cmd/tailscale: fix "tailscale ip $self-host-hostname"

And in the process, fix the related confusing error messages from
pinging your own IP or hostname.

Fixes #2803

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

wgengine/pendopen.go

@@ -117,7 +117,7 @@ func (e *userspaceEngine) trackOpenPostFilterOut(pp *packet.Parsed, t *tstun.Wra
 	// like:
 	//    open-conn-track: timeout opening (100.115.73.60:52501 => 17.125.252.5:443); no associated peer node
 	if runtime.GOOS == "ios" && flow.Dst.Port() == 443 && !tsaddr.IsTailscaleIP(flow.Dst.IP()) {
-		if _, err := e.peerForIP(flow.Dst.IP()); err != nil {
+		if _, _, err := e.peerForIP(flow.Dst.IP()); err != nil {
 			return
 		}
 	}
@@ -157,7 +157,7 @@ func (e *userspaceEngine) onOpenTimeout(flow flowtrack.Tuple) {
 	}
 
 	// Diagnose why it might've timed out.
-	n, err := e.peerForIP(flow.Dst.IP())
+	n, _, err := e.peerForIP(flow.Dst.IP())
 	if err != nil {
 		e.logf("open-conn-track: timeout opening %v; peerForIP: %v", flow, err)
 		return

wgengine/userspace.go

@@ -1244,7 +1244,7 @@ func (e *userspaceEngine) UpdateStatus(sb *ipnstate.StatusBuilder) {
 
 func (e *userspaceEngine) Ping(ip netaddr.IP, useTSMP bool, cb func(*ipnstate.PingResult)) {
 	res := &ipnstate.PingResult{IP: ip.String()}
-	peer, err := e.peerForIP(ip)
+	peer, self, err := e.peerForIP(ip)
 	if err != nil {
 		e.logf("ping(%v): %v", ip, err)
 		res.Err = err.Error()
@@ -1257,6 +1257,13 @@ func (e *userspaceEngine) Ping(ip netaddr.IP, useTSMP bool, cb func(*ipnstate.Pi
 		cb(res)
 		return
 	}
+	if self {
+		res.Err = fmt.Sprintf("%v is local Tailscale IP", ip)
+		res.IsLocalIP = true
+		cb(res)
+		return
+	}
+
 	pingType := "disco"
 	if useTSMP {
 		pingType = "TSMP"
@@ -1400,12 +1407,12 @@ func (e *userspaceEngine) WhoIsIPPort(ipport netaddr.IPPort) (tsIP netaddr.IP, o
 //
 // peerForIP acquires both e.mu and e.wgLock, but neither at the same
 // time.
-func (e *userspaceEngine) peerForIP(ip netaddr.IP) (n *tailcfg.Node, err error) {
+func (e *userspaceEngine) peerForIP(ip netaddr.IP) (n *tailcfg.Node, isSelf bool, err error) {
 	e.mu.Lock()
 	nm := e.netMap
 	e.mu.Unlock()
 	if nm == nil {
-		return nil, errors.New("no network map")
+		return nil, false, errors.New("no network map")
 	}
 
 	// Check for exact matches before looking for subnet matches.
@@ -1414,7 +1421,7 @@ func (e *userspaceEngine) peerForIP(ip netaddr.IP) (n *tailcfg.Node, err error)
 	for _, p := range nm.Peers {
 		for _, a := range p.Addresses {
 			if a.IP() == ip && a.IsSingleIP() && tsaddr.IsTailscaleIP(ip) {
-				return p, nil
+				return p, false, nil
 			}
 		}
 		for _, cidr := range p.AllowedIPs {
@@ -1427,6 +1434,11 @@ func (e *userspaceEngine) peerForIP(ip netaddr.IP) (n *tailcfg.Node, err error)
 			}
 		}
 	}
+	for _, a := range nm.Addresses {
+		if a.IP() == ip && a.IsSingleIP() && tsaddr.IsTailscaleIP(ip) {
+			return nm.SelfNode, true, nil
+		}
+	}
 
 	e.wgLock.Lock()
 	defer e.wgLock.Unlock()
@@ -1450,17 +1462,17 @@ func (e *userspaceEngine) peerForIP(ip netaddr.IP) (n *tailcfg.Node, err error)
 	if !bestKey.IsZero() {
 		for _, p := range nm.Peers {
 			if p.Key == bestKey {
-				return p, nil
+				return p, false, nil
 			}
 		}
 	}
 	if bestInNM == nil {
-		return nil, nil
+		return nil, false, nil
 	}
 	if bestInNMPrefix.Bits() == 0 {
-		return nil, errors.New("exit node found but not enabled")
+		return nil, false, errors.New("exit node found but not enabled")
 	}
-	return nil, fmt.Errorf("node %q found, but not using its %v route", bestInNM.ComputedNameWithHost, bestInNMPrefix)
+	return nil, false, fmt.Errorf("node %q found, but not using its %v route", bestInNM.ComputedNameWithHost, bestInNMPrefix)
 }
 
 type closeOnErrorPool []func()