Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 398 insertions, 0 deletions

diff --git a/pkg/sentry/fs/tty/dir.go b/pkg/sentry/fs/tty/dir.go
new file mode 100644
index 000000000..2c5b2aed6
--- /dev/null
+++ b/pkg/sentry/fs/tty/dir.go
@@ -0,0 +1,398 @@
+// 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 tty provide pseudoterminals via a devpts filesystem.
+package tty
+
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"sync"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/unix"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+)
+
+// dirInodeOperations is the root of a devpts mount.
+//
+// This indirectly manages all terminals within the mount.
+//
+// New Terminals are created by masterInodeOperations.GetFile, which registers
+// the slave Inode in the this directory for discovery via Lookup/Readdir. The
+// slave inode is unregistered when the master file is Released, as the slave
+// is no longer discoverable at that point.
+//
+// References on the underlying Terminal are held by masterFileOperations and
+// slaveInodeOperations.
+//
+// masterInodeOperations and slaveInodeOperations hold a pointer to
+// dirInodeOperations, which is reference counted by the refcount their
+// corresponding Dirents hold on their parent (this directory).
+//
+// dirInodeOperations implements fs.InodeOperations.
+type dirInodeOperations struct {
+	fsutil.DeprecatedFileOperations
+	fsutil.InodeNotSocket
+	fsutil.InodeNotRenameable
+	fsutil.InodeNotSymlink
+	fsutil.InodeNoExtendedAttributes
+	fsutil.NoMappable
+	fsutil.NoopWriteOut
+
+	// msrc is the super block this directory is on.
+	//
+	// TODO: Plumb this through instead of storing it here.
+	msrc *fs.MountSource
+
+	// mu protects the fields below.
+	mu sync.Mutex `state:"nosave"`
+
+	// attr contains the UnstableAttrs.
+	attr fsutil.InMemoryAttributes
+
+	// master is the master PTY inode.
+	master *fs.Inode
+
+	// slaves contains the slave inodes reachable from the directory.
+	//
+	// A new slave is added by allocateTerminal and is removed by
+	// masterFileOperations.Release.
+	//
+	// A reference is held on every slave in the map.
+	slaves map[uint32]*fs.Inode
+
+	// dentryMap is a SortedDentryMap used to implement Readdir containing
+	// the master and all entries in slaves.
+	dentryMap *fs.SortedDentryMap
+
+	// next is the next pty index to use.
+	//
+	// TODO: reuse indices when ptys are closed.
+	next uint32
+}
+
+var _ fs.InodeOperations = (*dirInodeOperations)(nil)
+
+// newDir creates a new dir with a ptmx file and no terminals.
+func newDir(ctx context.Context, m *fs.MountSource) *fs.Inode {
+	d := &dirInodeOperations{
+		attr: fsutil.InMemoryAttributes{
+			Unstable: fs.WithCurrentTime(ctx, fs.UnstableAttr{
+				Owner: fs.RootOwner,
+				Perms: fs.FilePermsFromMode(0555),
+			}),
+		},
+		msrc:      m,
+		slaves:    make(map[uint32]*fs.Inode),
+		dentryMap: fs.NewSortedDentryMap(nil),
+	}
+	// Linux devpts uses a default mode of 0000 for ptmx which can be
+	// changed with the ptmxmode mount option. However, that default is not
+	// useful here (since we'd *always* need the mount option, so it is
+	// accessible by default).
+	d.master = newMasterInode(ctx, d, fs.RootOwner, fs.FilePermsFromMode(0666))
+	d.dentryMap.Add("ptmx", fs.DentAttr{
+		Type:    d.master.StableAttr.Type,
+		InodeID: d.master.StableAttr.InodeID,
+	})
+
+	return fs.NewInode(d, m, fs.StableAttr{
+		DeviceID: ptsDevice.DeviceID(),
+		// N.B. Linux always uses inode id 1 for the directory. See
+		// fs/devpts/inode.c:devpts_fill_super.
+		//
+		// TODO: Since ptsDevice must be shared between
+		// different mounts, we must not assign fixed numbers.
+		InodeID:   ptsDevice.NextIno(),
+		BlockSize: usermem.PageSize,
+		Type:      fs.Directory,
+	})
+}
+
+// Release implements fs.InodeOperations.Release.
+func (d *dirInodeOperations) Release(ctx context.Context) {
+	d.master.DecRef()
+	if len(d.slaves) != 0 {
+		panic(fmt.Sprintf("devpts directory still contains active terminals: %+v", d))
+	}
+}
+
+// Lookup implements fs.InodeOperations.Lookup.
+func (d *dirInodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string) (*fs.Dirent, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	// Master?
