Merge release-20200323.0-177-g12bde95 (automated)

1 files changed, 667 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
new file mode 100755
index 000000000..97fa7f7ab
--- /dev/null
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -0,0 +1,667 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package host provides a filesystem implementation for host files imported as
+// file descriptors.
+package host
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fd"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// filesystemType implements vfs.FilesystemType.
+type filesystemType struct{}
+
+// GetFilesystem implements FilesystemType.GetFilesystem.
+func (filesystemType) GetFilesystem(context.Context, *vfs.VirtualFilesystem, *auth.Credentials, string, vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
+	panic("cannot instaniate a host filesystem")
+}
+
+// Name implements FilesystemType.Name.
+func (filesystemType) Name() string {
+	return "none"
+}
+
+// filesystem implements vfs.FilesystemImpl.
+type filesystem struct {
+	kernfs.Filesystem
+}
+
+// NewMount returns a new disconnected mount in vfsObj that may be passed to ImportFD.
+func NewMount(vfsObj *vfs.VirtualFilesystem) (*vfs.Mount, error) {
+	fs := &filesystem{}
+	fs.Init(vfsObj, &filesystemType{})
+	vfsfs := fs.VFSFilesystem()
+	// NewDisconnectedMount will take an additional reference on vfsfs.
+	defer vfsfs.DecRef()
+	return vfsObj.NewDisconnectedMount(vfsfs, nil, &vfs.MountOptions{})
+}
+
+// ImportFD sets up and returns a vfs.FileDescription from a donated fd.
+func ImportFD(mnt *vfs.Mount, hostFD int, isTTY bool) (*vfs.FileDescription, error) {
+	fs, ok := mnt.Filesystem().Impl().(*kernfs.Filesystem)
+	if !ok {
+		return nil, fmt.Errorf("can't import host FDs into filesystems of type %T", mnt.Filesystem().Impl())
+	}
+
+	// Retrieve metadata.
+	var s unix.Stat_t
+	if err := unix.Fstat(hostFD, &s); err != nil {
+		return nil, err
+	}
+
+	fileMode := linux.FileMode(s.Mode)
+	fileType := fileMode.FileType()
+
+	// Determine if hostFD is seekable. If not, this syscall will return ESPIPE
+	// (see fs/read_write.c:llseek), e.g. for pipes, sockets, and some character
+	// devices.
+	_, err := unix.Seek(hostFD, 0, linux.SEEK_CUR)
+	seekable := err != syserror.ESPIPE
+
+	i := &inode{
+		hostFD:   hostFD,
+		seekable: seekable,
+		isTTY:    isTTY,
+		canMap:   canMap(uint32(fileType)),
+		ino:      fs.NextIno(),
+		mode:     fileMode,
+		// For simplicity, set offset to 0. Technically, we should use the existing
+		// offset on the host if the file is seekable.
+		offset: 0,
+	}
+
+	// Non-seekable files can't be memory mapped, assert this.
+	if !i.seekable && i.canMap {
+		panic("files that can return EWOULDBLOCK (sockets, pipes, etc.) cannot be memory mapped")
+	}
+
+	d := &kernfs.Dentry{}
+	d.Init(i)
+	// i.open will take a reference on d.
+	defer d.DecRef()
+
+	return i.open(d.VFSDentry(), mnt)
+}
+
+// inode implements kernfs.Inode.
+type inode struct {
+	kernfs.InodeNotDirectory
+	kernfs.InodeNotSymlink
+
+	// When the reference count reaches zero, the host fd is closed.
+	refs.AtomicRefCount
+
+	// hostFD contains the host fd that this file was originally created from,
+	// which must be available at time of restore.
+	//
+	// This field is initialized at creation time and is immutable.
+	hostFD int
+
+	// seekable is false if the host fd points to a file representing a stream,
+	// e.g. a socket or a pipe. Such files are not seekable and can return
+	// EWOULDBLOCK for I/O operations.
