From cc5cfce4c6c9df1a44433681b87d411a67b09b28 Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Mon, 16 Nov 2020 14:32:57 -0800
Subject: Remove ARP address workaround

- Make AddressableEndpoint optional for NetworkEndpoint.
Not all NetworkEndpoints need to support addressing (e.g. ARP), so
AddressableEndpoint should only be implemented for protocols that
support addressing such as IPv4 and IPv6.

With this change, tcpip.ErrNotSupported will be returned by the stack
when attempting to modify addresses on a network endpoint that does
not support addressing.

Now that packets are fully handled at the network layer, and (with this
change) addresses are optional for network endpoints, we no longer need
the workaround for ARP where a fake ARP address was added to each NIC
that performs ARP so that packets would be delivered to the ARP layer.

PiperOrigin-RevId: 342722547
---
 pkg/tcpip/network/arp/arp.go | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

(limited to 'pkg/tcpip/network/arp/arp.go')

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 33a4a0720..3d5c0d270 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -31,17 +31,15 @@ import (
 const (
 	// ProtocolNumber is the ARP protocol number.
 	ProtocolNumber = header.ARPProtocolNumber
-
-	// ProtocolAddress is the address expected by the ARP endpoint.
-	ProtocolAddress = tcpip.Address("arp")
 )
 
-var _ stack.AddressableEndpoint = (*endpoint)(nil)
+// ARP endpoints need to implement stack.NetworkEndpoint because the stack
+// considers the layer above the link-layer a network layer; the only
+// facility provided by the stack to deliver packets to a layer above
+// the link-layer is via stack.NetworkEndpoint.HandlePacket.
 var _ stack.NetworkEndpoint = (*endpoint)(nil)
 
 type endpoint struct {
-	stack.AddressableEndpointState
-
 	protocol *protocol
 
 	// enabled is set to 1 when the NIC is enabled and 0 when it is disabled.
@@ -87,7 +85,7 @@ func (e *endpoint) Disable() {
 }
 
 // DefaultTTL is unused for ARP. It implements stack.NetworkEndpoint.
-func (e *endpoint) DefaultTTL() uint8 {
+func (*endpoint) DefaultTTL() uint8 {
 	return 0
 }
 
@@ -100,25 +98,23 @@ func (e *endpoint) MaxHeaderLength() uint16 {
 	return e.nic.MaxHeaderLength() + header.ARPSize
 }
 
-func (e *endpoint) Close() {
-	e.AddressableEndpointState.Cleanup()
-}
+func (*endpoint) Close() {}
 
-func (e *endpoint) WritePacket(*stack.Route, *stack.GSO, stack.NetworkHeaderParams, *stack.PacketBuffer) *tcpip.Error {
+func (*endpoint) WritePacket(*stack.Route, *stack.GSO, stack.NetworkHeaderParams, *stack.PacketBuffer) *tcpip.Error {
 	return tcpip.ErrNotSupported
 }
 
 // NetworkProtocolNumber implements stack.NetworkEndpoint.NetworkProtocolNumber.
-func (e *endpoint) NetworkProtocolNumber() tcpip.NetworkProtocolNumber {
+func (*endpoint) NetworkProtocolNumber() tcpip.NetworkProtocolNumber {
 	return ProtocolNumber
 }
 
 // WritePackets implements stack.NetworkEndpoint.WritePackets.
-func (e *endpoint) WritePackets(*stack.Route, *stack.GSO, stack.PacketBufferList, stack.NetworkHeaderParams) (int, *tcpip.Error) {
+func (*endpoint) WritePackets(*stack.Route, *stack.GSO, stack.PacketBufferList, stack.NetworkHeaderParams) (int, *tcpip.Error) {
 	return 0, tcpip.ErrNotSupported
 }
 
-func (e *endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt *stack.PacketBuffer) *tcpip.Error {
+func (*endpoint) WriteHeaderIncludedPacket(*stack.Route, *stack.PacketBuffer) *tcpip.Error {
 	return tcpip.ErrNotSupported
 }
 
@@ -216,9 +212,8 @@ func (p *protocol) Number() tcpip.NetworkProtocolNumber { return ProtocolNumber
 func (p *protocol) MinimumPacketSize() int              { return header.ARPSize }
 func (p *protocol) DefaultPrefixLen() int               { return 0 }
 
-func (*protocol) ParseAddresses(v buffer.View) (src, dst tcpip.Address) {
-	h := header.ARP(v)
-	return tcpip.Address(h.ProtocolAddressSender()), ProtocolAddress
+func (*protocol) ParseAddresses(buffer.View) (src, dst tcpip.Address) {
+	return "", ""
 }
 
 func (p *protocol) NewEndpoint(nic stack.NetworkInterface, linkAddrCache stack.LinkAddressCache, nud stack.NUDHandler, dispatcher stack.TransportDispatcher) stack.NetworkEndpoint {
@@ -228,7 +223,6 @@ func (p *protocol) NewEndpoint(nic stack.NetworkInterface, linkAddrCache stack.L
 		linkAddrCache: linkAddrCache,
 		nud:           nud,
 	}
-	e.AddressableEndpointState.Init(e)
 	return e
 }
 
@@ -311,10 +305,6 @@ func (*protocol) Parse(pkt *stack.PacketBuffer) (proto tcpip.TransportProtocolNu
 }
 
 // NewProtocol returns an ARP network protocol.
-//
-// Note, to make sure that the ARP endpoint receives ARP packets, the "arp"
-// address must be added to every NIC that should respond to ARP requests. See
-// ProtocolAddress for more details.
 func NewProtocol(s *stack.Stack) stack.NetworkProtocol {
 	return &protocol{stack: s}
 }
-- 
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