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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 12, 2026 at 04:52:31PM -0800, Bobby Eshleman wrote:
> 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 <bobbyeshleman@meta.com>
> > > > 
> > > > 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 <bobbyeshleman@meta.com>
> > > 
> > > ...
> > > 
> > > 
> > > >  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...

Also acceptable.