pkg/tcpip/transport/packet/endpoint.go - third_party/gvisor.dev/gvisor/netstack - Git at Google

 // 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 packet provides the implementation of packet sockets (see
 // packet(7)). Packet sockets allow applications to:
 //
 //   * manually write and inspect link, network, and transport headers
 //   * receive all traffic of a given network protocol, or all protocols
 //
 // Packet sockets are similar to raw sockets, but provide even more power to
 // users, letting them effectively talk directly to the network device.
 //
 // Packet sockets skip the input and output iptables chains.
 package packet

 import (
 	"fmt"
 	"io"

 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/waiter"
 )

 // +stateify savable
 type packet struct {
 	packetEntry
 	// data holds the actual packet data, including any headers and
 	// payload.
 	data buffer.VectorisedView `state:".(buffer.VectorisedView)"`
 	// timestampNS is the unix time at which the packet was received.
 	timestampNS int64
 	// senderAddr is the network address of the sender.
 	senderAddr tcpip.FullAddress
 	// packetInfo holds additional information like the protocol
 	// of the packet etc.
 	packetInfo tcpip.LinkPacketInfo
 }

 // endpoint is the packet socket implementation of tcpip.Endpoint. It is legal
 // to have goroutines make concurrent calls into the endpoint.
 //
 // Lock order:
 //   endpoint.mu
 //     endpoint.rcvMu
 //
 // +stateify savable
 type endpoint struct {
 	stack.TransportEndpointInfo
 	tcpip.DefaultSocketOptionsHandler

 	// The following fields are initialized at creation time and are
 	// immutable.
 	stack       *stack.Stack `state:"manual"`
 	netProto    tcpip.NetworkProtocolNumber
 	waiterQueue *waiter.Queue
 	cooked      bool

 	// The following fields are used to manage the receive queue and are
 	// protected by rcvMu.
 	rcvMu         sync.Mutex `state:"nosave"`
 	rcvList       packetList
 	rcvBufSizeMax int `state:".(int)"`
 	rcvBufSize    int
 	rcvClosed     bool

 	// The following fields are protected by mu.
 	mu       sync.RWMutex `state:"nosave"`
 	closed   bool
 	stats    tcpip.TransportEndpointStats `state:"nosave"`
 	bound    bool
 	boundNIC tcpip.NICID

 	// lastErrorMu protects lastError.
 	lastErrorMu sync.Mutex `state:"nosave"`
 	lastError   tcpip.Error

 	// ops is used to get socket level options.
 	ops tcpip.SocketOptions
 }

 // NewEndpoint returns a new packet endpoint.
 func NewEndpoint(s *stack.Stack, cooked bool, netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, tcpip.Error) {
 	ep := &endpoint{
 		stack: s,
 		TransportEndpointInfo: stack.TransportEndpointInfo{
 			NetProto: netProto,
 		},
 		cooked:        cooked,
 		netProto:      netProto,
 		waiterQueue:   waiterQueue,
 		rcvBufSizeMax: 32 * 1024,
 	}
 	ep.ops.InitHandler(ep, ep.stack, tcpip.GetStackSendBufferLimits)

 	// Override with stack defaults.
 	var ss tcpip.SendBufferSizeOption
 	if err := s.Option(&ss); err == nil {
 		ep.ops.SetSendBufferSize(int64(ss.Default), false /* notify */)
 	}

 	var rs stack.ReceiveBufferSizeOption
 	if err := s.Option(&rs); err == nil {
 		ep.rcvBufSizeMax = rs.Default
 	}

 	if err := s.RegisterPacketEndpoint(0, netProto, ep); err != nil {
 		return nil, err
 	}
 	return ep, nil
 }

 // Abort implements stack.TransportEndpoint.Abort.
 func (ep *endpoint) Abort() {
 	ep.Close()
 }

 // Close implements tcpip.Endpoint.Close.
 func (ep *endpoint) Close() {
 	ep.mu.Lock()
 	defer ep.mu.Unlock()

 	if ep.closed {
 		return
 	}

 	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)

 	ep.rcvMu.Lock()
 	defer ep.rcvMu.Unlock()

 	// Clear the receive list.
 	ep.rcvClosed = true
 	ep.rcvBufSize = 0
 	for !ep.rcvList.Empty() {
 		ep.rcvList.Remove(ep.rcvList.Front())
 	}

 	ep.closed = true
 	ep.bound = false
 	ep.waiterQueue.Notify(waiter.EventHUp | waiter.EventErr | waiter.EventIn | waiter.EventOut)
 }

