From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 96784 invoked by alias); 5 Feb 2018 13:34:56 -0000 Mailing-List: contact cygwin-help@cygwin.com; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner@cygwin.com Mail-Followup-To: cygwin@cygwin.com Received: (qmail 96729 invoked by uid 89); 5 Feb 2018 13:34:55 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-101.9 required=5.0 tests=AWL,BAYES_00,GOOD_FROM_CORINNA_CYGWIN,KAM_LAZY_DOMAIN_SECURITY,RCVD_IN_DNSWL_LOW,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=succeeding, reserved X-HELO: drew.franken.de Received: from mail-n.franken.de (HELO drew.franken.de) (193.175.24.27) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 05 Feb 2018 13:34:54 +0000 Received: from aqua.hirmke.de (aquarius.franken.de [193.175.24.89]) (Authenticated sender: aquarius) by mail-n.franken.de (Postfix) with ESMTPSA id 4A5A6721E281A for ; Mon, 5 Feb 2018 14:34:51 +0100 (CET) Received: from calimero.vinschen.de (calimero.vinschen.de [192.168.129.6]) by aqua.hirmke.de (Postfix) with ESMTP id D72A35E009F for ; Mon, 5 Feb 2018 14:34:50 +0100 (CET) Received: by calimero.vinschen.de (Postfix, from userid 500) id C4557A8076A; Mon, 5 Feb 2018 14:34:50 +0100 (CET) Date: Mon, 05 Feb 2018 13:34:00 -0000 From: Corinna Vinschen To: cygwin@cygwin.com Subject: Re: RPC clnt_create() adress already in use Message-ID: <20180205133450.GJ2912@calimero.vinschen.de> Reply-To: cygwin@cygwin.com Mail-Followup-To: cygwin@cygwin.com References: <59D90AF8D70E9740907BACDE2BCB520836E325EF@RESW102.resdom01.local> <5b897ca4-9a7d-df90-e7a0-dbdedbd1f179@maxrnd.com> <20180205112617.GB2912@calimero.vinschen.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="Dzs2zDY0zgkG72+7" Content-Disposition: inline In-Reply-To: <20180205112617.GB2912@calimero.vinschen.de> User-Agent: Mutt/1.9.1 (2017-09-22) X-SW-Source: 2018-02/txt/msg00033.txt.bz2 --Dzs2zDY0zgkG72+7 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-length: 2477 On Feb 5 12:26, Corinna Vinschen wrote: > On Feb 5 02:29, Mark Geisert wrote: > > Using Cygwin's bindresvport() is the best solution because Cygwin keeps > > track of the last port number it has allocated *to any Cygwin program*. > > This is the only approach that can deal with multiple programs and mult= iple > > calls in one program. So we need to nail down why it doesn't seem to w= ork > > for you. >=20 > Apart from all the above, there may still be a problem in the given scena= rio. >=20 > To reiterate the problem we observe: >=20 > - socket() > - setsockopt (SO_REUSEADDR) > - bind() succeeds > - connect() fails with EADDRINUSE while socket is still in TIME_WAIT >=20 > using bindresvport in place of bind only marginally changes the > situation, in particular if the second parameter is set and requests a > port number !=3D 0. What happens in that case is that bindresvport calls > bind with this port number and checks if bind returns EADDRINUSE. >=20 > Only then it tries to bind other port numbers in the reserved range. > But we now know that bind will never return EADDINUSE if the SO_REUSEADDR > socket option has been set. >=20 > Even assuming the process calls bindresvport(sock, NULL) we may end up > returning a port number already in use if the process is the only Cygwin > process on the system. The reason is that Cygwin uses a round robin > approach which relies on having a globally shared value called > last_used_bindresvport. If the process is the only Cygwin process on > the system, this information is lost after exiting the process, so the > next process will start with the same start port number and bind will > again fail to notice the client with EADDRINUSE. >=20 > What potential solutions to this problem do we have? >=20 > - bindresvport could enforce SO_EXCLUSIVEADDRUSE temporarily to make > sure bind fails. Nope, no way. Even enforcing SO_EXCLUSIVEADDRUSE results in the second bind succeeding and the subsequent connect failing. The entire SO_REUSEADDR/SO_EXCLUSIVEADDRUSE semantics only works as desired on the server side apparently > - bindresvport could check every local address for being free prior > to calling bind. However, there's a potential race here. >=20 > - DisconnectEx? Never tried this Winsock extension but it might be > worth a shot. Corinna --=20 Corinna Vinschen Please, send mails regarding Cygwin to Cygwin Maintainer cygwin AT cygwin DOT com Red Hat --Dzs2zDY0zgkG72+7 Content-Type: application/pgp-signature; name="signature.asc" Content-length: 833 -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEoVYPmneWZnwT6kwF9TYGna5ET6AFAlp4XXoACgkQ9TYGna5E T6BJEw/8Du4S5K8aUOwfVRUosL4qoGsE4PXMsMBLSsmWHVzh4huRiJoL8o67zzhW ACsbKZYB3/mlBNNVt/MjPV7S+0Am4gMrQsqe29ai17Ffix9QKrQGqlwLwmQKDeaG 8O9LwC/7ERZpyxYOZOkZ9JZ1sWG1mHR/up9KkukpjCKBhkfYv3QLpnWT4SIuZF/V 9VONQL2uRPLtLtU66JwLcYZz35YBnX2Gs3pgZgzWZKRDtwfF2iyVCYkw2E0ceR9E YxkgWayUypiWYeZN0Krs6wblaSMUfxC47uYbAoLqXNWA7qG0UlCqCBacCMuuJa70 MmkRzKM8wixLC5nn2V9UFY3hc6D/54RfDGxlb8XvIHhvdX4lMnNRJ7ITEIkxTkHz 3mlDiANlKTElt7CE7OfrPSXeAKA0KQGt/tMt7AKF1+HV9P2iCZn7czCrCBcNlMUn DqiBQlY65b/GOAL8dD7YAmfMRxgyT9X4FOBwsi3EEj4MTuT7CSZIGGrj0so7UOc5 +TtT5MVbsPz7M5T0pBL+B0mFGw6xl1erh0W9DN4dj6U1qc6KrgOohiqm7UU757wV 7f15Y1RW15X99O8LUHYAc2g1vLUWo5glUJedlMppawjQ56DaVL6M27KbvKP4vIkQ wQoVoQyKji1ogTy2I2mnSYC2QDXyi6xH879ZCvk1/yaRULoG1Kc= =3JUH -----END PGP SIGNATURE----- --Dzs2zDY0zgkG72+7--