+	if name == "ptmx" {
+		d.master.IncRef()
+		return fs.NewDirent(d.master, name), nil
+	}
+
+	// Slave number?
+	n, err := strconv.ParseUint(name, 10, 32)
+	if err != nil {
+		// Not found.
+		return nil, syserror.ENOENT
+	}
+
+	s, ok := d.slaves[uint32(n)]
+	if !ok {
+		return nil, syserror.ENOENT
+	}
+
+	s.IncRef()
+	return fs.NewDirent(s, name), nil
+}
+
+// Create implements fs.InodeOperations.Create.
+//
+// Creation is never allowed.
+func (d *dirInodeOperations) Create(ctx context.Context, dir *fs.Inode, name string, flags fs.FileFlags, perm fs.FilePermissions) (*fs.File, error) {
+	return nil, syserror.EACCES
+}
+
+// CreateDirectory implements fs.InodeOperations.CreateDirectory.
+//
+// Creation is never allowed.
+func (d *dirInodeOperations) CreateDirectory(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions) error {
+	return syserror.EACCES
+}
+
+// CreateLink implements fs.InodeOperations.CreateLink.
+//
+// Creation is never allowed.
+func (d *dirInodeOperations) CreateLink(ctx context.Context, dir *fs.Inode, oldname, newname string) error {
+	return syserror.EACCES
+}
+
+// CreateHardLink implements fs.InodeOperations.CreateHardLink.
+//
+// Creation is never allowed.
+func (d *dirInodeOperations) CreateHardLink(ctx context.Context, dir *fs.Inode, target *fs.Inode, name string) error {
+	return syserror.EACCES
+}
+
+// CreateFifo implements fs.InodeOperations.CreateFifo.
+//
+// Creation is never allowed.
+func (d *dirInodeOperations) CreateFifo(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions) error {
+	return syserror.EACCES
+}
+
+// Remove implements fs.InodeOperations.Remove.
+//
+// Removal is never allowed.
+func (d *dirInodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string) error {
+	return syserror.EPERM
+}
+
+// RemoveDirectory implements fs.InodeOperations.RemoveDirectory.
+//
+// Removal is never allowed.
+func (d *dirInodeOperations) RemoveDirectory(ctx context.Context, dir *fs.Inode, name string) error {
+	return syserror.EPERM
+}
+
+// Bind implements fs.InodeOperations.Bind.
+func (d *dirInodeOperations) Bind(ctx context.Context, dir *fs.Inode, name string, data unix.BoundEndpoint, perm fs.FilePermissions) error {
+	return syserror.EPERM
+}
+
+// GetFile implements fs.InodeOperations.GetFile.
+func (d *dirInodeOperations) GetFile(ctx context.Context, dirent *fs.Dirent, flags fs.FileFlags) (*fs.File, error) {
+	return fs.NewFile(ctx, dirent, flags, &dirFileOperations{di: d}), nil
+}
+
+// UnstableAttr implements fs.InodeOperations.UnstableAttr.
+func (d *dirInodeOperations) UnstableAttr(ctx context.Context, inode *fs.Inode) (fs.UnstableAttr, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.attr.Unstable, nil
+}
+
+// Check implements fs.InodeOperations.Check.
+func (d *dirInodeOperations) Check(ctx context.Context, inode *fs.Inode, p fs.PermMask) bool {
+	return fs.ContextCanAccessFile(ctx, inode, p)
+}
+
+// SetPermissions implements fs.InodeOperations.SetPermissions.
+func (d *dirInodeOperations) SetPermissions(ctx context.Context, inode *fs.Inode, p fs.FilePermissions) bool {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.attr.SetPermissions(ctx, p)
+}
+
+// SetOwner implements fs.InodeOperations.SetOwner.
+func (d *dirInodeOperations) SetOwner(ctx context.Context, inode *fs.Inode, owner fs.FileOwner) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.attr.SetOwner(ctx, owner)
+}
+
+// SetTimestamps implements fs.InodeOperations.SetTimestamps.
+func (d *dirInodeOperations) SetTimestamps(ctx context.Context, inode *fs.Inode, ts fs.TimeSpec) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.attr.SetTimestamps(ctx, ts)
+}
+
+// Truncate implements fs.InodeOperations.Truncate.
+func (d *dirInodeOperations) Truncate(ctx context.Context, inode *fs.Inode, size int64) error {
+	return syserror.EINVAL
+}
+
+// AddLink implements fs.InodeOperations.AddLink.
+func (d *dirInodeOperations) AddLink() {}
+
+// DropLink implements fs.InodeOperations.DropLink.
+func (d *dirInodeOperations) DropLink() {}
+
+// NotifyStatusChange implements fs.InodeOperations.NotifyStatusChange.
