vfs: Don't allow to splice in all file descriptors

We want to avoid unneeded side effects, so let's specify what file descriptors
allow to splice data in. Linux does the same thing.

For example, Splicing a big amout of data to eventfd can be slow, because
eventfd can consume only 8 bytes at once.

Reported-by: syzbot+b9610cff22c10d9bead4@syzkaller.appspotmail.com

pkg/sentry/devices/memdev/full.go

@@ -47,6 +47,7 @@ type fullFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 }
 
 // Release implements vfs.FileDescriptionImpl.Release.

pkg/sentry/devices/memdev/null.go

@@ -48,6 +48,7 @@ type nullFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 }
 
 // Release implements vfs.FileDescriptionImpl.Release.

pkg/sentry/devices/memdev/random.go

@@ -53,6 +53,7 @@ type randomFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 
 	// off is the "file offset". off is accessed using atomic memory
 	// operations.

pkg/sentry/devices/memdev/zero.go

@@ -50,6 +50,7 @@ type zeroFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 }
 
 // Release implements vfs.FileDescriptionImpl.Release.

pkg/sentry/devices/tundev/tundev.go

@@ -60,6 +60,7 @@ type tunFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 
 	device tun.Device
 }

pkg/sentry/fsimpl/devpts/master.go

@@ -90,6 +90,7 @@ type masterFileDescription struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	inode *masterInode
 	t     *Terminal

pkg/sentry/fsimpl/devpts/replica.go

@@ -102,6 +102,7 @@ type replicaFileDescription struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	inode *replicaInode
 }

pkg/sentry/fsimpl/eventfd/eventfd.go

@@ -42,6 +42,7 @@ type EventFileDescription struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.NoSpliceInFD
 
 	// queue is used to notify interested parties when the event object
 	// becomes readable or writable.

pkg/sentry/fsimpl/fuse/dev.go

@@ -57,6 +57,7 @@ type DeviceFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 
 	// nextOpID is used to create new requests.
 	nextOpID linux.FUSEOpID

pkg/sentry/fsimpl/fuse/directory.go

@@ -28,6 +28,7 @@ import (
 
 type directoryFD struct {
 	fileDescription
+	vfs.NoSpliceInFD
 }
 
 // Allocate implements directoryFD.Allocate.

pkg/sentry/fsimpl/fuse/regular_file.go

@@ -29,6 +29,7 @@ import (
 
 type regularFileFD struct {
 	fileDescription
+	vfs.SpliceInFD
 
 	// off is the file offset.
 	off int64

pkg/sentry/fsimpl/gofer/gofer.go

@@ -2443,6 +2443,7 @@ type fileDescription struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.SpliceInFD
 
 	lockLogging sync.Once `state:"nosave"`
 }

pkg/sentry/fsimpl/gofer/regular_file.go

@@ -45,6 +45,7 @@ func (d *dentry) isRegularFile() bool {
 // +stateify savable
 type regularFileFD struct {
 	fileDescription
+	vfs.SpliceInFD
 
 	// off is the file offset. off is protected by mu.
 	mu  sync.Mutex `state:"nosave"`

pkg/sentry/fsimpl/host/host.go

@@ -649,6 +649,7 @@ type fileDescription struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.SpliceInFD
 
 	// inode is vfsfd.Dentry().Impl().(*kernfs.Dentry).Inode().(*inode), but
 	// cached to reduce indirections and casting. fileDescription does not hold

pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go

@@ -89,6 +89,7 @@ type DynamicBytesFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DynamicBytesFileDescriptionImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	vfsfd vfs.FileDescription
 	inode Inode

pkg/sentry/fsimpl/mqfs/queue.go

@@ -61,6 +61,7 @@ type queueFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DynamicBytesFileDescriptionImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	vfsfd vfs.FileDescription
 	inode kernfs.Inode

pkg/sentry/fsimpl/overlay/regular_file.go

@@ -50,6 +50,7 @@ func (d *dentry) readlink(ctx context.Context) (string, error) {
 // +stateify savable
 type regularFileFD struct {
 	fileDescription
+	vfs.SpliceInFD
 
 	// If copiedUp is false, cachedFD represents
 	// fileDescription.dentry().lowerVDs[0]; otherwise, cachedFD represents

pkg/sentry/fsimpl/proc/task_files.go

@@ -434,6 +434,7 @@ type memFD struct {
 	vfsfd vfs.FileDescription
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.SpliceInFD
 
 	inode *memInode
 
@@ -678,6 +679,7 @@ type statusFD struct {
 	statusFDLowerBase
 	vfs.DynamicBytesFileDescriptionImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	vfsfd vfs.FileDescription
 
@@ -1173,6 +1175,7 @@ func (i *namespaceInode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *ker
 type namespaceFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.LockFD
+	vfs.NoSpliceInFD
 
 	vfsfd vfs.FileDescription
 	inode *namespaceInode

pkg/sentry/fsimpl/signalfd/signalfd.go

@@ -34,6 +34,7 @@ type SignalFileDescription struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.DentryMetadataFileDescriptionImpl
 	vfs.NoLockFD
+	vfs.NoSpliceInFD
 
 	// target is the original signal target task.
 	//

pkg/sentry/fsimpl/sys/kcov.go

@@ -67,6 +67,7 @@ func (i *kcovInode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.D
 type kcovFD struct {
 	vfs.FileDescriptionDefaultImpl
 	vfs.NoLockFD
+	vfs.SpliceInFD
 
 	vfsfd vfs.FileDescription
 	inode *kcovInode