Add VFS2 support for /proc/filesystems.

Updates #1195

PiperOrigin-RevId: 287269106

5 files changed, 69 insertions, 19 deletions

diff --git a/pkg/sentry/vfs/file_description_impl_util_test.go b/pkg/sentry/vfs/file_description_impl_util_test.go
index 678be07fe..9ed58512f 100644
--- a/pkg/sentry/vfs/file_description_impl_util_test.go
+++ b/pkg/sentry/vfs/file_description_impl_util_test.go
@@ -89,7 +89,7 @@ func TestGenCountFD(t *testing.T) {
 	creds := auth.CredentialsFromContext(ctx)
 
 	vfsObj := New() // vfs.New()
-	vfsObj.MustRegisterFilesystemType("testfs", FDTestFilesystemType{})
+	vfsObj.MustRegisterFilesystemType("testfs", FDTestFilesystemType{}, &RegisterFilesystemTypeOptions{})
 	mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "testfs", &GetFilesystemOptions{})
 	if err != nil {
 		t.Fatalf("failed to create testfs root mount: %v", err)
diff --git a/pkg/sentry/vfs/filesystem_type.go b/pkg/sentry/vfs/filesystem_type.go
index c335e206d..023301780 100644
--- a/pkg/sentry/vfs/filesystem_type.go
+++ b/pkg/sentry/vfs/filesystem_type.go
@@ -15,6 +15,7 @@
 package vfs
 
 import (
+	"bytes"
 	"fmt"
 
 	"gvisor.dev/gvisor/pkg/sentry/context"
@@ -43,28 +44,70 @@ type GetFilesystemOptions struct {
 	InternalData interface{}
 }
 
+type registeredFilesystemType struct {
+	fsType FilesystemType
+	opts   RegisterFilesystemTypeOptions
+}
+
+// RegisterFilesystemTypeOptions contains options to
+// VirtualFilesystem.RegisterFilesystem().
+type RegisterFilesystemTypeOptions struct {
+	// If AllowUserMount is true, allow calls to VirtualFilesystem.MountAt()
+	// for which MountOptions.InternalMount == false to use this filesystem
+	// type.
+	AllowUserMount bool
+
+	// If AllowUserList is true, make this filesystem type visible in
+	// /proc/filesystems.
+	AllowUserList bool
+
+	// If RequiresDevice is true, indicate that mounting this filesystem
+	// requires a block device as the mount source in /proc/filesystems.
+	RequiresDevice bool
+}
+
 // RegisterFilesystemType registers the given FilesystemType in vfs with the
 // given name.
-func (vfs *VirtualFilesystem) RegisterFilesystemType(name string, fsType FilesystemType) error {
+func (vfs *VirtualFilesystem) RegisterFilesystemType(name string, fsType FilesystemType, opts *RegisterFilesystemTypeOptions) error {
 	vfs.fsTypesMu.Lock()
 	defer vfs.fsTypesMu.Unlock()
 	if existing, ok := vfs.fsTypes[name]; ok {
-		return fmt.Errorf("name %q is already registered to filesystem type %T", name, existing)
+		return fmt.Errorf("name %q is already registered to filesystem type %T", name, existing.fsType)
+	}
+	vfs.fsTypes[name] = &registeredFilesystemType{
+		fsType: fsType,
+		opts:   *opts,
 	}
-	vfs.fsTypes[name] = fsType
 	return nil
 }
 
 // MustRegisterFilesystemType is equivalent to RegisterFilesystemType but
 // panics on failure.
-func (vfs *VirtualFilesystem) MustRegisterFilesystemType(name string, fsType FilesystemType) {
-	if err := vfs.RegisterFilesystemType(name, fsType); err != nil {
+func (vfs *VirtualFilesystem) MustRegisterFilesystemType(name string, fsType FilesystemType, opts *RegisterFilesystemTypeOptions) {
+	if err := vfs.RegisterFilesystemType(name, fsType, opts); err != nil {
 		panic(fmt.Sprintf("failed to register filesystem type %T: %v", fsType, err))
 	}
 }
 
