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[79.53.30.11]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4870bf1fad3sm6355913f8f.12.2026.09.16.05.57.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Sep 2026 05:58:00 -0700 (PDT) Date: Wed, 16 Sep 2026 14:57:43 +0200 From: Stefano Garzarella To: Bobby Eshleman Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Stefan Hajnoczi , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Shuah Khan , Randy Dunlap , virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, sargun@sargun.me, jlinbox@meta.com, Bobby Eshleman Subject: Re: [PATCH net-next 2/6] vsock: add IOCTL_VM_SOCKETS_ASSIGN_G2H_NETNS Message-ID: References: <20260902-vsock-guest-ns-v1-0-9995383e9a8b@meta.com> <20260902-vsock-guest-ns-v1-2-9995383e9a8b@meta.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: 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 >> > >> > 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 >> > 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(-) >> > [...] >> > + >> > +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? Thanks, Stefano