Implement an anon_inode equivalent for VFS2.

PiperOrigin-RevId: 291986033

5 files changed, 289 insertions, 188 deletions

diff --git a/pkg/sentry/vfs/BUILD b/pkg/sentry/vfs/BUILD
index 6b1009328..33516e6f7 100644
--- a/pkg/sentry/vfs/BUILD
+++ b/pkg/sentry/vfs/BUILD
@@ -5,6 +5,7 @@ licenses(["notice"])
 go_library(
     name = "vfs",
     srcs = [
+        "anonfs.go",
         "context.go",
         "debug.go",
         "dentry.go",
@@ -20,7 +21,6 @@ go_library(
         "pathname.go",
         "permissions.go",
         "resolving_path.go",
-        "testutil.go",
         "vfs.go",
     ],
     visibility = ["//pkg/sentry:internal"],
@@ -50,7 +50,6 @@ go_test(
         "//pkg/abi/linux",
         "//pkg/context",
         "//pkg/sentry/contexttest",
-        "//pkg/sentry/kernel/auth",
         "//pkg/sync",
         "//pkg/syserror",
         "//pkg/usermem",
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
+}
diff --git a/pkg/sentry/vfs/file_description_impl_util_test.go b/pkg/sentry/vfs/file_description_impl_util_test.go
index 1720d325d..0f44e7c8c 100644
--- a/pkg/sentry/vfs/file_description_impl_util_test.go
+++ b/pkg/sentry/vfs/file_description_impl_util_test.go
@@ -24,7 +24,6 @@ import (
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/contexttest"
-	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
@@ -46,9 +45,11 @@ type genCountFD struct {
 	count uint64 // accessed using atomic memory ops
 }
 
-func newGenCountFD(mnt *Mount, vfsd *Dentry) *FileDescription {
+func newGenCountFD(vfsObj *VirtualFilesystem) *FileDescription {
+	vd := vfsObj.NewAnonVirtualDentry("genCountFD")
+	defer vd.DecRef()
 	var fd genCountFD
-	fd.vfsfd.Init(&fd, 0 /* statusFlags */, mnt, vfsd, &FileDescriptionOptions{})
+	fd.vfsfd.Init(&fd, 0 /* statusFlags */, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{})
 	fd.DynamicBytesFileDescriptionImpl.SetDataSource(&fd)
 	return &fd.vfsfd
 }
@@ -86,18 +87,9 @@ func (fd *genCountFD) Generate(ctx context.Context, buf *bytes.Buffer) error {
 
 func TestGenCountFD(t *testing.T) {
 	ctx := contexttest.Context(t)
-	creds := auth.CredentialsFromContext(ctx)
 
 	vfsObj := New() // vfs.New()
-	vfsObj.MustRegisterFilesystemType("testfs", FDTestFilesystemType{}, &RegisterFilesystemTypeOptions{})
-	mntns, err := vfsObj.NewMountNamespace(ctx, creds, "", "testfs", &GetFilesystemOptions{})
-	if err != nil {
-		t.Fatalf("failed to create testfs root mount: %v", err)
-	}
-	vd := mntns.Root()
-	defer vd.DecRef()
-
-	fd := newGenCountFD(vd.Mount(), vd.Dentry())
+	fd := newGenCountFD(vfsObj)
 	defer fd.DecRef()
 
