Implement an anon_inode equivalent for VFS2.

PiperOrigin-RevId: 291986033

1 files changed, 259 insertions, 0 deletions

diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
new file mode 100644
index 000000000..2db25be49
--- /dev/null
+++ b/pkg/sentry/vfs/anonfs.go
@@ -0,0 +1,259 @@
+// Copyright 2020 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 vfs
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/fspath"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// NewAnonVirtualDentry returns a VirtualDentry with the given synthetic name,
+// consistent with Linux's fs/anon_inodes.c:anon_inode_getfile(). References
+// are taken on the returned VirtualDentry.
+func (vfs *VirtualFilesystem) NewAnonVirtualDentry(name string) VirtualDentry {
+	d := anonDentry{
+		name: name,
+	}
+	d.vfsd.Init(&d)
+	vfs.anonMount.IncRef()
+	// anonDentry no-ops refcounting.
+	return VirtualDentry{
+		mount:  vfs.anonMount,
+		dentry: &d.vfsd,
+	}
+}
+
+const anonfsBlockSize = usermem.PageSize // via fs/libfs.c:pseudo_fs_fill_super()
+
+// anonFilesystem is the implementation of FilesystemImpl that backs
+// VirtualDentries returned by VirtualFilesystem.NewAnonVirtualDentry().
+//
+// Since all Dentries in anonFilesystem are non-directories, all FilesystemImpl
+// methods that would require an anonDentry to be a directory return ENOTDIR.
+type anonFilesystem struct {
+	vfsfs Filesystem
+
+	devMinor uint32
+}
+
+type anonDentry struct {
+	vfsd Dentry
+
+	name string
+}
+
+// Release implements FilesystemImpl.Release.
+func (fs *anonFilesystem) Release() {
+}
+
+// Sync implements FilesystemImpl.Sync.
+func (fs *anonFilesystem) Sync(ctx context.Context) error {
+	return nil
+}
+
+// GetDentryAt implements FilesystemImpl.GetDentryAt.
+func (fs *anonFilesystem) GetDentryAt(ctx context.Context, rp *ResolvingPath, opts GetDentryOptions) (*Dentry, error) {
+	if !rp.Done() {
+		return nil, syserror.ENOTDIR
+	}
+	if opts.CheckSearchable {
+		return nil, syserror.ENOTDIR
+	}
+	// anonDentry no-ops refcounting.
+	return rp.Start(), nil
+}
+
+// GetParentDentryAt implements FilesystemImpl.GetParentDentryAt.
+func (fs *anonFilesystem) GetParentDentryAt(ctx context.Context, rp *ResolvingPath) (*Dentry, error) {
+	if !rp.Final() {
+		return nil, syserror.ENOTDIR
+	}
+	// anonDentry no-ops refcounting.
+	return rp.Start(), nil
+}
+
+// LinkAt implements FilesystemImpl.LinkAt.
+func (fs *anonFilesystem) LinkAt(ctx context.Context, rp *ResolvingPath, vd VirtualDentry) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// MkdirAt implements FilesystemImpl.MkdirAt.
+func (fs *anonFilesystem) MkdirAt(ctx context.Context, rp *ResolvingPath, opts MkdirOptions) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// MknodAt implements FilesystemImpl.MknodAt.
+func (fs *anonFilesystem) MknodAt(ctx context.Context, rp *ResolvingPath, opts MknodOptions) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// OpenAt implements FilesystemImpl.OpenAt.
+func (fs *anonFilesystem) OpenAt(ctx context.Context, rp *ResolvingPath, opts OpenOptions) (*FileDescription, error) {
+	if !rp.Done() {
+		return nil, syserror.ENOTDIR
+	}
+	return nil, syserror.ENODEV
+}
+
+// ReadlinkAt implements FilesystemImpl.ReadlinkAt.
+func (fs *anonFilesystem) ReadlinkAt(ctx context.Context, rp *ResolvingPath) (string, error) {
+	if !rp.Done() {
+		return "", syserror.ENOTDIR
+	}
+	return "", syserror.EINVAL
+}
+
+// RenameAt implements FilesystemImpl.RenameAt.
+func (fs *anonFilesystem) RenameAt(ctx context.Context, rp *ResolvingPath, oldParentVD VirtualDentry, oldName string, opts RenameOptions) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// RmdirAt implements FilesystemImpl.RmdirAt.
