Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 404 insertions, 0 deletions

diff --git a/pkg/sentry/fs/file.go b/pkg/sentry/fs/file.go
new file mode 100644
index 000000000..de2e80bf0
--- /dev/null
+++ b/pkg/sentry/fs/file.go
@@ -0,0 +1,404 @@
+// Copyright 2018 Google Inc.
+//
+// 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 fs
+
+import (
+	"math"
+	"sync/atomic"
+
+	"gvisor.googlesource.com/gvisor/pkg/amutex"
+	"gvisor.googlesource.com/gvisor/pkg/log"
+	"gvisor.googlesource.com/gvisor/pkg/refs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/lock"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/limits"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/uniqueid"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+)
+
+// FileMaxOffset is the maximum possible file offset.
+const FileMaxOffset = math.MaxInt64
+
+// File is an open file handle. It is thread-safe.
+//
+// File provides stronger synchronization guarantees than Linux. Linux
+// synchronizes lseek(2), read(2), and write(2) with respect to the file
+// offset for regular files and only for those interfaces. See
+// fs/read_write.c:fdget_pos, fs.read_write.c:fdput_pos and FMODE_ATOMIC_POS.
+//
+// In contrast, File synchronizes any operation that could take a long time
+// under a single abortable mutex which also synchronizes lseek(2), read(2),
+// and write(2).
+//
+// FIXME: Split synchronization from cancellation.
+type File struct {
+	refs.AtomicRefCount
+
+	// UniqueID is the globally unique identifier of the File.
+	UniqueID uint64
+
+	// Dirent is the Dirent backing this File. This encodes the name
+	// of the File via Dirent.FullName() as well as its identity via the
+	// Dirent's Inode. The Dirent is non-nil.
+	//
+	// A File holds a reference to this Dirent. Using the returned Dirent is
+	// only safe as long as a reference on the File is held. The association
+	// between a File and a Dirent is immutable.
+	//
+	// Files that are not parented in a filesystem return a root Dirent
+	// that holds a reference to their Inode.
+	//
+	// The name of the Dirent may reflect parentage if the Dirent is not a
+	// root Dirent or the identity of the File on a pseudo filesystem (pipefs,
+	// sockfs, etc).
+	//
+	// Multiple Files may hold a reference to the same Dirent. This is the
+	// common case for Files that are parented and maintain consistency with
+	// other files via the Dirent cache.
+	Dirent *Dirent
+
+	// flags are the File's flags. Setting or getting flags is fully atomic
+	// and is not protected by mu (below).
+	flags atomic.Value `state:".(FileFlags)"`
+
+	// mu is dual-purpose: first, to make read(2) and write(2) thread-safe
+	// in conformity with POSIX, and second, to cancel operations before they
+	// begin in response to interruptions (i.e. signals).
+	mu amutex.AbortableMutex `state:"nosave"`
+
+	// FileOperations implements file system specific behavior for this File.
+	FileOperations FileOperations
+
+	// offset is the File's offset. Updating offset is protected by mu but
+	// can be read atomically via File.Offset() outside of mu.
+	offset int64
+}
+
+// NewFile returns a File. It takes a reference on the Dirent and owns the
+// lifetime of the FileOperations. Files that do not support reading and
+// writing at an arbitrary offset should set flags.Pread and flags.Pwrite
+// to false respectively.
+func NewFile(ctx context.Context, dirent *Dirent, flags FileFlags, fops FileOperations) *File {
+	dirent.IncRef()
+	f := &File{
+		UniqueID:       uniqueid.GlobalFromContext(ctx),
+		Dirent:         dirent,
+		FileOperations: fops,
+	}
+	f.flags.Store(flags)
+	f.mu.Init()
+	return f
+}
+
+// DecRef destroys the File when it is no longer referenced.
+func (f *File) DecRef() {
+	f.DecRefWithDestructor(func() {
+		// Drop BSD style locks.
+		lockRng := lock.LockRange{Start: 0, End: lock.LockEOF}
+		f.Dirent.Inode.LockCtx.BSD.UnlockRegion(lock.UniqueID(f.UniqueID), lockRng)
+
+		// Release resources held by the FileOperations.
+		f.FileOperations.Release()
+
+		// Release a reference on the Dirent.
+		f.Dirent.DecRef()
+	})
+}
+
+// Flags atomically loads the File's flags.
+func (f *File) Flags() FileFlags {
+	return f.flags.Load().(FileFlags)
+}
+
+// SetFlags atomically changes the File's flags to the values contained
+// in newFlags. See SettableFileFlags for values that can be set.
+func (f *File) SetFlags(newFlags SettableFileFlags) {
+	flags := f.flags.Load().(FileFlags)
+	flags.Direct = newFlags.Direct
+	flags.NonBlocking = newFlags.NonBlocking
+	flags.Append = newFlags.Append
+	f.flags.Store(flags)
+}
+
+// Offset atomically loads the File's offset.
