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

[Stefano Garzarella <sgarzare@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...
>

Yeah, I was going to ask what inet does, also because I don't really 
like the code we have now (not your fault at all).

But maybe is too out of scope to resolve in this series, so I guess just 
moving what we have per-ns LGTM for now!

Stefano