+	//
+	// This field is initialized at creation time and is immutable.
+	seekable bool
+
+	// isTTY is true if this file represents a TTY.
+	//
+	// This field is initialized at creation time and is immutable.
+	isTTY bool
+
+	// canMap specifies whether we allow the file to be memory mapped.
+	//
+	// This field is initialized at creation time and is immutable.
+	canMap bool
+
+	// ino is an inode number unique within this filesystem.
+	//
+	// This field is initialized at creation time and is immutable.
+	ino uint64
+
+	// modeMu protects mode.
+	modeMu sync.Mutex
+
+	// mode is a cached version of the file mode on the host. Note that it may
+	// become out of date if the mode is changed on the host, e.g. with chmod.
+	//
+	// Generally, it is better to retrieve the mode from the host through an
+	// fstat syscall. We only use this value in inode.Mode(), which cannot
+	// return an error, if the syscall to host fails.
+	//
+	// FIXME(b/152294168): Plumb error into Inode.Mode() return value so we
+	// can get rid of this.
+	mode linux.FileMode
+
+	// offsetMu protects offset.
+	offsetMu sync.Mutex
+
+	// offset specifies the current file offset.
+	offset int64
+}
+
+// Note that these flags may become out of date, since they can be modified
+// on the host, e.g. with fcntl.
+func fileFlagsFromHostFD(fd int) (int, error) {
+	flags, err := unix.FcntlInt(uintptr(fd), syscall.F_GETFL, 0)
+	if err != nil {
+		log.Warningf("Failed to get file flags for donated FD %d: %v", fd, err)
+		return 0, err
+	}
+	// TODO(gvisor.dev/issue/1672): implement behavior corresponding to these allowed flags.
+	flags &= syscall.O_ACCMODE | syscall.O_DIRECT | syscall.O_NONBLOCK | syscall.O_DSYNC | syscall.O_SYNC | syscall.O_APPEND
+	return flags, nil
+}
+
+// CheckPermissions implements kernfs.Inode.
+func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
+	mode, uid, gid, err := i.getPermissions()
+	if err != nil {
+		return err
+	}
+	return vfs.GenericCheckPermissions(creds, ats, mode, uid, gid)
+}
+
+// Mode implements kernfs.Inode.
+func (i *inode) Mode() linux.FileMode {
+	mode, _, _, err := i.getPermissions()
+	if err != nil {
+		return i.mode
+	}
+
+	return linux.FileMode(mode)
+}
+
+func (i *inode) getPermissions() (linux.FileMode, auth.KUID, auth.KGID, error) {
+	// Retrieve metadata.
+	var s syscall.Stat_t
+	if err := syscall.Fstat(i.hostFD, &s); err != nil {
+		return 0, 0, 0, err
+	}
+
+	// Update cached mode.
+	i.modeMu.Lock()
+	i.mode = linux.FileMode(s.Mode)
+	i.modeMu.Unlock()
+	return linux.FileMode(s.Mode), auth.KUID(s.Uid), auth.KGID(s.Gid), nil
+}
+
+// Stat implements kernfs.Inode.
+func (i *inode) Stat(_ *vfs.Filesystem, opts vfs.StatOptions) (linux.Statx, error) {
+	if opts.Mask&linux.STATX__RESERVED != 0 {
+		return linux.Statx{}, syserror.EINVAL
+	}
+	if opts.Sync&linux.AT_STATX_SYNC_TYPE == linux.AT_STATX_SYNC_TYPE {
+		return linux.Statx{}, syserror.EINVAL
+	}
+
+	// Limit our host call only to known flags.
+	mask := opts.Mask & linux.STATX_ALL
+	var s unix.Statx_t
+	err := unix.Statx(i.hostFD, "", int(unix.AT_EMPTY_PATH|opts.Sync), int(mask), &s)
+	// Fallback to fstat(2), if statx(2) is not supported on the host.
+	//
+	// TODO(b/151263641): Remove fallback.
