Pass local link address to DeliverNetworkPacket

This allows a NetworkDispatcher to implement transparent bridging,
assuming all implementations of LinkEndpoint.WritePacket call eth.Encode
with header.EthernetFields.SrcAddr set to the passed
Route.LocalLinkAddress, if it is provided.

PiperOrigin-RevId: 213686651
Change-Id: I446a4ac070970202f0724ef796ff1056ae4dd72a

2 files changed, 118 insertions, 53 deletions

diff --git a/pkg/tcpip/link/sharedmem/sharedmem.go b/pkg/tcpip/link/sharedmem/sharedmem.go
index 5157f71e8..ce6e86767 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem.go
@@ -187,11 +187,16 @@ func (e *endpoint) LinkAddress() tcpip.LinkAddress {
 func (e *endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.NetworkProtocolNumber) *tcpip.Error {
 	// Add the ethernet header here.
 	eth := header.Ethernet(hdr.Prepend(header.EthernetMinimumSize))
-	eth.Encode(&header.EthernetFields{
+	ethHdr := &header.EthernetFields{
 		DstAddr: r.RemoteLinkAddress,
-		SrcAddr: e.addr,
 		Type:    protocol,
-	})
+	}
+	if r.LocalLinkAddress != "" {
+		ethHdr.SrcAddr = r.LocalLinkAddress
+	} else {
+		ethHdr.SrcAddr = e.addr
+	}
+	eth.Encode(ethHdr)
 
 	v := payload.ToView()
 	// Transmit the packet.
@@ -248,7 +253,7 @@ func (e *endpoint) dispatchLoop(d stack.NetworkDispatcher) {
 
 		// Send packet up the stack.
 		eth := header.Ethernet(b)
-		d.DeliverNetworkPacket(e, eth.SourceAddress(), eth.Type(), buffer.View(b[header.EthernetMinimumSize:]).ToVectorisedView())
+		d.DeliverNetworkPacket(e, eth.SourceAddress(), eth.DestinationAddress(), eth.Type(), buffer.View(b[header.EthernetMinimumSize:]).ToVectorisedView())
 	}
 
 	// Clean state.
diff --git a/pkg/tcpip/link/sharedmem/sharedmem_test.go b/pkg/tcpip/link/sharedmem/sharedmem_test.go
index 9a0348deb..9a6b7d929 100644
--- a/pkg/tcpip/link/sharedmem/sharedmem_test.go
+++ b/pkg/tcpip/link/sharedmem/sharedmem_test.go
@@ -17,10 +17,12 @@
 package sharedmem
 
 import (
+	"bytes"
 	"io/ioutil"
 	"math/rand"
 	"os"
 	"reflect"
+	"strings"
 	"sync"
 	"syscall"
 	"testing"
@@ -129,10 +131,10 @@ func newTestContext(t *testing.T, mtu, bufferSize uint32, addr tcpip.LinkAddress
 	return c
 }
 
-func (c *testContext) DeliverNetworkPacket(_ stack.LinkEndpoint, remoteAddr tcpip.LinkAddress, proto tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
+func (c *testContext) DeliverNetworkPacket(_ stack.LinkEndpoint, remoteLinkAddr, localLinkAddr tcpip.LinkAddress, proto tcpip.NetworkProtocolNumber, vv buffer.VectorisedView) {
 	c.mu.Lock()
 	c.packets = append(c.packets, packetInfo{
-		addr:  remoteAddr,
+		addr:  remoteLinkAddr,
 		proto: proto,
 		vv:    vv.Clone(nil),
 	})
@@ -259,62 +261,120 @@ func TestSimpleSend(t *testing.T) {
 	}
 
