On Tue, Nov 11, 2025 at 10:54:48PM -0800, Bobby Eshleman wrote:
From: Bobby Eshleman bobbyeshleman@meta.com
Add NS support to vsock loopback. Sockets in a global mode netns communicate with each other, regardless of namespace. Sockets in a local mode netns may only communicate with other sockets within the same namespace.
Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com
Changes in v9:
- remove per-netns vsock_loopback and workqueues, just re-using
the net and net_mode in skb->cb achieved the same result in a simpler way. Also removed need for pernet_subsys.
- properly track net references
Changes in v7:
- drop for_each_net() init/exit, drop net_rwsem, the pernet registration
handles this automatically and race-free
- flush workqueue before destruction, purge pkt list
- remember net_mode instead of current net mode
- keep space after INIT_WORK()
- change vsock_loopback in netns_vsock to ->priv void ptr
- rename `orig_net_mode` to `net_mode`
- remove useless comment
- protect `register_pernet_subsys()` with `net_rwsem`
- do cleanup before releasing `net_rwsem` when failure happens
- call `unregister_pernet_subsys()` in `vsock_loopback_exit()`
- call `vsock_loopback_deinit_vsock()` in `vsock_loopback_exit()`
Changes in v6:
- init pernet ops for vsock_loopback module
- vsock_loopback: add space in struct to clarify lock protection
- do proper cleanup/unregister on vsock_loopback_exit()
- vsock_loopback: use virtio_vsock_skb_net()
Changes in v5:
- add callbacks code to avoid reverse dependency
- add logic for handling vsock_loopback setup for already existing
namespaces
net/vmw_vsock/vsock_loopback.c | 41 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 40 insertions(+), 1 deletion(-)
diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c index d3ac056663ea..e62f6c516992 100644 --- a/net/vmw_vsock/vsock_loopback.c +++ b/net/vmw_vsock/vsock_loopback.c @@ -32,6 +32,9 @@ static int vsock_loopback_send_pkt(struct sk_buff *skb, struct net *net, struct vsock_loopback *vsock = &the_vsock_loopback; int len = skb->len;
- virtio_vsock_skb_set_net(skb, net);
- virtio_vsock_skb_set_net_mode(skb, net_mode);
- virtio_vsock_skb_queue_tail(&vsock->pkt_queue, skb); queue_work(vsock->workqueue, &vsock->pkt_work);
@@ -116,8 +119,10 @@ static void vsock_loopback_work(struct work_struct *work) { struct vsock_loopback *vsock = container_of(work, struct vsock_loopback, pkt_work);
enum vsock_net_mode net_mode; struct sk_buff_head pkts; struct sk_buff *skb;
struct net *net;
skb_queue_head_init(&pkts);
@@ -131,7 +136,41 @@ static void vsock_loopback_work(struct work_struct *work) */ virtio_transport_consume_skb_sent(skb, false); virtio_transport_deliver_tap_pkt(skb);
virtio_transport_recv_pkt(&loopback_transport, skb, NULL, 0);
/* In the case of virtio_transport_reset_no_sock(), the skb* does not hold a reference on the socket, and so does not* transitively hold a reference on the net.** There is an ABA race condition in this sequence:* 1. the sender sends a packet* 2. worker calls virtio_transport_recv_pkt(), using the* sender's net* 3. virtio_transport_recv_pkt() uses t->send_pkt() passing the* sender's net* 4. virtio_transport_recv_pkt() free's the skb, dropping the* reference to the socket* 5. the socket closes, frees its reference to the net* 6. Finally, the worker for the second t->send_pkt() call* processes the skb, and uses the now stale net pointer for* socket lookups.** To prevent this, we acquire a net reference in vsock_loopback_send_pkt()* and hold it until virtio_transport_recv_pkt() completes.** Additionally, we must grab a reference on the skb before* calling virtio_transport_recv_pkt() to prevent it from* freeing the skb before we have a chance to release the net.*/net_mode = virtio_vsock_skb_net_mode(skb);net = virtio_vsock_skb_net(skb);
Wait, we are adding those just for loopback (in theory used only for testing/debugging)? And only to support virtio_transport_reset_no_sock() use case?
Honestly I don't like this, do we have any alternative?
I'll also try to think something else.
Stefano
skb_get(skb);virtio_transport_recv_pkt(&loopback_transport, skb, net,net_mode);virtio_vsock_skb_clear_net(skb);kfree_skb(skb);}
-- 2.47.3