netdev - Re: [bpf-next, v4 1/5] flow_dissector: implements flow dissector BPF hook

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Message-ID: <CAF=yD-+e3-GdgJAvJ6veHLNEFtC9ZkKGSUBdQd6ub6iA=vwMVg@mail.gmail.com>
Date:   Tue, 18 Sep 2018 16:40:14 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Petar Penkov <peterpenkov96@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        simon.horman@...ronome.com, ecree@...arflare.com,
        songliubraving@...com, Tom Herbert <tom@...bertland.com>,
        Petar Penkov <ppenkov@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [bpf-next, v4 1/5] flow_dissector: implements flow dissector BPF hook

On Tue, Sep 18, 2018 at 2:09 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 09/14/2018 07:46 AM, Petar Penkov wrote:
> > From: Petar Penkov <ppenkov@...gle.com>
> >
> > Adds a hook for programs of type BPF_PROG_TYPE_FLOW_DISSECTOR and
> > attach type BPF_FLOW_DISSECTOR that is executed in the flow dissector
> > path. The BPF program is per-network namespace
>
> ...
>
> >
> > +     rcu_read_lock();
> > +     attached = skb ? rcu_dereference(dev_net(skb->dev)->flow_dissector_prog)
> > +                    : NULL;
>
>
> Some skbs have a NULL skb->dev, so we are going to crash here.

Ai. Thanks, Eric.

For these cases, we can probably infer the netns from sk->sk_net. That
is assuming that all skbs have at least one of skb->sk or skb->dev
set.