Fix runsc tests on VFS2 overlay.

- Check the sticky bit in overlay.filesystem.UnlinkAt(). Fixes
  StickyTest.StickyBitPermDenied.

- When configuring a VFS2 overlay in runsc, copy the lower layer's root
  owner/group/mode to the upper layer's root (as in the VFS1 equivalent,
  boot.addOverlay()). This makes the overlay root owned by UID/GID 65534 with
  mode 0755 rather than owned by UID/GID 0 with mode 01777. Fixes
  CreateTest.CreateFailsOnUnpermittedDir, which assumes that the test cannot
  create files in /.

- MknodTest.UnimplementedTypesReturnError assumes that the creation of device
  special files is not supported. However, while the VFS2 gofer client still
  doesn't support device special files, VFS2 tmpfs does, and in the overlay
  test dimension mknod() targets a tmpfs upper layer. The test initially has
  all capabilities, including CAP_MKNOD, so its creation of these files
  succeeds. Constrain these tests to VFS1.

- Rename overlay.nonDirectoryFD to overlay.regularFileFD and only use it for
  regular files, using the original FD for pipes and device special files. This
  is more consistent with Linux (which gets the original inode_operations, and
  therefore file_operations, for these file types from ovl_fill_inode() =>
  init_special_inode()) and fixes remaining mknod and pipe tests.

- Read/write 1KB at a time in PipeTest.Streaming, rather than 4 bytes. This
  isn't strictly necessary, but it makes the test less obnoxiously slow on
  ptrace.

Fixes #4407

PiperOrigin-RevId: 337971042

5 files changed, 179 insertions, 67 deletions

diff --git a/pkg/sentry/fsimpl/overlay/BUILD b/pkg/sentry/fsimpl/overlay/BUILD
index 8cf5b35d3..1e11b0428 100644
--- a/pkg/sentry/fsimpl/overlay/BUILD
+++ b/pkg/sentry/fsimpl/overlay/BUILD
@@ -21,14 +21,16 @@ go_library(
         "directory.go",
         "filesystem.go",
         "fstree.go",
-        "non_directory.go",
         "overlay.go",
+        "regular_file.go",
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
         "//pkg/context",
         "//pkg/fspath",
+        "//pkg/log",
+        "//pkg/sentry/arch",
         "//pkg/sentry/fs/lock",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/memmap",
@@ -37,5 +39,6 @@ go_library(
         "//pkg/sync",
         "//pkg/syserror",
         "//pkg/usermem",
+        "//pkg/waiter",
     ],
 )
diff --git a/pkg/sentry/fsimpl/overlay/copy_up.go b/pkg/sentry/fsimpl/overlay/copy_up.go
index 73b126669..4506642ca 100644
--- a/pkg/sentry/fsimpl/overlay/copy_up.go
+++ b/pkg/sentry/fsimpl/overlay/copy_up.go
@@ -75,8 +75,21 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		return syserror.ENOENT
 	}
 
-	// Perform copy-up.
+	// Obtain settable timestamps from the lower layer.
 	vfsObj := d.fs.vfsfs.VirtualFilesystem()
+	oldpop := vfs.PathOperation{
+		Root:  d.lowerVDs[0],
+		Start: d.lowerVDs[0],
+	}
+	const timestampsMask = linux.STATX_ATIME | linux.STATX_MTIME
+	oldStat, err := vfsObj.StatAt(ctx, d.fs.creds, &oldpop, &vfs.StatOptions{
+		Mask: timestampsMask,
+	})
+	if err != nil {
+		return err
+	}
+
+	// Perform copy-up.
 	newpop := vfs.PathOperation{
 		Root:  d.parent.upperVD,
 		Start: d.parent.upperVD,
@@ -101,10 +114,7 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 	}
 	switch ftype {
 	case linux.S_IFREG:
-		oldFD, err := vfsObj.OpenAt(ctx, d.fs.creds, &vfs.PathOperation{
-			Root:  d.lowerVDs[0],
-			Start: d.lowerVDs[0],
-		}, &vfs.OpenOptions{
+		oldFD, err := vfsObj.OpenAt(ctx, d.fs.creds, &oldpop, &vfs.OpenOptions{
 			Flags: linux.O_RDONLY,
 		})
 		if err != nil {
@@ -160,9 +170,11 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		}
 		if err := newFD.SetStat(ctx, vfs.SetStatOptions{
 			Stat: linux.Statx{
-				Mask: linux.STATX_UID | linux.STATX_GID,
-				UID:  d.uid,
-				GID:  d.gid,
+				Mask:  linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
+				UID:   d.uid,
+				GID:   d.gid,
+				Atime: oldStat.Atime,
+				Mtime: oldStat.Mtime,
 			},
 		}); err != nil {
 			cleanupUndoCopyUp()
@@ -179,9 +191,11 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		}
 		if err := vfsObj.SetStatAt(ctx, d.fs.creds, &newpop, &vfs.SetStatOptions{
 			Stat: linux.Statx{
-				Mask: linux.STATX_UID | linux.STATX_GID,
-				UID:  d.uid,
-				GID:  d.gid,
+				Mask:  linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
+				UID:   d.uid,
+				GID:   d.gid,
+				Atime: oldStat.Atime,
+				Mtime: oldStat.Mtime,
 			},
 		}); err != nil {
 			cleanupUndoCopyUp()
@@ -195,10 +209,7 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		d.upperVD = upperVD
 