 // ModerateRecvBuf implements tcpip.Endpoint.ModerateRecvBuf.
 func (ep *endpoint) ModerateRecvBuf(copied int) {}

 // Read implements tcpip.Endpoint.Read.
 func (ep *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, tcpip.Error) {
 	ep.rcvMu.Lock()

 	// If there's no data to read, return that read would block or that the
 	// endpoint is closed.
 	if ep.rcvList.Empty() {
 		var err tcpip.Error = &tcpip.ErrWouldBlock{}
 		if ep.rcvClosed {
 			ep.stats.ReadErrors.ReadClosed.Increment()
 			err = &tcpip.ErrClosedForReceive{}
 		}
 		ep.rcvMu.Unlock()
 		return tcpip.ReadResult{}, err
 	}

 	packet := ep.rcvList.Front()
 	if !opts.Peek {
 		ep.rcvList.Remove(packet)
 		ep.rcvBufSize -= packet.data.Size()
 	}

 	ep.rcvMu.Unlock()

 	res := tcpip.ReadResult{
 		Total: packet.data.Size(),
 		ControlMessages: tcpip.ControlMessages{
 			HasTimestamp: true,
 			Timestamp:    packet.timestampNS,
 		},
 	}
 	if opts.NeedRemoteAddr {
 		res.RemoteAddr = packet.senderAddr
 	}
 	if opts.NeedLinkPacketInfo {
 		res.LinkPacketInfo = packet.packetInfo
 	}

 	n, err := packet.data.ReadTo(dst, opts.Peek)
 	if n == 0 && err != nil {
 		return res, &tcpip.ErrBadBuffer{}
 	}
 	res.Count = n
 	return res, nil
 }

 func (*endpoint) Write(tcpip.Payloader, tcpip.WriteOptions) (int64, tcpip.Error) {
 	// TODO(gvisor.dev/issue/173): Implement.
 	return 0, &tcpip.ErrInvalidOptionValue{}
 }

 // Disconnect implements tcpip.Endpoint.Disconnect. Packet sockets cannot be
 // disconnected, and this function always returns tpcip.ErrNotSupported.
 func (*endpoint) Disconnect() tcpip.Error {
 	return &tcpip.ErrNotSupported{}
 }

 // Connect implements tcpip.Endpoint.Connect. Packet sockets cannot be
 // connected, and this function always returnes *tcpip.ErrNotSupported.
 func (*endpoint) Connect(addr tcpip.FullAddress) tcpip.Error {
 	return &tcpip.ErrNotSupported{}
 }

 // Shutdown implements tcpip.Endpoint.Shutdown. Packet sockets cannot be used
 // with Shutdown, and this function always returns *tcpip.ErrNotSupported.
 func (*endpoint) Shutdown(flags tcpip.ShutdownFlags) tcpip.Error {
 	return &tcpip.ErrNotSupported{}
 }

 // Listen implements tcpip.Endpoint.Listen. Packet sockets cannot be used with
 // Listen, and this function always returns *tcpip.ErrNotSupported.
 func (*endpoint) Listen(backlog int) tcpip.Error {
 	return &tcpip.ErrNotSupported{}
 }

 // Accept implements tcpip.Endpoint.Accept. Packet sockets cannot be used with
 // Accept, and this function always returns *tcpip.ErrNotSupported.
 func (*endpoint) Accept(*tcpip.FullAddress) (tcpip.Endpoint, *waiter.Queue, tcpip.Error) {
 	return nil, nil, &tcpip.ErrNotSupported{}
 }

 // Bind implements tcpip.Endpoint.Bind.
 func (ep *endpoint) Bind(addr tcpip.FullAddress) tcpip.Error {
 	// TODO(gvisor.dev/issue/173): Add Bind support.

 	// "By default, all packets of the specified protocol type are passed
 	// to a packet socket.  To get packets only from a specific interface
 	// use bind(2) specifying an address in a struct sockaddr_ll to bind
 	// the packet socket  to  an interface.  Fields used for binding are
 	// sll_family (should be AF_PACKET), sll_protocol, and sll_ifindex."
 	// - packet(7).

 	ep.mu.Lock()
 	defer ep.mu.Unlock()

 	if ep.bound && ep.boundNIC == addr.NIC {
 		// If the NIC being bound is the same then just return success.
 		return nil
 	}

 	// Unregister endpoint with all the nics.
 	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)
 	ep.bound = false