+	if err == syserror.ENOSYS {
+		return i.fstat(opts)
+	} else if err != nil {
+		return linux.Statx{}, err
+	}
+
+	ls := linux.Statx{Mask: mask}
+	// Unconditionally fill blksize, attributes, and device numbers, as indicated
+	// by /include/uapi/linux/stat.h.
+	//
+	// RdevMajor/RdevMinor are left as zero, so as not to expose host device
+	// numbers.
+	//
+	// TODO(gvisor.dev/issue/1672): Use kernfs-specific, internally defined
+	// device numbers. If we use the device number from the host, it may collide
+	// with another sentry-internal device number. We handle device/inode
+	// numbers without relying on the host to prevent collisions.
+	ls.Blksize = s.Blksize
+	ls.Attributes = s.Attributes
+	ls.AttributesMask = s.Attributes_mask
+
+	if mask&linux.STATX_TYPE != 0 {
+		ls.Mode |= s.Mode & linux.S_IFMT
+	}
+	if mask&linux.STATX_MODE != 0 {
+		ls.Mode |= s.Mode &^ linux.S_IFMT
+	}
+	if mask&linux.STATX_NLINK != 0 {
+		ls.Nlink = s.Nlink
+	}
+	if mask&linux.STATX_UID != 0 {
+		ls.UID = s.Uid
+	}
+	if mask&linux.STATX_GID != 0 {
+		ls.GID = s.Gid
+	}
+	if mask&linux.STATX_ATIME != 0 {
+		ls.Atime = unixToLinuxStatxTimestamp(s.Atime)
+	}
+	if mask&linux.STATX_BTIME != 0 {
+		ls.Btime = unixToLinuxStatxTimestamp(s.Btime)
+	}
+	if mask&linux.STATX_CTIME != 0 {
+		ls.Ctime = unixToLinuxStatxTimestamp(s.Ctime)
+	}
+	if mask&linux.STATX_MTIME != 0 {
+		ls.Mtime = unixToLinuxStatxTimestamp(s.Mtime)
+	}
+	if mask&linux.STATX_SIZE != 0 {
+		ls.Size = s.Size
+	}
+	if mask&linux.STATX_BLOCKS != 0 {
+		ls.Blocks = s.Blocks
+	}
+
+	// Use our own internal inode number.
+	if mask&linux.STATX_INO != 0 {
+		ls.Ino = i.ino
+	}
+
+	// Update cached mode.
+	if (mask&linux.STATX_TYPE != 0) && (mask&linux.STATX_MODE != 0) {
+		i.modeMu.Lock()
+		i.mode = linux.FileMode(s.Mode)
+		i.modeMu.Unlock()
+	}
+	return ls, nil
+}
+
+// fstat is a best-effort fallback for inode.Stat() if the host does not
+// support statx(2).
+//
+// We ignore the mask and sync flags in opts and simply supply
+// STATX_BASIC_STATS, as fstat(2) itself does not allow the specification
+// of a mask or sync flags. fstat(2) does not provide any metadata
+// equivalent to Statx.Attributes, Statx.AttributesMask, or Statx.Btime, so
+// those fields remain empty.
+func (i *inode) fstat(opts vfs.StatOptions) (linux.Statx, error) {
+	var s unix.Stat_t
+	if err := unix.Fstat(i.hostFD, &s); err != nil {
+		return linux.Statx{}, err
+	}
+
+	// Note that rdev numbers are left as 0; do not expose host device numbers.
+	ls := linux.Statx{
+		Mask:    linux.STATX_BASIC_STATS,
+		Blksize: uint32(s.Blksize),
+		Nlink:   uint32(s.Nlink),
+		UID:     s.Uid,
+		GID:     s.Gid,
+		Mode:    uint16(s.Mode),
+		Size:    uint64(s.Size),
+		Blocks:  uint64(s.Blocks),
+		Atime:   timespecToStatxTimestamp(s.Atim),
+		Ctime:   timespecToStatxTimestamp(s.Ctim),
+		Mtime:   timespecToStatxTimestamp(s.Mtim),
+	}
+
+	// Use our own internal inode number.
