On 12/11/2024 11:56, Sabrina Dubroca wrote:

2024-10-29, 11:47:30 +0100, Antonio Quartulli wrote:

quoted

diff --git a/drivers/net/ovpn/io.c b/drivers/net/ovpn/io.c
index 63c140138bf98e5d1df79a2565b666d86513323d..0e8a6f2c76bc7b2ccc287ad1187cf50f033bf261 100644
--- a/drivers/net/ovpn/io.c
+++ b/drivers/net/ovpn/io.c

@@ -135,6 +135,15 @@ void ovpn_decrypt_post(void *data, int ret)
  	/* keep track of last received authenticated packet for keepalive */
  	peer->last_recv = ktime_get_real_seconds();
  
+	if (peer->sock->sock->sk->sk_protocol == IPPROTO_UDP) {

What prevents peer->sock from being replaced and released
concurrently?

Technically nothing.
Userspace currently does not even support updating a peer socket at 
runtime, but I wanted ovpn to be flexible enough from the beginning.

One approach might be to go back to peer->sock being unmutable and 
forget about this.

OTOH, if we want to keep this flexibility (which I think is nice), I 
think I should make peer->sock an RCU pointer and access it accordingly.
Does it make sense?

Or possibly reading the error value that ovpn_socket_new can return
before peer->sock is reset to NULL, just noticed this in
ovpn_nl_peer_modify:

	if (attrs[OVPN_A_PEER_SOCKET]) {
		// ...
		peer->sock = ovpn_socket_new(sock, peer);
		if (IS_ERR(peer->sock)) {
			// ...
			peer->sock = NULL;


(ovpn_encrypt_post has a similar check on
peer->sock->sock->sk->sk_protocol that I don't think is safe either)

Yap, agreed.

quoted

+		/* check if this peer changed it's IP address and update
+		 * state
+		 */
+		ovpn_peer_float(peer, skb);
+		/* update source endpoint for this peer */
+		ovpn_peer_update_local_endpoint(peer, skb);

Why not do both in the same function? They're not called anywhere else
(at least in this version of the series). They both modify peer->bind
depending on skb_protocol_to_family(skb), and operate under
peer->lock.

I never considered to do so as I just always assumed the two to be two 
separate features/routines.

I think it's a good idea and I would get rid of a few common 
instructions (along with acquiring the lock twice). Thanks!

quoted

+void ovpn_peer_float(struct ovpn_peer *peer, struct sk_buff *skb)
+{
+	struct hlist_nulls_head *nhead;
+	struct sockaddr_storage ss;
+	const u8 *local_ip = NULL;
+	struct sockaddr_in6 *sa6;
+	struct sockaddr_in *sa;
+	struct ovpn_bind *bind;
+	sa_family_t family;
+	size_t salen;
+
+	rcu_read_lock();
+	bind = rcu_dereference(peer->bind);
+	if (unlikely(!bind)) {
+		rcu_read_unlock();
+		return;
+	}
+
+	spin_lock_bh(&peer->lock);

You could take the lock from the start, instead of using rcu_read_lock
to get peer->bind. It would guarantee that the bind we got isn't
already being replaced just as we wait to update it. And same in
ovpn_peer_update_local_endpoint, it would make sure we're updating the
local IP for the active bind.

(sorry I didn't think about that last time we discussed this)

no worries :) and I like the idea. will do that, thanks.

quoted

+	if (likely(ovpn_bind_skb_src_match(bind, skb)))
+		goto unlock;
+
+	family = skb_protocol_to_family(skb);
+

-- 
Antonio Quartulli
OpenVPN Inc.