Support reception of multicast data on more than one socket

This requires two changes:
1) Support for more than one socket to join a given multicast group.

2) Duplicate delivery of incoming multicast packets to all sockets listening
for it.

In addition, I tweaked the code (and added a test) to disallow duplicates
IP_ADD_MEMBERSHIP calls for the same group and NIC. This is how Linux does
it.

PiperOrigin-RevId: 246437315
Change-Id: Icad8300b4a8c3f501d9b4cd283bd3beabef88b72

1 files changed, 6 insertions, 6 deletions

diff --git a/pkg/tcpip/transport/udp/endpoint_state.go b/pkg/tcpip/transport/udp/endpoint_state.go
index 163dcbc13..74e8e9fd5 100644
--- a/pkg/tcpip/transport/udp/endpoint_state.go
+++ b/pkg/tcpip/transport/udp/endpoint_state.go
@@ -66,6 +66,12 @@ func (e *endpoint) loadRcvBufSizeMax(max int) {
 func (e *endpoint) afterLoad() {
 	e.stack = stack.StackFromEnv
 
+	for _, m := range e.multicastMemberships {
+		if err := e.stack.JoinGroup(e.netProto, m.nicID, m.multicastAddr); err != nil {
+			panic(err)
+		}
+	}
+
 	if e.state != stateBound && e.state != stateConnected {
 		return
 	}
@@ -103,10 +109,4 @@ func (e *endpoint) afterLoad() {
 	if err != nil {
 		panic(*err)
 	}
-
-	for _, m := range e.multicastMemberships {
-		if err := e.stack.JoinGroup(e.netProto, m.nicID, m.multicastAddr); err != nil {
-			panic(err)
-		}
-	}
 }