linux-kernel - Re: [PATCH bpf-next] bpf: Generate cookie for new non-initial net NS

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Message-ID: <840a9007-3dcb-457f-8746-7f8e6fa209c5@iogearbox.net>
Date:   Tue, 21 Jul 2020 22:17:58 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jianlin Lv <Jianlin.Lv@....com>, bpf@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org, yhs@...com,
        Song.Zhu@....com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Generate cookie for new non-initial net NS

On 7/20/20 4:09 PM, Jianlin Lv wrote:
> For non-initial network NS, the net cookie is generated when
> bpf_get_netns_cookie_sock is called for the first time, but it is more
> reasonable to complete the cookie generation work when creating a new
> network NS, just like init_net.
> net_gen_cookie() be moved into setup_net() that it can serve the initial
> and non-initial network namespace.
> 
> Signed-off-by: Jianlin Lv <Jianlin.Lv@....com>

What use-case are you trying to solve? Why should it be different than, say,
socket cookie generation? I'm currently not seeing much of a point in moving
this. When it's not used in the system, it would actually create more work.

> ---
>   net/core/net_namespace.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index dcd61aca343e..5937bd0df56d 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -336,6 +336,7 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns)
>   	idr_init(&net->netns_ids);
>   	spin_lock_init(&net->nsid_lock);
>   	mutex_init(&net->ipv4.ra_mutex);
> +	net_gen_cookie(net);
>   
>   	list_for_each_entry(ops, &pernet_list, list) {
>   		error = ops_init(ops, net);
> @@ -1101,7 +1102,6 @@ static int __init net_ns_init(void)
>   		panic("Could not allocate generic netns");
>   
>   	rcu_assign_pointer(init_net.gen, ng);
> -	net_gen_cookie(&init_net);
>   
>   	down_write(&pernet_ops_rwsem);
>   	if (setup_net(&init_net, &init_user_ns))
>