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Re: [Xen-devel] severe security issue on dom0/xend/xm/non-root users

Tommi Virtanen wrote:
Kurt Garloff wrote:

The frontend (that would acquire the privileged socket) would need
to be setuid root for this and then could enforce whatever policies,
much more flexible than the Unix group membership model if you want.

Oh, the group-restricted UNIX domain socket wins there, too.

Your model:

  - setuid client that only lets certain users open ports <1024

My model:

  - setgid client that only lets certain users connect to the protected
  - just add the certain users to the group, and let them access the
    protected socket.

The UNIX domain socket way is both more flexible and _more secure_
-- it only needs setgid where the port<1024 thing needs setuid.

Agree 100%. There are no advantages to the port<1024 method over using
Unix domain sockets.

Kurt Garloff wrote:
You're very flexible in your setuid root client.

1. You may restrict the set of users that is able to call the client,
e.g. it might be root:trusted 4750. This would impose the same restrictions as your group protection mechanism. 2. The first thing the client does it to acquire the privileged port and then drop capabilities immediately afterwards. Security
   flaws in the client will thus at most grant the exploiter a
   privileged socket. (This has nothing to do with xen, just a
   general rule for setuid root apps.)
3. The client can impose whatever restrictions it likes, e.g.
   checking SSL certificates, asking for passwords, checking
   a configuration file, whatever.

You can 1 and 3 just as easily with the Unix domain socket method.
Although you could also do 2, there's no need (2 is not a flexibility
advantage, it's just something you have to do to make the port<1024
method secure).

David Hopwood <david.nospam.hopwood@xxxxxxxxxxxxxxxx>

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