remove the risk of file descriptor reuse from arping

using sock.deinitialize() outside of the goroutine that is using the
socket leaves the potential for erroneous and unexpected behavior. When
calling Ping() very quickly the socket fd can be reused while a
goroutine is still trying to read from it and cause the goroutine to
deadlock.

Additionally removing the timeout from the select case because that
will/cannot work as intended. In linux close() does not cause system
calls using the socket to return. This contributes to the file
descriptor reuse issue mentioned above and with the defered
sock.deinitialize() can lead to double closing the socket.

Signed-off-by: Jacob Tanenbaum <[email protected]>

arping.go

@@ -121,7 +121,6 @@ func PingOverIface(dstIP net.IP, iface net.Interface) (net.HardwareAddr, time.Du
 	if err != nil {
 		return nil, 0, err
 	}
-	defer sock.deinitialize()
 
 	type PingResult struct {
 		mac      net.HardwareAddr
@@ -131,6 +130,7 @@ func PingOverIface(dstIP net.IP, iface net.Interface) (net.HardwareAddr, time.Du
 	pingResultChan := make(chan PingResult, 1)
 
 	go func() {
+		defer sock.deinitialize()
 		// send arp request
 		verboseLog.Printf("arping '%s' over interface: '%s' with address: '%s'\n", dstIP, iface.Name, srcIP)
 		if sendTime, err := sock.send(request); err != nil {
@@ -162,9 +162,6 @@ func PingOverIface(dstIP net.IP, iface net.Interface) (net.HardwareAddr, time.Du
 	select {
 	case pingResult := <-pingResultChan:
 		return pingResult.mac, pingResult.duration, pingResult.err
-	case <-time.After(timeout):
-		sock.deinitialize()
-		return nil, 0, ErrTimeout
 	}
 }
 

arping_linux.go

@@ -23,6 +23,9 @@ func initialize(iface net.Interface) (s *LinuxSocket, err error) {
 }
 
 func (s *LinuxSocket) send(request arpDatagram) (time.Time, error) {
+	socketTimeout := timeout.Nanoseconds * 2
+	t := syscall.NsecToTimeval(socketTimeout)
+	syscall.SetsockoptTimeval(s.sock, syscall.SOL_SOCKET, syscall.SO_SNDTIMEO, &t)
 	return time.Now(), syscall.Sendto(s.sock, request.MarshalWithEthernetHeader(), 0, &s.toSockaddr)
 }