+	//
+	// TODO(gvisor.dev/issue/1672): Use a kernfs-specific device number as well.
+	// If we use the device number from the host, it may collide with another
+	// sentry-internal device number. We handle device/inode numbers without
+	// relying on the host to prevent collisions.
+	ls.Ino = i.ino
+
+	return ls, nil
+}
+
+// SetStat implements kernfs.Inode.
+func (i *inode) SetStat(ctx context.Context, fs *vfs.Filesystem, creds *auth.Credentials, opts vfs.SetStatOptions) error {
+	s := opts.Stat
+
+	m := s.Mask
+	if m == 0 {
+		return nil
+	}
+	if m&^(linux.STATX_MODE|linux.STATX_SIZE|linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
+		return syserror.EPERM
+	}
+	mode, uid, gid, err := i.getPermissions()
+	if err != nil {
+		return err
+	}
+	if err := vfs.CheckSetStat(ctx, creds, &s, mode.Permissions(), uid, gid); err != nil {
+		return err
+	}
+
+	if m&linux.STATX_MODE != 0 {
+		if err := syscall.Fchmod(i.hostFD, uint32(s.Mode)); err != nil {
+			return err
+		}
+		i.modeMu.Lock()
+		i.mode = linux.FileMode(s.Mode)
+		i.modeMu.Unlock()
+	}
+	if m&linux.STATX_SIZE != 0 {
+		if err := syscall.Ftruncate(i.hostFD, int64(s.Size)); err != nil {
+			return err
+		}
+	}
+	if m&(linux.STATX_ATIME|linux.STATX_MTIME) != 0 {
+		ts := [2]syscall.Timespec{
+			toTimespec(s.Atime, m&linux.STATX_ATIME == 0),
+			toTimespec(s.Mtime, m&linux.STATX_MTIME == 0),
+		}
+		if err := setTimestamps(i.hostFD, &ts); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// DecRef implements kernfs.Inode.
+func (i *inode) DecRef() {
+	i.AtomicRefCount.DecRefWithDestructor(i.Destroy)
+}
+
+// Destroy implements kernfs.Inode.
+func (i *inode) Destroy() {
+	if err := unix.Close(i.hostFD); err != nil {
+		log.Warningf("failed to close host fd %d: %v", i.hostFD, err)
+	}
+}
+
+// Open implements kernfs.Inode.
+func (i *inode) Open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	return i.open(vfsd, rp.Mount())
+}
+
+func (i *inode) open(d *vfs.Dentry, mnt *vfs.Mount) (*vfs.FileDescription, error) {
+	mode, _, _, err := i.getPermissions()
+	if err != nil {
+		return nil, err
+	}
+	fileType := mode.FileType()
+	if fileType == syscall.S_IFSOCK {
+		if i.isTTY {
+			return nil, errors.New("cannot use host socket as TTY")
+		}
+		// TODO(gvisor.dev/issue/1672): support importing sockets.
+		return nil, errors.New("importing host sockets not supported")
+	}
+
+	// TODO(gvisor.dev/issue/1672): Whitelist specific file types here, so that
+	// we don't allow importing arbitrary file types without proper support.
+	var (
+		vfsfd  *vfs.FileDescription
+		fdImpl vfs.FileDescriptionImpl
+	)
+	if i.isTTY {
+		fd := &ttyFD{
+			fileDescription: fileDescription{inode: i},
+			termios:         linux.DefaultSlaveTermios,
+		}
+		vfsfd = &fd.vfsfd
+		fdImpl = fd
+	} else {
+		// For simplicity, set offset to 0. Technically, we should
+		// only set to 0 on files that are not seekable (sockets, pipes, etc.),
+		// and use the offset from the host fd otherwise.
