Implement tap/tun device in vfs.

PiperOrigin-RevId: 296526279

3 files changed, 425 insertions, 1 deletions

diff --git a/pkg/tcpip/link/tun/BUILD b/pkg/tcpip/link/tun/BUILD
index e5096ea38..e0db6cf54 100644
--- a/pkg/tcpip/link/tun/BUILD
+++ b/pkg/tcpip/link/tun/BUILD
@@ -4,6 +4,22 @@ package(licenses = ["notice"])
 
 go_library(
     name = "tun",
-    srcs = ["tun_unsafe.go"],
+    srcs = [
+        "device.go",
+        "protocol.go",
+        "tun_unsafe.go",
+    ],
     visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/refs",
+        "//pkg/sync",
+        "//pkg/syserror",
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/header",
+        "//pkg/tcpip/link/channel",
+        "//pkg/tcpip/stack",
+        "//pkg/waiter",
+    ],
 )
diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
new file mode 100644
index 000000000..6ff47a742
--- /dev/null
+++ b/pkg/tcpip/link/tun/device.go
@@ -0,0 +1,352 @@
+// 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 tun
+
+import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/refs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+const (
+	// drivers/net/tun.c:tun_net_init()
+	defaultDevMtu = 1500
+
+	// Queue length for outbound packet, arriving at fd side for read. Overflow
+	// causes packet drops. gVisor implementation-specific.
+	defaultDevOutQueueLen = 1024
+)
+
+var zeroMAC [6]byte
+
+// Device is an opened /dev/net/tun device.
+//
+// +stateify savable
+type Device struct {
+	waiter.Queue
+
+	mu           sync.RWMutex `state:"nosave"`
+	endpoint     *tunEndpoint
+	notifyHandle *channel.NotificationHandle
+	flags        uint16
+}
+
+// beforeSave is invoked by stateify.
+func (d *Device) beforeSave() {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	// TODO(b/110961832): Restore the device to stack. At this moment, the stack
+	// is not savable.
+	if d.endpoint != nil {
+		panic("/dev/net/tun does not support save/restore when a device is associated with it.")
+	}
+}
+
+// Release implements fs.FileOperations.Release.
+func (d *Device) Release() {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	// Decrease refcount if there is an endpoint associated with this file.
+	if d.endpoint != nil {
+		d.endpoint.RemoveNotify(d.notifyHandle)
+		d.endpoint.DecRef()
+		d.endpoint = nil
+	}
+}
+
+// SetIff services TUNSETIFF ioctl(2) request.
+func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if d.endpoint != nil {
+		return syserror.EINVAL
+	}
+
+	// Input validations.
+	isTun := flags&linux.IFF_TUN != 0
+	isTap := flags&linux.IFF_TAP != 0
+	supportedFlags := uint16(linux.IFF_TUN | linux.IFF_TAP | linux.IFF_NO_PI)
+	if isTap && isTun || !isTap && !isTun || flags&^supportedFlags != 0 {
+		return syserror.EINVAL
+	}
+
+	prefix := "tun"
+	if isTap {
+		prefix = "tap"
+	}
+
+	endpoint, err := attachOrCreateNIC(s, name, prefix)
+	if err != nil {
+		return syserror.EINVAL
+	}
+
+	d.endpoint = endpoint
+	d.notifyHandle = d.endpoint.AddNotify(d)
+	d.flags = flags
+	return nil
+}
+
+func attachOrCreateNIC(s *stack.Stack, name, prefix string) (*tunEndpoint, error) {
+	for {
+		// 1. Try to attach to an existing NIC.
+		if name != "" {
+			if nic, found := s.GetNICByName(name); found {
+				endpoint, ok := nic.LinkEndpoint().(*tunEndpoint)
+				if !ok {
+					// Not a NIC created by tun device.
+					return nil, syserror.EOPNOTSUPP
+				}
+				if !endpoint.TryIncRef() {
+					// Race detected: NIC got deleted in between.
+					continue
+				}
+				return endpoint, nil
+			}
+		}
+
+		// 2. Creating a new NIC.
