On Thu, Nov 16, 2017 at 03:53:04PM -0500, Chuck Lever wrote: > > > On Nov 16, 2017, at 10:25 AM, Stefan Hajnoczi <stefanha@xxxxxxxxxx> wrote: > > > > 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? > > I agree with Jeff that we need to think carefully about this. > > I don't especially care for the privileged port check, but: > > In this case, you are inventing an RPC transport that makes > it impossible to use strong security (ie, RPCSEC_GSS). We > should be careful about removing the check because only > AUTH_NULL and AUTH_UNIX security can be used in this kind > of deployment. > > Privileged ports are easy to spoof if there is an opportunity > for a MitM attack to alter the port number of RPCs in transit. > With VSOCK there may be no such opportunity, thus privileged > ports might provide an adequate level of security here. I > make that claim with no deep experience of VSOCK environments. > > When writing the VSOCK-related RFCs, you will need to provide > a very clear and concise rationale to the IESG for purposely > not supporting the use of RPCSEC_GSS. It will start with "well, > these RPCs do not flow on open networks and are thus not > subject to MitM attacks"; then proceed to careful discussion of > how the server will guard against rogue users on guests, and > assumptions about the trust relationship between the guests > and the host. You will have to make AUTH_UNIX into a defensible > deployment choice, and port privilege might be a part of that. > > Note also that the NFSv4 standards require that implementations > can support RPCSEC_GSS. NFSv4 on VSOCK cannot. Something will > have to be done about that. Thanks! I will cover it in the draft RFC. Stefan
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