+func (d *dirInodeOperations) NotifyStatusChange(ctx context.Context) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	d.attr.TouchStatusChangeTime(ctx)
+}
+
+// IsVirtual implements fs.InodeOperations.IsVirtual.
+func (d *dirInodeOperations) IsVirtual() bool {
+	return true
+}
+
+// StatFS implements fs.InodeOperations.StatFS.
+func (d *dirInodeOperations) StatFS(ctx context.Context) (fs.Info, error) {
+	return fs.Info{
+		Type: linux.DEVPTS_SUPER_MAGIC,
+	}, nil
+}
+
+// allocateTerminal creates a new Terminal and installs a pts node for it.
+//
+// The caller must call DecRef when done with the returned Terminal.
+func (d *dirInodeOperations) allocateTerminal(ctx context.Context) (*Terminal, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	n := d.next
+	if n == math.MaxUint32 {
+		return nil, syserror.ENOMEM
+	}
+
+	if _, ok := d.slaves[n]; ok {
+		panic(fmt.Sprintf("pty index collision; index %d already exists", n))
+	}
+
+	t := newTerminal(ctx, d, n)
+	d.next++
+
+	// The reference returned by newTerminal is returned to the caller.
+	// Take another for the slave inode.
+	t.IncRef()
+
+	// Create a pts node. The owner is based on the context that opens
+	// ptmx.
+	creds := auth.CredentialsFromContext(ctx)
+	uid, gid := creds.EffectiveKUID, creds.EffectiveKGID
+	slave := newSlaveInode(ctx, d, t, fs.FileOwner{uid, gid}, fs.FilePermsFromMode(0666))
+
+	d.slaves[n] = slave
+	d.dentryMap.Add(strconv.FormatUint(uint64(n), 10), fs.DentAttr{
+		Type:    slave.StableAttr.Type,
+		InodeID: slave.StableAttr.InodeID,
+	})
+
+	return t, nil
+}
+
+// masterClose is called when the master end of t is closed.
+func (d *dirInodeOperations) masterClose(t *Terminal) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	// The slave end disappears from the directory when the master end is
+	// closed, even if the slave end is open elsewhere.
+	//
+	// N.B. since we're using a backdoor method to remove a directory entry
+	// we won't properly fire inotify events like Linux would.
+	s, ok := d.slaves[t.n]
+	if !ok {
+		panic(fmt.Sprintf("Terminal %+v doesn't exist in %+v?", t, d))
+	}
+
+	s.DecRef()
+	delete(d.slaves, t.n)
+	d.dentryMap.Remove(strconv.FormatUint(uint64(t.n), 10))
+}
+
+// dirFileOperations are the fs.FileOperations for the directory.
+//
+// This is nearly identical to fsutil.DirFileOperations, except that it takes
+// df.di.mu in IterateDir.
+type dirFileOperations struct {
+	waiter.AlwaysReady `state:"nosave"`
+	fsutil.NoopRelease `state:"nosave"`
+	fsutil.GenericSeek `state:"nosave"`
+	fsutil.NoFsync     `state:"nosave"`
+	fsutil.NoopFlush   `state:"nosave"`
+	fsutil.NoMMap      `state:"nosave"`
+	fsutil.NoIoctl     `state:"nosave"`
+
+	// di is the inode operations.
+	di *dirInodeOperations
+
+	// dirCursor contains the name of the last directory entry that was
+	// serialized.
+	dirCursor string
+}
+
+var _ fs.FileOperations = (*dirFileOperations)(nil)
+
+// IterateDir implements DirIterator.IterateDir.
+func (df *dirFileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+	df.di.mu.Lock()
+	defer df.di.mu.Unlock()
+
+	n, err := fs.GenericReaddir(dirCtx, df.di.dentryMap)
+	return offset + n, err
+}
+
+// Readdir implements FileOperations.Readdir.
+func (df *dirFileOperations) Readdir(ctx context.Context, file *fs.File, serializer fs.DentrySerializer) (int64, error) {
+	root := fs.RootFromContext(ctx)
+	defer root.DecRef()
+	dirCtx := &fs.DirCtx{
+		Serializer: serializer,
+		DirCursor:  &df.dirCursor,
+	}
+	return fs.DirentReaddir(ctx, file.Dirent, df, root, dirCtx, file.Offset())
+}
+
+// Read implements FileOperations.Read
+func (df *dirFileOperations) Read(context.Context, *fs.File, usermem.IOSequence, int64) (int64, error) {
+	return 0, syserror.EISDIR
+}
+
+// Write implements FileOperations.Write.
+func (df *dirFileOperations) Write(context.Context, *fs.File, usermem.IOSequence, int64) (int64, error) {
+	return 0, syserror.EISDIR
+}