linux-kernel - Re: [PATCH net-next v24 16/23] ovpn: implement keepalive mechanism

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Message-ID: <39b4ca40-a4a8-447f-b2a7-7221437fad22@openvpn.net>
Date: Wed, 2 Apr 2025 14:11:43 +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 16/23] ovpn: implement keepalive mechanism

On 01/04/2025 14:51, Sabrina Dubroca wrote:
> 2025-03-18, 02:40:51 +0100, Antonio Quartulli wrote:
>> @@ -124,6 +154,13 @@ void ovpn_decrypt_post(void *data, int ret)
>>   			goto drop;
>>   		}
>>   
>> +		if (ovpn_is_keepalive(skb)) {
>> +			net_dbg_ratelimited("%s: ping received from peer %u\n",
>> +					    netdev_name(peer->ovpn->dev),
>> +					    peer->id);
>> +			goto drop_nocount;
>> +		}
>> +
>>   		net_info_ratelimited("%s: unsupported protocol received from peer %u\n",
>>   				     netdev_name(peer->ovpn->dev), peer->id);
>>   		goto drop;
>> @@ -149,6 +186,7 @@ void ovpn_decrypt_post(void *data, int ret)
>>   drop:
>>   	if (unlikely(skb))
>>   		dev_core_stats_rx_dropped_inc(peer->ovpn->dev);
>> +drop_nocount:
>>   	if (likely(peer))
>>   		ovpn_peer_put(peer);
>>   	if (likely(ks))
>>   	kfree_skb(skb);
>>   }
> 
> Again a small thing: in the case of a keepalive message, it would also
> be nice to use consume_skb instead of kfree_skb. Quoting from the doc
> for consume_skb:
> 
>   *	Functions identically to kfree_skb, but kfree_skb assumes that the frame
>   *	is being dropped after a failure and notes that

I agree! I always try to pay attention to when consume_skb() should be 
used, but I must have missed this special case.

> 
> 
> 
> Something like this maybe (not compiled):
> 
> 	/* skb is passed to upper layer - don't free it */
> 	skb = NULL;
> drop:
> 	if (unlikely(skb))
> 		dev_core_stats_rx_dropped_inc(peer->ovpn->dev);
> 	kfree_skb(skb);
> 	skb = NULL;
> drop_nocount:
> 	if (likely(peer))
> 		ovpn_peer_put(peer);
> 	if (likely(ks))
> 		ovpn_crypto_key_slot_put(ks);
> 	consume_skb(skb);
> 
> 
> 

Either that or I can call consume_skb(skb) and set skb = NULL before 
jumping to drop_nocount (haven't fully checked if possible).

I'll see which version is better.

Thanks for pointing this out!

Regards,


-- 
Antonio Quartulli
OpenVPN Inc.