netdev - RE: [PATCH bpf-next] bpf: Generate cookie for new non-initial net NS

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Date:   Wed, 22 Jul 2020 06:30:32 +0000
From:   Jianlin Lv <Jianlin.Lv@....com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>, "yhs@...com" <yhs@...com>,
        Song Zhu <Song.Zhu@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH bpf-next] bpf: Generate cookie for new non-initial net NS



> -----Original Message-----
> From: bpf-owner@...r.kernel.org <bpf-owner@...r.kernel.org> On Behalf
> Of Daniel Borkmann
> Sent: Wednesday, July 22, 2020 4:18 AM
> To: Jianlin Lv <Jianlin.Lv@....com>; bpf@...r.kernel.org
> Cc: davem@...emloft.net; kuba@...nel.org; ast@...nel.org; yhs@...com;
> Song Zhu <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.

This patch does not come from use-case, but based on the following points were considered:
1. setup_net() runs the initializers for the network namespace object, net_cookie is a member of struct net, and its initialization is more reasonable in setup_net();
2. For initial network namespaces, this patch does not introduce additional burden;
3. For systems that have not created non-initial network namespaces, this will not introduce additional work;
4. For newly created non-initial network namespaces, the added effort of net_gen_cookie() is weak for the entire network namespaces creation process, and net_cookie is only written once during the entire life cycle of network namespaces.

>
> > ---
> >   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))
> >

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