 	// Bind endpoint to receive packets from specific interface.
 	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, ep.netProto, ep); err != nil {
 		return err
 	}

 	ep.bound = true
 	ep.boundNIC = addr.NIC

 	return nil
 }

 // GetLocalAddress implements tcpip.Endpoint.GetLocalAddress.
 func (*endpoint) GetLocalAddress() (tcpip.FullAddress, tcpip.Error) {
 	return tcpip.FullAddress{}, &tcpip.ErrNotSupported{}
 }

 // GetRemoteAddress implements tcpip.Endpoint.GetRemoteAddress.
 func (*endpoint) GetRemoteAddress() (tcpip.FullAddress, tcpip.Error) {
 	// Even a connected socket doesn't return a remote address.
 	return tcpip.FullAddress{}, &tcpip.ErrNotConnected{}
 }

 // Readiness implements tcpip.Endpoint.Readiness.
 func (ep *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
 	// The endpoint is always writable.
 	result := waiter.EventOut & mask

 	// Determine whether the endpoint is readable.
 	if (mask & waiter.EventIn) != 0 {
 		ep.rcvMu.Lock()
 		if !ep.rcvList.Empty() || ep.rcvClosed {
 			result |= waiter.EventIn
 		}
 		ep.rcvMu.Unlock()
 	}

 	return result
 }

 // SetSockOpt implements tcpip.Endpoint.SetSockOpt. Packet sockets cannot be
 // used with SetSockOpt, and this function always returns
 // *tcpip.ErrNotSupported.
 func (ep *endpoint) SetSockOpt(opt tcpip.SettableSocketOption) tcpip.Error {
 	switch opt.(type) {
 	case *tcpip.SocketDetachFilterOption:
 		return nil

 	default:
 		return &tcpip.ErrUnknownProtocolOption{}
 	}
 }

 // SetSockOptInt implements tcpip.Endpoint.SetSockOptInt.
 func (ep *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) tcpip.Error {
 	switch opt {
 	case tcpip.ReceiveBufferSizeOption:
 		// Make sure the receive buffer size is within the min and max
 		// allowed.
 		var rs stack.ReceiveBufferSizeOption
 		if err := ep.stack.Option(&rs); err != nil {
 			panic(fmt.Sprintf("s.Option(%#v) = %s", rs, err))
 		}
 		if v > rs.Max {
 			v = rs.Max
 		}
 		if v < rs.Min {
 			v = rs.Min
 		}
 		ep.rcvMu.Lock()
 		ep.rcvBufSizeMax = v
 		ep.rcvMu.Unlock()
 		return nil

 	default:
 		return &tcpip.ErrUnknownProtocolOption{}
 	}
 }

 func (ep *endpoint) LastError() tcpip.Error {
 	ep.lastErrorMu.Lock()
 	defer ep.lastErrorMu.Unlock()

 	err := ep.lastError
 	ep.lastError = nil
 	return err
 }

 // UpdateLastError implements tcpip.SocketOptionsHandler.UpdateLastError.
 func (ep *endpoint) UpdateLastError(err tcpip.Error) {
 	ep.lastErrorMu.Lock()
 	ep.lastError = err
 	ep.lastErrorMu.Unlock()
 }

 // GetSockOpt implements tcpip.Endpoint.GetSockOpt.
 func (ep *endpoint) GetSockOpt(opt tcpip.GettableSocketOption) tcpip.Error {
 	return &tcpip.ErrNotSupported{}
 }

 // GetSockOptInt implements tcpip.Endpoint.GetSockOptInt.
 func (ep *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, tcpip.Error) {
 	switch opt {
 	case tcpip.ReceiveQueueSizeOption:
 		v := 0
 		ep.rcvMu.Lock()
 		if !ep.rcvList.Empty() {
 			p := ep.rcvList.Front()
 			v = p.data.Size()
 		}
 		ep.rcvMu.Unlock()
 		return v, nil

 	case tcpip.ReceiveBufferSizeOption:
 		ep.rcvMu.Lock()
 		v := ep.rcvBufSizeMax
 		ep.rcvMu.Unlock()
 		return v, nil

 	default:
 		return -1, &tcpip.ErrUnknownProtocolOption{}
 	}
 }

 // HandlePacket implements stack.PacketEndpoint.HandlePacket.
 func (ep *endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress, netProto tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
 	ep.rcvMu.Lock()

