Re: [PATCH net-next v12 04/12] vsock: add netns support to virtio transports

[Bobby Eshleman]

On Tue, Dec 02, 2025 at 11:18:14AM +0100, Paolo Abeni wrote:
> On 11/27/25 8:47 AM, Bobby Eshleman wrote:
> > @@ -674,6 +689,17 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
> >  		goto out;
> >  	}
> >  
> > +	net = current->nsproxy->net_ns;
> > +	vsock->net = get_net_track(net, &vsock->ns_tracker, GFP_KERNEL);
> > +
> > +	/* Store the mode of the namespace at the time of creation. If this
> > +	 * namespace later changes from "global" to "local", we want this vsock
> > +	 * to continue operating normally and not suddenly break. For that
> > +	 * reason, we save the mode here and later use it when performing
> > +	 * socket lookups with vsock_net_check_mode() (see vhost_vsock_get()).
> > +	 */
> > +	vsock->net_mode = vsock_net_mode(net);
> 
> I'm sorry for the very late feedback. I think that at very least the
> user-space needs a way to query if the given transport is in local or
> global mode, as AFAICS there is no way to tell that when socket creation
> races with mode change.

Are you thinking something along the lines of sockopt?

> 
> Also I'm a bit uneasy with the model implemented here, as 'local' socket
> may cross netns boundaris and connect to 'local' socket in other netns
> (if I read correctly patch 2/12). That in turns AFAICS break the netns
> isolation.

Local mode sockets are unable to communicate with local mode (and global
mode too) sockets that are in other namespaces. The key piece of code
for that is vsock_net_check_mode(), where if either modes is local the
namespaces must be the same.

> 
> Have you considered instead a slightly different model, where the
> local/global model is set in stone at netns creation time - alike what
> /proc/sys/net/ipv4/tcp_child_ehash_entries is doing[1] - and
> inter-netns connectivity is explicitly granted by the admin (I guess
> you will need new transport operations for that)?
> 
> /P
> 
> [1] tcp allows using per-netns established socket lookup tables - as
> opposed to the default global lookup table (even if match always takes
> in account the netns obviously). The mentioned sysctl specify such
> configuration for the children namespaces, if any.
> 

I'll save this discussion if the above doesn't resolve your concerns.

Best,
Bobby