4 files changed, 49 insertions, 40 deletions

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index f6106f762..5993fe582 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -104,6 +104,16 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, loopback
 func (n *NIC) enable() *tcpip.Error {
 	n.attachLinkEndpoint()
 
+	// Create an endpoint to receive broadcast packets on this interface.
+	if _, ok := n.stack.networkProtocols[header.IPv4ProtocolNumber]; ok {
+		if err := n.AddAddress(tcpip.ProtocolAddress{
+			Protocol:          header.IPv4ProtocolNumber,
+			AddressWithPrefix: tcpip.AddressWithPrefix{header.IPv4Broadcast, 8 * header.IPv4AddressSize},
+		}, NeverPrimaryEndpoint); err != nil {
+			return err
+		}
+	}
+
 	// Join the IPv6 All-Nodes Multicast group if the stack is configured to
 	// use IPv6. This is required to ensure that this node properly receives
 	// and responds to the various NDP messages that are destined to the
@@ -372,7 +382,7 @@ func (n *NIC) AllAddresses() []tcpip.ProtocolAddress {
 
 	addrs := make([]tcpip.ProtocolAddress, 0, len(n.endpoints))
 	for nid, ref := range n.endpoints {
-		// Don't include expired or tempory endpoints to avoid confusion and
+		// Don't include expired or temporary endpoints to avoid confusion and
 		// prevent the caller from using those.
 		switch ref.getKind() {
 		case permanentExpired, temporary:
@@ -624,21 +634,6 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, _ tcpip.LinkAddr
 
 	n.stack.AddLinkAddress(n.id, src, remote)
 
-	// If the packet is destined to the IPv4 Broadcast address, then make a
-	// route to each IPv4 network endpoint and let each endpoint handle the
-	// packet.
-	if dst == header.IPv4Broadcast {
-		// n.endpoints is mutex protected so acquire lock.
-		n.mu.RLock()
-		for _, ref := range n.endpoints {
-			if ref.isValidForIncoming() && ref.protocol == header.IPv4ProtocolNumber && ref.tryIncRef() {
-				handlePacket(protocol, dst, src, linkEP.LinkAddress(), remote, ref, vv)
-			}
-		}
-		n.mu.RUnlock()
-		return
-	}
-
 	if ref := n.getRef(protocol, dst); ref != nil {
 		handlePacket(protocol, dst, src, linkEP.LinkAddress(), remote, ref, vv)
 		return
diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index 5c8b7977a..0b09e6517 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -59,6 +59,8 @@ func makeRoute(netProto tcpip.NetworkProtocolNumber, localAddr, remoteAddr tcpip
 		loop = PacketLoop
 	} else if multicastLoop && (header.IsV4MulticastAddress(remoteAddr) || header.IsV6MulticastAddress(remoteAddr)) {
 		loop |= PacketLoop
+	} else if remoteAddr == header.IPv4Broadcast {
+		loop |= PacketLoop
 	}
 
 	return Route{
@@ -208,10 +210,17 @@ func (r *Route) Clone() Route {
 	return *r
 }
 
-// MakeLoopedRoute duplicates the given route and tweaks it in case of multicast.
+// MakeLoopedRoute duplicates the given route with special handling for routes
+// used for sending multicast or broadcast packets. In those cases the
+// multicast/broadcast address is the remote address when sending out, but for
+// incoming (looped) packets it becomes the local address. Similarly, the local
+// interface address that was the local address going out becomes the remote
+// address coming in. This is different to unicast routes where local and
+// remote addresses remain the same as they identify location (local vs remote)
+// not direction (source vs destination).
 func (r *Route) MakeLoopedRoute() Route {
 	l := r.Clone()
-	if header.IsV4MulticastAddress(r.RemoteAddress) || header.IsV6MulticastAddress(r.RemoteAddress) {
+	if r.RemoteAddress == header.IPv4Broadcast || header.IsV4MulticastAddress(r.RemoteAddress) || header.IsV6MulticastAddress(r.RemoteAddress) {
 		l.RemoteAddress, l.LocalAddress = l.LocalAddress, l.RemoteAddress
 		l.RemoteLinkAddress = l.LocalLinkAddress
 	}
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 90c2cf1be..ff574a055 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -902,7 +902,7 @@ func (s *Stack) FindRoute(id tcpip.NICID, localAddr, remoteAddr tcpip.Address, n
 		}
 	} else {
 		for _, route := range s.routeTable {
-			if (id != 0 && id != route.NIC) || (len(remoteAddr) != 0 && !isBroadcast && !route.Destination.Contains(remoteAddr)) {
+			if (id != 0 && id != route.NIC) || (len(remoteAddr) != 0 && !route.Destination.Contains(remoteAddr)) {
 				continue
 			}
 			if nic, ok := s.nics[route.NIC]; ok {
diff --git a/pkg/tcpip/stack/transport_demuxer.go b/pkg/tcpip/stack/transport_demuxer.go
index 8c768c299..92267ce4d 100644
--- a/pkg/tcpip/stack/transport_demuxer.go
+++ b/pkg/tcpip/stack/transport_demuxer.go
@@ -63,7 +63,7 @@ func (epsByNic *endpointsByNic) handlePacket(r *Route, id TransportEndpointID, v
 
