RFR: 8231260: (dc) DatagramChannel::disconnect changes the port of the local address to 0 (lnx)

[Florian Weimer]

* Alan Bateman:

> On 04/10/2019 16:25, Florian Weimer wrote:
>> :
>> @@ -873,10 +873,15 @@
>>                   synchronized (stateLock) {
>>                       ensureOpen();
>>                       if (state == ST_CONNECTED)
>>                           throw new AlreadyConnectedException();
>>   +                    // ensure that the socket is bound
>> +                    if (localAddress == null) {
>> +                        bindInternal(null);
>> +                    }
>> +
>>                       int n = Net.connect(family,
>>                                           fd,
>>                                           isa.getAddress(),
>>                                           isa.getPort());
>>                       if (n <= 0)
>>
>>
>> Doesn't it introduce a race condition where the socket has a port and
>> queue packets, but the kernel will not perform source address checking
>> because it is unconnected?
>>
> The socket is unbound, this change to the connect method in Daniel's
> patch just binds it before connecting. The kernel will do this anyway
> so it's not strictly needed here (at least for the case that the
> connect succeeds_.

The kernel will do it atomically during connect, so there is no race
condition.  With the change above, the port is selected and opened,
packets can arrive (from arbitrary addresses), and only then the socket
is bound to the remote address.

Thanks,
Florian