Port /dev/net/tun device to VFS2.

Updates #2912 #1035

PiperOrigin-RevId: 318162565

3 files changed, 216 insertions, 1 deletions

diff --git a/pkg/sentry/devices/tundev/BUILD b/pkg/sentry/devices/tundev/BUILD
new file mode 100644
index 000000000..71c59287c
--- /dev/null
+++ b/pkg/sentry/devices/tundev/BUILD
@@ -0,0 +1,23 @@
+load("//tools:defs.bzl", "go_library")
+
+licenses(["notice"])
+
+go_library(
+    name = "tundev",
+    srcs = ["tundev.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/context",
+        "//pkg/sentry/arch",
+        "//pkg/sentry/fsimpl/devtmpfs",
+        "//pkg/sentry/inet",
+        "//pkg/sentry/kernel",
+        "//pkg/sentry/socket/netstack",
+        "//pkg/sentry/vfs",
+        "//pkg/syserror",
+        "//pkg/tcpip/link/tun",
+        "//pkg/usermem",
+        "//pkg/waiter",
+    ],
+)
diff --git a/pkg/sentry/devices/tundev/tundev.go b/pkg/sentry/devices/tundev/tundev.go
new file mode 100644
index 000000000..dfbd069af
--- /dev/null
+++ b/pkg/sentry/devices/tundev/tundev.go
@@ -0,0 +1,178 @@
+// 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 tundev implements the /dev/net/tun device.
+package tundev
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/devtmpfs"
+	"gvisor.dev/gvisor/pkg/sentry/inet"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/socket/netstack"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/tcpip/link/tun"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+const (
+	netTunDevMajor = 10
+	netTunDevMinor = 200
+)
+
+// tunDevice implements vfs.Device for /dev/net/tun.
+type tunDevice struct{}
+
+// Open implements vfs.Device.Open.
+func (tunDevice) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, opts vfs.OpenOptions) (*vfs.FileDescription, error) {
+	fd := &tunFD{}
+	if err := fd.vfsfd.Init(fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{
+		UseDentryMetadata: true,
+	}); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, nil
+}
+
+// tunFD implements vfs.FileDescriptionImpl for /dev/net/tun.
+type tunFD struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+	vfs.NoLockFD
+
+	device tun.Device
+}
+
+// Ioctl implements vfs.FileDescriptionImpl.Ioctl.
+func (fd *tunFD) Ioctl(ctx context.Context, uio usermem.IO, args arch.SyscallArguments) (uintptr, error) {
+	request := args[1].Uint()
+	data := args[2].Pointer()
+
+	switch request {
+	case linux.TUNSETIFF:
+		t := kernel.TaskFromContext(ctx)
+		if t == nil {
+			panic("Ioctl should be called from a task context")
+		}
+		if !t.HasCapability(linux.CAP_NET_ADMIN) {
+			return 0, syserror.EPERM
+		}
+		stack, ok := t.NetworkContext().(*netstack.Stack)
+		if !ok {
+			return 0, syserror.EINVAL
+		}
+
+		var req linux.IFReq
+		if _, err := usermem.CopyObjectIn(ctx, uio, data, &req, usermem.IOOpts{
+			AddressSpaceActive: true,
+		}); err != nil {
+			return 0, err
+		}
+		flags := usermem.ByteOrder.Uint16(req.Data[:])
+		return 0, fd.device.SetIff(stack.Stack, req.Name(), flags)
+
+	case linux.TUNGETIFF:
+		var req linux.IFReq
+
+		copy(req.IFName[:], fd.device.Name())
+
+		// Linux adds IFF_NOFILTER (the same value as IFF_NO_PI unfortunately) when
+		// there is no sk_filter. See __tun_chr_ioctl() in net/drivers/tun.c.
+		flags := fd.device.Flags() | linux.IFF_NOFILTER
+		usermem.ByteOrder.PutUint16(req.Data[:], flags)
+
+		_, err := usermem.CopyObjectOut(ctx, uio, data, &req, usermem.IOOpts{
+			AddressSpaceActive: true,
+		})
+		return 0, err
+
+	default:
+		return 0, syserror.ENOTTY
+	}
+}
+
+// Release implements vfs.FileDescriptionImpl.Release.
+func (fd *tunFD) Release() {
+	fd.device.Release()
+}
+
+// PRead implements vfs.FileDescriptionImpl.PRead.
+func (fd *tunFD) PRead(ctx context.Context, dst usermem.IOSequence, offset int64, opts vfs.ReadOptions) (int64, error) {
+	return fd.Read(ctx, dst, opts)
+}
+
+// Read implements vfs.FileDescriptionImpl.Read.
