Do not filter frames in ethernet link endpoint

Ethernet frames are usually filtered at the hardware-level so there is
no need to filter the frames in software.

For test purposes, a new link endpoint was introduced to filter frames
based on their destination.

PiperOrigin-RevId: 350422941

3 files changed, 89 insertions, 4 deletions

diff --git a/pkg/tcpip/link/ethernet/BUILD b/pkg/tcpip/link/ethernet/BUILD
index ec92ed623..0ae0d201a 100644
--- a/pkg/tcpip/link/ethernet/BUILD
+++ b/pkg/tcpip/link/ethernet/BUILD
@@ -1,4 +1,4 @@
-load("//tools:defs.bzl", "go_library")
+load("//tools:defs.bzl", "go_library", "go_test")
 
 package(licenses = ["notice"])
 
@@ -13,3 +13,17 @@ go_library(
         "//pkg/tcpip/stack",
     ],
 )
+
+go_test(
+    name = "ethernet_test",
+    size = "small",
+    srcs = ["ethernet_test.go"],
+    deps = [
+        ":ethernet",
+        "//pkg/tcpip",
+        "//pkg/tcpip/buffer",
+        "//pkg/tcpip/header",
+        "//pkg/tcpip/link/channel",
+        "//pkg/tcpip/stack",
+    ],
+)
diff --git a/pkg/tcpip/link/ethernet/ethernet.go b/pkg/tcpip/link/ethernet/ethernet.go
index beefcd008..89e3e6164 100644
--- a/pkg/tcpip/link/ethernet/ethernet.go
+++ b/pkg/tcpip/link/ethernet/ethernet.go
@@ -49,10 +49,10 @@ func (e *Endpoint) DeliverNetworkPacket(_, _ tcpip.LinkAddress, _ tcpip.NetworkP
 		return
 	}
 
+	// Note, there is no need to check the destination link address here since
+	// the ethernet hardware filters frames based on their destination addresses.
 	eth := header.Ethernet(hdr)
-	if dst := eth.DestinationAddress(); dst == e.Endpoint.LinkAddress() || dst == header.EthernetBroadcastAddress || header.IsMulticastEthernetAddress(dst) {
-		e.Endpoint.DeliverNetworkPacket(eth.SourceAddress() /* remote */, dst /* local */, eth.Type() /* protocol */, pkt)
-	}
+	e.Endpoint.DeliverNetworkPacket(eth.SourceAddress() /* remote */, eth.DestinationAddress() /* local */, eth.Type() /* protocol */, pkt)
 }
 
 // Capabilities implements stack.LinkEndpoint.
diff --git a/pkg/tcpip/link/ethernet/ethernet_test.go b/pkg/tcpip/link/ethernet/ethernet_test.go
new file mode 100644
index 000000000..08a7f1ce1
--- /dev/null
+++ b/pkg/tcpip/link/ethernet/ethernet_test.go
@@ -0,0 +1,71 @@
+// Copyright 2021 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 ethernet_test
+
+import (
+	"testing"
+
+	"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/link/ethernet"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+var _ stack.NetworkDispatcher = (*testNetworkDispatcher)(nil)
+
+type testNetworkDispatcher struct {
+	networkPackets int
+}
+
+func (t *testNetworkDispatcher) DeliverNetworkPacket(_, _ tcpip.LinkAddress, _ tcpip.NetworkProtocolNumber, _ *stack.PacketBuffer) {
+	t.networkPackets++
+}
+
+func (*testNetworkDispatcher) DeliverOutboundPacket(_, _ tcpip.LinkAddress, _ tcpip.NetworkProtocolNumber, _ *stack.PacketBuffer) {
+}
+
+func TestDeliverNetworkPacket(t *testing.T) {
+	const (
+		linkAddr       = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06")
+		otherLinkAddr1 = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x07")
+		otherLinkAddr2 = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x08")
+	)
+
+	e := ethernet.New(channel.New(0, 0, linkAddr))
+	var networkDispatcher testNetworkDispatcher
+	e.Attach(&networkDispatcher)
+
+	if networkDispatcher.networkPackets != 0 {
+		t.Fatalf("got networkDispatcher.networkPackets = %d, want = 0", networkDispatcher.networkPackets)
+	}
+
+	// An ethernet frame with a destination link address that is not assigned to
+	// our ethernet link endpoint should still be delivered to the network
+	// dispatcher since the ethernet endpoint is not expected to filter frames.
+	eth := buffer.NewView(header.EthernetMinimumSize)
+	header.Ethernet(eth).Encode(&header.EthernetFields{
+		SrcAddr: otherLinkAddr1,
+		DstAddr: otherLinkAddr2,
+		Type:    header.IPv4ProtocolNumber,
+	})
+	e.DeliverNetworkPacket("", "", 0, stack.NewPacketBuffer(stack.PacketBufferOptions{
+		Data: eth.ToVectorisedView(),
+	}))
+	if networkDispatcher.networkPackets != 1 {
+		t.Fatalf("got networkDispatcher.networkPackets = %d, want = 1", networkDispatcher.networkPackets)
+	}
+}