visor/pkg/sentry/fsimpl/kernfs/synthetic_directory.go

// Copyright 2019 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 kernfs

import (
	"fmt"

	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/context"
	"gvisor.dev/gvisor/pkg/errors/linuxerr"
	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
	"gvisor.dev/gvisor/pkg/sentry/vfs"
)

// syntheticDirectory implements kernfs.Inode for a directory created by
// MkdirAt(ForSyntheticMountpoint=true).
//
// +stateify savable
type syntheticDirectory struct {
	InodeAlwaysValid
	InodeAttrs
	InodeNoStatFS
	InodeNotAnonymous
	InodeNotSymlink
	InodeWatches
	OrderedChildren
	syntheticDirectoryRefs
	InodeFSOwned

	locks vfs.FileLocks
}

var _ Inode = (*syntheticDirectory)(nil)

func newSyntheticDirectory(ctx context.Context, creds *auth.Credentials, perm linux.FileMode) Inode {
	if perm&^linux.PermissionsMask != 0 {
		panic(fmt.Sprintf("perm contains non-permission bits: %#o", perm))
	}
	dir := &syntheticDirectory{}
	dir.InitRefs()
	dir.InodeAttrs.Init(ctx, creds, 0 /* devMajor */, 0 /* devMinor */, 0 /* ino */, linux.S_IFDIR|perm)
	dir.OrderedChildren.Init(OrderedChildrenOptions{
		Writable: true,
	})
	return dir
}

// Open implements Inode.Open.
func (dir *syntheticDirectory) Open(ctx context.Context, rp *vfs.ResolvingPath, d *Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
	fd, err := NewGenericDirectoryFD(rp.Mount(), d, rp.Credentials(), &dir.OrderedChildren, &dir.locks, &opts, GenericDirectoryFDOptions{})
	if err != nil {
		return nil, err
	}
	return &fd.vfsfd, nil
}

// NewFile implements Inode.NewFile.
func (dir *syntheticDirectory) NewFile(ctx context.Context, name string, opts vfs.OpenOptions) (Inode, error) {
	return nil, linuxerr.EPERM
}

// NewDir implements Inode.NewDir.
func (dir *syntheticDirectory) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (Inode, error) {
	if !opts.ForSyntheticMountpoint {
		return nil, linuxerr.EPERM
	}
	subdirI := newSyntheticDirectory(ctx, auth.CredentialsFromContext(ctx), opts.Mode&linux.PermissionsMask)
	if err := dir.OrderedChildren.Insert(name, subdirI); err != nil {
		subdirI.DecRef(ctx)
		return nil, err
	}
	dir.TouchCMtime(ctx)
	return subdirI, nil
}

// NewLink implements Inode.NewLink.
func (dir *syntheticDirectory) NewLink(ctx context.Context, name string, target Inode) (Inode, error) {
	return nil, linuxerr.EPERM
}

// NewSymlink implements Inode.NewSymlink.
func (dir *syntheticDirectory) NewSymlink(ctx context.Context, name, target string) (Inode, error) {
	return nil, linuxerr.EPERM
}

// NewNode implements Inode.NewNode.
func (dir *syntheticDirectory) NewNode(ctx context.Context, name string, opts vfs.MknodOptions) (Inode, error) {
	return nil, linuxerr.EPERM
}

// DecRef implements Inode.DecRef.
func (dir *syntheticDirectory) DecRef(ctx context.Context) {
	dir.syntheticDirectoryRefs.DecRef(func() { dir.Destroy(ctx) })
}

// Keep implements Inode.Keep. This is redundant because inodes will never be
// created via Lookup and inodes are always valid. Makes sense to return true
// because these inodes are not temporary and should only be removed on RmDir.
func (dir *syntheticDirectory) Keep() bool {
	return true
}