Subject: A call to revise sockets behaviour

From: "Artem S. Tashkinov" <[email-masked]>
Date: Mon, 29 Jul 2013 15:10:34 +0000 (UTC)

Hello,

Currently the Linux kernel disallows to start listening on a TCP/UDP socket if
there are open connections against the port, regardless connections status. So even
if _all_ you have is some stale (i.e. no longer active connections pending destruction)
the kernel will not allow to reuse this socket.

Stephen Hemminger argues that this behaviour is expected even though it's 100%
counter productive, it defies common sense and I cannot think of any security implications
should this feature be allowed.

Besides, when discussing this bug on Wine's bugzilla I have shown that this behavior not
only affect Windows applications running under Wine, but also native POSIX applications.

If nothing else is listening to incoming connections how can _old_ _stale_ connections
prevent an application from listening on the port? Windows has no qualms about allowing
that, why the Linux kernel works differently?

I want to hear how the current apparently _broken_ behaviour, "The current socket API
behavior is unlikely to be changed because so many applications expect it", can be expected.

Also I'd like to know which applications depend on this "feature".

Imagine a situation,

You have an apache server serving connections on port 80. For some reasons a crash in
one of its modules causes the daemon crash but during the crash Apache had some open
connections on this port.

According to Stephen Hemminger I cannot relaunch Apache until the kernel waits arbitrary
time in order to clean stale connections for its networking pool.

I fail to see how this behaviour can be "expected".

More on it here:

https://bugzilla.kernel.org/show_bug.cgi?id=45571
http://bugs.winehq.org/show_bug.cgi?id=26031

Artem