[PATCH net-next v4 09/25] ovpn: introduce the ovpn_socket object

[Antonio Quartulli <antonio@openvpn.net>]

This specific structure is used in the ovpn kernel module
to wrap and carry around a standard kernel socket.

ovpn takes ownership of passed sockets and therefore an ovpn
specific objects is attached to them for status tracking
purposes.

Initially only UDP support is introduced. TCP will come in a later
patch.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
 drivers/net/ovpn/Makefile |   2 +
 drivers/net/ovpn/socket.c | 120 ++++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/socket.h |  49 ++++++++++++++++
 drivers/net/ovpn/udp.c    |  72 +++++++++++++++++++++++
 drivers/net/ovpn/udp.h    |  17 ++++++
 5 files changed, 260 insertions(+)
 create mode 100644 drivers/net/ovpn/socket.c
 create mode 100644 drivers/net/ovpn/socket.h
 create mode 100644 drivers/net/ovpn/udp.c
 create mode 100644 drivers/net/ovpn/udp.h

diff --git a/drivers/net/ovpn/Makefile b/drivers/net/ovpn/Makefile
index ce13499b3e17..56bddc9bef83 100644
--- a/drivers/net/ovpn/Makefile
+++ b/drivers/net/ovpn/Makefile
@@ -13,3 +13,5 @@ ovpn-y += io.o
 ovpn-y += netlink.o
 ovpn-y += netlink-gen.o
 ovpn-y += peer.o
+ovpn-y += socket.o
+ovpn-y += udp.o
diff --git a/drivers/net/ovpn/socket.c b/drivers/net/ovpn/socket.c
new file mode 100644
index 000000000000..090a3232ab0e
--- /dev/null
+++ b/drivers/net/ovpn/socket.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+/*  OpenVPN data channel offload
+ *
+ *  Copyright (C) 2020-2024 OpenVPN, Inc.
+ *
+ *  Author:	James Yonan <james@openvpn.net>
+ *		Antonio Quartulli <antonio@openvpn.net>
+ */
+
+#include <linux/net.h>
+#include <linux/netdevice.h>
+
+#include "ovpnstruct.h"
+#include "main.h"
+#include "io.h"
+#include "peer.h"
+#include "socket.h"
+#include "udp.h"
+
+static void ovpn_socket_detach(struct socket *sock)
+{
+	if (!sock)
+		return;
+
+	sockfd_put(sock);
+}
+
+/**
+ * ovpn_socket_release_kref - kref_put callback
+ * @kref: the kref object
+ */
+void ovpn_socket_release_kref(struct kref *kref)
+{
+	struct ovpn_socket *sock = container_of(kref, struct ovpn_socket,
+						refcount);
+
+	ovpn_socket_detach(sock->sock);
+	kfree_rcu(sock, rcu);
+}
+
+static bool ovpn_socket_hold(struct ovpn_socket *sock)
+{
+	return kref_get_unless_zero(&sock->refcount);
+}
+
+static struct ovpn_socket *ovpn_socket_get(struct socket *sock)
+{
+	struct ovpn_socket *ovpn_sock;
+
+	rcu_read_lock();
+	ovpn_sock = rcu_dereference_sk_user_data(sock->sk);
+	if (!ovpn_socket_hold(ovpn_sock)) {
+		pr_warn("%s: found ovpn_socket with ref = 0\n", __func__);
+		ovpn_sock = NULL;
+	}
+	rcu_read_unlock();
+
+	return ovpn_sock;
+}
+
+static int ovpn_socket_attach(struct socket *sock, struct ovpn_peer *peer)
+{
+	int ret = -EOPNOTSUPP;
+
+	if (!sock || !peer)
+		return -EINVAL;
+
+	if (sock->sk->sk_protocol == IPPROTO_UDP)
+		ret = ovpn_udp_socket_attach(sock, peer->ovpn);
+
+	return ret;
+}
+
+/**
+ * ovpn_socket_new - create a new socket and initialize it
+ * @sock: the kernel socket to embed
+ * @peer: the peer reachable via this socket
+ *
+ * Return: an openvpn socket on success or a negative error code otherwise
+ */
+struct ovpn_socket *ovpn_socket_new(struct socket *sock, struct ovpn_peer *peer)
+{
+	struct ovpn_socket *ovpn_sock;
+	int ret;
+
+	ret = ovpn_socket_attach(sock, peer);
+	if (ret < 0 && ret != -EALREADY)
+		return ERR_PTR(ret);
+
+	/* if this socket is already owned by this interface, just increase the
+	 * refcounter and use it as expected.
+	 *
+	 * Since UDP sockets can be used to talk to multiple remote endpoints,
+	 * openvpn normally instantiates only one socket and shares it among all
+	 * its peers. For this reason, when we find out that a socket is already
+	 * used for some other peer in *this* instance, we can happily increase
+	 * its refcounter and use it normally.
+	 */
+	if (ret == -EALREADY) {
+		/* caller is expected to increase the sock refcounter before
+		 * passing it to this function. For this reason we drop it if
+		 * not needed, like when this socket is already owned.
+		 */
+		ovpn_sock = ovpn_socket_get(sock);
+		sockfd_put(sock);
+		return ovpn_sock;
+	}
+
+	ovpn_sock = kzalloc(sizeof(*ovpn_sock), GFP_KERNEL);
+	if (!ovpn_sock)
+		return ERR_PTR(-ENOMEM);
+
+	ovpn_sock->ovpn = peer->ovpn;
+	ovpn_sock->sock = sock;
