Default local auth policy

[Adam Jackson]

On Mon, 2009-03-16 at 12:52 -0700, Eric Anholt wrote:
> On Fri, 2009-03-13 at 13:46 -0400, Adam Jackson wrote:
> > Currently, if you start X without -ac and without -auth, the default
> > connection policy is to allow connections from localhost.  In
> > particular, this means on every IPv[46] address, and any local
> > transports including unix sockets.
> > 
> > I'd like to see a mode where the default policy is effectively
> > +si:localuser:`id -un`, which would allow connections only from the uid
> > that started the server.  This is effectively the policy everyone's
> > trying to implement with xauth cookies, but cookies have to get stored
> > on disk somewhere which sucks for NFS and r/o images, etc.  For the gdm
> > case, the display manager would add the real user to the access list
> > once they've been authed, and then remove itself and start the session
> > as the user.
> > 
> > Normally I'd just change the default here, but I think this might be a
> > significant enough difference in behaviour that you should have to ask
> > for it.  So.  New -localuser option?  Change the default?  Bad idea,
> > give up, take up farming?
> 
> It sounds sensible, the only thing I'm concerned about is whether with
> this new default I could sudo <X app> and still get success.

It's not particularly well specified, at least for
getsockopt(SO_PEERCRED).  The Linux implementation appears to give you
the effective UID, not real, so suid apps would fail.  I'm not sure what
the other OS's implement offhand.

- ajax
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