+func (fs *anonFilesystem) RmdirAt(ctx context.Context, rp *ResolvingPath) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// SetStatAt implements FilesystemImpl.SetStatAt.
+func (fs *anonFilesystem) SetStatAt(ctx context.Context, rp *ResolvingPath, opts SetStatOptions) error {
+	if !rp.Done() {
+		return syserror.ENOTDIR
+	}
+	// Linux actually permits anon_inode_inode's metadata to be set, which is
+	// visible to all users of anon_inode_inode. We just silently ignore
+	// metadata changes.
+	return nil
+}
+
+// StatAt implements FilesystemImpl.StatAt.
+func (fs *anonFilesystem) StatAt(ctx context.Context, rp *ResolvingPath, opts StatOptions) (linux.Statx, error) {
+	if !rp.Done() {
+		return linux.Statx{}, syserror.ENOTDIR
+	}
+	// See fs/anon_inodes.c:anon_inode_init() => fs/libfs.c:alloc_anon_inode().
+	return linux.Statx{
+		Mask:     linux.STATX_TYPE | linux.STATX_MODE | linux.STATX_NLINK | linux.STATX_UID | linux.STATX_GID | linux.STATX_INO | linux.STATX_SIZE | linux.STATX_BLOCKS,
+		Blksize:  anonfsBlockSize,
+		Nlink:    1,
+		UID:      uint32(auth.RootKUID),
+		GID:      uint32(auth.RootKGID),
+		Mode:     0600, // no type is correct
+		Ino:      1,
+		Size:     0,
+		Blocks:   0,
+		DevMajor: 0,
+		DevMinor: fs.devMinor,
+	}, nil
+}
+
+// StatFSAt implements FilesystemImpl.StatFSAt.
+func (fs *anonFilesystem) StatFSAt(ctx context.Context, rp *ResolvingPath) (linux.Statfs, error) {
+	if !rp.Done() {
+		return linux.Statfs{}, syserror.ENOTDIR
+	}
+	return linux.Statfs{
+		Type:      linux.ANON_INODE_FS_MAGIC,
+		BlockSize: anonfsBlockSize,
+	}, nil
+}
+
+// SymlinkAt implements FilesystemImpl.SymlinkAt.
+func (fs *anonFilesystem) SymlinkAt(ctx context.Context, rp *ResolvingPath, target string) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// UnlinkAt implements FilesystemImpl.UnlinkAt.
+func (fs *anonFilesystem) UnlinkAt(ctx context.Context, rp *ResolvingPath) error {
+	if !rp.Final() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// ListxattrAt implements FilesystemImpl.ListxattrAt.
+func (fs *anonFilesystem) ListxattrAt(ctx context.Context, rp *ResolvingPath) ([]string, error) {
+	if !rp.Done() {
+		return nil, syserror.ENOTDIR
+	}
+	return nil, nil
+}
+
+// GetxattrAt implements FilesystemImpl.GetxattrAt.
+func (fs *anonFilesystem) GetxattrAt(ctx context.Context, rp *ResolvingPath, name string) (string, error) {
+	if !rp.Done() {
+		return "", syserror.ENOTDIR
+	}
+	return "", syserror.ENOTSUP
+}
+
+// SetxattrAt implements FilesystemImpl.SetxattrAt.
+func (fs *anonFilesystem) SetxattrAt(ctx context.Context, rp *ResolvingPath, opts SetxattrOptions) error {
+	if !rp.Done() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// RemovexattrAt implements FilesystemImpl.RemovexattrAt.
+func (fs *anonFilesystem) RemovexattrAt(ctx context.Context, rp *ResolvingPath, name string) error {
+	if !rp.Done() {
+		return syserror.ENOTDIR
+	}
+	return syserror.EPERM
+}
+
+// PrependPath implements FilesystemImpl.PrependPath.
+func (fs *anonFilesystem) PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error {
+	b.PrependComponent(fmt.Sprintf("anon_inode:%s", vd.dentry.impl.(*anonDentry).name))
+	return PrependPathSyntheticError{}
+}
+
+// IncRef implements DentryImpl.IncRef.
+func (d *anonDentry) IncRef() {
+	// no-op
+}
+
+// TryIncRef implements DentryImpl.TryIncRef.
+func (d *anonDentry) TryIncRef() bool {
+	return true
+}
+
+// DecRef implements DentryImpl.DecRef.
+func (d *anonDentry) DecRef() {
+	// no-op
+}