If the client connects to the nbd socket, and then disconnects without sending any data, nbd floods the logs

[jgrills]

Since the socket_read() in the server negotiation in negotiate(..) doesn't return any sort of error, the server acts on uninitialized data and can spin around the loop, each read/write spamming the error in socket_closed_negotiate()

[jgrills]

In particular, because magic was used to send the magic number, when it fails to read at https://github.com/NetworkBlockDevice/nbd/blob/master/nbd-server.c#L2678 it will have the correct magic number, and things will proceed.

opt is not initialized and just about anything could happen after that.

As a fix, I might suggest changing socket_read() to memset(buf, 0, len); if the read returns less than 0, here: https://github.com/NetworkBlockDevice/nbd/blob/master/nbd-server.c#L365