+func (fd *tunFD) Read(ctx context.Context, dst usermem.IOSequence, opts vfs.ReadOptions) (int64, error) {
+	data, err := fd.device.Read()
+	if err != nil {
+		return 0, err
+	}
+	n, err := dst.CopyOut(ctx, data)
+	if n > 0 && n < len(data) {
+		// Not an error for partial copying. Packet truncated.
+		err = nil
+	}
+	return int64(n), err
+}
+
+// PWrite implements vfs.FileDescriptionImpl.PWrite.
+func (fd *tunFD) PWrite(ctx context.Context, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
+	return fd.Write(ctx, src, opts)
+}
+
+// Write implements vfs.FileDescriptionImpl.Write.
+func (fd *tunFD) Write(ctx context.Context, src usermem.IOSequence, opts vfs.WriteOptions) (int64, error) {
+	data := make([]byte, src.NumBytes())
+	if _, err := src.CopyIn(ctx, data); err != nil {
+		return 0, err
+	}
+	return fd.device.Write(data)
+}
+
+// Readiness implements watier.Waitable.Readiness.
+func (fd *tunFD) Readiness(mask waiter.EventMask) waiter.EventMask {
+	return fd.device.Readiness(mask)
+}
+
+// EventRegister implements watier.Waitable.EventRegister.
+func (fd *tunFD) EventRegister(e *waiter.Entry, mask waiter.EventMask) {
+	fd.device.EventRegister(e, mask)
+}
+
+// EventUnregister implements watier.Waitable.EventUnregister.
+func (fd *tunFD) EventUnregister(e *waiter.Entry) {
+	fd.device.EventUnregister(e)
+}
+
+// isNetTunSupported returns whether /dev/net/tun device is supported for s.
+func isNetTunSupported(s inet.Stack) bool {
+	_, ok := s.(*netstack.Stack)
+	return ok
+}
+
+// Register registers all devices implemented by this package in vfsObj.
+func Register(vfsObj *vfs.VirtualFilesystem) error {
+	return vfsObj.RegisterDevice(vfs.CharDevice, netTunDevMajor, netTunDevMinor, tunDevice{}, &vfs.RegisterDeviceOptions{})
+}
+
+// CreateDevtmpfsFiles creates device special files in dev representing all
+// devices implemented by this package.
+func CreateDevtmpfsFiles(ctx context.Context, dev *devtmpfs.Accessor) error {
+	return dev.CreateDeviceFile(ctx, "net/tun", vfs.CharDevice, netTunDevMajor, netTunDevMinor, 0666 /* mode */)
+}
diff --git a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
index 142ee53b0..d0e06cdc0 100644
--- a/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
+++ b/pkg/sentry/fsimpl/devtmpfs/devtmpfs.go
@@ -136,6 +136,8 @@ func (a *Accessor) pathOperationAt(pathname string) *vfs.PathOperation {
 // CreateDeviceFile creates a device special file at the given pathname in the
 // devtmpfs instance accessed by the Accessor.
 func (a *Accessor) CreateDeviceFile(ctx context.Context, pathname string, kind vfs.DeviceKind, major, minor uint32, perms uint16) error {
+	actx := a.wrapContext(ctx)
+
 	mode := (linux.FileMode)(perms)
 	switch kind {
 	case vfs.BlockDevice:
@@ -145,12 +147,24 @@ func (a *Accessor) CreateDeviceFile(ctx context.Context, pathname string, kind v
 	default:
 		panic(fmt.Sprintf("invalid vfs.DeviceKind: %v", kind))
 	}
+
+	// Create any parent directories. See
+	// devtmpfs.c:handle_create()=>path_create().
+	for it := fspath.Parse(pathname).Begin; it.NextOk(); it = it.Next() {
+		pop := a.pathOperationAt(it.String())
+		if err := a.vfsObj.MkdirAt(actx, a.creds, pop, &vfs.MkdirOptions{
+			Mode: 0755,
+		}); err != nil {
+			return fmt.Errorf("failed to create directory %q: %v", it.String(), err)
+		}
+	}
+
 	// NOTE: Linux's devtmpfs refuses to automatically delete files it didn't
 	// create, which it recognizes by storing a pointer to the kdevtmpfs struct
 	// thread in struct inode::i_private. Accessor doesn't yet support deletion
 	// of files at all, and probably won't as long as we don't need to support
 	// kernel modules, so this is moot for now.
-	return a.vfsObj.MknodAt(a.wrapContext(ctx), a.creds, a.pathOperationAt(pathname), &vfs.MknodOptions{
+	return a.vfsObj.MknodAt(actx, a.creds, a.pathOperationAt(pathname), &vfs.MknodOptions{
 		Mode:     mode,
 		DevMajor: major,
 		DevMinor: minor,