 	case linux.S_IFLNK:
-		target, err := vfsObj.ReadlinkAt(ctx, d.fs.creds, &vfs.PathOperation{
-			Root:  d.lowerVDs[0],
-			Start: d.lowerVDs[0],
-		})
+		target, err := vfsObj.ReadlinkAt(ctx, d.fs.creds, &oldpop)
 		if err != nil {
 			return err
 		}
@@ -207,10 +218,12 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		}
 		if err := vfsObj.SetStatAt(ctx, d.fs.creds, &newpop, &vfs.SetStatOptions{
 			Stat: linux.Statx{
-				Mask: linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID,
-				Mode: uint16(d.mode),
-				UID:  d.uid,
-				GID:  d.gid,
+				Mask:  linux.STATX_MODE | linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
+				Mode:  uint16(d.mode),
+				UID:   d.uid,
+				GID:   d.gid,
+				Atime: oldStat.Atime,
+				Mtime: oldStat.Mtime,
 			},
 		}); err != nil {
 			cleanupUndoCopyUp()
@@ -224,25 +237,20 @@ func (d *dentry) copyUpLocked(ctx context.Context) error {
 		d.upperVD = upperVD
 
 	case linux.S_IFBLK, linux.S_IFCHR:
-		lowerStat, err := vfsObj.StatAt(ctx, d.fs.creds, &vfs.PathOperation{
-			Root:  d.lowerVDs[0],
-			Start: d.lowerVDs[0],
-		}, &vfs.StatOptions{})
-		if err != nil {
-			return err
-		}
 		if err := vfsObj.MknodAt(ctx, d.fs.creds, &newpop, &vfs.MknodOptions{
 			Mode:     linux.FileMode(d.mode),
-			DevMajor: lowerStat.RdevMajor,
-			DevMinor: lowerStat.RdevMinor,
+			DevMajor: oldStat.RdevMajor,
+			DevMinor: oldStat.RdevMinor,
 		}); err != nil {
 			return err
 		}
 		if err := vfsObj.SetStatAt(ctx, d.fs.creds, &newpop, &vfs.SetStatOptions{
 			Stat: linux.Statx{
-				Mask: linux.STATX_UID | linux.STATX_GID,
-				UID:  d.uid,
-				GID:  d.gid,
+				Mask:  linux.STATX_UID | linux.STATX_GID | oldStat.Mask&timestampsMask,
+				UID:   d.uid,
+				GID:   d.gid,
+				Atime: oldStat.Atime,
+				Mtime: oldStat.Mtime,
 			},
 		}); err != nil {
 			cleanupUndoCopyUp()
diff --git a/pkg/sentry/fsimpl/overlay/filesystem.go b/pkg/sentry/fsimpl/overlay/filesystem.go
index bd11372d5..78a01bbb7 100644
--- a/pkg/sentry/fsimpl/overlay/filesystem.go
+++ b/pkg/sentry/fsimpl/overlay/filesystem.go
@@ -765,7 +765,7 @@ func (fs *filesystem) OpenAt(ctx context.Context, rp *vfs.ResolvingPath, opts vf
 		if mustCreate {
 			return nil, syserror.EEXIST
 		}
-		if mayWrite {
+		if start.isRegularFile() && mayWrite {
 			if err := start.copyUpLocked(ctx); err != nil {
 				return nil, err
 			}
@@ -819,7 +819,7 @@ afterTrailingSymlink:
 	if rp.MustBeDir() && !child.isDir() {
 		return nil, syserror.ENOTDIR
 	}
-	if mayWrite {
+	if child.isRegularFile() && mayWrite {
 		if err := child.copyUpLocked(ctx); err != nil {
 			return nil, err
 		}
@@ -872,8 +872,11 @@ func (d *dentry) openCopiedUp(ctx context.Context, rp *vfs.ResolvingPath, opts *
 	if err != nil {
