[PATCH net-next v9 15/23] ovpn: implement keepalive mechanism

Antonio Quartulli
2024-10-16T01:04:12Z

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

This change implements the keepalive sending and timer expiring logic.

Signed-off-by: Antonio Quartulli <antonio@openvpn.net>
---
drivers/net/ovpn/io.c | 77 +++++++++++++++++
drivers/net/ovpn/io.h | 5 ++
drivers/net/ovpn/main.c | 3 +
drivers/net/ovpn/ovpnstruct.h | 2 +
drivers/net/ovpn/peer.c | 187 ++++++++++++++++++++++++++++++++++++++++++
drivers/net/ovpn/peer.h | 15 ++++
drivers/net/ovpn/proto.h | 2 -
7 files changed, 289 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index 1c0c553b4182762568ce9806a9670e3004076137..1c4cdbb16df4acc5c87707919c671f7a84bf4295 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c
@@ -28,6 +28,33 @@
#include "skb.h"
#include "socket.h"

+const unsigned char ovpn_keepalive_message[OVPN_KEEPALIVE_SIZE] = {
+ 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_message[0])
+ return false;
+
+ if (skb->len != OVPN_KEEPALIVE_SIZE)
+ return false;
+
+ if (!pskb_may_pull(skb, OVPN_KEEPALIVE_SIZE))
+ return false;
+
+ return !memcmp(skb->data, ovpn_keepalive_message, OVPN_KEEPALIVE_SIZE);
+}
+
/* Called after decrypt to write the IP packet to the device.
* This method is expected to manage/free the skb.
*/
@@ -105,6 +132,9 @@ void ovpn_decrypt_post(void *data, int ret)
goto drop;
}

+ /* keep track of last received authenticated packet for keepalive */
+ peer->last_recv = ktime_get_real_seconds();
+
/* point to encapsulated IP packet */
__skb_pull(skb, payload_offset);

@@ -121,6 +151,12 @@ void ovpn_decrypt_post(void *data, int ret)
goto drop;
}

+ if (ovpn_is_keepalive(skb)) {
+ net_dbg_ratelimited("%s: ping received from peer %u\n",
+ peer->ovpn->dev->name, peer->id);
+ goto drop;
+ }
+
net_info_ratelimited("%s: unsupported protocol received from peer %u\n",
peer->ovpn->dev->name, peer->id);
goto drop;
@@ -219,6 +255,10 @@ void ovpn_encrypt_post(void *data, int ret)
/* no transport configured yet */
goto err;
}
+
+ /* keep track of last sent packet for keepalive */
+ peer->last_sent = ktime_get_real_seconds();
+
/* skb passed down the stack - don't free it */
skb = NULL;
err:
@@ -357,3 +397,40 @@ 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
+ */
+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;
+ __skb_put_data(skb, 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);
+}
diff --git a/drivers/net/ovpn/io.h b/drivers/net/ovpn/io.h
index ad81dd86924689309b3299573575a1705eddaf99..eb224114152c29f42aadf026212e8d278006b490 100644
--- a/drivers/net/ovpn/io.h
+++ b/drivers/net/ovpn/io.h
@@ -10,9 +10,14 @@
#ifndef _NET_OVPN_OVPN_H_
#define _NET_OVPN_OVPN_H_

+#define OVPN_KEEPALIVE_SIZE 16
+extern const unsigned char ovpn_keepalive_message[OVPN_KEEPALIVE_SIZE];
+
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_xmit_special(struct ovpn_peer *peer, const void *data,
+ const unsigned int len);

void ovpn_encrypt_post(void *data, int ret);
void ovpn_decrypt_post(void *data, int ret);
diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c
index c7453127ab640d7268c1ce919a87cc5419fac9ee..1bd563e3f16f49dd01c897fbe79cbd90f4b8e9aa 100644
--- a/drivers/net/ovpn/main.c
+++ b/drivers/net/ovpn/main.c
@@ -191,6 +191,7 @@ static int ovpn_newlink(struct net *src_net, struct net_device *dev,
ovpn->dev = dev;
ovpn->mode = mode;
spin_lock_init(&ovpn->lock);
+ INIT_DELAYED_WORK(&ovpn->keepalive_work, ovpn_peer_keepalive_work);

err = ovpn_mp_alloc(ovpn);
if (err < 0)
@@ -244,6 +245,8 @@ static int ovpn_netdev_notifier_call(struct notifier_block *nb,
netif_carrier_off(dev);
ovpn->registered = false;

