[PATCH net-next v4 17/25] ovpn: implement keepalive mechanism

[Antonio Quartulli <antonio@openvpn.net>]

OpenVPN supports configuring a periodic keepalive "ping"
message to allow the remote endpoint detect link failures.

This change implements the ping sending and timer expiring logic.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
 drivers/net/ovpn/io.c   | 82 +++++++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/io.h   |  1 +
 drivers/net/ovpn/peer.c | 72 ++++++++++++++++++++++++++++++++++++
 drivers/net/ovpn/peer.h | 45 ++++++++++++++++++++++
 4 files changed, 200 insertions(+)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index 764b3df996bc..dedc4d4a1c72 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -25,6 +25,31 @@
 #include "udp.h"
 #include "skb.h"
 
+static const unsigned char ovpn_keepalive_message[] = {
+	0x2a, 0x18, 0x7b, 0xf3, 0x64, 0x1e, 0xb4, 0xcb,
+	0x07, 0xed, 0x2d, 0x0a, 0x98, 0x1f, 0xc7, 0x48
+};
+
+/**
+ * ovpn_is_keepalive - check if skb contains a keepalive message
+ * @skb: packet to check
+ *
+ * Assumes that the first byte of skb->data is defined.
+ *
+ * Return: true if skb contains a keepalive or false otherwise
+ */
+static bool ovpn_is_keepalive(struct sk_buff *skb)
+{
+	if (*skb->data != OVPN_KEEPALIVE_FIRST_BYTE)
+		return false;
+
+	if (!pskb_may_pull(skb, sizeof(ovpn_keepalive_message)))
+		return false;
+
+	return !memcmp(skb->data, ovpn_keepalive_message,
+		       sizeof(ovpn_keepalive_message));
+}
+
 /* Called after decrypt to write the IP packet to the device.
  * This method is expected to manage/free the skb.
  */
@@ -91,6 +116,9 @@ void ovpn_decrypt_post(struct sk_buff *skb, int ret)
 		goto drop;
 	}
 
+	/* note event of authenticated packet received for keepalive */
+	ovpn_peer_keepalive_recv_reset(peer);
+
 	/* point to encapsulated IP packet */
 	__skb_pull(skb, ovpn_skb_cb(skb)->payload_offset);
 
@@ -107,6 +135,12 @@ void ovpn_decrypt_post(struct sk_buff *skb, int ret)
 			goto drop;
 		}
 
+		if (ovpn_is_keepalive(skb)) {
+			netdev_dbg(peer->ovpn->dev,
+				   "ping received from peer %u\n", peer->id);
+			goto drop;
+		}
+
 		net_info_ratelimited("%s: unsupported protocol received from peer %u\n",
 				     peer->ovpn->dev->name, peer->id);
 		goto drop;
@@ -203,6 +237,7 @@ void ovpn_encrypt_post(struct sk_buff *skb, int ret)
 		/* no transport configured yet */
 		goto err;
 	}
+	ovpn_peer_keepalive_xmit_reset(peer);
 	/* skb passed down the stack - don't free it */
 	skb = NULL;
 err:
@@ -345,3 +380,50 @@ netdev_tx_t ovpn_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	kfree_skb_list(skb);
 	return NET_XMIT_DROP;
 }
+
+/**
+ * ovpn_xmit_special - encrypt and transmit an out-of-band message to peer
+ * @peer: peer to send the message to
+ * @data: message content
+ * @len: message length
+ *
+ * Assumes that caller holds a reference to peer
+ */
+static void ovpn_xmit_special(struct ovpn_peer *peer, const void *data,
+			      const unsigned int len)
+{
+	struct ovpn_struct *ovpn;
+	struct sk_buff *skb;
+
+	ovpn = peer->ovpn;
+	if (unlikely(!ovpn))
+		return;
+
+	skb = alloc_skb(256 + len, GFP_ATOMIC);
+	if (unlikely(!skb))
+		return;
+
+	skb_reserve(skb, 128);
+	skb->priority = TC_PRIO_BESTEFFORT;
+	memcpy(__skb_put(skb, len), data, len);
+
+	/* increase reference counter when passing peer to sending queue */
+	if (!ovpn_peer_hold(peer)) {
+		netdev_dbg(ovpn->dev, "%s: cannot hold peer reference for sending special packet\n",
+			   __func__);
+		kfree_skb(skb);
+		return;
+	}
+
+	ovpn_send(ovpn, skb, peer);
+}
+
+/**
+ * ovpn_keepalive_xmit - send keepalive message to peer
+ * @peer: the peer to send the message to
+ */
+void ovpn_keepalive_xmit(struct ovpn_peer *peer)
+{
+	ovpn_xmit_special(peer, ovpn_keepalive_message,
+			  sizeof(ovpn_keepalive_message));
+}
diff --git a/drivers/net/ovpn/io.h b/drivers/net/ovpn/io.h
index ad741552d742..63fcd576ddaf 100644
--- a/drivers/net/ovpn/io.h
+++ b/drivers/net/ovpn/io.h
@@ -13,6 +13,7 @@
 netdev_tx_t ovpn_net_xmit(struct sk_buff *skb, struct net_device *dev);
 
