Add O_PATH support in vfs2

PiperOrigin-RevId: 354367665

4 files changed, 153 insertions, 1 deletions

diff --git a/pkg/sentry/vfs/BUILD b/pkg/sentry/vfs/BUILD
index a3868bf16..df4990854 100644
--- a/pkg/sentry/vfs/BUILD
+++ b/pkg/sentry/vfs/BUILD
@@ -83,6 +83,7 @@ go_library(
         "mount.go",
         "mount_namespace_refs.go",
         "mount_unsafe.go",
+        "opath.go",
         "options.go",
         "pathname.go",
         "permissions.go",
diff --git a/pkg/sentry/vfs/opath.go b/pkg/sentry/vfs/opath.go
new file mode 100644
index 000000000..39fbac987
--- /dev/null
+++ b/pkg/sentry/vfs/opath.go
@@ -0,0 +1,139 @@
+// 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 (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/memmap"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// opathFD implements vfs.FileDescriptionImpl for a file description opened with O_PATH.
+//
+// +stateify savable
+type opathFD struct {
+	vfsfd FileDescription
+	FileDescriptionDefaultImpl
+	NoLockFD
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *opathFD) Release(context.Context) {
+	// noop
+}
+
+// Allocate implements vfs.FileDescriptionImpl.Allocate.
+func (fd *opathFD) Allocate(ctx context.Context, mode, offset, length uint64) error {
+	return syserror.EBADF
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *opathFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts ReadOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *opathFD) Read(ctx context.Context, dst usermem.IOSequence, opts ReadOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *opathFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts WriteOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *opathFD) Write(ctx context.Context, src usermem.IOSequence, opts WriteOptions) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// Ioctl implements vfs.FileDescriptionImpl.Ioctl.
+func (fd *opathFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
+	return 0, syserror.EBADF
+}
+
+// IterDirents implements vfs.FileDescriptionImpl.IterDirents.
+func (fd *opathFD) IterDirents(ctx context.Context, cb IterDirentsCallback) error {
+	return syserror.EBADF
+}
+
+// Seek implements vfs.FileDescriptionImpl.Seek.
+func (fd *opathFD) Seek(ctx context.Context, offset int64, whence int32) (int64, error) {
+	return 0, syserror.EBADF
+}
+
+// ConfigureMMap implements vfs.FileDescriptionImpl.ConfigureMMap.
+func (fd *opathFD) ConfigureMMap(ctx context.Context, opts *memmap.MMapOpts) error {
+	return syserror.EBADF
+}
+
+// ListXattr implements vfs.FileDescriptionImpl.ListXattr.
+func (fd *opathFD) ListXattr(ctx context.Context, size uint64) ([]string, error) {
+	return nil, syserror.EBADF
+}
+
+// GetXattr implements vfs.FileDescriptionImpl.GetXattr.
+func (fd *opathFD) GetXattr(ctx context.Context, opts GetXattrOptions) (string, error) {
+	return "", syserror.EBADF
+}
+
+// SetXattr implements vfs.FileDescriptionImpl.SetXattr.
+func (fd *opathFD) SetXattr(ctx context.Context, opts SetXattrOptions) error {
+	return syserror.EBADF
+}
+
+// RemoveXattr implements vfs.FileDescriptionImpl.RemoveXattr.
+func (fd *opathFD) RemoveXattr(ctx context.Context, name string) error {
+	return syserror.EBADF
+}
+
+// Sync implements vfs.FileDescriptionImpl.Sync.
+func (fd *opathFD) Sync(ctx context.Context) error {
+	return syserror.EBADF
+}
+
+// SetStat implements vfs.FileDescriptionImpl.SetStat.
+func (fd *opathFD) SetStat(ctx context.Context, opts SetStatOptions) error {
+	return syserror.EBADF
+}
+
+// Stat implements vfs.FileDescriptionImpl.Stat.
+func (fd *opathFD) Stat(ctx context.Context, opts StatOptions) (linux.Statx, error) {
+	vfsObj := fd.vfsfd.vd.mount.vfs
+	rp := vfsObj.getResolvingPath(auth.CredentialsFromContext(ctx), &PathOperation{
+		Root:  fd.vfsfd.vd,
+		Start: fd.vfsfd.vd,
+	})
+	stat, err := fd.vfsfd.vd.mount.fs.impl.StatAt(ctx, rp, opts)
+	vfsObj.putResolvingPath(ctx, rp)
+	return stat, err
+}
+
+// StatFS returns metadata for the filesystem containing the file represented
+// by fd.
+func (fd *opathFD) StatFS(ctx context.Context) (linux.Statfs, error) {
+	vfsObj := fd.vfsfd.vd.mount.vfs
+	rp := vfsObj.getResolvingPath(auth.CredentialsFromContext(ctx), &PathOperation{
+		Root:  fd.vfsfd.vd,
+		Start: fd.vfsfd.vd,
+	})
+	statfs, err := fd.vfsfd.vd.mount.fs.impl.StatFSAt(ctx, rp)
+	vfsObj.putResolvingPath(ctx, rp)
+	return statfs, err
+}
diff --git a/pkg/sentry/vfs/options.go b/pkg/sentry/vfs/options.go
index bc79e5ecc..c9907843c 100644
--- a/pkg/sentry/vfs/options.go
+++ b/pkg/sentry/vfs/options.go
@@ -129,7 +129,7 @@ type OpenOptions struct {
 	//
 	// FilesystemImpls are responsible for implementing the following flags:
 	// O_RDONLY, O_WRONLY, O_RDWR, O_APPEND, O_CREAT, O_DIRECT, O_DSYNC,
-	// O_EXCL, O_NOATIME, O_NOCTTY, O_NONBLOCK, O_PATH, O_SYNC, O_TMPFILE, and
+	// O_EXCL, O_NOATIME, O_NOCTTY, O_NONBLOCK, O_SYNC, O_TMPFILE, and
 	// O_TRUNC. VFS is responsible for handling O_DIRECTORY, O_LARGEFILE, and
 	// O_NOFOLLOW. VFS users are responsible for handling O_CLOEXEC, since file
 	// descriptors are mostly outside the scope of VFS.
diff --git a/pkg/sentry/vfs/vfs.go b/pkg/sentry/vfs/vfs.go
index 6fd1bb0b2..0aff2dd92 100644
--- a/pkg/sentry/vfs/vfs.go
+++ b/pkg/sentry/vfs/vfs.go
@@ -425,6 +425,18 @@ func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credential
 		rp.mustBeDir = true
 		rp.mustBeDirOrig = true
 	}
+	if opts.Flags&linux.O_PATH != 0 {
+		vd, err := vfs.GetDentryAt(ctx, creds, pop, &GetDentryOptions{})
+		if err != nil {
+			return nil, err
+		}
+		fd := &opathFD{}
+		if err := fd.vfsfd.Init(fd, opts.Flags, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{}); err != nil {
+			return nil, err
+		}
+		vd.DecRef(ctx)
+		return &fd.vfsfd, err
+	}
 	for {
 		fd, err := rp.mount.fs.impl.OpenAt(ctx, rp, *opts)
 		if err == nil {