linux-kernel - Re: [PATCH net-next v24 07/23] ovpn: implement basic TX path (UDP)

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Message-ID: <Z-vu7AWTwWE2D_df@krikkit>
Date: Tue, 1 Apr 2025 15:49:32 +0200
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 v24 07/23] ovpn: implement basic TX path (UDP)

2025-03-18, 02:40:42 +0100, Antonio Quartulli wrote:
> +static int ovpn_udp_output(struct ovpn_peer *peer, struct dst_cache *cache,
> +			   struct sock *sk, struct sk_buff *skb)
> +{
> +	struct ovpn_bind *bind;
> +	int ret;
> +
> +	/* set sk to null if skb is already orphaned */
> +	if (!skb->destructor)
> +		skb->sk = NULL;
> +
> +	/* always permit openvpn-created packets to be (outside) fragmented */
> +	skb->ignore_df = 1;

Have you tested this with IPv4 encap? AFAICT it doesn't have any
effect because of the call chain:

ovpn_udp4_output -> udp_tunnel_xmit_skb -> iptunnel_xmit -> skb_scrub_packet

which does

    skb->ignore_df = 0;


But since you pass df = 0 to udp_tunnel_xmit_skb, I suspect it works
as intended despite skb_scrub_packet.


[note: that was the last comment I wanted to send, I have a few more
suggestions that don't need to be addressed at this time]

> +
> +	rcu_read_lock();
> +	bind = rcu_dereference(peer->bind);
> +	if (unlikely(!bind)) {
> +		net_warn_ratelimited("%s: no bind for remote peer %u\n",
> +				     netdev_name(peer->ovpn->dev), peer->id);
> +		ret = -ENODEV;
> +		goto out;
> +	}
> +
> +	switch (bind->remote.in4.sin_family) {
> +	case AF_INET:
> +		ret = ovpn_udp4_output(peer, bind, cache, sk, skb);
> +		break;
> +#if IS_ENABLED(CONFIG_IPV6)
> +	case AF_INET6:
> +		ret = ovpn_udp6_output(peer, bind, cache, sk, skb);
> +		break;
> +#endif
> +	default:
> +		ret = -EAFNOSUPPORT;
> +		break;
> +	}
> +
> +out:
> +	rcu_read_unlock();
> +	return ret;
> +}

-- 
Sabrina