 	// Drop the packet if our buffer is currently full.
 	if ep.rcvClosed {
 		ep.rcvMu.Unlock()
 		ep.stack.Stats().DroppedPackets.Increment()
 		ep.stats.ReceiveErrors.ClosedReceiver.Increment()
 		return
 	}

 	if ep.rcvBufSize >= ep.rcvBufSizeMax {
 		ep.rcvMu.Unlock()
 		ep.stack.Stats().DroppedPackets.Increment()
 		ep.stats.ReceiveErrors.ReceiveBufferOverflow.Increment()
 		return
 	}

 	wasEmpty := ep.rcvBufSize == 0

 	// Push new packet into receive list and increment the buffer size.
 	var packet packet
 	// TODO(gvisor.dev/issue/173): Return network protocol.
 	if !pkt.LinkHeader().View().IsEmpty() {
 		// Get info directly from the ethernet header.
 		hdr := header.Ethernet(pkt.LinkHeader().View())
 		packet.senderAddr = tcpip.FullAddress{
 			NIC:  nicID,
 			Addr: tcpip.Address(hdr.SourceAddress()),
 		}
 		packet.packetInfo.Protocol = netProto
 		packet.packetInfo.PktType = pkt.PktType
 	} else {
 		// Guess the would-be ethernet header.
 		packet.senderAddr = tcpip.FullAddress{
 			NIC:  nicID,
 			Addr: tcpip.Address(localAddr),
 		}
 		packet.packetInfo.Protocol = netProto
 		packet.packetInfo.PktType = pkt.PktType
 	}

 	if ep.cooked {
 		// Cooked packets can simply be queued.
 		switch pkt.PktType {
 		case tcpip.PacketHost:
 			packet.data = pkt.Data().ExtractVV()
 		case tcpip.PacketOutgoing:
 			// Strip Link Header.
 			var combinedVV buffer.VectorisedView
 			if v := pkt.NetworkHeader().View(); !v.IsEmpty() {
 				combinedVV.AppendView(v)
 			}
 			if v := pkt.TransportHeader().View(); !v.IsEmpty() {
 				combinedVV.AppendView(v)
 			}
 			combinedVV.Append(pkt.Data().ExtractVV())
 			packet.data = combinedVV
 		default:
 			panic(fmt.Sprintf("unexpected PktType in pkt: %+v", pkt))
 		}

 	} else {
 		// Raw packets need their ethernet headers prepended before
 		// queueing.
 		var linkHeader buffer.View
 		if pkt.PktType != tcpip.PacketOutgoing {
 			if pkt.LinkHeader().View().IsEmpty() {
 				// We weren't provided with an actual ethernet header,
 				// so fake one.
 				ethFields := header.EthernetFields{
 					SrcAddr: tcpip.LinkAddress([]byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00}),
 					DstAddr: localAddr,
 					Type:    netProto,
 				}
 				fakeHeader := make(header.Ethernet, header.EthernetMinimumSize)
 				fakeHeader.Encode(&ethFields)
 				linkHeader = buffer.View(fakeHeader)
 			} else {
 				linkHeader = append(buffer.View(nil), pkt.LinkHeader().View()...)
 			}
 			combinedVV := linkHeader.ToVectorisedView()
 			combinedVV.Append(pkt.Data().ExtractVV())
 			packet.data = combinedVV
 		} else {
 			packet.data = buffer.NewVectorisedView(pkt.Size(), pkt.Views())
 		}
 	}
 	packet.timestampNS = ep.stack.Clock().NowNanoseconds()

 	ep.rcvList.PushBack(&packet)
 	ep.rcvBufSize += packet.data.Size()

 	ep.rcvMu.Unlock()
 	ep.stats.PacketsReceived.Increment()
 	// Notify waiters that there's data to be read.
 	if wasEmpty {
 		ep.waiterQueue.Notify(waiter.EventIn)
 	}
 }

 // State implements socket.Socket.State.
 func (*endpoint) State() uint32 {
 	return 0
 }

 // Info returns a copy of the endpoint info.
 func (ep *endpoint) Info() tcpip.EndpointInfo {
 	ep.mu.RLock()
 	// Make a copy of the endpoint info.
 	ret := ep.TransportEndpointInfo
 	ep.mu.RUnlock()
 	return &ret
 }

 // Stats returns a pointer to the endpoint stats.
 func (ep *endpoint) Stats() tcpip.EndpointStats {
 	return &ep.stats
 }

 // SetOwner implements tcpip.Endpoint.SetOwner.
 func (ep *endpoint) SetOwner(owner tcpip.PacketOwner) {}

