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

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Message-ID: <aS9FYWd3SDYu6U1v@devvm11784.nha0.facebook.com>
Date: Tue, 2 Dec 2025 12:00:33 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, g@...0.facebook.com
Cc: Stefano Garzarella <sgarzare@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	Bryan Tan <bryan-bt.tan@...adcom.com>,
	Vishnu Dasa <vishnu.dasa@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux.dev, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-hyperv@...r.kernel.org,
	linux-kselftest@...r.kernel.org, berrange@...hat.com,
	Sargun Dhillon <sargun@...gun.me>,
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v12 04/12] vsock: add netns support to virtio
 transports

On Tue, Dec 02, 2025 at 09:56:02AM -0800, Bobby Eshleman wrote:
> 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?
> 

To clarify... do we want the user to be able to query the socket for
which namespace mode it is in (so the results of the race can be
queried), or are you looking for a way for the user to query if the
transport supports local mode (maybe via /dev/vsock ioctl).

I'm not sure we can attach a namespace to a transport per-se, as
different namespaces in different modes can use the same transport.

Best,
Bobby

> > 
> > 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