 	for iters := 1000; iters > 0; iters-- {
-		// Prepare and send packet.
-		n := rand.Intn(10000)
-		hdr := buffer.NewPrependable(n + int(c.ep.MaxHeaderLength()))
-		hdrBuf := hdr.Prepend(n)
-		randomFill(hdrBuf)
-
-		n = rand.Intn(10000)
-		buf := buffer.NewView(n)
-		randomFill(buf)
-
-		proto := tcpip.NetworkProtocolNumber(rand.Intn(0x10000))
-		if err := c.ep.WritePacket(&r, hdr, buf.ToVectorisedView(), proto); err != nil {
-			t.Fatalf("WritePacket failed: %v", err)
-		}
+		func() {
+			// Prepare and send packet.
+			n := rand.Intn(10000)
+			hdr := buffer.NewPrependable(n + int(c.ep.MaxHeaderLength()))
+			hdrBuf := hdr.Prepend(n)
+			randomFill(hdrBuf)
+
+			n = rand.Intn(10000)
+			buf := buffer.NewView(n)
+			randomFill(buf)
+
+			proto := tcpip.NetworkProtocolNumber(rand.Intn(0x10000))
+			if err := c.ep.WritePacket(&r, hdr, buf.ToVectorisedView(), proto); err != nil {
+				t.Fatalf("WritePacket failed: %v", err)
+			}
 
-		// Receive packet.
-		desc := c.txq.tx.Pull()
-		pi := queue.DecodeTxPacketHeader(desc)
-		contents := make([]byte, 0, pi.Size)
-		for i := 0; i < pi.BufferCount; i++ {
-			bi := queue.DecodeTxBufferHeader(desc, i)
-			contents = append(contents, c.txq.data[bi.Offset:][:bi.Size]...)
-		}
-		c.txq.tx.Flush()
+			// Receive packet.
+			desc := c.txq.tx.Pull()
+			pi := queue.DecodeTxPacketHeader(desc)
+			if pi.Reserved != 0 {
+				t.Fatalf("Reserved value is non-zero: 0x%x", pi.Reserved)
+			}
+			contents := make([]byte, 0, pi.Size)
+			for i := 0; i < pi.BufferCount; i++ {
+				bi := queue.DecodeTxBufferHeader(desc, i)
+				contents = append(contents, c.txq.data[bi.Offset:][:bi.Size]...)
+			}
+			c.txq.tx.Flush()
+
+			defer func() {
+				// Tell the endpoint about the completion of the write.
+				b := c.txq.rx.Push(8)
+				queue.EncodeTxCompletion(b, pi.ID)
+				c.txq.rx.Flush()
+			}()
+
+			// Check the ethernet header.
+			ethTemplate := make(header.Ethernet, header.EthernetMinimumSize)
+			ethTemplate.Encode(&header.EthernetFields{
+				SrcAddr: localLinkAddr,
+				DstAddr: remoteLinkAddr,
+				Type:    proto,
+			})
+			if got := contents[:header.EthernetMinimumSize]; !bytes.Equal(got, []byte(ethTemplate)) {
+				t.Fatalf("Bad ethernet header in packet: got %x, want %x", got, ethTemplate)
+			}
 
-		if pi.Reserved != 0 {
-			t.Fatalf("Reserved value is non-zero: 0x%x", pi.Reserved)
-		}
+			// Compare contents skipping the ethernet header added by the
+			// endpoint.
+			merged := append(hdrBuf, buf...)
+			if uint32(len(contents)) < pi.Size {
+				t.Fatalf("Sum of buffers is less than packet size: %v < %v", len(contents), pi.Size)
+			}
+			contents = contents[:pi.Size][header.EthernetMinimumSize:]
 
-		// Check the thernet header.
-		ethTemplate := make(header.Ethernet, header.EthernetMinimumSize)
-		ethTemplate.Encode(&header.EthernetFields{
-			SrcAddr: localLinkAddr,
-			DstAddr: remoteLinkAddr,
-			Type:    proto,
-		})
-		if got := contents[:header.EthernetMinimumSize]; !reflect.DeepEqual(got, []byte(ethTemplate)) {
-			t.Fatalf("Bad ethernet header in packet: got %x, want %x", got, ethTemplate)
-		}
+			if !bytes.Equal(contents, merged) {
+				t.Fatalf("Buffers are different: got %x (%v bytes), want %x (%v bytes)", contents, len(contents), merged, len(merged))
+			}
+		}()
+	}
+}
 