 		return nil, err
 	}
+	if ftype != linux.S_IFREG {
+		return layerFD, nil
+	}
 	layerFlags := layerFD.StatusFlags()
-	fd := &nonDirectoryFD{
+	fd := &regularFileFD{
 		copiedUp:    isUpper,
 		cachedFD:    layerFD,
 		cachedFlags: layerFlags,
@@ -969,7 +972,7 @@ func (fs *filesystem) createAndOpenLocked(ctx context.Context, rp *vfs.Resolving
 	}
 	// Finally construct the overlay FD.
 	upperFlags := upperFD.StatusFlags()
-	fd := &nonDirectoryFD{
+	fd := &regularFileFD{
 		copiedUp:    true,
 		cachedFD:    upperFD,
 		cachedFlags: upperFlags,
@@ -1293,6 +1296,9 @@ func (fs *filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if !child.isDir() {
 		return syserror.ENOTDIR
 	}
+	if err := vfs.CheckDeleteSticky(rp.Credentials(), linux.FileMode(atomic.LoadUint32(&parent.mode)), auth.KUID(atomic.LoadUint32(&child.uid))); err != nil {
+		return err
+	}
 	child.dirMu.Lock()
 	defer child.dirMu.Unlock()
 	whiteouts, err := child.collectWhiteoutsForRmdirLocked(ctx)
@@ -1528,12 +1534,38 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 		return err
 	}
 
+	parentMode := atomic.LoadUint32(&parent.mode)
 	child := parent.children[name]
 	var childLayer lookupLayer
+	if child == nil {
+		if parentMode&linux.S_ISVTX != 0 {
+			// If the parent's sticky bit is set, we need a child dentry to get
+			// its owner.
+			child, err = fs.getChildLocked(ctx, parent, name, &ds)
+			if err != nil {
+				return err
+			}
+		} else {
+			// Determine if the file being unlinked actually exists. Holding
+			// parent.dirMu prevents a dentry from being instantiated for the file,
+			// which in turn prevents it from being copied-up, so this result is
+			// stable.
+			childLayer, err = fs.lookupLayerLocked(ctx, parent, name)
+			if err != nil {
+				return err
+			}
+			if !childLayer.existsInOverlay() {
+				return syserror.ENOENT
+			}
+		}
+	}
 	if child != nil {
 		if child.isDir() {
 			return syserror.EISDIR
 		}
+		if err := vfs.CheckDeleteSticky(rp.Credentials(), linux.FileMode(parentMode), auth.KUID(atomic.LoadUint32(&child.uid))); err != nil {
+			return err
+		}
 		if err := vfsObj.PrepareDeleteDentry(mntns, &child.vfsd); err != nil {
 			return err
 		}
@@ -1546,18 +1578,6 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 		} else {
 			childLayer = lookupLayerLower
 		}
-	} else {
-		// Determine if the file being unlinked actually exists. Holding
-		// parent.dirMu prevents a dentry from being instantiated for the file,
-		// which in turn prevents it from being copied-up, so this result is
-		// stable.
-		childLayer, err = fs.lookupLayerLocked(ctx, parent, name)
-		if err != nil {
-			return err
-		}
-		if !childLayer.existsInOverlay() {
-			return syserror.ENOENT
-		}
 	}
 