 // SocketOptions implements tcpip.Endpoint.SocketOptions.
 func (ep *endpoint) SocketOptions() *tcpip.SocketOptions {
 	return &ep.ops
 }
	// 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 packet provides the implementation of packet sockets (see
	// packet(7)). Packet sockets allow applications to:
	//
	// * manually write and inspect link, network, and transport headers
	// * receive all traffic of a given network protocol, or all protocols
	//
	// Packet sockets are similar to raw sockets, but provide even more power to
	// users, letting them effectively talk directly to the network device.
	//
	// Packet sockets skip the input and output iptables chains.
	package packet

	import (
	"fmt"
	"io"

	"gvisor.dev/gvisor/pkg/sync"
	"gvisor.dev/gvisor/pkg/tcpip"
	"gvisor.dev/gvisor/pkg/tcpip/buffer"
	"gvisor.dev/gvisor/pkg/tcpip/header"
	"gvisor.dev/gvisor/pkg/tcpip/stack"
	"gvisor.dev/gvisor/pkg/waiter"
	)

	// +stateify savable
	type packet struct {
	packetEntry
	// data holds the actual packet data, including any headers and
	// payload.
	data buffer.VectorisedView `state:".(buffer.VectorisedView)"`
	// timestampNS is the unix time at which the packet was received.
	timestampNS int64
	// senderAddr is the network address of the sender.
	senderAddr tcpip.FullAddress
	// packetInfo holds additional information like the protocol
	// of the packet etc.
	packetInfo tcpip.LinkPacketInfo
	}

	// endpoint is the packet socket implementation of tcpip.Endpoint. It is legal
	// to have goroutines make concurrent calls into the endpoint.
	//
	// Lock order:
	// endpoint.mu
	// endpoint.rcvMu
	//
	// +stateify savable
	type endpoint struct {
	stack.TransportEndpointInfo
	tcpip.DefaultSocketOptionsHandler

	// The following fields are initialized at creation time and are
	// immutable.
	stack *stack.Stack `state:"manual"`
	netProto tcpip.NetworkProtocolNumber
	waiterQueue *waiter.Queue
	cooked bool

	// The following fields are used to manage the receive queue and are
	// protected by rcvMu.
	rcvMu sync.Mutex `state:"nosave"`
	rcvList packetList
	rcvBufSizeMax int `state:".(int)"`
	rcvBufSize int
	rcvClosed bool

	// The following fields are protected by mu.
	mu sync.RWMutex `state:"nosave"`
	closed bool
	stats tcpip.TransportEndpointStats `state:"nosave"`
	bound bool
	boundNIC tcpip.NICID

	// lastErrorMu protects lastError.
	lastErrorMu sync.Mutex `state:"nosave"`
	lastError tcpip.Error

	// ops is used to get socket level options.
	ops tcpip.SocketOptions
	}

	// NewEndpoint returns a new packet endpoint.
	func NewEndpoint(s stack.Stack, cooked bool, netProto tcpip.NetworkProtocolNumber, waiterQueue waiter.Queue) (tcpip.Endpoint, tcpip.Error) {
	ep := &endpoint{
	stack: s,
	TransportEndpointInfo: stack.TransportEndpointInfo{
	NetProto: netProto,
	},
	cooked: cooked,
	netProto: netProto,
	waiterQueue: waiterQueue,
	rcvBufSizeMax: 32 * 1024,
	}
	ep.ops.InitHandler(ep, ep.stack, tcpip.GetStackSendBufferLimits)

	// Override with stack defaults.
	var ss tcpip.SendBufferSizeOption
	if err := s.Option(&ss); err == nil {
	ep.ops.SetSendBufferSize(int64(ss.Default), false /* notify */)
	}

	var rs stack.ReceiveBufferSizeOption
	if err := s.Option(&rs); err == nil {
	ep.rcvBufSizeMax = rs.Default
	}

	if err := s.RegisterPacketEndpoint(0, netProto, ep); err != nil {
	return nil, err
	}
	return ep, nil
	}

	// Abort implements stack.TransportEndpoint.Abort.
	func (ep *endpoint) Abort() {
	ep.Close()
	}

	// Close implements tcpip.Endpoint.Close.
	func (ep *endpoint) Close() {
	ep.mu.Lock()
	defer ep.mu.Unlock()

	if ep.closed {
	return
	}

	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)

	ep.rcvMu.Lock()
	defer ep.rcvMu.Unlock()

