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Date: Fri, 8 Mar 2019 15:11:18 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Logging-in using ssh elevates the user privilege.
Message-ID: <20190308141118.GM3785@calimero.vinschen.de>
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References: <20190307010000 DOT fc28b73739c2dd66e609982b AT nifty DOT ne DOT jp> <381052629 DOT 20190307141955 AT yandex DOT ru> <51233666 DOT 20190307182445 AT yandex DOT ru> <20190308230138 DOT b7f6b5ac90c9a14cde2647c1 AT nifty DOT ne DOT jp>
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On Mar  8 23:01, Takashi Yano wrote:
> Hello,
>=20
> Thank you for the information.
>=20
> On Thu, 7 Mar 2019 18:24:45 +0300 Andrey Repin wrote:
> > > GNU screen freeze without much of an effort under Cygwin.
> > > Try detaching from running screen and then running screen -ls.
> >=20
> > Past discussion
> > http://sourceware.org/ml/cygwin/2017-05/msg00448.html
> > mid:16810313565 DOT 20170527142723 AT yandex DOT ru
>=20
> I looked into this problem of GNU screen and found the
> cause is very different from that of the problem I had
> reported.
>=20
> The problem I had reported is due to the failure of
> sending signal, which is caused by mismatch of tokens
> between ssh session and mintty session.
>=20
> On the other hand, the problem you mentioned is due
> to the difference in the behaviour of socket API.
>=20
> In Linux, connect() in the client returns befor the
> server calls accept(). However, in cygwin, connect()
> does not return until the server calls accept().

This is a result of the handshake to exchange credentials for
getpeereid().  To workaround this issue, try building screen
with a tweak.  Server and as client should call

  setsockopt (sock, SOL_SOCKET, SO_PEERCRED, NULL, 0);

before calling accept or connect.


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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