+		fd := &fileDescription{inode: i}
+		vfsfd = &fd.vfsfd
+		fdImpl = fd
+	}
+
+	flags, err := fileFlagsFromHostFD(i.hostFD)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := vfsfd.Init(fdImpl, uint32(flags), mnt, d, &vfs.FileDescriptionOptions{}); err != nil {
+		return nil, err
+	}
+	return vfsfd, nil
+}
+
+// fileDescription is embedded by host fd implementations of FileDescriptionImpl.
+//
+// TODO(gvisor.dev/issue/1672): Implement Waitable interface.
+type fileDescription struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+
+	// inode is vfsfd.Dentry().Impl().(*kernfs.Dentry).Inode().(*inode), but
+	// cached to reduce indirections and casting. fileDescription does not hold
+	// a reference on the inode through the inode field (since one is already
+	// held via the Dentry).
+	//
+	// inode is immutable after fileDescription creation.
+	inode *inode
+}
+
+// SetStat implements vfs.FileDescriptionImpl.
+func (f *fileDescription) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
+	creds := auth.CredentialsFromContext(ctx)
+	return f.inode.SetStat(ctx, nil, creds, opts)
+}
+
+// Stat implements vfs.FileDescriptionImpl.
+func (f *fileDescription) Stat(_ context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+	return f.inode.Stat(nil, opts)
+}
+
+// Release implements vfs.FileDescriptionImpl.
+func (f *fileDescription) Release() {
+	// noop
+}
+
+// PRead implements FileDescriptionImpl.
+func (f *fileDescription) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	i := f.inode
+	if !i.seekable {
+		return 0, syserror.ESPIPE
+	}
+
+	return readFromHostFD(ctx, i.hostFD, dst, offset, opts.Flags)
+}
+
+// Read implements FileDescriptionImpl.
+func (f *fileDescription) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	i := f.inode
+	if !i.seekable {
+		n, err := readFromHostFD(ctx, i.hostFD, dst, -1, opts.Flags)
+		if isBlockError(err) {
+			// If we got any data at all, return it as a "completed" partial read
+			// rather than retrying until complete.
+			if n != 0 {
+				err = nil
+			} else {
+				err = syserror.ErrWouldBlock
+			}
+		}
+		return n, err
+	}
+	// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
+	i.offsetMu.Lock()
+	n, err := readFromHostFD(ctx, i.hostFD, dst, i.offset, opts.Flags)
+	i.offset += n
+	i.offsetMu.Unlock()
+	return n, err
+}
+
+func readFromHostFD(ctx context.Context, hostFD int, dst usermem.IOSequence, offset int64, flags uint32) (int64, error) {
+	// TODO(gvisor.dev/issue/1672): Support select preadv2 flags.
+	if flags != 0 {
+		return 0, syserror.EOPNOTSUPP
+	}
+
+	var reader safemem.Reader
+	if offset == -1 {
+		reader = safemem.FromIOReader{fd.NewReadWriter(hostFD)}
+	} else {
+		reader = safemem.FromVecReaderFunc{
+			func(srcs [][]byte) (int64, error) {
+				n, err := unix.Preadv(hostFD, srcs, offset)
+				return int64(n), err
+			},
+		}
+	}
+	n, err := dst.CopyOutFrom(ctx, reader)
+	return int64(n), err
+}
+
+// PWrite implements FileDescriptionImpl.
+func (f *fileDescription) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	i := f.inode
+	if !i.seekable {
+		return 0, syserror.ESPIPE
+	}
+
+	return writeToHostFD(ctx, i.hostFD, src, offset, opts.Flags)
+}
+
+// Write implements FileDescriptionImpl.
+func (f *fileDescription) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	i := f.inode
+	if !i.seekable {
+		n, err := writeToHostFD(ctx, i.hostFD, src, -1, opts.Flags)
+		if isBlockError(err) {
+			err = syserror.ErrWouldBlock
+		}
+		return n, err
+	}
+	// TODO(gvisor.dev/issue/1672): Cache pages, when forced to do so.
