Re: [PATCH net-next v18 05/25] ovpn: introduce the ovpn_peer object

[Antonio Quartulli]

On 02/02/2025 23:56, Sabrina Dubroca wrote:
> 2025-01-13, 10:31:24 +0100, Antonio Quartulli wrote:
> > +static int ovpn_peer_del_p2p(struct ovpn_peer *peer,
> > +			     enum ovpn_del_peer_reason reason)
> > +{
> > +	struct ovpn_peer *tmp;
> > +
> > +	lockdep_assert_held(&peer->ovpn->lock);
> > +
> > +	tmp = rcu_dereference_protected(peer->ovpn->peer,
> > +					lockdep_is_held(&peer->ovpn->lock));
> > +	if (tmp != peer) {
> > +		DEBUG_NET_WARN_ON_ONCE(1);
>
> I think this WARN should be removed. If 2 almost-simultanenous
> DEL_PEER manage to fetch the peer, the first will delete it and NULL
> peer->ovpn->peer, then when it releases ovpn->lock, the 2nd will find
> NULL != peer and hit this WARN.
>
> (probably not happening in practical cases, but syzbot will manage to
> hit it)

I can see this happening with two almost-simultaneous netlink PEER_DEL 
calls.

Thanks, will get rid of the warning.

Regards,

> > +		return -ENOENT;
> > +	}
> > +
> > +	ovpn_peer_remove(peer, reason);
> > +
> > +	return 0;
> > +}

--
Antonio Quartulli
OpenVPN Inc.