From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Artem S. Tashkinov" Subject: Re: A call to revise sockets behaviour Date: Mon, 29 Jul 2013 15:47:57 +0000 (UTC) Message-ID: <2063167407.40450.1375112877907.JavaMail.mail@webmail09> References: <2066879158.39771.1375110634453.JavaMail.mail@webmail09><20130729083519.5d574f16@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: stephen@networkplumber.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 if _all_ you have is some stale (i.e. no longer active connections pending destruction) 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: >> >> https://bugzilla.kernel.org/show_bug.cgi?id=45571 >> http://bugs.winehq.org/show_bug.cgi?id=26031 > >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 >period. > >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. http://bugs.winehq.org/show_bug.cgi?id=26031#c21 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) Artem