From 102eab95f025b4d3f3a6c0a858400aca2af2fe52 Mon Sep 17 00:00:00 2001 From: Bobby Eshleman Date: Mon, 23 Feb 2026 14:38:33 -0800 Subject: vsock: lock down child_ns_mode as write-once Two administrator processes may race when setting child_ns_mode as one process sets child_ns_mode to "local" and then creates a namespace, but another process changes child_ns_mode to "global" between the write and the namespace creation. The first process ends up with a namespace in "global" mode instead of "local". While this can be detected after the fact by reading ns_mode and retrying, it is fragile and error-prone. Make child_ns_mode write-once so that a namespace manager can set it once and be sure it won't change. Writing a different value after the first write returns -EBUSY. This applies to all namespaces, including init_net, where an init process can write "local" to lock all future namespaces into local mode. Fixes: eafb64f40ca4 ("vsock: add netns to vsock core") Suggested-by: Daan De Meyer Suggested-by: Stefano Garzarella Co-developed-by: Stefano Garzarella Signed-off-by: Stefano Garzarella Signed-off-by: Bobby Eshleman Reviewed-by: Stefano Garzarella Link: https://patch.msgid.link/20260223-vsock-ns-write-once-v3-2-c0cde6959923@meta.com Signed-off-by: Paolo Abeni --- include/net/af_vsock.h | 13 +++++++++++-- include/net/netns/vsock.h | 3 +++ 2 files changed, 14 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index d3ff48a2fbe0..533d8e75f7bb 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -276,10 +276,19 @@ static inline bool vsock_net_mode_global(struct vsock_sock *vsk) return vsock_net_mode(sock_net(sk_vsock(vsk))) == VSOCK_NET_MODE_GLOBAL; } -static inline void vsock_net_set_child_mode(struct net *net, +static inline bool vsock_net_set_child_mode(struct net *net, enum vsock_net_mode mode) { - WRITE_ONCE(net->vsock.child_ns_mode, mode); + int new_locked = mode + 1; + int old_locked = 0; /* unlocked */ + + if (try_cmpxchg(&net->vsock.child_ns_mode_locked, + &old_locked, new_locked)) { + WRITE_ONCE(net->vsock.child_ns_mode, mode); + return true; + } + + return old_locked == new_locked; } static inline enum vsock_net_mode vsock_net_child_mode(struct net *net) diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h index b34d69a22fa8..dc8cbe45f406 100644 --- a/include/net/netns/vsock.h +++ b/include/net/netns/vsock.h @@ -17,5 +17,8 @@ struct netns_vsock { enum vsock_net_mode mode; enum vsock_net_mode child_ns_mode; + + /* 0 = unlocked, 1 = locked to global, 2 = locked to local */ + int child_ns_mode_locked; }; #endif /* __NET_NET_NAMESPACE_VSOCK_H */ -- cgit v1.2.3