+ cancel_delayed_work_sync(&ovpn->keepalive_work);
+
switch (ovpn->mode) {
case OVPN_MODE_P2P:
ovpn_peer_release_p2p(ovpn);
diff --git a/drivers/net/ovpn/ovpnstruct.h b/drivers/net/ovpn/ovpnstruct.h
index 12ed5e22c2108c9f143d1984048eb40c887cac63..4ac00d550ecb9f84c6c132dd2bdc0a3fc0ab342c 100644
--- a/drivers/net/ovpn/ovpnstruct.h
+++ b/drivers/net/ovpn/ovpnstruct.h
@@ -43,6 +43,7 @@ struct ovpn_peer_collection {
* @peer: in P2P mode, this is the only remote peer
* @dev_list: entry for the module wide device list
* @gro_cells: pointer to the Generic Receive Offload cell
+ * @keepalive_work: struct used to schedule keepalive periodic job
*/
struct ovpn_struct {
struct net_device *dev;
@@ -54,6 +55,7 @@ struct ovpn_struct {
struct ovpn_peer __rcu *peer;
struct list_head dev_list;
struct gro_cells gro_cells;
+ struct delayed_work keepalive_work;
};

#endif /* _NET_OVPN_OVPNSTRUCT_H_ */
diff --git a/drivers/net/ovpn/peer.c b/drivers/net/ovpn/peer.c
index c7dc9032c2b55fd42befc1f3e7a0eca893a96576..fa1883d12dfd6ce3e2ad1f9835f15aa7db5c8290 100644
--- a/drivers/net/ovpn/peer.c
+++ b/drivers/net/ovpn/peer.c
@@ -22,6 +22,34 @@
#include "peer.h"
#include "socket.h"

+/**
+ * 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)
+{
+ time64_t now = ktime_get_real_seconds();
+
+ 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;
+ peer->last_sent = now;
+ peer->keepalive_xmit_exp = now + interval;
+
+ peer->keepalive_timeout = timeout;
+ peer->last_recv = now;
+ peer->keepalive_recv_exp = now + timeout;
+
+ /* now that interval and timeout have been changed, kick
+ * off the worker so that the next delay can be recomputed
+ */
+ mod_delayed_work(system_wq, &peer->ovpn->keepalive_work, 0);
+}
+
/**
* ovpn_peer_new - allocate and initialize a new peer object
* @ovpn: the openvpn instance inside which the peer should be created
@@ -815,6 +843,19 @@ int ovpn_peer_del(struct ovpn_peer *peer, enum ovpn_del_peer_reason reason)
}
}

