Implement Broadcast support

This change adds support for the SO_BROADCAST socket option in gVisor Netstack.
This support includes getsockopt()/setsockopt() functionality for both UDP and
TCP endpoints (the latter being a NOOP), dispatching broadcast messages up and
down the stack, and route finding/creation for broadcast packets. Finally, a
suite of tests have been implemented, exercising this functionality through the
Linux syscall API.

PiperOrigin-RevId: 234850781
Change-Id: If3e666666917d39f55083741c78314a06defb26c

3 files changed, 9 insertions, 0 deletions

diff --git a/pkg/dhcp/client.go b/pkg/dhcp/client.go
index 3330c4998..6d48eec7e 100644
--- a/pkg/dhcp/client.go
+++ b/pkg/dhcp/client.go
@@ -141,6 +141,9 @@ func (c *Client) Request(ctx context.Context, requestedAddr tcpip.Address) (cfg
 	}, nil); err != nil {
 		return Config{}, fmt.Errorf("dhcp: connect failed: %v", err)
 	}
+	if err := ep.SetSockOpt(tcpip.BroadcastOption(1)); err != nil {
+		return Config{}, fmt.Errorf("dhcp: setsockopt SO_BROADCAST: %v", err)
+	}
 
 	epin, err := c.stack.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, &wq)
 	if err != nil {
diff --git a/pkg/dhcp/dhcp_test.go b/pkg/dhcp/dhcp_test.go
index a21dce6bc..026064394 100644
--- a/pkg/dhcp/dhcp_test.go
+++ b/pkg/dhcp/dhcp_test.go
@@ -287,6 +287,9 @@ func TestTwoServers(t *testing.T) {
 	if err = ep.Bind(tcpip.FullAddress{Port: ServerPort}, nil); err != nil {
 		t.Fatalf("dhcp: server bind: %v", err)
 	}
+	if err = ep.SetSockOpt(tcpip.BroadcastOption(1)); err != nil {
+		t.Fatalf("dhcp: setsockopt: %v", err)
+	}
 
 	serverCtx, cancel := context.WithCancel(context.Background())
 	defer cancel()
diff --git a/pkg/dhcp/server.go b/pkg/dhcp/server.go
index 3e06ab4c7..c72c3b70d 100644
--- a/pkg/dhcp/server.go
+++ b/pkg/dhcp/server.go
@@ -123,6 +123,9 @@ func newEPConnServer(ctx context.Context, stack *stack.Stack, addrs []tcpip.Addr
 	if err := ep.Bind(tcpip.FullAddress{Port: ServerPort}, nil); err != nil {
 		return nil, fmt.Errorf("dhcp: server bind: %v", err)
 	}
+	if err := ep.SetSockOpt(tcpip.BroadcastOption(1)); err != nil {
+		return nil, fmt.Errorf("dhcp: server setsockopt: %v", err)
+	}
 	c := newEPConn(ctx, wq, ep)
 	return NewServer(ctx, c, addrs, cfg)
 }