 void ovpn_recv(struct ovpn_peer *peer, struct sk_buff *skb);
+void ovpn_keepalive_xmit(struct ovpn_peer *peer);
 
 void ovpn_encrypt_post(struct sk_buff *skb, int ret);
 void ovpn_decrypt_post(struct sk_buff *skb, int ret);
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index 8c23268db916..289fe3f84ed4 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -22,6 +22,63 @@
 #include "peer.h"
 #include "socket.h"
 
+/**
+ * ovpn_peer_ping - timer task for sending periodic keepalive
+ * @t: timer object that triggered the task
+ */
+static void ovpn_peer_ping(struct timer_list *t)
+{
+	struct ovpn_peer *peer = from_timer(peer, t, keepalive_xmit);
+
+	netdev_dbg(peer->ovpn->dev, "%s: sending ping to peer %u\n", __func__,
+		   peer->id);
+	ovpn_keepalive_xmit(peer);
+}
+
+/**
+ * ovpn_peer_expire - timer task for incoming keepialive timeout
+ * @t: the timer that triggered the task
+ */
+static void ovpn_peer_expire(struct timer_list *t)
+{
+	struct ovpn_peer *peer = from_timer(peer, t, keepalive_recv);
+
+	netdev_dbg(peer->ovpn->dev, "%s: peer %u expired\n", __func__,
+		   peer->id);
+	ovpn_peer_del(peer, OVPN_DEL_PEER_REASON_EXPIRED);
+}
+
+/**
+ * ovpn_peer_keepalive_set - configure keepalive values for peer
+ * @peer: the peer to configure
+ * @interval: outgoing keepalive interval
+ * @timeout: incoming keepalive timeout
+ */
+void ovpn_peer_keepalive_set(struct ovpn_peer *peer, u32 interval, u32 timeout)
+{
+	u32 delta;
+
+	netdev_dbg(peer->ovpn->dev,
+		   "%s: scheduling keepalive for peer %u: interval=%u timeout=%u\n",
+		   __func__, peer->id, interval, timeout);
+
+	peer->keepalive_interval = interval;
+	if (interval > 0) {
+		delta = msecs_to_jiffies(interval * MSEC_PER_SEC);
+		mod_timer(&peer->keepalive_xmit, jiffies + delta);
+	} else {
+		timer_delete(&peer->keepalive_xmit);
+	}
+
+	peer->keepalive_timeout = timeout;
+	if (timeout) {
+		delta = msecs_to_jiffies(timeout * MSEC_PER_SEC);
+		mod_timer(&peer->keepalive_recv, jiffies + delta);
+	} else {
+		timer_delete(&peer->keepalive_recv);
+	}
+}
+
 /**
  * ovpn_peer_new - allocate and initialize a new peer object
  * @ovpn: the openvpn instance inside which the peer should be created
@@ -63,9 +120,22 @@ struct ovpn_peer *ovpn_peer_new(struct ovpn_struct *ovpn, u32 id)
 
 	netdev_hold(ovpn->dev, NULL, GFP_KERNEL);
 
