Re: The problem with TUN/TAP devices

[Paul Moore <paul.moore@hp.com>]

On Tuesday 30 June 2009 11:32:30 pm Casey Schaufler wrote:
> Paul Moore wrote:
> > Unfortunately we have a problem with the network access controls and
> > TUN/TAP devices.  The basic issue is that packets entering the stack via
> > a TUN device, e.g. QEMU/KVM guest instance operating with a bridged
> > network configuration, do not have a fully initialized sock associated
> > with them.  I say "fully initialized" because the basic initialization
> > has been done (memory allocated, initial values set to
> > SECINITSID_UNLABELED, etc.) but the last step where we assign the sock a
> > label/SID never happens.  Why?  Because the TUN driver code only calls
> > sk_alloc() and nothing else in the TUN code paths finish the SELinux sock
> > setup.
>
> So what should it be calling and why is the fact that it isn't not a bug
> in the TUN driver?

...

> As this would appear to be a flaw in the TUN driver, get the TUN
> developers to fix their broken driver. I certainly dislike a special
> purpose LSM hook for this.

I do too.

> Do you see this as a problem for all users of labeled networking,
> or is it isolated to SELinux?

The issue first came up with respect to SELinux so that is where I've been 
looking/thinking.  While there is a potential for Smack to be affected I doubt 
that will be he case since Smack doesn't really care about stuff at the 
postrouting level; although Smack may want to enforce some level of access 
control but I need to go re-remember how Smack does outbound access control.  
TOMOYO should be unaffected since they don't mess with labels.

-- 
paul moore
linux @ hp


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