netdev - Re: [PATCH net-next 10/10] ovpn: ensure sk is still valid during cleanup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <fc2758fd-834a-4a8c-9bdd-87cc6e874005@openvpn.net>
Date: Tue, 13 May 2025 16:55:44 +0200
From: Antonio Quartulli <antonio@...nvpn.net>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>, Sabrina Dubroca <sd@...asysnail.net>,
 Al Viro <viro@...iv.linux.org.uk>, Qingfang Deng <dqfext@...il.com>,
 Gert Doering <gert@...enie.muc.de>
Subject: Re: [PATCH net-next 10/10] ovpn: ensure sk is still valid during
 cleanup

On 13/05/2025 11:19, Antonio Quartulli wrote:
[...]

>> Side note: the ovpn_socket refcount release/detach path looks wrong, at
>> least in case of an UDP socket, as ovpn_udp_socket_detach() calls
>> setup_udp_tunnel_sock() which in turns will try to _increment_ various
>> core counters, instead of decreasing them (i.e. udp_encap_enable should
>> be wrongly accounted after that call).
> 
> You're right.
> I had the impression I needed to "undo" the setup.
> I see now that the encap key is decremented in the UDP sock destroy, 
> right after having called my implementation of .destroy().
> 
> I'll drop the call to setup_udp_tunnel_sock() with empty config then.

Paolo, the reason for calling setup_udp_tunnel_sock() with an empty 
config was to "reset" its encap state (for udp_tunnel).

Technically a UDP socket could go back to being a pure userspace socket 
only (i.e. when all peers using that socket have been deleted), 
therefore I wanted to make sure that the kernel would not try to 
intercept its packets anymore.

I understand setup_udp_tunnel_sock(cfg={}) is not correct, but what are 
my options?

1) I could nullify manually sk_user_data and udp_sk(sk)->encap_type;

2) I could implement something like "stop_udp_tunnel_sock()" that 
reverts what setup_udp_tunnel_sock() had done and call it.

Opinions?
I'd go with 2.

Thanks a lot!

-- 
Antonio Quartulli
OpenVPN Inc.