linux-kernel - Re: [PATCH net-next v18 07/25] ovpn: implement basic TX path (UDP)

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Message-ID: <Z6I9yn3Nh-9Ebvv9@hog>
Date: Tue, 4 Feb 2025 17:18:18 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: Antonio Quartulli <antonio@...nvpn.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 07/25] ovpn: implement basic TX path (UDP)

2025-02-03, 10:52:41 +0100, Sabrina Dubroca wrote:
> 2025-01-13, 10:31:26 +0100, Antonio Quartulli wrote:
> > +static void ovpn_encrypt_post(struct sk_buff *skb, int ret)
> > +{
> > +	struct ovpn_peer *peer = ovpn_skb_cb(skb)->peer;
> > +
> > +	if (unlikely(ret < 0))
> > +		goto err;
> > +
> > +	skb_mark_not_on_list(skb);
> > +
> > +	switch (peer->sock->sock->sk->sk_protocol) {
> 
> We have a ref on the peer, but not on the ovpn_sock. DEL_PEER could
> have detached the sock by the time the crypto completes.
> 
> (unfortunately I don't have any idea to fix this yet)

Maybe an idea:

Since ovpn_sock itself lives under RCU (because of sk_user_data),
peer->sock should be an RCU pointer and also follow RCU rules. For
most parts (io.c, netlink.c) the conversion is not too
problematic. TCP is more difficult.

I still need to think about whether this works, and whether this is
worth the complexity, or if we could solve this in another way.

-- 
Sabrina