+func (f *File) Offset() int64 {
+	return atomic.LoadInt64(&f.offset)
+}
+
+// Readiness implements waiter.Waitable.Readiness.
+func (f *File) Readiness(mask waiter.EventMask) waiter.EventMask {
+	return f.FileOperations.Readiness(mask)
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (f *File) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	f.FileOperations.EventRegister(e, mask)
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (f *File) EventUnregister(e *waiter.Entry) {
+	f.FileOperations.EventUnregister(e)
+}
+
+// Seek calls f.FileOperations.Seek with f as the File, updating the file
+// offset to the value returned by f.FileOperations.Seek if the operation
+// is successful.
+//
+// Returns syserror.ErrInterrupted if seeking was interrupted.
+func (f *File) Seek(ctx context.Context, whence SeekWhence, offset int64) (int64, error) {
+	if !f.mu.Lock(ctx) {
+		return 0, syserror.ErrInterrupted
+	}
+	defer f.mu.Unlock()
+
+	newOffset, err := f.FileOperations.Seek(ctx, f, whence, offset)
+	if err == nil {
+		atomic.StoreInt64(&f.offset, newOffset)
+	}
+	return newOffset, err
+}
+
+// Readdir reads the directory entries of this File and writes them out
+// to the DentrySerializer until entries can no longer be written. If even
+// a single directory entry is written then Readdir returns a nil error
+// and the directory offset is advanced.
+//
+// Readdir unconditionally updates the access time on the File's Inode,
+// see fs/readdir.c:iterate_dir.
+//
+// Returns syserror.ErrInterrupted if reading was interrupted.
+func (f *File) Readdir(ctx context.Context, serializer DentrySerializer) error {
+	if !f.mu.Lock(ctx) {
+		return syserror.ErrInterrupted
+	}
+	defer f.mu.Unlock()
+
+	offset, err := f.FileOperations.Readdir(ctx, f, serializer)
+	atomic.StoreInt64(&f.offset, offset)
+	return err
+}
+
+// Readv calls f.FileOperations.Read with f as the File, advancing the file
+// offset if f.FileOperations.Read returns bytes read > 0.
+//
+// Returns syserror.ErrInterrupted if reading was interrupted.
+func (f *File) Readv(ctx context.Context, dst usermem.IOSequence) (int64, error) {
+	if !f.mu.Lock(ctx) {
+		return 0, syserror.ErrInterrupted
+	}
+
+	n, err := f.FileOperations.Read(ctx, f, dst, f.offset)
+	if n > 0 {
+		atomic.AddInt64(&f.offset, n)
+	}
+	f.mu.Unlock()
+	return n, err
+}
+
+// Preadv calls f.FileOperations.Read with f as the File. It does not
+// advance the file offset. If !f.Flags().Pread, Preadv should not be
+// called.
+//
+// Otherwise same as Readv.
+func (f *File) Preadv(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+	if !f.mu.Lock(ctx) {
+		return 0, syserror.ErrInterrupted
+	}
+
+	n, err := f.FileOperations.Read(ctx, f, dst, offset)
+	f.mu.Unlock()
+	return n, err
+}
+
+// Writev calls f.FileOperations.Write with f as the File, advancing the
+// file offset if f.FileOperations.Write returns bytes written > 0.
+//
+// Writev positions the write offset at EOF if f.Flags().Append. This is
+// unavoidably racy for network file systems. Writev also truncates src
+// to avoid overrunning the current file size limit if necessary.
+//
+// Returns syserror.ErrInterrupted if writing was interrupted.
+func (f *File) Writev(ctx context.Context, src usermem.IOSequence) (int64, error) {
+	if !f.mu.Lock(ctx) {
+		return 0, syserror.ErrInterrupted
+	}
+
+	offset, err := f.checkWriteLocked(ctx, &src, f.offset)
+	if err != nil {
+		f.mu.Unlock()
+		return 0, err
+	}
+	n, err := f.FileOperations.Write(ctx, f, src, offset)
+	if n >= 0 {
+		atomic.StoreInt64(&f.offset, offset+n)
+	}
+	f.mu.Unlock()
+	return n, err
+}
+
+// Pwritev calls f.FileOperations.Write with f as the File. It does not
+// advance the file offset. If !f.Flags().Pwritev, Pwritev should not be
+// called.
+//
+// Otherwise same as Writev.
+func (f *File) Pwritev(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	if !f.mu.Lock(ctx) {
+		return 0, syserror.ErrInterrupted
+	}
+
+	offset, err := f.checkWriteLocked(ctx, &src, offset)
+	if err != nil {
+		f.mu.Unlock()
+		return 0, err
+	}
+	n, err := f.FileOperations.Write(ctx, f, src, offset)
+	f.mu.Unlock()
+	return n, err
+}
+
+// checkWriteLocked returns the offset to write at or an error if the write
+// would not succeed. May update src to fit a write operation into a file
+// size limit.
