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Date: Mon, 29 May 2017 11:48:30 +0200
From: Houder <houder AT xs4all DOT nl>
To: cygwin AT cygwin DOT com
Subject: Re: openssh: privilege separation no longer supported on Cygwin?
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On 2017-05-29 10:39, Marco Atzeri wrote:
> On 29/05/2017 07:23, Houder wrote:

[snip]
>> ... because, that is, I think, what I am seeing:
>> 
>>  - the userid of child sshd is still 'cyg_server' ...
>>  - and I get an elevated shell when I login ...
>> 
>> Not what I expected ...
>> 
>> Gr. Henri
>> 
> 
> Hi Houder,
> please read the last Announcement
> 
> https://sourceware.org/ml/cygwin-announce/2017-03/msg00028.html

[snip]
> It seems you misunderstood the communication:
> - the possibility to NOT use "privilege separation" is deprecated
> - "privilege separation" will became mandatory

Hi Marco,

Sorry for the misunderstanding. Yes, to my knowledge, PS, privilege
separation, is now mandatory (using a new mechanism under Linux [1]).

[1] sandboxing?

Because of PS, I expect to see an UNprivileged sshd process talking
to the user process (where the ssh command has been executed).

But above all, I expect an UNelevated shell when I login in ...

However, what I get after login (after providing my credentials) is
an ELEVATED shell (yes, Administrators is part of the group set).

Now I wonder if this happens because I do NOT observe PS.

Look below, please ... After executing the ssh command, ssh asks for
my credentials ... in stead of providing my credentials, I execute
the ps command in a second terminal. To my surprise, the grandchild
of the listener is executed using "cyg_server" and not "sshd" ...

Currently, I am looking at:

     https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-setuid-overview

Regards,
Henri

-----
  - pre-authentication:

Shell 1:
64-@@ ssh -p 222 -l Henri 192.168.178.15
Enter passphrase for key '/home/Henri/.ssh/id_rsa': <==== passphrase not 
yet entered

Shell 2: (observer)
64-@@# ps -af
      UID     PID    PPID  TTY        STIME COMMAND
    Henri    2308    4356 pty0     11:01:41 /usr/bin/ssh
    Henri    5092     176 pty1     11:01:58 /usr/bin/ps
    Henri    4356    3744 pty0     10:57:56 /usr/bin/bash
    Henri    3744       1 ?        10:57:50 /usr/bin/mintty-273
    Henri     176    4604 pty1     10:58:21 /usr/bin/bash
cyg_serv    4992    2476 ?        11:01:03 /usr/sbin/sshd               
privileged listener
cyg_serv    2476       1 ?        11:01:03 /usr/bin/cygrunsrv
    Henri    4604       1 ?        10:58:21 /usr/bin/mintty-273
cyg_serv    1496    3032 ?        11:01:42 /usr/sbin/sshd               
should be using sshd as userid
cyg_serv    3032    4992 ?        11:01:42 /usr/sbin/sshd               
privileged monitor (child of listener)

  - post-authentication:

Shell 1:
64-@@ ssh -p 222 -l Henri 192.168.178.15
Enter passphrase for key '/home/Henri/.ssh/id_rsa': <==== passphrase has 
been entered
Last login: Mon May 29 10:07:00 2017 from 192.168.178.15
64-@@#  <===== ///// PROBLEM: this shell is ELEVATED /////

Shell 2: (observer)
64-@@# ps -af
      UID     PID    PPID  TTY        STIME COMMAND
    Henri    2496    3032 pty3     11:02:31 /usr/bin/bash                
remote shell (but it is an elevated shell! ?????)
    Henri    2308    4356 pty0     11:01:41 /usr/bin/ssh
    Henri    4356    3744 pty0     10:57:56 /usr/bin/bash
    Henri    3744       1 ?        10:57:50 /usr/bin/mintty-273
    Henri     176    4604 pty1     10:58:21 /usr/bin/bash
cyg_serv    4992    2476 ?        11:01:03 /usr/sbin/sshd               
privileged listener
    Henri    4996     176 pty1     11:06:05 /usr/bin/ps
cyg_serv    2476       1 ?        11:01:03 /usr/bin/cygrunsrv
    Henri    4604       1 ?        10:58:21 /usr/bin/mintty-273
cyg_serv    3032    4992 ?        11:01:42 /usr/sbin/sshd               
privileged monitor (child of listener)

=====

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