Alon Bar-Lev wrote:
I do not understand either.
If you run OpenVPN from unprivileged user from startup, this apposed
of letting OpenVPN to setuid(), what do you need to protect in middle
of operation?
On Tue, Jul 28, 2009 at 11:33 AM, Sebastien
Raveau<sebastien.rav...@epita.fr> wrote:
I'm not sure I understand you...
As I explained in
http://article.gmane.org/gmane.network.openvpn.devel/2700 it is indeed
possible to apply SELinux "from the outside" of a program, like
chroot, and just like chroot doing that is less efficient and less
practical.
I hope I'm not interrupting badly now.
A little basic part, for those wanting to understand the depths. What
SELinux provides is access control on different kind of layers inside the
kernel space, also on system calls. For a brief overview over SELinux,
have a look here:
http://www.ibm.com/developerworks/linux/library/l-sppriv.html,
http://www.ibm.com/developerworks/linux/library/l-selinux/index.html?S_TACT=105AGX03&S_CMP=EDU
(A lot of more good SELinux information is available on IBM's
developerWorks site)
It makes sense to do a security context switch after OpenVPN has
initialised and chrooted, then changing security context and drop the rest
of the privileges. In the new OpenVPN security context, it should then not
be allowed to do any chrooting or network configuration (as this is a part
of the initialisation, IMO), and even if possible, setuid() should be
disallowed. That way you can really lock down everything OpenVPN should
not do - just allowing what it needs to do. Basically, the OpenVPN
security context should only be allowed to write to log files, execute code
in plug-ins, read a limited range of files, and read/write to a network
device granting access to the openvpn context.
What I am lacking in this patch, is a security context definition (at least
an example of how to configure a proper context for OpenVPN). Further; has
it been investigated if there need to be done some other context changes to
the TUN/TAP devices? What about other files? If a log file is labelled
var_log_t, will the new openvpn security context be allowed to write to
this log file? How would this work with the security context of the
directory of the log file? (It might be that the easy approach would to do
logging via syslog()) Then what about plug-ins, how would OpenVPN work in
these settings when the SELinux context is changed? F.ex. how would this
patch work against the down-root.so plugin?
I do agree, implementing SELinux in the openvpn code is an important step!
But it seems to be just too easy to do setcon(). It is just missing a
consequence analysis of what else needs to be changed in addition to this
patch.
I'm not an SELinux expert, and Sebastien might know far more about SElinux
than anyone of us. I don't want to trample on anyone feet ... but I just
wanted to have clarified these issues before I can give 100% support to
this patch, as it just seemed to be too easy.
--
kind regards,
David Sommerseth