 	pop := vfs.PathOperation{
diff --git a/pkg/sentry/fsimpl/overlay/overlay.go b/pkg/sentry/fsimpl/overlay/overlay.go
index e5f506d2e..4c5de8d32 100644
--- a/pkg/sentry/fsimpl/overlay/overlay.go
+++ b/pkg/sentry/fsimpl/overlay/overlay.go
@@ -18,7 +18,7 @@
 //
 // Lock order:
 //
-// directoryFD.mu / nonDirectoryFD.mu
+// directoryFD.mu / regularFileFD.mu
 //   filesystem.renameMu
 //     dentry.dirMu
 //       dentry.copyMu
@@ -453,7 +453,7 @@ type dentry struct {
 	// - If this dentry is copied-up, then wrappedMappable is the Mappable
 	// obtained from a call to the current top layer's
 	// FileDescription.ConfigureMMap(). Once wrappedMappable becomes non-nil
-	// (from a call to nonDirectoryFD.ensureMappable()), it cannot become nil.
+	// (from a call to regularFileFD.ensureMappable()), it cannot become nil.
 	// wrappedMappable is protected by mapsMu and dataMu.
 	//
 	// - isMappable is non-zero iff wrappedMappable is non-nil. isMappable is
diff --git a/pkg/sentry/fsimpl/overlay/non_directory.go b/pkg/sentry/fsimpl/overlay/regular_file.go
index 853aee951..2b89a7a6d 100644
--- a/pkg/sentry/fsimpl/overlay/non_directory.go
+++ b/pkg/sentry/fsimpl/overlay/regular_file.go
@@ -19,14 +19,21 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"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"
+	"gvisor.dev/gvisor/pkg/waiter"
 )
 
+func (d *dentry) isRegularFile() bool {
+	return atomic.LoadUint32(&d.mode)&linux.S_IFMT == linux.S_IFREG
+}
+
 func (d *dentry) isSymlink() bool {
 	return atomic.LoadUint32(&d.mode)&linux.S_IFMT == linux.S_IFLNK
 }
@@ -40,7 +47,7 @@ func (d *dentry) readlink(ctx context.Context) (string, error) {
 }
 
 // +stateify savable
-type nonDirectoryFD struct {
+type regularFileFD struct {
 	fileDescription
 
 	// If copiedUp is false, cachedFD represents
@@ -52,9 +59,13 @@ type nonDirectoryFD struct {
 	copiedUp    bool
 	cachedFD    *vfs.FileDescription
 	cachedFlags uint32
+
+	// If copiedUp is false, lowerWaiters contains all waiter.Entries
+	// registered with cachedFD. lowerWaiters is protected by mu.
+	lowerWaiters map[*waiter.Entry]waiter.EventMask
 }
 
-func (fd *nonDirectoryFD) getCurrentFD(ctx context.Context) (*vfs.FileDescription, error) {
+func (fd *regularFileFD) getCurrentFD(ctx context.Context) (*vfs.FileDescription, error) {
 	fd.mu.Lock()
 	defer fd.mu.Unlock()
 	wrappedFD, err := fd.currentFDLocked(ctx)
@@ -65,7 +76,7 @@ func (fd *nonDirectoryFD) getCurrentFD(ctx context.Context) (*vfs.FileDescriptio
 	return wrappedFD, nil
 }
 
-func (fd *nonDirectoryFD) currentFDLocked(ctx context.Context) (*vfs.FileDescription, error) {
+func (fd *regularFileFD) currentFDLocked(ctx context.Context) (*vfs.FileDescription, error) {
 	d := fd.dentry()
 	statusFlags := fd.vfsfd.StatusFlags()
 	if !fd.copiedUp && d.isCopiedUp() {
@@ -87,10 +98,21 @@ func (fd *nonDirectoryFD) currentFDLocked(ctx context.Context) (*vfs.FileDescrip
 				return nil, err
 			}
 		}
+		if len(fd.lowerWaiters) != 0 {
+			ready := upperFD.Readiness(^waiter.EventMask(0))
+			for e, mask := range fd.lowerWaiters {
+				fd.cachedFD.EventUnregister(e)
+				upperFD.EventRegister(e, mask)
+				if ready&mask != 0 {
+					e.Callback.Callback(e)
+				}
+			}
+		}
 		fd.cachedFD.DecRef(ctx)
 		fd.copiedUp = true
 		fd.cachedFD = upperFD
 		fd.cachedFlags = statusFlags
+		fd.lowerWaiters = nil
 	} else if fd.cachedFlags != statusFlags {
 		if err := fd.cachedFD.SetStatusFlags(ctx, d.fs.creds, statusFlags); err != nil {
 			return nil, err
@@ -101,13 +123,13 @@ func (fd *nonDirectoryFD) currentFDLocked(ctx context.Context) (*vfs.FileDescrip
 }
 
