfs root mount: %v", err)
 	}
 	root := mntns.Root()
+	root.IncRef()
 	devpop := vfs.PathOperation{
 		Root:  root,
 		Start: root,
diff --git a/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go b/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
index c349b886e..2ee7cc7ac 100644
--- a/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
+++ b/pkg/sentry/fsimpl/ext/benchmark/benchmark_test.go
@@ -70,6 +70,7 @@ func setUp(b *testing.B, imagePath string) (context.Context, *vfs.VirtualFilesys
 	}
 
 	root := mntns.Root()
+	root.IncRef()
 
 	tearDown := func() {
 		root.DecRef(ctx)
diff --git a/pkg/sentry/fsimpl/ext/ext_test.go b/pkg/sentry/fsimpl/ext/ext_test.go
index 0989558cd..d9fd4590c 100644
--- a/pkg/sentry/fsimpl/ext/ext_test.go
+++ b/pkg/sentry/fsimpl/ext/ext_test.go
@@ -82,6 +82,7 @@ func setUp(t *testing.T, imagePath string) (context.Context, *vfs.VirtualFilesys
 	}
 
 	root := mntns.Root()
+	root.IncRef()
 
 	tearDown := func() {
 		root.DecRef(ctx)
diff --git a/pkg/sentry/fsimpl/gofer/BUILD b/pkg/sentry/fsimpl/gofer/BUILD
index 16787116f..ad0afc41b 100644
--- a/pkg/sentry/fsimpl/gofer/BUILD
+++ b/pkg/sentry/fsimpl/gofer/BUILD
@@ -52,6 +52,7 @@ go_library(
         "//pkg/fspath",
         "//pkg/log",
         "//pkg/p9",
+        "//pkg/refs",
         "//pkg/safemem",
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/lock",
diff --git a/pkg/sentry/fsimpl/proc/tasks_test.go b/pkg/sentry/fsimpl/proc/tasks_test.go
index 6975af5a7..2582ababd 100644
--- a/pkg/sentry/fsimpl/proc/tasks_test.go
+++ b/pkg/sentry/fsimpl/proc/tasks_test.go
@@ -109,9 +109,12 @@ func setup(t *testing.T) *testutil.System {
 	if err != nil {
 		t.Fatalf("NewMountNamespace(): %v", err)
 	}
+	root := mntns.Root()
+	root.IncRef()
+	defer root.DecRef(ctx)
 	pop := &vfs.PathOperation{
-		Root:  mntns.Root(),
-		Start: mntns.Root(),
+		Root:  root,
+		Start: root,
 		Path:  fspath.Parse("/proc"),
 	}
 	if err := k.VFS().MkdirAt(ctx, creds, pop, &vfs.MkdirOptions{Mode: 0777}); err != nil {
@@ -119,8 +122,8 @@ func setup(t *testing.T) *testutil.System {
 	}
 
 	pop = &vfs.PathOperation{
-		Root:  mntns.Root(),
-		Start: mntns.Root(),
+		Root:  root,
+		Start: root,
 		Path:  fspath.Parse("/proc"),
 	}
 	mntOpts := &vfs.MountOptions{
diff --git a/pkg/sentry/fsimpl/testutil/testutil.go b/pkg/sentry/fsimpl/testutil/testutil.go
index 568132121..1a8525b06 100644
--- a/pkg/sentry/fsimpl/testutil/testutil.go
+++ b/pkg/sentry/fsimpl/testutil/testutil.go
@@ -46,16 +46,18 @@ type System struct {
 