+static int ovpn_peer_del_nolock(struct ovpn_peer *peer,
+ enum ovpn_del_peer_reason reason)
+{
+ switch (peer->ovpn->mode) {
+ case OVPN_MODE_MP:
+ return ovpn_peer_del_mp(peer, reason);
+ case OVPN_MODE_P2P:
+ return ovpn_peer_del_p2p(peer, reason);
+ default:
+ return -EOPNOTSUPP;
+ }
+}
+
/**
* ovpn_peers_free - free all peers in the instance
* @ovpn: the instance whose peers should be released
@@ -830,3 +871,149 @@ void ovpn_peers_free(struct ovpn_struct *ovpn)
ovpn_peer_unhash(peer, OVPN_DEL_PEER_REASON_TEARDOWN);
spin_unlock_bh(&ovpn->peers->lock);
}
+
+static time64_t ovpn_peer_keepalive_work_single(struct ovpn_peer *peer,
+ time64_t now)
+{
+ time64_t next_run1, next_run2, delta;
+ unsigned long timeout, interval;
+ bool expired;
+
+ spin_lock_bh(&peer->lock);
+ /* we expect both timers to be configured at the same time,
+ * therefore bail out if either is not set
+ */
+ if (!peer->keepalive_timeout || !peer->keepalive_interval) {
+ spin_unlock_bh(&peer->lock);
+ return 0;
+ }
+
+ /* check for peer timeout */
+ expired = false;
+ timeout = peer->keepalive_timeout;
+ delta = now - peer->last_recv;
+ if (delta < timeout) {
+ peer->keepalive_recv_exp = now + timeout - delta;
+ next_run1 = peer->keepalive_recv_exp;
+ } else if (peer->keepalive_recv_exp > now) {
+ next_run1 = peer->keepalive_recv_exp;
+ } else {
+ expired = true;
+ }
+
+ if (expired) {
+ /* peer is dead -> kill it and move on */
+ spin_unlock_bh(&peer->lock);
+ netdev_dbg(peer->ovpn->dev, "peer %u expired\n",
+ peer->id);
+ ovpn_peer_del_nolock(peer, OVPN_DEL_PEER_REASON_EXPIRED);
+ return 0;
+ }
+
+ /* check for peer keepalive */
+ expired = false;
+ interval = peer->keepalive_interval;
+ delta = now - peer->last_sent;
+ if (delta < interval) {
+ peer->keepalive_xmit_exp = now + interval - delta;
+ next_run2 = peer->keepalive_xmit_exp;
+ } else if (peer->keepalive_xmit_exp > now) {
+ next_run2 = peer->keepalive_xmit_exp;
+ } else {
+ expired = true;
+ next_run2 = now + interval;
+ }
+ spin_unlock_bh(&peer->lock);
+
+ if (expired) {
+ /* a keepalive packet is required */
+ netdev_dbg(peer->ovpn->dev,
+ "sending keepalive to peer %u\n",
+ peer->id);
+ ovpn_xmit_special(peer, ovpn_keepalive_message,
+ sizeof(ovpn_keepalive_message));
+ }
+
+ if (next_run1 < next_run2)
+ return next_run1;
+
+ return next_run2;
+}
+
+static time64_t ovpn_peer_keepalive_work_mp(struct ovpn_struct *ovpn,
+ time64_t now)
+{
+ time64_t tmp_next_run, next_run = 0;
+ struct hlist_node *tmp;
+ struct ovpn_peer *peer;
+ int bkt;
+
+ spin_lock_bh(&ovpn->peers->lock);
+ hash_for_each_safe(ovpn->peers->by_id, bkt, tmp, peer, hash_entry_id) {
+ tmp_next_run = ovpn_peer_keepalive_work_single(peer, now);
+ if (!tmp_next_run)
+ continue;
+
+ /* the next worker run will be scheduled based on the shortest
+ * required interval across all peers
+ */
+ if (!next_run || tmp_next_run < next_run)
+ next_run = tmp_next_run;
+ }
+ spin_unlock_bh(&ovpn->peers->lock);
+
+ return next_run;
+}
+
+static time64_t ovpn_peer_keepalive_work_p2p(struct ovpn_struct *ovpn,
+ time64_t now)
+{
+ struct ovpn_peer *peer;
+ time64_t next_run;
+
+ spin_lock_bh(&ovpn->lock);
+ peer = rcu_dereference_protected(ovpn->peer,
+ lockdep_is_held(&ovpn->lock));
+ next_run = ovpn_peer_keepalive_work_single(peer, now);
+ spin_unlock_bh(&ovpn->lock);
+
+ return next_run;
