linux-kernel - Re: [PATCH net-next v18 05/25] ovpn: introduce the ovpn

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Message-ID: <1c53012a-5771-47d7-9bf4-104f8d9093a6@openvpn.net>
Date: Mon, 3 Feb 2025 09:41:18 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: netdev@...r.kernel.org, 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+netdev@...n.ch>,
 Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Xiao Liang <shaw.leon@...il.com>
Subject: Re: [PATCH net-next v18 05/25] ovpn: introduce the ovpn_peer object

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.