 // Release implements vfs.FileDescriptionImpl.Release.
-func (fd *nonDirectoryFD) Release(ctx context.Context) {
+func (fd *regularFileFD) Release(ctx context.Context) {
 	fd.cachedFD.DecRef(ctx)
 	fd.cachedFD = nil
 }
 
 // OnClose implements vfs.FileDescriptionImpl.OnClose.
-func (fd *nonDirectoryFD) OnClose(ctx context.Context) error {
+func (fd *regularFileFD) OnClose(ctx context.Context) error {
 	// Linux doesn't define ovl_file_operations.flush at all (i.e. its
 	// equivalent to OnClose is a no-op). We pass through to
 	// fd.cachedFD.OnClose() without upgrading if fd.dentry() has been
@@ -128,7 +150,7 @@ func (fd *nonDirectoryFD) OnClose(ctx context.Context) error {
 }
 
 // Stat implements vfs.FileDescriptionImpl.Stat.
-func (fd *nonDirectoryFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
+func (fd *regularFileFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux.Statx, error) {
 	var stat linux.Statx
 	if layerMask := opts.Mask &^ statInternalMask; layerMask != 0 {
 		wrappedFD, err := fd.getCurrentFD(ctx)
@@ -149,7 +171,7 @@ func (fd *nonDirectoryFD) Stat(ctx context.Context, opts vfs.StatOptions) (linux
 }
 
 // Allocate implements vfs.FileDescriptionImpl.Allocate.
-func (fd *nonDirectoryFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
+func (fd *regularFileFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
 	wrappedFD, err := fd.getCurrentFD(ctx)
 	if err != nil {
 		return err
@@ -159,7 +181,7 @@ func (fd *nonDirectoryFD) Allocate(ctx context.Context, mode, offset, length uin
 }
 
 // SetStat implements vfs.FileDescriptionImpl.SetStat.
-func (fd *nonDirectoryFD) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
+func (fd *regularFileFD) SetStat(ctx context.Context, opts vfs.SetStatOptions) error {
 	d := fd.dentry()
 	mode := linux.FileMode(atomic.LoadUint32(&d.mode))
 	if err := vfs.CheckSetStat(ctx, auth.CredentialsFromContext(ctx), &opts, mode, auth.KUID(atomic.LoadUint32(&d.uid)), auth.KGID(atomic.LoadUint32(&d.gid))); err != nil {
@@ -191,12 +213,61 @@ func (fd *nonDirectoryFD) SetStat(ctx context.Context, opts vfs.SetStatOptions)
 }
 
 // StatFS implements vfs.FileDescriptionImpl.StatFS.
-func (fd *nonDirectoryFD) StatFS(ctx context.Context) (linux.Statfs, error) {
+func (fd *regularFileFD) StatFS(ctx context.Context) (linux.Statfs, error) {
 	return fd.filesystem().statFS(ctx)
 }
 
+// Readiness implements waiter.Waitable.Readiness.
+func (fd *regularFileFD) Readiness(mask waiter.EventMask) waiter.EventMask {
+	ctx := context.Background()
+	wrappedFD, err := fd.getCurrentFD(ctx)
+	if err != nil {
+		// TODO(b/171089913): Just use fd.cachedFD since Readiness can't return
+		// an error. This is obviously wrong, but at least consistent with
+		// VFS1.
+		log.Warningf("overlay.regularFileFD.Readiness: currentFDLocked failed: %v", err)
+		fd.mu.Lock()
+		wrappedFD = fd.cachedFD
+		wrappedFD.IncRef()
+		fd.mu.Unlock()
+	}
+	defer wrappedFD.DecRef(ctx)
+	return wrappedFD.Readiness(mask)
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (fd *regularFileFD) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	fd.mu.Lock()
+	defer fd.mu.Unlock()
+	wrappedFD, err := fd.currentFDLocked(context.Background())
+	if err != nil {
+		// TODO(b/171089913): Just use fd.cachedFD since EventRegister can't
+		// return an error. This is obviously wrong, but at least consistent
+		// with VFS1.
+		log.Warningf("overlay.regularFileFD.EventRegister: currentFDLocked failed: %v", err)
+		wrappedFD = fd.cachedFD
+	}
+	wrappedFD.EventRegister(e, mask)
+	if !fd.copiedUp {
+		if fd.lowerWaiters == nil {
+			fd.lowerWaiters = make(map[*waiter.Entry]waiter.EventMask)
+		}
+		fd.lowerWaiters[e] = mask
+	}
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (fd *regularFileFD) EventUnregister(e *waiter.Entry) {
+	fd.mu.Lock()
+	defer fd.mu.Unlock()
+	fd.cachedFD.EventUnregister(e)
+	if !fd.copiedUp {
+		delete(fd.lowerWaiters, e)
+	}
+}
+
 // PRead implements vfs.FileDescriptionImpl.PRead.
-func (fd *nonDirectoryFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
 	wrappedFD, err := fd.getCurrentFD(ctx)
 	if err != nil {
 		return 0, err
@@ -206,7 +277,7 @@ func (fd *nonDirectoryFD) PRead(ctx context.Context, dst usermem.IOSequence, off
 }
 
