OpenVPN is a userspace software existing since around 2005 that allows users to create secure tunnels.
So far OpenVPN has implemented all operations in userspace, which implies several back and forth between kernel and user land in order to process packets (encapsulate/decapsulate, encrypt/decrypt, rerouting..).
With `ovpn` we intend to move the fast path (data channel) entirely in kernel space and thus improve user measured throughput over the tunnel.
`ovpn` is implemented as a simple virtual network device driver, that can be manipulated by means of the standard RTNL APIs. A device of kind `ovpn` allows only IPv4/6 traffic and can be of type: * P2P (peer-to-peer): any packet sent over the interface will be encapsulated and transmitted to the other side (typical OpenVPN client or peer-to-peer behaviour); * P2MP (point-to-multipoint): packets sent over the interface are transmitted to peers based on existing routes (typical OpenVPN server behaviour).
After the interface has been created, OpenVPN in userspace can configure it using a new Netlink API. Specifically it is possible to manage peers and their keys.
The OpenVPN control channel is multiplexed over the same transport socket by means of OP codes. Anything that is not DATA_V2 (OpenVPN OP code for data traffic) is sent to userspace and handled there. This way the `ovpn` codebase is kept as compact as possible while focusing on handling data traffic only (fast path).
Any OpenVPN control feature (like cipher negotiation, TLS handshake, rekeying, etc.) is still fully handled by the userspace process.
When userspace establishes a new connection with a peer, it first performs the handshake and then passes the socket to the `ovpn` kernel module, which takes ownership. From this moment on `ovpn` will handle data traffic for the new peer. When control packets are received on the link, they are forwarded to userspace through the same transport socket they were received on, as userspace is still listening to them.
Some events (like peer deletion) are sent to a Netlink multicast group.
Although it wasn't easy to convince the community, `ovpn` implements only a limited number of the data-channel features supported by the userspace program.
Each feature that made it to `ovpn` was attentively vetted to avoid carrying too much legacy along with us (and to give a clear cut to old and probalby-not-so-useful features).
Notably, only encryption using AEAD ciphers (specifically ChaCha20Poly1305 and AES-GCM) was implemented. Supporting any other cipher out there was not deemed useful.
Both UDP and TCP sockets are supported.
As explained above, in case of P2MP mode, OpenVPN will use the main system routing table to decide which packet goes to which peer. This implies that no routing table was re-implemented in the `ovpn` kernel module.
This kernel module can be enabled by selecting the CONFIG_OVPN entry in the networking drivers section.
NOTE: this first patch introduces the very basic framework only. Features are then added patch by patch, however, although each patch will compile and possibly not break at runtime, only after having applied the full set it is expected to see the ovpn module fully working.
Cc: steffen.klassert@secunet.com Cc: antony.antony@secunet.com Signed-off-by: Antonio Quartulli antonio@openvpn.net --- MAINTAINERS | 8 ++++++++ drivers/net/Kconfig | 8 ++++++++ drivers/net/Makefile | 1 + drivers/net/ovpn/Makefile | 10 +++++++++ drivers/net/ovpn/main.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 79 insertions(+)
diff --git a/MAINTAINERS b/MAINTAINERS index 1248443035f437b903dafa739cf0cea30b71f785..d0d77f43c5af370a895b1056f21988daa0389c78 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -18125,6 +18125,14 @@ F: arch/openrisc/ F: drivers/irqchip/irq-ompic.c F: drivers/irqchip/irq-or1k-*
+OPENVPN DATA CHANNEL OFFLOAD +M: Antonio Quartulli antonio@openvpn.net +L: openvpn-devel@lists.sourceforge.net (subscribers-only) +L: netdev@vger.kernel.org +S: Supported +T: git https://github.com/OpenVPN/linux-kernel-ovpn.git +F: drivers/net/ovpn/ + OPENVSWITCH M: Aaron Conole aconole@redhat.com M: Eelco Chaudron echaudro@redhat.com diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig index 271520510b5fc6866bbf4fc6a0d728d110e6b5e4..5fbe25ae1e11e558aa9aaa857cf110127e459854 100644 --- a/drivers/net/Kconfig +++ b/drivers/net/Kconfig @@ -115,6 +115,14 @@ config WIREGUARD_DEBUG
Say N here unless you know what you're doing.
