wgengine/magicsock: use cloud metadata to get public IPs

Updates #12774

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I1661b6a2da7966ab667b075894837afd96f4742f

wgengine/magicsock/magicsock.go

@@ -133,6 +133,9 @@ type Conn struct {
 	// bind is the wireguard-go conn.Bind for Conn.
 	bind *connBind
 
+	// cloudInfo is used to query cloud metadata services.
+	cloudInfo *cloudInfo
+
 	// ============================================================
 	// Fields that must be accessed via atomic load/stores.
 
@@ -425,9 +428,10 @@ func (o *Options) derpActiveFunc() func() {
 
 // newConn is the error-free, network-listening-side-effect-free based
 // of NewConn. Mostly for tests.
-func newConn() *Conn {
+func newConn(logf logger.Logf) *Conn {
 	discoPrivate := key.NewDisco()
 	c := &Conn{
+		logf:         logf,
 		derpRecvCh:   make(chan derpReadResult, 1), // must be buffered, see issue 3736
 		derpStarted:  make(chan struct{}),
 		peerLastDerp: make(map[key.NodePublic]int),
@@ -435,6 +439,7 @@ func newConn() *Conn {
 		discoInfo:    make(map[key.DiscoPublic]*discoInfo),
 		discoPrivate: discoPrivate,
 		discoPublic:  discoPrivate.Public(),
+		cloudInfo:    newCloudInfo(logf),
 	}
 	c.discoShort = c.discoPublic.ShortString()
 	c.bind = &connBind{Conn: c, closed: true}
@@ -462,10 +467,9 @@ func NewConn(opts Options) (*Conn, error) {
 		return nil, errors.New("magicsock.Options.NetMon must be non-nil")
 	}
 
-	c := newConn()
+	c := newConn(opts.logf())
 	c.port.Store(uint32(opts.Port))
 	c.controlKnobs = opts.ControlKnobs
-	c.logf = opts.logf()
 	c.epFunc = opts.endpointsFunc()
 	c.derpActiveFunc = opts.derpActiveFunc()
 	c.idleFunc = opts.IdleFunc
@@ -952,6 +956,27 @@ func (c *Conn) determineEndpoints(ctx context.Context) ([]tailcfg.Endpoint, erro
 		addAddr(ap, tailcfg.EndpointExplicitConf)
 	}
 
+	// If we're on a cloud instance, we might have a public IPv4 or IPv6
+	// address that we can be reached at. Find those, if they exist, and
+	// add them.
+	if addrs, err := c.cloudInfo.GetPublicIPs(ctx); err == nil {
+		var port4, port6 uint16
+		if addr := c.pconn4.LocalAddr(); addr != nil {
+			port4 = uint16(addr.Port)
+		}
+		if addr := c.pconn6.LocalAddr(); addr != nil {
+			port6 = uint16(addr.Port)
+		}
+
+		for _, addr := range addrs {
+			if addr.Is4() && port4 > 0 {
+				addAddr(netip.AddrPortFrom(addr, port4), tailcfg.EndpointLocal)
+			} else if addr.Is6() && port6 > 0 {
+				addAddr(netip.AddrPortFrom(addr, port6), tailcfg.EndpointLocal)
+			}
+		}
+	}
+
 	// Update our set of endpoints by adding any endpoints that we
 	// previously found but haven't expired yet. This also updates the
 	// cache with the set of endpoints discovered in this function.