netdev - Re: [patch net-next v3 5/9] genetlink: implement release callback and free sk_user

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Date: Mon, 20 Nov 2023 18:50:22 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org, pabeni@...hat.com, davem@...emloft.net,
 edumazet@...gle.com, jacob.e.keller@...el.com, jhs@...atatu.com,
 johannes@...solutions.net, andriy.shevchenko@...ux.intel.com,
 amritha.nambiar@...el.com, sdf@...gle.com, horms@...nel.org
Subject: Re: [patch net-next v3 5/9] genetlink: implement release callback
 and free sk_user_data there

On Mon, 20 Nov 2023 09:46:53 +0100 Jiri Pirko wrote:
> If any generic netlink family would like to allocate data store the
> pointer to sk_user_data, there is no way to do cleanup in the family
> code.

How is this supposed to work?

genetlink sockets are not bound to a family. User can use a single
socket to subscribe to notifications from all families and presumably
each one of the would interpret sk->sk_user_data as their own state?

You need to store the state locally in the family, keyed
on pid, and free it using the NETLINK_URELEASE notifier...