+config OVPN + tristate "OpenVPN data channel offload" + depends on NET && INET + depends on IPV6 || !IPV6 + help + This module enhances the performance of the OpenVPN userspace software + by offloading the data channel processing to kernelspace. + config EQUALIZER tristate "EQL (serial line load balancing) support" help diff --git a/drivers/net/Makefile b/drivers/net/Makefile index 75333251a01a87e18d6c1bc9eec97b96b571b77b..73bc63ecd65ff45c9458a31d7f67447b37e18cdb 100644 --- a/drivers/net/Makefile +++ b/drivers/net/Makefile @@ -11,6 +11,7 @@ obj-$(CONFIG_IPVLAN) += ipvlan/ obj-$(CONFIG_IPVTAP) += ipvlan/ obj-$(CONFIG_DUMMY) += dummy.o obj-$(CONFIG_WIREGUARD) += wireguard/ +obj-$(CONFIG_OVPN) += ovpn/ obj-$(CONFIG_EQUALIZER) += eql.o obj-$(CONFIG_IFB) += ifb.o obj-$(CONFIG_MACSEC) += macsec.o diff --git a/drivers/net/ovpn/Makefile b/drivers/net/ovpn/Makefile new file mode 100644 index 0000000000000000000000000000000000000000..876800ebaa21a5f758ddf60f637801710437f70e --- /dev/null +++ b/drivers/net/ovpn/Makefile @@ -0,0 +1,10 @@ +# SPDX-License-Identifier: GPL-2.0 +# +# ovpn -- OpenVPN data channel offload in kernel space +# +# Copyright (C) 2020-2025 OpenVPN, Inc. +# +# Author: Antonio Quartulli antonio@openvpn.net + +obj-$(CONFIG_OVPN) := ovpn.o +ovpn-y += main.o diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c new file mode 100644 index 0000000000000000000000000000000000000000..d5d4ac8da6d78e18960e18cd5f8d522185900542 --- /dev/null +++ b/drivers/net/ovpn/main.c @@ -0,0 +1,52 @@ +// SPDX-License-Identifier: GPL-2.0 +/* OpenVPN data channel offload + * + * Copyright (C) 2020-2025 OpenVPN, Inc. + * + * Author: Antonio Quartulli antonio@openvpn.net + * James Yonan james@openvpn.net + */ + +#include <linux/module.h> +#include <linux/netdevice.h> +#include <net/rtnetlink.h> + +static int ovpn_newlink(struct net_device *dev, + struct rtnl_newlink_params *params, + struct netlink_ext_ack *extack) +{ + return -EOPNOTSUPP; +} + +static struct rtnl_link_ops ovpn_link_ops = { + .kind = "ovpn", + .netns_refund = false, + .newlink = ovpn_newlink, + .dellink = unregister_netdevice_queue, +}; + +static int __init ovpn_init(void) +{ + int err = rtnl_link_register(&ovpn_link_ops); + + if (err) { + pr_err("ovpn: can't register rtnl link ops: %d\n", err); + return err; + } + + return 0; +} + +static __exit void ovpn_cleanup(void) +{ + rtnl_link_unregister(&ovpn_link_ops); + + rcu_barrier(); +} + +module_init(ovpn_init); +module_exit(ovpn_cleanup); + +MODULE_DESCRIPTION("OpenVPN data channel offload (ovpn)"); +MODULE_AUTHOR("Antonio Quartulli antonio@openvpn.net"); +MODULE_LICENSE("GPL");