wgengine, magicsock: add a CreateBind method

Signed-off-by: David Crawshaw <crawshaw@tailscale.com>

wgengine/magicsock/magicsock.go

@@ -1094,6 +1094,11 @@ func (a *AddrSet) Addrs() []wgcfg.Endpoint {
 	return eps
 }
 
+// CreateBind is called by WireGuard to create a UDP binding.
+func (c *Conn) CreateBind(uint16) (conn.Bind, uint16, error) {
+	return c, c.LocalPort(), nil
+}
+
 // CreateEndpoint is called by WireGuard to connect to an endpoint.
 // The key is the public key of the peer and addrs is a
 // comma-separated list of UDP ip:ports.

wgengine/userspace.go

@@ -15,7 +15,6 @@ import (
 	"sync"
 	"time"
 
-	"github.com/tailscale/wireguard-go/conn"
 	"github.com/tailscale/wireguard-go/device"
 	"github.com/tailscale/wireguard-go/tun"
 	"github.com/tailscale/wireguard-go/wgcfg"
@@ -173,9 +172,7 @@ func newUserspaceEngineAdvanced(logf logger.Logf, tundev tun.Device, routerGen R
 			}
 			logf("ERROR: peer %s has unexpected AllowedIPs: %v", peerKey.ShortString(), allowedIPs)
 		},
-		CreateBind: func(uint16) (conn.Bind, uint16, error) {
-			return e.magicConn, e.magicConn.LocalPort(), nil
-		},
+		CreateBind:     e.magicConn.CreateBind,
 		CreateEndpoint: e.magicConn.CreateEndpoint,
 		SkipBindUpdate: true,
 	}