2 files changed, 19 insertions, 4 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)
+}
diff --git a/pkg/tcpip/transport/udp/endpoint_state.go b/pkg/tcpip/transport/udp/endpoint_state.go
index 4a3c30115..5cbb56120 100644
--- a/pkg/tcpip/transport/udp/endpoint_state.go
+++ b/pkg/tcpip/transport/udp/endpoint_state.go
@@ -97,7 +97,8 @@ func (e *endpoint) Resume(s *stack.Stack) {
 		if err != nil {
 			panic(err)
 		}
-	} else if len(e.id.LocalAddress) != 0 { // stateBound
+	} else if len(e.id.LocalAddress) != 0 && !isBroadcastOrMulticast(e.id.LocalAddress) { // stateBound
+		// A local unicast address is specified, verify that it's valid.
 		if e.stack.CheckLocalAddress(e.regNICID, netProto, e.id.LocalAddress) == 0 {
 			panic(tcpip.ErrBadLocalAddress)
 		}