Re: Logging-in using ssh elevates the user privilege.

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Mar  8 23:01, Takashi Yano wrote:
> Hello,
> 
> Thank you for the information.
> 
> 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.
> > 
> > Past discussion
> > http://sourceware.org/ml/cygwin/2017-05/msg00448.html
> > mid:16810313565.20170527142723@yandex.ru
> 
> I looked into this problem of GNU screen and found the
> cause is very different from that of the problem I had
> reported.
> 
> 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.
> 
> On the other hand, the problem you mentioned is due
> to the difference in the behaviour of socket API.
> 
> 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

-- 
Corinna Vinschen
Cygwin Maintainer

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