+}
+
+/**
+ * ovpn_peer_keepalive_work - run keepalive logic on each known peer
+ * @work: pointer to the work member of the related ovpn object
+ *
+ * Each peer has two timers (if configured):
+ * 1. peer timeout: when no data is received for a certain interval,
+ * the peer is considered dead and it gets killed.
+ * 2. peer keepalive: when no data is sent to a certain peer for a
+ * certain interval, a special 'keepalive' packet is explicitly sent.
+ *
+ * This function iterates across the whole peer collection while
+ * checking the timers described above.
+ */
+void ovpn_peer_keepalive_work(struct work_struct *work)
+{
+ struct ovpn_struct *ovpn = container_of(work, struct ovpn_struct,
+ keepalive_work.work);
+ time64_t next_run = 0, now = ktime_get_real_seconds();
+
+ switch (ovpn->mode) {
+ case OVPN_MODE_MP:
+ next_run = ovpn_peer_keepalive_work_mp(ovpn, now);
+ break;
+ case OVPN_MODE_P2P:
+ next_run = ovpn_peer_keepalive_work_p2p(ovpn, now);
+ break;
+ }
+
+ /* prevent rearming if the interface is being destroyed */
+ if (next_run > 0 && ovpn->registered) {
+ netdev_dbg(ovpn->dev,
+ "scheduling keepalive work: now=%llu next_run=%llu delta=%llu\n",
+ next_run, now, next_run - now);
+ schedule_delayed_work(&ovpn->keepalive_work,
+ (next_run - now) * HZ);
+ }
+}
diff --git a/drivers/net/ovpn/peer.h b/drivers/net/ovpn/peer.h
index 942b90c84a0fb9e6fbb96f6df7f7842a9f738caf..952927ae78a3ab753aaf2c6cc6f77121bdac34be 100644
--- a/drivers/net/ovpn/peer.h
+++ b/drivers/net/ovpn/peer.h
@@ -43,6 +43,12 @@
* @crypto: the crypto configuration (ciphers, keys, etc..)
* @dst_cache: cache for dst_entry used to send to peer
* @bind: remote peer binding
+ * @keepalive_interval: seconds after which a new keepalive should be sent
+ * @keepalive_xmit_exp: future timestamp when next keepalive should be sent
+ * @last_sent: timestamp of the last successfully sent packet
+ * @keepalive_timeout: seconds after which an inactive peer is considered dead
+ * @keepalive_recv_exp: future timestamp when the peer should expire
+ * @last_recv: timestamp of the last authenticated received packet
* @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
@@ -91,6 +97,12 @@ struct ovpn_peer {
struct ovpn_crypto_state crypto;
struct dst_cache dst_cache;
struct ovpn_bind __rcu *bind;
+ unsigned long keepalive_interval;
+ unsigned long keepalive_xmit_exp;
+ time64_t last_sent;
+ unsigned long keepalive_timeout;
+ unsigned long keepalive_recv_exp;
+ time64_t last_recv;
bool halt;
struct ovpn_peer_stats vpn_stats;
struct ovpn_peer_stats link_stats;
@@ -137,4 +149,7 @@ 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);

+void ovpn_peer_keepalive_set(struct ovpn_peer *peer, u32 interval, u32 timeout);
+void ovpn_peer_keepalive_work(struct work_struct *work);
+
#endif /* _NET_OVPN_OVPNPEER_H_ */
diff --git a/drivers/net/ovpn/proto.h b/drivers/net/ovpn/proto.h
index 32af6b8e574381fb719a1b3b9de3ae1071cc4846..0de8bafadc89ebb85ce40de95ef394588738a4ad 100644
--- a/drivers/net/ovpn/proto.h
+++ b/drivers/net/ovpn/proto.h
@@ -35,8 +35,6 @@
#define OVPN_OP_SIZE_V2 4
#define OVPN_PEER_ID_MASK 0x00FFFFFF
#define OVPN_PEER_ID_UNDEF 0x00FFFFFF
-/* first byte of keepalive message */
-#define OVPN_KEEPALIVE_FIRST_BYTE 0x2a
/* first byte of exit message */
#define OVPN_EXPLICIT_EXIT_NOTIFY_FIRST_BYTE 0x28

--
2.45.2