netdev - Re: AF_VSOCK unimplemented sockopts

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Message-ID: <20170815083618.GD32702@stefanha-x1.localdomain>
Date:   Tue, 15 Aug 2017 09:36:18 +0100
From:   Stefan Hajnoczi <stefanha@...hat.com>
To:     "Jorgen S. Hansen" <jhansen@...are.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: AF_VSOCK unimplemented sockopts

On Fri, Aug 11, 2017 at 09:23:17AM +0000, Jorgen S. Hansen wrote:
> > On Aug 3, 2017, at 12:41 PM, Stefan Hajnoczi <stefanha@...hat.com> wrote:
> > 
> > Hi Jorgen,
> > There are 3 sockopts defined in include/uapi/linux/vm_sockets.h that are
> > currently not implemented in net/vmw_vsock/af_vsock.c:
> > 
> > * SO_VM_SOCKETS_PEER_HOST_VM_ID
> > * SO_VM_SOCKETS_TRUSTED
> > * SO_VM_SOCKETS_NONBLOCK_TXRX
> > 
> > I noticed this because SO_VM_SOCKETS_TRUSTED is interesting for
> > virtio-vsock.  Services listening on AF_VSOCK inside the guest may not
> > want arbitrary unprivileged host processes to connect.  Instead of
> > inventing a new solution I wanted to look into SO_VM_SOCKETS_TRUSTED but
> > found it is not implemented in linux.git.
> > 
> > What is the status of these sockets?
> 
> These options were only implemented for ESX host endpoints, so were never part of the Linux host side support. It looks like they could have been omitted from vm_sockets.h, when the initial upstreaming was performed.
> 
> On ESX, the equivalent of SO_VM_SOCKETS_TRUSTED, is used for retrieving the value of s->trusted of a VMCI socket. It cannot be used to mark a socket as trusted. On Linux, trusted is tied to the CAP_NET_ADMIN capability of the socket creator. VMCI based vSockets will per default only allow host side sockets that are trusted, or are created by the same user as the VM, to communicate with a given VM. This is achieved by per default creating VMs with the VMCI privilege flag VMCI_PRIVILEGE_FLAG_RESTRICTED. It is possible to create a VM that isn’t restricted, in which case any host process will be able to communicate with the VM.
> 
> So it should be straight forward to implement the getsockopt part of SO_VM_SOCKETS_TRUSTED, since it just needs to return s->trusted.

Currently virtio-vsock does not implement the 'restricted' mode but I'm
evaluating using it by default for stronger security.  Thanks for your
response!

Stefan

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