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

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Message-ID: <5e968611-407b-4496-a333-82aa7c22ca29@openvpn.net>
Date: Wed, 2 Apr 2025 14:01:30 +0200
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 v24 07/23] ovpn: implement basic TX path (UDP)

On 01/04/2025 15:49, Sabrina Dubroca wrote:
> 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.

Yeah, seems so. Passing df = 0 basically does what we need.
So you're right, that ignore_df = 1 is useless.
Will drop it.

> 
> 
> [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]

Thanks! :-)
I'll answer all other open comments in the meantime..

Regards,

> 
>> +
>> +	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;
>> +}
> 

-- 
Antonio Quartulli
OpenVPN Inc.