Support binding to multicast and broadcast addresses

This fixes the issue of not being able to bind to either a multicast or
broadcast address as well as to send and receive data from it. The way to solve
this is to treat these addresses similar to the ANY address and register their
transport endpoint ID with the global stack's demuxer rather than the NIC's.
That way there is no need to require an endpoint with that multicast or
broadcast address. The stack's demuxer is in fact the only correct one to use,
because neither broadcast- nor multicast-bound sockets care which NIC a
packet was received on (for multicast a join is still needed to receive packets
on a NIC).

I also took the liberty of refactoring udp_test.go to consolidate a lot of
duplicate code and make it easier to create repetitive tests that test the same
feature for a variety of packet and socket types. For this purpose I created a
"flowType" that represents two things: 1) the type of packet being sent or
received and 2) the type of socket used for the test. E.g., a "multicastV4in6"
flow represents a V4-mapped multicast packet run through a V6-dual socket.

This allows writing significantly simpler tests. A nice example is testTTL().

PiperOrigin-RevId: 264766909

1 files changed, 17 insertions, 3 deletions

diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 935ac622e..ac5905772 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -249,6 +249,11 @@ func (e *endpoint) prepareForWrite(to *tcpip.FullAddress) (retry bool, err *tcpi
 // specified address is a multicast address.
 func (e *endpoint) connectRoute(nicid tcpip.NICID, addr tcpip.FullAddress, netProto tcpip.NetworkProtocolNumber) (stack.Route, tcpip.NICID, *tcpip.Error) {
 	localAddr := e.id.LocalAddress
+	if isBroadcastOrMulticast(localAddr) {
+		// A packet can only originate from a unicast address (i.e., an interface).
+		localAddr = ""
+	}
+
 	if header.IsV4MulticastAddress(addr.Addr) || header.IsV6MulticastAddress(addr.Addr) {
 		if nicid == 0 {
 			nicid = e.multicastNICID
@@ -448,7 +453,12 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		}
 
 		nicID := v.NIC
-		if v.InterfaceAddr == header.IPv4Any {
+
+		// The interface address is considered not-set if it is empty or contains
+		// all-zeros. The former represent the zero-value in golang, the latter the
+		// same in a setsockopt(IP_ADD_MEMBERSHIP, &ip_mreqn) syscall.
+		allZeros := header.IPv4Any
+		if len(v.InterfaceAddr) == 0 || v.InterfaceAddr == allZeros {
 			if nicID == 0 {
 				r, err := e.stack.FindRoute(0, "", v.MulticastAddr, header.IPv4ProtocolNumber, false /* multicastLoop */)
 				if err == nil {
@@ -914,8 +924,8 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 	}
 
 	nicid := addr.NIC
-	if len(addr.Addr) != 0 {
-		// A local address was specified, verify that it's valid.
+	if len(addr.Addr) != 0 && !isBroadcastOrMulticast(addr.Addr) {
+		// A local unicast address was specified, verify that it's valid.
 		nicid = e.stack.CheckLocalAddress(addr.NIC, netProto, addr.Addr)
 		if nicid == 0 {
 			return tcpip.ErrBadLocalAddress
@@ -1064,3 +1074,7 @@ func (e *endpoint) State() uint32 {
 	// TODO(b/112063468): Translate internal state to values returned by Linux.
 	return 0
 }
+
+func isBroadcastOrMulticast(a tcpip.Address) bool {
+	return a == header.IPv4Broadcast || header.IsV4MulticastAddress(a) || header.IsV6MulticastAddress(a)
+}