linux-kernel - Re: [RFC] Privilege dropping security module

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Message-ID: <20090923223110.GA1449@c.hsd1.tn.comcast.net>
Date:	Wed, 23 Sep 2009 22:31:10 +0000
From:	Andy Spencer <andy753421@...il.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] Privilege dropping security module

> Hi Andy. Git is a wonderful tool, but if you want people to review
> your work you need to post patches.

Thanks for letting me know, I've posted a separate message with patch.

> And what do you propose as an interesting use case for dpriv?

I think the two most important things about dpriv is that it can be used
by ordinary users and that is can create policies programmatically.

Being able to use dpriv as a non root user is pretty strait forward. For
example, a user of a multi-user system may want to try some untrusted
code without risking access to the rest of the system:

  $ cd ~/my_project
  $ echo rxRX   /                > /sys/kernel/security/dpriv/stage
  $ echo X      $HOME            > /sys/kernel/security/dpriv/stage
  $ echo rwxRWX $HOME/my_project > /sys/kernel/security/dpriv/stage
  $ echo commit                  > /sys/kernel/security/dpriv/control
  $ patch < untrusted.patch
  $ make && ./src/some_exe

The above example also demonstrates how dpriv can be used
programmatically. That is, a policy for allowing read-write-exec access
to build and test tools in ~/my_project didn't have to exist ahead of
time.

A more realistic example might be for a virtual hosting web server where
you want apache to only have access to the files for the current virtual
host.

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