X2Go Bug report logs - #835
x2gobroker-ssh: cannot execute x2gobroker-agent if agent-query-mode is set to LOCAL

version graph

Package: x2gobroker-ssh; Maintainer for x2gobroker-ssh is X2Go Developers <x2go-dev@lists.x2go.org>; Source for x2gobroker-ssh is src:x2gobroker.

Reported by: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>

Date: Thu, 2 Apr 2015 13:25:01 UTC

Severity: important

Tags: pending

Found in version 0.0.3.0-preview

Fixed in version 0.0.3.0

Done: X2Go Release Manager <git-admin@x2go.org>

Bug is archived. No further changes may be made.

Full log

🔗 View this message in rfc822 format

X-Loop: owner@bugs.x2go.org
Subject: Bug#835: x2gobroker-ssh: cannot execute x2gobroker-agent if agent-query-mode is set to LOCAL
Reply-To: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>, 835@bugs.x2go.org
Resent-From: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>
Resent-To: x2go-dev@lists.x2go.org
Resent-CC: X2Go Developers <x2go-dev@lists.x2go.org>
X-Loop: owner@bugs.x2go.org
Resent-Date: Thu, 02 Apr 2015 13:25:01 +0000
Resent-Message-ID: <handler.835.B.142798096326365@bugs.x2go.org>
Resent-Sender: owner@bugs.x2go.org
X-X2Go-PR-Message: report 835
X-X2Go-PR-Package: x2gobroker-ssh
X-X2Go-PR-Keywords: 
Received: via spool by submit@bugs.x2go.org id=B.142798096326365
          (code B); Thu, 02 Apr 2015 13:25:01 +0000
Received: (at submit) by bugs.x2go.org; 2 Apr 2015 13:22:43 +0000
X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on
	ymir.das-netzwerkteam.de
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,URIBL_BLOCKED
	autolearn=ham version=3.3.2
Received: from freya.das-netzwerkteam.de (freya.das-netzwerkteam.de [88.198.48.199])
	by ymir.das-netzwerkteam.de (Postfix) with ESMTPS id 1F0315DAD1
	for <submit@bugs.x2go.org>; Thu,  2 Apr 2015 15:22:42 +0200 (CEST)
Received: from grimnir.das-netzwerkteam.de (grimnir.das-netzwerkteam.de [78.46.204.98])
	by freya.das-netzwerkteam.de (Postfix) with ESMTPS id AB3AD3D3
	for <submit@bugs.x2go.org>; Thu,  2 Apr 2015 15:22:41 +0200 (CEST)
Received: from localhost (localhost [127.0.0.1])
	by grimnir.das-netzwerkteam.de (Postfix) with ESMTP id F04E63C173
	for <submit@bugs.x2go.org>; Thu,  2 Apr 2015 15:22:40 +0200 (CEST)
X-Virus-Scanned: Debian amavisd-new at grimnir.das-netzwerkteam.de
Received: from grimnir.das-netzwerkteam.de ([127.0.0.1])
	by localhost (grimnir.das-netzwerkteam.de [127.0.0.1]) (amavisd-new, port 10024)
	with ESMTP id ReLNbWgRUMDS for <submit@bugs.x2go.org>;
	Thu,  2 Apr 2015 15:22:40 +0200 (CEST)
Received: from grimnir.das-netzwerkteam.de (localhost [127.0.0.1])
	by grimnir.das-netzwerkteam.de (Postfix) with ESMTPS id 7B1E73BE7E
	for <submit@bugs.x2go.org>; Thu,  2 Apr 2015 15:22:40 +0200 (CEST)
Received: from bifrost.das-netzwerkteam.de (bifrost.das-netzwerkteam.de
 [178.62.101.154]) by mail.das-netzwerkteam.de (Horde Framework) with HTTP;
 Thu, 02 Apr 2015 13:22:40 +0000
Date: Thu, 02 Apr 2015 13:22:40 +0000
Message-ID: <20150402132240.Horde.YvyFyWtaWF1i5VjrhgSNow2@mail.das-netzwerkteam.de>
From: Mike Gabriel <mike.gabriel@das-netzwerkteam.de>
To: submit@bugs.x2go.org
User-Agent: Internet Messaging Program (IMP) H5 (6.2.2)
Accept-Language: de,en
Organization: DAS-NETZWERKTEAM
X-Originating-IP: 178.62.101.154
X-Remote-Browser: Mozilla/5.0 (X11; Linux x86_64; rv:32.0) Gecko/20100101
 Firefox/32.0 Iceweasel/32.0
Content-Type: multipart/signed; boundary="=_mwM9hAZYZ1nQSMXcdtDteQ1";
 protocol="application/pgp-signature"; micalg=pgp-sha1
MIME-Version: 1.0

