On Tue, 15 Sept 2026 at 17:28, Stefano Garzarella <[email protected]> wrote:
>
> On Wed, Sep 02, 2026 at 04:00:48PM -0700, Bobby Eshleman wrote:
> >From: Bobby Eshleman <[email protected]>
> >
> >Namespaces let a host isolate a VM's vsock traffic to a specific
> >namespace, but in a guest vsock traffic cannot be isolated to a
> >namespace. The vsock device is hardcoded to global mode and can't be
> >moved into a local-mode namespace.
> >
> >Introduce ioctl IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS on /dev/vsock that
>
> We already discussed about netlink, but I'm not sure how much work can
> take, here just another alternative, what about adding
> /proc/sys/net/vsock/g2h_owner sysctl that can be read/write where:
> 0 - no owner
> 1 - owner
>
> 0 -> 1 transition, move the device in the new nets
> 1 -> 0 transition, reset back to init_ns
>
> >gives userspace a way to move the device to the calling pid's namespace.
> >The call requires CAP_NET_ADMIN in the root user namespace. A privileged
> >user wishing to "unassign" the device can move it to the init_netns,
> >which is hardcoded to global mode (so no unassign call is necessary).
> >
> >A getter to read the current assignment back was considered, returning
> >either the namespace's net_cookie or its nsfs inode number, but neither
> >seemed useful enough to bake into the uAPI now. It can be added later if
> >a user turns up that needs it.
> >
> >Add a transport hook to indicate support for guest namespacing, so that
> >transports may opt in/out. A transport that opts out keeps the
> >reachability rules it had before this ioctl existed.
> >
> >Sockets are reset when the underlying device moves to a different
> >namespace, so as to prevent reachability from the previous and now
> >disallowed namespace.
> >
> >Following the approach of netdevs, the device returns to init_net when
> >its namespace is removed. Care is taken to not break flows when the
> >device is inside a global namespace that is being torn down and alive
> >sockets are in a different global namespace. In this scenario, the
> >device's netns getter pre-emptively falls back to the init_net (always
> >global) so that these flows are not disrupted. If init_netns ever
> >supports local-mode in the future, this logic will have to be changed.
> >
> >Suggested-by: Stefano Garzarella <[email protected]>
> >Link: https://lore.kernel.org/all/20200427142518.uwssa6dtasrp3bfc@steredhat/
> >Signed-off-by: Bobby Eshleman <[email protected]>
> >---
> > Documentation/admin-guide/sysctl/net.rst | 18 +++
> > include/net/af_vsock.h | 7 ++
> > include/uapi/linux/vm_sockets.h | 6 +
> > net/vmw_vsock/af_vsock.c | 198
> > ++++++++++++++++++++++++++++++-
> > 4 files changed, 228 insertions(+), 1 deletion(-)
> >
> >diff --git a/Documentation/admin-guide/sysctl/net.rst
> >b/Documentation/admin-guide/sysctl/net.rst
> >index e586e17fc7a5..1e9c0d2be7b8 100644
> >--- a/Documentation/admin-guide/sysctl/net.rst
> >+++ b/Documentation/admin-guide/sysctl/net.rst
> >@@ -515,6 +515,24 @@ their hosts. The behavior of VSOCK sockets in a network
> >namespace is determined
> > by the namespace's mode (``global`` or ``local``), which controls how CIDs
> > (Context IDs) are allocated and how sockets interact across namespaces.
> >
> >+In a guest, the vsock device owned by the guest-to-host (G2H) transport
> >belongs
> >+to one network namespace at a time. The
> >``IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS``
> >+ioctl on ``/dev/vsock`` moves it to the namespace of the calling process,
> >which
> >+requires ``CAP_NET_ADMIN`` in the initial user namespace. The namespace's
> >mode
> >+decides who may then use the device:
> >+
> >+- ``global`` - every ``global`` mode namespace may use it.
> >+- ``local`` - only that namespace may use it, which reserves the connection
> >to
> >+ the host for it alone.
> >+
> >+The device starts out in the initial namespace, so until the ioctl is issued
> >+nothing has moved and no mode has changed.
> >+
> >+Connections made before the move, from a namespace that can no longer reach
> >the
> >+device, are reset. The device returns to the initial namespace when the
> >+namespace it was moved to is deleted, so assigning it to the initial
> >namespace
> >+is how an assignment is undone.
> >+
> > ns_mode
> > -------
> >
> >diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
> >index 87fdec60ba45..64c4b205a11b 100644
> >--- a/include/net/af_vsock.h
> >+++ b/include/net/af_vsock.h
> >@@ -190,6 +190,9 @@ struct vsock_transport {
> >
> > /* Zero-copy. */
> > bool (*msgzerocopy_allow)(void);
> >+
> >+ /* True if the transport honours IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS. */
>
> "if the G2H transport ..."