	// Clear the receive list.
	ep.rcvClosed = true
	ep.rcvBufSize = 0
	for !ep.rcvList.Empty() {
	ep.rcvList.Remove(ep.rcvList.Front())
	}

	ep.closed = true
	ep.bound = false
	ep.waiterQueue.Notify(waiter.EventHUp \| waiter.EventErr \| waiter.EventIn \| waiter.EventOut)
	}

	// ModerateRecvBuf implements tcpip.Endpoint.ModerateRecvBuf.
	func (ep *endpoint) ModerateRecvBuf(copied int) {}

	// Read implements tcpip.Endpoint.Read.
	func (ep *endpoint) Read(dst io.Writer, opts tcpip.ReadOptions) (tcpip.ReadResult, tcpip.Error) {
	ep.rcvMu.Lock()

	// If there's no data to read, return that read would block or that the
	// endpoint is closed.
	if ep.rcvList.Empty() {
	var err tcpip.Error = &tcpip.ErrWouldBlock{}
	if ep.rcvClosed {
	ep.stats.ReadErrors.ReadClosed.Increment()
	err = &tcpip.ErrClosedForReceive{}
	}
	ep.rcvMu.Unlock()
	return tcpip.ReadResult{}, err
	}

	packet := ep.rcvList.Front()
	if !opts.Peek {
	ep.rcvList.Remove(packet)
	ep.rcvBufSize -= packet.data.Size()
	}

	ep.rcvMu.Unlock()

	res := tcpip.ReadResult{
	Total: packet.data.Size(),
	ControlMessages: tcpip.ControlMessages{
	HasTimestamp: true,
	Timestamp: packet.timestampNS,
	},
	}
	if opts.NeedRemoteAddr {
	res.RemoteAddr = packet.senderAddr
	}
	if opts.NeedLinkPacketInfo {
	res.LinkPacketInfo = packet.packetInfo
	}

	n, err := packet.data.ReadTo(dst, opts.Peek)
	if n == 0 && err != nil {
	return res, &tcpip.ErrBadBuffer{}
	}
	res.Count = n
	return res, nil
	}

	func (*endpoint) Write(tcpip.Payloader, tcpip.WriteOptions) (int64, tcpip.Error) {
	// TODO(gvisor.dev/issue/173): Implement.
	return 0, &tcpip.ErrInvalidOptionValue{}
	}

	// Disconnect implements tcpip.Endpoint.Disconnect. Packet sockets cannot be
	// disconnected, and this function always returns tpcip.ErrNotSupported.
	func (*endpoint) Disconnect() tcpip.Error {
	return &tcpip.ErrNotSupported{}
	}

	// Connect implements tcpip.Endpoint.Connect. Packet sockets cannot be
	// connected, and this function always returnes *tcpip.ErrNotSupported.
	func (*endpoint) Connect(addr tcpip.FullAddress) tcpip.Error {
	return &tcpip.ErrNotSupported{}
	}

	// Shutdown implements tcpip.Endpoint.Shutdown. Packet sockets cannot be used
	// with Shutdown, and this function always returns *tcpip.ErrNotSupported.
	func (*endpoint) Shutdown(flags tcpip.ShutdownFlags) tcpip.Error {
	return &tcpip.ErrNotSupported{}
	}

	// Listen implements tcpip.Endpoint.Listen. Packet sockets cannot be used with
	// Listen, and this function always returns *tcpip.ErrNotSupported.
	func (*endpoint) Listen(backlog int) tcpip.Error {
	return &tcpip.ErrNotSupported{}
	}

	// Accept implements tcpip.Endpoint.Accept. Packet sockets cannot be used with
	// Accept, and this function always returns *tcpip.ErrNotSupported.
	func (endpoint) Accept(tcpip.FullAddress) (tcpip.Endpoint, *waiter.Queue, tcpip.Error) {
	return nil, nil, &tcpip.ErrNotSupported{}
	}

	// Bind implements tcpip.Endpoint.Bind.
	func (ep *endpoint) Bind(addr tcpip.FullAddress) tcpip.Error {
	// TODO(gvisor.dev/issue/173): Add Bind support.

