Subject: Re: [PATCH RFC net-next v13 02/13] vsock: add netns to vsock core

From: Bobby Eshleman <[email-masked]>
Date: Mon, 12 Jan 2026 16:52:31 -0800

On Mon, Jan 12, 2026 at 03:34:31PM -0800, Bobby Eshleman wrote:
> On Sun, Jan 11, 2026 at 01:43:37AM -0500, Michael S. Tsirkin wrote:
> > On Tue, Dec 23, 2025 at 04:28:36PM -0800, Bobby Eshleman wrote:
> > > From: Bobby Eshleman <[email-masked]>
> > > 
> > > Add netns logic to vsock core. Additionally, modify transport hook
> > > prototypes to be used by later transport-specific patches (e.g.,
> > > *_seqpacket_allow()).
> > > 
> > > Namespaces are supported primarily by changing socket lookup functions
> > > (e.g., vsock_find_connected_socket()) to take into account the socket
> > > namespace and the namespace mode before considering a candidate socket a
> > > "match".
> > > 
> > > This patch also introduces the sysctl /proc/sys/net/vsock/ns_mode to
> > > report the mode and /proc/sys/net/vsock/child_ns_mode to set the mode
> > > for new namespaces.
> > > 
> > > Add netns functionality (initialization, passing to transports, procfs,
> > > etc...) to the af_vsock socket layer. Later patches that add netns
> > > support to transports depend on this patch.
> > > 
> > > dgram_allow(), stream_allow(), and seqpacket_allow() callbacks are
> > > modified to take a vsk in order to perform logic on namespace modes. In
> > > future patches, the net will also be used for socket
> > > lookups in these functions.
> > > 
> > > Signed-off-by: Bobby Eshleman <[email-masked]>
> > 
> > ...
> > 
> > 
> > >  static int __vsock_bind_connectible(struct vsock_sock *vsk,
> > >  				    struct sockaddr_vm *addr)
> > >  {
> > > +	struct net *net = sock_net(sk_vsock(vsk));
> > >  	static u32 port;
> > >  	struct sockaddr_vm new_addr;
> > >
> > 
> > 
> > Hmm this static port gives me pause. So some port number info leaks
> > between namespaces. I am not saying it's a big security issue
> > and yet ... people expect isolation.
> 
> Probably the easiest solution is making it per-ns, my quick rough draft
> looks like this:
> 
> diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
> index e2325e2d6ec5..b34d69a22fa8 100644
> --- a/include/net/netns/vsock.h
> +++ b/include/net/netns/vsock.h
> @@ -11,6 +11,10 @@ enum vsock_net_mode {
>  
>  struct netns_vsock {
>  	struct ctl_table_header *sysctl_hdr;
> +
> +	/* protected by the vsock_table_lock in af_vsock.c */
> +	u32 port;
> +
>  	enum vsock_net_mode mode;
>  	enum vsock_net_mode child_ns_mode;
>  };
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 9d614e4a4fa5..cd2a47140134 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -748,11 +748,10 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
>  				    struct sockaddr_vm *addr)
>  {
>  	struct net *net = sock_net(sk_vsock(vsk));
> -	static u32 port;
>  	struct sockaddr_vm new_addr;
>  
> -	if (!port)
> -		port = get_random_u32_above(LAST_RESERVED_PORT);
> +	if (!net->vsock.port)
> +		net->vsock.port = get_random_u32_above(LAST_RESERVED_PORT);
>  
>  	vsock_addr_init(&new_addr, addr->svm_cid, addr->svm_port);
>  
> @@ -761,11 +760,11 @@ static int __vsock_bind_connectible(struct vsock_sock *vsk,
>  		unsigned int i;
>  
>  		for (i = 0; i < MAX_PORT_RETRIES; i++) {
> -			if (port == VMADDR_PORT_ANY ||
> -			    port <= LAST_RESERVED_PORT)
> -				port = LAST_RESERVED_PORT + 1;
> +			if (net->vsock.port == VMADDR_PORT_ANY ||
> +			    net->vsock.port <= LAST_RESERVED_PORT)
> +				net->vsock.port = LAST_RESERVED_PORT + 1;
>  
> -			new_addr.svm_port = port++;
> +			new_addr.svm_port = net->vsock.port++;
>  
>  			if (!__vsock_find_bound_socket_net(&new_addr, net)) {
>  				found = true;
> 
> 
> 

Another option being to follow inet's path and use
siphash_4u32() the way that secure_ipv4_port_ephemeral() does...