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Message-ID: <ZypfnyfToF1b6YAZ@hog>
Date: Tue, 5 Nov 2024 19:10:39 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: Antonio Quartulli <antonio@...nvpn.net>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Donald Hunter <donald.hunter@...il.com>,
Shuah Khan <shuah@...nel.org>, ryazanov.s.a@...il.com,
Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v11 15/23] ovpn: implement keepalive mechanism
2024-10-29, 11:47:28 +0100, Antonio Quartulli wrote:
> @@ -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();
It doesn't look like we're locking the peer here so that should be a
WRITE_ONCE() (and READ_ONCE(peer->last_recv) for all reads).
> +
> /* 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;
To help with debugging connectivity issues, maybe keepalives shouldn't
be counted as drops? (consume_skb instead of kfree_skb, and not
incrementing rx_dropped)
The packet was successfully received and did all it had to do.
> + }
> +
> net_info_ratelimited("%s: unsupported protocol received from peer %u\n",
> peer->ovpn->dev->name, peer->id);
> goto drop;
> @@ -221,6 +257,10 @@ 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();
And another WRITE_ONCE() here (also paired with READ_ONCE() on the
read side).
> +static int ovpn_peer_del_nolock(struct ovpn_peer *peer,
> + enum ovpn_del_peer_reason reason)
> +{
> + switch (peer->ovpn->mode) {
> + case OVPN_MODE_MP:
I think it would be nice to add
lockdep_assert_held(&peer->ovpn->peers->lock);
> + return ovpn_peer_del_mp(peer, reason);
> + case OVPN_MODE_P2P:
and here
lockdep_assert_held(&peer->ovpn->lock);
(I had to check that ovpn_peer_del_nolock is indeed called with those
locks held since they're taken by ovpn_peer_keepalive_work_{mp,p2p},
adding these assertions would make it clear that ovpn_peer_del_nolock
is not an unsafe version of ovpn_peer_del)
> + 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 +871,150 @@ 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;
I'm not sure that's always > 0 if we finish decrypting a packet just
as the workqueue starts:
ovpn_peer_keepalive_work
now = ...
ovpn_decrypt_post
peer->last_recv = ...
ovpn_peer_keepalive_work_single
delta: now < peer->last_recv
> + if (delta < timeout) {
> + peer->keepalive_recv_exp = now + timeout - delta;
I'd shorten that to
peer->keepalive_recv_exp = peer->last_recv + timeout;
it's a bit more readable to my eyes and avoids risks of wrapping
values.
So I'd probably get rid of delta and go with:
last_recv = READ_ONCE(peer->last_recv)
if (now < last_recv + timeout) {
peer->keepalive_recv_exp = last_recv + timeout;
next_run1 = peer->keepalive_recv_exp;
} else if ...
> + next_run1 = peer->keepalive_recv_exp;
> + } else if (peer->keepalive_recv_exp > now) {
> + next_run1 = peer->keepalive_recv_exp;
> + } else {
> + expired = true;
> + }
[...]
> + /* 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;
and same here
--
Sabrina
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