On 12/11/2024 11:56, Sabrina Dubroca wrote:
2024-10-29, 11:47:30 +0100, Antonio Quartulli wrote:
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.



+               /* 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!



+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.


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


--
Antonio Quartulli
OpenVPN Inc.


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