>
> >+ bool (*netns_assign_allow)(void);
>
> What about having just a bool (and maybe we should do the same for
> msgzerocopy_allow())?
>
> > };
> >
> > /**** CORE ****/
> >@@ -235,6 +238,10 @@ void vsock_for_each_connected_socket(const struct
> >vsock_transport *transport,
> > int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk);
> > bool vsock_find_cid(unsigned int cid);
> > void vsock_linger(struct sock *sk);
> >+struct net *vsock_g2h_net_get(void);
> >+bool vsock_g2h_net_reachable(struct net *net);
> >+bool vsock_g2h_reachable_sk(struct vsock_sock *vsk);
> >+bool vsock_maybe_set_connected(struct vsock_sock *vsk);
> >
> > /**** TAP ****/
> >
> >diff --git a/include/uapi/linux/vm_sockets.h
> >b/include/uapi/linux/vm_sockets.h
> >index e05280e41522..894b0d65b458 100644
> >--- a/include/uapi/linux/vm_sockets.h
> >+++ b/include/uapi/linux/vm_sockets.h
> >@@ -195,6 +195,12 @@ struct sockaddr_vm {
> >
> > #define IOCTL_VM_SOCKETS_GET_LOCAL_CID _IO(7, 0xb9)
> >
> >+/* Assign the guest's vsock device to the network namespace of the calling
> >+ * process. Requires CAP_NET_ADMIN in the initial user namespace. To undo an
> >+ * assignment, assign the device to the initial network namespace.
> >+ */
> >+#define IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS _IO(7, 0xba)
> >+
> > /* MSG_ZEROCOPY notifications are encoded in the standard error format,
> > * sock_extended_err. See Documentation/networking/msg_zerocopy.rst in
> > * kernel source tree for more details.
> >diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> >index 29cde17e08f3..ad11f0f56eb8 100644
> >--- a/net/vmw_vsock/af_vsock.c
> >+++ b/net/vmw_vsock/af_vsock.c
> >@@ -130,6 +130,24 @@
> > * a different transport that *does* support local mode. For
> > * example, virtio-vsock may not support local mode, but the socket
> > * may still accept a connection from vhost-vsock which does.
> >+ *
> >+ * - A guest has a single vsock device, owned by the guest->host transport.
> >+ * IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS on /dev/vsock assigns it to the
> >+ * namespace of the caller. It starts out in init_net. The mode rules then
> >+ * decide who may use it, and which namespace packets from the host are
> >+ * delivered to:
> >+ *
> >+ * - assigned to a global mode namespace - every global mode namespace may
> >+ * use it. Until the ioctl is issued nothing has moved and no mode has
> >+ * changed, so the default is the behaviour that predates it.
> >+ * - assigned to a local mode namespace - only that namespace may use it.
> >+ * This is how a nested VM is isolated from the rest of the guest.
> >+ *
> >+ * Connections made before an assignment, from a namespace that can no
> >+ * longer reach the device, are reset.
> >+ *
> >+ * No reference is taken on the assigned namespace. As is done for
> >netdevs,
> >+ * the device is moved back to init_net when that namespace is destroyed.
> > */
> >
> > #include <linux/compat.h>
> >@@ -208,6 +226,11 @@ static const struct vsock_transport *transport_dgram;
> > static const struct vsock_transport *transport_local;
> > static DEFINE_MUTEX(vsock_register_mutex);
> >
> >+/* Network namespace of the g2h device. Protected by
> >+ * vsock_register_mutex/RCU.
> >+ */
> >+static struct net __rcu *vsock_g2h_net = RCU_INITIALIZER(&init_net);
> >+
> > /**** UTILS ****/
> >
> > /* Each bound VSocket is stored in the bind hash table and each connected
> >@@ -548,6 +571,17 @@ static void vsock_deassign_transport(struct vsock_sock
> >*vsk)
> > vsk->transport = NULL;
> > }
> >
> >+/* Return true if the loaded g2h transport honours namespace assignment. One
> >+ * that does not keeps the reachability rules it had before the ioctl
> >existed.
> >+ *
> >+ * Must be called with vsock_register_mutex held.
> >+ */
> >+static bool vsock_g2h_netns_assignable(void)
> >+{
> >+ return transport_g2h && transport_g2h->netns_assign_allow &&
> >+ transport_g2h->netns_assign_allow();
> >+}
> >+
> > /* Assign a transport to a socket and call the .init transport callback.
