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, 14 insertions, 2 deletions

diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index f204ca790..c82822ee2 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -1062,10 +1062,22 @@ func (s *Stack) RemoveTCPProbe() {
 // JoinGroup joins the given multicast group on the given NIC.
 func (s *Stack) JoinGroup(protocol tcpip.NetworkProtocolNumber, nicID tcpip.NICID, multicastAddr tcpip.Address) *tcpip.Error {
 	// TODO: notify network of subscription via igmp protocol.
-	return s.AddAddressWithOptions(nicID, protocol, multicastAddr, NeverPrimaryEndpoint)
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	if nic, ok := s.nics[nicID]; ok {
+		return nic.joinGroup(protocol, multicastAddr)
+	}
+	return tcpip.ErrUnknownNICID
 }
 
 // LeaveGroup leaves the given multicast group on the given NIC.
 func (s *Stack) LeaveGroup(protocol tcpip.NetworkProtocolNumber, nicID tcpip.NICID, multicastAddr tcpip.Address) *tcpip.Error {
-	return s.RemoveAddress(nicID, multicastAddr)
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	if nic, ok := s.nics[nicID]; ok {
+		return nic.leaveGroup(multicastAddr)
+	}
+	return tcpip.ErrUnknownNICID
 }