+	kref_init(&ovpn_sock->refcount);
+
+	rcu_assign_sk_user_data(sock->sk, ovpn_sock);
+
+	return ovpn_sock;
+}
diff --git a/drivers/net/ovpn/socket.h b/drivers/net/ovpn/socket.h
new file mode 100644
index 000000000000..08ca1ec25aa2
--- /dev/null
+++ b/drivers/net/ovpn/socket.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*  OpenVPN data channel offload
+ *
+ *  Copyright (C) 2020-2024 OpenVPN, Inc.
+ *
+ *  Author:	James Yonan <james@openvpn.net>
+ *		Antonio Quartulli <antonio@openvpn.net>
+ */
+
+#ifndef _NET_OVPN_SOCK_H_
+#define _NET_OVPN_SOCK_H_
+
+#include <linux/net.h>
+#include <linux/kref.h>
+#include <linux/ptr_ring.h>
+#include <net/sock.h>
+
+struct ovpn_struct;
+struct ovpn_peer;
+
+/**
+ * struct ovpn_socket - a kernel socket referenced in the ovpn code
+ * @ovpn: ovpn instance owning this socket (UDP only)
+ * @sock: the low level sock object
+ * @refcount: amount of contexts currently referencing this object
+ * @rcu: member used to schedule RCU destructor callback
+ */
+struct ovpn_socket {
+	struct ovpn_struct *ovpn;
+	struct socket *sock;
+	struct kref refcount;
+	struct rcu_head rcu;
+};
+
+void ovpn_socket_release_kref(struct kref *kref);
+
+/**
+ * ovpn_socket_put - decrease reference counter
+ * @sock: the socket whose reference counter should be decreased
+ */
+static inline void ovpn_socket_put(struct ovpn_socket *sock)
+{
+	kref_put(&sock->refcount, ovpn_socket_release_kref);
+}
+
+struct ovpn_socket *ovpn_socket_new(struct socket *sock,
+				    struct ovpn_peer *peer);
+
+#endif /* _NET_OVPN_SOCK_H_ */
diff --git a/drivers/net/ovpn/udp.c b/drivers/net/ovpn/udp.c
new file mode 100644
index 000000000000..c10474d252e1
--- /dev/null
+++ b/drivers/net/ovpn/udp.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/*  OpenVPN data channel offload
+ *
+ *  Copyright (C) 2019-2024 OpenVPN, Inc.
+ *
+ *  Author:	Antonio Quartulli <antonio@openvpn.net>
+ */
+
+#include <linux/netdevice.h>
+#include <linux/socket.h>
+#include <net/udp.h>
+
+#include "ovpnstruct.h"
+#include "main.h"
+#include "socket.h"
+#include "udp.h"
+
+/**
+ * ovpn_udp_socket_attach - set udp-tunnel CBs on socket and link it to ovpn
+ * @sock: socket to configure
+ * @ovpn: the openvp instance to link
+ *
+ * After invoking this function, the sock will be controlled by ovpn so that
+ * any incoming packet may be processed by ovpn first.
+ *
+ * Return: 0 on success or a negative error code otherwise
+ */
+int ovpn_udp_socket_attach(struct socket *sock, struct ovpn_struct *ovpn)
+{
+	struct ovpn_socket *old_data;
+	int ret = 0;
+
+	/* sanity check */
+	if (sock->sk->sk_protocol != IPPROTO_UDP) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+
+	/* make sure no pre-existing encapsulation handler exists */
+	rcu_read_lock();
+	old_data = rcu_dereference_sk_user_data(sock->sk);
+	if (!old_data) {
+		/* socket is currently unused - we can take it */
+		rcu_read_unlock();
+		return 0;
+	}
+
+	/* socket is in use. We need to understand if it's owned by this ovpn
+	 * instance or by something else.
+	 * In the former case, we can increase the refcounter and happily
+	 * use it, because the same UDP socket is expected to be shared among
+	 * different peers.
+	 *
+	 * Unlikely TCP, a single UDP socket can be used to talk to many remote
+	 * hosts and therefore openvpn instantiates one only for all its peers
+	 */
+	if ((READ_ONCE(udp_sk(sock->sk)->encap_type) == UDP_ENCAP_OVPNINUDP) &&
+	    old_data->ovpn == ovpn) {
+		netdev_dbg(ovpn->dev,
+			   "%s: provided socket already owned by this interface\n",
+			   __func__);
+		ret = -EALREADY;
+	} else {
+		netdev_err(ovpn->dev,
+			   "%s: provided socket already taken by other user\n",
+			   __func__);
+		ret = -EBUSY;
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
diff --git a/drivers/net/ovpn/udp.h b/drivers/net/ovpn/udp.h
new file mode 100644
index 000000000000..f2507f8f2c71
--- /dev/null
+++ b/drivers/net/ovpn/udp.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*  OpenVPN data channel offload
+ *
+ *  Copyright (C) 2019-2024 OpenVPN, Inc.
+ *
+ *  Author:	Antonio Quartulli <antonio@openvpn.net>
+ */
+
+#ifndef _NET_OVPN_UDP_H_
+#define _NET_OVPN_UDP_H_
+
+struct ovpn_struct;
+struct socket;
+
+int ovpn_udp_socket_attach(struct socket *sock, struct ovpn_struct *ovpn);
+
+#endif /* _NET_OVPN_UDP_H_ */
-- 
2.44.2