	// "By default, all packets of the specified protocol type are passed
	// to a packet socket. To get packets only from a specific interface
	// use bind(2) specifying an address in a struct sockaddr_ll to bind
	// the packet socket to an interface. Fields used for binding are
	// sll_family (should be AF_PACKET), sll_protocol, and sll_ifindex."
	// - packet(7).

	ep.mu.Lock()
	defer ep.mu.Unlock()

	if ep.bound && ep.boundNIC == addr.NIC {
	// If the NIC being bound is the same then just return success.
	return nil
	}

	// Unregister endpoint with all the nics.
	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)
	ep.bound = false

	// Bind endpoint to receive packets from specific interface.
	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, ep.netProto, ep); err != nil {
	return err
	}

	ep.bound = true
	ep.boundNIC = addr.NIC

	return nil
	}

	// GetLocalAddress implements tcpip.Endpoint.GetLocalAddress.
	func (*endpoint) GetLocalAddress() (tcpip.FullAddress, tcpip.Error) {
	return tcpip.FullAddress{}, &tcpip.ErrNotSupported{}
	}

	// GetRemoteAddress implements tcpip.Endpoint.GetRemoteAddress.
	func (*endpoint) GetRemoteAddress() (tcpip.FullAddress, tcpip.Error) {
	// Even a connected socket doesn't return a remote address.
	return tcpip.FullAddress{}, &tcpip.ErrNotConnected{}
	}

	// Readiness implements tcpip.Endpoint.Readiness.
	func (ep *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
	// The endpoint is always writable.
	result := waiter.EventOut & mask

	// Determine whether the endpoint is readable.
	if (mask & waiter.EventIn) != 0 {
	ep.rcvMu.Lock()
	if !ep.rcvList.Empty() \|\| ep.rcvClosed {
	result \|= waiter.EventIn
	}
	ep.rcvMu.Unlock()
	}

	return result
	}

	// SetSockOpt implements tcpip.Endpoint.SetSockOpt. Packet sockets cannot be
	// used with SetSockOpt, and this function always returns
	// *tcpip.ErrNotSupported.
	func (ep *endpoint) SetSockOpt(opt tcpip.SettableSocketOption) tcpip.Error {
	switch opt.(type) {
	case *tcpip.SocketDetachFilterOption:
	return nil

	default:
	return &tcpip.ErrUnknownProtocolOption{}
	}
	}

	// SetSockOptInt implements tcpip.Endpoint.SetSockOptInt.
	func (ep *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) tcpip.Error {
	switch opt {
	case tcpip.ReceiveBufferSizeOption:
	// Make sure the receive buffer size is within the min and max
	// allowed.
	var rs stack.ReceiveBufferSizeOption
	if err := ep.stack.Option(&rs); err != nil {
	panic(fmt.Sprintf("s.Option(%#v) = %s", rs, err))
	}
	if v > rs.Max {
	v = rs.Max
	}
	if v < rs.Min {
	v = rs.Min
	}
	ep.rcvMu.Lock()
	ep.rcvBufSizeMax = v
	ep.rcvMu.Unlock()
	return nil

	default:
	return &tcpip.ErrUnknownProtocolOption{}
	}
	}

	func (ep *endpoint) LastError() tcpip.Error {
	ep.lastErrorMu.Lock()
	defer ep.lastErrorMu.Unlock()

	err := ep.lastError
	ep.lastError = nil
	return err
	}

	// UpdateLastError implements tcpip.SocketOptionsHandler.UpdateLastError.
	func (ep *endpoint) UpdateLastError(err tcpip.Error) {
	ep.lastErrorMu.Lock()
	ep.lastError = err
	ep.lastErrorMu.Unlock()
	}

	// GetSockOpt implements tcpip.Endpoint.GetSockOpt.
	func (ep *endpoint) GetSockOpt(opt tcpip.GettableSocketOption) tcpip.Error {
	return &tcpip.ErrNotSupported{}
	}

	// GetSockOptInt implements tcpip.Endpoint.GetSockOptInt.
	func (ep *endpoint) GetSockOptInt(opt tcpip.SockOptInt) (int, tcpip.Error) {
	switch opt {
	case tcpip.ReceiveQueueSizeOption:
	v := 0
	ep.rcvMu.Lock()
	if !ep.rcvList.Empty() {
	p := ep.rcvList.Front()
	v = p.data.Size()
	}
	ep.rcvMu.Unlock()
	return v, nil

	case tcpip.ReceiveBufferSizeOption:
	ep.rcvMu.Lock()
	v := ep.rcvBufSizeMax
	ep.rcvMu.Unlock()
	return v, nil

	default:
	return -1, &tcpip.ErrUnknownProtocolOption{}
	}
	}

	// HandlePacket implements stack.PacketEndpoint.HandlePacket.
	func (ep endpoint) HandlePacket(nicID tcpip.NICID, localAddr tcpip.LinkAddress, netProto tcpip.NetworkProtocolNumber, pkt stack.PacketBuffer) {
	ep.rcvMu.Lock()