> > *
> > * Note: for connection oriented socket this must be called when
> > vsk->remote_addr
> >@@ -622,6 +656,13 @@ int vsock_assign_transport(struct vsock_sock *vsk,
> >struct vsock_sock *psk)
> > goto err;
> > }
> >
> >+ if (new_transport && new_transport == transport_g2h &&
> >+ vsock_g2h_netns_assignable() &&
> >+ !vsock_g2h_net_reachable(sock_net(sk))) {
> >+ ret = -ENETUNREACH;
> >+ goto err;
> >+ }
> >+
> > /* We increase the module refcnt to prevent the transport unloading
> > * while there are open sockets assigned to it.
> > */
> >@@ -710,6 +751,140 @@ bool vsock_find_cid(unsigned int cid)
> > }
> > EXPORT_SYMBOL_GPL(vsock_find_cid);
> >
> >+/* Return the g2h devices' namespace with a reference held, or NULL if that
> >+ * namespace is being destroyed.
> >+ */
> >+struct net *vsock_g2h_net_get(void)
> >+{
> >+ struct net *assigned;
> >+ struct net *net;
> >+
> >+ rcu_read_lock();
> >+ assigned = rcu_dereference(vsock_g2h_net);
> >+ net = maybe_get_net(assigned);
> >+
> >+ /* !net means the net is about to be destroyed, at which point the g2h
> >+ * device will move to the init_net. If the init_net and the dying
> >net
> >+ * are both global mode, we use the init_net as a fallback to avoid
> >+ * disrupting global-mode flows. The per-net destructor hook will
> >+ * eventually move the g2h device to the init_net anyway.
> >+ */
> >+ if (!net && vsock_net_check_mode(&init_net, assigned))
> >+ net = get_net(&init_net);
> >+ rcu_read_unlock();
> >+
> >+ return net;
> >+}
> >+EXPORT_SYMBOL_GPL(vsock_g2h_net_get);
> >+
> >+bool vsock_g2h_net_reachable(struct net *net)
> >+{
> >+ bool reachable;
> >+
> >+ rcu_read_lock();
> >+ reachable = vsock_net_check_mode(net, rcu_dereference(vsock_g2h_net));
> >+ rcu_read_unlock();
> >+
> >+ return reachable;
> >+}
> >+EXPORT_SYMBOL_GPL(vsock_g2h_net_reachable);
> >+
> >+bool vsock_g2h_reachable_sk(struct vsock_sock *vsk)
> >+{
> >+ const struct vsock_transport *t = vsk->transport;
> >+
> >+ if (!t || !t->netns_assign_allow || !t->netns_assign_allow())
> >+ return true;
Can we have a single helper and call it with t or transport_g2h here
and where vsock_g2h_netns_assignable() is used?
> >+
> >+ return vsock_g2h_net_reachable(sock_net(sk_vsock(vsk)));
> >+}
> >+EXPORT_SYMBOL_GPL(vsock_g2h_reachable_sk);
>
> This seems used only in af_vsock.c
>
> >+
> >+/* Move @vsk to TCP_ESTABLISHED and into the connected table, unless the
> >device
> >+ * has moved to a namespace @vsk cannot reach. Returns false without doing
> >+ * either in that case.
> >+ *
> >+ * vsock_g2h_net_assign() resets the sockets it finds in the same table
> >under
> >+ * the same lock. Either vsock_g2h_net_assign() sees the vsk in the table
> >and
> >+ * resets it, or it does not see the @vsk in the table and this function
> >+ * refuses to add it. This avoids netns assignment racing with outstanding
> >+ * connection responses and incoming connection requests.
> >+ */
> >+bool vsock_maybe_set_connected(struct vsock_sock *vsk)
> >+{
> >+ struct list_head *list = vsock_connected_sockets(&vsk->remote_addr,
> >+ &vsk->local_addr);
> >+ bool reachable;
> >+
> >+ spin_lock_bh(&vsock_table_lock);
> >+ reachable = vsock_g2h_reachable_sk(vsk);
> >+ if (reachable) {
> >+ sk_vsock(vsk)->sk_state = TCP_ESTABLISHED;
> >+ __vsock_insert_connected(list, vsk);
> >+ }
> >+ spin_unlock_bh(&vsock_table_lock);
> >+
> >+ return reachable;
> >+}
> >+EXPORT_SYMBOL_GPL(vsock_maybe_set_connected);
> >+
> >+static void vsock_reset_unreachable_sock(struct sock *sk)
> >+{
> >+ if (vsock_g2h_net_reachable(sock_net(sk)))
> >+ return;
> >+
> >+ sk->sk_state = TCP_CLOSE;
> >+ sk->sk_err = ECONNRESET;
> >+ sk_error_report(sk);
>
> Should we send the reset to the other peer too?