 // Read implements vfs.FileDescriptionImpl.Read.
-func (fd *nonDirectoryFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+func (fd *regularFileFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
 	// Hold fd.mu during the read to serialize the file offset.
 	fd.mu.Lock()
 	defer fd.mu.Unlock()
@@ -218,7 +289,7 @@ func (fd *nonDirectoryFD) Read(ctx context.Context, dst usermem.IOSequence, opts
 }
 
 // PWrite implements vfs.FileDescriptionImpl.PWrite.
-func (fd *nonDirectoryFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
 	wrappedFD, err := fd.getCurrentFD(ctx)
 	if err != nil {
 		return 0, err
@@ -228,7 +299,7 @@ func (fd *nonDirectoryFD) PWrite(ctx context.Context, src usermem.IOSequence, of
 }
 
 // Write implements vfs.FileDescriptionImpl.Write.
-func (fd *nonDirectoryFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+func (fd *regularFileFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
 	// Hold fd.mu during the write to serialize the file offset.
 	fd.mu.Lock()
 	defer fd.mu.Unlock()
@@ -240,7 +311,7 @@ func (fd *nonDirectoryFD) Write(ctx context.Context, src usermem.IOSequence, opt
 }
 
 // Seek implements vfs.FileDescriptionImpl.Seek.
-func (fd *nonDirectoryFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+func (fd *regularFileFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
 	// Hold fd.mu during the seek to serialize the file offset.
 	fd.mu.Lock()
 	defer fd.mu.Unlock()
@@ -252,7 +323,7 @@ func (fd *nonDirectoryFD) Seek(ctx context.Context, offset int64, whence int32)
 }
 
 // Sync implements vfs.FileDescriptionImpl.Sync.
-func (fd *nonDirectoryFD) Sync(ctx context.Context) error {
+func (fd *regularFileFD) Sync(ctx context.Context) error {
 	fd.mu.Lock()
 	if !fd.dentry().isCopiedUp() {
 		fd.mu.Unlock()
@@ -269,8 +340,18 @@ func (fd *nonDirectoryFD) Sync(ctx context.Context) error {
 	return wrappedFD.Sync(ctx)
 }
 
+// Ioctl implements vfs.FileDescriptionImpl.Ioctl.
+func (fd *regularFileFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
+	wrappedFD, err := fd.getCurrentFD(ctx)
+	if err != nil {
+		return 0, err
+	}
+	defer wrappedFD.DecRef(ctx)
+	return wrappedFD.Ioctl(ctx, uio, args)
+}
+
 // ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
-func (fd *nonDirectoryFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+func (fd *regularFileFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
 	if err := fd.ensureMappable(ctx, opts); err != nil {
 		return err
 	}
@@ -278,7 +359,7 @@ func (fd *nonDirectoryFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOp
 }
 
 // ensureMappable ensures that fd.dentry().wrappedMappable is not nil.
-func (fd *nonDirectoryFD) ensureMappable(ctx context.Context, opts *memmap.MMapOpts) error {
+func (fd *regularFileFD) ensureMappable(ctx context.Context, opts *memmap.MMapOpts) error {
 	d := fd.dentry()
 
 	// Fast path if we already have a Mappable for the current top layer.