[Message part 1 (text/plain, inline)]
Package: x2gobroker-ssh
Severity: important
Version: 0.0.3.0-preview

x2gobroker-ssh cannot execute x2gobroker-agent if agent-query-mode is  
set to LOCAL.

Reason:

/usr/bin/x2gobroker-ssh is installed with these permissions:

-r-sr-x--- 1 x2gobroker <x2gobroker-users> 6168 Apr  1 06:24  
/usr/bin/x2gobroker-ssh

That means: only users that are members of the POSIX group  
<x2gobroker-users> (in Debian/Ubuntu, this is configurable via  
DebConf) can launch a fully featured X2Go Session Broker instance via  
SSH brokerage.

A user that is member of group <x2gobroker-users> launches  
x2gobroker-ssh and the process permissions are these:

  real uid: <uidNumber-of-the-user>
  real gid: <gidNumber-if-the-user>
  effective uid: x2gobroker
  effective gid: <gidNumber-if-the-user>

So, the setuid flag on /usr/bin/x2gobroker-ssh changes the effective  
user ID, but not the effective group ID.

If agent-query-mode is set to LOCAL, x2gobroker-ssh directly calls  
/usr/lib/x2go/x2gobroker-agent (via subprocess.Popen) and fails,  
because of insufficient priveleges:

-rwsr-x--- 1 root x2gobroker 6168 Apr  2 06:39 /usr/lib/x2go/x2gobroker-agent

Only users that are members of POSIX group "x2gobroker" can launch the  
x2gobroker-agent script (and gain root priveleges). In a sane  
environment, no user is member of this group (except the user  
"x2gobroker").

Solution:
---------

(root@medoc) {~} # cat /etc/sudoers.d/x2gobroker-ssh
# Allow members of group x2gobroker-users to execute any  
/usr/lib/x2go/x2gobroker-agent
%x2gobroker-users	ALL=(:x2gobroker) /usr/lib/x2go/x2gobroker-agent

If the user launching x2gobroker-ssh is member of the group  
<x2gobroker-users>, then the LOCAL query to the x2gobroker-agent is  
run via sudo. If the evoking user is not a member of the  
<x2gobroker-users> group, then no sudo gets used (e.g. for executing  
the x2gobroker-agent via agent-query-mode SSH or via agent-query-mode  
through the http broker implementation.

A patch is in prep and should be committed soon.

Mike
-- 

DAS-NETZWERKTEAM
mike gabriel, herweg 7, 24357 fleckeby
fon: +49 (1520) 1976 148

GnuPG Key ID 0x25771B31
mail: mike.gabriel@das-netzwerkteam.de, http://das-netzwerkteam.de

freeBusy:
https://mail.das-netzwerkteam.de/freebusy/m.gabriel%40das-netzwerkteam.de.xfb

[Message part 2 (application/pgp-signature, inline)]

Send a report that this bug log contains spam.

X2Go Developers <owner@bugs.x2go.org>. Last modified: Thu Nov 21 21:02:56 2024; Machine Name: ymir.das-netzwerkteam.de

X2Go Bug tracking system

Debbugs is free software and licensed under the terms of the GNU Public License version 2. The current version can be obtained from https://bugs.debian.org/debbugs-source/.

Copyright © 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson, 2005-2017 Don Armstrong, and many other contributors.