[PATCH RFC net-next v13 01/13] vsock: add per-net vsock NS mode state

[Bobby Eshleman <bobbyeshleman@gmail.com>]

From: Bobby Eshleman <bobbyeshleman@meta.com>

Add the per-net vsock NS mode state. This only adds the structure for
holding the mode and some of the functions for setting/getting and
checking the mode, but does not integrate the functionality yet.

Future patches add the uAPI and transport-specific usage of these
structures and helpers.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
Changes in v13:
- remove net_mode because net->vsock.mode becomes immutable, no need to
  save the mode when vsocks are created.
- add the new helpers for child_ns_mode to support ns_mode inheriting
  the mode from child_ns_mode.
- because ns_mode is immutable and child_ns_mode can be changed multiple
  times, remove the write-once lock.
- simplify vsock_net_check_mode() to no longer take mode arguments since
  the mode can be accessed via the net pointers without fear of the mode
  changing.
- add logic in vsock_net_check_mode() to infer VSOCK_NET_MODE_GLOBAL
  from NULL namespaces in order to allow only net pointers to be passed
  to vsock_net_check_mode(), while still allowing namespace-unaware
  transports to force global mode.

Changes in v10:
- change mode_locked to int (Stefano)

Changes in v9:
- use xchg(), WRITE_ONCE(), READ_ONCE() for mode and mode_locked (Stefano)
- clarify mode0/mode1 meaning in vsock_net_check_mode() comment
- remove spin lock in net->vsock (not used anymore)
- change mode from u8 to enum vsock_net_mode in vsock_net_write_mode()

Changes in v7:
- clarify vsock_net_check_mode() comments
- change to `orig_net_mode == VSOCK_NET_MODE_GLOBAL && orig_net_mode == vsk->orig_net_mode`
- remove extraneous explanation of `orig_net_mode`
- rename `written` to `mode_locked`
- rename `vsock_hdr` to `sysctl_hdr`
- change `orig_net_mode` to `net_mode`
- make vsock_net_check_mode() more generic by taking just net pointers
  and modes, instead of a vsock_sock ptr, for reuse by transports
  (e.g., vhost_vsock)

Changes in v6:
- add orig_net_mode to store mode at creation time which will be used to
  avoid breakage when namespace changes mode during socket/VM lifespan

Changes in v5:
- use /proc/sys/net/vsock/ns_mode instead of /proc/net/vsock_ns_mode
- change from net->vsock.ns_mode to net->vsock.mode
- change vsock_net_set_mode() to vsock_net_write_mode()
- vsock_net_write_mode() returns bool for write success to avoid
  need to use vsock_net_mode_can_set()
- remove vsock_net_mode_can_set()
---
 MAINTAINERS                 |  1 +
 include/net/af_vsock.h      | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/net/net_namespace.h |  4 ++++
 include/net/netns/vsock.h   | 17 +++++++++++++++++
 4 files changed, 64 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 454b8ed119e9..38d24e5a957c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27516,6 +27516,7 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 F:	drivers/vhost/vsock.c
 F:	include/linux/virtio_vsock.h
+F:	include/net/netns/vsock.h
 F:	include/uapi/linux/virtio_vsock.h
 F:	net/vmw_vsock/virtio_transport.c
 F:	net/vmw_vsock/virtio_transport_common.c
diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index d40e978126e3..6f5bc9dbefa5 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -10,6 +10,7 @@
 
 #include <linux/kernel.h>
 #include <linux/workqueue.h>
+#include <net/netns/vsock.h>
 #include <net/sock.h>
 #include <uapi/linux/vm_sockets.h>
 
@@ -256,4 +257,45 @@ static inline bool vsock_msgzerocopy_allow(const struct vsock_transport *t)
 {
 	return t->msgzerocopy_allow && t->msgzerocopy_allow();
 }
+
+static inline enum vsock_net_mode vsock_net_mode(struct net *net)
+{
+	return READ_ONCE(net->vsock.mode);
+}
+
+static inline void vsock_net_set_child_mode(struct net *net,
+					    enum vsock_net_mode mode)
+{
+	WRITE_ONCE(net->vsock.child_ns_mode, mode);
+}
+
+static inline enum vsock_net_mode vsock_net_child_mode(struct net *net)
+{
+	return READ_ONCE(net->vsock.child_ns_mode);
+}
+
+/* Return true if two namespaces pass the mode rules. Otherwise, return false.
+ *
+ * A NULL namespace is treated as VSOCK_NET_MODE_GLOBAL.
+ *
+ * Read more about modes in the comment header of net/vmw_vsock/af_vsock.c.
+ */
+static inline bool vsock_net_check_mode(struct net *ns0, struct net *ns1)
+{
+	enum vsock_net_mode mode0, mode1;
+
+	/* Any vsocks within the same network namespace are always reachable,
+	 * regardless of the mode.
+	 */
+	if (net_eq(ns0, ns1))
+		return true;
+
+	mode0 = ns0 ? vsock_net_mode(ns0) : VSOCK_NET_MODE_GLOBAL;
+	mode1 = ns1 ? vsock_net_mode(ns1) : VSOCK_NET_MODE_GLOBAL;
+
+	/* Different namespaces are only reachable if they are both
+	 * global mode.
+	 */
+	return mode0 == VSOCK_NET_MODE_GLOBAL && mode0 == mode1;
+}
 #endif /* __AF_VSOCK_H__ */
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index cb664f6e3558..66d3de1d935f 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -37,6 +37,7 @@
 #include <net/netns/smc.h>
 #include <net/netns/bpf.h>
 #include <net/netns/mctp.h>
+#include <net/netns/vsock.h>
 #include <net/net_trackers.h>
 #include <linux/ns_common.h>
 #include <linux/idr.h>
@@ -196,6 +197,9 @@ struct net {
 	/* Move to a better place when the config guard is removed. */
 	struct mutex		rtnl_mutex;
 #endif
+#if IS_ENABLED(CONFIG_VSOCKETS)
+	struct netns_vsock	vsock;
+#endif
 } __randomize_layout;
 
 #include <linux/seq_file_net.h>
diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
new file mode 100644
index 000000000000..e2325e2d6ec5
--- /dev/null
+++ b/include/net/netns/vsock.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_NET_NAMESPACE_VSOCK_H
+#define __NET_NET_NAMESPACE_VSOCK_H
+
+#include <linux/types.h>
+
+enum vsock_net_mode {
+	VSOCK_NET_MODE_GLOBAL,
+	VSOCK_NET_MODE_LOCAL,
+};
+
+struct netns_vsock {
+	struct ctl_table_header *sysctl_hdr;
+	enum vsock_net_mode mode;
+	enum vsock_net_mode child_ns_mode;
+};
+#endif /* __NET_NET_NAMESPACE_VSOCK_H */

-- 
2.47.3