[PATCH] net: wireguard: Allow binding to specific ifindex

[greearb@candelatech.com]

From: Ben Greear <greearb@candelatech.com>

Which allows us to bind to VRF.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---

NOTE:  Modified user-space to utilize this may be found here:
https://github.com/greearb/wireguard-tools-ct
Only the 'wg' part has been tested with this new feature as of today.

 drivers/net/wireguard/device.h  |  1 +
 drivers/net/wireguard/netlink.c | 12 +++++++++++-
 drivers/net/wireguard/socket.c  |  8 +++++++-
 include/uapi/linux/wireguard.h  |  3 +++
 4 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireguard/device.h b/drivers/net/wireguard/device.h
index 43c7cebbf50b..9698d9203915 100644
--- a/drivers/net/wireguard/device.h
+++ b/drivers/net/wireguard/device.h
@@ -53,6 +53,7 @@ struct wg_device {
 	atomic_t handshake_queue_len;
 	unsigned int num_peers, device_update_gen;
 	u32 fwmark;
+	int lowerdev; /* ifindex of lower level device to bind UDP transport */
 	u16 incoming_port;
 };
 
diff --git a/drivers/net/wireguard/netlink.c b/drivers/net/wireguard/netlink.c
index f7055180ba4a..5de3d59a17b0 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_LOWERDEV]		= { .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_LOWERDEV, wg->lowerdev) ||
 		    nla_put_u32(skb, WGDEVICE_A_IFINDEX, wg->dev->ifindex) ||
 		    nla_put_string(skb, WGDEVICE_A_IFNAME, wg->dev->name))
 			goto out;
@@ -530,6 +532,14 @@ static int wg_set_device(struct sk_buff *skb, struct genl_info *info)
 			wg_socket_clear_peer_endpoint_src(peer);
 	}
 
+	if (info->attrs[WGDEVICE_A_LOWERDEV]) {
+		struct wg_peer *peer;
+
+		wg->lowerdev = nla_get_u32(info->attrs[WGDEVICE_A_LOWERDEV]);
+		list_for_each_entry(peer, &wg->peer_list, peer_list)
+			wg_socket_clear_peer_endpoint_src(peer);
+	}
+
 	if (info->attrs[WGDEVICE_A_LISTEN_PORT]) {
 		ret = set_port(wg,
 			nla_get_u16(info->attrs[WGDEVICE_A_LISTEN_PORT]));
diff --git a/drivers/net/wireguard/socket.c b/drivers/net/wireguard/socket.c
index 0414d7a6ce74..a7cb1c7c3112 100644
--- a/drivers/net/wireguard/socket.c
+++ b/drivers/net/wireguard/socket.c
@@ -25,7 +25,8 @@ static int send4(struct wg_device *wg, struct sk_buff *skb,
 		.daddr = endpoint->addr4.sin_addr.s_addr,
 		.fl4_dport = endpoint->addr4.sin_port,
 		.flowi4_mark = wg->fwmark,
-		.flowi4_proto = IPPROTO_UDP
+		.flowi4_proto = IPPROTO_UDP,
+		.flowi4_oif = wg->lowerdev,
 	};
 	struct rtable *rt = NULL;
 	struct sock *sock;
@@ -111,6 +112,9 @@ static int send6(struct wg_device *wg, struct sk_buff *skb,
 	struct sock *sock;
 	int ret = 0;
 
+	if (wg->lowerdev)
+		fl.flowi6_oif = wg->lowerdev,
+
 	skb_mark_not_on_list(skb);
 	skb->dev = wg->dev;
 	skb->mark = wg->fwmark;
@@ -360,6 +364,7 @@ int wg_socket_init(struct wg_device *wg, u16 port)
 		.family = AF_INET,
 		.local_ip.s_addr = htonl(INADDR_ANY),
 		.local_udp_port = htons(port),
+		.bind_ifindex = wg->lowerdev,
 		.use_udp_checksums = true
 	};
 #if IS_ENABLED(CONFIG_IPV6)
@@ -369,6 +374,7 @@ int wg_socket_init(struct wg_device *wg, u16 port)
 		.local_ip6 = IN6ADDR_ANY_INIT,
 		.use_udp6_tx_checksums = true,
 		.use_udp6_rx_checksums = true,
+		.bind_ifindex = wg->lowerdev,
 		.ipv6_v6only = true
 	};
 #endif
diff --git a/include/uapi/linux/wireguard.h b/include/uapi/linux/wireguard.h
index ae88be14c947..f3784885389a 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_LOWERDEV: 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_LOWERDEV: NLA_U32, ifindex to bind lower transport, 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_LOWERDEV,
 	__WGDEVICE_A_LAST
 };
 #define WGDEVICE_A_MAX (__WGDEVICE_A_LAST - 1)
-- 
2.42.0