	// Drop the packet if our buffer is currently full.
	if ep.rcvClosed {
	ep.rcvMu.Unlock()
	ep.stack.Stats().DroppedPackets.Increment()
	ep.stats.ReceiveErrors.ClosedReceiver.Increment()
	return
	}

	if ep.rcvBufSize >= ep.rcvBufSizeMax {
	ep.rcvMu.Unlock()
	ep.stack.Stats().DroppedPackets.Increment()
	ep.stats.ReceiveErrors.ReceiveBufferOverflow.Increment()
	return
	}

	wasEmpty := ep.rcvBufSize == 0

	// Push new packet into receive list and increment the buffer size.
	var packet packet
	// TODO(gvisor.dev/issue/173): Return network protocol.
	if !pkt.LinkHeader().View().IsEmpty() {
	// Get info directly from the ethernet header.
	hdr := header.Ethernet(pkt.LinkHeader().View())
	packet.senderAddr = tcpip.FullAddress{
	NIC: nicID,
	Addr: tcpip.Address(hdr.SourceAddress()),
	}
	packet.packetInfo.Protocol = netProto
	packet.packetInfo.PktType = pkt.PktType
	} else {
	// Guess the would-be ethernet header.
	packet.senderAddr = tcpip.FullAddress{
	NIC: nicID,
	Addr: tcpip.Address(localAddr),
	}
	packet.packetInfo.Protocol = netProto
	packet.packetInfo.PktType = pkt.PktType
	}

	if ep.cooked {
	// Cooked packets can simply be queued.
	switch pkt.PktType {
	case tcpip.PacketHost:
	packet.data = pkt.Data().ExtractVV()
	case tcpip.PacketOutgoing:
	// Strip Link Header.
	var combinedVV buffer.VectorisedView
	if v := pkt.NetworkHeader().View(); !v.IsEmpty() {
	combinedVV.AppendView(v)
	}
	if v := pkt.TransportHeader().View(); !v.IsEmpty() {
	combinedVV.AppendView(v)
	}
	combinedVV.Append(pkt.Data().ExtractVV())
	packet.data = combinedVV
	default:
	panic(fmt.Sprintf("unexpected PktType in pkt: %+v", pkt))
	}

	} else {
	// Raw packets need their ethernet headers prepended before
	// queueing.
	var linkHeader buffer.View
	if pkt.PktType != tcpip.PacketOutgoing {
	if pkt.LinkHeader().View().IsEmpty() {
	// We weren't provided with an actual ethernet header,
	// so fake one.
	ethFields := header.EthernetFields{
	SrcAddr: tcpip.LinkAddress([]byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00}),
	DstAddr: localAddr,
	Type: netProto,
	}
	fakeHeader := make(header.Ethernet, header.EthernetMinimumSize)
	fakeHeader.Encode(&ethFields)
	linkHeader = buffer.View(fakeHeader)
	} else {
	linkHeader = append(buffer.View(nil), pkt.LinkHeader().View()...)
	}
	combinedVV := linkHeader.ToVectorisedView()
	combinedVV.Append(pkt.Data().ExtractVV())
	packet.data = combinedVV
	} else {
	packet.data = buffer.NewVectorisedView(pkt.Size(), pkt.Views())
	}
	}
	packet.timestampNS = ep.stack.Clock().NowNanoseconds()

	ep.rcvList.PushBack(&packet)
	ep.rcvBufSize += packet.data.Size()

	ep.rcvMu.Unlock()
	ep.stats.PacketsReceived.Increment()
	// Notify waiters that there's data to be read.
	if wasEmpty {
	ep.waiterQueue.Notify(waiter.EventIn)
	}
	}

	// State implements socket.Socket.State.
	func (*endpoint) State() uint32 {
	return 0
	}

	// Info returns a copy of the endpoint info.
	func (ep *endpoint) Info() tcpip.EndpointInfo {
	ep.mu.RLock()
	// Make a copy of the endpoint info.
	ret := ep.TransportEndpointInfo
	ep.mu.RUnlock()
	return &ret
	}

	// Stats returns a pointer to the endpoint stats.
	func (ep *endpoint) Stats() tcpip.EndpointStats {
	return &ep.stats
	}

	// SetOwner implements tcpip.Endpoint.SetOwner.
	func (ep *endpoint) SetOwner(owner tcpip.PacketOwner) {}

	// SocketOptions implements tcpip.Endpoint.SocketOptions.
	func (ep endpoint) SocketOptions() tcpip.SocketOptions {
	return &ep.ops
	}