Implement IP_MULTICAST_LOOP.

IP_MULTICAST_LOOP controls whether or not multicast packets sent on the default
route are looped back. In order to implement this switch, support for sending
and looping back multicast packets on the default route had to be implemented.

For now we only support IPv4 multicast.

PiperOrigin-RevId: 237534603
Change-Id: I490ac7ff8e8ebef417c7eb049a919c29d156ac1c

1 files changed, 36 insertions, 7 deletions

diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 4108cb09c..3693abae5 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -81,6 +81,7 @@ type endpoint struct {
 	multicastTTL   uint8
 	multicastAddr  tcpip.Address
 	multicastNICID tcpip.NICID
+	multicastLoop  bool
 	reusePort      bool
 	broadcast      bool
 
@@ -124,6 +125,7 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		//
 		// Linux defaults to TTL=1.
 		multicastTTL:  1,
+		multicastLoop: true,
 		rcvBufSizeMax: 32 * 1024,
 		sndBufSize:    32 * 1024,
 	}
@@ -274,7 +276,7 @@ func (e *endpoint) connectRoute(nicid tcpip.NICID, addr tcpip.FullAddress) (stac
 	}
 
 	// Find a route to the desired destination.
-	r, err := e.stack.FindRoute(nicid, localAddr, addr.Addr, netProto)
+	r, err := e.stack.FindRoute(nicid, localAddr, addr.Addr, netProto, e.multicastLoop)
 	if err != nil {
 		return stack.Route{}, 0, 0, err
 	}
@@ -458,13 +460,19 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 
 	case tcpip.AddMembershipOption:
 		nicID := v.NIC
-		if v.InterfaceAddr != header.IPv4Any {
+		if v.InterfaceAddr == header.IPv4Any {
+			if nicID == 0 {
+				r, err := e.stack.FindRoute(0, "", v.MulticastAddr, header.IPv4ProtocolNumber, false /* multicastLoop */)
+				if err == nil {
+					nicID = r.NICID()
+					r.Release()
+				}
+			}
+		} else {
 			nicID = e.stack.CheckLocalAddress(nicID, e.netProto, v.InterfaceAddr)
 		}
 		if nicID == 0 {
-			// TODO: Allow adding memberships without
-			// specifing an interface.
-			return tcpip.ErrNoRoute
+			return tcpip.ErrUnknownDevice
 		}
 
 		// TODO: check that v.MulticastAddr is a multicast address.
@@ -479,11 +487,19 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 
 	case tcpip.RemoveMembershipOption:
 		nicID := v.NIC
-		if v.InterfaceAddr != header.IPv4Any {
+		if v.InterfaceAddr == header.IPv4Any {
+			if nicID == 0 {
+				r, err := e.stack.FindRoute(0, "", v.MulticastAddr, header.IPv4ProtocolNumber, false /* multicastLoop */)
+				if err == nil {
+					nicID = r.NICID()
+					r.Release()
+				}
+			}
+		} else {
 			nicID = e.stack.CheckLocalAddress(nicID, e.netProto, v.InterfaceAddr)
 		}
 		if nicID == 0 {
-			return tcpip.ErrNoRoute
+			return tcpip.ErrUnknownDevice
 		}
 
 		// TODO: check that v.MulticastAddr is a multicast address.
@@ -503,6 +519,11 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 			}
 		}
 
+	case tcpip.MulticastLoopOption:
+		e.mu.Lock()
+		e.multicastLoop = bool(v)
+		e.mu.Unlock()
+
 	case tcpip.ReusePortOption:
 		e.mu.Lock()
 		e.reusePort = v != 0
@@ -578,6 +599,14 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 		e.mu.Unlock()
 		return nil
 
+	case *tcpip.MulticastLoopOption:
+		e.mu.RLock()
+		v := e.multicastLoop
+		e.mu.RUnlock()
+
+		*o = tcpip.MulticastLoopOption(v)
+		return nil
+
 	case *tcpip.ReusePortOption:
 		e.mu.RLock()
 		v := e.reusePort