 	// If this is a broadcast or multicast datagram, deliver the datagram to all
 	// endpoints bound to the right device.
-	if id.LocalAddress == header.IPv4Broadcast || header.IsV4MulticastAddress(id.LocalAddress) || header.IsV6MulticastAddress(id.LocalAddress) {
+	if isMulticastOrBroadcast(id.LocalAddress) {
 		mpep.handlePacketAll(r, id, vv)
 		epsByNic.mu.RUnlock() // Don't use defer for performance reasons.
 		return
@@ -338,23 +338,14 @@ func (d *transportDemuxer) deliverPacket(r *Route, protocol tcpip.TransportProto
 		return false
 	}
 
-	// If a sender bound to the Loopback interface sends a broadcast,
-	// that broadcast must not be delivered to the sender.
-	if loopbackSubnet.Contains(r.RemoteAddress) && r.LocalAddress == header.IPv4Broadcast && id.LocalPort == id.RemotePort {
-		return false
-	}
-
-	// If the packet is a broadcast, then find all matching transport endpoints.
-	// Otherwise, try to find a single matching transport endpoint.
-	destEps := make([]*endpointsByNic, 0, 1)
 	eps.mu.RLock()
 
-	if protocol == header.UDPProtocolNumber && id.LocalAddress == header.IPv4Broadcast {
-		for epID, endpoint := range eps.endpoints {
-			if epID.LocalPort == id.LocalPort {
-				destEps = append(destEps, endpoint)
-			}
-		}
+	// Determine which transport endpoint or endpoints to deliver this packet to.
+	// If the packet is a broadcast or multicast, then find all matching
+	// transport endpoints.
+	var destEps []*endpointsByNic
+	if protocol == header.UDPProtocolNumber && isMulticastOrBroadcast(id.LocalAddress) {
+		destEps = d.findAllEndpointsLocked(eps, vv, id)
 	} else if ep := d.findEndpointLocked(eps, vv, id); ep != nil {
 		destEps = append(destEps, ep)
 	}
@@ -426,10 +417,11 @@ func (d *transportDemuxer) deliverControlPacket(n *NIC, net tcpip.NetworkProtoco
 	return true
 }
 
-func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, vv buffer.VectorisedView, id TransportEndpointID) *endpointsByNic {
+func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, vv buffer.VectorisedView, id TransportEndpointID) []*endpointsByNic {
+	var matchedEPs []*endpointsByNic
 	// Try to find a match with the id as provided.
 	if ep, ok := eps.endpoints[id]; ok {
-		return ep
+		matchedEPs = append(matchedEPs, ep)
 	}
 
 	// Try to find a match with the id minus the local address.
@@ -437,7 +429,7 @@ func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, vv buffer
 
 	nid.LocalAddress = ""
 	if ep, ok := eps.endpoints[nid]; ok {
-		return ep
+		matchedEPs = append(matchedEPs, ep)
 	}
 
 	// Try to find a match with the id minus the remote part.
@@ -445,15 +437,24 @@ func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, vv buffer
 	nid.RemoteAddress = ""
 	nid.RemotePort = 0
 	if ep, ok := eps.endpoints[nid]; ok {
-		return ep
+		matchedEPs = append(matchedEPs, ep)
 	}
 
 	// Try to find a match with only the local port.
 	nid.LocalAddress = ""
 	if ep, ok := eps.endpoints[nid]; ok {
-		return ep
+		matchedEPs = append(matchedEPs, ep)
 	}
 
+	return matchedEPs
+}
+
+// findEndpointLocked returns the endpoint that most closely matches the given
+// id.
+func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, vv buffer.VectorisedView, id TransportEndpointID) *endpointsByNic {
+	if matchedEPs := d.findAllEndpointsLocked(eps, vv, id); len(matchedEPs) > 0 {
+		return matchedEPs[0]
+	}
 	return nil
 }
 
@@ -491,3 +492,7 @@ func (d *transportDemuxer) unregisterRawEndpoint(netProto tcpip.NetworkProtocolN
 		}
 	}
 }
+
+func isMulticastOrBroadcast(addr tcpip.Address) bool {
+	return addr == header.IPv4Broadcast || header.IsV4MulticastAddress(addr) || header.IsV6MulticastAddress(addr)
+}