lib/connections: Validate device id before assuming success (fixes #5934) (#5935)

* lib/connections: Validate device id before assuming success (fixes #5934)

* Vet

go.mod

@@ -46,7 +46,6 @@ require (
 	gopkg.in/asn1-ber.v1 v1.0.0-20170511165959-379148ca0225 // indirect
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
 	gopkg.in/ldap.v2 v2.5.1
-	gopkg.in/yaml.v2 v2.2.2 // indirect
 )
 
 go 1.12

go.sum

@@ -5,6 +5,7 @@ github.com/AudriusButkevicius/pfilter v0.0.0-20190627213056-c55ef6137fc6/go.mod
 github.com/AudriusButkevicius/recli v0.0.5 h1:xUa55PvWTHBm17T6RvjElRO3y5tALpdceH86vhzQ5wg=
 github.com/AudriusButkevicius/recli v0.0.5/go.mod h1:Q2E26yc6RvWWEz/TJ/goUp6yXvipYdJI096hpoaqsNs=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/StackExchange/wmi v0.0.0-20180116203802-5d049714c4a6 h1:fLjPD/aNc3UIOA6tDi6QXUemppXK3P9BI7mr2hd6gx8=
 github.com/StackExchange/wmi v0.0.0-20180116203802-5d049714c4a6/go.mod h1:3eOhrUMpNV+6aFIbp5/iudMxNCF27Vw2OZgy4xEx0Fg=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=
 github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
@@ -37,6 +38,7 @@ github.com/getsentry/raven-go v0.2.0 h1:no+xWJRb5ZI7eE8TWgIq1jLulQiIoLG0IfYxv5JY
 github.com/getsentry/raven-go v0.2.0/go.mod h1:KungGk8q33+aIAZUIVWZDr2OfAEBsO49PX4NzFV5kcQ=
 github.com/go-kit/kit v0.8.0/go.mod h1:xBxKIO96dXMWWy0MnWVtmwkA9/13aqxPnvrjFYMA2as=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
+github.com/go-ole/go-ole v1.2.1 h1:2lOsA72HgjxAuMlKpFiCbHTvu44PIVkZ5hqm3RSdI/E=
 github.com/go-ole/go-ole v1.2.1/go.mod h1:7FAglXiTm7HKlQRDeOQ6ZNUHidzCWXuZWq/1dTyBNF8=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
 github.com/gobwas/glob v0.0.0-20170212200151-51eb1ee00b6d h1:IngNQgbqr5ZOU0exk395Szrvkzes9Ilk1fmJfkw7d+M=

lib/connections/quic_dial.go

@@ -36,7 +36,7 @@ type quicDialer struct {
 	tlsCfg *tls.Config
 }
 
-func (d *quicDialer) Dial(id protocol.DeviceID, uri *url.URL) (internalConn, error) {
+func (d *quicDialer) Dial(_ protocol.DeviceID, uri *url.URL) (internalConn, error) {
 	uri = fixupPort(uri, config.DefaultQUICPort)
 
 	addr, err := net.ResolveUDPAddr("udp", uri.Host)

lib/connections/service.go

@@ -231,7 +231,7 @@ func (s *service) handle(stop chan struct{}) {
 			continue
 		}
 
-		c.SetDeadline(time.Now().Add(20 * time.Second))
+		_ = c.SetDeadline(time.Now().Add(20 * time.Second))
 		hello, err := protocol.ExchangeHello(c, s.model.GetHello(remoteID))
 		if err != nil {
 			if protocol.IsVersionMismatch(err) {
@@ -255,7 +255,7 @@ func (s *service) handle(stop chan struct{}) {
 			c.Close()
 			continue
 		}
-		c.SetDeadline(time.Time{})
+		_ = c.SetDeadline(time.Time{})
 
 		// The Model will return an error for devices that we don't want to
 		// have a connection with for whatever reason, for example unknown devices.
@@ -850,8 +850,15 @@ func (s *service) dialParallel(deviceID protocol.DeviceID, dialTargets []dialTar
 			wg.Add(1)
 			go func(tgt dialTarget) {
 				conn, err := tgt.Dial()
-				s.setConnectionStatus(tgt.addr, err)
 				if err == nil {
+					// Closes the connection on error
+					err = s.validateIdentity(conn, deviceID)
+				}
+				s.setConnectionStatus(tgt.addr, err)
+				if err != nil {
+					l.Debugln("dialing", deviceID, tgt.uri, "error:", err)
+				} else {
+					l.Debugln("dialing", deviceID, tgt.uri, "success:", conn)
 					res <- conn
 				}
 				wg.Done()
@@ -884,3 +891,36 @@ func (s *service) dialParallel(deviceID protocol.DeviceID, dialTargets []dialTar
 	}
 	return internalConn{}, false
 }
+
+func (s *service) validateIdentity(c internalConn, expectedID protocol.DeviceID) error {
+	cs := c.ConnectionState()
+
+	// We should have received exactly one certificate from the other
+	// side. If we didn't, they don't have a device ID and we drop the
+	// connection.
+	certs := cs.PeerCertificates
+	if cl := len(certs); cl != 1 {
+		l.Infof("Got peer certificate list of length %d != 1 from peer at %s; protocol error", cl, c)
+		c.Close()
+		return fmt.Errorf("expected 1 certificate, got %d", cl)
+	}
+	remoteCert := certs[0]
+	remoteID := protocol.NewDeviceID(remoteCert.Raw)
+
+	// The device ID should not be that of ourselves. It can happen
+	// though, especially in the presence of NAT hairpinning, multiple
+	// clients between the same NAT gateway, and global discovery.
+	if remoteID == s.myID {
+		l.Infof("Connected to myself (%s) at %s - should not happen", remoteID, c)
+		c.Close()
+		return fmt.Errorf("connected to self")
+	}
+
+	// We should see the expected device ID
+	if !remoteID.Equals(expectedID) {
+		c.Close()
+		return fmt.Errorf("unexpected device id, expected %s got %s", expectedID, remoteID)
+	}
+
+	return nil
+}

lib/connections/structs.go

@@ -215,11 +215,5 @@ type dialTarget struct {
 
 func (t dialTarget) Dial() (internalConn, error) {
 	l.Debugln("dialing", t.deviceID, t.uri, "prio", t.priority)
-	conn, err := t.dialer.Dial(t.deviceID, t.uri)
-	if err != nil {
-		l.Debugln("dialing", t.deviceID, t.uri, "error:", err)
-	} else {
-		l.Debugln("dialing", t.deviceID, t.uri, "success:", conn)
-	}
-	return conn, err
+	return t.dialer.Dial(t.deviceID, t.uri)
 }

lib/connections/tcp_dial.go

@@ -30,7 +30,7 @@ type tcpDialer struct {
 	tlsCfg *tls.Config
 }
 
-func (d *tcpDialer) Dial(id protocol.DeviceID, uri *url.URL) (internalConn, error) {
+func (d *tcpDialer) Dial(_ protocol.DeviceID, uri *url.URL) (internalConn, error) {
 	uri = fixupPort(uri, config.DefaultTCPPort)
 
 	conn, err := dialer.DialTimeout(uri.Scheme, uri.Host, 10*time.Second)