# Re: \[PATCH net-next 2/6\] vsock: add IOCTL\_VM\_SOCKETS\_ASSIGN\_G2H\_NETNS - From: Stefano Garzarella \ - Date: 2026-09-15 15:28:36 - List: netdev - Page: https://ratatoskr.run/netdev/2026/09/17580525 - Thread: https://ratatoskr.run/virtualization/2026/09/17501255/t.md ```text On Wed, Sep 02, 2026 at 04:00:48PM -0700, Bobby Eshleman wrote: >From: Bobby Eshleman > >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 >Link: https://lore.kernel.org/all/20200427142518.uwssa6dtasrp3bfc@steredhat/ >Signed-off-by: Bobby Eshleman >--- > 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 >@@ -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; >+ >+ 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 > ```