>
> Or avoid to set TCP_CLOSE, so the user will see the error and close it?
>
> >+}
> >+
> >+/* Move the g2h device to @net. Returns -ENODEV if no g2h transport is
> >loaded
> >+ * and -EOPNOTSUPP if the loaded one cannot be moved.
> >+ */
> >+static int vsock_g2h_net_assign(struct net *net)
> >+{
> >+ int ret = 0;
> >+
> >+ mutex_lock(&vsock_register_mutex);
> >+ if (!transport_g2h) {
> >+ ret = -ENODEV;
> >+ } else if (!vsock_g2h_netns_assignable()) {
> >+ ret = -EOPNOTSUPP;
> >+ } else {
> >+ /* See vsock_maybe_set_connected() comment about synchronizing
> >+ * with connecting sockets.
> >+ */
> >+ rcu_assign_pointer(vsock_g2h_net, net);
> >+ vsock_for_each_connected_socket(transport_g2h,
> >+ vsock_reset_unreachable_sock);
> >+ }
> >+ mutex_unlock(&vsock_register_mutex);
> >+
> >+ return ret;
> >+}
> >+
> >+/* Move the g2h device back to init_net if it lives in @net, which is about
> >to
> >+ * be destroyed.
> >+ */
> >+static void vsock_g2h_net_reset(struct net *net)
> >+{
> >+ bool reset = false;
> >+
> >+ /* Avoid taking the mutex if the namespaces don't match. */
> >+ if (likely(rcu_access_pointer(vsock_g2h_net) != net))
> >+ return;
> >+
> >+ mutex_lock(&vsock_register_mutex);
> >+ if (rcu_access_pointer(vsock_g2h_net) == net) {
> >+ rcu_assign_pointer(vsock_g2h_net, &init_net);
> >+ reset = true;
> >+ }
> >+ mutex_unlock(&vsock_register_mutex);
> >+
> >+ if (reset)
> >+ synchronize_rcu();
> >+}
> >+
> > static struct sock *vsock_dequeue_accept(struct sock *listener)
> > {
> > struct vsock_sock *vlistener;
> >@@ -2745,6 +2920,15 @@ static long vsock_dev_do_ioctl(struct file *filp,
> > retval = -EFAULT;
> > break;
> >
> >+ case IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS:
> >+ if (!capable(CAP_NET_ADMIN)) {
> >+ retval = -EPERM;
> >+ break;
> >+ }
> >+
> >+ retval = vsock_g2h_net_assign(current->nsproxy->net_ns);
> >+ break;
> >+
> > default:
> > retval = -ENOIOCTLCMD;
> > }
> >@@ -2978,6 +3162,7 @@ static __net_init int vsock_sysctl_init_net(struct net
> >*net)
> >
> > static __net_exit void vsock_sysctl_exit_net(struct net *net)
> > {
> >+ vsock_g2h_net_reset(net);
>
> Why calling this in the sysctl_exit ?
>
> > vsock_sysctl_unregister(net);
> > }
> >
> >@@ -3104,13 +3289,21 @@ EXPORT_SYMBOL_GPL(vsock_core_register);
> >
> > void vsock_core_unregister(const struct vsock_transport *t)
> > {
> >+ bool g2h_net_reset = false;
> >+
> > mutex_lock(&vsock_register_mutex);
> >
> > if (transport_h2g == t)
> > transport_h2g = NULL;
> >
> >- if (transport_g2h == t)
> >+ if (transport_g2h == t) {
> > transport_g2h = NULL;
> >+ /* The device is gone, so is its namespace assignment. */
> >+ if (rcu_access_pointer(vsock_g2h_net) != &init_net) {
> >+ rcu_assign_pointer(vsock_g2h_net, &init_net);
> >+ g2h_net_reset = true;
> >+ }
> >+ }
> >
> > if (transport_dgram == t)
> > transport_dgram = NULL;
> >@@ -3119,6 +3312,9 @@ void vsock_core_unregister(const struct
> >vsock_transport *t)
> > transport_local = NULL;
> >
> > mutex_unlock(&vsock_register_mutex);
> >+
> >+ if (g2h_net_reset)
> >+ synchronize_rcu();
>
> Why we need this? (I'd add also a comment with the reason)
>
> > }
> > EXPORT_SYMBOL_GPL(vsock_core_unregister);
> >
> >
> >--
> >2.53.0-Meta
> >
