netdev - Re: [PATCH net-next 1/4] ovpn: properly deconfigure UDP-tunnel

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Message-ID: <39ca5468-733b-49c4-a00d-27c2ab85b795@redhat.com>
Date: Thu, 29 May 2025 11:25:59 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Antonio Quartulli <antonio@...nvpn.net>, netdev@...r.kernel.org
Cc: Sabrina Dubroca <sd@...asysnail.net>,
 "David S . Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>,
 Oleksandr Natalenko <oleksandr@...alenko.name>
Subject: Re: [PATCH net-next 1/4] ovpn: properly deconfigure UDP-tunnel

On 5/27/25 3:46 PM, Antonio Quartulli wrote:
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index dde52b8050b8..9ffc4e0b1644 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2900,7 +2900,7 @@ void udp_destroy_sock(struct sock *sk)
>  			if (encap_destroy)
>  				encap_destroy(sk);
>  		}
> -		if (udp_test_bit(ENCAP_ENABLED, sk)) {
> +		if (udp_test_and_clear_bit(ENCAP_ENABLED, sk)) {

Nothing should use 'sk' after udp_destroy_sock(), no need to clear the
bit (same in ipv6 code)

>  			static_branch_dec(&udp_encap_needed_key);
>  			udp_tunnel_cleanup_gro(sk);
>  		}
> diff --git a/net/ipv4/udp_tunnel_core.c b/net/ipv4/udp_tunnel_core.c
> index 2326548997d3..624b6afcf812 100644
> --- a/net/ipv4/udp_tunnel_core.c
> +++ b/net/ipv4/udp_tunnel_core.c
> @@ -98,6 +98,28 @@ void setup_udp_tunnel_sock(struct net *net, struct socket *sock,
>  }
>  EXPORT_SYMBOL_GPL(setup_udp_tunnel_sock);
>  
> +void cleanup_udp_tunnel_sock(struct sock *sk)
> +{
> +	/* Re-enable multicast loopback */
> +	inet_set_bit(MC_LOOP, sk);
> +
> +	/* Disable CHECKSUM_UNNECESSARY to CHECKSUM_COMPLETE conversion */
> +	inet_dec_convert_csum(sk);
> +
> +	udp_sk(sk)->encap_type = 0;
> +	udp_sk(sk)->encap_rcv = NULL;
> +	udp_sk(sk)->encap_err_rcv = NULL;
> +	udp_sk(sk)->encap_err_lookup = NULL;
> +	udp_sk(sk)->encap_destroy = NULL;
> +	udp_sk(sk)->gro_receive = NULL;
> +	udp_sk(sk)->gro_complete = NULL;
> +
> +	rcu_assign_sk_user_data(sk, NULL);
> +	udp_tunnel_encap_disable(sk);
> +	udp_tunnel_cleanup_gro(sk);
> +}
> +EXPORT_SYMBOL_GPL(cleanup_udp_tunnel_sock);

IMHO the above code should not land into a generic tunnel helper, as the
tunnel scope always correspond to the sk scope - except for openvpn.

Also IMHO no need to do udp_tunnel_encap_disable(), it will called as
needed at sk close() time. Yep, that means that the stack will have
transient additional overhead until the sock is not destroyed, but IMHO
it's not worthy the extra complexity (export symbol, additional stub,
more files touched...)

/P