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, 11 insertions, 5 deletions

diff --git a/runsc/boot/network.go b/runsc/boot/network.go
index 0cadf48d6..40bc147ca 100644
--- a/runsc/boot/network.go
+++ b/runsc/boot/network.go
@@ -112,7 +112,7 @@ func (n *Network) CreateLinksAndRoutes(args *CreateLinksAndRoutesArgs, _ *struct
 		linkEP := loopback.New()
 
 		log.Infof("Enabling loopback interface %q with id %d on addresses %+v", link.Name, nicID, link.Addresses)
-		if err := n.createNICWithAddrs(nicID, link.Name, linkEP, link.Addresses); err != nil {
+		if err := n.createNICWithAddrs(nicID, link.Name, linkEP, link.Addresses, true /* loopback */); err != nil {
 			return err
 		}
 
@@ -144,7 +144,7 @@ func (n *Network) CreateLinksAndRoutes(args *CreateLinksAndRoutesArgs, _ *struct
 		})
 
 		log.Infof("Enabling interface %q with id %d on addresses %+v (%v)", link.Name, nicID, link.Addresses, mac)
-		if err := n.createNICWithAddrs(nicID, link.Name, linkEP, link.Addresses); err != nil {
+		if err := n.createNICWithAddrs(nicID, link.Name, linkEP, link.Addresses, false /* loopback */); err != nil {
 			return err
 		}
 
@@ -169,9 +169,15 @@ func (n *Network) CreateLinksAndRoutes(args *CreateLinksAndRoutesArgs, _ *struct
 
 // createNICWithAddrs creates a NIC in the network stack and adds the given
 // addresses.
-func (n *Network) createNICWithAddrs(id tcpip.NICID, name string, linkEP tcpip.LinkEndpointID, addrs []net.IP) error {
-	if err := n.Stack.CreateNamedNIC(id, name, sniffer.New(linkEP)); err != nil {
-		return fmt.Errorf("CreateNamedNIC(%v, %v, %v) failed: %v", id, name, linkEP, err)
+func (n *Network) createNICWithAddrs(id tcpip.NICID, name string, linkEP tcpip.LinkEndpointID, addrs []net.IP, loopback bool) error {
+	if loopback {
+		if err := n.Stack.CreateNamedLoopbackNIC(id, name, sniffer.New(linkEP)); err != nil {
+			return fmt.Errorf("CreateNamedLoopbackNIC(%v, %v, %v) failed: %v", id, name, linkEP, err)
+		}
+	} else {
+		if err := n.Stack.CreateNamedNIC(id, name, sniffer.New(linkEP)); err != nil {
+			return fmt.Errorf("CreateNamedNIC(%v, %v, %v) failed: %v", id, name, linkEP, err)
+		}
 	}
 
 	// Always start with an arp address for the NIC.