 	// The first read causes Generate to be called to fill the FD's buffer.
diff --git a/pkg/sentry/vfs/testutil.go b/pkg/sentry/vfs/testutil.go
deleted file mode 100644
index 392c7611e..000000000
--- a/pkg/sentry/vfs/testutil.go
+++ /dev/null
@@ -1,173 +0,0 @@
-// 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 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"
-)
-
-// FDTestFilesystemType is a test-only FilesystemType that produces Filesystems
-// for which all FilesystemImpl methods taking a path return EPERM. It is used
-// to produce Mounts and Dentries for testing of FileDescriptionImpls that do
-// not depend on their originating Filesystem.
-type FDTestFilesystemType struct{}
-
-// FDTestFilesystem is a test-only FilesystemImpl produced by
-// FDTestFilesystemType.
-type FDTestFilesystem struct {
-	vfsfs Filesystem
-}
-
-// GetFilesystem implements FilesystemType.GetFilesystem.
-func (fstype FDTestFilesystemType) GetFilesystem(ctx context.Context, vfsObj *VirtualFilesystem, creds *auth.Credentials, source string, opts GetFilesystemOptions) (*Filesystem, *Dentry, error) {
-	var fs FDTestFilesystem
-	fs.vfsfs.Init(vfsObj, &fs)
-	return &fs.vfsfs, fs.NewDentry(), nil
-}
-
-// Release implements FilesystemImpl.Release.
-func (fs *FDTestFilesystem) Release() {
-}
-
-// Sync implements FilesystemImpl.Sync.
-func (fs *FDTestFilesystem) Sync(ctx context.Context) error {
-	return nil
-}
-
-// GetDentryAt implements FilesystemImpl.GetDentryAt.
-func (fs *FDTestFilesystem) GetDentryAt(ctx context.Context, rp *ResolvingPath, opts GetDentryOptions) (*Dentry, error) {
-	return nil, syserror.EPERM
-}
-
-// GetParentDentryAt implements FilesystemImpl.GetParentDentryAt.
-func (fs *FDTestFilesystem) GetParentDentryAt(ctx context.Context, rp *ResolvingPath) (*Dentry, error) {
-	return nil, syserror.EPERM
-}
-
-// LinkAt implements FilesystemImpl.LinkAt.
-func (fs *FDTestFilesystem) LinkAt(ctx context.Context, rp *ResolvingPath, vd VirtualDentry) error {
-	return syserror.EPERM
-}
-
-// MkdirAt implements FilesystemImpl.MkdirAt.
-func (fs *FDTestFilesystem) MkdirAt(ctx context.Context, rp *ResolvingPath, opts MkdirOptions) error {
-	return syserror.EPERM
-}
-
-// MknodAt implements FilesystemImpl.MknodAt.
-func (fs *FDTestFilesystem) MknodAt(ctx context.Context, rp *ResolvingPath, opts MknodOptions) error {
-	return syserror.EPERM
-}
-
-// OpenAt implements FilesystemImpl.OpenAt.
-func (fs *FDTestFilesystem) OpenAt(ctx context.Context, rp *ResolvingPath, opts OpenOptions) (*FileDescription, error) {
-	return nil, syserror.EPERM
-}
-
-// ReadlinkAt implements FilesystemImpl.ReadlinkAt.
-func (fs *FDTestFilesystem) ReadlinkAt(ctx context.Context, rp *ResolvingPath) (string, error) {
-	return "", syserror.EPERM
-}
-
-// RenameAt implements FilesystemImpl.RenameAt.
-func (fs *FDTestFilesystem) RenameAt(ctx context.Context, rp *ResolvingPath, oldParentVD VirtualDentry, oldName string, opts RenameOptions) error {
-	return syserror.EPERM
-}
-
-// RmdirAt implements FilesystemImpl.RmdirAt.
-func (fs *FDTestFilesystem) RmdirAt(ctx context.Context, rp *ResolvingPath) error {
-	return syserror.EPERM
-}
-
-// SetStatAt implements FilesystemImpl.SetStatAt.
-func (fs *FDTestFilesystem) SetStatAt(ctx context.Context, rp *ResolvingPath, opts SetStatOptions) error {
-	return syserror.EPERM
-}
-
-// StatAt implements FilesystemImpl.StatAt.
-func (fs *FDTestFilesystem) StatAt(ctx context.Context, rp *ResolvingPath, opts StatOptions) (linux.Statx, error) {
-	return linux.Statx{}, syserror.EPERM
-}
-
-// StatFSAt implements FilesystemImpl.StatFSAt.
-func (fs *FDTestFilesystem) StatFSAt(ctx context.Context, rp *ResolvingPath) (linux.Statfs, error) {
-	return linux.Statfs{}, syserror.EPERM
-}
-
-// SymlinkAt implements FilesystemImpl.SymlinkAt.
-func (fs *FDTestFilesystem) SymlinkAt(ctx context.Context, rp *ResolvingPath, target string) error {
-	return syserror.EPERM
-}
-
-// UnlinkAt implements FilesystemImpl.UnlinkAt.
-func (fs *FDTestFilesystem) UnlinkAt(ctx context.Context, rp *ResolvingPath) error {
-	return syserror.EPERM
-}
-
-// ListxattrAt implements FilesystemImpl.ListxattrAt.
-func (fs *FDTestFilesystem) ListxattrAt(ctx context.Context, rp *ResolvingPath) ([]string, error) {
-	return nil, syserror.EPERM
-}
-
-// GetxattrAt implements FilesystemImpl.GetxattrAt.
-func (fs *FDTestFilesystem) GetxattrAt(ctx context.Context, rp *ResolvingPath, name string) (string, error) {
-	return "", syserror.EPERM
-}
-
-// SetxattrAt implements FilesystemImpl.SetxattrAt.
-func (fs *FDTestFilesystem) SetxattrAt(ctx context.Context, rp *ResolvingPath, opts SetxattrOptions) error {
-	return syserror.EPERM
-}
-
-// RemovexattrAt implements FilesystemImpl.RemovexattrAt.
-func (fs *FDTestFilesystem) RemovexattrAt(ctx context.Context, rp *ResolvingPath, name string) error {
-	return syserror.EPERM
-}
-
-// PrependPath implements FilesystemImpl.PrependPath.
-func (fs *FDTestFilesystem) PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error {
-	b.PrependComponent(fmt.Sprintf("vfs.fdTestDentry:%p", vd.dentry.impl.(*fdTestDentry)))
-	return PrependPathSyntheticError{}
-}
-
-type fdTestDentry struct {
-	vfsd Dentry
-}
-
-// NewDentry returns a new Dentry.
-func (fs *FDTestFilesystem) NewDentry() *Dentry {
-	var d fdTestDentry
-	d.vfsd.Init(&d)
-	return &d.vfsd
-}
-
-// IncRef implements DentryImpl.IncRef.
-func (d *fdTestDentry) IncRef() {
-}
-
-// TryIncRef implements DentryImpl.TryIncRef.
-func (d *fdTestDentry) TryIncRef() bool {
-	return true
-}
-
-// DecRef implements DentryImpl.DecRef.
-func (d *fdTestDentry) DecRef() {
-}
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index b2bf48853..d730530b9 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -75,6 +75,14 @@ type VirtualFilesystem struct {
 	// mountpoints is analogous to Linux's mountpoint_hashtable.
 	mountpoints map[*Dentry]map[*Mount]struct{}
 
