Re: A call to revise sockets behaviour

From: Artem S. Tashkinov
Date: Mon Jul 29 2013 - 11:48:05 EST

Jul 29, 2013 09:35:25 PM, Stephen wrote:
On Mon, 29 Jul 2013 15:10:34 +0000 (UTC)
>"Artem S. Tashkinov" wrote:
>> 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 if _all_ you have is some stale (i.e. no longer active connections pending destruction)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:
>I understand your problem, people have been having to deal with it for 30 years.
>The attitude in your response makes it seem like you just discovered fire,
>read a book like Steven's network programming if you need more info.
>If you don't use SO_REUSEADDR then yes application has to wait for time wait
>If you do enable SO_REUSEADDR then it is possible to bind to a port with existing
>stale connections.

A wine developer clearly showed that this option simply doesn't work.

Output of strace:
getsockopt(24, SOL_SOCKET, SO_REUSEADDR, [0], [4]) = 0
setsockopt(24, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
bind(24, {sa_family=AF_INET, sin_port=htons(43012), sin_addr=inet_addr("0.
0.0.0")}, 16) = -1 EADDRINUSE (Address already in use)

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