+	// TODO(gvisor.dev/issue/1672): Write to end of file and update offset if O_APPEND is set on this file.
+	i.offsetMu.Lock()
+	n, err := writeToHostFD(ctx, i.hostFD, src, i.offset, opts.Flags)
+	i.offset += n
+	i.offsetMu.Unlock()
+	return n, err
+}
+
+func writeToHostFD(ctx context.Context, hostFD int, src usermem.IOSequence, offset int64, flags uint32) (int64, error) {
+	// TODO(gvisor.dev/issue/1672): Support select pwritev2 flags.
+	if flags != 0 {
+		return 0, syserror.EOPNOTSUPP
+	}
+
+	var writer safemem.Writer
+	if offset == -1 {
+		writer = safemem.FromIOWriter{fd.NewReadWriter(hostFD)}
+	} else {
+		writer = safemem.FromVecWriterFunc{
+			func(srcs [][]byte) (int64, error) {
+				n, err := unix.Pwritev(hostFD, srcs, offset)
+				return int64(n), err
+			},
+		}
+	}
+	n, err := src.CopyInTo(ctx, writer)
+	return int64(n), err
+}
+
+// Seek implements FileDescriptionImpl.
+//
+// Note that we do not support seeking on directories, since we do not even
+// allow directory fds to be imported at all.
+func (f *fileDescription) Seek(_ context.Context, offset int64, whence int32) (int64, error) {
+	i := f.inode
+	if !i.seekable {
+		return 0, syserror.ESPIPE
+	}
+
+	i.offsetMu.Lock()
+	defer i.offsetMu.Unlock()
+
+	switch whence {
+	case linux.SEEK_SET:
+		if offset < 0 {
+			return i.offset, syserror.EINVAL
+		}
+		i.offset = offset
+
+	case linux.SEEK_CUR:
+		// Check for overflow. Note that underflow cannot occur, since i.offset >= 0.
+		if offset > math.MaxInt64-i.offset {
+			return i.offset, syserror.EOVERFLOW
+		}
+		if i.offset+offset < 0 {
+			return i.offset, syserror.EINVAL
+		}
+		i.offset += offset
+
+	case linux.SEEK_END:
+		var s syscall.Stat_t
+		if err := syscall.Fstat(i.hostFD, &s); err != nil {
+			return i.offset, err
+		}
+		size := s.Size
+
+		// Check for overflow. Note that underflow cannot occur, since size >= 0.
+		if offset > math.MaxInt64-size {
+			return i.offset, syserror.EOVERFLOW
+		}
+		if size+offset < 0 {
+			return i.offset, syserror.EINVAL
+		}
+		i.offset = size + offset
+
+	case linux.SEEK_DATA, linux.SEEK_HOLE:
+		// Modifying the offset in the host file table should not matter, since
+		// this is the only place where we use it.
+		//
+		// For reading and writing, we always rely on our internal offset.
+		n, err := unix.Seek(i.hostFD, offset, int(whence))
+		if err != nil {
+			return i.offset, err
+		}
+		i.offset = n
+
+	default:
+		// Invalid whence.
+		return i.offset, syserror.EINVAL
+	}
+
+	return i.offset, nil
+}
+
+// Sync implements FileDescriptionImpl.
+func (f *fileDescription) Sync(context.Context) error {
+	// TODO(gvisor.dev/issue/1672): Currently we do not support the SyncData optimization, so we always sync everything.
+	return unix.Fsync(f.inode.hostFD)
+}
+
+// ConfigureMMap implements FileDescriptionImpl.
+func (f *fileDescription) ConfigureMMap(_ context.Context, opts *memmap.MMapOpts) error {
+	if !f.inode.canMap {
+		return syserror.ENODEV
+	}
+	// TODO(gvisor.dev/issue/1672): Implement ConfigureMMap and Mappable interface.
+	return syserror.ENODEV
+}