+	// anonMount is a Mount, not included in mounts or mountpoints,
+	// representing an anonFilesystem. anonMount is used to back
+	// VirtualDentries returned by VirtualFilesystem.NewAnonVirtualDentry().
+	// anonMount is immutable.
+	//
+	// anonMount is analogous to Linux's anon_inode_mnt.
+	anonMount *Mount
+
 	// devices contains all registered Devices. devices is protected by
 	// devicesMu.
 	devicesMu sync.RWMutex
@@ -110,6 +118,22 @@ func New() *VirtualFilesystem {
 		filesystems:           make(map[*Filesystem]struct{}),
 	}
 	vfs.mounts.Init()
+
+	// Construct vfs.anonMount.
+	anonfsDevMinor, err := vfs.GetAnonBlockDevMinor()
+	if err != nil {
+		panic(fmt.Sprintf("VirtualFilesystem.GetAnonBlockDevMinor() failed during VirtualFilesystem construction: %v", err))
+	}
+	anonfs := anonFilesystem{
+		devMinor: anonfsDevMinor,
+	}
+	anonfs.vfsfs.Init(vfs, &anonfs)
+	vfs.anonMount = &Mount{
+		vfs:  vfs,
+		fs:   &anonfs.vfsfs,
+		refs: 1,
+	}
+
 	return vfs
 }