+		id := tcpip.NICID(s.UniqueID())
+		endpoint := &tunEndpoint{
+			Endpoint: channel.New(defaultDevOutQueueLen, defaultDevMtu, ""),
+			stack:    s,
+			nicID:    id,
+			name:     name,
+		}
+		if endpoint.name == "" {
+			endpoint.name = fmt.Sprintf("%s%d", prefix, id)
+		}
+		err := s.CreateNICWithOptions(endpoint.nicID, endpoint, stack.NICOptions{
+			Name: endpoint.name,
+		})
+		switch err {
+		case nil:
+			return endpoint, nil
+		case tcpip.ErrDuplicateNICID:
+			// Race detected: A NIC has been created in between.
+			continue
+		default:
+			return nil, syserror.EINVAL
+		}
+	}
+}
+
+// Write inject one inbound packet to the network interface.
+func (d *Device) Write(data []byte) (int64, error) {
+	d.mu.RLock()
+	endpoint := d.endpoint
+	d.mu.RUnlock()
+	if endpoint == nil {
+		return 0, syserror.EBADFD
+	}
+	if !endpoint.IsAttached() {
+		return 0, syserror.EIO
+	}
+
+	dataLen := int64(len(data))
+
+	// Packet information.
+	var pktInfoHdr PacketInfoHeader
+	if !d.hasFlags(linux.IFF_NO_PI) {
+		if len(data) < PacketInfoHeaderSize {
+			// Ignore bad packet.
+			return dataLen, nil
+		}
+		pktInfoHdr = PacketInfoHeader(data[:PacketInfoHeaderSize])
+		data = data[PacketInfoHeaderSize:]
+	}
+
+	// Ethernet header (TAP only).
+	var ethHdr header.Ethernet
+	if d.hasFlags(linux.IFF_TAP) {
+		if len(data) < header.EthernetMinimumSize {
+			// Ignore bad packet.
+			return dataLen, nil
+		}
+		ethHdr = header.Ethernet(data[:header.EthernetMinimumSize])
+		data = data[header.EthernetMinimumSize:]
+	}
+
+	// Try to determine network protocol number, default zero.
+	var protocol tcpip.NetworkProtocolNumber
+	switch {
+	case pktInfoHdr != nil:
+		protocol = pktInfoHdr.Protocol()
+	case ethHdr != nil:
+		protocol = ethHdr.Type()
+	}
+
+	// Try to determine remote link address, default zero.
+	var remote tcpip.LinkAddress
+	switch {
+	case ethHdr != nil:
+		remote = ethHdr.SourceAddress()
+	default:
+		remote = tcpip.LinkAddress(zeroMAC[:])
+	}
+
+	pkt := tcpip.PacketBuffer{
+		Data: buffer.View(data).ToVectorisedView(),
+	}
+	if ethHdr != nil {
+		pkt.LinkHeader = buffer.View(ethHdr)
+	}
+	endpoint.InjectLinkAddr(protocol, remote, pkt)
+	return dataLen, nil
+}
+
+// Read reads one outgoing packet from the network interface.
+func (d *Device) Read() ([]byte, error) {
+	d.mu.RLock()
+	endpoint := d.endpoint
+	d.mu.RUnlock()
+	if endpoint == nil {
+		return nil, syserror.EBADFD
+	}
+
+	for {
+		info, ok := endpoint.Read()
+		if !ok {
+			return nil, syserror.ErrWouldBlock
+		}
+
+		v, ok := d.encodePkt(&info)
+		if !ok {
+			// Ignore unsupported packet.
+			continue
+		}
+		return v, nil
+	}
+}
+
+// encodePkt encodes packet for fd side.
+func (d *Device) encodePkt(info *channel.PacketInfo) (buffer.View, bool) {
+	var vv buffer.VectorisedView
+
+	// Packet information.
+	if !d.hasFlags(linux.IFF_NO_PI) {
+		hdr := make(PacketInfoHeader, PacketInfoHeaderSize)
+		hdr.Encode(&PacketInfoFields{
+			Protocol: info.Proto,
+		})
+		vv.AppendView(buffer.View(hdr))
+	}
+
+	// If the packet does not already have link layer header, and the route
+	// does not exist, we can't compute it. This is possibly a raw packet, tun
+	// device doesn't support this at the moment.
+	if info.Pkt.LinkHeader == nil && info.Route.RemoteLinkAddress == "" {
+		return nil, false
+	}
+
+	// Ethernet header (TAP only).
+	if d.hasFlags(linux.IFF_TAP) {
+		// Add ethernet header if not provided.
