On Wed, Sep 16, 2026 at 02:57:43PM +0200, Stefano Garzarella wrote: > On Tue, Sep 15, 2026 at 11:50:10AM -0700, Bobby Eshleman wrote: > > On Tue, Sep 15, 2026 at 05:28:25PM +0200, Stefano Garzarella 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 > > > > That seems reasonable, but if multi-device support ever lands, this > > might be harder to adapt cleanly? > > I see, but maybe we can have a dev0/ dev1/ subfolders in that case. > > > > > > > > > > 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(-) > > > > > > [...] > > > > > + > > > > +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? > > > > Sending the reset sounds good. At least the peer won't be waiting around > > forever. Will work that into v2. > > If it's too much of work, we can skip it, it's not a strong opinion on my > side. It was more a question of what we should do ;-) > > > > > > > > > > +} > > > > + > > > > +/* 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 ? > > > > Should we add another pernet_operations? I agree the name of > > vsock_sysctl_ops does not really fit as a general "do all per-net > > operations here" location. > > Aaaaa, it's not really related to sysctl. > > Maybe we can rename it or add another pernet_operations. > > > > > > > > > > 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) > > > > We might actually be able to drop it... I do think we need to keep it in > > vsock_g2h_net_reset() because it makes sure that vsock_g2h_net_get() > > doesn't dereference a destroyed net. > > > > vsock_core_unregister() isn't on the teardown path, so even if we > > re-assign to init_net the previous net is still alive. > > Agree. > > > > > > > One thing I realized when answering your uAPI questions and looking at > > the code is that IOCTL_VM_SOCKETS_GET_LOCAL_CID is not namespace aware, > > but I think it probably should be? I remember for host ns we strived for > > truly strong isolation. > > Can you elabore a bit more? >
I'm wondering if IOCTL_VM_SOCKETS_GET_LOCAL_CID should not reveal the CID of the g2h device if the device has been moved to an inaccessible namespace? In this case, fallback to the results of h2g/local and through to returning VMADDR_CID_ANY if neither of those transports are loaded. I also considered whether or not /dev/vsock should even be visible from within an inaccessible namespace in order to not leak even the mere presence of the vsock device, but it seems to me that /dev/vsock's presence doesn't leak anything besides the presence of the vsock module. Best, Bobby
