[PATCH wireguard-linux] Basic support for binding the transport socket to a device

[Marvin Gaube <dev@marvingaube.de>]

This patch depends on da5095d052860baa7fe2932fb1209628dd3e3813 from udp_tunnel module,
and allows to bind the transport socket to a specific interface.

With this patch, it is possible to use wireguard with VRFs:
The transport uses a separate "WAN" VRF, cleanly isolating Local/VPN and WAN Routing.

The userspace API is designed to transmit the device index of the device to listen on.
Listening on a device does only work if the socketdev_index is set/changed before the socket is brought up.

Signed-off-by: Marvin Gaube <dev@marvingaube.de>
---
 drivers/net/wireguard/device.h  |  1 +
 drivers/net/wireguard/netlink.c |  8 +++++++-
 drivers/net/wireguard/socket.c  | 10 ++++++++++
 include/uapi/linux/wireguard.h  |  3 +++
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireguard/device.h b/drivers/net/wireguard/device.h
index 854bc3d97150..a08f0893f687 100644
--- a/drivers/net/wireguard/device.h
+++ b/drivers/net/wireguard/device.h
@@ -56,6 +56,7 @@ struct wg_device {
 	struct list_head device_list, peer_list;
 	unsigned int num_peers, device_update_gen;
 	u32 fwmark;
+	u32 socketdev_index;
 	u16 incoming_port;
 };
 
diff --git a/drivers/net/wireguard/netlink.c b/drivers/net/wireguard/netlink.c
index d0f3b6d7f408..c594a7063038 100644
--- a/drivers/net/wireguard/netlink.c
+++ b/drivers/net/wireguard/netlink.c
@@ -27,7 +27,8 @@ static const struct nla_policy device_policy[WGDEVICE_A_MAX + 1] = {
 	[WGDEVICE_A_FLAGS]		= { .type = NLA_U32 },
 	[WGDEVICE_A_LISTEN_PORT]	= { .type = NLA_U16 },
 	[WGDEVICE_A_FWMARK]		= { .type = NLA_U32 },
-	[WGDEVICE_A_PEERS]		= { .type = NLA_NESTED }
+	[WGDEVICE_A_PEERS]		= { .type = NLA_NESTED },
+	[WGDEVICE_A_SOCKETDEV_INDEX]	= { .type = NLA_U32 }
 };
 
 static const struct nla_policy peer_policy[WGPEER_A_MAX + 1] = {
@@ -232,6 +233,7 @@ static int wg_get_device_dump(struct sk_buff *skb, struct netlink_callback *cb)
 		if (nla_put_u16(skb, WGDEVICE_A_LISTEN_PORT,
 				wg->incoming_port) ||
 		    nla_put_u32(skb, WGDEVICE_A_FWMARK, wg->fwmark) ||
+		    nla_put_u32(skb, WGDEVICE_A_SOCKETDEV_INDEX, wg->socketdev_index) ||
 		    nla_put_u32(skb, WGDEVICE_A_IFINDEX, wg->dev->ifindex) ||
 		    nla_put_string(skb, WGDEVICE_A_IFNAME, wg->dev->name))
 			goto out;
@@ -538,6 +540,10 @@ static int wg_set_device(struct sk_buff *skb, struct genl_info *info)
 			goto out;
 	}
 
+	if (info->attrs[WGDEVICE_A_SOCKETDEV_INDEX]) {
+		wg->socketdev_index = nla_get_u32(info->attrs[WGDEVICE_A_SOCKETDEV_INDEX]);
+	}
+
 	if (flags & WGDEVICE_F_REPLACE_PEERS)
 		wg_peer_remove_all(wg);
 
diff --git a/drivers/net/wireguard/socket.c b/drivers/net/wireguard/socket.c
index d9ad850daa79..885d8a890079 100644
--- a/drivers/net/wireguard/socket.c
+++ b/drivers/net/wireguard/socket.c
@@ -370,8 +370,18 @@ int wg_socket_init(struct wg_device *wg, u16 port)
 		.use_udp6_rx_checksums = true,
 		.ipv6_v6only = true
 	};
+	if (wg->socketdev_index > 0) {
+		port6.bind_ifindex = wg->socketdev_index;
+	} else {
+		port6.bind_ifindex = 0;
+	}
 #endif
 
+	if (wg->socketdev_index > 0) {
+		port4.bind_ifindex = wg->socketdev_index;
+	} else {
+		port4.bind_ifindex = 0;
+	}
 	rcu_read_lock();
 	net = rcu_dereference(wg->creating_net);
 	net = net ? maybe_get_net(net) : NULL;
diff --git a/include/uapi/linux/wireguard.h b/include/uapi/linux/wireguard.h
index ae88be14c947..52b1bd422f50 100644
--- a/include/uapi/linux/wireguard.h
+++ b/include/uapi/linux/wireguard.h
@@ -29,6 +29,7 @@
  *    WGDEVICE_A_PUBLIC_KEY: NLA_EXACT_LEN, len WG_KEY_LEN
  *    WGDEVICE_A_LISTEN_PORT: NLA_U16
  *    WGDEVICE_A_FWMARK: NLA_U32
+ *    WGDEVICE_A_SOCKETDEV_INDEX: NLA_U32
  *    WGDEVICE_A_PEERS: NLA_NESTED
  *        0: NLA_NESTED
  *            WGPEER_A_PUBLIC_KEY: NLA_EXACT_LEN, len WG_KEY_LEN
@@ -83,6 +84,7 @@
  *    WGDEVICE_A_PRIVATE_KEY: len WG_KEY_LEN, all zeros to remove
  *    WGDEVICE_A_LISTEN_PORT: NLA_U16, 0 to choose randomly
  *    WGDEVICE_A_FWMARK: NLA_U32, 0 to disable
+ *    WGDEVICE_A_SOCKETDEV_INDEX: NLA_U32, 0 to disable
  *    WGDEVICE_A_PEERS: NLA_NESTED
  *        0: NLA_NESTED
  *            WGPEER_A_PUBLIC_KEY: len WG_KEY_LEN
@@ -157,6 +159,7 @@ enum wgdevice_attribute {
 	WGDEVICE_A_LISTEN_PORT,
 	WGDEVICE_A_FWMARK,
 	WGDEVICE_A_PEERS,
+	WGDEVICE_A_SOCKETDEV_INDEX,
 	__WGDEVICE_A_LAST
 };
 #define WGDEVICE_A_MAX (__WGDEVICE_A_LAST - 1)
-- 
2.25.1