[PATCH net-next v4 18/25] ovpn: add support for updating local UDP endpoint

[Antonio Quartulli <antonio@openvpn.net>]

In case of UDP links, the local endpoint used to communicate with a
given peer may change without a connection restart.

Add support for learning the new address in case of change.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
 drivers/net/ovpn/io.c   |  5 +++++
 drivers/net/ovpn/peer.c | 42 +++++++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/peer.h |  3 +++
 3 files changed, 50 insertions(+)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index dedc4d4a1c72..9188afe0f47e 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -119,6 +119,11 @@ void ovpn_decrypt_post(struct sk_buff *skb, int ret)
 	/* note event of authenticated packet received for keepalive */
 	ovpn_peer_keepalive_recv_reset(peer);
 
+	if (peer->sock->sock->sk->sk_protocol == IPPROTO_UDP) {
+		/* update source endpoint for this peer */
+		ovpn_peer_update_local_endpoint(peer, skb);
+	}
+
 	/* point to encapsulated IP packet */
 	__skb_pull(skb, ovpn_skb_cb(skb)->payload_offset);
 
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index 289fe3f84ed4..ec3064438753 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -455,6 +455,48 @@ struct ovpn_peer *ovpn_peer_get_by_id(struct ovpn_struct *ovpn, u32 peer_id)
 	return peer;
 }
 
+/**
+ * ovpn_peer_update_local_endpoint - update local endpoint for peer
+ * @peer: peer to update the endpoint for
+ * @skb: incoming packet to retrieve the destination address (local) from
+ */
+void ovpn_peer_update_local_endpoint(struct ovpn_peer *peer,
+				     struct sk_buff *skb)
+{
+	struct ovpn_bind *bind;
+
+	rcu_read_lock();
+	bind = rcu_dereference(peer->bind);
+	if (unlikely(!bind))
+		goto unlock;
+
+	switch (skb_protocol_to_family(skb)) {
+	case AF_INET:
+		if (unlikely(bind->local.ipv4.s_addr != ip_hdr(skb)->daddr)) {
+			netdev_dbg(peer->ovpn->dev,
+				   "%s: learning local IPv4 for peer %d (%pI4 -> %pI4)\n",
+				   __func__, peer->id, &bind->local.ipv4.s_addr,
+				   &ip_hdr(skb)->daddr);
+			bind->local.ipv4.s_addr = ip_hdr(skb)->daddr;
+		}
+		break;
+	case AF_INET6:
+		if (unlikely(memcmp(&bind->local.ipv6, &ipv6_hdr(skb)->daddr,
+				    sizeof(bind->local.ipv6)))) {
+			netdev_dbg(peer->ovpn->dev,
+				   "%s: learning local IPv6 for peer %d (%pI6c -> %pI6c\n",
+				   __func__, peer->id, &bind->local.ipv6,
+				   &ipv6_hdr(skb)->daddr);
+			bind->local.ipv6 = ipv6_hdr(skb)->daddr;
+		}
+		break;
+	default:
+		break;
+	}
+unlock:
+	rcu_read_unlock();
+}
+
 /**
  * ovpn_peer_get_by_dst - Lookup peer to send skb to
  * @ovpn: the private data representing the current VPN session
diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index fd7e9d57b38a..1f12ba141d80 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h
@@ -189,4 +189,7 @@ static inline void ovpn_peer_keepalive_xmit_reset(struct ovpn_peer *peer)
 
 void ovpn_peer_keepalive_set(struct ovpn_peer *peer, u32 interval, u32 timeout);
 
+void ovpn_peer_update_local_endpoint(struct ovpn_peer *peer,
+				     struct sk_buff *skb);
+
 #endif /* _NET_OVPN_OVPNPEER_H_ */
-- 
2.44.2