Make HandleLocal apply to all non-loopback interfaces.

HandleLocal is very similar conceptually to MULTICAST_LOOP, so we can unify
the implementations. This has the benefit of making HandleLocal apply even when
the fdbased link endpoint isn't in use.

In addition, move looping logic to route creation so that it doesn't need to be
run for each packet. This should improve performance.

PiperOrigin-RevId: 238099480
Change-Id: I72839f16f25310471453bc9d3fb8544815b25c23

1 files changed, 12 insertions, 9 deletions

diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index c9603ad5e..86fb728b2 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -47,19 +47,27 @@ type Route struct {
 	// starts.
 	ref *referencedNetworkEndpoint
 
-	multicastLoop bool
+	// loop controls where WritePacket should send packets.
+	loop PacketLooping
 }
 
 // makeRoute initializes a new route. It takes ownership of the provided
 // reference to a network endpoint.
-func makeRoute(netProto tcpip.NetworkProtocolNumber, localAddr, remoteAddr tcpip.Address, localLinkAddr tcpip.LinkAddress, ref *referencedNetworkEndpoint, multicastLoop bool) Route {
+func makeRoute(netProto tcpip.NetworkProtocolNumber, localAddr, remoteAddr tcpip.Address, localLinkAddr tcpip.LinkAddress, ref *referencedNetworkEndpoint, handleLocal, multicastLoop bool) Route {
+	loop := PacketOut
+	if handleLocal && localAddr != "" && remoteAddr == localAddr {
+		loop = PacketLoop
+	} else if multicastLoop && (header.IsV4MulticastAddress(remoteAddr) || header.IsV6MulticastAddress(remoteAddr)) {
+		loop |= PacketLoop
+	}
+
 	return Route{
 		NetProto:         netProto,
 		LocalAddress:     localAddr,
 		LocalLinkAddress: localLinkAddr,
 		RemoteAddress:    remoteAddr,
 		ref:              ref,
-		multicastLoop:    multicastLoop,
+		loop:             loop,
 	}
 }
 
@@ -137,12 +145,7 @@ func (r *Route) IsResolutionRequired() bool {
 
 // WritePacket writes the packet through the given route.
 func (r *Route) WritePacket(hdr buffer.Prependable, payload buffer.VectorisedView, protocol tcpip.TransportProtocolNumber, ttl uint8) *tcpip.Error {
-	loop := PacketOut
-	if r.multicastLoop && (header.IsV4MulticastAddress(r.RemoteAddress) || header.IsV6MulticastAddress(r.RemoteAddress)) {
-		loop |= PacketLoop
-	}
-
-	err := r.ref.ep.WritePacket(r, hdr, payload, protocol, ttl, loop)
+	err := r.ref.ep.WritePacket(r, hdr, payload, protocol, ttl, r.loop)
 	if err == tcpip.ErrNoRoute {
 		r.Stats().IP.OutgoingPacketErrors.Increment()
 	}