+func (f *File) checkWriteLocked(ctx context.Context, src *usermem.IOSequence, offset int64) (int64, error) {
+	// Handle append only files. Note that this is still racy for network
+	// filesystems.
+	if f.Flags().Append {
+		uattr, err := f.Dirent.Inode.UnstableAttr(ctx)
+		if err != nil {
+			// This is an odd error, most likely it is evidence
+			// that something is terribly wrong with the filesystem.
+			// Return a generic EIO error.
+			log.Warningf("Failed to check write of inode %#v: %v", f.Dirent.Inode.StableAttr, err)
+			return offset, syserror.EIO
+		}
+		offset = uattr.Size
+	}
+
+	// Is this a regular file?
+	if IsRegular(f.Dirent.Inode.StableAttr) {
+		// Enforce size limits.
+		fileSizeLimit := limits.FromContext(ctx).Get(limits.FileSize).Cur
+		if fileSizeLimit <= math.MaxInt64 {
+			if offset >= int64(fileSizeLimit) {
+				return offset, syserror.ErrExceedsFileSizeLimit
+			}
+			*src = src.TakeFirst64(int64(fileSizeLimit) - offset)
+		}
+	}
+
+	return offset, nil
+}
+
+// Fsync calls f.FileOperations.Fsync with f as the File.
+//
+// Returns syserror.ErrInterrupted if syncing was interrupted.
+func (f *File) Fsync(ctx context.Context, start int64, end int64, syncType SyncType) error {
+	if !f.mu.Lock(ctx) {
+		return syserror.ErrInterrupted
+	}
+	defer f.mu.Unlock()
+
+	return f.FileOperations.Fsync(ctx, f, start, end, syncType)
+}
+
+// Flush calls f.FileOperations.Flush with f as the File.
+//
+// Returns syserror.ErrInterrupted if syncing was interrupted.
+func (f *File) Flush(ctx context.Context) error {
+	if !f.mu.Lock(ctx) {
+		return syserror.ErrInterrupted
+	}
+	defer f.mu.Unlock()
+
+	return f.FileOperations.Flush(ctx, f)
+}
+
+// ConfigureMMap calls f.FileOperations.ConfigureMMap with f as the File.
+//
+// Returns syserror.ErrInterrupted if interrupted.
+func (f *File) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	if !f.mu.Lock(ctx) {
+		return syserror.ErrInterrupted
+	}
+	defer f.mu.Unlock()
+
+	return f.FileOperations.ConfigureMMap(ctx, f, opts)
+}
+
+// MappedName implements memmap.MappingIdentity.MappedName.
+func (f *File) MappedName(ctx context.Context) string {
+	name, _ := f.Dirent.FullName(RootFromContext(ctx))
+	return name
+}
+
+// DeviceID implements memmap.MappingIdentity.DeviceID.
+func (f *File) DeviceID() uint64 {
+	return f.Dirent.Inode.StableAttr.DeviceID
+}
+
+// InodeID implements memmap.MappingIdentity.InodeID.
+func (f *File) InodeID() uint64 {
+	return f.Dirent.Inode.StableAttr.InodeID
+}
+
+// Msync implements memmap.MappingIdentity.Msync.
+func (f *File) Msync(ctx context.Context, mr memmap.MappableRange) error {
+	return f.Fsync(ctx, int64(mr.Start), int64(mr.End-1), SyncData)
+}
+
+// FileReader implements io.Reader and io.ReaderAt.
+type FileReader struct {
+	// Ctx is the context for the file reader.
+	Ctx context.Context
+
+	// File is the file to read from.
+	File *File
+}
+
+// Read implements io.Reader.Read.
+func (r *FileReader) Read(buf []byte) (int, error) {
+	n, err := r.File.Readv(r.Ctx, usermem.BytesIOSequence(buf))
+	return int(n), err
+}
+
+// ReadAt implementes io.Reader.ReadAt.
+func (r *FileReader) ReadAt(buf []byte, offset int64) (int, error) {
+	n, err := r.File.Preadv(r.Ctx, usermem.BytesIOSequence(buf), offset)
+	return int(n), err
+}
+
+// FileWriter implements io.Writer and io.WriterAt.
+type FileWriter struct {
+	// Ctx is the context for the file writer.
+	Ctx context.Context
+
+	// File is the file to write to.
+	File *File
+}
+
+// Write implements io.Writer.Write.
+func (w *FileWriter) Write(buf []byte) (int, error) {
+	n, err := w.File.Writev(w.Ctx, usermem.BytesIOSequence(buf))
+	return int(n), err
+}
+
+// WriteAt implements io.Writer.WriteAt.
+func (w *FileWriter) WriteAt(buf []byte, offset int64) (int, error) {
+	n, err := w.File.Pwritev(w.Ctx, usermem.BytesIOSequence(buf), offset)
+	return int(n), err
+}