linux-kernel - Re: [PATCH net-next v11 05/23] ovpn: keep carrier always on

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Message-ID: <89ae26a2-0a09-4758-989e-8f45a707a41b@openvpn.net>
Date: Fri, 15 Nov 2024 15:13:27 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc: 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>, sd@...asysnail.net,
 Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v11 05/23] ovpn: keep carrier always on

On 09/11/2024 02:11, Sergey Ryazanov wrote:
> On 29.10.2024 12:47, Antonio Quartulli wrote:
>> An ovpn interface will keep carrier always on and let the user
>> decide when an interface should be considered disconnected.
>>
>> This way, even if an ovpn interface is not connected to any peer,
>> it can still retain all IPs and routes and thus prevent any data
>> leak.
>>
>> Signed-off-by: Antonio Quartulli <antonio@...nvpn.net>
>> Reviewed-by: Andrew Lunn <andrew@...n.ch>
>> ---
>>   drivers/net/ovpn/main.c | 7 +++++++
>>   1 file changed, 7 insertions(+)
>>
>> diff --git a/drivers/net/ovpn/main.c b/drivers/net/ovpn/main.c
>> index 
>> eead7677b8239eb3c48bb26ca95492d88512b8d4..eaa83a8662e4ac2c758201008268f9633643c0b6 100644
>> --- a/drivers/net/ovpn/main.c
>> +++ b/drivers/net/ovpn/main.c
>> @@ -31,6 +31,13 @@ static void ovpn_struct_free(struct net_device *net)
>>   static int ovpn_net_open(struct net_device *dev)
>>   {
>> +    /* ovpn keeps the carrier always on to avoid losing IP or route
>> +     * configuration upon disconnection. This way it can prevent leaks
>> +     * of traffic outside of the VPN tunnel.
>> +     * The user may override this behaviour by tearing down the 
>> interface
>> +     * manually.
>> +     */
>> +    netif_carrier_on(dev);
> 
> If a user cares about the traffic leaking, then he can create a 
> blackhole route with huge metric:
> 
> # ip route add blackhole default metric 10000
> 
> Why the network interface should implicitly provide this functionality? 
> And on another hand, how a routing daemon can learn a topology change 
> without indication from the interface?

This was discussed loooong ago with Andrew. Here my last response:

https://lore.kernel.org/all/d896bbd8-2709-4834-a637-f982fc51fc57@openvpn.net/


Regards,

> 
>>       netif_tx_start_all_queues(dev);
>>       return 0;
>>   }
>>
> 

-- 
Antonio Quartulli
OpenVPN Inc.