netdev - Re: [PATCH bpf-next v2 1/2] bpf: Allow bpf_get_netns_cookie in BPF_PROG_TYPE_CGROUP

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Message-Id: <YRbittzJQjF/KqKU@google.com>
Date:   Fri, 13 Aug 2021 14:23:02 -0700
From:   sdf@...gle.com
To:     Martin KaFai Lau <kafai@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v2 1/2] bpf: Allow bpf_get_netns_cookie in BPF_PROG_TYPE_CGROUP_SOCKOPT

On 08/13, Martin KaFai Lau wrote:
> On Thu, Aug 12, 2021 at 08:30:10AM -0700, Stanislav Fomichev wrote:
> > This is similar to existing BPF_PROG_TYPE_CGROUP_SOCK
> > and BPF_PROG_TYPE_CGROUP_SOCK_ADDR.
> >
> > Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> > ---
> >  kernel/bpf/cgroup.c | 19 +++++++++++++++++++
> >  1 file changed, 19 insertions(+)
> >
> > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> > index b567ca46555c..ca5af8852260 100644
> > --- a/kernel/bpf/cgroup.c
> > +++ b/kernel/bpf/cgroup.c
> > @@ -1846,11 +1846,30 @@ const struct bpf_verifier_ops  
> cg_sysctl_verifier_ops = {
> >  const struct bpf_prog_ops cg_sysctl_prog_ops = {
> >  };
> >
> > +#ifdef CONFIG_NET
> > +BPF_CALL_1(bpf_get_netns_cookie_sockopt, struct bpf_sockopt_kern *,  
> ctx)
> > +{
> > +	struct sock *sk = ctx ? ctx->sk : NULL;
> > +	const struct net *net = sk ? sock_net(sk) : &init_net;
> A nit.

> ctx->sk can not be NULL here, so it only depends on ctx is NULL or not.

> If I read it correctly, would it be less convoluted to directly test ctx
> and use ctx->sk here, like:

> 	const struct net *net = ctx ? sock_net(ctx->sk) : &init_net;

> and the previous "struct sock *sk = ctx ? ctx->sk : NULL;" statement
> can also be removed.
Agreed, makes sense. Let me also add bpf_get_netns_cookie to some
existing BPF prog to make sure it's executed. That ctx.c isn't
really running the prog..