-		// Compare contents skipping the ethernet header added by the
-		// endpoint.
-		merged := append(hdrBuf, buf...)
-		if uint32(len(contents)) < pi.Size {
-			t.Fatalf("Sum of buffers is less than packet size: %v < %v", len(contents), pi.Size)
-		}
-		contents = contents[:pi.Size][header.EthernetMinimumSize:]
+// TestPreserveSrcAddressInSend calls WritePacket once with LocalLinkAddress
+// set in Route (using much of the same code as TestSimpleSend), then checks
+// that the encoded ethernet header received includes the correct SrcAddr.
+func TestPreserveSrcAddressInSend(t *testing.T) {
+	c := newTestContext(t, 20000, 1500, localLinkAddr)
+	defer c.cleanup()
 
-		if !reflect.DeepEqual(contents, merged) {
-			t.Fatalf("Buffers are different: got %x (%v bytes), want %x (%v bytes)", contents, len(contents), merged, len(merged))
-		}
+	newLocalLinkAddress := tcpip.LinkAddress(strings.Repeat("0xFE", 6))
+	// Set both remote and local link address in route.
+	r := stack.Route{
+		RemoteLinkAddress: remoteLinkAddr,
+		LocalLinkAddress:  newLocalLinkAddress,
+	}
+
+	// WritePacket panics given a prependable with anything less than
+	// the minimum size of the ethernet header.
+	hdr := buffer.NewPrependable(header.EthernetMinimumSize)
+
+	proto := tcpip.NetworkProtocolNumber(rand.Intn(0x10000))
+	if err := c.ep.WritePacket(&r, hdr, buffer.VectorisedView{}, proto); err != nil {
+		t.Fatalf("WritePacket failed: %v", err)
+	}
 
+	// Receive packet.
+	desc := c.txq.tx.Pull()
+	pi := queue.DecodeTxPacketHeader(desc)
+	if pi.Reserved != 0 {
+		t.Fatalf("Reserved value is non-zero: 0x%x", pi.Reserved)
+	}
+	contents := make([]byte, 0, pi.Size)
+	for i := 0; i < pi.BufferCount; i++ {
+		bi := queue.DecodeTxBufferHeader(desc, i)
+		contents = append(contents, c.txq.data[bi.Offset:][:bi.Size]...)
+	}
+	c.txq.tx.Flush()
+
+	defer func() {
 		// Tell the endpoint about the completion of the write.
 		b := c.txq.rx.Push(8)
 		queue.EncodeTxCompletion(b, pi.ID)
 		c.txq.rx.Flush()
+	}()
+
+	// Check that the ethernet header contains the expected SrcAddr.
+	ethTemplate := make(header.Ethernet, header.EthernetMinimumSize)
+	ethTemplate.Encode(&header.EthernetFields{
+		SrcAddr: newLocalLinkAddress,
+		DstAddr: remoteLinkAddr,
+		Type:    proto,
+	})
+	if got := contents[:header.EthernetMinimumSize]; !bytes.Equal(got, []byte(ethTemplate)) {
+		t.Fatalf("Bad ethernet header in packet: got %x, want %x", got, ethTemplate)
 	}
 }
 
@@ -583,7 +643,7 @@ func TestSimpleReceive(t *testing.T) {
 		c.mu.Unlock()
 
 		contents = contents[header.EthernetMinimumSize:]
-		if !reflect.DeepEqual(contents, rcvd) {
+		if !bytes.Equal(contents, rcvd) {
 			t.Fatalf("Unexpected buffer contents: got %x, want %x", rcvd, contents)
 		}