 // NewSystem constructs a System.
 //
-// Precondition: Caller must hold a reference on MntNs, whose ownership
+// Precondition: Caller must hold a reference on mns, whose ownership
 // is transferred to the new System.
 func NewSystem(ctx context.Context, t *testing.T, v *vfs.VirtualFilesystem, mns *vfs.MountNamespace) *System {
+	root := mns.Root()
+	root.IncRef()
 	s := &System{
 		t:     t,
 		Ctx:   ctx,
 		Creds: auth.CredentialsFromContext(ctx),
 		VFS:   v,
 		MntNs: mns,
-		Root:  mns.Root(),
+		Root:  root,
 	}
 	return s
 }
@@ -254,10 +256,10 @@ func (d *DirentCollector) Contains(name string, typ uint8) error {
 	defer d.mu.Unlock()
 	dirent, ok := d.dirents[name]
 	if !ok {
-		return fmt.Errorf("No dirent named %q found", name)
+		return fmt.Errorf("no dirent named %q found", name)
 	}
 	if dirent.Type != typ {
-		return fmt.Errorf("Dirent named %q found, but was expecting type %s, got: %+v", name, linux.DirentType.Parse(uint64(typ)), dirent)
+		return fmt.Errorf("dirent named %q found, but was expecting type %s, got: %+v", name, linux.DirentType.Parse(uint64(typ)), dirent)
 	}
 	return nil
 }
diff --git a/pkg/sentry/fsimpl/tmpfs/benchmark_test.go b/pkg/sentry/fsimpl/tmpfs/benchmark_test.go
index 5209a17af..3cc63e732 100644
--- a/pkg/sentry/fsimpl/tmpfs/benchmark_test.go
+++ b/pkg/sentry/fsimpl/tmpfs/benchmark_test.go
@@ -193,6 +193,7 @@ func BenchmarkVFS2TmpfsStat(b *testing.B) {
 
 			// Create nested directories with given depth.
 			root := mntns.Root()
+			root.IncRef()
 			defer root.DecRef(ctx)
 			vd := root
 			vd.IncRef()
@@ -387,6 +388,7 @@ func BenchmarkVFS2TmpfsMountStat(b *testing.B) {
 
 			// Create the mount point.
 			root := mntns.Root()
+			root.IncRef()
 			defer root.DecRef(ctx)
 			pop := vfs.PathOperation{
 				Root:  root,
diff --git a/pkg/sentry/fsimpl/tmpfs/pipe_test.go b/pkg/sentry/fsimpl/tmpfs/pipe_test.go
index be29a2363..2f856ce36 100644
--- a/pkg/sentry/fsimpl/tmpfs/pipe_test.go
+++ b/pkg/sentry/fsimpl/tmpfs/pipe_test.go
@@ -165,6 +165,7 @@ func setup(t *testing.T) (context.Context, *auth.Credentials, *vfs.VirtualFilesy
 
 	// Create the pipe.
 	root := mntns.Root()
+	root.IncRef()
 	pop := vfs.PathOperation{
 		Root:  root,
 		Start: root,
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs_test.go b/pkg/sentry/fsimpl/tmpfs/tmpfs_test.go
index 99c8e3c0f..fc5323abc 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs_test.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs_test.go
@@ -46,6 +46,7 @@ func newTmpfsRoot(ctx context.Context) (*vfs.VirtualFilesystem, vfs.VirtualDentr
 		return nil, vfs.VirtualDentry{}, nil, fmt.Errorf("failed to create tmpfs root mount: %v", err)
 	}
 	root := mntns.Root()
+	root.IncRef()
 	return vfsObj, root, func() {
 		root.DecRef(ctx)
 		mntns.DecRef(ctx)
diff --git a/pkg/sentry/fsimpl/verity/verity_test.go b/pkg/sentry/fsimpl/verity/verity_test.go
index 8d0926bc4..e301d35f5 100644
--- a/pkg/sentry/fsimpl/verity/verity_test.go
+++ b/pkg/sentry/fsimpl/verity/verity_test.go
@@ -70,6 +70,7 @@ func newVerityRoot(ctx context.Context, t *testing.T) (*vfs.VirtualFilesystem, v
 		return nil, vfs.VirtualDentry{}, fmt.Errorf("NewMountNamespace: %v", err)
 	}
 	root := mntns.Root()
+	root.IncRef()
 	t.Helper()
 	t.Cleanup(func() {
 		root.DecRef(ctx)