On Tue, Nov 07, 2017 at 09:01:26AM -0500, Jeff Layton wrote:
> On Tue, 2017-11-07 at 13:31 +0000, Stefan Hajnoczi wrote:
> > On Tue, Oct 31, 2017 at 10:10:38AM -0400, Jeff Layton wrote:
> > > On Fri, 2017-06-30 at 14:23 +0100, Stefan Hajnoczi wrote:
> > > > @@ -595,6 +609,10 @@ int svc_port_is_privileged(struct sockaddr *sin)
> > > >  	case AF_INET6:
> > > >  		return ntohs(((struct sockaddr_in6 *)sin)->sin6_port)
> > > >  			< PROT_SOCK;
> > > > +	case AF_VSOCK:
> > > > +		return ((struct sockaddr_vm *)sin)->svm_port <=
> > > > +			LAST_RESERVED_PORT;
> > > > +
> > > >  	default:
> > > >  		return 0;
> > > >  	}
> > > 
> > > Does vsock even have the concept of a privileged port? I would imagine
> > > that root in a guest VM would carry no particular significance from an
> > > export security standpoint
> > > 
> > > Since you're defining a new transport here, it might be nice write the
> > > RFCs to avoid that distinction, if possible.
> > > 
> > > Note that RDMA just has svc_port_is_privileged always return 1.
> > 
> > AF_VSOCK has the same 0-1023 privileged port range as TCP.
> > 
> 
> But why? And, given that you have 32-bits for a port with AF_VSOCK vs
> the 16 bits on an AF_INET/AF_INET6, why is the range so pitifully small?
> 
> Reserved ports are a bit of a dinosaur holdover from when being root on
> a machine on the Internet meant something. With v4.1 it's much less of
> an issue, but in the "olden days", reserved port exhaustion could be a
> real problem.
> 
> Mandating low ports can also be a problem in other way. Some well known
> services use ports in the ephemeral range, and if your service starts
> late and someone else has taken the port for an ephemeral one, you're
> out of luck.
> 
> I think we have to ask ourselves:
> 
> Should the ability to open a low port inside of a VM carry any
> significance at all to an RPC server? I'd suggest not, and I think it'd
> be good to word the RFC to make that explicitly clear.

AF_VSOCK has had the reserved port range since it was first merged in
2013.  That's before my time but I do see some use for identifying
connections coming from privileged processes.

Given that TCP has the same privileged port range, is there any reason
why AF_VSOCK would be any worse off than TCP for having it?

Stefan