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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Stefan Hajnoczi , Shuah Khan , Bobby Eshleman , "Michael S. Tsirkin" , Jonathan Corbet , Shuah Khan Cc: virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, Daan De Meyer X-Mailer: b4 0.14.3 From: Bobby Eshleman 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") Signed-off-by: Bobby Eshleman Suggested-by: Daan De Meyer Suggested-by: Stefano Garzarella --- include/net/af_vsock.h | 20 +++++++++++++++++--- include/net/netns/vsock.h | 9 ++++++++- net/vmw_vsock/af_vsock.c | 15 ++++++++++----- 3 files changed, 35 insertions(+), 9 deletions(-) diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index d3ff48a2fbe0..9bd42147626d 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -276,15 +276,29 @@ 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 locked = mode + VSOCK_NET_MODE_LOCKED; + int cur; + + cur = READ_ONCE(net->vsock.child_ns_mode); + if (cur == locked) + return true; + if (cur >= VSOCK_NET_MODE_LOCKED) + return false; + + if (try_cmpxchg(&net->vsock.child_ns_mode, &cur, locked)) + return true; + + return cur == locked; } static inline enum vsock_net_mode vsock_net_child_mode(struct net *net) { - return READ_ONCE(net->vsock.child_ns_mode); + int mode = READ_ONCE(net->vsock.child_ns_mode); + + return mode & (VSOCK_NET_MODE_LOCKED - 1); } /* Return true if two namespaces pass the mode rules. Otherwise, return false. diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h index b34d69a22fa8..d20ab6269342 100644 --- a/include/net/netns/vsock.h +++ b/include/net/netns/vsock.h @@ -7,6 +7,7 @@ enum vsock_net_mode { VSOCK_NET_MODE_GLOBAL, VSOCK_NET_MODE_LOCAL, + VSOCK_NET_MODE_LOCKED, }; struct netns_vsock { @@ -16,6 +17,12 @@ struct netns_vsock { u32 port; enum vsock_net_mode mode; - enum vsock_net_mode child_ns_mode; + + /* 0 (GLOBAL) + * 1 (LOCAL) + * 2 (GLOBAL + LOCKED) + * 3 (LOCAL + LOCKED) + */ + int child_ns_mode; }; #endif /* __NET_NET_NAMESPACE_VSOCK_H */ diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 9880756d9eff..50044a838c89 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -90,16 +90,20 @@ * * - /proc/sys/net/vsock/ns_mode (read-only) reports the current namespace's * mode, which is set at namespace creation and immutable thereafter. - * - /proc/sys/net/vsock/child_ns_mode (writable) controls what mode future + * - /proc/sys/net/vsock/child_ns_mode (write-once) controls what mode future * child namespaces will inherit when created. The initial value matches * the namespace's own ns_mode. * * Changing child_ns_mode only affects newly created namespaces, not the * current namespace or existing children. A "local" namespace cannot set - * child_ns_mode to "global". At namespace creation, ns_mode is inherited - * from the parent's child_ns_mode. + * child_ns_mode to "global". child_ns_mode is write-once, so that it may be + * configured and locked down by a namespace manager. Writing a different + * value after the first write returns -EBUSY. At namespace creation, ns_mode + * is inherited from the parent's child_ns_mode. * - * The init_net mode is "global" and cannot be modified. + * The init_net mode is "global" and cannot be modified. The init_net + * child_ns_mode is also write-once, so an init process (e.g. systemd) can + * set it to "local" to ensure all new namespaces inherit local mode. * * The modes affect the allocation and accessibility of CIDs as follows: * @@ -2853,7 +2857,8 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write, new_mode == VSOCK_NET_MODE_GLOBAL) return -EPERM; - vsock_net_set_child_mode(net, new_mode); + if (!vsock_net_set_child_mode(net, new_mode)) + return -EBUSY; } return 0; -- 2.47.3