Re: RFC: [PATCH] SCM_CREDS support

[Samuel Thibault]

Svante Signell, le Thu 24 Oct 2013 17:04:58 +0200, a écrit :
> On Thu, 2013-10-24 at 16:08 +0200, Samuel Thibault wrote:
> > Svante Signell, le Thu 24 Oct 2013 15:38:11 +0200, a écrit :
> 
> > > > > +      goto label;
> > > > 
> > > > Why skipping SCM_RIGHTS support?  The message may contain *both*
> > > > SCM_RIGHT and SCM_CREDS, we have to support that.  Likewise on the
> > > > receiver side.
> > > 
> > > I have never seen any application using that.
> > 
> > That doesn't mean that we can avoid supporting it.
> 
> This can easily be changed, if the -nz option is scrapped.

What is the relation with the -nz option?

> > > What about the _hurd_check_ids() call?
> > 
> > That is a completely different thing: _hurd_check_ids talks with the
> > auth server of the process, which it trusts.
> 
> In the patch there is a call to _hurd_check_ids first.

Ah.  Err, what is it useful for actually?

> > > > So I'd say a completely different way is needed to check the pid of the
> > > > sender. The matter here is that only pflocal has a port to the sender,
> > > > the receiver doesn't have one. Another noticeable thing is that the
> > > > receiver trusts pflocal, so if pflocal provides information about the
> > > > sender (such as a task port of the sender), the receiver can trust it,
> > > > and safely use proc_task2pid etc. to get information about it from its
> > > > own proc and auth servers.  So probably adding something to pflocal can
> > > > provide a solution.
> > > 
> > > Can you elaborate?
> > 
> > I mean something like extending pflocal RPCs, to include the task port
> > of the sender along the socket_send/recv path.  I however don't know how
> > the pflocal side of S_socket_send can know which task emitted the RPC.
> > That's probably the main problem to be solved.
> 
> This in non-trivial, right?

I don't know without thinking more about it.  Possibly it is, digging
the issue would tell.

> So modifying S_io_reauthenticate used for SCM_CREDS is not workable?

I'm not sure what you mean exactly, but using *_reauthenticate
might be a since way without having to modify pflocal, yes: see
the hurd-talk.html page on the wiki, “Establishing trusted
connections”, the sender would pass the rendez-vous port through
the socket, call auth_user_authenticate, and the receiver would call
auth_server_authenticate with the rendez-vous port.  That should work at
least for the uid/gid part, getting that part working would already be
useful.  Something similar is perhaps available to get the pid securely,
or else extending proc should be not too hard.

Samuel