+	timer_setup(&peer->keepalive_xmit, ovpn_peer_ping, 0);
+	timer_setup(&peer->keepalive_recv, ovpn_peer_expire, 0);
+
 	return peer;
 }
 
+/**
+ * ovpn_peer_timer_delete_all - killall keepalive timers
+ * @peer: peer for which timers should be killed
+ */
+static void ovpn_peer_timer_delete_all(struct ovpn_peer *peer)
+{
+	timer_shutdown_sync(&peer->keepalive_xmit);
+	timer_shutdown_sync(&peer->keepalive_recv);
+}
+
 /**
  * ovpn_peer_release - release peer private members
  * @peer: the peer to release
@@ -77,6 +147,8 @@ static void ovpn_peer_release(struct ovpn_peer *peer)
 
 	ovpn_crypto_state_release(&peer->crypto);
 	ovpn_bind_reset(peer, NULL);
+	ovpn_peer_timer_delete_all(peer);
+
 	dst_cache_destroy(&peer->dst_cache);
 }
 
diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index 6e92e09a3504..fd7e9d57b38a 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h
@@ -50,6 +50,10 @@
  * @crypto: the crypto configuration (ciphers, keys, etc..)
  * @dst_cache: cache for dst_entry used to send to peer
  * @bind: remote peer binding
+ * @keepalive_xmit: timer used to send the next keepalive
+ * @keepalive_interval: seconds after which a new keepalive should be sent
+ * @keepalive_recv: timer used to check for received keepalives
+ * @keepalive_timeout: seconds after which an inactive peer is considered dead
  * @halt: true if ovpn_peer_mark_delete was called
  * @vpn_stats: per-peer in-VPN TX/RX stays
  * @link_stats: per-peer link/transport TX/RX stats
@@ -98,6 +102,10 @@ struct ovpn_peer {
 	struct ovpn_crypto_state crypto;
 	struct dst_cache dst_cache;
 	struct ovpn_bind __rcu *bind;
+	struct timer_list keepalive_xmit;
+	unsigned long keepalive_interval;
+	struct timer_list keepalive_recv;
+	unsigned long keepalive_timeout;
 	bool halt;
 	struct ovpn_peer_stats vpn_stats;
 	struct ovpn_peer_stats link_stats;
@@ -144,4 +152,41 @@ struct ovpn_peer *ovpn_peer_get_by_dst(struct ovpn_struct *ovpn,
 bool ovpn_peer_check_by_src(struct ovpn_struct *ovpn, struct sk_buff *skb,
 			    struct ovpn_peer *peer);
 
+/**
+ * ovpn_peer_keepalive_recv_reset - reset keepalive timeout
+ * @peer: peer for which the timeout should be reset
+ *
+ * To be invoked upon reception of an authenticated packet from peer in order
+ * to report valid activity and thus reset the keepalive timeout
+ */
+static inline void ovpn_peer_keepalive_recv_reset(struct ovpn_peer *peer)
+{
+	u32 delta = msecs_to_jiffies(peer->keepalive_timeout * MSEC_PER_SEC);
+
+	if (unlikely(!delta))
+		return;
+
+	mod_timer(&peer->keepalive_recv, jiffies + delta);
+}
+
+/**
+ * ovpn_peer_keepalive_xmit_reset - reset keepalive sending timer
+ * @peer: peer for which the timer should be reset
+ *
+ * To be invoked upon sending of an authenticated packet to peer in order
+ * to report valid outgoing activity and thus reset the keepalive sending
+ * timer
+ */
+static inline void ovpn_peer_keepalive_xmit_reset(struct ovpn_peer *peer)
+{
+	u32 delta = msecs_to_jiffies(peer->keepalive_interval * MSEC_PER_SEC);
+
+	if (unlikely(!delta))
+		return;
+
+	mod_timer(&peer->keepalive_xmit, jiffies + delta);
+}
+
+void ovpn_peer_keepalive_set(struct ovpn_peer *peer, u32 interval, u32 timeout);
+
 #endif /* _NET_OVPN_OVPNPEER_H_ */
-- 
2.44.2