+		if info.Pkt.LinkHeader == nil {
+			hdr := &header.EthernetFields{
+				SrcAddr: info.Route.LocalLinkAddress,
+				DstAddr: info.Route.RemoteLinkAddress,
+				Type:    info.Proto,
+			}
+			if hdr.SrcAddr == "" {
+				hdr.SrcAddr = d.endpoint.LinkAddress()
+			}
+
+			eth := make(header.Ethernet, header.EthernetMinimumSize)
+			eth.Encode(hdr)
+			vv.AppendView(buffer.View(eth))
+		} else {
+			vv.AppendView(info.Pkt.LinkHeader)
+		}
+	}
+
+	// Append upper headers.
+	vv.AppendView(buffer.View(info.Pkt.Header.View()[len(info.Pkt.LinkHeader):]))
+	// Append data payload.
+	vv.Append(info.Pkt.Data)
+
+	return vv.ToView(), true
+}
+
+// Name returns the name of the attached network interface. Empty string if
+// unattached.
+func (d *Device) Name() string {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+	if d.endpoint != nil {
+		return d.endpoint.name
+	}
+	return ""
+}
+
+// Flags returns the flags set for d. Zero value if unset.
+func (d *Device) Flags() uint16 {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+	return d.flags
+}
+
+func (d *Device) hasFlags(flags uint16) bool {
+	return d.flags&flags == flags
+}
+
+// Readiness implements watier.Waitable.Readiness.
+func (d *Device) Readiness(mask waiter.EventMask) waiter.EventMask {
+	if mask&waiter.EventIn != 0 {
+		d.mu.RLock()
+		endpoint := d.endpoint
+		d.mu.RUnlock()
+		if endpoint != nil && endpoint.NumQueued() == 0 {
+			mask &= ^waiter.EventIn
+		}
+	}
+	return mask & (waiter.EventIn | waiter.EventOut)
+}
+
+// WriteNotify implements channel.Notification.WriteNotify.
+func (d *Device) WriteNotify() {
+	d.Notify(waiter.EventIn)
+}
+
+// tunEndpoint is the link endpoint for the NIC created by the tun device.
+//
+// It is ref-counted as multiple opening files can attach to the same NIC.
+// The last owner is responsible for deleting the NIC.
+type tunEndpoint struct {
+	*channel.Endpoint
+
+	refs.AtomicRefCount
+
+	stack *stack.Stack
+	nicID tcpip.NICID
+	name  string
+}
+
+// DecRef decrements refcount of e, removes NIC if refcount goes to 0.
+func (e *tunEndpoint) DecRef() {
+	e.DecRefWithDestructor(func() {
+		e.stack.RemoveNIC(e.nicID)
+	})
+}
diff --git a/pkg/tcpip/link/tun/protocol.go b/pkg/tcpip/link/tun/protocol.go
new file mode 100644
index 000000000..89d9d91a9
--- /dev/null
+++ b/pkg/tcpip/link/tun/protocol.go
@@ -0,0 +1,56 @@
+// 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 tun
+
+import (
+	"encoding/binary"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+const (
+	// PacketInfoHeaderSize is the size of the packet information header.
+	PacketInfoHeaderSize = 4
+
+	offsetFlags    = 0
+	offsetProtocol = 2
+)
+
+// PacketInfoFields contains fields sent through the wire if IFF_NO_PI flag is
+// not set.
+type PacketInfoFields struct {
+	Flags    uint16
+	Protocol tcpip.NetworkProtocolNumber
+}
+
+// PacketInfoHeader is the wire representation of the packet information sent if
+// IFF_NO_PI flag is not set.
+type PacketInfoHeader []byte
+
+// Encode encodes f into h.
+func (h PacketInfoHeader) Encode(f *PacketInfoFields) {
+	binary.BigEndian.PutUint16(h[offsetFlags:][:2], f.Flags)
+	binary.BigEndian.PutUint16(h[offsetProtocol:][:2], uint16(f.Protocol))
+}
+
+// Flags returns the flag field in h.
+func (h PacketInfoHeader) Flags() uint16 {
+	return binary.BigEndian.Uint16(h[offsetFlags:])
+}
+
+// Protocol returns the protocol field in h.
+func (h PacketInfoHeader) Protocol() tcpip.NetworkProtocolNumber {
+	return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(h[offsetProtocol:]))
+}