-func (vfs *VirtualFilesystem) getFilesystemType(name string) FilesystemType {
+func (vfs *VirtualFilesystem) getFilesystemType(name string) *registeredFilesystemType {
 	vfs.fsTypesMu.RLock()
 	defer vfs.fsTypesMu.RUnlock()
 	return vfs.fsTypes[name]
 }
+
+// GenerateProcFilesystems emits the contents of /proc/filesystems for vfs to
+// buf.
+func (vfs *VirtualFilesystem) GenerateProcFilesystems(buf *bytes.Buffer) {
+	vfs.fsTypesMu.RLock()
+	defer vfs.fsTypesMu.RUnlock()
+	for name, rft := range vfs.fsTypes {
+		if !rft.opts.AllowUserList {
+			continue
+		}
+		var nodev string
+		if !rft.opts.RequiresDevice {
+			nodev = "nodev"
+		}
+		fmt.Fprintf(buf, "%s\t%s\n", nodev, name)
+	}
+}
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index ec23ab0dd..00177b371 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -112,11 +112,11 @@ type MountNamespace struct {
 // configured by the given arguments. A reference is taken on the returned
 // MountNamespace.
 func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth.Credentials, source, fsTypeName string, opts *GetFilesystemOptions) (*MountNamespace, error) {
-	fsType := vfs.getFilesystemType(fsTypeName)
-	if fsType == nil {
+	rft := vfs.getFilesystemType(fsTypeName)
+	if rft == nil {
 		return nil, syserror.ENODEV
 	}
-	fs, root, err := fsType.GetFilesystem(ctx, vfs, creds, source, *opts)
+	fs, root, err := rft.fsType.GetFilesystem(ctx, vfs, creds, source, *opts)
 	if err != nil {
 		return nil, err
 	}
@@ -136,11 +136,14 @@ func (vfs *VirtualFilesystem) NewMountNamespace(ctx context.Context, creds *auth
 
 // MountAt creates and mounts a Filesystem configured by the given arguments.
 func (vfs *VirtualFilesystem) MountAt(ctx context.Context, creds *auth.Credentials, source string, target *PathOperation, fsTypeName string, opts *MountOptions) error {
-	fsType := vfs.getFilesystemType(fsTypeName)
-	if fsType == nil {
+	rft := vfs.getFilesystemType(fsTypeName)
+	if rft == nil {
 		return syserror.ENODEV
 	}
-	fs, root, err := fsType.GetFilesystem(ctx, vfs, creds, source, opts.GetFilesystemOptions)
+	if !opts.InternalMount && !rft.opts.AllowUserMount {
+		return syserror.ENODEV
+	}
+	fs, root, err := rft.fsType.GetFilesystem(ctx, vfs, creds, source, opts.GetFilesystemOptions)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/sentry/vfs/options.go b/pkg/sentry/vfs/options.go
index 87d2b0d1c..b7774bf28 100644
--- a/pkg/sentry/vfs/options.go
+++ b/pkg/sentry/vfs/options.go
@@ -50,6 +50,10 @@ type MknodOptions struct {
 type MountOptions struct {
 	// GetFilesystemOptions contains options to FilesystemType.GetFilesystem().
 	GetFilesystemOptions GetFilesystemOptions
+
+	// If InternalMount is true, allow the use of filesystem types for which
+	// RegisterFilesystemTypeOptions.AllowUserMount == false.
+	InternalMount bool
 }
 
 // OpenOptions contains options to VirtualFilesystem.OpenAt() and
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 3e4df8558..a3bdb5805 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -75,23 +75,23 @@ type VirtualFilesystem struct {
 	// mountpoints is analogous to Linux's mountpoint_hashtable.
 	mountpoints map[*Dentry]map[*Mount]struct{}
 
+	// fsTypes contains all registered FilesystemTypes. fsTypes is protected by
+	// fsTypesMu.
+	fsTypesMu sync.RWMutex
+	fsTypes   map[string]*registeredFilesystemType
+
 	// filesystems contains all Filesystems. filesystems is protected by
 	// filesystemsMu.
 	filesystemsMu sync.Mutex
 	filesystems   map[*Filesystem]struct{}
-
-	// fsTypes contains all FilesystemTypes that are usable in the
-	// VirtualFilesystem. fsTypes is protected by fsTypesMu.
-	fsTypesMu sync.RWMutex
-	fsTypes   map[string]FilesystemType
 }
 
 // New returns a new VirtualFilesystem with no mounts or FilesystemTypes.
 func New() *VirtualFilesystem {
 	vfs := &VirtualFilesystem{
 		mountpoints: make(map[*Dentry]map[*Mount]struct{}),
+		fsTypes:     make(map[string]*registeredFilesystemType),
 		filesystems: make(map[*Filesystem]struct{}),
-		fsTypes:     make(map[string]FilesystemType),
 	}
 	vfs.mounts.Init()
 	return vfs